Even the Midwest floods of 1993 did not cause us to rethink the risks. After all, outside a few problems with federal levees, the levee system perform

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1 ASCE Fall Technical Seminar Standard of Practice for Levee Design Chris Groves October 2009 Before Katrina one could describe levees as the stepchild of the engineering profession After Katrina our attitude about the risk posed by the levee system was different 1

2 Even the Midwest floods of 1993 did not cause us to rethink the risks. After all, outside a few problems with federal levees, the levee system performed quite well. Overtopping of the agricultural levees had been expected and as a matter of policy this overtopping help protect the urban levees. Katrina managed to change our understanding of acceptable levee performance overnight. The lessons learned in the 1927 Mississippi River flood had long since been forgotten Flooding criteria has led too most of the problems we have experienced A 100-year or greater flood has a 26% probability of occurrence in the life of a 30-year mortgage. People are dropping the flood insurance when they have only 100- year protection. Banks require fire and storm insurance for much less likely events. Banks should require flood insurance until a much higher level of protection is provided. From a public safety prospective, society should keep the general public out of the flood plain until a much higher level of protection is provided. 2

3 How is flood frequency currently being defined? The term free board is being replaced. Now it is the 90 or 95 percent probability of nonexceedance. EM has become the manual for levee design. Other documents are referenced On the first page the document states Even though levees are similar to small earth dams they differ from earth dams in the following important respects: a) A levee embankment may become saturated for only a short period of time beyond the limit of capillary saturation, b) Levee alignment is dictated primarily by flood protection requirement, which often results in construction on poor foundation, and. 3

4 Modes of failure are identified as, Overtopping Surface erosion Internal erosion (piping) Slides within the levee embankment or the foundation soil. The differences in urban levees and agricultural levees. Agricultural levees are generally constructed to provide a crest elevation above the 50-to100-yr level of protection. Agricultural levees were generally not designed by a geotechnal engineer. Agricultural levees have seen poor construction and repair practices. Urban levees have been constructed over the top of agricultural levees. Urban levees have had some borings and geotechnical input. Urban levees protect lives. Manual describes a phased investigation including Preliminary geological investigation including an office study based on available information and a field survey to define the topography, evidence of past problems, and natural and manmade features. Subsurface explorations with two phases of borings, test pits, geophysics, pump test, etc. 4

5 While aerial photographs are mentioned a geomorphologic study is not specifically described Seepage and stability analysis are described as the same scope one would do for a dam. Case I End of Construction Case II Sudden drawdown Case III Steady Seepage from full flood stage Case IV Earthquake (normally not required) Steady Seepage becomes a problem for most unzoned homogenous embankments. When the phreatic surface breaks out on the face of the embankment the factor of safety drops. This issue is often addressed with one or more of the following. A small cohesion of say 100 psf for clay Ignoring shallow circles that do not reach the crest. Also addressed in section 6-8 of EM Transient seepage analysis (results subject to assumptions) A rule-of-thumb seepage geometry has been assumed. Seepage berms. 5

6 Factor of safety criteria are as follows 1.4 for steady seepage. 1.3 for end of construction 1.0 to 1.2 for rapid drawdown A series of exceptions are also stated. Guidance for design of levees generally follows guidance for earth dam. Then why does it appear that levees perform poorly in comparison? What are the principal hazards for levees (failure modes)? Overtopping Underseepage Slope Stability Through Seepage and Penetration Animal Borros 6

7 Overtopping could be a low spot or flood could exceed the design Under seepage starts as a small boil and deteriorates with each flood Slope instability usually the result of a seepage problem 7

8 Through seepage a construction problem, a utility, or animal burrow Animal Borrow What is Acceptable Risk? What is risk? Who determines what is acceptable? 8

9 Definition Risk = (probability) X (consequences) Risk Risk is never acceptable unconditionally. Risk is only acceptable if some benefit can compensate for the risk. Fischhoff 1981 Dams A dam is constructed for the benefit of the owner of the dam It is not acceptable to increase the risk to people downstream who receive no benefit. Therefore, we use very high standards in the design and construction of a dam. 9

10 Criteria Levees A levee is constructed for the benefit of the people who live behind the levee. Can they accept some risk? Engineers know that a dam should have an impervious zone and a pervious drainage zone it is not acceptable for seepage to breakout on the downstream face. Engineers followed the practice of the farmers for the levees. 10

11 Typical Embankment USACE Manual Perceptions Farmers understood the risk. They kept an eye on the river and were quick to evacuate farm equipment and personal belongings. Prosperous farmers would move family up on bluffs and continue farming flood plains. Perceptions When the general public began moving onto the flood plain they did not understand the risk. They were often not sure where the river was located. They did not know what levees looked like, who constructed them, or who maintained them. 11

12 Perceptions The general public does not know what a 100-year levee is. Does it mean that the flood comes about every 100 years? Does it mean that because there was a large flood 10 years ago there will be 90 years before the next one? I don t plan to live another 90 years, so I must be ok. Perceptions I am protected by a levee. Protected means there will never be a flood greater than the levee s capability to protect. Perceptions Has this misconception of terminology been cleared up by FEMA and the USACE? NO! But lately they have been trying. 12

13 Congress and FEMA Has defined the Base Flood as the flood with a 1 percent chance of exceedance on an annual basis. When a levee provides protection for a flood with a 1% probability, people within the protected zone are not required to purchase flood insurance. BAD IDEA! Reality In a 30-year period there is a 26% chance that an event with a 1% annual probability will occur People that pass on the flood insurance for their home are betting they will not lose their greatest asset for the sake of saving on insurance. Reality Most people in the Midwest have storm insurance. The banks require it with the mortgage. Is one home in four destroyed by tornados? Who carries much of the blame when the levee is overtopped? USACE took the blame for New Orleans. 13

14 From a social standpoint What is wrong with the system? A 1% chance of failure each year is unacceptable when people understand the risk. The path followed Farmers want to sell the land for development and retire. Developers want to develop the valuable floodplain near cities for a profit. Cities want the tax base 14

15 Compounding risk Congress and FEMA has set a standard with too much risk. Engineers are willing to use a level of practice that results in too many failures. Home owners do not want to purchase the insurance. Who is to blame? From an Engineering Standpoint What is wrong with the system? Engineering Hydrology criteria who would design a bridge or building with a 26% chance of failure in a 30- year design life? Geotechnical exploration who would design a structure with borings spaced at 1,000 feet with closer spacing at identified problems 15

16 Engineering Geotechnical analysis who would design a dam without internal drainage features? Geotechnical stability and underseepage who would consider observation during loading to be an important tool to find design deficiencies? Finding the hidden problem Residual Risk 120 year flood 100 year flood Levee Residual Risk 16

17 Lessons What have we learned and what should we do? Go for a 500-year (.2% probability) criteria and stress that there is still a 6% probability of failure in a 30-year period, or suggest Probable Maximum Storm criteria used in sizing spillways for dams Lessons Stress the education of risk Stress that potential for loss of life should be considered in residential zoning. When a warehouse or factory is flooded the risk to life is much less Go for greater levee setbacks from the river banks Questions??? 17

18 10/28/2009 AUGER CAST PILES Richard W. Stephenson, Ph.D., P.E. 1 Auger-Cast Piles Also Known As: Augered Pressure Grouted Pile (APG) Augered Cast-in-Place Piles Continuous Flight Auger Piles Intruded Mortar Piles Auger Piles Grouted Bored Piles Augered Grout-Injected Piles 2 10/28/

19 10/28/2009 Auger-Cast Piles 0.3 to 0.9 m (12 to 36) Inches Diameter Up to 30 m (100 feet) Deep Capacities as for Driven Piles of Same Size 4 Single piles Sound wall Light pole Groups Bridges Etc. 10/28/ Reinforcement Confined to upper 10 to 15 m (33-50 ft) Occasionally full length reinforcement 10/28/

20 10/28/2009 Differences between ACIP and drilled shafts The main difference is that the use of casing or slurry to temporarily support the hole is avoided. Drilling the hole in one continuous process is faster than drilling a shaft excavation, 10/28/ The torque requirement to install the continuous auger is high compared with a conventional drilled shaft of similar diameter; therefore, The diameter and length of ACIP piles are generally less than drilled shafts. The use of a continuous auger for installation also limits ACIP piles to soil or very weak rock profiles 10/28/ Differences between ACIP and driven piles Noise and vibration due to pile driving are minimized ACIP piles also eliminate splices and cutoffs. Soil heave due to driving can be eliminated 10/28/

21 10/28/2009 A disadvantage of ACIP piles compared to driven piles is that the available QA methods to verify the structural integrity and pile bearing capacity for ACIP piles are less reliable than those for driven piles. Another disadvantage of ACIP piles is that ACIP piles generate soil spoils that require collection and disposal. 10/28/ Construction Techniques and Materials 10/28/ Drill Rigs Crane Mounted Continuous- flight hollow- stem auger Crowd limited to total weight of gearbox, augers above ground and soil on auger flights 10/28/

22 10/28/2009 torque capacities for crane- attached rigs range from 20 to 120 kn-m (15,000 to 90,000 ft-lbs); 7to50kNm kn-m (20,000 to 36,000 ft-lbs) are most common for private commercial work. 10/28/ /28/ Hydraulic Rig 10/28/

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25 10/28/ /28/ Grout or Concrete? Grout mixes are sometimes preferred for easier insertion of steel reinforcement into the pile; Grout mixes tend to be more fluid and have greater workability; and Grout mixes tend to be easier to pump, and many contractors, who have historically used grout mixes, have grout pumps and equipment that may not be suitable for use with concrete. 10/28/ Grout will generally have a higher unit cost than concrete; Grout will tend to have a slightly lower elastic modulus than concrete; and Grout will tend to be less stable within the hole when drilling through extremely soft soils (such as organic clays or silt). 10/28/

26 10/28/ /28/ Wider acceptance of ACIP Piles in commercial rather than transportation Simple foundation requirements: a large number of piles are commonly used in a compact area primarily to support large concentrated dead loads. Speed of installation ti of ACIP piles over other pile types. Increased use of design-build contracting in private work, in which contractors are highly motivated toward speed, economy, and innovations to those means. 10/28/ Increased requirements to minimize noise and vibrations from pile installation in heavily populated areas. A reluctance by many owners to utilize ACIP piles because of concerns about quality control and structural integrity. The typical demand on bridges for uplift and lateral load capacity, scour considerations, and/or seismic considerations, require pile diameters and possibly lengths up to a range not commonly used with ACIP piles in private commercial work in U.S. markets. 10/28/

27 10/28/2009 Advantages and Limitations of ACIP Piles 10/28/ Favorable Geotechnical Conditions Medium to very stiff clay soils. clays are generally stable during drilling and less subject to concerns about soil mining i during drilling. Cemented sands or weak limestone Residual soils. 10/28/ Medium dense to dense silty sands and well-graded sands. Rock overlain by stiff or cemented deposits. 10/28/

28 10/28/2009 Unfavorable Geotechnical Conditions Very soft soils. Loose sands or very clean uniformly graded sands under groundwater Geologic formations containing voids, pockets of water, lenses of very soft soils, and/or flowing water. 10/28/ Hard soil or rock overlain by soft soil or loose, granular soil. Sand-bearing stratum underlying stiff clay. Highly variable ground conditions. Conditions requiring penetration of very hard strata. 10/28/ Ground conditions requiring uncommonly long piles. Ground conditions with deep scour or liquefiable sand layers. 10/28/

29 10/28/2009 Project Conditions Affecting the Selection and Use of ACIP Piles 10/28/ Projects where speed of installation is important. Batter Piles Required. Projects where large numbers of piles are required. Low headroom conditions. 10/28/ Secant or tangent pile walls up to 10 m (33 ft) of exposed wall height. Sound walls in favorable soil conditions Pile-supported embankments. 10/28/

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31 10/28/2009 EVALUATION OF STATIC CAPACITY OF AUGERED-CAST CAST-IN IN-PLACE PILES 10/28/ General Design Equation Q v, ult = q p A + b f A s s where, q p = ultimate unit end bearing capacity, A b = cross-sectional area of the pile base, f s = ultimate unit friction capacity, and A s = perimeter area of the pile. 10/28/ The behavior of ACIP piles falls somewhere between that of drilled shafts and driven piles 10/28/

32 10/28/2009 Zelada and Stephenson (2000) SCOPE OF WORK This study compared computed theoretical load capacity using eight different published techniques, with the results from a field load test database of ACIP piles constructed in cohesionless soils. Recommendations were made regarding the design approach most appropriate for these foundations and the best procedure for estimating ultimate capacity from pile load tests. 10/28/ Auger Cast Piles Sand Tip Capacities Empirical formulas based on sixty load tests on piles from 12 to 24 inches diameter Embedments of from feet Capacity is based on the auger diameter, not the eventual constructed pile diameter. 44 Neely (1991) q p = 1.9N 75tsf q ( tsf ) p FHWA 1999 = 0.6N q ( MPa) = 4.3N p for 0 N for N > N 60 is the SPT-N value at 60% efficiency near the tip of the pile (1 diameter above to 2 or 3 diameters below the pile tip) 10/28/

33 10/28/2009 Auger Cast Piles Sand Side Capacities 10/28/ Neely (1991) fs = β p' o 1. 4tsf 10/28/ Wright and Reese (1978) (McVay et al., 1994) Where K s is taken as 1.1, p o is the f = p' K tan φ 1. 6 tsf average effective s 0 s 6 2 q = N 40tsf 0.05d 3 stress along the length of the pile and φ is the angle of internal friction of the soil 10/28/

34 10/28/2009 Reese and O Neill (FHWA, 1988) K tanφ = β = z β 1.2 The end bearing is taken as 0.6N (tsf) at the tip, for N values less than 75. For N values greater than 75, the unit end bearing is assumed to be a constant 45 tsf (4 MPa). 10/28/ RESULTS 10/28/ New Equations Zelada and Stephenson (2000) β = f s z = β p ' q b = 1.7 N 75 tsf o /28/

35 10/28/ Tip 250 stan 200 sf) TIP RESISTANCE represent derived values from measured loads. Meyerhof (Driven Piles) Avg. Unit Tip = 1.7N Neely Reese & O'Neill SPT N-value 10/28/ COHESIVE SOIL 10/28/ American Petroleum Institute (16) Cohesive Soil The shaft friction in cohesive soil can be calculated at any point along the pile by the following: f s = αc u (24) where α = a dimensionless factor c u = undrained shear strength of the soil at the point in question α = 0.5ψ -0.5 for ψ 1 (25) α = 0.5ψ for ψ > 1 (26) with the constraint that α 1.0. ψ = c u/σ v for the point of interest (27) where σ v = effective overburden pressure at the point in question. 10/28/

36 10/28/2009 FHWA 1999 f αc α s = u = a 0.55 for cu / P 1.5 P a = atmospheric pressure 10/28/ The unit point resistance for piles in bearing in cohesive soil can be calculated by the following. q p = 9c u 10/28/ Unconservative Conservative API Coyle et. al FHWA LPC German Standard Measured/Predicted Load Ratio 10/28/

37 10/28/2009 AUGER CAST PILES QA/AC Richard W. Stephenson, Ph.D., P.E. 10/28/ Recommended Records 1. Pile location and plumbness; 2. Ground surface elevation; 3. Pile toe (bottom) depth/elevation; 4. Depth/Elevation of top of grout/concrete; 5. Pile length; Auger diameter; 7. Details of the reinforcing steel (number, size, and grade of longitudinal bars, size and spacing of transverse steel; outside diameter and length of cage); 8. Flow cone efflux time and volume of grout placed, or slump and volume of concrete placed; 9. Theoretical volume of excavation (theoretical diameter = diameter of auger); 10. Depth/Elevation to which reinforcing steel was 60 placed; 20

38 10/28/ Date/Time of beginning of drilling; 12. Date/Time of completion of drilling; 13. Date/Time grout or concrete was mixed; 14. Date/Time ready-mix grout or concrete truck arrived at project site, and copies of all grout or concrete batch tickets used for the pile construction; 15. Date/Time of beginning of grout or concrete pumping; Date/Time of completion of grout or concrete pumping; 17. Date/Time of placement of reinforcing steel; 18. Weather conditions, including air temperature, at time of grout or concrete placement; 19. Identification of all grout or concrete samples taken from the pile; 20. All other pertinent data relative to the pile installation; and 21. All readings made by the automated measuring and recording equipment to include as a minimum: a. auger rotation vs. depth for every 0.6-m (2-ft) increment, or less, of pile advancement during the drilling process, and during placement of grout or concrete (if auger is rotated during this placement); and b. volume of grout or concrete placed versus depth of outlet orifice for every 0.6-m(2-ft) increment, or less, of pile placed; 21

39 10/28/2009 c. Average maximum and minimum pump stroke pressures at ground level for every 0.6-m (2-ft) increment, or less, of pile placed; d. Average maximum and minimum pump stroke pressure at or near the auger head for every 0.6-m (2-ft) increment, or less, of pile placed, if directed by the engineer; and e. Additionally, the engineer may also specify that the torque and crowd force (downward thrust on auger) measurements be made at every 0.6-m (2-ft) increment, or less, of pile advancement during the drilling process. PERFORMANCE MONITORING AND CONTROL DURING CONSTRUCCTION Past Practice Importance of a skilled operator Use of visual observations of the drilling Crude estimates of grout/concrete pumped 22

40 10/28/2009 MONITORING AND CONTROL OF THE DRILLING PHASE Goals of Monitoring and Control: Ensure that excessive flighting of soil does not occur and The appropriate level of soil displacement occurs General Guidelines for Auger Penetration Rate for CFA Piles Soil Type Rate of Penetration (Revolutions per Auger Pitch) Clay soils 2 to 3 Cohesionless soils 1.5 to 2 23

41 10/28/2009 In the Manual Control System: Auger speed is predetermined by the gearbox setting The depth of penetration is monitored by direct observation of the to of the auger in the leads, and The rate of penetration is observed using a stopwatch. Better method: Depth encoder and revolution counter to monitor and display the rate of penetration graphically in units of revolutions per meter of penetration Use with hydraulic fixed mast drilling equipment that allows control of crowd, torque and speed of revolution. 24

42 10/28/2009 Crane Mounted: Depth encoder and a clock to monitor the rate of penetration. The speed of auger rotation is controlled via the gearbox. Monitoring and Control of the Grouting/Concreting Phase Perhaps the most important aspect of QA/QC for ACIP Piles Objective: Adequate grout or concrete be delivered to the discharge point of the auger at the proper pressure. Both pressure and volume must be monitored as a function of auger depth. Monitor the extraction of the auger. The lift speed of the auger must be controlled so that the proper volume of concrete is delivered under sufficient pressure. 25

43 10/28/2009 Observe and document: Position of the auger tip Lifting speed Volume of grout/concrete delivered Pressure with which the grout/concrete is delivered. The manual method of monitoring and documenting the grouting/concrete operation involves the following: the position of the auger tip is monitored visually by observing the height of the auger in the leads; the lifting speed is controlled by the operator by feel and by observing the height of the auger in the leads while timing the withdrawal using a stopwatch; the volume of grout is measured by estimating the volume per stroke of the pump, and by manually counting the pump strokes; and the pressure with which the grout is delivered is monitored by a gauge in the line near the pump. 26

44 10/28/2009 The system recommended for transportation projects includes automated monitoring of the auger position; volume of grout/concrete that is delivered; pressure with which it is delivered; and rotation and lifting speed of the auger. Such system should provide the following: the position of the auger tip [monitored automatically by a position sensor ; the volume of grout [measured by an in-line flowmeter that provides a reliable and accurate measure of the grout/concrete that is delivered in real time]; 27

45 10/28/2009 the pressure with which the grout/concrete is delivered [monitored using a gauge in the line near the swivel at the top of the auger, or in the auger itself near the tip (latter option is better)]; the rotation of the auger [monitored by a sensor]; the lifting speed [controlled by the operator based on real time observation of the control parameters noted above, displayed graphically in the cab of the rig, and compared to target values]; and the entire operation [recorded as a part of the documentation process]. CONCLUSIONS ACIP Piles are becoming a dominant player in the Midwest Resistance to use is primarily related to the lack of conventional QA/QC procedures Design equations exist 84 28

46 10/28/2009 References Dan A. Brown, Ph.D., P.E., Steven D. Dapp, Ph.D., P.E., W. Robert Thompson, III, P.E., and Carlos A. Lazarte, Ph.D., P.E., GEOTECHNICAL ENGINEERING CIRCULAR NO. 8 Design and Construction of Continuous Flight Auger (CFA) Piles Bustamante, M., and Gianeselli, L. (1981). Portance Réele et Portance Calculée des Pieux Isolés Sollicités Verticalement, Revue Francaise de Geotéchnique, No. 16, Presses de l ENPC, France. Bustamante, M., and Gianeselli, L. (1982). Pile Bearing Capacity by Means of Static Penetrometer CPT, In Proceedings of the 2nd European Symposium on Penetration Testing. Amsterdam, pp Chin, F.K. (1970). Estimation of the Ultimate Load of Piles not Carried to Failure, Proceedings of the Second Southeast Asian Conference on Soil Engineering, Singapore, Vol. 1, pp Clemente, J.L.M., Davie, J.R., and Senapathy, H. (2000). Design and Load Testing of Augercast Piles in Stiff Clay, Geotechnical Special Publication No. 100, Ed. By N. D. Dennis, R. Castelli, and M. W. O Neill (Eds.), ASCE, August, pp /28/ Coleman, D.M. and Arcement, B.J. (2002). Evaluation of Design Methods for Auger Cast Piles in Mixed Soil Conditions, Proceedings of the International Deep Foundations Congress 2002, February 14-16, 16, 2002 Orlando, Florida; M.W. O Neill and F.C. Townsend (Eds.), ASCE, pp Coyle H. M., and Castello, R. R. (1981). New Design Correlations for Piles on Sand, Journal of the Geotechnical Engineering Division, ASCE, Vol. 106 No. GT7, pp Decourt, L. (2003). Behaviour of a CFA Pile in a Lateric Clay, Proceedings of the 4 th International Geotechnical Seminar on Deep Foundations on Bored and Auger Piles, BAP IV, Ghent, Belgium, pp DFI (2005). Manual for Non Destructive Testing and Evaluation of Drilled Shafts, Deep Foundations Institute, Chernauskas, L.E. (Ed.) Hawthorne, NJ. Douglas, D. J. (1983). Discussion on Paper 17-22: Case Histories, Proceeding, Conference on Piling and Ground Treatment, Institution of Civil Engineering, London, pp /28/ Fleming, W.G.K. (1995). The Understanding of Continuous Flight Auger Piling, Its Monitoring and Control, Proceedings, Institution of Civil Engineers Geotechnical Engineering, Vol. 113, July, pp Discussion by R. Smyth-Osbourne and reply, Vol. 119, Oct., 1996, p Frizzi, R.P. and Meyer, M.E. (2000). Augercast Piles: South Florida Experience, Geotechnical Special Publication No. 100, N. D. Dennis, R. Castelli, and M. W. O Neill (Eds.), ASCE, August, pp McVay, M., Armaghani, B, and Casper, R. (1994). Design and Construction of Auger-Cast Piles in Florida, Transportation Research Record 1447, Design and Construction of Auger Cast Piles, and Other Foundation Issues, Washington, pp Neely, W. J. (1991) Bearing Capacity of Auger-Cast Piles in Sand, Journal of Geotechnical Engineering, ASCE, Vol. 117, No. 2, pp O Neill, M. W., Ata, A., Vipulanandan, C., and Yin, S. (2002). Axial Performance of ACIP Piles in Texas Coastal Soils, Geotechnical Special Publication No. 116, Ed. by M. W. O Neill and F. C. Townsend (Eds.), ASCE, February, Vol. 1, pp /28/

47 10/28/2009 O Neill, M. W., Vipulanandan, C., Ata, A., Tan, F. (1999). Axial Performance of Continuous- Flight-Auger Piles for Bearing, Final report to the Texas Department of Transportation, Report No , August, 254. O Neill, M.W. and Reese, L.C. (1999). Drilled Shafts: Construction Procedures and Design Methods, FHWA Report No. IF , Federal Highway Administration, Washington, D.C. O Neill, M.W., Vipulanandan, C., and Hassan, K. (2000). Modeling of Laterally Loaded ACIP Piles in Overconsolidated Clay, Geotechnical Special Publication No. 100, N. D. Dennis, R. Castelli, and M. W. O Neill (Eds.), ASCE, August, pp Reese, L. C., and O Neill M. W. (1988). Drilled Shaft: Construction Procedures and Design Methods, FHWA-HI HI , Federal Highway Administration, Washington, D.C. Viggiani, C. (1993) Further Experiences with Auger Piles in Naples Area, Proceedings of the 2nd International Geotechnical Seminar on Deep 10/28/ Zelada, G. A., and Stephenson, R. W. (2000). Design Methods for Auger CIP piles in Compression, New Technological and Design Developments in Deep Foundations, ASCE Geotechnical Special Publication No. 100, N. D. Dennis, R. Castelli and M. W. O Neill (Eds.), ASCE, August, pp /28/ THANK YOU 10/28/

48 Design and Construction of Micropiles John R. Wolosick, P.E. Hayward Baker Inc. Fall Technical Seminar ASCE Geotechnical Subcommittee St. Louis October 30, 2009 Hayward Baker 2003 Calendar Art Micropiles are High capacity (up to 500 tons design load), typically small diameter (2-12 +) piles that are used in almost any type of ground to transfer structural load to competent bearing strata. Micropiles are easily installed in restricted access and limited headroom situations. Also known as minipiles, pin piles, root piles, pipe piles, etc. 1

49 Typical Micropile Program Involves Drilling holes, diameter The construction of a pile shaft consisting of highstrength steel pipes or steel bars The filling of the hole with high strength cement grout Micropiles Drilled and Grouted Steel Pipe Piles Micropile Types Soil Piles Type S-1 Composite Pile Type S-2 Full Length Steel Pipe Rock Piles Type R-1 Composite Pile Type R-2 Full Length Steel Pipe 2

50 Micropile Types Founded in Dense Soils Founded in Rock S-1 S-2 R-1 R-2 Micropile Installation Process Construction Sequence S-1 Pile Drill Grout Install reinforcement Pressure Grout 3

51 Construction Sequence R-1 Pile Drill casing to rock Drill rock socket Grout Install reinforcement Micropiles Typically Used For: New Construction Underpinning Existing Foundations Limited Access or Headroom Foundations where Obstructed Drilling is Required Replacement for Drilled Shafts Micropiles Range of Ground Conditions: Obstructions or Old Foundations Variable Urban Fills Karstic Limestone Geology Glacial Till with Boulders Mined Rock Geology High Water Table 4

52 Micropiles Physical Constraints to Installation: Limited Overhead Clearance Limited Access Vibration Sensitive Environments Settlement Sensitive Projects Close Proximity to Existing Structures Micropiles Piling Materials: Steel Pipe API N80 Yield Strength = 80 ksi Special Machine Flush Joint Threads High Strength Steel Reinforcing Bars Grade 75, 80, 95 or 150 Grout Neat Cement Water / Cement Ratio = 0.45 Strength = 4000 psi 3. Structural Design Components Cased length Uncased length Grout to steel bond Transitions between reinforcement types Strain compatibility Casing or bar splice and connection Footing connection 5

53 Structural Design (Internal): Grout & steel Transfer zone (plunge) Bond zone { { { Typical range of code allowable stresses (ASD): Grout: *f c Steel: *fy Connection Details Shear transfer from grout Bearing plate Shear rings Bearing Plate Stiffener Hewlett Packard Corvallis, OR Seismic Upgrade Connection 6

54 Micropiles Geotechnical Aspects of Piles: Friction Bond Soil or Rock! Compression and Tension Loads tons Working Load Lateral Load Capacity: 5 15 tons Battering is not a problem Micropiles for the Spalation Neutron Source FACILITY OAK RIDGE, TENNESSEE Hayward Baker/Nicholson JV SITE Oak Ridge Nashville Knoxville Chattanooga 7

55 OAK RIDGE Y-12 ETT Park (ORGDP) SITE ORNL - Lawrence Berkeley Los Alamos/Jefferson - Brookhaven - Oak Ridge Argonne/Oak Ridge Project Information 8

56 Project Scope Layers of weathered rock, soil filled cavities Anticipated depths ranged from 40 to 200 ft. Owner required three drilling operations 186 calendar day schedule Project Scope Total of inch dia. Minipiles in bid 400 kip compression & tension capacity 60 kip lateral load Install four No. 6 rebar w/#3 cage - top 8 ft. Install ten feet into bedrock in karst terrain Alternate Bid Submitted 9-5/8 in. dia. w/0.545 in. wall to full depth 11-7/8 in dia. w/0.534 in. wall upper 20 ft. Single rebar of adequate size Two predrill rigs for open hole drilling Two drill rigs for installation of pipe 9

57 Site Conditions Bldg. North SNS Site -- October, 2000 TOP OF SOUND ROCK 10

58 TOP OF SOUND ROCK Project Conditions Office Area Equipment Laydown & Cutting Yard 11

59 Air Compressor Bank & Batch Plant Operations Working Area 200 ton crane w/power unit 12

60 Hydraulic Drill Motor Drilling with DHH, air & water 13

61 Typical Operation Pipe Installation Operation Setting 11-7/8 in. pipe w/100 ton service crane 14

62 Pipe Installation Completed Pile prior to Rebar Extension Pile Load Tests Compression Tests - 4 planned (4 test & 1 production pile conducted) 800 Kips Tension Tests - 2 planned (2 conducted) 800 Kips Lateral Tests - 2 planned (2 conducted) 60 Kips 15

63 Compression Test Tension Test T-3 Installation Lateral Test L-1 Pile 16

64 Compression Test C-3B Compression Test C-3B Load Load (kips) Deflection (inch es) Pile Butt Deflection Telltale Deflection Project Challenges 17

65 Available Work Area 18

66 Rebar Forest PROJECT ANALYSIS Projected No. of Piles ,087 Actual No. of Piles Projected Drilling Footage - 113,500 Actual Drilling Footage ,240 Projected Grout Qty. (cyd) - 13,500 Actual Grout Qty. (cyd) ,560 19

67 GKN Aerospace Press Mat Foundation St. Louis, Missouri A new machining press with movable static loads required a thick concrete mat supported on many lightly loaded friction piles The pile section provided by HBI satisfied the structural engineer s specifications for deflection GKN owned Hayward Baker until 1990! GKN Aerospace Press Mat Foundation St. Louis, Missouri Subsurface Exploration Location Sketch 20

68 Boring Log Log of CPT Micropiles were installed using DK50 and Klemm 708 rigs working in limited headroom 21

69 Load Test Set-up and Reaction Frame GKN Aerospace Press Mat Foundation St. Louis, Missouri Load Test The End Questions? 22