EXTENSIVE TEST PILE AND PRODUCTION PILE PROGRAMS AT THE UC DAVIS

Transcription

1 EXTENSIVE TEST PILE AND PRODUCTION PILE PROGRAMS AT THE UC DAVIS MEDICAL CENTER Camilo A. Alvarez, GRL Engineers, Inc., Los Angeles, California This paper presents a case history from the Test Pile and Production Pile programs for the Auger Pressure Grouted (APG) piles installed at the University of California at Davis, Medical Center (UCDMC), Surgery and Emergency Services Pavilion (SESP) Project in Sacramento, California. Initially, a total of eleven piles were installed at the project site and were subjected to compression and tension static load tests. Additionally five of the eleven piles were subjected to high strain dynamic load tests. During the Production Pile program, ten additional dynamic load tests were performed on piles around the jobsite, and all tiedown piles were subjected to tension tests for quality assurance. The testing results, as well as load testing comparison between the static and dynamic tests, are included in this manuscript. TESTING PROGRAM Introduction Since it is a healthcare facility, the University of California Medical Center project was subjected by the Office of Statewide Healthcare Planning and Development (OSHPD) to more stringent regulation and quality control when executing the design and construction of the foundation system. For the first time, Auger Pressure Grouted (APG) piles were considered in an OSHPD project, and thus, extensive testing was required for quality control and pile approval. The piles installed at this jobsite had 14-inch and 18-inch diameters. All 14-inch piles were designed as tiedown piles and the 18-inch piles were designed to sustain both compression and tension loads. The final design called for pile lengths ranging between 40 and 60 feet. Test Pile and Production Pile programs, which included multiple tension and compression static load tests as well as compression high strain dynamic tests, were part for the quality assurance of the APG piles installed by Berkel and Company Contractors. GRL Engineers, Inc., and Geodaq, Inc., performed the required tests for this project. This paper presents the results from both the static and the high strain dynamic load testing for the Test Pile and Production Pile programs. Comparisons between the two testing procedures are also presented. TEST PILE PROGRAM During the Test Pile program, two (2) 14-inch and nine (9) 18-inch APG piles were installed and subjected to static and dynamic load tests. Table 1 provides a summary of pile lengths and diameters. Table 2 includes the maximum test loads to which the piles were subjected statically and dynamically. Table 1. Test Pile Details Pile Designation Approximate Pile Embedded Diameter Length (feet) (inches) TP1 (Tiedown) TP2 (Tiedown) TP TP TP TP TP TP TP TP TP

2 Table 2. Test Pile Results Pile Maximum Test Maximum Test Load Static Load - Dynamic TP1 200 kips Tension - TP2 330 kips Tension - TP3 560 kips Compression 880 TP4 460, 640 kips Compression 900 TP5 500 kips Tension - TP6 460 kips Compression 940 TP7 420 kips Tension - TP8 560 kips Compression 960 TP9 460 kips Compression 1040 TP kips Tension - TP kips Tension - All static and dynamic testing, was executed during the initial two weeks after pile installation. All dynamic compression testing was done prior to the static compression testing. STATIC LOAD TESTS Static load testing was performed by Geodaq, Inc. Each pile load test was instrumented with a load cell and four electronic displacement transducers. Compression and Tension Load Tests were conducted in general conformance with ASTM D1143 and D3689 using the quick load procedure with 10-minute load increments. Tests on the APG piles were accomplished with increasing increments equal to 10% of the maximum test load and decreasing load increments of approximately 25%. Test Results All test piles maintained the maximum test loads without indication of geotechnical failure. Compression Tests failure. Figure 1 depicts the statically measured load set curves for the compression tests. D i s p l a c e m e n t ( i n ) Load-Set Curves Test Pile 3 5 Test Pile Test Pile 6 Test Pile 8 Test Pile 9 Figure 1. Static Compression Load-Set Curves Tension Tests Load set plots measured during the uplift tests of the tension piles exhibit a generally bilinear behavior Both portions of these curves are generally linear suggesting that the mobilized soil strength was largely elastic. The 18-inch diameter 60 and 50-foot long piles were loaded to the required ultimate capacities of 500 and 420 kips, respectively. The 14-inch tiedown piles were loaded to the required ultimate pile capacities of 200 and 330 kips in tension for the 40 and 60 feet piles, respectively. Figures 2 and 3 show the uplift load set curves obtained for the 14-inch tiedowns and 18-inch piles, respectively. The design loads for the APG piles installed at this site were 230 and 280 kips for the 40 and the 60 feet long piles, respectively. The static load tests were required to load the piles to a safety factor of 2.0 or 460 and 560 kips. All of the piles tested exhibited a predominantly linearelastic relationship between the applied load and displacement, suggesting that the soil strength behavior was below the ultimate capacity. After initial successful loading to 460 kips, Test Pile 4 was loaded to 640 kips without an indication of

3 D is p la c e m e n t (in ) Load-Set Curves Test Pile 1 5 Test Pile Figure 2. Static Tension Load-Set Curves, 14-inch Tiedowns Piles D is p la c e m e n t (in ) Load-Set Curves Test Pile 5 0 Test Pile Test Pile 10 Test Pile 11 Figure 3. Static Tension Load-Set Curves, 18-inch Piles DYNAMIC LOAD TESTS The dynamic load testing was performed by GRL Engineers, Inc. Each pile test was performed with the Pile Driving Analyzer (PDA). Load set curves and shaft resistance distribution were obtained utilizing the CAPWAP program. Dynamic pile load testing was performed in accordance with ASTM D4945. The hammer system utilized was GRL s APPLE I (15 ton) drop hammer system. Figure 4 presents a photo of this drop testing system. Figure 4. APPLE 15 Ton Drop System. Test Results During the testing of the initial five test piles the mobilized soil resistance ranged between 880 kips and 1040 kips. The simulated load set curves obtained by CAPWAP indicate that the soil resistance was still mostly linear-elastic, although greater sets were obtained when the testing loads exceeded 900 kips. Most possibly the ultimate soil resistance was neither completely mobilized during the static nor during the dynamic tests. The CAPWAP estimated shaft resistance for these piles ranged between 620 and 790 kips. Figure 5 presents the simulated static load set curves calculated by CAPWAP from the high strain dynamic test records.

4 Static Load Set Curves TP3 TP 4 TP 6 TP 8 TP 9 Load Set Curves - Test Pile 4 TP4 - Static TP 4 - Dynamic Figure 5. Simulated Load-Set Curves from dynamic tests Figure 7. Comparison of Load-Set Curves for Test Pile 4 STATIC AND DYNAMIC LOAD TEST COMPARISON Based on the compression static load testing and the high strain testing of the test piles, load set curves for both testing procedures can be compared. Plots for the results of TP3, TP4, TP6, TP8 and TP9 are included in Figures 6 through 10. D is p la c e m e n t (in ) Load Set Curves - Test Pile 3 TP 3 Static TP3- Dynamic Load Set Curves - Test Pile 6 TP6 - Static TP 6 - Dynamic Figure 8. Comparison of Load-Set Curves for Test Pile 6 Figure 6. Comparison of Load-Set Curves for Test Pile 3

5 Load Set Curves - Test Pile 8 TP 8 - Static TP 8 - Dynamic Table 3. Displacements at Required Pile Capacities. Pile Designation Displacement Displacement (Ultimate Load) Static Test Dyn. Test (in) (in) TP3 (560 kips) 2 5 TP4 (640 kips)* 0 9 TP6 (460 kips) 2 8 TP8 (560 kips) 4 6 TP9 (460 kips) 4 7 Figure 9. Comparison of Load-Set Curves for Test Pile 8 *Load taken to 640 kips instead of 460 kips Load Set Curves - Test Pile 9 TP 9 - Static TP 9 - Dynamic Figure 10. Comparison of Load-Set Curves Test for Pile 9 Although static testing capacity levels were lower than those mobilized in the dynamic testing, over the tested load range static and dynamic load set curves compared well for the five piles tested under both methods. Table 3 includes the cumulative sets obtained under both methods at the required ultimate pile capacities for this project. It is important to mention that neither the quick static load testing nor the high strain dynamic testing account for additional settlements due to consolidation, soil and pile creep. PRODUCTION PILE PROGRAM Based on the pile performance obtained after extensive load testing, and given the good load test comparison between the testing procedures, the production pile program was limited to dynamic load tests around the jobsite for the 18- inch piles. Additional tension static load testing was performed for the 14-inch tiedown piles. Tension Tests A total of fifty-seven (57) proof tests and three (3) performance tests were performed on the APG piles during the Production Pile program. The proof piles were loaded to a maximum load of 150 percent of the design load of 100 kips for the 14-inch 40 feet piles, and 165 kips for the 60 feet long piles. During the performance tests the piles were loaded to 150, 200 and 330 percent of the design capacities. No clear indication of geotechnical failure was evident during the production testing of any of the tiedown piles. High Strain Dynamic Compression Tests Two sets of high strain dynamic compression tests (each set included the testing of five production piles) were required during the Production Pile program. Table 4 includes a summary of the APG 18-inch production piles tested during the initial set of tests of the Production Pile program, and includes their

6 respective penetration length and installation and test dates. Table 5 lists the mobilized capacities for the tested production piles, and Figure 11 presents the simulated load set curves for the tested piles calculated with the CAPWAP program. Table 4. Set 1. Production Pile Tests Pile Length Installation Test Date (ft) Date A Feb 1-05 Mar B Feb 2-05 Mar C Feb 2-05 Mar K Jan Mar L Jan Mar Table 5. Set 1. Mobilized Pile Capacities. Pile Mobilized Capacities A B C K L Production Pile program included two piles which were tested approximately five and nine months after installation, as presented in Table 6. Table 7 includes the mobilized pile capacities for these tested piles, and Figure 12 includes the mobilized load set curves. Table 6. Set 2. Production Pile Tests Pile Length Installation Test Date (ft) Date A Feb 1-05 July G Oct Nov I Feb Nov I-24-1A 50 Oct Nov L Nov 3-05 Nov Table 7. Set 2. Mobilized Pile Capacities Pile Mobilized Capacities A G I I-24-1A 850 L Static Load Set Curves A-19-1 B-18-3 C-23-1 K-18-1 L-24-5 Figure 11. Set 1. CAPWAP simulated Load-Set Curves As shown in Table 4, all piles were tested six to eight weeks following the installation and exceeded the required pile capacities of this project. No clear indication of geotechnical failure was evident during the testing of the initial set of piles during the production pile program. The second set of piles tested during the Displacem ent (in ) Static Load Set Curves A-20-1 G-24-1 I-16-3 I-24-1A L Figure 12. Set 2. CAPWAP simulated Load-Set Curves All compression piles exceeded the ultimate pile capacities required in the project. Most of the piles did not show evidence of geotechnical failure. Load-set curves obtained for those piles tested five to nine months after installation, demonstrate an increase of stiffness of the pile/soil system compared to the piles tested

7 after a shorter waiting time. This improvement of stiffness may be due to an increase in soil set up after initial pile installation, or to an increase of pile stiffness due to an increasing concrete elastic modulus. Conclusions For the first time, Auger Pressure Grouted (APG) piles were considered in an OSHPD project. An extensive initial test pile program was followed by an additional test program for the production piles thereby achieving a high level of quality assurance GRL Report Project Production Pile Program Results, UC Davis Medical Center, Surgery and Emergency Services Pavilion, March 29, GRL Report Project Production Pile Program Results, UC Davis Medical Center, Surgery and Emergency Services Pavilion, November 23, The Test Pile program included static and high strain dynamic testing. The production pile test program included static testing of the tiedown piles, as well as dynamic testing of ten (10) production piles. Comparison of static and dynamically acquired load set curves yielded good agreement. However, only the elastic portion of the load test curves could be compared because of the much higher available capacity than achieved statically. All testing results exceeded both the required compression and tension ultimate pile capacities required. In most cases, geotechnical failure was not evident during either the compression tests or the tension tests. Dynamic testing mobilized capacities as much as twice the required ultimate pile capacities of the project. Long term pile testing demonstrated an increase of pile and/or soil stiffness with time. This improvement may be due to soil set up or due to an increase in the concrete pile elastic modulus. REFERENCES GEODAQ Report Project Pilot Test Program Results, UC Davis Medical Center, Surgery and Emergency Services Pavilion, December 27, GEODAQ Report Project Interim Pile Test Results, UC Davis Medical Center, Surgery and Emergency Services Pavilion, March 11, GRL Report Project Pilot Test Program Results, UC Davis Medical Center, Surgery and Emergency Services Pavilion, December 23,