High-pressure-bearing square deep foundation pit applicable to water-rich sand gravel stratum and excavation method of high-pressure-bearing square deep foundation pit

Abstract

The invention discloses a high-pressure-bearing square deep foundation pit applicable to a water-rich sand gravel stratum and an excavation method of the high-pressure-bearing square deep foundation pit. The foundation pit comprises a dewatering excavation area on the upper portion of the foundation pit and a water entrainment excavation area on the lower portion of the foundation pit. A dewatering well is arranged in the dewatering excavation area. A pit external groove sidewall reinforcing device and a pit internal groove sidewall reinforcing device are arranged inside and outside a diaphragm wall of the whole dewatering excavation area correspondingly. The whole dewatering excavation area is further provided with at least two reinforced concrete waist supporting beams and reinforced concrete supports. The water entrainment excavation area is provided with muddy water sucking equipment and filtered water recharge equipment, and multiple stages of settling ponds are arranged outside the foundation pit correspondingly. The stepped excavation method that the reinforced concrete supports are arranged and unwatering excavation is adopted on the upper portion and water entrainment excavation is adopted on the lower portion is adopted. The construction quality of the diaphragm wall is effectively ensured, the probability that water seepage, water burst and sand burst appear in the diaphragm wall is lowered, the excavation safety of the foundation pit is ensured, the excavation schedule of the foundation pit is accelerated, and the excavation cost of the foundation pit is reduced.

Description

technical field [0001] The invention belongs to the field of square deep foundation pit excavation in the fields of urban rail transit construction and bridge construction. Background technique [0002] In the field of urban rail transit construction and the excavation of square deep foundation pits in the field of bridge construction, since the foundation pit is located in a highly permeable water-rich sand layer, the foundation pit needs to bear huge water pressure and earth pressure during the excavation process. The deformation of the square foundation pit is large after being stressed, and the self-stability is poor. [0003] 1. The excavation of square deep foundation pits in this type of water-rich sand egg layer has the following characteristics: [0004] 1) The deep foundation pit is located in the sand egg layer, and the formation permeability coefficient is very large. [0005] 2) The excavation depth of the foundation pit is deep, and some excavation depths exc...

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Problems solved by technology

[0005] 2) The excavation depth of the foundation pit is deep, and some excavation depths exceed 40 meters. The earth pressure generated by the excavation is large, and the deformation of the foundation pit is large during the excavation process. It is difficult to use precipitation to dry and dig to the bottom

[0006] 3) The enclosure structure is a square structure, and the structure itself has relatively poor resistance to earth pressure

[0007] 4) Excavation is difficult, and the safety risk of excavation is very high. If the excavation method is improper, it may easily cause water and sand gushing in the enclosure structure, and even cause the foundation pit to collapse.

[0012] 3. Limitations of the traditional method of "excavating with water" for high pressure-bearing square deep foundation pits in water-rich sand layers:

[0013] 1) During the excavation process, the deformation of the ground connection wall is large and the safety risk is high: since the concrete support cannot be constructed during the excavation process with water, and the steel support cannot be installed, there is only one concrete support on the top of the entire foundation pit. When the excavation of the foundation pit is deep When the water pressure in the foundation pit cannot balance the earth pressure outside the foundation pit, the ground connection wall needs to bear a large earth pressure, resulting in excessive deformation of the foundation pit, and even cracking and collapse of the ground connection wall

[0014] 2) The excavation depth is greatly affected by the groundwater level and the stiffness of the ground connection wall, and the excavation depth is relatively small: when the groundwater level is high, the water head difference provided by irrigation in the foundation pit is very limited, and it must rely on the ground connection wall itself. Resist the unbalanced earth pressure produced by part of the excavation. Since the ground connection wall has only one concrete support, and the foundation pit enclosure structure is square, the ability of the ground connection wall itself to resist soil pressure is very limited, which greatly restricts the foundation. pit excavation depth

[0015] 3) The ground connection wall is thicker, the project volume is large, and the total cost is high

Since all excavations with water are adopted, the ground connection wall cannot be provided with concrete supports or steel supports in the excavation area, resulting in poor stress on the ground connection wall. When the excavation depth is deep, the ground connection wall must be greatly increased. Thickness, in order to ensure the safety of the foundation pit, this will increase the engineering quantity of the ground connection wall, thereby increasing the construction cost

[0016] 4) Water gushing and sand gushing occurred during the pumping process of the ground connection wall. It is difficult to plug the leakage and takes a long time, which seriously affects the construction progress: during the excavation process, the ground connection wall is easily deformed and cracked, so that the originally intact and impermeable ground connection During the pumping process of the foundation pit, water seepage, water gushing or sand gushing occurred on the wall, which brought a greater safety risk to the later pumping process

In addition, whether it is the construction quality of the ground connection wall itself or the cracks generated during the excavation process, once water and sand gushing in the ground connection wall are caused during the pumping process, it will be very difficult to deal with, and minor water seepage needs to be carried out on the water surface Leakage plugging, larger ones need to be refilled in the pit and then grouted outside the pit. It is no longer possible to simply place sandbags in the foundation pit for back pressure. This will cause a long processing time and have a great impact on the construction progress

[0017] 5) Underwater excavation is difficult, low in efficiency, slow in excavation progress and high in excavation cost

[0018] 6) The reinforcement of the groove wall is short, which reduces the construction quality of the ground connection wall

The reinforcement depth of the groove wall constructed by this method is relatively short, because the reinforcement of the groove wall is difficult to excavate underwater, so the groove wall is easy to collapse during the construction of the ground connection wall, which reduces the construction quality of the ground connection wall and increases the probability of water seepage in the ground connection wall

[0019] 7) In the process of pumping water, it is necessary to construct waist beams above the water surface and install steel supports. The work on the water is difficult, the construction risk is high, and the efficiency is low

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