Evaluation Report on Pile Load Test

Evaluation Report on Pile Load Testof Zayed Center Lahore Pakistan : 

Evaluation Report on Pile Load Testof Zayed Center Lahore Pakistan Presented by: Farhan Ali 2007-MS-GEO-20

Zayed Center Pakistan : 

Zayed Center Pakistan

Topics to be discussed : 

Topics to be discussed Construction of Test piles and Instrumentation Instrumentation Details Loading Mechanism Evaluation of allowable load Carrying Capacity Interpretation As Per Proposed Deflection by LERA

Pile Load Testing Program : 

Pile Load Testing Program A total of six (06) piles were tested during the testing program

Slide 5: 

Boreholes for all the test piles were drilled using a bucket type auger. In order to stabilize the boreholes ,Bentonite mud was used during the drilling. Piles P1& P3 (1500 mm diameter) were drilled down from El. (–) 18 m while other piles P2,P4,P5 & P6 (1200 mm diameter) were drilled down from the proposed basement floor level of El. (–) 16.5 m.

Construction of Test piles and Instrumentation : 

Construction of Test piles and Instrumentation Bored Cast-in-Place Concrete piles. Drill rigs with Bucket augers. Bentonite slurry was used as a stabilizing fluid The piles were drilled utilizing crane mounted pile diggers. The drilling unit bored a pilot hole approximately 20 mm larger in diameter than the diameter of the pile being installed. A temporary casing approximately 2-3 meters long.

Slide 7: 

The bore was cleaned out using a purpose made cleaning bucket (where required), which removed all loose material from the bottom of the bore. Prior to the cage lowering and concreting operations the bentonite sand content in the borehole was checked. The cage was lowered. Concrete was placed by means of a tremmie lowered and raised by the service crane. sufficient embedded (2 - 3) meters of the tremmie was maintained in the concrete concrete being poured had a slump of 180mm. Temporary casing (2-3 meter long) was extracted.

Material Properties : 

Material Properties Concrete having cylinder strength 41 MPa was specified for construction of all test piles. Lawrencepur sand and admixture SP 337 by FOSROC were used. Bentonite slurry was used to protect against bore collapse. Reinforcing Steel of diameter 12, 25 and 32 mm was used.

Instrumentation Details : 

Instrumentation Details Details of various instruments used Vibrating Type Strain Gages Extensometers Linear Variable Differential Transducers (LVDT) Dial Gages Image Analysis System

Vibrating Type Strain Gages : 

Vibrating Type Strain Gages With the cage at each 3 m interval to record deformation of pile. The average of four gages for each interval was taken to compute skin friction in each pile section.

Extensometers : 

Extensometers Three extensometers were installed with the cage at equal intervals to observe elastic shortening of the piles during loading.

Linear Variable Differential Transducers (LVDT) : 

Linear Variable Differential Transducers (LVDT) In order to record the settlement of pile head during compressive testing of piles P1, P2 & P6 four LVDT’s were installed around the pile head during the load tests. The data was recorded using automatic data acquisition system.

Dial Gages : 

Dial Gages Two dial gages were also set at the head of the pile to record total settlement of the pile manually.

Image Analysis System : 

Image Analysis System To monitor the total deformation of pile head in two dimensions (2D), image analysis system was introduced. In this method, high resolution digital camera was fixed at a suitable distance from the pile to capture photos of the imprinted grid on the pile during loading. Camera was attached to a laptop computer through cables and control was automatically made using the keyboard.

Loading Mechanism : 

Loading Mechanism Four types of loading mechanisms were Axial Compression Pile Load Testing Mechanism Lateral Pile Load Testing Mechanism Pile Dynamic Analysis (PDA) Mechanism Sonic Integrity Testing (SIT) Mechanism

Axial Compression Pile Load Testing Mechanism : 

Axial Compression Pile Load Testing Mechanism Kentledge system as per ASTM D1143 was employed to apply compression pile load test using concrete blocks The arrangement of loading system was capable of performing static pile load test up to 3000tons

Kentledge System : 

Kentledge System Grid for image analysis attached to pile head One of the Hydraulic Jack reaching against kentledge

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LVDTs and dial gage attached to pile head Camera used for image analysis

Lateral Pile Load Testing Mechanism : 

Lateral Pile Load Testing Mechanism Loading arrangements were made as per ASTM D3966-90. Test loads of 2400 kN and 1500 kN were planned to be applied. Measurement of horizontal movement of pile shaft, tilt of the pile head and rotation (twist) of the pile head by four numbers of LVDTs. Load cells readings.

Slide 20: 

Taking reading of inclinometer Set up for lateral load test along with grid for image analysis

Pile Dynamic Analysis (PDA) Mechanism : 

Pile Dynamic Analysis (PDA) Mechanism The purpose of the including PDA testing in this test program was to calibrate this method of testing with actual load tests, so that working piles would be tested with this quick method. PDA test was conducted on pile P5 following ASTM D4945-96.

Sonic Integrity Testing (SIT) Mechanism : 

Sonic Integrity Testing (SIT) Mechanism The identified pile for test was first checked to ensure that the pile head was clean, of sound concrete and free from standing water, loose concrete and blinding concrete. The sonic echo integrity test was carried out by tapping the pile head with a light plastic headed hammer to generate a downwards traveling acoustic wave. The wave was reflected by any changes in the pile shaft impedance (normally corresponding to changes in pile shaft cross-sectional area) and detected at the pile head by a transducer held firmly to the pile head.

Pile Load Tests : 

Pile Load Tests

Test Results and Evaluation : 

Test Results and Evaluation A test load of 3 times the anticipated Safe Working Load (SWL) was to be applied on this pile The load was planned to be applied in 3 cycles, the first cycle was planned up to 1 x SWL; the second cycle to 2 x SWL and the last cycle to the final test load. Between the cycles the load was reduced to zero and held for a minimum period of 1 hour to allow the measurement of net settlement “Rate of settlement in a period of 15 minutes is less than or equal to 0.06 mm. This equals to the ASTM value of 0.25 mm in 60 minutes”.

Loading schedule for test : 

Loading schedule for test

Evaluation of allowable load Carrying Capacity : 

Evaluation of allowable load Carrying Capacity

Graph B/W Axial Displacement & Load : 

Graph B/W Axial Displacement & Load

Graph B/W Axial Load & Displacement : 

Graph B/W Axial Load & Displacement

Interpretation of Load Test Data : 

Interpretation of Load Test Data Load test results obtained for the load testing program provide load settlement behavior of single piles. However, for working piles, the behavior of the particular pile group is to be considered. From the prescribed settlement of pile group it is possible to predict the expected settlement of a single pile using correlations suggested by various researchers. One such correlation is proposed by Tomlinson, M.J. (1977); which has been used here to determine permissible settlement of a single pile, the permissible settlement of single piles has been evaluated for a range of permissible settlement of pile groups. From the evaluated permissible settlement of single piles, the pile load test results have been utilized to determine the allowable pile capacity

Allowable load in compression for a single pile : 

Allowable load in compression for a single pile

Interpretation As Per Proposed Deflection by LERA : 

Interpretation As Per Proposed Deflection by LERA For individual pile caps supporting the smaller buildings: 10 mm For the major structures supported on the pile-supported mats: 20 mm Capacity of Single Piles: The allowable settlement for an individual pile is 10 mm. therefore, the individual pile capacities are as follows; Allowable pile load capacity of P1 (1500 mm diameter pile) = 547 Tons The average shaft friction obtained from vibrating type strain gages attached with the cage is as follows; P1 = 270 kN/m.

Capacity of individual piles as per recommendation of LERA. : 

Capacity of individual piles as per recommendation of LERA.

Refrences : 

Refrences www.google.com www.geotechlinks.com Foundation analysis and design by Joseph E Bowles Principles of geotechnical engineering by Baraja M. Das

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