1103 TYPE OF PILES
The piles may be of reinforced concrete, prestressed concrete, steel or timber. The piles may be of solid or hollow sections or steel cased piles filled with concrete. Concrete piles may driven cast-in-situ or precast or bored cast-in-situ or precast piles driven into preformed bores. The shape of piles may be circular, square, hexagonal, octagonal, “H” or “I” Section.
1113. PILE TESTS
In any case, the initial load tests shall not be less than 2 in number, while the routine load tests
Up to 50 pile 2 test
50- 150 3 test
Beyond 150 2% of total piles (Fraction number to next higher integer number
1115.2. Bored Cast-in-Situ Piles
1115.2.1. While concreting uncased piles, voids in concrete shall be avoided and sufficient head of concrete is to be maintained to prevent inflow of soil or water into the concrete. It is also necessary to take precautions during concreting to minimise the softening of the soil by excess water. Uncased cast-in-situ piles shall not be allowed where mudflow conditions exist.
1115.2.2. The drilling mud such as bentonite suspension shall be maintained at a level sufficiently above the surrounding ground water level to ensure the stability of the strata which is being penetrated throughout the boring process until the pile has been concreted.
1115.2.3. Where bentonite suspension is used to maintain the stability of the borehole, it is essential that the properties of the material be carefully controlled at stages of mixing, supply to the bore-hole and immediately before concrete is placed. It is usual to limit:
i) The density of bentonite suspension to 1.05 g/cc
ii) The marsh cone viscosity between 30 and 40
iii) The pH value between 9.5 and 12
iv) The silt content less than 1 per cent
v) The liquid limit of bentonite not less than 400 per cent
These aspects shall act as controlling factors for preventing contamination of bentonite slurry for clay and silt.
1115.2.4. The bores shall be washed by bentonite flushing to ensure clean bottom at two stages viz. after completion of boring and prior to concreting after placing of reinforcement cage. Flushing of bentonite shall be done continuously with fresh bentonite slurry till the consistency of inflowing and out-lowing slurry is similar.
1115.2.5. Tremie of 150 mm to 200 mm diameter shall be used for concreting. The tremie should have uniform and smooth cross-section inside, and shall be withdrawn slowly ensuring adequate height of concrete outside the tremie pipe at all stages of withdrawal. Other recommendations for tremie concreting are:
(i) The sides of the bore-hole have to be stable throughout.
(ii) The tremie shall be water-tight throughout its length and have a hopper attached at its
head by a water-tight connection.
(iii) The tremie pipe shall be large enough in relation to the size of aggregates. For 20 mm
aggregate the tremie pipe shall be of diameter not less than 150 mm and for large size
aggregate tremie pipe of diameter is required.
(iv) The tremie pipe shall be lowered to the bottom of the bore-hole, allowing water or
drilling mud to rise inside it before pouring concrete.
(v) The tremie pipe shall always be kept full of concrete and shall penetrate well into the
concrete in the bore-hole with adequate margin of safety against accidental withdrawal if
the pipe is surged to discharge the concrete.
1115.2.6. For very long or large diameter piles, use of retarding plasticiser in
concrete is desirable.
1115.2.7. For large diameter piles, it may be essential to conduct non-destructive
pile integrity tests to evaluate integrity of the pile.
1115.2.8. Where possible, it may be desirable to grout the base of pile with
cement slurry under suitable pressure after concrete in the pile attains the desired
strength. For this purpose, conduit pipes with easily removable plugs at the bottom end
should be placed in the bore alongwith reinforcement cage before concreting.
1116.1. Permissible Tolerances for Pile
a) Variation in cross-sectional dimensions : + 50 mm,
- 10 mm
b) Variation from vertical or specified rake : 1 in 50
c) Variation in the final position of the head in plan : 50 mm
d) Variation of level of top of piles : + 25 mm