preboring works to dwall with air-lift & rcd core barrer - 17.6.14.pdf
TRANSCRIPT
-
8/11/2019 Preboring Works to DWall with Air-lift & RCD Core Barrer - 17.6.14.pdf
1/18
PRE-BORING WORK
PRIOR TO
DIAPHRAGM WALL CONSTRUCTION
-
8/11/2019 Preboring Works to DWall with Air-lift & RCD Core Barrer - 17.6.14.pdf
2/18
CONTENTS
OBJECTIVE
PRE-BORE METHODOLOGY ------------------------------------------------------ 3
A) AIR-LIFT METHOD -------------------------------------------------------------- 4
Guide Wall and Casing Installation ---------------------------------------------- 4
Pre-boring --------------------------------------------------------------------------- 5
Pre-coring --------------------------------------------------------------------------- 6Backfilling -------------------------------------------------------------------------- 8
Diaphragm Wall Soil Excavation ----------------------------------------------- 10
Pre-boring P3 & P4 --------------------------------------------------------------- 11
Pre-boring P5 & P6 --------------------------------------------------------------- 12
Diaphragm Wall Rock Coring --------------------------------------------------- 13
B) RCD(REVERSE CIRCULATION METHOD) ------------------------------- 15
APPENDIX A - LAYOUT PLAN OF PRE-BORING
- ENLARGE LAYOUT OF PRE-BORING
-
8/11/2019 Preboring Works to DWall with Air-lift & RCD Core Barrer - 17.6.14.pdf
3/18
Objective: To remove hard strata prior to diaphragm wall construction
1. Pre-boring Methodology
Pre-boring is selected to ease the excavation for diaphragm wall at hard strata / high rock level in these
area prior to diaphragm wall excavation. It entails the process since inception of guide wall
construction, pre-casing installation, coring and backfill with LSS(Liquefied Soil Stabilizer) and lean
concrete at above rock bed and within rock bed zone for backfilling respectively.
Based on current available bore-log information, pre-boring of 1000mm diameter along Dwall
alignment, please see Appendix A have been selected for such works. Thus, 2 pre-boring methodology
will be used to carry out, namely; Air-lift and RCD(Reverse Circulation Drill) methods.
A) Air-lift method:Using a boring rig attach with kally-bar mounted with a self-collecting box core
barrel to perform pre-boring with air supply to create suction effect to clear out drilling
fragments from pile toe. The air-lift method of clearing the drilling from pile toe are air-lifted into
collection box situated above the core barrel, thus every interval of an hour may be required to
retrieve its kally-bar to empty those loose rock fragment being collected in the collection box or
deemed at the operator opinion that the collection box is fully filled.
B) RCD method: Using a boring rig attach with RCD rod instead of kally-bar, mounted with core
barrel with air supply to create suction effect to clear out drilling fragments. The RCD method
tends to be a one-time process to continuously clean out the drillings from pile toe.
The above 2 methodology of pre-boring are similar with the used of casing installed by either vibro-
-
8/11/2019 Preboring Works to DWall with Air-lift & RCD Core Barrer - 17.6.14.pdf
4/18
A) Air-lift method
Casing Installation
1. Construct the guide wall for diaphragm wall alignment accordingly to pre-bore location layout,
catering for the outer casing diameter of 1050mm.
2. Only applying for pre-bore location, its guide wall internal face to internal face width shall be
constructed as in Figure 1 to suit the casing installation for pre-boring works.
3. Pre-arrange with marking of each diaphragm wall(D-wall) joints on guide wall top for initial casing
setting out for pile 1 and 2 at every joint of D-wall.
4. Pre-excavate by means of backhoe or excavator to depth of guide wall if necessary at site discretion
for the initial insertion of casing setting/positioning. Commence pile 1 casing installation by vibro
hammer or casing-driving adapter of the boring rig into ground. Check the verticality of casing
during installation by spirit level. Drive casing until some refusal from ground. Commence boring
at pile 1 while pile 2 may continue to start installation of casing into hard strata by mean of vibro
Figure 1 / Section A A (N.T.S)
P1 P2
-
8/11/2019 Preboring Works to DWall with Air-lift & RCD Core Barrer - 17.6.14.pdf
5/18
Pre-boring
1. Pre-bore to clear out materials with boring bucket within casing at pile 1 until hard strata/rock top
level as shown below Figure 2; similarly for P2 casing and its pre-boring works as well as for all the
intended pre-boring location are apply.
P1 P2
-
8/11/2019 Preboring Works to DWall with Air-lift & RCD Core Barrer - 17.6.14.pdf
6/18
Pre-Coring
1. Replace boring bucket with Roller Bit Core Barrel, Figure 3 next page; to continue rock head
coring. The core barrel is fitted with a conceal pipe within its wall, and connected to the suction
channel to supply air from a compressor unit, so as to create a suction-effect within the suction
channel to air-lift the crush strata beneath the roller bit at pile toe level into the collection box
located above the roller bit.
Suction channel for
hard strata fragment
clearing from pile toe
Suction channel forhard fragment clearingfrom pile toe
Figure 3 Roller Bit Core Barrel
Note: Hard strata level shall be
recorded in the Confirmation of GIIIRock Level and witness by all and in-
charge person to sign-off as in
Appendix B.
-
8/11/2019 Preboring Works to DWall with Air-lift & RCD Core Barrer - 17.6.14.pdf
7/18
Enlarge Details on Core Barrel Process
Suction
channel
Air supply inletfrom compressor
Collection box collection point of fragment chiptransported by air-lift within core barrel during coring
Rock fragments
sink into
collection box
-
8/11/2019 Preboring Works to DWall with Air-lift & RCD Core Barrer - 17.6.14.pdf
8/18
Backfilling
1. Once the desire depth of that D-wall panel is reached, retrieve core barrel and kelly-bar. Moved off
boring rig to pile 2 continue pre-boring works in similar manner described earlier.
2. While pile 1 is prepared with the lowering of tremie pipe, G20 shall be used for the backfilling from
pile toe to the earlier hard strata/rock level. Remaining from hard strata/rock level to guide wall
toe/base shall be backfilled with LSS/Grade7 lean concrete as shown below;
P1 P2
LSS / G7
-
8/11/2019 Preboring Works to DWall with Air-lift & RCD Core Barrer - 17.6.14.pdf
9/18
in jumping manner at the construction manager discretion so as to provide a continuous pre-boring
within site constraint.
4. Pre-bore and cast in similar manner to the rest of the pile. In event of more pre-bore holes are
requires to carry out at others location other-than those shown in Appendix A, upon further
information are obtained from the probing soil investigation, new location to be pre-bored shall be
added and revised for information.
-
8/11/2019 Preboring Works to DWall with Air-lift & RCD Core Barrer - 17.6.14.pdf
10/18
Diaphragm wall Soil Excavtion
1. Commence grabbing or use cutter with Bentonite slurry, if available to pre-excavate out those
earlier backfilled LSS/G7 lean concrete and remaining soil shown below until earlier hard strata /
rock head again;
Re-excavate earlier
LSS & soil
Earlier hard strata /
rock head level
-
8/11/2019 Preboring Works to DWall with Air-lift & RCD Core Barrer - 17.6.14.pdf
11/18
Pre-boring P3 & P4
1. Installed casing into excavated trench to setout remaining pre-bore location P3 and P4 on guide wall
top. Repeat using roller bit to desintegrate the hard strata / rock bed again at P3 & P4.
P2
P2
P1
P1 P3P4
P3P4
-
8/11/2019 Preboring Works to DWall with Air-lift & RCD Core Barrer - 17.6.14.pdf
12/18
Pre-boring P5 & P6
1. Upon hard strata / rock bed are cleared. No backfilling of G20 is required for these last pre-bore
piles but to retrieve casing for the cutter for further excavation with Bentonite slurry.
P6P5
-
8/11/2019 Preboring Works to DWall with Air-lift & RCD Core Barrer - 17.6.14.pdf
13/18
Diaphragm Wall Rock Coring
1. After casing removal, position cutter for excavation as shown below with Bentonite slurry;
-
8/11/2019 Preboring Works to DWall with Air-lift & RCD Core Barrer - 17.6.14.pdf
14/18
2. Continue excavation rock bed until desire Dwall design depth is reached. Proceed to desanding,
lower steel cages and casting.
-
8/11/2019 Preboring Works to DWall with Air-lift & RCD Core Barrer - 17.6.14.pdf
15/18
B) RCD method
In RCD methodology, the pre-boring procedures and coring of hard strata / Rock bed drilling
arrangement is similar described as in air-lift method, but for RCD method, RCD drilling section of
pipe are used instead of kally-bar; core barrel is connected to RCD pipe with supply of air into RCD
pipe to create suction-effect within RCD pipe to air-lift the drilling chippings/fragments with
bentonite slurry within core barrel via RCD pipe into collection tank at ground level as shown below;
Air Flush &
Drill chips
-
8/11/2019 Preboring Works to DWall with Air-lift & RCD Core Barrer - 17.6.14.pdf
16/18
APPENDIX A
PRE-BORED PILES LAYOUT
-
8/11/2019 Preboring Works to DWall with Air-lift & RCD Core Barrer - 17.6.14.pdf
17/18
17
-
8/11/2019 Preboring Works to DWall with Air-lift & RCD Core Barrer - 17.6.14.pdf
18/18
18