Larsen Steel Sheet Pile Construction Technology Explanation

Construction process

Construction preparation → Three connections and one leveling on site → Preparation of equipment, tools, and materials (pre-purchase of steel sheet piles, on-site inspection of steel sheet piles, hoisting and transportation of steel sheet piles, and storage of steel sheet piles) → Pile position marking → On-site injection equipment → Equipment commissioning and positioning → Hoisting and delivering steel sheet piles → Pile clamping and positioning → Pile insertion (verticality control, plane position control) → Hammering piles → Stop hammering (pile top elevation control) → Move the pile driver (until the construction is completed).

Detailed construction process

The construction mainly uses Larsen III steel sheet piles as diversion channels, and the length of the steel sheet piles is 6m and 9m.

(1) Construction process and method of steel sheet piles After the Larsen steel sheet piles are in place with a lift, they are driven by the hydraulic vibrator of the crawler hydraulic excavator PC-300. Before driving, you must be familiar with the conditions of underground pipelines and structures. Considering that the steel sheet piles are long, they are easy to tilt to one side during driving. Since the accumulated tilt error is difficult to correct, it is difficult to control the straightness of the steel sheet pile wall. Therefore, the steel sheet pile construction is planned to adopt the screen-type driving method. When the second steel sheet pile is hoisted, the tongue and groove are locked and driven into the soil by vibration. This operation is repeated until the construction of the foundation pit steel sheet pile is completed. The screen-type driving method does not easily cause the sheet piles to bend, twist, tilt, and the wall surface to be uneven. It has high driving accuracy and is easy to achieve closure. During construction, 10 to 20 steel sheet piles are inserted into the guide frame in a row to make it screen-shaped and then driven.

(2) General requirements for steel sheet pile construction
① The location of steel sheet piles should meet the design requirements to facilitate the construction of bridge culverts and open channel structures in the later stage.
② The plane layout shape of the steel sheet piles of the diversion channel should be as straight and neat as possible, avoiding irregular corners, to facilitate the use and support set of standard steel sheet piles. The peripheral dimensions should conform to the sheet pile modulus as much as possible.
③ During the construction of bridge culverts and open channel structures, during the construction operations such as excavation, lifting, steel bar tying, and concrete pouring, it is strictly forbidden to collide with the support, arbitrarily dismantle the support, arbitrarily cut or weld on the support, and heavy objects should not be placed on the support.
④ Inspection of steel sheet piles For steel sheet piles, there are generally material inspections and appearance inspections, to correct steel sheet piles that do not meet the requirements and reduce the difficulties in the piling process.
Appearance inspection: including surface defects, length, width, thickness, height, end rectangular ratio, flatness, and lock shape.
b Material inspection: Comprehensive test of the chemical composition and mechanical properties of the steel sheet pile parent material.

(3) Steel sheet pile construction Larsen steel sheet pile construction is related to construction water stopping and safety and is one of the most critical processes in this project. During construction, the following construction requirements should be noted:

a Larsen steel sheet piles are driven by crawler excavators (with vibrating hammers). Before driving, be sure to be familiar with the conditions of underground pipelines and structures.

b Before driving, check each steel sheet pile and remove those with rust or severe deformation at the connection lock. Unqualified ones can only be used after repair.

c Before driving, apply grease to the lock of the steel sheet pile to facilitate driving in and out.

d During the driving process, measure and monitor the slope of each pile at any time to ensure that it does not exceed 2%. When the deflection is too large to be adjusted by the pulling method, pull it out and drive it again. The tolerance standards for steel sheet pile driving are shown in the following table.

e. The screen-type driving method is used for steel sheet pile driving. The screen-type driving method does not easily cause the sheet pile to bend, twist, tilt, and wall surface unevenness, with high driving accuracy and easily achieve closure. During construction, 10-20 steel sheet piles are inserted into the guide frame in a row to make it screen-shaped and then driven. Usually, a group of steel sheet piles at both ends of the screen wall are driven to the design elevation or a certain depth, and the verticality is strictly controlled. They are fixed on the purlin by electric welding, and then driven in the middle in sequence at 1/3 or 1/2 of the sheet pile height. The driving depth is generally 0.5 to 3.0m. The construction sequence of the screen-type driving method includes forward sequence, reverse sequence, reciprocating sequence, center division sequence, neutralization sequence, and composite sequence. The driving sequence has a direct impact on the verticality, displacement, expansion, and contraction in the axial direction, unevenness of the sheet pile wall, and pile driving efficiency of the sheet pile. Therefore, the driving sequence is one of the keys to the sheet pile construction process. The selection principle is: when the sheet piles at both ends of the screen wall are tilted in the opposite direction, they should be driven in the forward sequence; otherwise, they should be driven in the reverse sequence; when the sheet piles at both ends of the screen wall remain vertical, they can be driven in a reciprocating sequence; when the length of the sheet pile wall is very long, they can be driven in a composite sequence. The tolerance standards for steel sheet pile driving are shown in the following table.

f. Ensure that the depth of the pile after excavation is not less than 3 meters, and ensure that the steel sheet piles are smoothly closed;

g. After the piles are driven, the water tightness of the pile body should be checked in time, and the leaking parts should be welded and repaired. A special person should be assigned to check the pile body every day.

Precautions
(1) After the guide piles are driven, they should be welded firmly with channel steel to ensure that the guide piles do not shake, to improve the accuracy when driving the piles.

(2) When driving the line piles, after the steel sheet piles are lifted, the piles are inserted into the lock mouth manually, and the movement is slow to prevent damage to the lock mouth. After insertion, the lifting rope can be slightly loosened to allow the piles to slide in with their weight.
(3) When the steel sheet pile is vibrated and driven to a depth less than 40 cm below the design elevation, be careful during construction to prevent over-depth.

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