GROUND MOVEMENT THE CORDEK SOLUTION CELLCORE CLAYMASTER CELLFORM

Transcription

1 GROUND MOVEMENT THE CORDEK SOLUTION CELLCORE CLAYMASTER CELLFORM

2 Identifying The Problem cause and effect The problem of ground movement is well known to engineers and builders. It affects construction sites throughout the UK, and particularly those in the South East. Whether the cause is clay heave from naturally occurring shrinkable clay soils, expansive shales or overburden recovery associated with excavation, if the movement is restrained the lateral and uplift forces produced are massive. To avoid the build up of these potentially damaging forces, foundations must be designed to accommodate any ground movement that is anticipated. The amount of ground movement that may occur will vary by site, and be dependent on a number of factors including; The Plasticity Index of the soil The degree of dessication of the soil The removal or planting of vegetation and trees Ground levels and excavation depth A suitably detailed Site Investigation should indicate the extent of ground movement expected. The Engineer can then design appropriate protection measures to ensure the long term integrity of foundations and ground floor slabs. The NHBC standard Building Near Trees (chapter 4.2), supported by information from the BRE, provides detailed and informative data on the subject. Additionally, there are now many companies offering specialist services in this field. Cordek products that are available to the structural designer for this purpose are extremely efficient, economic, easy to design and quick to install.

3 For piled beams, pile caps, and reinforced ground floor slabs Cellcore consists of a honeycomb made from expanded polystyrene. It is Agrément approved and produced by a computer controlled manufacturing process, utilising materials that are quality assured to ISO 9001 or 2. PAGE CELLCORE 2 RESIDENTIAL 8 COMMERCIAL 10 As ground movement occurs Cellcore compresses and buckles to accommodate it, thereby reducing the forces that would otherwise be transmitted to the foundations. It is used extensively in both residential and commercial applications. Claymaster is a low density expanded polystyrene, designed to compress under load and so reduce the lateral forces of the ground movement on the foundation. It is coloured pink to aid recognition on site. PAGE CLAYMASTER 6 RESIDENTIAL 8 COMMERCIAL 10 Like Cellcore, Claymaster is unaffected by water and is available in a range of standard thicknesses, designed to accommodate differing levels of ground movement. It is used for both domestic and commercial projects, generally in conjunction with Cellcore. And where shuttering is required Cellform is a permanent shuttering system which offers built in protection against ground movement. The unique design minimises concrete wastage and reduces excavation, making it a fast and economic solution for constructing in-situ ground beams and pile caps, on sites with ground movement problems. Used on commercial and residential projects, Cellform is water resistant, light, durable and quick to install. PAGE CELLFORM 4 RESIDENTIAL 8 COMMERCIAL 10 Cellform is always tailor-made to the site requirements for beam size/pile caps.

4 The Cordek Solution Answering the problem of Ground Movement Since 1973 Cordek has built a reputation for creating innovative, cost effective, solutions to traditional construction problems. A typical example is the development of products to alleviate the effects of ground movement. Terminal 5 Heathrow Royal Opera House Canary Wharf Station Claymaster was introduced in 1983 while Cellcore was developed a few years later. Both are Agrément approved and have become the first choice solution on projects where ground movement is anticipated, in the UK and overseas. Chelsea Village Development

5 Mansion House Osaka International Conference Centre Japan Royal Albert Hall The New Wembley Stadium Millennium Dome

6 Cellcore Product design and application TYPE CC For piled beams and pile caps TYPE CP For slabs Cellcore is designed to support the weight of a given thickness of concrete plus a live load allowance of 1.5 kn/m 2, without creep compression during the 16 hour curing period. The total of these is defined as the SAFE LOAD and is expressed in kn/m 2. When ground movement occurs, the Cellcore honeycomb will compress and buckle when a pre-determined load is reached. Defined as the FAIL LOAD, in kn/m 2, it is the maximum load that will be transmitted to the foundations. The variables which determine the performance of Cellcore are the leg depth of the panel (selected to accommodate the predicted amount of ground movement at the Fail Load), and the compressive strength of the legs which is defined by the density or the thickness of the polystyrene honeycomb. This flexibility of product design allows selection of the optimum grade of Cellcore to suit the designer s particular requirements. Cellcore is manufactured with two different tops: TYPE CC for use beneath piled beams and pile caps, incorporates a heavy-duty polypropylene top. In certain circumstances a protection layer of concrete blinding may be required. TYPE CP for use beneath suitably reinforced concrete slabs. It includes a 50mm thick polystyrene top, protected by a 2mm thick polypropylene sheet that provides a high degree of insulation. This can be improved by increasing the thickness of the top. Unlike other anti-heave products, Cellcore does not rely on material degradation for the system to become effective. Once the Cellcore panels are laid and the joints sealed, the surface is ready to receive the reinforcement and the concrete. Cellcore is unaffected by water so, in wet weather or when foundations are below the water table, work can continue without reducing its effectiveness. On sites where water pressure is a potential problem or the water table is expected to rise, special grades of Cellcore are available with drainage apertures. To assist specifiers, the tables below detail the standard Cellcore range. Patent Numbers for Cellcore and Cellform Standard Grades of Cellcore Table 1 Concrete Depth and Load characteristics Cellcore Maximum Cellcore Safe Load Fail Load Grade Concrete Type kn/m 2 kn/m 2 *Thickness 8/12 270mm CP /15 350mm CC CP /22 550mm CC CP Sizes Standard Panel: 2.44m x 1.22m Beams: Manufactured to width in 2.44m lengths For non standard sizes please contact Cordek 20/30 770mm CC CP *Allows for 1.5kNm 2 Live Load When concrete thickness exceeds 770mm please contact Cordek Proven Cellcore Grades are available for concrete thickness up to 2,000mm For depths in excess of this thickness please contact our Technical Services Department 2

7 Standard Depths for Cellcore Table 2 Compression characteristics Selection of Cellcore Table 3 Ground movement and void characteristics Cellcore Type Compression Type CC Type CP* at Fail Load Depth mm Depth mm mm The depth of Cellcore selected will depend on the predicted measure of ground movement at the Fail Load *Depth of the EPS top can be increased to improve insulation values Results NHBC Predicted Ground Depth of Cellcore of Category Movement, or required to achieve Soil BRE/NHBC Equivalent Void Analysis requirement Plasticity Shrinkage Void Index Potential dimension (mm) Type CC Type CP Low mm 150mm Medium mm 225mm High mm 300mm Above 60 Very High mm 350mm This category is applicable when potential ground movement exceeds the NHBC range 3

8 Cellform Product design and application The Benefits the project variations Arrives on site tailor made for Quick and simple to install with basic hand tools Can be easily adapted to site Minimises concrete wastage Reduces muck-away and the landfill tax it attracts A full range of accessories ensures secure construction Cellform is a unique permanent shuttering system for the construction of in-situ concrete ground beams and pile caps, in areas where ground movement is predicted. Manufactured from expanded polystyrene and heavy duty polypropylene, it incorporates the proven Cellcore technology for protection against upward movement, and is used in conjunction with Claymaster to accommodate lateral movement. Suitable for all types of projects, Cellform is tailor made to site requirements. Cordek s technical department will provide a full scheme detailing all necessary components, the optimum grade and depth of Cellform to be used and the Claymaster requirements, including pile collars. Double Infill Panel Straight Connector Corner Connector Formbrace Claymaster Single Infill Panel Claymaster Pile Collar 4

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10 Claymaster Product design and application Claymaster is a compressible expanded polystyrene, specially manufactured within a critical density range. It is Agrément approved and designed to alleviate the lateral force of ground movement on foundations. (see table 4) Claymaster does not compress significantly until loads exceed 20kN/m 2. Dimensions Claymaster is produced in a standard size panel 2400mm long, by 1200mm wide, with thicknesses ranging from 50mm - 300mm. However, Cordek provide a made to measure service on length and width, with special shapes like circular sections cut to order. A load of 40kN/m 2 is needed to produce 50% compression. Consequently its use is not recommended under ground floor slabs. Typical PIled Ground Beam Note : The lateral pressure from clayheave invariably occurs from the inside of the construction, and Claymaster should be positioned accordingly. Claymaster is totally unaffected by water, and like Cellcore it can be used on sites where the foundations are below the water table. It is available in a range of thicknesses, that will compress to accommodate selected levels of predicted ground movement (see table 4 ). Typical Deep Trench Fill Deep Trenchfill is a traditional type of house foundation, and where necessary Claymaster is used to protect the sides against ground movement. Due to more economic piling methods, the disposal cost of excavated material and stricter Health & Safety regulations, its use is declining. Selection of Claymaster Table 4 lateral ground movement and void characteristics Shrinkage Predicted lateral movement Claymaster thickness Potential NHBC recommended void for equivalent void Low Zero Zero Medium 25mm 50mm High 35mm 75mm *Very High 60mm 100mm * This category is recognised by the BRE 6

11 The Markets Involved Overview of applications The potential for ground movement presents a problem to the designers of both residential and commercial projects. While clay heave is the primary cause of ground movement on residential sites, for the larger commercial/industrial projects overburden recovery creates an additional and significant problem. Cordek s ground movement solutions apply to both market sectors, but the applications differ as explained in the summary below. Residential - HOUSES & FLATS In the housing market, piled ground beams with pre-cast beam and block floor is now the most common method of construction on sites subject to ground movement. The use of Cordek products (Cellcore and Claymaster) has generally been confined to protecting the piled ground beams. However, Cellcore reaches ultimate compression at much lower loads than standard compressible fills, with the Fail Load ranging from 12-30kN/m 2 depending on the grade selected. This is important for all applications, but is particularly significant when the deadload is limited; i.e. bungalows, beneath patio doors, garages, etc. The suitability of Cellcore for such applications is now well recognised and its usage has increased dramatically in recent years. For blocks of flats, the design often requires concrete floors to be constructed in-situ. Cellcore is the ideal solution for this application as the much greater deadweight involved ensures that the effects of ground movement can be adequately resisted. Commercial In commercial construction, Cellcore is extensively used for protecting suspended in-situ ground floor slabs, as well as pile caps and ground beams, from the effects of ground movement. Due to the greater superstructure loads it is generally possible to design the in-situ slab and foundations to accommodate the uplift forces. Because of its design flexibility, and the capacity to accept a load of up to 2 metres of concrete without significant compression, Cellcore is widely used beneath piled beams and pile caps. Projects undertaken include schools, airport terminals, supermarkets, prisons, offices and town centre re-developments, with the use of Cellcore ranging from 50 to 100,000 sq mtrs. 7

12 Residential Applications The declining use of deep trench fill foundations means that in areas susceptible to ground movement, piled ground beams are now the most common type of foundation for residential buildings. On those sites where ground movement is predicted, protection for the beams is therefore a priority. Solutions In designing a safe and effective solution the limited deadweight offered by the overall structure, including its foundations, becomes an important consideration. The chosen product must be able to fully accommodate the predicted amount of ground movement. The design must allow for the residual upward force, and ensure that it is adequately resisted by the total deadweight of the structure. Cellcore is the ideal solution for piled ground beams, reaching ultimate compression at much lower loads than standard compressible fills. Fail Loads range from 12-30kN/m 2 depending on the grade, and the Cellcore honeycomb is designed to progressively collapse and therefore minimise the uplift forces on the foundations. Now used extensively throughout the housing sector, the detailed performance characteristics for Cellcore and Claymaster are shown on pages 2 & 6 respectively. They provide accurate data for designing a solution that will safely protect foundations against upward and lateral ground movement. While the standard range of Cellcore grades are suitable for most residential projects, Cordek can quickly tailor a product to meet site-specific requirements. Cellform, combined with Claymaster, provides a complete and economic solution for the construction of ground beams in soil susceptible to ground movement. 8

13 Design DESIGN EXAMPLE 1 Once the potential for ground movement has been established, the designer must quantify the possible degree of movement. The NHBC standard Building Near Trees (chapter 4.2), supported by information from the BRE, provides detailed and informative data to help predict this figure. Having established the magnitude of the problem, the designer can then develop the best technical solution for the specific site circumstances. For example, using the Cellcore performance characteristics detailed in the tables on pages 2 & 3, the design solution and product specification for a typical 450mm deep ground beam would be formulated as shown in design example 1. Note: A range of Standard Details are available on our website, and can be downloaded for incorporation into plans and drawings. Please visit For this example assume the soil survey showed a plasticity index of Table 3 on page 3 shows the potential for ground movement is medium - BRE/NHBC data recommends a clear Void of 100mm. - The beam depth is 450mm 1. Total deadweight/downward load is Self weight of 450mm concrete beam: 0.45m x 24kN/m 3 = 10.8kN/m 2 + Live load allowance = 1.5kN/m 2 TOTAL LOAD = 12.3kN/m 2 2. Table 1 on page 2 shows the next SAFE LOAD value is 15kN/m 2 (Fail Load of 22kN/m 2 ) The appropriate Cellcore grade = 15/ mm of ground movement is predicted and Table 3 on page 3 shows that, The Cellcore depth to accommodate this = 175mm So, the full product specification = Cellcore 175 CC 15/22 However, Table 1 on page 2 shows this Cellcore specification has a FAIL LOAD of 22kN/m 2 The beam must therefore accommodate a Residual Upward Force derived as follows: Cellcore Fail Load - Self weight of beam = Residual Upward Force = 11.2kN/m 2 Typically two modes of failure should be considered at this point. i) Lifting the beams off the top of the piles ii) Failure of the beam in bending or shear due to the uplift forces Note: Table 4 on page 6 shows the recommended void for lateral movement in medium shrinkability soils is 25mm and that a 50mm thick Claymaster grade would be required to accommodate the lateral movement if the design incorporates any perimeter downstand beams. 9

14 Commercial Applications In the commercial market, as opposed to the domestic field, Cellcore is extensively used under suitably re-inforced in-situ ground floor slabs. These are generally thick enough to make it both practical and economic to withstand the uplift forces, and there is sufficient deadweight to prevent the structure lifting. Where applicable Claymaster is used in conjunction with Cellcore, to counter the effect of lateral ground movement on the foundations Because of its design flexibility, and capacity to accept large loads without compressing before the Safe Load is reached, Cellcore is also widely used beneath piled beams, piled raft foundations, pile caps and suspended ground floor slabs. Apart from the standard grades shown on page 2, Cordek have tailormade over 100 site specific types of Cellcore. Cordek make no extra charge for the design, testing and production of these unique grades of Cellcore. Additionally, the honeycomb design of Cellcore can also be tailored to accommodate particular site conditions. For example, the rising water table in Greater London is now an important issue. Because of this the Cellcore used during refurbishment of the Royal Opera House included cell to cell drainage slots, to alleviate a potential build up of water pressure. For non-standard designs please contact our Technical Services Department. Solutions For the applications described above, Cellcore is the most widely specified and proven solution for protection against the upward forces of ground movement. Generally Claymaster will be used to protect against the lateral movement. Unlike products that rely on material degradation both Cellcore and Claymaster are water resistant, so groundwork can progress below the water table and during wet weather, without compromising performance or product integrity Its design flexibility is such that grades can be produced which will safely accommodate a Safe Load of 50kN/m 2, or up to 2 metres of concrete, before significant compression occurs. Equally, for deep excavation where considerable overburden recovery is predicted, a design to accommodate up to 400mm of heave can be provided. 10

15 Design DESIGN EXAMPLE 2 Invariably a soil survey is conducted prior to the construction of commercial buildings to identify the likelihood of movement due to clay heave or overburden recovery. It will also provide a reasonable indication of the amount of movement that might be expected. This data will then allow the designer to develop a Cordek solution that is technically suited to both the structural requirements and site conditions. Tables 1,2,3 & 4 of this brochure show the grades and performance characteristics for Cellcore and Claymaster, which can be used to select the correct product specification. The example on this page is indicative of the process involved. Light Slab (200mm thick) - Assume the soil survey showed a plasticity index of 14 - Table 3 on page 3 shows soil heave potential is low shrinkability - Survey/BRE/NHBC data recommends a clear Void of 50mm. 1. Total deadweight/downward load is:- Self weight of 200mm concrete slab: 0.20m x 24kN/m 3 = 4.8kN/m 2 + Live load allowance = 1.5kN/m 2 TOTAL LOAD = 6.3kN/m 2 2. Table 1 on page 2 shows the next SAFE LOAD value is 8kN/m 2 (Fail Load of 12kN/m 2 ) The appropriate Cellcore grade = 8/12 3. A maximum 50mm of ground movement is predicted and Table 3 on page 3 shows that, The Cellcore depth to accommodate this in CP form = 150mm So, the product specification = Cellcore 150 CP 8/12 However, Table 1 on page 3 shows this Cellcore specification has a FAIL LOAD of 12kN/m 2 The slab must therefore accommodate a Residual Upward Force, derived as follows: Cellcore Fail Load - Self weight of beam = Residual Upward Force = 7.2kN/m 2 Typically two modes of failure should be considered at this point. i) Lifting the slab off the foundations ii) Failure of the slab in bending or shear due to the uplift forces Note : The table 4 on page 6 shows that no void is required for lateral movement in low shrinkability soils, so there is no Claymaster application for this design. 11

16 On-Site Application Delivery Cellcore, Claymaster and Cellform are delivered to site stretch wrapped in polythene, for protection and ease of handling. Cutting to size The products are lightweight and easy to handle and if cutting is necessary, either a hot wire cutter (which can be hired or purchased) or a fine toothed saw is recommended. Storage While panels should be weighted down when stored on site, no special storage conditions are required as the product performance is unaffected by water. Most damage, particularly to Cellcore, occurs during handling and storage. Cellcore is designed to collapse, so sensible precautions should be taken. Installation While the procedure is straightforward, the following points are relevant. Cellcore and Cellform should be placed on a firm level surface which will ensure uniform loading on the legs. A layer of concrete blinding will usually be necessary to achieve this condition. Seal joints between panels with a suitable formwork tape which is available from Cordek. Alternatively if a dpm is specified under slab/beams this will adequately seal the joints. Place the steel reinforcement in position using Cordek s galvanised steel spreader plates or big foot plastic spacers, to distribute the load across the Cellcore. Do not overload with steel. Do not surcharge with concrete. Before a project commences on-site, one of Cordek s technical sales executives will be available to provide technical support and advice. Additional support is also available via Cordek s technical sales line

17 Tailor-made solutions and technical support The Cordek solution to ground movement problems is much more than just a choice of products. While Cellcore and Claymaster are fully certificated and proven on projects throughout the UK and overseas, it is their design flexibility plus Cordek s technical and engineering expertise that helps transform them into complete solutions. Often this results in a solution that is tailor-made to the specific site conditions, and project design. In addition to the standard product grades and sizes shown in this brochure, a wide range of options and technical support are available on request. Cellcore Beam width panels Drainage holes to increase permeability Grades to accommodate up to 2 metres head of concrete No charge for development and testing In-house estimating and detailing department, using AutoCAD Site specific detailing to customer requirements Depths to accommodate heave of up to 400mm Cellform Product tailor-made to site requirements Detailed take offs provided free of charge Options available to suit customers preferred method of working Claymaster Available in a wide variety of thicknesses to a maximum of 600mm No charge for cutting to size Pile collars cut to shape and size Over 20 years experience with ground movement problems, has provided Cordek with a wealth of practical, problem solving knowledge. That knowledge is only a phone call or away, and there is no charge or commitment! Standard details for many ground movement applications are available on our website They can be downloaded and incorporated directly into plans or drawings. 13

18 For our detailed literature on these other Cordek Solutions, please call our technical sales on: +44 (0) Ventform For venting hazardous gases from under buildings Trough Moulds For forming ribbed concrete floors Waffle Moulds For forming two-way spanning floors Correx & Seekure For temporary protection applications Formwork Solutions Including archways, columns, staircases, voidformers, landscaping Groundform A formwork system for in-situ ground beams and pile caps Tipform A system for constructing steep sided landfill sites Piling Accessories A range of product solutions and systems Cordek Bentonite WM For below ground waterproofing applications If the contents of this brochure do not point to a solution for a particular ground movement problem, we urge engineers and specifiers to call our Technical Sales line on Our reputation is built on innovation and we have a wealth of problem solving experience for you to call on. Cordek Limited Spring Copse Business Park Slinfold West Sussex RH13 0SZ England Telephone +44 (0) Facsimile +44 (0) sales@cordek.com The contents of this brochure are the copyright of Cordek Limited and may not be reproduced without permission. January