OBJECTIVE
- To outline the instruction by which the piling works for bored cast-in-place piles are carried out.
MATERIALS
- Concrete grade 30
- Reinforcement as specified
- Rotary auger, Tremie attached with hopper, Hydraulic ram or Jaw.
- Obtain approved construction drawings from the client / client’s representatives.
- Setting out shall be carried out from reference lines and points shown in the drawings. Immediately before installation of the pile, the pile position shall be marked with suitable identifiable pins or markers. The maximum permitted deviation of the finished pile from the center point shown on the setting out drawing shall be 75mm in any direction. The permitted deviation of the finished pile from the vertical is 1 in 75.
- Boring through soil shall be by rotary auger only. Boring through rock shall be by use of approved rock drilling equipment. Boring shall be carried out to depths instructed by the S.O Standard penetration tests shall be carried out in pile borings to the requirements of test 19 BS 1377;1975.
- During the process of boring a pile through weak strata, drilling fluid materials bentonite shall be used to maintain the stability of the bore. The level of drilling fluid in the excavation shall be maintained so that internal fluid pressure exceeds the external ground water pressure.
- A permanent casing will be installed up to a stable stratum (SPT value=50). Then continue boring operation to founding level. Rock tools or chiselling shall be used for boring through rock where auger can not be used.
- If the soil below casing toe level is still found unstable then extend length of permanent casing by welding and push the casing further down to a stable stratum.
- On completion of boring and where inspection of a dry pile bore indicates the necessity, loose, disturbed or softened soil shall be removed from the bore.
- Each pile boring shall be inspected prior to the placing of concrete in it and cage then placed. Steel reinforcement shall be provided for the whole length of piles and shall be fixed in the form of a cage with lateral ties.
- Cast concrete to the required level. If the bore hole is dry, concrete will be discharged through a hopper with a short guide trunk. If the bore hole is filled with water, concreting will be done through a tremie pipe with an attached hopper. The pipe shall rest on the base of the boring at the commencement of the concrete pouring and it shall at all times penetrate into the concrete which has previously been poured. The concrete mix shall be such that a continuous compacted concrete shaft is formed. For piles with permanent casing, vibrators may be used when required, poke or immersion type vibrators shall only be used from the bottom of pile upwards.
- Drawings as specified for recording “as built” location of works shall be prepared and approved by S.O.
- Comprehensive records of all strata penetrate or bored shall be kept together with boring samples. The record shall include the following information: -
a) Contract section
b) Reduced level of pile position
c) Pile reference number
d) Nominal diameter of the bore hole
e) Length of the bore hole
f) Nominal diameter of the under ream
g) Standing ground water level
h) Date bored
i) Date completed
j) Depth from working level to pile toe
k) Depth from working level to specified cut off level
l) Length of temporary casing used
m) Length of permanent casing used
n) Soil samples taken and in-situ tests carried out inclusive of the interpretation and description of soils
o) Length and details of reinforcement cage used
p) Concrete mix used
i) Water cement ratio
ii) Slumps
q) Concrete test cube results
r) Volume of concrete supplied to pile
s) Time spent in overcoming obstruction, delays and other interruption to the sequence of the works
t) Weather report
