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PILE TESTING (2) (Dynamic Load Testing) Mike Turner (Applied Geotechnical Engineering)

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Types of load testing You will recall that we highlighted: Static load testing Static load testing Maintained Load (ML) Maintained Load (ML) Constant Rate of Penetration (CRP) Constant Rate of Penetration (CRP) Dynamic load testing Dynamic load testing

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Dynamic load tests on micropiles Features (again): High slenderness ratio (=Aspect Ratio) High slenderness ratio (=Aspect Ratio) Relatively high elastic shortening Relatively high elastic shortening This Implies: Long piles = large pile head settlement Long piles = large pile head settlement Want to discuss: Comparison with Static load tests Comparison with Static load tests

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Dynamic load testing Features: Striking the pile top with a falling mass Striking the pile top with a falling mass Pile-driving hammer Pile-driving hammer Pile head: Reinforced and cast to accept the impact Reinforced and cast to accept the impact Pile top movement/velocity and force applied are measured Pile top movement/velocity and force applied are measured

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Dynamic load testing (2) Measurement: Accelerometer to measure velocity Accelerometer to measure velocity Strain gauge to measure force Strain gauge to measure force Electronic theodolite to measure penetration and elastic displacement (‘quake’) Electronic theodolite to measure penetration and elastic displacement (‘quake’)

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Dynamic load testing (3) Interpretation: Pile resistance = dynamic + static resistance Pile resistance = dynamic + static resistance Identify and separate out ‘dynamic’ effects Identify and separate out ‘dynamic’ effects Leaving static effects Leaving static effects Modern-day Hiley or ENR formula Modern-day Hiley or ENR formula Needs calibration Needs calibration

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Dynamic load testing (3) Techniques and systems: ‘Case’ and CAPWAPC ‘Case’ and CAPWAPC TNOWave, PiD, SVIDYN TNOWave, PiD, SVIDYN Simbat (CEBTP) Simbat (CEBTP)

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Dynamic load testing (4) Aim of the test: To produce a ‘conventional’ load versus settlement relationship for the pile To produce a ‘conventional’ load versus settlement relationship for the pile So.. Let’s look at some results …..

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Pile length vs Pile head settlement at working load: Dynamic load tests (rock)

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Pile length vs Pile head settlement at working load: Dynamic load tests (rock) (2) 0.36mm/m 0.7mm/m 0.15mm/m

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Summary (1) For a wide variety of rocks: Gross pile settlement at working load is Proportional to pile length Proportional to pile length Around 0.36mm/metre Around 0.36mm/metre (As high as 0.7 to 0.9 mm/metre) (As high as 0.7 to 0.9 mm/metre) (As low as 0.15mm/metre) (As low as 0.15mm/metre) Independent of diameter (Again!) Independent of diameter (Again!)

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Summary (2) Comparison with static tests Tests on micropiles socketed into rock (Gross pile settlement at working load) Static Dynamic Static Dynamic Av mm/metre Av mm/metre Av mm/metre Av mm/metre Max. 0.4 mm/m Max mm/m Max. 0.4 mm/m Max mm/m Min. 0.2 mm/m Min mm/m Min. 0.2 mm/m Min mm/m

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Still spooky!

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Pile head settlement vs working load: Dynamic load tests (rock)

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Pile head settlement vs working load: Dynamic load tests (rock) (2)

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Pile head settlement vs working load: Dynamic load tests (rock) (3) 0.01mm/kN 0.005mm/kN

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Summary (1) For a wide range of rock type (and pile size): Gross pile head settlement at working load: Averages around 0.01mm/kN at 100kN SWL Averages around 0.01mm/kN at 100kN SWL reducing to approx 0.005mm/kN at 1200kN. reducing to approx 0.005mm/kN at 1200kN. Does not show a linear relationship Does not show a linear relationship Not so independent of length? Not so independent of length?

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Summary (2) Comparison with static tests Tests on micropiles socketed into rock Gross pile settlement at working load is: Static Dynamic Static Dynamic Av mm/kN Av to 0.005mm/kN Av mm/kN Av to 0.005mm/kN Max mm/kN Max mm/m Max mm/kN Max mm/m Min mm/kN Min mm/kN Min mm/kN Min mm/kN

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Conclusion/discussion To be continued …….but ….. …….Some points to ponder…….. …….Some points to ponder…….. At design working load: DLT and Static testing appear to give generally comparable load/settlement results DLT and Static testing appear to give generally comparable load/settlement results However, DLT gives greater scatter However, DLT gives greater scatter Are values such as 0.35 mm/m ‘reasonable’? Are values such as 0.35 mm/m ‘reasonable’? Are values such as 0.01mm/kN ‘reasonable’ Are values such as 0.01mm/kN ‘reasonable’

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………..Thank you!

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