Construction of large buildings or structures In a limited space Must have built a retaining wall system to prevent soil erosion when digging the soil into the foundation of a building or The foundations of the post-proponent (Pylon) electric trains that have to be built in a limited space and also has the weight of the vehicle that creates vibration until it affects the movement of the soil around Wells prepared To work in underground structures. It is known that the soil layer in Bangkok Approximately 10.00-12.00 meters deep from the soil surface is a clay that has no bonding value and the shear strength is small When building underground Temporary structural systems to prevent soil collapse have to be used. Sheet Pile Walls are one form of soil protection structure that has been chosen. There are many types of Sheet Pile Walls as follows. Cantilever sheet pile Walls are embedded in the wall to sink into the ground at the lower end of the wall is fastened and able to bear lateral earth pressure without falling down. Anchored sheet pile Walls It looks like a Cantilever sheet pile Walls, but with the help of an Anchor or Tie Rod to secure the upper part of the retaining wall to the soil or a weighted material. Brace Cuts or Brace Cofferdam The strength depends on the support. Strut, in which sheet piles are hammered down before digging and installing Wale and Strut at the level designed before digging. Here, we will discuss how to use the sheet pile brace cut system Mainly because it is a system commonly seen in construction in the area Bangkok, with a little mention of design theory in order to Know the principles Design guidelines with calculating lists
1. Principles of design of retaining wall systems
1.1 Design Guidelines When designing Sheet Pile in the Brace Cut system in soft clay, consider the following
1) Sheet Pile must be able to resist lateral forces from soil, water pressure, SurCharge without buckling in Sheet Pile.
2) In the structure of the bracing system must be strong enough to withstand soil movement.
3) To avoid the movement of surrounding soil, Pre-Load or Jacking and Strut systems should be used.
4) Bracing can also transfer weight to a permanent structure and does not cause permanent structure to be dangerous.
5) Sheet Pile should be able to be withdrawn again. (Re-use)
1.2 Calculation of lateral earth pressure Of the Sheet Pile With Brace Cut system consisting of pressure from the soil mass Taken through soil beads And the water pressure entering the Sheet Pile. Need to know the form of failure In order to make Model Simulation as close to reality as in the Sheet Pile With Brace Cut system, the design must calculate the total horizontal stress The occurrence of heave in the excavated area and the overall stability of the sheet pile system (Overall Stability). The potential catastrophe in this system is the occurrence of heave in the excavation area, especially in the project where the excavation is in the area. wide And the movement of soil hits the wall Sheet Pile With Brace Cut. Requires a stronger retaining wall system The Diagram model shows the earth pressure in Sheet Pile With Brace Cut. The most commonly used is the Diagram presented by Peck (1969) which is divided into equations to find Pressure in sand and soil pressure in Undrained Cohesion Ø = 0
2 Braced Cuts Design In designing Braced Cuts, each part in Braced Cuts is designed after the Lateral Eath Pressure. The details of each part are as follows
2.1 Strut design Strut It is a horizontal compression column which receives the bending moment with a vertical distance of not less than 2.75 meters and the load of the Strut will depend on the Slenderness Ratio L / R of the part to be built. Is a strut to calculate the reaction force acting on the strut from the sheet pile wall. Once the strut load is known, the cross-sectional size and length of the strut can be calculated by the design of the compression-compression component.
2.2 Sheet Pile Design
1) Designed by considering the maximum Bending Moment value of the sheet sheet wall / wall width 1.00 meters.
2) Bending Moment values. Consider using the maximum value per wall design.
3) Calculate Section Modulus by calculating the bending resistance parts.
4) The Sheet Pile's Allowable Flexural Stress can be searched for from a supplier or lessor of Sheet Pile.
2.3 Wale design
1) Wale is a continuous beam that has support at the position of the Strut. The force acting on the Wale Is the earth pressure passing through the wall of the sheet pile in the form of a linier or Distribution Load
2) Calculate Bending Moment
3) Calculate Section Modulus and follow the method for calculating bending strength parts. But should choose the cross-section of the same size as the Strut for ease of welding
3. Considerations for the Construction of Structural Retaining Wall Sheet Pile With BraceCut
1) The sheet pile must be away from the edge of the foundation with sufficient distance. For foundation installation and demolition of wood
2) The King Post supporting struts to support the weight taken from the strut must be of a specified length and vertical.
3) The strut and the wale must be straight so that the axial force can be transferred for the intended purpose.
4) The welding axis of the steel structure must be welded to achieve the designed welding length and size. Strictly come For the strength and safety of the structure
5) After the installation of the soil protection system is completed and the soil is dug in the digging hole, the movement of the retaining wall must be checked daily before construction. Until the construction of the underground part is completed To be used as information in determining the stability of the retaining wall to be safe or not
4. Retaining Wall Construction
Before proceeding with construction, all the details must be studied To understand clearly before working
Construction methods are as follows.
1) Must find information about whether the underground area has public utilities or not, such as electrical pipes, water pipes, if any, have to move out of the construction area first To prevent damage that will occur
2) Choose tools that are suitable for the job site, such as Sheet Pile. At present, the popular PC300, PC500 is equipped with a Vibro Hammer which is easy to move. And work to hammer and pull the steel sheet (Sheet Pile), not much work space compared to the conventional machinery that is a crawler crane (Crawer Crane) and should provide space for the transportation of soil to dig out from the well.
3) Laying the sheet pile in the general way (generally less than 1.00 -1.50 meters) as appropriate
4) Stitch the sheet pile along the line and hammer the sheet pile one by one to the desired level.
5) Install the Wale and Strut, place it in the specified direction, and connect at the connection point in the bracing section. In the middle of the digging hole, Kirin Jack must be installed for compression. Pre-load for compression in all directions of the retaining wall In the actual construction work, the pile foundation work is completed before the soil protection system work. Therefore, digging the soil to install the bracing system, both steel strand (Wale) and steel bracing (Strut) at each step, must dig the soil and cut the pile head down to layer one by one because the pile makes it impossible to dig the soil down.
5. Stability checking Of Pile Wall Stability
After installing the retaining wall structure, the materials and methods of installation must be strictly inspected at all stages of installation. After that, when digging the soil and working in the area inside the wall Retaining Wall Structure Will be in the condition of carrying weight both from the earth pressure trying to move towards Digging holes and vibrating from machinery or traffic of vehicles Or payload From Surcharge Load as well as from rainwater that will increase the weight pressed into the soil around the wall That will affect the movement together to cause deformation of the wall
From various factors mentioned Resulting in failure or destruction of the retaining wall structure Which will cause damage Both a great life and property Must have measures to control and monitor to prevent the occurrence of the incident by creating a plan to check the stability of the retaining wall. To keep an eye on the incident By checking as follows
6. Demolition of the retaining wall structure
After the construction of the underground structure was completed We have to demolish the temporary retaining wall structure. With the following steps
1) Filling the soil into the well, digging holes to the level of the bracing.
2) Demolish the bracing and round the steel.
3) Fill the soil or sand to the full level around the digging hole.
4) Removing the sheet pile, arranged in order by one by one
5) In the case of sheet pile embroidery at a very deep level, such as 10.00 meters or more, the soil movement should be taken into consideration One way to prevent the movement of soil is to compress the lime water. Down to the end of the sheet depth to replace the gap of the soil Cement slurry is a mixture of Cement and Bentonite by connecting the Tremie pipe and using Grout Pump to compress Cement Bentonite while withdrawing the slab so that the water overflows to the top. With the distance of sending pipes into the underground every 5.00 meters
6) Eject sheets one row at a time until completion
From the process of designing and constructing a retaining wall system It can be seen that it requires data from soil surveying. Designs from directly experienced people And construction supervision at all stages, from site preparation Alignment, piling, sheet pile, installation of structural components and compression of the pvc-load with Kirin Jack. Each step must be closely monitored. Including when digging the soil inside the wall Must check the strength and safety of all walls. When the demolition process Must have a plan and control to ensure that the plan is well implemented to prevent damage from soil movement.
Therefore, when chasing all steps from beginning to end of the underground wall work Which is a special structure Workers involved in every step must have expertise. And requires a lot of caution In operation Engineer Must follow And closely inspected To ensure quality in every process And highly secure.
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