Construction of steel sheet piles

The following article will introduce the steel sheet pile construction specifications and construction process in detail.

First, steel sheet pile construction specifications

(1) The location of the steel sheet piles must meet the design requirements to facilitate the earthwork construction of the trench foundation, that is, there is room for formwork support and removal outside the most prominent edge of the foundation.

(2) The support plane layout shape of the foundation pit trench steel sheet piles should be as straight and neat as possible, and irregular corners should be avoided to facilitate the use and support installation of standard steel sheet piles. The surrounding dimensions should be combined with the board module as much as possible.

(3) During the entire foundation construction period, during construction operations such as excavation, lifting, reinforcing steel bars, and concrete pouring, it is strictly prohibited to collide with supports, arbitrarily dismantle supports, and arbitrarily cut or weld on supports, nor should they be left alone on supports. heavy objects.

Second, steel sheet pile construction process

1.Construction process:

Construction preparation → Measurement and positioning → Guide pile production → Steel sheet pile driving → Steel sheet pile inner support 1 → Drainage → Leak plugging → Steel sheet pile inner support 2 → Drainage → Leak plugging → Dredging → Back cover → Cushion layer → Steel bar binding → Template installation → Concrete pouring → Steel sheet pile cofferdam removal (Note: High-pressure water jet dredging operations are also carried out in the boldfaced parts).

1.1 Selection of steel sheet piles

This project uses water-stopping steel sheet piles imported from Japan for construction. The steel sheet piles have small locks and good water-stopping capabilities. They are 40cm wide and weigh 77.7kg/m. Taking into account the needs of the geological conditions of this project, the pile length is planned to be It is a 20-meter steel sheet pile. First, the steel sheet piles are classified and sorted at the sheet pile stacking base. Sheet piles of the same type are selected, bent, modified, cut, and welded to sort out the types, specifications, and quantities of steel sheet piles required for construction.

Steel sheet piles need to be inspected and sorted before entering the site, and any defects found can be adjusted at any time. After sorting, try not to bend or deform them during transportation and stacking to avoid collisions, especially the interlocking openings cannot be damaged.

Before driving the pile, seal the bottom of the groove at the pile tip to prevent soil from squeezing in. The lock mouth should be coated with butter or other grease. Steel sheet piles with deformed or severely rusted lock mouths should be repaired and corrected. Use 90-degree corner stakes at the corners.

1.2 Calculation of theoretical dosage of steel sheet piles:

Calculation of perimeter of steel sheet pile cofferdam:

  19.6×2＋10.4×2=60m

Calculation of the number of steel sheet piles: corner piles are 0.2m×0.2m, with a total of 4 pieces.

(60-0.4×4m)/0.4m=146 pieces, 146+4=150 pieces

Steel sheet pile weight calculation:

150×20×77.7＝233.100t

1.3 Enter

1.3.1 Construction setting out and positioning

(1) Mark the control points in the construction area and effectively protect them after reviewing them.

(2) Since the steel sheet pile cofferdam of this project has been enclosed with steel pipe piles for the pile foundation construction platform, the existing steel pipe piles can be used for positioning, and I-beams can be welded on the steel pipe piles. To ensure that the driven steel sheet piles are in a straight line. Warning signs are painted on the parts of the steel pipe piles that are exposed to the water, and channel steel is welded for reinforcement to serve as guide positions and elevation control signs during piling. The location arrangement of positioning piles and piles to be constructed is shown in the figure below.

1.3.2 Overall construction process of steel sheet pile driving

The steel sheet piles are driven from the center of the cofferdam on the east side of the river to the first piece of steel sheet piles, and then gradually driven to both sides, closing at the lower reaches of the river (see diagram). The position and direction of the first two steel sheet piles must be ensured. accuracy to serve as a model. Calibrate the measurement once every 3 meters to ensure it is on the same straight line. After each steel sheet pile is driven, it will be welded firmly to the channel steel. According to the lifting capacity, it is determined to insert the roots one by one to a stable depth, which is generally 2-3m. After all insertions are completed, they are then driven to the design elevation one by one. Through precise calculations, the steel sheet pile joint determines the position of the dragon's mouth and configures special-shaped steel sheet piles of corresponding specifications. The angle and size of the special-shaped steel sheet piles are measured on site, and the special-shaped steel sheet piles are cut and welded according to the actual situation to ensure the sealing of the entire cofferdam.

1.3.3 Steel sheet pile driving construction technology

(1) The floating crane is parked about 4m away from the piling point, and construction is carried out sideways to facilitate observation by surveyors. Hang up the vibrating hammer, raise it, and straighten out the oil pipes and cables.

(2) Lower the hammer, open the hydraulic port, pull a pile under the pile driving hammer, apply lubricating oil to the lock, and lift the hammer.

(3) Stop rising when the tip of the steel sheet pile is 30cm above the water surface. The hammer is lowered to move the pile into the clamping mouth, and the hydraulic press is started to clamp the pile. Raise the hammer and pile to the pile driving location.

(4) Align the lock mouth of the pile and the positioning pile, lower the hammer, and press the pile by the weight of the hammer and the pile until it cannot drop to a certain depth below the mud.

(5) Try turning on the pile driving hammer for about 30 seconds, stop the vibration, use the inertia of the hammer to drive the pile to a solid soil layer, start the vibrating hammer to drive the pile down, control the speed of the pile driving hammer’s descent, and keep the pile upright as much as possible so that the lock can be smooth Bite, improve water stopping ability.

(6) When the sheet pile reaches 40cm before the design height, the vibration stops, and the vibrating hammer continues to rotate for a certain period of time due to inertia, and the pile is driven to the design height.

(7) Release the hydraulic clamp, raise the hammer, and drive the second pile, and so on until all piles are driven.

Before piling, the lock mouth should generally be coated with a mixture of butter, sawdust, etc. After driving the steel sheet pile, the water stop treatment in the steel sheet pile cofferdam should be started.

1.4 Construction precautions

(1) After the guide pile is driven, weld it firmly with channel steel to ensure that the guide pile does not shake, so as to improve the accuracy when driving the pile.

(2) When inserting wire piles, after lifting the steel sheet pile, manually insert the pile into the lock mouth. Move slowly to prevent damage to the lock mouth. After insertion, you can loosen the hanging rope slightly to allow the pile to slide in by its own weight.

(3) When the steel sheet pile is vibrated and driven to 40cm below the design elevation, construction must be done carefully to prevent over-depth from occurring.

(4) When sealing, accurately calculate the size of the special-shaped steel sheet pile to ensure water-stopping quality.

2. Cofferdam pumping and support

Pumping is carried out after the steel sheet pile cofferdam is closed. During the pumping process, the pumping speed and height should be strictly controlled, and a safety support should be set at the top of the cofferdam.

When the water pumping reaches the predetermined depth, support and protection should be added in time. All steel sheet piles are welded firmly to the guide channel steel.

Considering that the construction site of this project is small, the underwater geological conditions are poor, and the surrounding dynamic loads and active earth pressures are large, it was decided to use Ф529×7mm steel pipe piles to form a skeleton inside the cofferdam for support to ensure safety. Considering that there is 1.5m thick backing concrete, the internal support is divided into two layers, respectively supported at an elevation of +1.5m and -1.5m to ensure the stability of the steel sheet pile cofferdam. Double-jointed I36 I-beams are used at both ends to make diagonal braces. Please see the overall floor plan and calculation section for specific support forms and calculations.

3. Dredging

During the process of pumping water and internal support, a mud pump is used together with high-pressure water injection to remove the silt in the cofferdam. During the removal process, a pump is used to dredge and replenish water in the cofferdam to ensure that the difference between the internal and external water heads is not greater than 50cm to ensure that the cofferdam is Safety. During dredging, measure the pit bottom elevation in time. If the design bottom elevation is reached, stop high-pressure water injection. If it is found that the desilting is not in place after pumping water, the remaining silt must be removed manually.

4. Concrete back-sealing pouring

Since the use of underwater bottom sealing may cause the steel sheet piles to be unable to be pulled out, water is pumped and supported first, and then the bottom sealing is performed. When the dredging meets the requirements, dry bottom sealing construction can be carried out as usual. When sealing the back cover, formwork is installed on the inside of the steel sheet pile cofferdam. The strength grade of the back seal concrete is C20, and the thickness is calculated to be 1.5m.

5. Anti-seepage and plugging

Before driving steel sheet piles, the lock mouth should generally be coated with a mixture such as butter and sawdust. When the lock is not tight and leaks, use cotton wool to stuff it on the inside, and wrap a layer of waterproof colored strips on the outside to achieve the dual effects of waterproofing and reducing water pressure. When pumping water, sprinkle a large amount of wood chips or The mixture of chaff and slag causes it to be carried by water to the leakage area and block it on its own. At the leakage area at the pile foot, measures such as partial concrete bottom sealing are adopted. If the water leakage is serious and it is difficult to plug the leakage, add wooden pile cofferdam outside the steel sheet pile, lay colored strips of cloth on the inside of the wooden pile cofferdam, and fill with clay between the colored strips of cloth and the steel sheet pile cofferdam for sealing.

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