Progress of Steel Sheet Piles in Foundation Pit Support Engineering
1.0 Research on the application of steel sheet pile in support engineering
In the support engineering field, steel sheet pile has been widely used, for it has a better performance in strength, safety and convenience than other methods. To be more specific, the steel sheet pile is lighter but has enough strength, and low space requirement is its another advantage. However, the use of steel sheet piles will also bring some other problems. For example, steel sheet pile in construction will lead to the deformation in the nearby area, as well as the loud noise. With the improper setting of steel sheet pile, the deformation will be more serious. Also, the use of steel sheet pile will be restricted in a deep foundation pit. After completing the construction, these steel sheet piles need to be pulled back. It will also affect the surrounding foundation, surrounding buildings and surface soil, and even cause ground cracks.
The joint of steel sheet pile is very easy to be broken. To solve this problem, workers have to ensure the stiffness of the joint should be equal to the stiffness of other parts during construction. Under this situation, the safety and stability of this support system can be guaranteed. With the development of foundation pit engineering, Lassen Steel Sheet Pile is generated to support the foundation pit when the simple supporting system cannot meet the requirements of construction safety. Since Lassen Steel Sheet Pile has good bending resistance, it has been applied in some foundation pit support projects, bringing a great reputation to this product.
In the soft soil area of China, steel sheet pile with a row of piles has been widely used in the foundation pit support engineering. However, there are some defects in the single-row pile support structure, such as low bending strength, poor bending ability and relatively large horizontal displacement at the top of the pile. It is very likely to occur bending deformation of the steel sheet piles in some foundation pits with poor geological conditions and rich water content. Because of these reasons, there will be a great limitation for the steel sheet pile support structure system with a single row of piles in the engineering which strictly requires the horizontal displacement.
In the view of these shortcomings of single row steel sheet pile supporting structure, the structure with double row steel sheet pile is generated to adopt the soft soil area. This double-row pile support system is an entirely new support structure system. It can effectively overcome some drawbacks of single-row steel sheet pile support system in the soil area. Also, the construction cost is unchanged, which has relatively high application value. In the single-row steel sheet pile supporting structure, the horizontal displacement of pile-top is large, but this displacement can be effectively reduced by the double-row pile supporting system. Moreover, a double row of piles can seal water and also work as the retaining wall.
As water and soil retaining structure, steel sheet pile cofferdam has been widely applied in the infrastructure construction in areas with low water levels. Also, most steel sheet piles work as the temporary support system, which does not require complex procedures. To meet the safety requirement, workers need to pay attention to prevent the lock from leaking during the process of steel sheet pile construction, ensuring there is no water in the foundation pile.
Before making an optimization plan, there is a need to take local geological conditions, soil parameters, underground water level and surrounding environment into full consideration. Currently, there are two kinds of steel sheet piles commonly used in road and bridge construction, H-bar steel sheet pile and Lassen Steel Sheet Pile. In general, H-bar steel sheet piles are used in combination with cement-soil mixed piles, which will exert the effect of sealing water. Lassen Steel Sheet Pile is a type of steel sheet with a lock, and continuous steel sheet pile support system is formed through interlocking.
We conducted monitoring and analysis on the force and deformation of the anchored steel sheet pile. We found that the horizontal displacement of the anchored sheet pile structure is the greatest at the top, and the force in the soil in front of the sheet pile is inversely proportional to the depth. As it is not easy to control its horizontal displacement,
anchored sheet pile structure is not the best choice.
We have also done a numerical analysis of finite element on steel sheet pile cofferdam. The calculation results of the force analysis show that the corner of the steel sheet pile is a fragile and dangerous force position. The connection and control of the corner steel sheet pile should be strengthened during the construction process. When we are considering the design of steel sheet pile cofferdam, it is difficult to determine the earth pressure under its working condition. It is suggested to calculate the static earth pressure during the design process, and it helps to ensure the safety of the designed steel sheet pile. It informs that the vulnerable spot should be well-controlled during the construction process to prevent the leakage of lock and some other problems. Then, the application of steel sheet piles will be guaranteed.
2.0 Research on the current situation of the steel sheet pile compound system
For projects with the poor geological condition and deep excavation, the single use of steel sheet pile as the support system is limited by some defects. We proposed to compound methods to cope with these problems by using soil nailed wall, steel sheet pile and internal support. Compared with the traditional pile row system with internal support, it has better performance in safety, construction period and project cost.
In soft soil area, to ensure the safety of the project, we apply this system with soil nailed wall, steel sheet pile and internal support. In this system, a steel sheet pile and other row pile support system is used at the bottom of the foundation pit, and soil nailing wall support system is used at the top of foundation pit. This method is an innovative application, which can combine the advantages of various supporting forms to the greatest extent.
We analyze the structure changes and force in the continuous wall and the compound steel sheet pile under different construction conditions. In the compound steel sheet pile plan, double row steel sheet pile structure is chosen, and the results show that this system is advantageous to the deformation control and stability control. It also has a better performance in lateral deformation than the continuous underground wall. Soil nailing wall and the combination of steel sheet piles and internal support display a considerable advantage. It does not only manifest the benefits of steel sheet pile but also effectively avert the drawbacks of steel sheet pile. It is a smart move to combine the strength of different methods in the foundation pit engineering in the future, ensuring the safety and stability of the project.