Bored Pile Construction -Chris

GTC Presentation

Bored Pile and Driven H-Pile Construction (24 June 2011) Christopher Leung (Geotechnics) 1

Secondment at Tysan Foundation Limited {

{

Oct 2011 – Jan 2011 (3 months) z Construction of Public Rental Housing at Kai Tak Site 1B (~1100 Nos. of mixed driven H-pile and socketted H-pile) Jan 2011 – Jun 2011 (6 months) z Piling Works for the Proposed Industrial Building at No. 6-28 Chai Wan Kok Street, Tsuen Wan (33 Nos. of bored piles and 53 Nos. of driven H-pile)

2

Bored Pile Construction - Procedures, plants and equipment

3

Bored Pile Construction – Typical Procedures 1. 2. 3. 4. 5. 6. 7. 8. 9.

Pre-drilling (at each pile location) Setting out Casing driving through soft layer and excavation Rock socket and bell-out forming (by RCD) Air-lifting Koden test Steel cage installation Concreting Interface/ full-depth concrete coring 4

Bored Pile Construction – Pre-drilling {

{ {

{

{

Determination of rockhead level before construction At each pile location Continuous 5m of Grade III or better rock with TCR over 85% Double or triple-tube (for fragmented rock) corebarrel T2/TN size barrel 5

General site arrangement Casing driving RCD Steel cage fabrication Air lifting Concreting

6

Chai Wan Kok Street (Feb 2011)

Casing driving { { { {

Welded Splice/ Bolted Joint Common size: 2.0m, 2.5m & 3.0m Commonly by oscillator Down to bedrock/hard stratum

7

Other common methods for casing driving

Rotator Vibrator 8

Excavation { {

By crawler crane simultaneously with casing driving By hammer grab and rock chisel

9

Rock socket forming { { {

Reverse Circulation Drill (RCD) Vertical drill-bit Rock sample inspection at rockhead, founding and pile base levels

10

Swivel Head

Rock socket forming by RCD

Drilling Platform Clamping Collar

Water Tank Air Comp

Drum Stabilizer

Power Pack

Drill Rod

Stabilizer

Drill Bit

Cutter 11

Bell-out tools { { { {

Reverse Circulation Drill (RCD) Replaced with bell-out bit No further drilling downwards but only extending the arms “Travel” calibration

Founding Level Pile Base Level 12

Air-lifting Air Compressor

Flush out to Sedimentation Tank

Recycle water / Fresh Water

Air Hose Tremie Pipe

13

Koden Test {

{ {

Common acoustic device to verify verticality & bell-out size Require sufficient clarity of water DO NOT expect very exact values

14

Steel cage installation {

Aware of possible cage collapse z z

Use crawler crane with sufficient power Aware of design with heavier top reinforcement

{

Ensure sufficient lapping length

{

Sufficient nos. of reservation pipes (150mm dia.)

15

Concreting Skip

Ramp

Concreting Platform

Tremie Pipe

16

Concreting {

{

Simultaneous with casing extraction and removal and tremie pipe Casing supported securely by oscillator/ crawler crane

17

Quality Problems in Association with Construction Technology and Design Quality Problems { { { { {

Pile Inclination and Off-Centre Necking Pile Shaft Thermal Cracking of Concrete Air Voids and Honeycomb in Concrete Sediments at Pile Base

Unknown underground condition!

18

Quality Problems in Association with Construction Technology and Design

{

Design Consideration Dimension z

{

Concrete and reinforcement z z z

{

Avoid Very Large, Extremely Long Piles (e.g. 3m diameter more than 80m deep) and Large Bell-Out (e.g. 4.8m) Use High Grade Concrete with Care (e.g. Grade 50) Maintain Sufficient Clear Spacing between Reinforcing Bars Ensure Sufficient Stiffness of the Reinforcement Cage

Ground condition z

Use Permanent Casing in Very Soft Ground or Subject to Tidal Effect and Underground Stream

19

Tests on Bored Pile Construction Interface Coring z z z

Coring through reservation pipes On each bored pile after concreting for a certain period Visual inspection on the contact of the pile base and the founding rock

Example of good contact 20

Tests on Bored Pile Construction Full-depth Concrete Coring z z z z

Coring from the top of pile into the founding rock Nos. subject to criteria of completion (e.g. 5%) Concrete cores selected for compressive test As alternative to interface coring

21

Interface and full-depth concrete coring Common imperfections { Concrete core z z

{

Thermal joint Air voids and honeycomb in concrete

Interface contact z

z

No recovery (inferred as soil inclusion) due to sediment at pile toe Loss of contact at the interface due to inaccessibility of concrete mix into rock fragments

22

Interface and full-depth concrete coring {

Process control to minimize the occurrence of segregation z z z

Introduce grout/bentonite in advance of concrete discharging Use high slump concrete Use of additional retarder to enhance workability

23

Remedial Actions for Pile Base Imperfections 1. 2. 3. 4.

Additional coreholes Clean the pile toe with high pressure water jet Pressurized cement grout Verification cores As specified by RSE to which extent of remedial works should be performed

24

Remedial Actions for Pile Base Imperfections Caution!!! { This method may only work in intact rock situation with confined defects {

In highly fractured rock zones, high-pressure water jetting and grouting may induce more collapses and aggravate the situation ⇒ progressive creation of cavity ⇒ induce further collapses at pile toe

25

Driven H-Pile Construction - Procedures, plants and equipment

26

Driven H-Pile Construction – Typical Procedures 1. 2. 3. 4. 5.

Pre-drilling (piles covered by 5m radius) Setting out H-pile section inspection Pitching of 1st section Splice more sections and welded joint inspection (Visual, some with non-destructive test) 6. Final set (some with PDA) 7. Load test

27

H-pile inspection { {

{

Mill cert, stocklist, s/n record Length measurement (VERY important especially for sections cut from other piles) Pile tip inspection

28

Pile pitching/driving { {

Hydraulic Hammer Offset control z z z

{

Limit power in the first few blows Close monitoring by pile worker Pile extraction if necessary

Noise permit

Hydraulic hammer 29

Better co-ordination and recording for large site • KT1B Site with over 1000 nos. of H-piles of average 5,6 sections

30

Splice sections by welding { { {

Better arrangement of welding period/ welders Allow certain time of cooling before driving Visual inspection by RE

31

Non-destructive test on welds {

Ultrasonic test z

z z

Required for a certain ratio of piles By pulse reflection of transducer Discontinuity of weld

32

Final set { { {

Use of drop hammer of specified weight Specified drop height for 10 blows Final set graph

Cp+Cq

Final set process

s 33

Calibration { { { {

Weight of drop hammer, helmet & follower Temporary compression of helmet (Cc) Coefficient of restitution (e) Hammer efficiency (k)

Hiley’s formula

Wr + (Wh + W f + P) * e 2 k*E * Ru = s + 0.5(Cc + C p + Cq ) Wr + (Wh + W f + P)

Depending on the specification requirement 34

Pile Driving Analysis (PDA) { { { { {

For a certain ratio of piles specified (e.g. 5%) Can be done simultaneously with final set Wave signal analysis during driving Wave equation model Induced pile capacity as additional verification

35

Post-construction drilling {

{ {

In case the pile founding level is higher than designed level from pre-drilling Minimum nos. as specified Process similar to pre-drilling z

Rockhead/SPT

36

Load Test { { { {

Loading to ultimate pile capacity Kentledge with sufficient loading Four dial gauge extensometer Allowable maximum and residual settlement

Kentledge and hydraulic jack 37

Conclusion {

{

Typical procedures for Bored Pile and Driven H-Pile construction Examples from the projects involved

END 38