Abstract: As we all know, pile foundation is one of the common foundation treatment methods, and bored pile is a common construction method for pile foundation construction. This paper analyzes the common problems in the pile foundation construction with this method, and puts forward the corresponding solutions.

Keywords: pile foundation; Bored cast-in-place pile; Quality problems; Treatment measures

Bored pile foundation is a kind of foundation construction form that can adapt to various geological conditions and has been widely used in various fields of engineering construction. Therefore, we should attach great importance to the construction process, grasp the problems that are easy to occur in the construction process and solve them efficiently.

1. Common quality problems in pile foundation construction

The common problems in pile foundation construction are drilling and concrete pouring. Below I will do a series of analysis on these two aspects.

1. 1 drilling construction problems

In the process of drilling construction, the hole collapse can not guarantee the drilling quality. This is because the collapse of the orifice will lead to the loosening of the soil at the bottom of the casing, and the backfill behind it is not firm enough. Sometimes the soil around the casing will be soaked by rain for a long time, which will cause the casing to be unstable or fall off, thus leading to the casing displacement. Sometimes, the rig may get stuck due to the irregular operation of the rig operator, sudden change when crossing the rock stratum, sudden failure of the rig, mechanical failure and other reasons. During drilling construction, if the plastic soil expands, the aperture will be bent and locally reduced, resulting in abnormal drilling construction; In the soft soil layer like Xinjiang, if the penetration speed is fast, the hoisting reinforcing cage collides with the hole wall, or the standard mud is not prepared according to the construction technology requirements, the hole collapse problem will occur, which will lead to the drilling construction problem; In drilling, if the wire rope of the drilling rig breaks, the drilling rig has mechanical failure or the drilling hole collapses, the drill bit will fall to the bottom of the hole and cannot work normally.

1.2 underwater concrete pouring problem

This kind of construction problems are mainly caused by the failure of back sealing, drilling sticking and steel cage floating. The main reason for the failure of bottom sealing is that the thickness of sediment at the bottom of the hole exceeds the specified standard range, which leads to the failure of underwater concrete bottom sealing after concrete pouring and causes construction problems; Due to the poor workability of concrete and insufficient impact force when pouring concrete, coupled with the fact that there are many large aggregates or cement blocks solidified by water in concrete, the pipe plugging problem occurs and the normal operation of pouring concrete cannot be carried out; Because the manufacture, stacking, hoisting and transportation of the reinforcing cage do not meet the requirements of the construction specification, the distance between the inner diameter of the reinforcing cage and the outer wall of the conduit does not meet the specified size, the conduit is hung with the reinforcing cage during the hoisting process, or the concrete surface rises to the bottom of the reinforcing cage to generate upward "buoyancy", which causes the reinforcing cage to float; Due to improper mix proportion of concrete, unqualified raw materials, or local sundries, dirt, etc. invading concrete and poor workability during concrete pouring, the construction problems of broken piles will directly or indirectly occur.

2. Treatment measures for common problems in the construction process

2. 1 Countermeasures for drilling construction problems

First of all, the depth of the pile casing buried in the soil layer must be greater than the height of the water head, and it must pass through the loose soil layer and silt layer. In addition, the backfill soil around the casing must be rammed and compacted. Furthermore, if there is a sticking construction problem, don't pull out the drill directly, but shake the rope, so that the drill bit can be lifted or inserted into the high-pressure water pipe to replace the mud after loosening, that is, lower the drill bit first, and then lift it quickly, so that the rock stratum suddenly changes or retracts due to strong impact, so as to lift the drill bit, and it is forbidden to pull it; In the process of construction, methods such as increasing mud density, raising water head and burying casing were adopted. When the hole collapse problem is serious, it must be backfilled and re-drilled to avoid increasing construction problems. If impact drilling is used, pebbles can be clamped with clay blocks and squeezed into the hole wall with low hammer impact to prevent the hole from collapsing. When the hole collapses due to the hoisting of the reinforcing cage, the reinforcing cage shall be hoisted out immediately, and mud shall be added to protect the wall to clean up the collapsed objects. Reinstall the reinforcing cage after confirming that the hole will not collapse again.

2.2 Countermeasures for underwater concrete pouring problems

First, the poured concrete should be thoroughly cleaned by installing a high-pressure air duct in the conduit, and then the underwater concrete pouring should be resumed. We can also remove the conduit first, pull out the reinforcing cage, backfill the unfilled concrete part, then take out the poured concrete with a drill bit, and then restart the underwater concrete pouring. During construction, the conduit is slowly lifted first, and then quickly lowered, which can increase the concrete pouring amount, then quickly lift and then quickly lower the impact conduit, which is convenient for dredging. The length of the upper conduit can be appropriately extended, and then a large amount of concrete is used to impact the concrete at one time to achieve the purpose of dredging; Finally, attention should be paid to the floating problem of reinforcing cage caused by too fast concrete pouring. Faced with this construction problem, we should immediately control the pouring quantity and pouring speed of concrete and shake the conduit up and down repeatedly. If the floating phenomenon of reinforcing cage cannot be cured by this method, the pouring of concrete must be stopped immediately, the conduit must be pulled out and the clay in the hole should be backfilled, and the pile will be scrapped, and the supervisor and the designer should be contacted in time to fill the pile.

3. Matters needing attention in the process of pile foundation construction

3. 1 Matters needing attention during drilling

Before drilling, the pile position should be measured repeatedly, and at the same time, the casing should be painted with red paint in a cross way, which is convenient for the construction technology verification of the pile position after drilling. In the process of drilling, it is necessary to record the changes of stratum geology in detail and accurately. In order to record drilling records in detail, accurately and seriously, it is very important for technicians to take the initiative to understand the geological changes and reflect the relevant situation to their superiors in time, especially to provide reasonable basis and real data for engineering changes. In order to accurately understand and master the geological changes, the best way is to sample the drilling slag in time and keep the slag sample.

3.2 Strengthen pore-forming detection

First of all, the construction personnel should carefully check the detailed and true drilling records, accurately grasp the unstable strata, and formulate practical and reasonable grouting schemes according to different terrains. Secondly, record all the test data in detail, especially the hole depth. The main purpose of this is to calculate the settling speed and depth of mud, so as to make a reasonable judgment and adopt a reasonable grouting method. Finally, we should do a good job of preparation before irrigation, and do a good job of pressure test of the conduit according to the different texture of the soil layer to ensure the watertightness of the conduit meets the requirements.

4. Conclusion

As we all know, bored pile foundation is one of the main methods of foundation treatment, so its construction quality will determine the quality of engineering construction, so we should attach great importance to it, understand what problems may occur in the construction process, make preparations in advance, focus on prevention, standardize the construction process, do a good job in quality control, and formulate practical and effective preventive measures for possible quality problems to reduce quality problems and prevent quality accidents.

References:

[1] China Institute of Building Science. JGJ 94-2008 Technical Specification for Building Pile Foundation [S]. Beijing: China Building Industry Press, 2008.

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