PILE TESTING 2 Dynamic Load Testing Mike Turner

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

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

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

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

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

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

Dynamic load testing (3) Techniques and systems: n ‘Case’ and CAPWAPC n TNOWave, Pi. D, SVIDYN n Simbat (CEBTP)

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

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

Pile length vs Pile head settlement at working load: Dynamic load tests (rock) (2) 0. 7 mm/m 0. 36 mm/m 0. 15 mm/m

Summary (1) For a wide variety of rocks: Gross pile settlement at working load is n Proportional to pile length n Around 0. 36 mm/metre n (As high as 0. 7 to 0. 9 mm/metre) n (As low as 0. 15 mm/metre) n Independent of diameter (Again!)

Summary (2) Comparison with static tests Tests on micropiles socketed into rock (Gross pile settlement at working load) Static Av. 0. 35 mm/metre Max. 0. 4 mm/m Min. 0. 2 mm/m Dynamic Av. 0. 36 mm/metre Max. 0. 7 -0. 9 mm/m Min. 0. 15 mm/m

Still spooky!

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

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

Pile head settlement vs working load: Dynamic load tests (rock) (3) 0. 005 mm/k. N 0. 01 mm/k. N

Summary (1) For a wide range of rock type (and pile size): Gross pile head settlement at working load: n Averages around 0. 01 mm/k. N at 100 k. N SWL reducing to approx 0. 005 mm/k. N at 1200 k. N. n Does not show a linear relationship n Not so independent of length?

Summary (2) Comparison with static tests Tests on micropiles socketed into rock Gross pile settlement at working load is: Static Av. 0. 01 mm/k. N Max. 0. 035 mm/k. N Min. 0. 005 mm/k. N Dynamic Av. 0. 01 to 0. 005 mm/k. N Max. 0. 018 mm/m Min. 0. 0045 mm/k. N

Conclusion/discussion To be continued ……. but …. . ……. Some points to ponder……. . At design working load: n DLT and Static testing appear to give generally comparable load/settlement results n However, DLT gives greater scatter n Are values such as 0. 35 mm/m ‘reasonable’? n Are values such as 0. 01 mm/k. N ‘reasonable’

………. . Thank you!