Design & Execution Manual AS 500 straight web steel sheet piles

Transcription

1 Design & Execution Manual AS 500 straight web steel sheet piles

2 Cover: 2 nd Incheon Bridge, South Korea

3 Table of content 1. Introduction 3 2. Characteristics Straight web steel sheet piles Junction piles Bent piles Delivery conditions 6 3. Handling Geoetrical paraeters Deterination of ratio and equivalent width w e Definition of Syste and Standard Solution Geoetrical values Layout considerations Circular cell structures Diaphrag cell structures Additional layouts Optiization Design Functional characteristics and stability analysis Design criteria Exaples of applications: partial safety factors approach Exaples of applications: global safety factor approach Construction of cellular structures Circular cells Diaphrag cells Conventional sybols References 59 1

4 Project: Marina Pez Vela, Costa Rica Sections: AS & AS Quantity: tonnes 2

5 1. Introduction Cellular cofferdas can be designed as self-supporting gravity walls not requiring any suppleentary waling and anchoring. They can be founded directly on bedrock, without any ebedent. They are econoical solutions for works in deep waters, high retaining works, and long structures. The applications of straight web steel sheet piles fall into two categories: for teporary works and for peranent works. When used for teporary works, a series of individual sheet pile cells for assive cellular cofferdas enabling large and deep excavations to be carried out in the dry in or alongside riverbeds, etc., where the excavations often go down to bedrock. For peranent structures, cellular sheet pile cofferdas are used above all in the aritie-engineering sector, to build: assive quay walls: the structure serves as a retaining wall and as a berth for ships; piers and jetties which can be used to berth ships on both sides; dolphins: works ade up of a single cell, used for berthing or guidance of ships; breakwaters: harbour-protection structures (berthing not usually possible). It is less coon for cells to be used on land, but they can be chosen for assive retaining structures, taking advantage of their weight to prevent slips. There are ainly two types of cells built with straight web sheet piles: Circular cells Diaphrag cells Fig. 1.1.: Elevation and plan view of a circular cell. Fig. 1.2.: Elevation and plan view of diaphrag cells. The differences between these two types of constructions will be explained in the following chapters. The engineering departent of ArcelorMittal Coercial RPS has been involved in the design and installation of ajor cellular structures all around the world in the past decades. Even though this anual is eant to be an invaluable aid, project owners, design engineers and contractors can count on ArcelorMittal's dedicated civil engineers to assist with these challenging foundation projects. 3

6 Project: Arsenal of Brest, France Sections: AS Quantity: 675 tonnes 4

7 2. Characteristics 2.1. Straight web steel sheet piles finger t thub ~ 92 b Fig. 2.1.: Characteristics of AS 500 straight web sheet piles. Table 2.1.: Characteristics of AS 500 sections Section Width 1) Web thickness Deviation angle 2) Perieter Steel section (single pile) Mass Mass per 2 of wall Moent of inertia Section odulus (single pile) Coating area 3) b t c c 2 kg/ kg/ 2 c 4 c 3 2 / AS AS AS AS AS AS ) Note: all straight web sections interlock with each other. 1) The calculation width, to be taken into account for design purposes and layout, is 503 for all AS 500 sheet piles. 2) Max. deviation angle 4.0 for pile length > 20. 3) One side, excluding inside of interlocks. 4) Please contact ArcelorMittal Sheet Piling for further inforation. 5

8 2.2. Junction piles In general, junction piles are ade by welding in accordance with EN b/2 b/ b/2 b/2 b/2 b/2 BI 35 BP 35 Y 120 b/2 b/2 b/2 b/2 90 b/2 b/2 150 Fig. 2.2.: Characteristics of junction piles. BI 145 BP 145 X 90 Connecting angles q in the range fro 30 to 45 are recoended. It is nevertheless possible to have angles up to Bent piles Fig. 2.3.: Bend angle of AS 500 piles. CP CI If deviation angles exceeding the values given in Table 2.1. are required, piles prebent in the ill ay be used. The axiu possible pile bend angle is about Delivery conditions Interlock resistance The following characteristic interlock resistance can be guaranteed: Section R k,s [kn/] 1) AS AS AS AS AS AS For verification of the piles both, yielding of the web and failure of the interlock, should be checked. The test procedure is based on Annex D of pren (2007). 1) For the related steel grade and further inforation, please contact ArcelorMittal Sheet Piling. 6

9 Watertightness of interlocks Due to the huge tensile forces in the interlocks of straight web sheet piles, steady contact is established between the two interlocked ating surfaces over the whole length of the sheet pile. This contact is so strong that generally no further easures are required to ake the sheet piling structure watertight. Coating A coating syste can be applied to straight web sheet piles. For further inforation, refer to our specific docuentation. Handling holes D Y Sheet pile sections are norally supplied without handling holes. If requested, they can be provided with handling holes on the centreline of the section. Diaeter D [] Distance Y [] Diaeter D [in] 2.5 Distance Y [in] 9 Fig. 2.4.: Diensions of handling holes. Rolling length The axiu rolled length provided by the ill is Greater length ay nevertheless be ade to order, by fabrication. Special requireents Straight web steel sheet piles are usually supplied as single piles. Double piles can nevertheless be delivered on request. Note: Double piles call for specific care during storage, handling and lifting. Geoetric tolerances according to EN Designation Tolerance Mass ±5% Length (L) ± 200 Thickness (t) t > 8.5 : ± 6% Width single pile (b) ± 2% b Width double pile (2b) ± 3% 2b Straightness (q) < 0.2% L Ends out of square ± 2% b Markings The following arkings can be supplied on request: colour arks defining section, length and steel grade; AS S355GP adhesive stickers showing the custoer s nae, destination, order nuber, type and length of profile and steel grade. Made in Luxebourg CIVIL ENGINERING CO. DAMIETTA 77

10 Steel grades of sheet pile sections AS 500 sections are delivered in the steel grades based on EN Steel grade EN Min. yield strength R eh MPa Min. tensile strength R MPa Min. elongation L o = 5.65 S o % Cheical coposition (% ax) C Mn Si P S N S 270 GP S 320 GP S 355 GP S 390 GP S 430 GP Materials to other specifications including ASTM A572, as well as special steels with iproved corrosion resistance (ASTM A 690), or copper addition in accordance with EN Part 1, Chapter 10.4, can be supplied on request. Europe EN S 270 GP S 320 GP S 355 GP S 390 GP S 430 GP USA ASTM A A 572 Gr.50; A 690 A 572 Gr.55 A 572 Gr. 60 Canada CSA Gr. 260 W Gr. 300 W Gr. 350 W Gr. 400 W - Japan JIS SY SY Galvanisation has an influence on the cheical coposition of the steel and ust therefore be specified in the purchase orders. We strongly recoend inforing us of all surface treatent to be applied to the product when placing orders. Fig. 2.5.: Exaple of layout. 8

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12 Project: Puerto de Mejillones, Chile Sections: AS Quantity: tonnes 10

13 3. Handling Straight web sheet piles have low flexural stiffness, which eans care should be taken when considering handling. Guidance is given in EN Incorrect storage could cause peranent deforation, aking interlock threading difficult if not ipossible. It is therefore vital to have a sufficient nuber of wood packing pieces between each bundle of stacked sheet piles, and to position these pieces above each other to liit the risk of deforation. Wood packing h=70 c a b b a Fig. 3.1.: Storage of straight web sheet piles. Max. bundle weight Overhang Spacing of packing Offset of bundle Wood packing to be aligned in the vertical plane 7.5 t a 1.5 b 4.0 c > straight web steel sheet piles slings Fig. 3.2.: Handling of straight web sheet piles. uncoated steel sheet piles coated steel sheet piles 11

14 When sheet piles have to be oved fro the horizontal storage position to another storage location, lifting beas or brackets ade fro pile sections threaded into the interlocks prior to lifting should be used. When pitching piles up to 15 long into the vertical position, only one point of support near the top (the handling hole) is necessary. Straight web sheet piles ore than 15 long should be lifted at two or even three points, in order to avoid plastic deforation. a a b b 0.15 L 0.40 L 0.45 L L > 15 b a = points of support b = fastening in the handling hole lifting operation Fig. 3.3.: Lifting of long straight web sheet piles. 12

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16 Project: 2 nd Incheon bridge, South Korea Sections: AS Quantity: tonnes 14

17 4. Geoetrical paraeters 4.1. Deterination of Ratio and Equivalent Width we Circular cells Circular cell with 2 arcs Developent Circular cell with 1 arc Equivalent width we Equivalent width we Syste length x Area Syste length x Fig. 4.1.: Deterination of the Equivalent Width w e and Ratio for a circular cell. The Ratio shown on tables indicates how econoical the chosen cellular construction will be. It is defined as follows: The Equivalent Width w e which is required for stability verification, is deterined by the geoetry chosen for the cellular construction (for definitions see section 4.3.). It is calculated with: Ratio = Developent 1 cell + Developent 1 (or 2) arc(s) Syste length x w e = Area within 1 cell + Area within 1 (or 2) arc(s) Syste length x Diaphrag cells The Equivalent Width w e for a diaphrag cell is defined as: w e = Area within 1 diaphrag = diaphrag length (dl) + 2 c Syste length x with c = Area of arc segent Syste length x Area A Equivalent width we x c = A x Syste length x Fig : Deterination of the Equivalent Width w e of a diaphrag cell. 15

18 4.2. Definition of Syste and Standard Solution Circular cells with 2 arcs 1 Syste = 2 half cells + 2 arcs Nuber of piles for 1 Syste = 2 nuber of piles for 1 2 cell + 2 nuber of piles for 1 arc + 4 junction piles = 2 (L + M) + 2 N + 4 S The Standard Solution for circular cells is built with an even nuber of piles (junction piles included) for the cell and an odd nuber of piles for each arc (Table 4.1.). The connecting angle of the junction piles for the Standard Solution is: q = 35 Diaphrag cells 1 Syste = 1 diaphrag + 2 arcs Nuber of piles for 1 Syste = 1 nuber of piles for 1 diaphrag + 2 nuber of piles for 1 arc + 2 junction piles. = N + 2 M + 2 The Standard Solution for diaphrag cells is built with an odd nuber of piles (junction piles not included) for the diaphrag, an odd nuber of piles for each arc and 2 junction piles (Table 4.3.). The connecting angle of the Y-junction piles for the Standard Solution is Geoetrical values Having copleted the design process to deterine the Equivalent Width (w e ), the geoetry of the cell can be chosen. This can be done with the help of tables or with coputer progras. Several solutions are possible for both circular and diaphrag cells with a given equivalent width Circular cells with junction piles Fig. 4.3.: Geoetrical values for circular cells. The ost iportant paraeters for circular cells are (Fig. 4.3.): the radius of the ain cell (r ); the radius of the connecting arcs (r a ); the angle between the ain cell and the connecting arc (q); the syste length (x); the positive or negative offset between the connecting arcs and the tangent planes of the ain cells (d y ); the Equivalent Width (w e ). The following relationships apply : the greater the angle (q) between cell and arc, the greater the ratio of r a /r. For q = 90 and d y = 0: r = r a ; with constant r and increasing r a, the syste length (x); also increases and the equivalent width decreases, if d y = 0 ; the governing circuferential tensile force increases as the r a /r ratio increases; the developed pile wall surface per etre of cofferda decreases as the r a /r ratio increases; with respect to circuferential tensile force, the solution with the sallest possible angle q is the optiu for a given Equivalent Width (w e ), but also the ost unfavourable with respect to the quantities of aterial required; if the straight web piles have any residual resistance to be obilized, the optiu solution will have an angle between 30 and 45. For design reasons (welding), this angle ay not be less than q = 30. Note: A cellular cofferda is a flexible structure. After the closure of the cell structure and eventual filling, the cell will undergo horizontal oveents of the piling ring at the top of the structure resulting in an increase of the cell diaeter, as well as local deforations due to the barrelling effect (section , fig ). This has to be taken into consideration while designing cellular constructions by assuing that the theoretically designed geoetry of the cell will be slightly different fro the geoetry practically obtained on site. The calculation width of 503 has been used in following tables (Table 4.1. to 4.3.). 16

19 Table 4.1.: Circular cells with θ = 35 standard junction piles L No. of piles per Geoetrical values Interlock deviation Design values Cell Arc Syste Cell Arc 2 Arcs M S N d=2 r r a x d y a w e R a

20 L No. of piles per Geoetrical values Interlock deviation Design values Cell Arc Syste Cell Arc 2 Arcs M S N d=2 r r a x d y a w e R a

21 L No. of piles per Geoetrical values Interlock deviation Design values Cell Arc Syste Cell Arc 2 Arcs M S N d=2 r r a x d y a w e R a

22 L No. of piles per Geoetrical values Interlock deviation Design values Cell Arc Syste Cell Arc 2 Arcs M S N d=2 r r a x d y a w e R a

23 Table 4.2.: Circular cells with θ = 90 junction piles L No. of piles per Geoetrical values Interlock deviation Design values Cell Arc Syste Cell Arc 2 Arcs M S N d=2 r r a x d y a w e R a ,

24 L No. of piles per Geoetrical values Interlock deviation Design values Cell Arc Syste Cell Arc 2 Arcs M S N d=2 r r a x d y a w e R a

25 Diaphrag cells with Y 120 junction piles d y w e c 60 M r θ N dl 150 θ = 120 c x = r Fig. 4.4.: Geoetrical values for diaphrag cells. The ost iportant paraeters for diaphrag cells are (see Fig. 4.4.): the radius (r); the angle between the arc and the diaphrag (θ); the Equivalent Width (w e ); the arc height (d y ); the syste length (x); the equivalent arc height (c); the diaphrag wall length (dl). The following relationships apply: the greater the angle (θ) between arc and diaphrag, the saller the arc radius; the syste length (x) of the diaphrag cells follows fro the nuber of sections in the arc and the corresponding radius; the total width of the cell follows fro the appropriate arc height (d y ) and the nuber of sections in the diaphrag; the optiu aterial usage is with an angle θ = 120. In this particular case, the syste length (x) of the diaphrag cell is equal to the radius (r); the tensile forces in the arc and diaphrag are balanced. Tables 4.3. a) and 4.3. b): Diaphrag cells with Y 120 junction piles Geoetry diaphrag wall Nuber of piles Wall length Nuber of piles N Table 4.3. a) Geoetrical values. dl M Radius Syste length x = r Geoetry arc (Standard Solution) Arc height d y Equivalent arc height c Interlock deviation Table 4.3. b) Geoetrical values for arc of diaphrag cells. Both tables should be used separately following the required nuber of piles for the arc and the diaphrag wall. Note: Total width = diaphrag length (dl) + 2 d y a 23

26 Project: Daietta, Egypt Sections: AS Quantity: tonnes 24

27 5. Layout considerations The two ost coon layouts for cellular structures are circular cells and diaphrag cells Circular cell structures The cofferda is ade up of a series of relatively closely-spaced circular cells linked by connecting arcs. Each cell is self-supporting once it is filled. It is therefore independent of adjacent cells, which akes it easy to build this type of cofferda in water. Main cell Arc cell Fig. 5.1.: Coponents of circular cells. Soe applications where circular cell structures ay be used are: deep quay wall structures, deep aritie locks, harbour front structures, breakwaters, teporary cofferdas and dry docks. Circular cells in the construction of cofferdas offer several advantages: circular cells ay be filled iediately after they have been built, regardless of the relative height of fill in adjacent cells; filled cells can be used as the working platfor for the installation of the new cells. The diaeter of the cell is liited by the characteristic interlock resistance. 25

28 The junction piles are a key eleent which require special attention. θ Fig. 5.2.: Detail of junction piles. A 90 junction akes it easy to have a cofferda whose ain circular cells and arc cells have the sae radius (with d y = 0), giving a ore regular face. However, forces are balanced in the junction pile only if it undergoes significant deforation. For this reason 90 junction piles are only used in the case of low tensile forces, i.e. for sall radii. Please contact our technical departent for further inforation. If high tensile forces have to be transitted, angles between 30 and 45 are recoended. This configuration transits less stress to the ain cell than the 90 junction pile and, by foring a longer connecting arc, provides ore flexibility during the installation process. It is easy to change the direction of a cofferda alignent by siply changing the position of the junction piles on the circular cells (Fig. 5.3.). Main cell Arc cell Fig. 5.3.: Changing cofferda alignent Diaphrag cell structures Diaphrag celi structures consist of a series of two circular arcs norally joined by 120 junction piles and straight transverse sheet-pile diaphrags. 60 r 150 θ = 120 Fig. 5.4.: Diaphrag cells. 26

29 With this layout the cells are not self-supporting during the construction phase, which akes it difficult to build such a cofferda in water, without building an ebankent beforehand. However, the diaphrag cell layout does have two ajor advantages : since the length of the coon wall within the straight diaphrag does not ipact the tensile force in the sheet piles, its length is not liited. This solution is therefore an alternative to circular cells when the axiu diaeter allowed by the interlock resistance is exceeded; tensile forces in the 120 Y-type junction piles are balanced. The ends of a diaphrag-cell structure ust consist of a circular closure cell, or a clover-leaf type closure cell, if the cofferda is very wide. Fig. 5.5.: Closures of diaphrag cell structures Additional layouts Circular cells without rear arcs This layout akes savings by dispensing with the rear arcs and junction piles. This ust be taken into account when calculating the equivalent width (see 4.). Main cell Arc cell Fig. 5.6.: Circular cells without rear arcs. Cloverleaf-type cells The cloverleaf-type cell is norally used where the height and ass required for stability prohibit the use of circular cells. The cloverleaf-type cell will require ore piling than the standard cell, but like the circular cell, it has the advantage of being a selfsupporting unit. Because of its stability, the half-cloverleaf cell is often used for end cells, corner cells and tie-ins for diaphrag-cell structures. Fig. 5.7.: Cloverleaf-type cell. 27

30 Single circular cells Single circular cells are used in the construction of piers or dolphins, and can be used as foundations for offshore windills, as they are self-supporting units. For the introduction of the weight of the superstructure, please refer to section Fig. 5.8.: Single circular cells in the construction of piers. hrag Cells 5.4. Optiization Diaphrag Cells Optiization ay be achieved through staggering of steel sheet pile length. In certain situations, like a sloped bedrock, staggered steel sheet piles can be utilised. Fig. 5.9.a: Noral layout of straight web steel sheet piles. Fig. 5.9.b: Staggered layout of straight web steel sheet piles. fig.5.9a fig. 5.9b 28

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32 Project: Mussafah, Abu Dhabi Sections: AS Quantity: tonnes 30

33 6. Design 6.1. Functional characteristics and stability analysis The ore or less horizontal forces induced by the pressure of water and earth are counteracted by self-weight and the lateral passive earth pressure obilized by the cofferda. Within the individual cells, lateral earth pressure and, if present, water pressure develop on the air or water side of the sheet pile wall as a result of soil self-weight and any relevant surcharges. These pressures are taken up by the straight-web sheet piles, arranged in circles, and are transitted to the individual cells as horizontal tensile forces (circuferential tensile force). In the case of diaphrag cells, when calculating the tensile forces in the diaphrag wall, the tensile forces exerted by the arc are integrated vectorially. The design of a cellular cofferda requires consideration of the following failure odes at the design stage: Overall stability a) Sliding as a rigid body, if there is little or no penetration of the sheet piles b) Tilting due to shear failure in the fill/foundation soil c) Bearing capacity failure d) Overall stability 90 - ϕ hard layer Fig. 6.1.: Failure ode a) on rock or bearing soil. Fig. 6.2.: Failure ode b) on bearing soil ϕ hard layer Failure surface Fig. 6.3.: Failure ode b) on rock. Fig. 6.4.: Failure ode c) on bearing soil. 31

34 Slip surface Fig. 6.5.: Failure ode d), on bearing soil. Structural failure of the steel sheet piles under tensile stress e) Failure by bursting of interlocks Fig. 6.6.: Failure ode e). Failure ode a), sliding as a rigid body, does generally not govern design (Fig. 6.1.). When the shear strength of the soil in the cofferda is exceeded, as in failure ode b), tilting due to shear failure in the fill/ foundation soil, two different failies of failure surfaces can develop within the cell, depending on ebedent depth, and the structures can tilt as shown in Figs. 6.2./6.3. The failure lines can be represented as concentric sections of logarithic spirals intercepted by a faily of straight lines that intersect in the locus of the spiral [Jelinek]. Where the cofferda is only shallowly ebedded in a soil with low bearing capacity, failure ode c) can be the governing ode and thus deterine the design of the cofferda (see Fig. 6.4.). Analysis can be perfored with classical bearing capacity failure ethods, e.g. in accordance with EN Analysis of overall stability d) is based on well-known procedures (Bishop, Krey, Terzaghi, etc.) (Fig. 6.5.). As a rule of thub, the equivalent width of a cofferda varies between 0.9 and 1.1 ties the head of water pressure Overall stability Tilting due to shear failure in the fill / foundation soil (Figs and 6.3.) The ter «equivalent width» is used in relation to cofferdas designed as a series of circular or diaphrag cells. The equivalent width corresponds to the footprint of the cellular cofferda converted to a rectangle of equal area and equal syste width, as shown in Figs and 4.2. Verification ust take account of this equivalent width. This involves representing the cells as two parallel walls, one on the air side and one on the land side, separated by the equivalent width. The failure surfaces can be envisaged as arcs of logarithic spirals intercepting the toes of both walls. At failure, a convex failure surface develops between the toes of the cofferda walls. The failure surface can be assued to be a logarithic spiral with the corresponding internal friction angle. A logarithic spiral is defined as (Fig. 6.7.): r = r o e q tan j 32

35 w e H r 0 r = r 0 e tan Fig. 6.7.: Failure surface: logarithic spiral. The advantage to use a logarithic spiral is that the force resulting fro the friction along the failure surface passes through its pole, and therefore it does not add any resisting or driving oent around the pole. In order to verify stability, it is necessary to differentiate the types of strata the cofferda is founded in: a) The cofferda rests directly on bedrock (Fig. 6.8.) w e copletely drained fill G GrW P w water pressure difference failure surface (log. spiral) Q rock Fig. 6.8.: Cofferda resting on rock. pole of the spiral resistance force of the soil at failure b) The cofferda rests on bedrock overlain by further strata, or is shallowly ebedded in load-bearing soil (Figs and 6.10.) copletely drained fill w e w e failure surface (log. spiral) pole of the spiral P p with K p = 1 G Q GrW P w P a resistance force of the soil at failure water pressure difference earth pressure rock saturated fill calculated with uplift failure surface (log. spiral) pole of the spiral P p with K p = 1 G GrW Q soil P w P a water pressure difference earth pressure resistance force of the soil at failure Fig. 6.9.: Cofferda resting on rock overlain with other soil strata. In this case, the active earth pressure and laterally copensating passive earth pressure are to be considered, as well as the forces acting on the load side. Considering the low deforation values, the passive earth pressure should be assued to be low, Fig : Cofferda ebedded a shallow depth into load-bearing soil. generally with K p = 1 and, for deeper ebedent into the load bearing soil, with K p for p = 0. 33

36 c) The cofferda is ebedded deeply into the load bearing soil (Fig ) w e saturated fill calculated with uplift G GrW P w water pressure difference pole of the spiral P p with δ p = 0 P a earth pressure failure surface (log. spiral) soil Q resistance force of the soil at failure Fig : Additional investigation in case of deep ebedent. One eans of increasing the stability of the cofferda is to ebed the sheet piles ore deeply. In this case, verifications should also be run with a concave failure surface. General considerations This stability analysis verifies both tilting and sliding safety. Cofferda stability can also be increased by widening the structure and by selecting ore suitable fill aterial. Where possible, up to a certain level, greater ebedent depth ay increase stability. The verification is carried out with the ratio of oents about the appropriate pole of the spiral. This procedure can be used for analysis both with a global safety factor and with partial safety factors and ust satisfy the following conditions: M r M s S F for analysis with a global safety factor and M R,d M E,d for analysis with partial safety factors. If odelling is perfored using partial safety factors, suitable decreental or increental factors are to be applied to the resisting and driving forces and oents given below. The values of these safety factors are to be taken fro the appropriate regulations. The resisting oents (M r or M R,d ) include the oents resulting fro: self-weight of the cell (fill aterial), respectively friction and cohesion resistance along the failure surface; passive earth pressure in front of the cell; peranent surcharge loads on the cell; resisting single loads and pressures; resistance of anchors or piles that intersect the sliding surface. The driving oents (M S or M E,d ) include the oents resulting fro: active earth pressure behind the cell; excess water pressure, resulting fro differential head; variable surcharge loads, single loads or pressures, behind the cofferda; bollard loads. As there are several spirals intercepting the toes of the front and rear walls, analysis is an iterative process carried out until the pole is found where the ratio M R,d M E,d reaches a iniu. When a global safety factor is used, the iteration process is continued until the iniu safety factor S F is obtained Bearing capacity failure and deep-seated sliding (Figs and 6.5.) Analysis of d) (Fig 6.5.), deep-seated sliding should be perfored with circular or polygonal failure or slip lines. In ost cases, the critical failure line will pass through the toe of the front or rear cell wall, depending on the geoetry of the structure. For shallowly ebedded cells on soil other than bedrock, bearing capacity analysis c) (Fig 6.4.) ust also be perfored. For structures founded on bedrock, both of these analyses are generally unnecessary Piping due to heave Depending on the ebedent depth (generally for shallow ebedent), the soil conditions (sandy soil) and the agnitude of the water pressure difference, it can be necessary to perfor an analysis on piping due to heave following EN

37 Verification of resistance to structural failure (Fig. 6.6.) The following design approach is based on the partial safety factor ethod as given in the Eurocodes, but other ethods ay be acceptable Resistance of straight web steel sheet piles The tensile resistance F ts,rd of straight web steel sheet piles (other than junction piles) shall be taken as the lesser of the interlock resistance and the resistance of the web, using: F ts,rd = b R R k,s / M0 but F ts,rd t w f y / M0 [6.1.] Where: f y : yield strength R k,s : characteristic interlock resistance : web thickness t w R : reduction factor for interlock resistance, taken as 0.8 M0 : partial safety factor, taken as 1.0 The characteristic resistance of the interlock R k,s depends upon the cross-section of the interlock and the steel grade adopted. The characteristic interlock resistance R k,s is deterined by testing according to Annex D of pren (2007). Note: R and MO ay be specified in National Annexes of Eurocodes or local standards Verification of piles used in single cells The verification of the piles used in single cells should be done in the governing horizontal plane of the structure. Fro field observations, it appears that the plane of axiu expansion is located between 1/3 H and 1/4 H for cells built on rock (Fig ). It can be assued that the axiu piling tension also occurs in this plane (barrelling effect). In a safe-sided approach, the horizontal plane located at H/4 is therefore used for verification of cells built on rock. H Maxiu expansion H/4 Fig : Plane of axiu piling tension for cells built on rock. If the cell structure is not built on rock, a safe-sided approach uses the tension at the excavation/dredge level. Plain straight web piles should be verified using: F t,ed F ts,rd [6.2.] Where: F ts,rd : design tensile resistance according to expression [6.1.] F t,ed : the design value of the circuferential tensile force deterined with F t,ed = p,ed r [6.3.] where: p,ed : design value of the internal pressure acting in the ain cell at the governing horizontal plane due to water pressure and due to the at-rest pressure of the fill (Fig ) r : the radius of the ain cell (Fig ) F t,ed p,ed r "X" Fig : Circuferential tensile force. F t,ed Detail "X" 35

38 Verification of piles used in cellular cofferdas The verification of piles used in circular cells should be done in the governing horizontal plane as explained in section Main cell Arc cell r a r p,ed Fig : Geoetry and definitions for circular cells. Verification of the arc cell and ain cell For the verification of the arc cell and ain cell, straight web piles should be verified using expression [6.2.] which requires: F t,ed F ts,rd Verification of welded junction piles F t,ed t F t,ed θ Fig : Typical junction piles for circular cells. F ta,ed The following design concept regarding verification of welded junction piles is based on the results of a nuerical odel calibrated by extensive laboratory tests on welded junction piles (bi-axial tensile strength tests) foring part of an international research project. The nuerical odel takes account of the filling procedure of the cells, the behaviour of the fill and the non-linear behaviour of the junction pile itself. The cofferda is assued to be loaded by the self-weight of the fill only. Provided that the following criteria are fulfilled: welding is carried out according to the procedure given in section B.6. of EN 12063:1999 (see Fig. B.5.); the steel sheet pile aterial is in accordance with EN 10248, the welded junction pile can be verified using: F t,ed T F ts,rd [6.5.] where: F ts,rd : design tensile resistance of the pile according to expression [6.1.] F t,ed : design tensile force in the ain cell given by F t,ed = p,ed r [6.6.] where: p,ed : design value of the internal pressure acting in the ain cell at the governing horizontal plane due to water pressure and due to the at-rest pressure of the fill (Fig ) r : radius of the ain cell (Fig ) T : reduction factor taking into account the behaviour of the welded junction pile at ultiate liit states, and which should be taken as follows: T = 0.9 ( r a ) (1-0.3 tanj k) [6.7.] r in which r a and r are the radii of the connecting arc and of the ain cell according to Fig and j k is the characteristic value of the internal friction angle of the fill aterial. Notes : 1) Factor T takes account of the rotation capacity (ductility) of the junction pile as well as the rotation deand (up to 20) according to the odel described above. 2) Although developed for cellular structures with aligned arcs (Fig ) expression [6.7.] yields acceptable results for alternative configurations. 36

39 Verification of piles used in diaphrag cells Cellular arc Diaphrag wall r 60 F ta,ed 30 F ta,ed θ = 120 F td,ed Fig : Diaphrag cells. Diaphrag Cells The verification of piles used in cellular cofferdas should be done in the governing horizontal plane as explained in section Verification of the piles in the arc The verification of the piles located in the arc ay be carried out using an expression siilar to [6.2.]: F ta,ed F ts,rd [6.2'.] where: F ts,rd : tensile resistance according to expression [6.1.] F ta,ed : design value of the hoop tension deterined according to an expression siilar to [6.3.]: Verification of the piles in the diaphrag wall No verification of the piles used in the diaphrag wall is required due to the fact that the tension forces acting in the diaphrag wall have the sae agnitude as the forces acting in the arc wall: F td,ed = 2 sin 30 F ta,ed = F ta,ed F ta,ed = p,ed r [6.3'.] Verification of the welded Y-pile If the Y-pile is fabricated in accordance with section B.6. of EN 12063:1999 (Fig. B.5.), it requires no further verification Design criteria One iportant criterion is the required equivalent width (w e ), as this influences the entire geoetry of the proposed cofferda. The larger the equivalent width (w e ), the larger the corresponding radii and stresses in the circular-cell sections will becoe. For diaphrag cells, the length (dl) of the diaphrags increases in proportion to the equivalent width (w e ). The necessary equivalent width (w e ) is influenced on the one hand by the friction angle of the in-situ soil and fill, and on the other hand by external loads such as earth pressure and excess water pressure. The larger the friction angle and the saller the loads, the saller the required equivalent width (w e ). It is obvious fro the above that cellular cofferdas are not well suitable for cohesive and soft soils such as highly plastic clays or ud, for instance Soil conditions Cellular cofferdas should be erected on ground of sufficient bearing capacity. Where cohesive soil is present, an attept should be ade to replace this with granular aterial, or at least to iprove it by the appropriate eans and thus increase the friction angle and initiate consolidation. Coarse aterial should be used for the fill. The stability of the cofferda also depends on the buoyant (effective) unit weight and the internal friction angle j k of the fill aterial. A aterial of high unit weight and high friction angle should therefore be used for the fill Horizontal and vertical loads Straight web sheet piles can only resist horizontal loads and are in principle not foreseen to transit vertical loads. Decks and superstructures can be founded directly on the fill aterial, crane rails shall be founded on separate bearing piles. Appropriate detailing provisions should be ade to keep the straight web sections free of vertical loads (Fig ). 37

40 Fender Concrete structure Copressible aterial Water Fill Straight-web sheet piles Fig : Detailing for transfer of vertical loads. Hydrostatic pressure and earth pressure within the cells have an influence on the stresses in the sheet piles. To keep stresses as low as possible, when water pressures are high, it is recoended that suitable easures be taken to reduce the water pressures as uch as possible. If ebankents are necessary, only granular aterial with a high friction angle should be used. Cell structures are considered to be rigid and to allow little displaceent, at least in the toe area. For this reason, the obilized passive earth pressures on the outside of cells with only shallow socketing into the foundation should be calculated with K ph = 1 only, or with a wall / soil friction angle of p = 0 for deeper ebedent Earthquake effects Additional horizontal forces develop during earthquakes. Active earth pressure on the structure increases and the passive earth pressure decreases due to horizontal ass acceleration. The water level behind and within the cell rises, and the water level in front of the cell sinks. When dealing with cohesive soils, analysis of additional forces should include confined pore water in the deterination of the asses at play. It is assued that the soil / water response behaviour for granular soils is uncoupled. As long as the soils do not display a tendency to liquefy, design values for the friction angle and cohesion need not be reduced further. For ore inforation on the design in seisic regions, please contact our technical departent Durability Like all steel structures, unprotected cell structures are subject to corrosion. Corrosion phenoena depend on the location of the structure and on the surrounding ediu. Material loss resulting fro atospheric corrosion is negligible. Structures in fresh water are less susceptible to corrosion than those in sea water. Moreover, the distribution of aterial loss across the affected surfaces is variable: for exaple, the highest corrosion rates on cells in water are to be expected in the low water and splash zones, whereas losses are substantially lower in the area of peranent iersion. The highest corrosion rates are fortunately in areas where the stresses in the sections are relatively sall. The effects of corrosion are to be considered in the analysis of peranent structures. Corrosion rates can be taken fro the literature or the appropriate standards. Unless otherwise specified, the reduction in thickness for parts of sheet pile walls in contact with soil (with or without groundwater), or in contact with river or sea water can be taken fro Tables 6.1. and 6.2. (table 4.1. and 4.2. fro EN (2007)) which vary with the required design working life. Table 6.1.: Loss of thickness [] due to corrosion for piles and sheet piles in soils, with or without groundwater Required design working life 5 years 25 years 50 years 75 years 100 years Undisturbed natural soils (sand, silt, clay, schist,...) Polluted natural soils and industrial sites Aggressive natural soils (swap, arsh, peat,...) Non-copacted and non-aggressive fills (clay, schist, sand, silt,...) Non-copacted and aggressive fills (ashes, slag,...) Notes: 1) Corrosion rates in copacted fills are lower than those in non-copacted ones. In copacted fills the figures in the tables should be divided by two. 2) The values given for 5 and 25 years are based on easureents, whereas the other values are extrapolated. 38

41 Table 6.2.: Loss of thickness [] due to corrosion for piles and sheet piles in fresh water or in sea water Required design working life 5 years 25 years 50 years 75 years 100 years Coon fresh water (river, ship canal,...) in the zone of high attack (water line) Very polluted fresh water (sewage, industrial effluent,...) in the zone of high attack (water line) Sea water in teperate cliate in the zone of high attack (low water and splash zones) Sea water in teperate cliate in the zone of peranent iersion or in the intertidal zone Notes: 1) The highest corrosion rate is usually found in the splash zone or at the low water level in tidal waters. However, in ost cases, the highest stresses are in the peranent iersion zone (Fig.6.18.). 2) The values given for 5 and 25 years are based on easureents, whereas the other values are extrapolated. If required, the influence of corrosion on the tensile resistance F ts,rd of straight web sheet piles can be deterined by applying the reduction factor cor to the governing equation [6.1.]. where: F ts,rd,cor = cor r R k,s cor = 1 - t t w : web thickness t : reduction in thickness due to corrosion t w M0 [6.8.] [6.9.] Note: Forula 6.9. has been established based on tests which have been evaluated statistically based on a nuerical ethod in accordance with ANNEX D of EN The verification of the tensile resistance in the governing horizontal plane should take into account the variation of both the tensile forces due to fill and the corrosion rates over the height of the cell (Fig and 6.18.). In order to axiize the design working life of the structure several solutions ay be analysed: coating the sections in the low water zone, and, if necessary, cathodic protection of the peranently suberged zone ay be considered. This can be done by eans of sacrificial anodes or ipressed current. MHW Zone of high attack Splash zone MLW Intertidal zone Zone of high attack Low water zone Loss of thickness Fill Corrosion rates Peranent iersion zone Earth pressure (at rest) Undisturbed natural soil Undisturbed natural soil a) Vertical zoning of seawater aggressivity b) Corrosion rate distribution c) Typical earth pressure distribution Fig : Typical corrosion rate distribution in arine environent. MHW = Mean High Water MLW = Mean Low Water 39

42 Design Flowchart Soil properties (geotechnical report, boreholes,...) Water levels, groundwater level,... Design assuptions Geoetry of planned structure: excavation & top levels, tip level of AS 500 piles,... Backfill properties (granular soil: ϕ, γ,...) Loads (variable, peranent, accidental,...) Special requireents (seisic,...) Service lifetie Overall stability Calculate required equivalent width w e : Jelinek ethod (using a software like Coffda ) Verify additional stability criteria (bearing capacity, deep-seated sliding, piping) when relevant Choose cell type: first option = circular cells Select adequate geoetry of cells (Tables ) 4 several iterations necessary 3 Structural resistance of sheet piles Calculate internal cell pressure at governing plane (p at H/4 or excavation/dredge level or...) Select AS 500 pile: thickness & interlock resistance Verify resistance of chosen sheet pile of ain cells, respectively of junction piles (forula fro EC3-5) 1 2 if applicable 1 Estiate loss of steel thickness based on design life & environent (i.e. using tables fro EC3-5) 5 Durability Deterine reduced section properties of AS 500 at end of service life Verify resistance of AS 500 sheet pile (plain sheet pile / junction pile) 1 Optiize AS 500 sheet pile section: if safety factor is too low, choose a larger section & vice versa If highest interlock resistance available for AS 500 is insufficient 2) or 3) or 4) 2 Change cell geoetry: reduce diaeter of arcs / ain cell, etc 3 Change cell type: circular diaphrag 4 Change assuptions (i.e. tip of steel sheet piles, structure geoetry, loads, etc) 5 Optiization of cell structure = iterative process: vary paraeters to deterine the ost cost-effective solution 40

43 6.3. Exaples of applications: partial safety factors approach Following exaples are based on the design according to EAU 2004 [8], working with the partial safety factors recoended by the coittee of the EAU. The verification of the steel sheet pile is based on EN 1993 Part 5, version 2007 [2]. Please note that the verification of the resistance of the pile in EN (2007) and EAU 2004 are different. Besides, for the design of the cells, it is iportant to consider local regulations and applicable standards. In Europe, partial safety factors are recoended in the Eurocodes, but soe ay be changed by the different countries in their NAD (National Application Docuent). Furtherore, the overall stability of the cells ay have to be verified by different forulas than the ones in the EAU It is the designer s responsibility to select the correct design ethod. In other countries, the ethod and values described in following exaples ay have to be adapted to take into account local design regulations, for instance when designing based on global safety. The design ethod considered in the EAU utilizes following equation for the overall stability (EAU 2004: ): M Ed = M kg g G + M w g G + M kq g Q MR kg [6.10.] However, the forula should be adapted to take into account the earth resistance in front of the cells when the ebedent of the sheet piles is not negligible. ArcelorMittal proposes following revised equation: M Ed M Rd [6.10-a.] M Ed = M kg g G + M w g G + M kq g Q MR kg M R + Ep M R + c = M g Rd Gl g Ep g c g Gl [6.10-b.] where: M Ed : design value of the oent effect M Rd : design value of the oent resistance M kg : characteristic value of single oent due to active earth pressure forces M w : characteristic value of single oent due to water pressure forces M kq : characteristic value of single oent due to external variable forces M R kg : characteristic value of single oent due to the force of cofferda fill M R Ep : characteristic value of single oent due to passive earth pressure forces M R c : characteristic value of single oent due to cohesion on the failure surface and: g G = 1.35 (under soe circustances, could be reduced to g G,red = 1.20 for the water) g Q = 1.50 g Gl = 1.10 g Ep = 1.40 g c = 1.25 Above partial safety factors are taken fro load case "LS 1B LC 1" (EAU 2004). Furtherore, as entioned in previous chapters, chosen factors for use with EN are: b R = 0.8 g M0 = 1.0 Note: It is iportant to first deterine the resultant of an action in order to verify whether the force generates a driving or a resisting oent Exaple 1: peranent circular cells A quay wall is to be erected in water at a spot with shallow bedrock. Fill will be placed behind the quay wall. The bedrock is overlain by an approxiately 4 thick layer of ediu-dense sand and a 2 to 3 thick tidal ud deposit. Design life of the structure is 50 years ud sand bedrock Fig : Initial conditions. 41

44 Assuptions Before erection the tidal ud deposit is dredged fro the cofferda footprint and fro the area behind it. Characteristic soil properties: / kn/ 3 j k d k c' k kpa in-situ sand layer 18 / ± 12 0 sand fill 18 / Because of the shallow ebedent depth, the passive earth pressure is calculated with K p = 1.0. Water levels: HWL = LWL = 4.00 Water levels for overall stability & for interlock resistance verification: water in front of wall: water behind wall: [= (HWL + LWL)/2. Siplified assuption] Dredge level: noinal depth: design depth = noinal depth - dredging tolerance = = with: assued dredging tolerance = 0.80 (differs fro EAU 2004, chap ) Variable vertical loads: P 1 = P 2 = 40 kn/ 2. Note: Variable load P 1 is required for analysis of the internal cell pressure, but it has to be neglected for the stability analysis because of its stabilizing effect. The line pull (fro bollard) is assued to have a horizontal coponent of 40 kn/ and a vertical, upwards coponent of 20 kn/. The vertical coponent acts as a resistance, but does not have any significant influence on the overall stability analysis, and therefore is neglected. P z = 40 / 20 kn/ P 1 = 40 kn/² w e = P 2 = 40 kn/² fill Dredge level Design level sand bedrock Fig : Final conditions Overall stability a) Calculation of required equivalent width, verification of resistance to tilting due to shear failure in the fill/foundation soil Analysis is perfored with coputer software based on the assuptions given above. For an equivalent width w e = 22.0, following oents can be deterined: M kg = 15,977 kn/ M w = 6,960 kn/ M kq = 6,495 kn/ M R kg = 50,457 kn/ M R Ep = 180 kn/ Using forula fro EAU 2004 with the suggested change [6.10-b.] and the partial safety factors: M Ed = 15, , , = 40,707 kn/ M Rd = 50,457/ / 1.40 = 45,999 kn/ M Ed = 40,707 < M Rd = 45,999 OK Note: If the ebedent of the flat sheet piles is sall, MEp R does not have a significant influence on the result and ight be neglected. 42

45 LOGARITHMIC SPIRAL SLIP PLANE ANALYSIS SOIL 1 SOIL 2 SOIL Force1 = Eah = Wph = Eav = Wph = Eph = Epv = Weight = Lengths, Levels [], Forces [kn/] Iteration Origin 2.08 / Width Average Friction Angle in Slip Plane Fig : Coputer calculation of required equivalent width w e, verification of resistance to tilting due to shear failure in the fill/foundation soil. Software: Coffda 4.0. [10]. As the cell structure is founded on bedrock, bearing capacity and deep-seated sliding analyses are not required. b) Deterination of cell geoetry The angle of the junction piles is chosen as q = Fro Table 4.1., following geoetry can be selected for an equivalent width w e = No. of piles per Geoetrical values Interlock deviation Design values Cell Arc Syste Cell Arc 2 Arcs L M S N d=2 r r a x d y a w e R a cell diaeter d = radius of the ain cell r = radius of connecting arc r a = 4.75 syste length x = offset d y = 0.45 angle = angle deviation in arc d a = 6.07 Nb. of ssp for 1 syste 218 Nb. of ssp for cell 160 = 2 (L+M) + 4 S (including 4 junction piles) Nb. of ssp for 2 arcs 58 = 2 N 43

46 Verification against structural failure a) Calculation of governing internal cell pressure As the cell is founded directly on bedrock, the governing internal pressure can be assued to be that exerted one-quarter of the height of the cell above the bedrock surface, i.e. at elevation However, under certain circustances, it ight be advisable to consider a deeper elevation, and in soe cases the dredge elevation is used. Vertical stresses at : weight of soil s v1 = = kn/ 2 variable loads s v2 = 40.0 kn/ 2 design value s v = g G s v1 + g Q s v2 = = kn/ 2 b) Analysis of resistance of straight web sheet piles AS straight web sheet piles are selected with: R k,s = 5,500 kn/ t w = 12.5 f y = 355 N/ 2 F t,ed F ts,rd [6.2.] Interlock resistance: F ts,rd = b R R k,s / g M0 = 0.8 5,500 / 1.0 [6.1.] = 4,400 kn/ Resistance of web: F ts,rd = t w f y / g M0 = / 1.0 [6.1.] = 4,438 kn/ Durability Loss of thickness due to corrosion of steel is based on tables 4.1. and 4.2. fro EN The design life assued for this structure is 50 years without any additional protection (sacrificial steel thickness exclusively). Verification of the sheet pile is done in the area where the interlock tension is highest, which is in the peranent iersion zone. Assuing that the backfill is not aggressive and that it will be copacted, the loss of steel thickness can be estiated as follows: front: peranent iersion zone back: non aggressive and copacted fill Total loss of steel thickness: Dt = = Coefficient of earth pressure at-rest: K o = 1 - sin j k = 1 - sin 32.5 = Horizontal earth pressure: s h = K O s v = = kn/ 2 Hydrostatic pressure: characteristic value p w1 = = 25.0 kn/ 2 design value p w = g G p w1 = = 33.8 kn/ 2 Total horizontal stress: s h,tot = s h + p w = = kn/ 2 = p,ed Deterining resistance: F ts,rd = 4,400 kn/ Junction pile: r = cell radius = r a = connecting arc radius = 4.75 b T = 0.9 ( r a ) (1-0.3 tan jk ) r b T = 0.9 ( /12.81) (1-0.3 tan (32.5)) = F t,ed = p,ed r = = 2,581 kn/ < b T F ts,rd = ,400 = 3,212 kn/ OK [6.5.] Reduced interlock resistance due to corrosion of the AS : b cor = t w- t t w b cor = ( ) / = F ts,rd,cor = b cor F ts,rd = ,400 [6.8.] F ts,rd,cor = 3,573 kn/ Verification of the junction pile: F t,ed = 2,581 kn/ < b T F ts,rd,cor = ,573 = 2,608 kn/ OK 44

47 Exaple 2: diaphrag cell structure The excavation for a dry-dock is to be supported by eans of a cofferda. The soil consists of loose to ediu-dense sands to approx Below this layer follows ediu-dense to dense sands. The NGL (natural ground level) is at El Design life of the structure is 50 years loose to ediudense sand ediudense to dense sand Fig : Initial conditions Assuptions Characteristic soil properties: / kn/ 3 Because of the relative large ebedent depth, the passive earth pressure is calculated with K p (d p = 0). Water levels: groundwater at j k d k c' k kpa upper sand layer 18 / lower sand layer 19 / Excavation level: noinal depth: design depth = noinal depth - excavation tolerance = = with: excavation tolerance = 0.50 (EN 1997 [3]. Local standards ight ipose different values) Variable vertical loads: P 1 = P 2 = 20 kn/ 2. Note: Variable load P 1 is required for analysis of the internal cell pressure, but it has to be neglected for the stability analysis because of its stabilizing effect P 1 = 20 kn/² P 2 = 20 kn/² w e = loose to ediudense sand Dredge level Design level ediudense to dense sand Fig : Final conditions. 45

48 Overall stability a) Calculation of required equivalent width, verification of resistance to tilting due to shear failure in the fill/foundation soil Analysis is perfored with coputer software using the assuptions given above. For an equivalent width w e = 30.5, following oents can be deterined: M kg = 36,542 kn/ M w = 60,360 kn/ M k,q = 5,179 kn/ M R kg = 125,070 kn/ M R Ep = 37,015 kn/ Using forula fro EAU 2004 with the suggested change [6.10.-b] and the partial safety factors: M Ed = 36, , , = 138,586 kn/ M Rd = 125,070 / ,015 / 1.40 = 140,139 kn/ M Ed = 138,586 < M Rd = 140,139 OK LOGARITHMIC SPIRAL SLIP PLANE ANALYSIS SOIL 1 SOIL 2 SOIL Eah = Eav = 0.00 Wph = Wph = Eph = Epv = Weight = Lengths, Levels [], Forces [kn/] Iteration Origin 1.75 / Width Average Friction Angle in Slip Plane Fig : Coputer calculation of required equivalent width w e, verification of resistance to tilting due to shear failure in the fill/foundation soil. Software: Coffda 4.0. [10]. As the cell structure is not founded on bedrock, bearing capacity and deep-seated sliding analyses should be perfored. In addition, piping (hydraulic failure) should also be verified for this type of structure. b) Deterination of cell geoetry As the structure is very deep and the equivalent width is large, a diaphrag wall is selected. The angle of the Y-junction piles is chosen as q = 120. Fro Table 4.3. a) and 4.3. b), following geoetry can be chosen for an equivalent width w e = : Geoetry diaphrag wall Geoetry arc Nuber of piles Wall length Nuber of piles Radius Syste length Arc height Equivalent arc height Interlock deviation N dl M x = r d y c a arc radius r = syste length x = diaphrag wall length dl = angle deviation in arc d a = 2.78 arc height d y = 1.39 equivalent arc height c = 0.94 Nb. of ssp for 1 diaphrag 57 = N Nb. of ssp for 2 arcs 42 = 2 M Nb. of junction piles 2 Nb. of ssp for 1 syste 101 = N + 2 M + 2 Thus: w e = dl + 2 c = =

49 Verification against structural failure a) Calculation of governing internal cell pressure As the cell is ebedded in the soil (and not founded directly on bedrock), the governing internal pressure can be assued to be that exerted at the botto of the excavation, i.e. at elevation Vertical stress at : weight of soil s v1 = = kn/ 2 variable loads s v2 = 20.0 kn/ 2 design value s v = g G s v1 + g Q s v2 = = kn/ 2 Coefficient of earth pressure at-rest: K o = 1 - sin j k = 1 - sin 35.0 = Horizontal earth pressure: h = K o s v = = kn/ 2 Hydrostatic pressure: characteristic value p w1 = = kn/ 2 design value p w = g G p w1 = = kn/ 2 Total horizontal stress: s h,tot = s h + p w = = kn/ 2 = p,ed b) Analysis of resistance of straight web sheet piles AS straight web sheet piles are selected with: R k,s = 5,500 kn/ t w = 12.5 f y = 355 N/ 2 F ta,ed F ts,rd [6.2'.] Interlock resistance: F ts,rd = b R R k,s / g M0 = 0.8 5,500 /1.0 = 4,400 kn/ [6.1.] Resistance of web: F ts,rd = t w f y / g M0 = / 1.0 = 4,438 kn/ [6.1.] Deterining resistance: F ts,rd = 4,400 kn/ Junction Y-pile with q = 120: F ta,ed = F td,ed = p,ed r p,ed = kn/ 2 r = F ta,ed = = 3,673 kn/ < F ts,rd = 4,400 kn/ [6.3'.] The junction pile is anufactured in accordance with Section B 6 of EN [7]; special verification of the welds is therefore not required Durability Loss of thickness due to corrosion of steel is based on Tables 4.1. and 4.2. fro EN The design life assued for this structure is 50 years without any additional protection (sacrificial steel thickness exclusively). Verification of the sheet pile is done in the area where the interlock tension is highest (excavation level). Considering the elevation just below the excavation level, the loss of steel thickness can be estiated as follows: front: natural soil 0.60 back: natural soil 0.60 Total loss of steel thickness: Dt = = 1.20 Reduced interlock resistance due to corrosion of the AS : b cor = t w- t t w b cor = ( ) / = F ts,rd,cor = ,500 / 1.0 = 3,978 kn/ F ts,rd,cor = cor R R k,s / M0 [6.8.] F ta,ed = 3,673 kn/ < F ts,rd,cor = 3,978 kn/ OK 47

50 6.4. Exaples of applications: global safety factor approach Following exaple is based on the global safety ethod, which uses a global safety factor for the overall stability of the cell, and two different safety factors for the structural verification of the straight web steel sheet pile. Those safety factors have been used for the design of any circular cells during the last decades and are still coonly used nowadays. The design ethod considered checks the overall stability: M S M r S F [6.11.] where: M s destabilizing oent (active earth pressure, water behind the cells, variable loads, ) M r stabilizing oent (passive earth pressure, water in front of the cells, ) S F global safety factor The overall stability is based on the logarithic slip plane failure assued by Jelinek, and illustrated in chapter 6.1. above and in chapter 8.3. of EAU 1990 [9]. The ethod is based on standard soil paraeters, usually written as «j» or «cal j», which are values that represent the soil properties. These are not average values, and they should not be ixed with characteristic soil paraeters or design paraeters, as used in the new Eurocodes. Typical values for granular and cohesive soils used with this global safety ethod can be found in chapter 1, Table R.9.1., EAU 1990 for instance. Furtherore, the safety factors for the different loading cases that ay have to be analysed are given in chapter of the Recoendations EAU Many different forulae have been used worldwide for the verification of the straight web steel sheet piles. For the next exaple, the forulae used in EN (2007) have been slightly adapted to take into account the global safety ethod. The verification of the resistance of the straight web steel sheet pile is done with following equations (siilar to [6.1.]): Interlock resistance: F t,r = R k,s [6.12.-a] Resistance of web: S F,1 F t,r = t w f y S F,2 [6.12.-b] where: F t,r straight web steel sheet pile resistance taking into account the web and the interlock R k,s interlock resistance of the straight web steel sheet pile t w thickness of the web of the straight web steel sheet pile yield strength f y Note: The convention chosen for the paraeters in this section is siilar to the one fro Eurocodes, yet slightly different in order to avoid confusion. Global safety factors recoended are: S F = 1.50 S F,1 = 2.00 S F,2 = 1.50 As a siplification, for this chapter, the notation used for the soil paraeters is j, c Exaple 3: teporary circular cells A bridge pier is to be built in the iddle of a river, and a teporary cofferda is to be erected at a spot with shallow bedrock. The cell will be backfilled with sand. Design life of the structure is only 2 years ± bedrock Fig : Initial conditions. 48

51 Assuptions Before erection any deposit above the bedrock is dredged fro the cofferda footprint. Soil properties: / kn/ 3 j' d c' kpa backfill (sand) 18 / bedrock 20 / No ebedent of the tip of the steel sheet piles in the rock is assued. Provisions to prevent loss of fill aterial through gaps between the sheet pile tip and the bedrock have to be ade. Water levels: HWL = LWL = Water levels for overall stability & for interlock resistance verification: in front of wall: behind wall: [= HWL] inside the cell: The water level inside the cell is an arbitrary, yet plausible, choice ade by the design engineer. This assuption has to be strictly enforced during the short lifetie of the structure. Any deviation fro this design criterion needs to be evaluated by the design engineer and alternative solutions have to be elaborated in case this water elevation cannot be guaranteed at any stage of the project. Excavation level: noinal depth: design depth = noinal depth - excavation tolerance = = with: assued excavation tolerance = 0.50 (assuption by design engineer) Vertical loads: P = 30 kn/ 2. Note: Surcharge load P is required for analysis of the internal cell pressure, but it has to be neglected for the stability analysis because of its stabilizing effect. P = 30 kn/² fill ± w e = bedrock Design Fig : Final conditions Overall stability a) Calculation of required equivalent width, verification of resistance to tilting due to shear failure in the fill/foundation soil Analysis is perfored with coputer software based on the assuptions given above. For an equivalent width w e = 17.5, following oents can be deterined: M s = 20,664 kn/ M r = 32,508 kn/ Note: An ebedent of the steel sheet pile in a thin layer overlying the bedrock has not a significant influence on the result, and in ost cases it can be neglected. In this exaple, even if there were a thin deposit layer over the bedrock, it could be neglected. Using above forula the global safety factor of the structure is: S F = M r = 32,508 = OK M s 20,664 49

52 LOGARITHMIC SPIRAL SLIP PLANE ANALYSIS SOIL 1 SOIL 2 SOIL Wph = Eah = 0.00 Eav = Weight = Safety = 1.57 Lengths, Levels [], Forces [kn/], Moents [kn/] Iteration Origin 0.14 / Resistances kn/ - Actions kn/ Width Average Friction Angle in Slip Plane Min.Safety 1.57 Fig : Coputer calculation of required equivalent width we, verification of resistance to tilting due to shear failure in the fill/foundation soil. Software: "Coffda 4.0." [10]. As the cell structure is founded on bedrock, bearing capacity and deep-seated sliding analyses are not required. b) Deterination of cell geoetry The angle of the junction piles is chosen as q = Fro Table 4.1., following geoetry can be selected for an equivalent width w e = No. of piles per Geoetrical values Interlock deviation Design values L Cell Arc Syste Cell Arc 2 Arcs M S N d=2 r r a x d y a w e R a cell diaeter d = radius of the ain cell r = 9.93 radius of connecting arc r a = 4.17 syste length x = offset d y = 0.10 angle = angle deviation in arc a = 6.91 Nb. of ssp for 1 syste 174 Nb. of ssp for cell 124 = 2 (L+M) + 4 S (including 4 junction piles) Nb. of ssp for 2 arcs 50 = 2 N 50

53 Verification against structural failure a) Calculation of governing internal cell pressure As the cell is founded directly on bedrock, the governing internal pressure can be assued to be that exerted one quarter of the height of the cell above the bedrock surface, i.e. at approxiately elevation However, under certain circustances, it ight be advisable to consider a deeper elevation, and in soe cases the excavation elevation is used. Vertical stresses at : weight of soil v1 = = kn/ 2 variable loads v2 = 30.0 kn/ 2 total value v = v1 + v2 = = kn/ 2 b) Analysis of resistance of straight web sheet piles AS straight web sheet piles are selected with: R k,s = 5,500 kn/ t w = 12.5 f y = 355 N/ 2 F t F t,r [6.2-bis.] Coefficient of earth pressure at-rest: K o = 1 - sin j = 1 - sin 30.0 = Horizontal earth pressure: h = K o v = = kn/ 2 Hydrostatic pressure: p w = = 55.0 kn/ 2 Total horizontal stress: h,tot = h + p w = = kn/ 2 = p T = 0.9 ( r a ) (1-0.3 tan j k ) r Note: Above forula fro EN has been deterined with characteristic values of the internal friction angle j k. In this particular case, j k can be deterined with following forula (adapted fro EAU 1990): where: F t : circuferential tensile force in the ain arc deterined with an expression siilar to [6.3.]: F t = p r [6.3-bis.] Interlock resistance: F t,r = Rk,s = 5,500 = 2,750 kn/ S F,1 2.0 Resistance of web: [6.12-a.] tan (j') = tan j k 1.1 Hence: j k = arctan ( tan (30) 1.1 ) = T = 0.9 ( ) (1-0.3 tan (32.42)) 9.93 = F t = p r = = 1,638 kn/ < T F t,r = ,750 = 1,931 kn/ OK [6.5-bis.] F t,r = t w f y = = 2,958 kn/ S F,2 1.5 Deterining resistance: F t,r = 2,750 kn/ Junction pile: r = cell radius = 9.93 r a = connecting arc radius = 4.17 [6.12-b.] Durability As the structure is only for teporary use (2 years), it is not necessary to take into account any loss of steel thickness during its service life. 51

54 Project: Paraíso, Panaa Canal Sections: AS Quantity: tonnes 52

55 7. Construction of cellular structures 7.1. Circular cells Usual construction sequence for circular cell structures: pitch the ain cells, using a teplate; drive the sheet piles in the ain cells; fill the ain cells; pitch the connecting arcs between two copleted ain cells, using a teplate; drive the connecting arcs; fill between the ain cells Teplate Straight web sheet piles have no inherent flexural stiffness. Therefore a teplate is necessary to stabilize the cell during assebly and backfill operations. The design of the teplate is governed by following considerations: installation on land; installation in water: - open sea conditions (waves, wind, current velocity, installation ethod, ), - river conditions (current velocity, installation ethod, ); nuber of cells to be constructed and reuse of the teplate; length of sheet piles; capacity of lifting equipent; safety considerations for work crew. The teplate ust have at least two guiding levels with sufficient distance fro each other to assure proper sheet pile alignent. The lower guide shall be positioned as close to the ground as possible. It shall be ovable to allow easy handling during installation and backfill. Siilar conditions apply to the upper guide. Additionally, this upper guide shall provide a safe working platfor for the crew. The theoretical external diaeter of the teplate is deterined by following forula: R ext = N ssp () [7.1.] 2 with N ssp : nuber of steel sheet piles of the cell ~30 ~48 platfor guide teplate Rext = Int. cell diaeter Ext. teplate diaeter Fig. 7.1.: Recoended teplate diaeter. Additionally, to take into account rolling tolerances of the sheet piles and fabrication tolerances of the teplate, the radius R ext should be reduced by further 30. The design shall follow local standards and be ade by experienced design engineers. 53

56 Cell assebly After installing the teplate at the correct position, the straight web sections shall be placed around the teplate, starting with the junction piles. The exact position of the junction piles has to be deterined by a surveyor. Verticality of these piles has to be checked carefully. All piles shall be fixed teporarily to the teplate. The correct position of the sheet piles shall be checked constantly, for instance by easuring or using fixed arks on the teplate. Closing of the cell shall occur in the iddle between two junction piles. This enables a axiu of flexibility taking into account all the tolerances entioned above. To close the cell, the last piles can be pushed or pulled easily using standard construction equipent (ropes, chain pull) in order to widen or shorten the gap between the piles already in place. To speed up the installation process previously paired double piles can be of advantage. For load transfer reasons, it is generally not recoended to put grease in the interlocks Pile driving After the cell is copleted as described above, the teporary fixation of the first pile to be driven is reoved. This ust be one of the junction piles. Driving is done in stages of less than 2.0, depending on soil conditions. The driving shall proceed in one direction fro this point on until one reaches the first junction pile again. Driving direction shall change to prevent leaning of the piles in one direction. This procedure is repeated until design depth is reached. To allow sooth working progress, the upper guide of the teplate should ove stepwise with the piles. Alternatives are possible, for exaple using a special follower. Before starting filling of the ain cell, at least two piles of the interediary arcs shall be pitched to iniize the ipact of deforation during filling. Interediary arcs shall be installed only after filling of the adjacent cells is copleted. Preferred installation equipent is a vibratory haer, selected according to the specific job-site conditions. If an ipact haer is used, the energy level shall be onitored closely to prevent daages to the sheet piles. To speed up the installation process, driving of panels with double or triple piles is possible Filling of the cells The ain cells can be backfilled independently. It is essential that the teplate reains in place and guarantees the stability of the cell. Generally, backfill should reach 2/3 of the cell height at least before reoving the teplate. The filling operation shall be carried out fro the centre of the cell to avoid any unbalanced loadings. Conveyor belts or hydraulic fills are norally used. During the filling the sheet piles develop tensile resistance which translates into a sall increase of the diaeter, and corresponds to the barrel effect. Granular soils (well graded sands, gravels, quarry aterial) are recoended as fill aterial. This allows to choose correct design paraeters, and helps the consolidation process. If the cell fill is to be copacted additional earth pressure has to be taken into account in the design. Vertical drains ay reduce the consolidation tie of the fill. guiding platfor bearing piles Seabed - predredging of ud layer if applicable - superstructure copleted - arcs filled after adjacent cells copleted Main cell - cell filling copleted - stage 2 filling operation - teplate extracted - sheet piles driven - stage 1 filling operation - teplate partially lifted - teplate installed - pitching of sheet piles Arc cell Figure 7.2 Fig. 7.2.: Installation phases of circular cell structures. 54

57 Superstructures and loadings Fender, bollards, crane loads, surcharge loads, and peranent loads will be transferred either directly into the fill, or respectively introduced through bearing piles. Any direct vertical loading of the straight web sheet piles shall be avoided. All peranent superstructure works shall be executed once the cofferda has fully stabilized Construction tie Assuing appropriate job-site organization and equipent, it is possible to execute one cell syste per seven working days. This can be subdivided into following construction stages for one cell: installation, positioning and fixing of teplate pitching of sheet piles driving filling execution of arcs (not on the critical path) Variations are possible and influenced by local experience and specific job-site conditions. 2 days 2 days 1 day 2 days 2 days 7.2. Diaphrag cells The principal installation steps are siilar to the ones for circular cells. The ain differences consist in ulti-staggering of sheet piles, the andatory use of a second teplate and specific care of filling operations (if applicable). Please contact our technical departent for ore details on installation procedures. Fig. 7.3 Fig. 7.3.: Typical installation steps for a diaphrag cell structure on land. 55

58 Project: Bal Haf, Yeen Sections: AS Quantity: tonnes 56

59 8. Conventional sybols Whenever possible, sybols and abbreviations are based on the docuents that are referenced. Otherwise, they confor as far as possible to the rules and principles fro Eurocode 1. However, soe abbreviations, indexes and so on ight be specific to this brochure either because they do not exist in the referenced docuents or because the version of the docuents / standards has changed. Sybols used only once in the docuent or which are defined each tie they are used are not entioned in this chapter Greek letters Sybol Definition Units b pre-bent angle of a straight web steel sheet pile b cor b R b T factor accounting for the corrosion of straight web steel sheet piles factor accounting for the interlock resistance of straight web steel sheet piles factor accounting for the behaviour of a welded junction pile at ultiate liit states d structure-ground interface friction angle d a deviation angle of the sheet piles in the arc cell d deviation angle of the sheet piles in the ain cell g weight density of soil kn/ 3 g effective weight density of soil (suberged) kn/ 3 g w weight density of water kn/ 3 g c g Ep g G g Q g Gl partial factor for the effective cohesion partial factor for earth resistance partial factor for a peranent action partial factor for a variable action partial factor for a peranent stabilising action j' angle of shearing resistance in ters of effective stress q connecting angle of the junction piles s v vertical stress kpa s h horizontal coponent of the vertical stress kpa s h,tot horizontal stress at the governing level for cell structures kpa 57

60 8.2. Latin letters Sybol Definition Units c cohesion intercept of soil kpa c cohesion intercept in ters of effective stress kpa c u undrained shear strength of soil kpa dl length of the diaphrag wall d y offset of the arc cell to the ain cell; arc height fy yield strength of straight web steel sheet piles MPa p,ed design value of the internal pressure acting in the ain cell of a cellular cofferda kpa p w water pressure kpa r radius r a initial radius of the arc cell in a cellular cofferda r initial radius of the ain cell in a cellular cofferda t f noinal flange thickness of a steel sheet pile t w noinal web thickness of a steel sheet pile w e equivalent width of a cellular / diaphrag cell syste x syste length of a cellular / diaphrag cell syste HWL High Water Level LWL Low Water Level K a K 0 K p coefficient of active earth pressure coefficient of at-rest earth pressure coefficient of passive earth pressure F t,ed design value of the circuferential tensile force in a cellular cofferda kn/ F ta,ed design tensile force in the arc cell of a cellular cofferda kn/ F t,ed design tensile force in the ain cell of a cellular cofferda kn/ F ts,rd design tensile resistance of siple straight web steel sheet piles kn/ 8.3. Subscripts Sybol cor d k red Definition corroded design value characteristic value reduced Note: Subscripts ay have different eanings. 58

61 9. References Standards [1] EN 1991 Eurocode 1: Actions on structures. CEN [2] EN 1993 Eurocode 3: Design of steel structures. Part 5: Piling. Version CEN [3] EN 1997 Eurocode 7: Geotechnical design. CEN [4] EN 1998 Eurocode 8: Earthquake resistant design of structures. CEN [5] EN Hot rolled sheet piling of non alloy steels. CEN [6] EN Cold fored sheet piling of non alloy steels. CEN [7] EN Execution of special geotechnical work - Sheet-pile walls. CEN Books [8] EAU Recoendations of the Coittee for Waterfront Structures. Ernst & Sohn. Berlin [9] EAU Recoendations of the Coittee for Waterfront Structures. Ernst & Sohn. Berlin Software [10] Coffda 4.0. Software by Marco Mascarin (2001) 2 nd Incheon Bridge, South Korea Ohio River, USA 59

62 Disclaier The data and coentary contained within this steel sheet piling docuent is for general inforation purposes only. It is provided without warranty of any kind. ArcelorMittal Coercial RPS S.à r.l. shall not be held responsible for any errors, oissions or isuse of any of the enclosed inforation and hereby disclais any and all liability resulting fro the ability or inability to use the inforation contained within. Anyone aking use of this aterial does so at his/her own risk. In no event will ArcelorMittal Coercial RPS S.à r.l. be held liable for any daages including lost profits, lost savings or other incidental or consequential daages arising fro use of or inability to use the inforation contained within. Our sheet pile range is liable to change without notice. Printed on FSC paper. The FSC label certifies that the wood coes fro forests or plantations that are anaged in a responsible and sustainable way (the FSC principles proote the social, econoical, environental and cultural needs of today s and the next generations). Edition August ArcelorMittal Coercial RPS S.à r.l. All rights reserved. 60