Scope of this work method statement shall apply on the reinforced concrete works and the objective is to define and establish the work method of statement for the reinforced concrete work for the
installation of micro pile.
The piling installation work shall be done in compliance with construction drawings and contract specifications.
Following personnel are having their roles in the micropile works.
- Site Engineer/ Site Supervision Staff
- Surveyor
- Machine Operator
- Bar Bender, Bar Cutter & Carpenter
- Concreters
- General Workers
DRILLING EQUIPMENT
All Hydraulic Rotary Crawler or Skid Rig is employed for installation of Micropile. Model of Rig used is either KRUPP 130LC or equivalent.
DRILLING PROCEDURE
From probing tests and caisson excavation works, the formation across the site is found to be consisted of:
Overlying with soft to loose deposits of Clay and Sand with high water table.
Sometimes muddy soils are following into caisson shaft from the base during excavation works.
Residual soil and interspersed with boulders.
In view of the above, it is proposed to install the micro pile with permanent casing.
It is a usual practice and requirement for soils which are too soft (Clay) or loose (Sand or Gravels) or cavities or boulder formation are encountered, permanent casing is adopted instead of temporary casing.
The used of permanent casing is:
- To prevent extensive lost of grout.
- To prevent necking of pile due to collapse of hole walls and grout lost.
- To ensure the reinforcement tube is properly embraced by cement grout and the micro pile formed is according to design.
The installation of permanent casing is via Tubex /Odex System Tubex 240 is proposed in the project which can open a hole of 306 in diameter and simultaneously install permanent casing respectively.
Tubex method is based on a special pilot bit and an eccentric reamer.
As the pilot bit continues to drill, the reamer drills a hole large enough for a casing tube to slide down after the reamer.
The micropile holes is continuously line and stabilize with the Permanent Casing tubes sliding down through their own weight and impact force from the hammer while simultaneously drilling the hole deeper.
Thus the TUBEX Method was quickly and easily provide lined stable hole through the overburden.
During the drilling, the flushing media (pneumatic air) and cuttings are forced upwards inside the casing by means of the guide device.
Flushing is controlled to best suit the application.
When the drilling has reached 0.5m into fresh rock, the drill string is rotated in the opposite direction, whereby the reamer is folded in.
The drill string with the TUBEX bit is retracted up inside the casing. Impact energy from the hammer is diverted to the casing tube to anchor it.
After changing to a conventional DTH Bit, the drill string is lowered into the casing and drilling is resumed till the required socket length of 3 ̴ 4 m is achieved.
PILE GROUTING METHOD
Grouting Equipment’s
Each set of Grouting Equipment is consisting of a high pressure piston pump and Two Grout Mixers.
The type and model of Grouting Equipment’s used are as follows:
a) Grout Pump: Koken BG Grout Pump or equivalent Pressure Range = 0 ~ 30 kg / cm²
b) Grout Mixer: KLG-100 Grout Mixers or Equivalent Volume = 450 liters
Grout Mix
The grout mix consists of Ordinary Portland Cement (MS522), anti shrink admixture and clean water.
Water cement ratio is 0.5. The 28 day works cube strength of cement Grout is not less than 30 N/mm².
Grouting Procedure
Grout is mixed on site and pumped into micropile hole using suitable pipe as soon as possible not exceeding 1 hour after mixing.
Grouting is carried out immediately after drilling, cleaning and inserting of reinforcement tube.
The grout is Tremie up to not less than 300mmm above the cut off level via the API pipe.
If temporary casing is adopted in drilling, temporary casing shall be withdrawn slowly as soon as the Tremie grout has displaced the water and neat grout flows out.
Grout Cube
At least 6 representative cubes are prepared on each day of grouting works.
The prepared grout cubes is tested according to BS 1881 in the following sequence:
a. 2 Nos. after 7 days.
b. 2 Nos. after 28 days.
c. The rest as spare cubes.
Reinforcements Tube
Used API Drill Pipe (Grade N80) of size 1778.8mm OD x 10.3mm x 9.0 ~ 12.0 M (L) is used as Reinforcement Tube.
PROPOSED TEST PILE PROCEDURE TO MICROPILE
A cast in place micropile is constructed by making a hole in the ground to the required depth and then fill it with Cementitious Grout upon the confirmation by the Consulting Engineer as a preliminary working test pile.
There action of the pile was provided using Tension anchors which were supported by a series of steel beams as shown in the sketches attached.
The test pile was conducted in 2 cycle.
It was intended that the pile is loaded up to 3 times the working load and subsequently unloaded to zero again.
With the results, load settlement curve is then plotted for further discussion.
MAINTAINED LOAD TEST
Test Loading Procedures
Micro pile to be tested shall be built up or cut down to a suitable level and mild steel plate or plywood packing of suitable thickness is fixed on the pile, to carry the test load jack.
The kentledge system is then built up around the pile to be tested and so positioned that the hydraulic jack placed centrally over the pile on the mild steel plate or plywood packing, lies
centrally under the kentledge.
The kentledge loads are derived from Tension anchors loads.
Loading Procedure
1st Cycle:
From zero to working load, in increments of 25% working load at intervals of 1 hours provided stability has been obtained.
At working load, load maintained for 2 hours after stability has been reached.
No increments / decrement of load will be permitted until settlement / recovery has stabilized.
2nd Cycle:
From zero to test load, in increments of 20% test load at intervals of 1 hours provided stability has been obtained.
At test load, load maintained for 24 hours after stability has been reached.
No increment / decrement of load will be permitted until settlement / recovery has stabilized.
Unloading Procedure
1st Cycle:
From working load to zero load, the test pile shall be unloaded in four equal increments at half hour interval until the full load is removed.
Reading should be taken at 15 minutes intervals throughout the unloading exercise.
2nd Cycle:
From test load to zero load, the test pile shall be unloaded in four equal increments at one hour interval until the full load is removed.
Reading should be taken at 15 minutes intervals throughout the unloading exercise.
METHOD OF MEASUREMENT
Load: The load applied to the pile is measured by means of a pressure gauge attached to the jacking system, the pressure gauge would be calibrated.
Settlement:
Four dial gauges would be placed at corners of the Test Pile to measure settlement of the pile.
These dial gauges are supported by an independent frame. In addition, one scale ruler would attached to the jack, two at the independent frame and one serve as TBM plant outside the test pile area.
The movement of the frame would be monitored, if any.