Seepage and sand gushing

1) Phenomenon: When the excavation of the foundation pit was halfway through, the leakage of the steel sheet piling was found, mainly at the joints and corners, and sand was still gushing in some places.

2) Reason analysis:

1. There are many old Larsen steel sheet piles, which have not been calibrated and repaired before use or the overhaul is incomplete, and the water-locking parts are not well engaged, so that the joints are prone to water leakage.

1. In order to close the corners, there should be a special form of corner piles. Such corner piles must undergo cutting and welding procedures, which may be deformed.

1. When laying Larsen steel sheet piles, the locks of the two sheet piles may not be inserted tightly and do not meet the requirements.

1. The verticality of the Larson steel sheet pile does not meet the requirements, resulting in water leakage in the lock.

3) Preventive measures:

The old steel sheet piles need to be rectified before they are set up. The correction should be carried out on the platform, and the bending deformation of the steel sheet pile can be corrected by means of hydraulic jack pressing or fire drying. Prepare the purlin bracket to ensure that the steel sheet pile is driven vertically and the steel sheet pile wall is straight after driving. To prevent the displacement of the centerline of the steel sheet pile lock, a clamping plate can be set at the steel sheet pile lock in the direction of the pile driving to prevent the displacement of the sheet pile. Because the steel sheet piles are inclined when driving and there are gaps in the lock joints, it is difficult to close the closure. The first solution is to use special-shaped sheet piles (this method is more difficult); the second is to use the axis closure method (this method is more convenient).

Steel sheet pile roll

1) Phenomenon: The excavator and the earth-moving vehicle that used the steel sheet pile to excavate the earth were set on the side of the ground steel sheet pile. Soon after the excavation, it was found that the top of the steel sheet pile was tilted, the soil at the bottom of the pit was raised, and the ground cracked and sunk.

2) Reason analysis:

1. These steel sheet piles are constructed in soft soil areas, and the designed embedment depth is not enough, so the ground behind the piles sinks and the pit bottom soil uplifts is a manifestation of piping.

1. During the excavation operation, the excavator and the earth-moving vehicle are on the side of the steel sheet pile, which increases the ground load of the soil and causes the pile top to move sideways.

3) Prevention measures:

The embedded depth of steel sheet piles must be determined by calculation and implemented in accordance with the "Technical Regulations for Building Foundation Pit Support" (JGJ 120-1999). Excavators and earth-moving vehicles are not allowed to operate near the foundation pit. If construction is necessary, the load should be included in the design to increase the depth of the pile. In general Larsen pile construction, compaction grouting is used in conjunction with steel sheet pile support around it. The base water pressure is relatively high. In order to better waterproof, the base is compacted and grouted, and its thickness depends on the soil quality. In addition, the corners of the steel sheet pile support are not tightly connected, and quicksand should occur. Therefore, compaction grouting is required, for example, the number of grouting is 3 to 4. If the groundwater level is high, light well point dewatering coordination is required.

Co-connect

1) Phenomenon: When the sheet pile is driven, it sinks together with the driven adjacent pile.

2) Reason analysis:

The inclined bending of the steel sheet pile increases the resistance of the notch and often makes the adjacent piles super deep.

3) Prevention measures:

? Correct the inclination of the sheet pile in time;

? Use angle steel electric welding to temporarily fix one or several piles of co-connected piles and other piles.