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14 CHAPTER 2 FINDINGS 2.1 STATE OF PRACTICE use drilled shafts. Of those responding, 64% prefer the use of driven piles and 5% prefer drilled shafts or other foundation 2.1.1 Questionnaire and Survey type. When using driven piles, 21% primarily use prestressed concrete piles; 52%, steel H piles; 2%, open-ended steel pipe Code development requires examining the state of practice piles; and 25%, closed-end steel pipe piles. in design and construction in order to address the needs, research the performance, and examine alternatives. The iden- tification of current design and construction methodologies was carried out via a questionnaire along with a survey, which 2.1.2.3 Driven Piles--Design Considerations was independently developed and analyzed by Mr. A. Munoz of the FHWA. The questionnaire was distributed to 298 state 1. The most common methods used for evaluating the highway officials, TRB representatives, and state and FHWA static axial capacity of driven piles were as follows: 59%: -method (Tomlinson, 1987), geotechnical engineers. A total of 45 surveys were returned 25%: -method (Esrig & Kirby, 1979), and analyzed (43 states and 2 FHWA personnel). The survey 5%: -method (Vijayvergiya and Focht, 1972), elicited information concerning design methodology in geo- 75%: Nordlund's method (Nordlund, 1963), technical and structural design, foundation alternatives, and 5%: Nottingham and Schmertmann's method: CPT design and constitution considerations for both driven piles and drilled shafts. The questionnaire, the survey, and their (1975), 9%: Schmertmann's method: SPT (Sharp, 1987), analyzed results are presented in Appendix A. A summary 14%: Meyerhof's method (1976) modified by Zeitlen analysis of the survey results is presented below. and Paikowsky (1982), and 25%: in-house methods and other less common methods. 2.1.2 Major Findings Of the computer programs used in design, 39% were developed in-house, 2.1.2.1 Design Methodology 75% were FHWA developed, and 20% were from commercial vendors. Averaging the responses for driven piles and drilled shafts, 2. Of the primary tests used to assess strength parameters about 90% of the respondents used ASD, 35% used AASHTO in design, 86% used SPT-N values, 11% used CPT data, Load Factor Design (LFD), and 28% used AASHTO Load 2% used Dilatometer data, and none used Pressure- and Resistance Factors Design (LRFD), suggesting that most meter data. of the respondents that use LRFD or LFD use it in parallel 3. The majority of the states used Tomlinson's method to with WSD. assess the side friction coefficient in cohesive soil (CA - Among the respondents using ASD to evaluate capacity, adhesion) and Nordland's method in cohesionless soil 95% used a global safety factor ranging from 2.0 to 3.0, ( - interfacial friction angle). depending on construction control and 5% used partial safety 4. Pile settlement in the design was considered by 48%, factors of 1.5 to 2.0 for side friction (3.0 for drilled shafts) with settlement ranging from 0.25 to 1.0 inches being and 3.0 for end bearing (2.0 to 3.0 for drilled shafts). tolerable. 5. Simplified methods (e.g., Broms, 1964) were used by 34% of the respondents in the lateral pile design meth- 2.1.2.2 Foundation Alternatives ods and/or computer programs, and 88% used methods based on p-y curves. Of the computer programs used in The majority of the respondents use primarily driven pile design, 14% were in-house, 82% were from the FHWA, foundations (75%), 14% use shallow foundations, and 11% and 55% came from commercial vendors.

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15 6. Responses for the estimated risk or failure probability 2. Of the primary parameters used, 70% were based on SPT of the group foundation design were as follows: values, 7% were obtained from the CPT test, 2% were 27% less than 0.1%, based on Pressuremeter data, and 2% were based on 4% between 0.1 and 1%, Dilatometer data. 1% of the responses were between 1% and 10%, and 3. Of the 16% considering the roughness of the borehole 67% were unknown. wall in rock socket design, all did so by assumption. 4. Shaft settlement was considered by 61% of the respon- The assessment for the acceptable maximum failure proba- dents, with tolerable settlements ranging from 0.25 to bility ranged from about 0 to 1%. Pile failure had been expe- 2.0 in. rienced by 14% of the respondents. 5. Simplified (e.g., Brooms, 1964) lateral drilled shaft design methods and/or computer programs were used by 27%, and 82% used methods based on p-y curves. 2.1.2.4 Driven Piles--Construction 6. For drilled shafts subjected to lateral load, the tolerable Considerations deflection ranged from 0.25 to 2.0 in., and the safety factor of lateral pile capacity ranged from 1.5 to 3.0. 1. Of the respondents, 77% performed static pile load test 7. About 30% of the respondents did not take into account during construction, and the primary test method was the construction method in design. the Quick Method. 8. Concerning the estimated risk or probability of failure 2. The most common dynamic methods used for capacity of group foundation designs based on the safety factor evaluation of driven piles included the following: used, the following responses were made: Wave Equation Analysis using the program GRL- 20%: less than 0.1%, 7%: between 0.1 and 1%, WEAP (GRL Engineers, Inc. Wave Equation Analy- 2%: between 1 and 10%, and sis Program) was used by 80% of the respondents. 71%: unknown. 45% used the ENR formula, 16% used Gate's equation with safety factors rang- ing from 2.0 to 3.5, and The assessment for the acceptable maximum failure prob- 1 state used its own dynamic formula. ability ranged from about 0% to 5%. 3. Dynamic pile load tests were performed during con- struction by 84 % of respondents, testing 1% to 10% of the piles per bridge. 2.1.2.6 Drilled Shafts--Constructions 4. When setting production pile length and driving crite- Considerations ria, 82% used EOD conditions, 52% used BOR condi- 1. 66% performed static load testing during tions, and 36% did not consider pile freeze or relax- construction. ation effects in determining driving criteria. 2. The type of load test used included conventional static load testing (32%), Osterberg load cell (43%), Stat- namic load testing (11%), and Dynamic load testing 2.1.2.5 Drilled Shafts--Design Considerations (7%). 3. The methods used in drilled shaft installations included 1. The most common methods used for evaluating the drilling in dry (64%), wet (52%), and casing methods static axial capacity of drilled shafts were as follows: (86%). 36%: the -method (total stress approach) (Reese 4. For the drilling slurry used during construction, 25% and O'Neill, 1998; Kulhawy, 1989), used a mineral slurry of processed Attapulgite, 52% 41%: the -method (effective stress approach) (Reese used a mineral slurry of Bentonite clays, and 36% used and O'Neill, 1988), synthetic polymer slurries. 9%: the Reese and Wright (1977) approach for side 5. A majority of the States use the AASHTO Specifica- friction in cohesionless soils, tions for shaft cleanliness, which requires more than 39%: the FHWA (O'Neill et al., 1996) approach for 50% of the base to have less than 0.5 in. of sediment intermediate geomaterials (soft rock), and maximum sediment thickness to be less than 1.5 in. 11%: Carter and Kulhawy (1988) approach for inter- 6. 54% performed inspection of the shaft bottom, in mediate geomaterials (soft rock), and which only one State has a specific inspection device. 27%: other methods. The rest performed inspection by using manual probes Of the computer programs used, 18% were developed or an underwater camera and camcorder. in-house, 50% came from the FHWA, 29% from com- 7. 16% did not perform integrity testing for drilled mercial vendors, and 20% from others. shaft quality control; 64% used Cross Sonic Logging