【Excerpts】9 problems of bored piles solved at once!

       Various problems are often encountered in the drilling construction. Targeted preventive measures should be taken to solve different problems, so as to prevent them in advance, avoid them in things and deal with them timely afterwards. In order to ensure the quality of construction, we should not only strictly ensure that each process meets the requirements, but also actively avoid all kinds of common problems.

Specific requirements of each step

1、Prepare mud to determine the mud consistency according to the drilling method and the formation conditions. If the mud is too thin, it will lead to the small slag discharge capacity and the poor effect of wall protection; and the thick mud will reduce the impact capacity of the drill bit and affect the drilling speed.

2、When the drilling depth is large, the water pressure will cause the collapse of the hole wall below the underground water level, so the buried cylinder can balance the water pressure of the underground water outside the hole or increase the water pressure in the hole, in order to prevent collapse, and can also isolate the surface water.

3、Installation and positioning Because the stability of the foundation will affect whether the drill is inclined, so for the soft foundation, the bulldozer can flatten and pad the steel plate to make it have enough stability.

4、During drilling construction, constantly add mud and thick slag, and observe whether the hole is deviated at any time. Plan the drilling sequence reasonably to ensure that the construction of the pile hole will not affect the previous pile hole, and the movement distance of the drilling rig should not be too far.

5、Clear the hole immediately after the last pile hole meets the design requirements to ensure that the borehole will not collapse due to mud precipitation due to too long interval.

6、Concrete pouring When the hole cleaning operation is completed, the precast reinforced cage can be lifted vertically into the hole, and fixed after positioning, fill the concrete with the pipe, do not stop the pouring, otherwise the pile breaking phenomenon will occur.

Common disease phenomenon and prevention and treatment

1、Water discharge from the shield 【The water leakage from the outer wall of the shield will cause the foundation subsidence, tilt and displacement of the shield, resulting in the pile hole deviation.】

Prophylactico-therapeutic measures

(1) when burying the bottom of the pit and the best water content to choose the clay layered compaction;

(2) Open the hole at the appropriate height of the shield to keep the head height in the casing with 1~1.5m;

(3) prevent collision with the guard barrel when taking off and landing the drill bit;

(4) the clay can be filled around the reinforcement, if the cylinder is seriously sunk or displaced, it should be reworked and buried.

2、Very slow or no footage drilling 【drilling in the hard plastic clay layer for 8~10h, accounting for 60%~70% of the single pile drilling time.】

Prophylactico-therapeutic measures

Replace the appropriate drill bit, arrange the correct tool Angle, shape, arrangement direction, increase the counterweight, strengthen the slag discharge, reduce the mud specific gravity or use the drilling method.

3、The wall collapse of the pile hole 【After the hole or hole, the mud discharged from the hole continues to appear bubbles, and the water level in the protective cylinder suddenly drops.】

Prophylactico-therapeutic measures

(1) appropriately bury the cylinder deeply, densely backfill the soil, improve the proportion and viscosity of the mud, raise the cylinder, replenish the mud after the final hole, ensure the quality of the steel cage and prevent deformation;

(2) the lifting should be aimed at the hole, lifting straight and steady, slowly sinking, to prevent the collision of the hole wall;

(3) The perfusion time after hole formation is generally not more than 3h, and the perfusion should be completed as soon as possible;

(4) In the case of no hole in the steel cage, the slurry sand, clay mixture backfill to 1~2m above the collapse hole depth, or the whole hole backfill and compaction with the original drill bit and high quality mud sweep hole;

(5) In the case of slight collapse caused by the steel cage touching the wall of the steel cage, the drill bit with a diameter less than the inner diameter of the steel cage is used to sweep the hole with high quality mud or clear the hole with a pipe.

4、Broken pile【In the process of pouring concrete, because the pipe is separated from the concrete interface, the muddy water enters the pipe, resulting in the pile body becoming smaller or the broken pile occurs.】

Prophylactico-therapeutic measures

(1) When the catheter is pulled out, the catheter should be quickly inserted into the concrete, and the water in the catheter should be drawn out through small water pumps and other equipment, and then continue to be poured concrete.

(2) Quickly put forward the catheter, set up the water trap to rush out of the catheter, so that the catheter will continue to drop until the catheter can not be inserted. At this time, the catheter should be slightly lifted and the concrete should be poured.

5、Falling of the steel cage【For the steel bars that have been sunk to the design depth, the steel cage falls in the process of concrete pouring, and the steel bar skeleton is lower than the original design position.】

Prophylactico-therapeutic measures

After the foundation pit excavation, the pile head floating slurry is excavated, and the pile repair work should be carried out again, or the corresponding reinforcement measures should be taken on the foundation structure approved by relevant designers.

6、Steel cage floating【The steel cage floating steel frame has sunk to the design depth position. In the process of concrete pouring, the skeleton position is higher than the original design position.】

Prophylactico-therapeutic measures

(1) If the steel cage can be pulled out, it is necessary to stop pouring concrete, pull out the steel cage and heavily drill in place, and wash the concrete with high pressure water, and then conduct in situ drilling, hole cleaning and a series of processes.

(2) if the steel cage can not be pulled out, can continue to pour concrete, so that the steel cage floating at the same time to cut, until it can be pulled out, and then in situ drilling, hole cleaning and a series of processes.

7、Local shrinkage of pile hole【Local shrinkage means that the local aperture is smaller than the designed aperture.】

Prophylactico-therapeutic measures

(1) Use high-quality mud to control the proportion and viscosity of mud and reduce water loss;

(2) When the design pile distance is <4d, jump between 1~2 piles for construction;

(3) The new pile as far as possible 36h after the formation of the adjacent pile;

(4) Choose the cage drill bit with double guide positive environmental protection diameter;

(5) with mud and size drill holes;

(6) Fill the concrete as soon as possible after clearing the hole.

8、Pile hole offset and tilt 【After hole formation, the pile hole appears large vertical deviation or bending.】

Prophylactico-therapeutic measures

(1) The rig installation is positive, horizontal, stable, no bundle leading edge cutting point, turntable center and cylinder center;

(2) The protective pipe is not inclined, the drill pipe is not bent, the active drill pipe is kept vertical, add the guide frame, control the water diversion tap, as far as possible;

(3) Remove underground obstacles;

(4) In addition to the technical parameters of light pressure and slow rotation, from the soft plastic clay layer, especially the flow plastic clay layer and sand layer into the hard plastic clay layer or from the clay layer into the bedrock, the conical guide small drill at the bottom of the cage drill should be converted to flat bottom guide small drill, or directly with the flat bottom drill with no small guide drill bit;

(5) Remove underground obstacles by caisson, hole control pile and other methods;

(6) When the hard plastic clay layer is deviated, the sand and soil mixture is used to backfill the deviation above 1~2m, and the flat alloy drill bit is gently pressed and slowly turn inclined after compacting;

(7) 20~40mm particle size gravel can be cast, slightly higher than the deflection, with flat bottom alloy drill, tooth roller drill or flat bottom steel drill after hit dense.

9、Too much sediment at the bottom of the hole【the bottom of the hole is silted up, the residual mud and sand is too thick or the hole wall soil is collapsed on the bottom of the hole.】

Prophylactico-therapeutic measures

(1) After the final hole, raise the bottom of the hole by 10~20cm, maintain the slow speed idling, and maintain the circulation hole clearing time of not less than 30min;

(2) clear the hole using high-quality mud, control the mud specific gravity and viscosity do not directly use clear water replacement, the steel cage vertical slow into the hole;

(3) The sediment thickness shall be calculated according to different types of drills;

(4) Use secondary water from the pipe, and the punching time shall prevail if the sediment thickness of the hole bottom measured in the pipe meets the standard requirements;

(5) Improve the impact force of concrete on the bottom of the hole, the bottom of the bottom of the pipe is controlled at 30~40cm from the bottom of the hole, the amount of primary pouring concrete must meet the requirement that the bottom of the pipe can be buried in concrete more than 1.0m, and use water plug and concrete to wash the residual sediment.

——Source: Basic Engineering Network

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