Comparison of Static and Dynamic Load Test of Pile C. Rajagopal Post Graduate Student Applied Mechanics Department., S. V. National Institute of Technology, Surat-395007, India [email protected]

C. H. Solanki Associate Professor Applied Mechanics Department, S. V. National Institute of Technology, Surat-395007, India [email protected]

Y. K. Tandel Research scholar Applied Mechanics Department, S. V. National Institute of Technology, Surat-395007, India [email protected]

ABSTRACT In recent decade, dynamic load test is increasingly being used for pile load testing. Compare to static pile loading test, dynamic load test offers a considerable savings of time, cost and requires less space. This paper discuss the results of three dynamic and static load test on cast-in-situ bored pile of length to diameter ratio 28, 25.5 and 23.47. The load-settlement response of dynamic and static load tests are compared. The load-settlement response of both tests are in good agreement upto 0.50-1.3 times design load. Also, load in the pile and unit friction developed along the length of pile was presented.

KEYWORDS:

Pile, static load test, dynamic load test.

INTRODUCTION Ordinary static pile load tests using kentledge or reaction piles are used in India. Owing to increasing time and cost, particularly with the difficulties associated with transporting static load testing accessories into congested city centers and the lack of space on many sites, contractors are seeking an alternative system for pile testing. The tendency is for contractors to use dynamic techniques in order to supplement ordinary static tests. Dynamic load test (or PDA test) has become a common pile test procedure for evaluating pile capacity and pile integrity for the driven and cast-in-situ pile. The derived pile capacity generally shows satisfactory agreement with the static load carrying capacity (Rausche et al. 1985). The most attractive advantages are the cost of the test is much cheaper as compared with the cost of ordinary static load test and the duration of the test is very short. The dynamic test is common for - 1905 -

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driven piles mainly because similar driven or hammer used for the pile installation can be used for the test. As for the cast-in-situ pile especially the large diameter piles, the dynamic test is relatively less common because extra effort to bring in hammer for the test is required. In addition, design pile capacity for large diameter cast-in-situ pile is generally large, a very heavy hammer is required. As a general guideline, in order to verify the pile capacity, the required hammer weight is about 1.5% of the pile static load carrying capacity (Hussein et al. 1996). Many researchers reported the results of static and dynamic load tests (Davisson 1991; Gue and Chen 1998; Nayak et al. 2000; Uddin and Tungsanga 2001; Liew et al. 2004; Vaidya 2006; Long 2007; Basarkar et al. 2011). The results of static and dynamic load tests reported by above researchers are in good agreement. Exceptional test results were also found for some of the Test Piles in the mention literatures. Therefore attempt is made in this study to correlate the results of static and dynamic load tests on bored piles. The results include load transfer mechanism through pile for dynamic load test, the load-settlement comparison between static and dynamic load tests.

SUBSOIL CONDITIONS Sub soil conditions at different Test Piles are described in the following paragraph. Test pile 1: 0-3m (filled up soil); 3-6m (blackish low plastic silty clay with sand); 6-12 (yellowish low plastic silty clay with sand and gravel); 12-16.5m (yellowish low plastic silty clay with sand and gravel); 16.5-28.5m (blackish coarse sand with gravel); 28.5-36m (yellowish plastic silty clay with sand); 36-45m (sand with gravel). Figure 1 summarizes the variation of the main geotechnical properties of the sub soil with depth at Test Pile 1. Ground water level can be found at a depth of 5 m below the ground surface. Test pile 2: 0-1.5m (blackish high plastic clay with sand and gravel); 1.5-3m (yellowish high plastic clay with sand); 3-6m (yellowish low plastic silty clay with sand and gravel); 6-9m (yellowish low plastic silty clay with sand and gravel); 9-13.5m (yellowish low plastic silty clay with sand and gravel); 13.5-15m (blackish silty sand with gravel); 15-18m (yellowish low plastic silty clay with sand and gravel); 18-30m (yellowish plastic clayey sand with gravel). Geotechnical parameters for the different sub soil strata are shown in Figure 2. The water table was at 16.50 m from the natural ground surface. Test pile 3: 0-7.25m (blackish low plastic silty clay); 7.25-10.25m (blackish medium to coarse sand); 10.25-18m (coarse sand); 18-24m (yellowish low to high plastic clay with sand); 24-35m (yellow high plastic clay with sand and conglomerate). Figure 3 shows the various geotechnical properties of the site at Test Pile 3. The water table at this site was found at 5m below ground level.

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TESTING METHODOLOGY Dynamic load test was carried out using 11 tons hammer with a series of impact starting from 0.5 to 3m. Cushion system consisting of plywood sheets of 50 mm was applied for transferring impact load to pile top. The displacement after each impact was measured to assess the load carrying capacity. Two types of sensors namely, strain gauge and accelerometer were installed at 2 times the pile diameter below the top of the pile. Pile Driving Analyzer (PDA) was used for recording forces and motion after each drop of hammer. The pile load carrying capacity was analyzed by CASE method. A computer program, CAPWAP was used to compute the pile capacity in later stage based on the recorded data. For static load test, kentledge reaction system was used. The load is applied through a hydraulic jack resting on the kentledge girder. The applied load was measured by load cell. The load is applied in a series of vertical downward incremental each increment being of about 20 percent of safe load on the pile. Settlement on top of the pile was be recorded with four dial gauges, each positioned at equal distance around the piles and normally held by datum bars resting on immovable supports at a distance of three time pile diameter from the edge of the piles. Test pile1 was cast-in-situ of 1.5 m diameter and 42 m long from ground surface, Test Pile 2 was cat-in-situ of 1m diameter and 25.5 m long form ground surface and Test Pile 3 was 1.5m diameter, 35.2 m long from ground surface. Typical load test arrangement for dynamic and static load test is seen in Figure 4 and 5 respectively.

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Figure 5: Static load test at site

DISCUSSIONS AND RESULTS Dynamic load test is commonly carried out as an alternative to ordinary static load test owing to high cost and time consuming of the static load test. Also, pile integrity assessment is an additional advantage of dynamic load test. Test Pile 1: Load settlement response of top of the pile measured by dynamic and static pile tests are plotted in Figure 6. Figure 7 and 8 shows the vertical load and unit friction measured by the dynamic load test along the pile length. Form the Figure 5, it is seen that, at the initial stage of load (i.e. upto 0.75 times design load), the settlement measured from static load test is consistent with settlement predicted by dynamic load test. As the test load increase, the settlement predicted by dynamic load test is quite less than the settlement measured from static load test. Test Pile 2: Figure 9 shows the load settlement response of pile top measured by dynamic and static pile tests. Similar to test pie 1, here also settlement measured by dynamic and static load tests is consistent only for smaller load i.e. upto 0.5 times design load. Vertical load and unit friction measured along the pile length by the dynamic load test were presented in Figure 10 and 11. Test Pile 3: Load settlement graph is plotted for static and dynamic load test for pile 3 in Figure 12. Test pile 3 was design for 4600 kN load carrying capacity. Form the Figure 12, is observed that static and dynamic load test correlate well upto 1.3 times design load. Berserker et al. (2011) reported that the static and dynamic load tests are well compare upto 1.5 times the design load. Figure 13 and 14 presents the vertical load on the top of the pile and unit friction measured through dynamic load test.

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Likins et al. (2000) reported that the shaft friction could be fully mobilized if the penetration of pile after each impact is more than 2.5 mm. The pile capacity derived from dynamic load test for both projects could be underestimated due to very low penetration of piles after each impact.

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CONCLUSIONS This paper discusses the reliability of dynamic tests by comparing the results of dynamic and static tests on piles from the same site. The following conclusions can be drawn.    

The load settlement behaviour of piles show good agreement with the static load test when the test load is low. When the test load increase, the dynamic load test may underestimate the settlement. Dynamic load test could play an important role for predicting the pile capacity and pile integrity provided proper care should be taken in comparison. Dynamic load test could be cost effective and also less time consuming for larger diameter bored pile as compare to static load test. From the present study, it is suggested that dynamic test should be calibrated by at least one static load test for a given project.

REFERENCES 1. Basarkar, S.S., Manish, K. and Vaidya, R. (2011) “High Strain Dynamic Pile Testing Practices in India-Favourable Situations and Correlation Studies,” Proceedings of Indian Geotechnical Conference, Kochi, India, 1039-1042. 2. Davisson, M. T. (1991). “Reliability of Pile Prediction Methods,” Proceedings of Deep Foundation Institute Conference, Chicago. 3. Gue, S. S. and Chen, C.S. (1998) “A Comparison of Dynamic and Static Load Tests on Reinforced Concrete Driven Pile,” Proceedings of the 13th Southeast Asian Geotechnical Conference, Taipei, Taiwan, 497-501. 4. Hussein, M., Likins, G. and Rausche, F. (1996) “Selection of a Hammer for HighStrain Dynamic Testing of Cast-in-Place Shafts,” Proceedings of Fifth International Conference on the Applications of Stress-Wave Theory to Piles, Orlando, Florida, USA. 5. Liew, S. S., Ng, H. B. & Lee, K. K. (2004) “Comparison of High Strain Dynamic Pile Test Results, Pile Designs and Static Load Test Results of Driven Concrete Pile at Residual Soils in Malaysia,” Malaysian Geotechnical Conference, Sheraton Subang, Petaling Jaya, Malaysia. 6. Likins, G. Rausche, F. And Goble, G. (2000) “High Strain Dynamic Pile Testing, Equipment and Practice,” Proceedings of the Sixth International Conference on the Application of Stress-wave Theory to Piles, Sao Paulo, Brazil. 7. Long, M. (2007), “Comparing Dynamic and Static Test Results of Bored Piles,” Proceedings of the Institution of Civil Engineers Geotechnical Engineering 160, Issue GE1, 43-49. 8. Nayak, N. V., Kanhere, D.K. and Vaidya, R. (2000) “Static and High Strain Dynamic Test Co-relation Studies on Cast-in-situ Concrete Bored Piles,” Proceedings of Deep Foundation Institute 2000, New York, USA. 9. Rausche, F., Goble, G. and Likins, G. (1985) “Dynamic Determination of Pile Capacity,” Journal of Geotechnical Engineering, ASCE, 111 (3), 367-383.

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10. Uddin, M. K. and Tungsanga, K. (2001) “Dynamic Pile Testing and its Correlation with Static Load Test,” journal of Civil Engineering, The Institution of Engineers, Bangladesh, 29 (1), 2001. 11. Vaidya, R. (2006) “Introduction to high strain Dynamic Pile Testing and Reliability Studies in Southern India,” Proceedings of Indian Geotechnical Conference, Chennai, India, 901-904.

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