With the rapid development of the national economy, high-rise and super high-rise buildings, Luqiao, geological hazard control, water conservancy and hydropower projects are also showing a thriving prospect. Most of these projects involve the foundation pit engineering. The foundation pit is the surrounding environment in order to ensure the construction site is not damaged, the safety of the main underground structures and foundation pit construction in general rainfall, design and construction of foundation pit support, earth excavation and backfill, such as engineering and development, is a comprehensive and practical system engineering. It usually involves investigation, design, construction, monitoring and so on. In order to keep pace with the development of construction projects, as a basic and preliminary work for construction projects, foundation engineering must also be developed and perfected continuously.
2 pile wall retaining structures are mainly composed of four types, namely row type bored pile retaining structure, sheet pile retaining structure, cement retaining wall retaining structure and trough wall diaphragm wall structure. Different construction types, their construction methods and construction techniques are also different. They are limited to space. In this section, the construction technology and methods of the first two structural types are introduced in detail.
The 2.1 row pile retaining structure construction for retaining structure of pile in the construction, should meet the following requirements: (1) punching (drilling) hole filling pile bottom sediment thickness not more than 200mm, especially when used as a load-bearing structure; (2) a direction perpendicular to the axis of the pile pile and along the axis of the retaining structure deviation should be below 50mm, the verticality deviation of pile shall not exceed 0.5%; (3) beam before construction shall be clean float slurry supporting piles, reinforced pile top chisel exposed length should also be in the range of requirements; (4) in the reinforcing cage hoisting and laying the binding and uneven reinforcement, to ensure consistency of reinforced cage put direction and design direction, and a protective layer of steel to meet the requirements. (5) for the pile, the construction method of jumping should be adopted, and the construction of the bored pile should be carried out after 24 hours of concrete filling with adjacent pile concrete.
The construction of plate pile retaining structure of 2.2 plate pile retaining structure includes the structure of reinforced concrete slab pile and steel sheet pile structure. Among them, reinforced concrete sheet pile is usually made up of precast reinforced concrete sheet pile. If we consider reusing, we usually use precast prestressed concrete slab pile. The shape of the cross section of the pile can be used to determine the heating area by the size of the I-shaped and T - shaped air pressure stations. It can only run in winter, other seasons need to switch to other heat recovery systems, resulting in complex system and high initial investment and maintenance costs. In the design phase of the system, a detailed technical and economic comparison needs to be done.
3 other energy saving measures, besides the above two main air compressor stations, we can also consider the following aspects to reduce the energy consumption of the air compressor station as far as possible when designing the air compressor station.
The air compressor station ventilation should be good. The station when the indoor temperature is too high pressure, easy to cause the deterioration of the operating conditions, resulting in air compressor shutdown frequently, resulting in increased power consumption of equipment life decreases. In order to avoid this situation, it is necessary to do a good job in air pressure station indoor ventilation design. The application of air compressor air duct is discharged to the outside, and according to the equipment cooling air shuttle station is the natural ventilation area is adequate, whether to need to add mechanical ventilation.
By using blast heating or compression heat regenerative adsorption dryer. The common compressed air dryer is divided into two kinds, which are frozen and adsorbed according to the working principle. According to the relevant test data, the proportion of dryer equivalent to the power consumption of the compressor, refrigeration power consumption is about 35%, the heating regeneration adsorption of about 810%, no heat, tepefaction regeneration regenerative design selection of 18%. dryer, can use refrigeration dryer, do not use the adsorption dryer; using adsorption dryer, or rectangular should do that is generally rectangular. The steel sheet pile support structure usually uses Z shape or U shaped section shape. When the foundation pit is deeper and the load is larger, H steel, steel pipe and other composite section steel can also be used. When the foundation pit is shallow, the positive and reverse channel steel can also be used.
Steel sheet piles usually sink into the soil individually or in combination with vibration, static pressure or hammering. Before sinking the pile, the steel sheet pile should be numbered and checked by block. The size deviation of the steel sheet pile should be within the requirement of the error range. For example, the length of the deflection should be less than 1%, width deviation should be between -5mm and 10mm, pile end surface roughness is less than 3mm, the height of cross section of deviation is in the range of -3mm to 3mm. when the length of the plate is not enough, in accordance with the principle of equal strength with the same type of pile pile, advanced for butt welding, after welding reinforcing plate.
The steel sheet pile should not be entered separately, and should be broken into. For the semi closed or closed retaining structure, should be pre calculated number of their needs, should ensure that the pile verticality of steel sheet pile into the first block, and the ratio of conditions after long 2m-3m. if steel sheet pile sinking allowed in piling before the best on the ground along the retaining structure position preset guide frame. Usually, the steel sheet pile is used as a temporary retaining structure for the foundation pit, and it can be removed once the underground main body is completed.
However, during the process of steel sheet pile removal, the settlement and lateral movement of the surrounding soil are easy to cause, resulting in the safety of the surrounding environment can not be guaranteed. In order to avoid this phenomenon, two measures are usually taken. First, when the steel sheet pile is lifted, insert plastic bags or cloth bags directly into the pile holes.