Automatic dewatering device and method for large planar shallow foundation pit with weakly permeable interlayer

Abstract

The application discloses a kind of weak water-permeable interlayer large plane shallow foundation pit automatic drainage device, comprising: drainage ditch, it includes annular drainage ditch and straight line drainage ditch, annular drainage ditch is arranged around the unexcavated area, sump, it is set at annular drainage ditch and straight line drainage ditch intersection;Water seepage blind drain is composed of steel wire net, steel reinforcement cage and broken stone;Steel reinforcement cage is placed in sump, submersible pump is placed in the bottom of steel reinforcement cage, float ball switch water level controller is connected submersible pump, start-stop is controlled, to pump out the water seepage in sump, through the grid layout of annular drainage ditch, straight line drainage ditch combined sump, again combined submersible pump and float ball switch water level controller, water seepage can be realized quickly gathering and discharging, drainage efficiency is improved by more than 40%, especially suitable for weak water-permeable interlayer geological conditions of large plane shallow foundation pit.

Description

Technical Field

[0001] This invention relates to the field of self-drainage for foundation pits. More specifically, this invention relates to an automatic dewatering device and method for shallow foundation pits with a large planar surface containing a weakly permeable interlayer. Background Technology

[0002] During construction, structures typically transfer the load and weight above ground to the foundation below ground. The foundation then transfers the load and weight to the bearing stratum, ensuring structural stability and safety. During foundation pit construction, if the groundwater level is higher than the excavation bottom, groundwater will continuously seep into the pit, leading to slope instability, quicksand, pit bottom heave, piping, and a decrease in the bearing capacity of the foundation. To ensure construction can proceed under dry conditions, dewatering is necessary to maintain a certain distance between the highest water level in the construction area and the bottom of the pit. Common methods include open ditch dewatering with sump pits, lightweight wellpoint dewatering, jet dewatering, electro-osmotic wellpoint dewatering, and deep wellpoint dewatering.

[0003] When the excavation depth of the foundation pit is shallow but the soil layer contains a weakly permeable layer or an impermeable layer, if dewatering is not carried out, there will be water-covered work, which may lead to unstable slopes that are prone to collapse and insufficient bearing capacity of the foundation, posing safety risks and quality hazards.

[0004] The conventional approach is as follows: (1) Wellpoint dewatering is adopted, and a certain number of dewatering wells are set up around the foundation pit according to the actual situation. (2) Drainage ditches and water collection pits of a certain depth are excavated, and submersible pumps are used for open drainage dewatering.

[0005] The conventional approach has the following shortcomings: (1) Well point dewatering costs are high and the well drilling cycle is relatively long. The construction cycle of shallow foundation pits is relatively short, which is relatively unreasonable from an economic point of view. (2) When excavating drainage ditches and sump pits to a certain depth, if the soil layer contains a weakly permeable layer or an impermeable layer, the water seepage rate of the soil layer is small, and the water accumulation rate is less than the drainage rate, so continuous dewatering is not possible. It is necessary to arrange a certain number of workers to patrol the site. If the pipeline in the middle sump pit is too long and there is no suitable drainage point nearby, it is necessary to drain the water to a sump pit closer to the edge of the foundation pit for relay drainage. The labor cost is high and there is a situation where drainage is not timely. If the drainage ditch and sump pit are excavated too deep, if they contain unstable soil such as sand layers, there are problems such as easy collapse. Summary of the Invention

[0006] To achieve these objectives and other advantages according to the invention, a preferred embodiment of the invention provides an automatic dewatering device for a large, shallow foundation pit with a weakly permeable interlayer, used for dewatering the foundation pit, which includes a central undisturbed area and a surrounding excavated area. The automatic dewatering device includes:

[0007] The drainage ditch includes circular drainage ditches and straight drainage ditches. Multiple circular drainage ditches are arranged around the unexcavated area. Adjacent circular drainage ditches are spaced a certain distance apart and are connected by straight drainage ditches.

[0008] A sump pit is located at the intersection of a circular drainage ditch and a straight drainage ditch.

[0009] A seepage blind ditch is composed of wire mesh, a steel reinforcement frame and gravel. The wire mesh has a hollow structure, and the gravel is filled inside the wire mesh. The steel reinforcement frame is inserted inside the wire mesh. The seepage blind ditch is placed in a drainage ditch.

[0010] A steel cage is placed inside a water-collecting pit. A submersible pump is placed at the bottom of the steel cage. A float switch water level controller is connected to the submersible pump to control its start and stop, so as to pump out the seepage water in the water-collecting pit.

[0011] Preferably, the reinforcing steel cage is welded together from four reinforcing steel bars arranged along the length of the blind drain, six reinforcing steel bars in the width direction, and six reinforcing steel bars in the depth direction.

[0012] Preferably, a fine-mesh mesh is wrapped and fixed around the outside of the reinforcing cage and the submersible pump for filtering sand and gravel.

[0013] Preferably, the bottom of the sump is lower than the bottom of the drainage ditch.

[0014] Preferably, the annular drainage ditch adopts a gradient slope structure, forming a slope of 3-5‰ from the side away from the unexcavated area to the side closer to the unexcavated area, and the slope directions of adjacent annular drainage ditches are opposite, forming an alternating confluence path.

[0015] Preferably, an air pressure balancing pipe is installed in the water accumulation pit. The air pressure balancing pipe is vertically fixed to the side wall of the steel cage, with its upper end above the ground and equipped with an adjustable pressure exhaust valve, and its lower end extending 20cm above the bottom of the pit. Honeycomb-shaped ventilation holes are opened in the pipe wall.

[0016] Preferably, the bottom of the water accumulation pit is covered with an elastic permeable cushion layer, which is formed by mixing and compacting rubber particles and graded crushed stone in a volume ratio of 1:3. An annular air guide pipe is pre-embedded in the elastic permeable cushion layer and connected to the air pressure balance pipe. The diameter d of the annular air guide pipe and the diameter D of the air pressure balance pipe satisfy d = 0.6D.

[0017] Preferably, the operation method of the pressure balancing pipe is as follows:

[0018] Real-time monitoring of the air pressure P in the sump and the cumulative running time (T) of the submersible pump.

[0019] The exhaust valve adjustment is initiated when either of the following conditions is met: a) P < -1.5 kPa and T > 2 h, or b) P < -2.0 kPa; wherein, the exhaust valve opening is adjusted according to the formula: θ = 15° × |P| / Pmax +5°, where P max This is the maximum permissible negative pressure of the air pressure balancer.

[0020] Preferably, the construction method of the elastic permeable cushion layer 9-1 is dynamically linked with the air pressure balance system, including the following steps:

[0021] A. First, by adjusting the opening of the exhaust valve, an initial negative pressure of P0 = -1.0 kPa is formed and maintained in the water accumulation pit; then, the elastic permeable cushion layer is laid, and the air pressure fluctuation is monitored in real time during the laying process, with an allowable deviation range of ±0.2 kPa.

[0022] B. Lay a ring-shaped air duct. After the air duct network is laid, conduct a combined negative pressure and flow rate test.

[0023] a) Adjust the opening of the air vent valve to θ = 30° and record the permeability coefficient K of the subbase;

[0024] b) When K < 1 × 10 -3 When the speed reaches cm / s, the secondary vibration compaction of the subbase is triggered until the permeability coefficient K of the subbase is ≥5×10-3cm / s.

[0025] On the other hand, a preferred embodiment of the present invention provides a dewatering method for a large-scale shallow foundation pit containing a weakly permeable interlayer, comprising the following steps:

[0026] S1. Process and manufacture seepage blind drains and steel cages, and vertically install air pressure balance pipes on the side walls of the steel cages;

[0027] S2. Install the submersible pump and float switch level controller inside the steel cage and wrap it with dense mesh netting;

[0028] S3. A ring-shaped drainage ditch is excavated around the unexcavated area of ​​the foundation pit. There are multiple ring-shaped drainage ditches. There is a certain distance between two adjacent ring-shaped drainage ditches, and the two are connected by an excavated straight drainage ditch. The seepage blind ditch is placed in the drainage ditch.

[0029] S4. Excavate a water collection pit at the intersection of the circular drainage ditch and the straight drainage ditch, ensuring that the bottom of the water collection pit is lower than the bottom of the drainage ditch. Place the steel cage in the water collection pit and lay an elastic permeable pad at the bottom of the water collection pit.

[0030] S5. After all seepage blind drains are installed and all drainage ditches are connected to the water collection pit, the area around and top of the seepage blind drains can be backfilled.

[0031] S6. After the water level in the sump reaches the set drainage level, the submersible pump will be automatically controlled by the float switch water level controller to drain the water until the water level reaches the set drainage level.

[0032] S7. After the drainage is completed, the seepage blind ditch and steel cage are lifted out for reuse.

[0033] The present invention has at least the following beneficial effects:

[0034] This invention is simple, reliable, and easy to operate. It not only ensures the effectiveness of precipitation but also reduces the risk of collapse of ditches and puddles, thus improving construction efficiency.

[0035] ① High safety. The use of gabion mesh blind drains and submersible pumps with steel cages reduces the safety risk of collapse of side ditches and water pits. After the gabion mesh is placed in the drainage ditch and the submersible pump with steel cage is placed in the water pit, backfilling can be carried out around and above the gabion mesh and around the steel cage.

[0036] ② It is economical. The equipment mainly uses steel bars, protective mesh netting, galvanized steel wire, gravel, submersible pumps, float switches and water level controllers available on the construction site. The materials are widely available, and the equipment processing cost is low.

[0037] ③ Highly practical. The device allows for the setting of the length and depth of gabion-type blind drains based on the water seepage conditions of the foundation pit soil at the construction site. The length of the steel cage to be inserted into the submersible pump can be customized according to the site conditions, and it can be reused multiple times.

[0038] Other advantages, objectives and features of the present invention will be apparent in part from the following description, and in part from the understanding of those skilled in the art through study and practice of the invention. Attached Figure Description

[0039] Figure 1 This is a distribution diagram of the dewatering and drainage devices during the excavation of the foundation pit in this invention;

[0040] Figure 2 This is a schematic diagram of the seepage blind ditch in this invention.

[0041] Figure 3 This is a schematic diagram of the steel cage structure in this invention.

[0042] Figure 4 This is a schematic diagram of the structure of the elastic permeable pad in this invention. Detailed Implementation

[0043] The present invention will now be described in further detail with reference to the accompanying drawings, so that those skilled in the art can implement it based on the description.

[0044] The following description is intended to disclose the present invention and enable those skilled in the art to implement it. The preferred embodiments described below are merely examples, and other obvious modifications will occur to those skilled in the art. The basic principles of the invention defined in the following description can be applied to other embodiments, modifications, improvements, equivalents, and other technical solutions that do not depart from the spirit and scope of the invention.

[0045] Those skilled in the art should understand that, in the disclosure of this invention, the terms "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the above terms should not be construed as limiting this invention.

[0046] It is understood that the term "a" should be understood as "at least one" or "one or more", that is, in one embodiment, the number of an element can be one, while in another embodiment, the number of the element can be multiple, and the term "a" should not be understood as a limitation on the number.

[0047] like Figure 1-4 As shown, a preferred embodiment of the present invention provides an automatic dewatering device for a large, shallow foundation pit containing a weakly permeable interlayer, used for dewatering the foundation pit. The foundation pit includes an unexcavated area 3-1 at the center and an excavated area 3-2 around it. The automatic dewatering device includes:

[0048] Drainage ditch 4 includes circular drainage ditches and straight drainage ditches. Multiple circular drainage ditches are arranged around the unexcavated area. Adjacent circular drainage ditches are spaced a certain distance apart and are connected by straight drainage ditches.

[0049] A water collection pit 5 is located at the intersection of a circular drainage ditch and a straight drainage ditch, with the bottom of the drainage ditch lower than the required level to ensure that water flows into the water collection pit;

[0050] The seepage blind ditch is composed of wire mesh 1-1, steel reinforcement frame 1-2 and crushed stone 1-3. The wire mesh has a hollow structure. The crushed stone 1-3 is filled inside the wire mesh 1-1. The steel reinforcement frame 1-2 is inserted into the wire mesh. The seepage blind ditch is placed in the drainage ditch.

[0051] The steel cage 2-1 is placed inside the sump. The submersible pump 2-2 is placed at the bottom of the steel cage 2-1. The float switch water level controller 2-3 is connected to the submersible pump to control its start and stop, so as to pump out the seepage water in the sump.

[0052] In the above technical solution, the annular drainage ditches are arranged concentrically around the unexcavated area of ​​the foundation pit, and the straight drainage ditches connect adjacent annular drainage ditches radially to ensure that water flows quickly into the sump. The wire mesh 1-1 of the seepage blind ditch is woven from galvanized steel wire with a mesh size of 10mm×10mm. The reinforcing steel frame 1-2 is welded from 8mm diameter threaded steel. The crushed stone 1-3 has a particle size of 20-40mm and a filling density of 1.8t / m³. 3 The steel cage 2-1 is a frame structure welded from steel bars with a diameter of 12mm. The submersible pump 2-2 is fixed inside. The float switch water level controller 2-3 is linked to the submersible pump 2-2 through a linkage mechanism. When the water level reaches the set height, drainage is automatically started.

[0053] This device achieves efficient water collection and drainage efficiency by combining ring-shaped and straight drainage ditches, increasing drainage efficiency by over 40%. The three-layer structure of the seepage blind ditch (wire mesh + steel reinforcement frame + crushed stone) enables a permeability rate of 2.5 L / (min·m). 2 The compressive strength is ≥15kPa. The linkage control error between the float switch and the submersible pump is small, significantly reducing the frequency of manual intervention.

[0054] In another technical solution, the steel reinforcement cage 1-2 is welded together from 4 steel bars arranged along the length of the blind drain, 6 steel bars in the width direction, and 6 steel bars in the depth direction.

[0055] The four reinforcing bars along the length are made of 8mm diameter threaded steel; the six reinforcing bars along the width are made of 6mm diameter round steel; and the six reinforcing bars along the depth are made of 6mm diameter round steel. All intersections of the reinforcing bars are welded using arc welding, with a weld height ≥3mm. The overall dimensions of the reinforcing bar skeleton 1-2 match those of the wire mesh 1-1 to ensure uniform filling of the crushed stone 1-3.

[0056] This frame structure increases the bending stiffness of the blind drain to 320 N·m. 2 Under a backfill soil pressure of 10 kPa, the deformation is <2 mm, and the uniformity deviation of the pore distribution in the crushed stone layer is <8%.

[0057] Another technical solution is to use a fine mesh 2-4, which is wrapped and fixed to the outside of the steel cage and submersible pump for filtering sand and gravel.

[0058] Another technical solution is to have the bottom of the drainage ditch lower than the bottom of the drainage ditch.

[0059] Another technical solution is that the annular drainage ditch adopts a gradient slope structure, forming a slope of 3-5‰ from the side away from the unexcavated area to the side closer to the unexcavated area, and the slope directions of adjacent annular drainage ditches are opposite, forming an alternating confluence path.

[0060] The alternating slope design creates eddies in the water flow, increasing the sedimentation efficiency of suspended particles by 60% and reducing the turbidity of the drainage.

[0061] Another technical solution is to install an air pressure balance pipe 8 in the water accumulation pit. The air pressure balance pipe is vertically fixed to the side wall of the steel cage, with the upper end above the ground and equipped with an adjustable pressure exhaust valve, and the lower end extending to 20cm above the bottom of the pit. The pipe wall is provided with honeycomb-shaped ventilation holes.

[0062] Through the linkage control of the air pressure balance pipe 8 and the exhaust valve, the negative pressure in the sump is always maintained within a safe range (below -3.0 kPa), preventing the weakly permeable interlayer from collapsing due to excessive negative pressure. The honeycomb-shaped vent holes increase the air pressure balance speed to stabilize a 2 kPa pressure difference within 10 seconds, which is 3 times more efficient than traditional pressure relief methods.

[0063] Another technical solution is that an elastic permeable pad 9-1 is laid at the bottom of the water accumulation pit. It is formed by mixing and compacting rubber particles and graded crushed stone in a volume ratio of 1:3. An annular air guide pipe 9-2 is pre-embedded in the elastic permeable pad and connected to the air pressure balance pipe 8. The diameter d of the annular air guide pipe 9-2 and the diameter D of the air pressure balance pipe 8 satisfy d = 0.6D.

[0064] The pre-embedded annular air guide pipe 9-2 is connected to the air pressure balance pipe 8, which optimizes the efficiency of the two-phase flow of air and water and increases the drainage speed by 20%. The air pressure balance pipe, the air vent valve and the elastic permeable pad (9-1) work together to prevent the pad from being compressed and deformed under negative pressure conditions, ensuring long-term permeability.

[0065] Another technical solution involves the following operation method for the pressure balancing pipe:

[0066] Real-time monitoring of the air pressure P in the sump and the cumulative running time (T) of submersible pump 2-2.

[0067] The exhaust valve adjustment is initiated when either of the following conditions is met: a) P < -1.5 kPa and T > 2 h, or b) P < -2.0 kPa; wherein, the exhaust valve opening is adjusted according to the formula: θ = 15° × |P| / Pmax + 5°, where P max This is the maximum permissible negative pressure of the air pressure balancer.

[0068] In the above technical solution, based on the dual-parameter control of air pressure (P) and submersible pump running time, the exhaust valve opening adjustment error is <0.5°, and the air pressure fluctuation amplitude is controlled within ±0.3kPa.

[0069] Another technical solution involves a construction method for the elastic permeable cushion layer 9-1 that is dynamically linked to the air pressure balance system, including the following steps:

[0070] A. First, by adjusting the opening of the exhaust valve, an initial negative pressure of P0 = -1.0 kPa is formed and maintained in the water accumulation pit; then, the elastic permeable cushion layer is laid, and the air pressure fluctuation is monitored in real time during the laying process, with an allowable deviation range of ±0.2 kPa.

[0071] B. Lay the ring-shaped air duct 9-2. After the air duct network is laid, conduct a combined negative pressure and flow rate test:

[0072] a) Adjust the opening of the air vent valve to θ = 30° and record the permeability coefficient K of the subbase;

[0073] b) When K < 1 × 10 -3 When the speed reaches cm / s, the secondary vibration compaction of the subbase is triggered until the permeability coefficient K of the subbase is ≥5×10-3cm / s.

[0074] In the above technical solution, an initial negative pressure (P0 = -1.0 kPa) is applied during the laying of the subbase to prevent blockage of permeable channels during the compaction of the backfill soil. By laying the subbase under initial negative pressure (P0 = -1.0 kPa), the permeability coefficient after secondary vibration compaction achieves the required rate (K ≥ 5 × 10⁻³). cm / s) greatly improved.

[0075] Another technical solution provides a dewatering method for an automatic dewatering device for large-scale shallow foundation pits containing a weakly permeable interlayer, characterized by comprising the following steps:

[0076] S1. Process and manufacture seepage blind drains and steel cages 2-1, and vertically install air pressure balance pipes on the side walls of the steel cages;

[0077] S2. Install the submersible pump 2-2 and the float switch water level controller 2-3 inside the steel cage and wrap it with dense mesh netting 2-4;

[0078] S3. A ring-shaped drainage ditch is excavated around the unexcavated area of ​​the foundation pit. There are multiple ring-shaped drainage ditches. There is a certain distance between two adjacent ring-shaped drainage ditches, and the two are connected by an excavated straight drainage ditch. The seepage blind ditch is placed in the drainage ditch.

[0079] S4. Excavate a water collection pit at the intersection of the ring drainage ditch and the straight drainage ditch, ensuring that the bottom of the water collection pit is lower than the bottom of the drainage ditch. Place the steel cage in the water collection pit and lay an elastic permeable pad 9-1 at the bottom of the water collection pit.

[0080] S5. After all seepage blind drains are installed and all drainage ditches are connected to the water collection pit, the area around and top of the seepage blind drains can be backfilled.

[0081] S6. After the water level in the sump reaches the set drainage level, the submersible pump will be automatically controlled by the float switch water level controller to drain the water until the water level reaches the set drainage level.

[0082] S7. After the drainage is completed, the seepage blind ditch and steel cage are lifted out for reuse.

[0083] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and illustrations shown and described herein.

Claims

1. An automatic dewatering device for a shallow, large-scale foundation pit containing a weakly permeable interlayer, used for dewatering the foundation pit, which includes an unexcavated area at the center and an excavated area around it, characterized in that... Automatic drainage devices include: The drainage ditch includes circular drainage ditches and straight drainage ditches. Multiple circular drainage ditches are arranged around the unexcavated area. Adjacent circular drainage ditches are spaced a certain distance apart and are connected by straight drainage ditches. A sump pit is located at the intersection of a circular drainage ditch and a straight drainage ditch. A seepage blind ditch is composed of wire mesh, a steel reinforcement frame and gravel. The wire mesh has a hollow structure, and the gravel is filled inside the wire mesh. The steel reinforcement frame is inserted inside the wire mesh. The seepage blind ditch is placed in a drainage ditch. A steel cage is placed inside a water-filled pit. A submersible pump is placed at the bottom of the steel cage. A float switch water level controller is connected to the submersible pump to control its start and stop, so as to pump out the seepage water in the water-filled pit. An air pressure balance pipe is installed in the water accumulation pit. The air pressure balance pipe is vertically fixed to the side wall of the steel cage. The upper end is above the ground and is equipped with an adjustable pressure exhaust valve. The lower end extends to 20cm above the bottom of the pit. Honeycomb-shaped ventilation holes are opened in the pipe wall. Dense mesh netting is wrapped and fixed to the outside of the steel cage and submersible pump to filter sand and gravel.

2. The automatic dewatering device for shallow foundation pits with weakly permeable interlayers according to claim 1, characterized in that, The steel reinforcement cage is welded together from four steel bars arranged along the length of the blind drain, six steel bars in the width direction, and six steel bars in the depth direction.

3. The automatic dewatering device for shallow foundation pits with weakly permeable interlayers according to claim 1, characterized in that, The bottom of the puddles is lower than the bottom of the drainage ditch.

4. The automatic dewatering device for shallow foundation pits with weakly permeable interlayers according to claim 1, characterized in that, The annular drainage ditch adopts a gradient slope structure, forming a slope of 3-5‰ from the side away from the unexcavated area to the side closer to the unexcavated area, and the slope directions of adjacent annular drainage ditches are opposite, forming an alternating confluence path.

5. The automatic dewatering device for a shallow foundation pit with a weakly permeable interlayer as described in claim 1, characterized in that, The bottom of the sump is covered with an elastic permeable cushion layer, which is formed by mixing and compacting rubber particles and graded crushed stone in a volume ratio of 1:

3. An annular air guide pipe is pre-embedded in the elastic permeable cushion layer and connected to the air pressure balance pipe. The diameter d of the annular air guide pipe and the diameter D of the air pressure balance pipe satisfy d=0.6D.

6. A dewatering method based on the automatic dewatering device for large-scale shallow foundation pits containing a weakly permeable interlayer as described in any one of claims 1-5, characterized in that, Includes the following steps: S1. Process and manufacture seepage blind drains and steel cages, and vertically install air pressure balance pipes on the side walls of the steel cages; S2. Install the submersible pump and float switch level controller inside the steel cage and wrap it with dense mesh netting; S3. A ring-shaped drainage ditch is excavated around the unexcavated area of ​​the foundation pit. There are multiple ring-shaped drainage ditches. There is a certain distance between two adjacent ring-shaped drainage ditches, and the two are connected by an excavated straight drainage ditch. The seepage blind ditch is placed in the drainage ditch. S4. Excavate a water collection pit at the intersection of the ring drainage ditch and the straight drainage ditch, place the steel cage in the water collection pit, and lay an elastic permeable cushion layer at the bottom of the water collection pit. S5. After all seepage blind drains are installed and all drainage ditches are connected to the water collection pit, backfill the area around and top of the seepage blind drains. S6. After the water level in the sump reaches the set drainage level, the submersible pump will be automatically controlled by the float switch water level controller to drain the water until the water level drops to the set drainage level. S7. After the drainage is completed, the seepage blind ditch and steel cage are lifted out for reuse.

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