Foundation pit construction method and system above existing underground structure

Abstract

The present application relates to the field of building construction technology, and provides a method and system for constructing a foundation pit above an existing underground structure, the method comprising the following steps: constructing a first row of engineering piles and a second row of engineering piles; excavating the soil in the target area according to a preset excavation sequence, so that the soil in the target area is excavated one by one to the bottom surface of the target foundation pit; placing a flexible package on the bottom surface of the first excavated target foundation pit, injecting a fluid medium into the flexible package, so that the ballast surface and pressure of the flexible package on the bottom surface of the target foundation pit increase synchronously with the excavation of the soil in the target area one by one; placing a back pressure block on the flexible package to discharge the fluid medium in the flexible package; connecting the back pressure block to the first row of engineering piles and the second row of engineering piles to form a portal frame. The replacement of ballast and the excavation of soil are synchronized in the present invention, thereby realizing micro-disturbance construction, speeding up the foundation pit construction speed, and ensuring excavation efficiency.

Description

Technical Field

[0001] The present invention belongs to the technical field of building construction, and in particular relates to a foundation pit construction method and system above an existing underground structure. Background Art

[0002] With the rapid economic growth and expansion of urban planning in my country, the demand for high-capacity, high-quality transportation has rapidly increased. Urban rail transit, as a key solution to urban public transportation issues, has been comprehensively developed in urban construction. The development of urban rail transit has enabled metro transportation to cover densely populated areas such as major commercial and economic zones.

[0003] With the development of rail transit, the development of high-rise buildings and underground shopping malls near subway stations will accelerate. Large building foundation pits are often located adjacent to subway stations or directly straddle existing underground structures, including underground tunnels, underground subways, and underground shopping malls. For example, the Zhuhai Cross Gate open-cut tunnel crosses the existing Zhuhai-Macao Intercity Railway with a perpendicular length of 40 meters; Shenzhen Metro Line 2 passes diagonally below the Shenzhou Digital foundation pit with a length of 136 meters. The unloading thickness of the foundation pit exceeds 50% of the original overburden thickness above the subway. The unloading of the upper foundation pit will inevitably affect the deformation of the underlying subway tunnel. Research on deep foundation pit construction technology adjacent to the subway under the foundation will ensure both the safety of subway operations and the normal progress of deep foundation pit construction. With land resources in downtown areas becoming increasingly scarce and underground space increasingly valued, the application prospects of this technology are very broad.

[0004] Currently, the foundation pits above existing operating subways are reinforced with grouting on both sides and above the tunnel, dewatering wells, heap loading and weighting, and layered excavation. Existing tunnel grouting, dewatering, and heap loading and weighting methods are difficult to inject when encountering soft strata such as silt and clay. The grouting diffusion path cannot be predicted, which can easily cause environmental pollution. Moreover, heap loading and weighting are only carried out after the tunnel has been detected to be floating, which has a lag effect. During skip excavation and layered excavation, work must be stopped for one day for observation after each layer is excavated, which reduces construction efficiency and is unpredictable. It requires continuous feedback and adjustment based on the amount of tunnel floating. Therefore, there is a need for a method and system that can dynamically and effectively control the floating of existing underground structures (such as subway tunnels) in line with the excavation progress, ensuring rapid excavation of the foundation pit without disturbing the underground structure. Summary of the Invention

[0005] In response to the above-mentioned problems in the prior art, the present invention proposes a foundation pit construction method and system above an existing underground structure, which utilizes the pressure of the fluid and combines its flow characteristics to dynamically control the buoyancy of the underground structure.

[0006] In the first aspect, the present invention proposes a method for constructing a foundation pit above an existing underground structure, comprising the following steps: constructing a first row of engineering piles and a second row of engineering piles on opposite sides of the existing underground structure; excavating the soil in the target area according to a preset excavation sequence, so that the soil in the target area is excavated one by one to the bottom surface of the target foundation pit; wherein the soil in the target area includes the soil located between the first row of engineering piles and the second row of engineering piles and located above the existing underground structure; arranging a flexible package on the bottom surface of the first excavated target foundation pit, and injecting a fluid medium into the flexible package, so that the ballast surface and pressure of the flexible package on the bottom surface of the target foundation pit increase synchronously with the excavation of the soil in the target area one by one; arranging a back pressure block on the flexible package to discharge the fluid medium in the flexible package; connecting the back pressure block to the first row of engineering piles and the second row of engineering piles to form a portal frame.

[0007] Furthermore, before excavating the soil in the target area according to the preset excavation sequence, the method further includes:

[0008] Dividing the soil in the target area into a plurality of sections distributed longitudinally along the existing underground structure, and dividing the soil in each section into a plurality of units distributed transversely along the existing underground structure;

[0009] The step of excavating the soil in the target area according to a preset excavation sequence includes:

[0010] excavating soil in a plurality of sections within the target area according to a first excavation sequence;

[0011] According to the second excavation sequence, soil in a plurality of units in each of the sections is excavated.

[0012] Furthermore, the step of excavating soil in multiple sections within the target area according to the first excavation sequence includes:

[0013] The multiple sections within the target area are divided into multiple groups along the longitudinal distribution direction, and each group includes at least two sections distributed along the longitudinal direction; based on the skipping method, after the soil of all units in the first section along the longitudinal direction of each group is excavated to the bottom surface of the target foundation pit, the soil of all units in the second section along the longitudinal direction of each group is excavated to the bottom surface of the target foundation pit, until the soil of all units in the last section along the longitudinal direction of each group is excavated to the bottom surface of the target foundation pit.

[0014] Furthermore, the step of excavating the soil in the plurality of units in each of the sections according to the second excavation sequence includes:

[0015] Along the lateral distribution direction of the multiple units in the section, after excavating the soil in one unit to the bottom surface of the target foundation pit, the soil in the next adjacent unit is excavated to the bottom surface of the target foundation pit, until the soil in all units in the section is excavated to the bottom surface of the target foundation pit.

[0016] Furthermore, before excavating the soil in the target area according to the preset excavation sequence, the method further includes:

[0017] The soil above the first row of engineering piles and the second row of engineering piles is excavated, and slope treatment is performed to form a first slope surface with the bottom of the slope extending to the top of the first row of engineering piles and a second slope surface with the bottom of the slope extending to the top of the second row of engineering piles.

[0018] Furthermore, before arranging the back pressure block on the flexible packaging member, the method further comprises:

[0019] The counter-pressure block is prefabricated on the first slope surface; the counter-pressure block includes a concrete strip and a first lifting member, a second lifting member, a first anchor and a second anchor arranged on the concrete strip.

[0020] Furthermore, the step of placing the back pressure block on the flexible package to discharge the fluid medium in the flexible package includes:

[0021] The back-pressure block on the first slope is flipped onto the flexible package by using a lifting and flipping assembly, and the back-pressure block is slowly pressed down and squeezed by using the lifting and flipping assembly, while the valve provided on the flexible package is opened to discharge the fluid medium in the flexible package through the valve.

[0022] Furthermore, the step of connecting the back pressure block with the first row of engineering piles and the second row of engineering piles to form a portal frame includes:

[0023] When the remaining amount of the fluid medium in the flexible packaging reaches a preset range, removing the flexible packaging;

[0024] Using a lifting and flipping assembly to press the counter-pressure block downward on the bottom surface of the target foundation pit;

[0025] The first anchoring piece preset on the counter-pressure block is connected to the pile foundation steel bar preset on the top of the first row of engineering piles, and concrete is poured; the second anchoring piece preset on the counter-pressure block is connected to the pile foundation steel bar preset on the top of the second row of engineering piles, and concrete is poured; a portal frame is formed.

[0026] Furthermore, the injection amount of the fluid medium in the flexible package is controlled according to the rebound amount δ of the target foundation pit bottom surface caused by the pressure of the flexible package on the target foundation pit bottom surface offsetting the weight of the excavated soil on the target foundation pit bottom surface is less than 8mm.

[0027] In the second aspect, the present invention also proposes a foundation pit construction system above an existing underground structure, comprising: a first row of engineering piles, a second row of engineering piles, a flexible package and a back-pressure block; the first row of engineering piles and the second row of engineering piles are respectively arranged on opposite sides of the existing underground structure; the flexible package is ballasted on the bottom surface of the first excavated target foundation pit in the target area, and a fluid medium is injected into the interior of the flexible package so that the ballast surface and pressure of the flexible package on the bottom surface of the target foundation pit increase synchronously with the excavation of the soil in the target area one by one; wherein the soil in the target area includes the soil located between the first row of engineering piles and the second row of engineering piles, and located above the existing underground structure; the back-pressure block is arranged on the flexible package, for squeezing the flexible package to discharge the fluid medium in the flexible package; the back-pressure block is also connected to the first row of engineering piles and the second row of engineering piles to form a portal frame.

[0028] Furthermore, the system also includes a lifting and flipping assembly for lifting and flipping the back pressure block onto the flexible package, and adjusting the pressure applied by the back pressure block on the flexible package to displace the pressure applied by the fluid medium discharged from the flexible package on the bottom surface of the target foundation pit.

[0029] Furthermore, after the soil above the first row of engineering piles is excavated and sloped, a first slope is formed, and the bottom of the first slope extends to the top of the first row of engineering piles; after the soil above the second row of engineering piles is excavated and sloped, a second slope is formed; the bottom of the second slope extends to the top of the second row of engineering piles; the slopes of the first slope and the second slope are 0-20°.

[0030] Furthermore, the back pressure block is prefabricated on the first slope; the back pressure block includes a concrete strip and a first lifting member, a second lifting member, a first anchor and a second anchor arranged on the concrete strip; the first lifting member is arranged on the end face of the concrete strip facing the first slope, and the second lifting member is arranged on the end face of the concrete strip facing away from the first slope; the first anchor is arranged on the end face of the concrete strip close to the bottom of the first slope, and the second anchor is arranged on the end face of the concrete strip away from the bottom of the first slope.

[0031] Furthermore, the first anchor is connected to the pile foundation steel bar at the top of the first row of engineering piles, and the second anchor is connected to the pile foundation steel bar at the top of the second row of engineering piles.

[0032] In some embodiments, the lifting and flipping assembly includes a first winch and a truck crane; the first winch is arranged at the top of the first slope, the truck crane is arranged on the ground outside the target area, and the truck crane is connected to the second lifting component for lifting and flipping the concrete strips on the first slope to the flexible packaging component; the steel wire rope of the first winch is connected to the first lifting component, and the pressure applied by the concrete strips to the flexible packaging component is adjusted by adjusting the tightness of the steel wire rope.

[0033] In some embodiments, the lifting and flipping assembly includes a first winch and a second winch; the first winch is arranged at the top of the first slope, and the wire rope of the first lifting member is connected to the first lifting member; the second winch is arranged at the top of the second slope, and the wire rope of the second winch is connected to the second lifting member; the first winch and the second winch flip the concrete strips on the first slope to the flexible packaging by adjusting the retraction and extension of their respective wire ropes, and the first winch and the second winch adjust the pressure applied by the concrete strips on the flexible packaging by adjusting the retraction and extension and tightness of their respective wire ropes.

[0034] Furthermore, the flexible packaging comprises a water bag, and the fluid medium comprises water.

[0035] Furthermore, the existing underground structure includes a tunnel.

[0036] The beneficial effects of the present invention include:

[0037] 1. By placing the flexible packaging on the bottom surface of the first excavated target foundation pit and injecting fluid medium into the flexible packaging, the ballast surface and pressure of the flexible packaging on the bottom surface of the target foundation pit will increase synchronously with the excavation of the soil one by one. The ballast weight of the flexible packaging is replaced with the ballast weight of the soil to achieve dynamic ballast during the soil excavation process, thereby strictly limiting the floating of the existing underground structure before the counter-pressure block is connected with the first row of engineering piles and the second row of engineering piles to form a portal frame.

[0038] 2. Existing excavation of foundation pits above subways often relies on grouting and dewatering to control the subway's buoyancy. Grouting is performed before excavation to increase the deadweight of the soil above the tunnel. Dewatering is then used to adjust the subway's buoyancy after it has risen beyond a certain range. Grouting is often difficult in soft strata, resulting in significant slurry loss and soil pollution. Dewatering can also easily cause internal stress distribution in the tunnel, posing a safety hazard. The present invention eliminates these drawbacks. Ballast replacement and soil excavation are synchronized, achieving micro-disturbance construction, accelerating foundation pit construction and ensuring excavation efficiency.

[0039] 3. The present invention can realize dynamic excavation by simply controlling the water injection speed / injection volume without affecting the excavation speed. It also adopts block-by-block excavation to effectively improve the excavation efficiency and save a lot of construction time. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 It is a schematic flow chart of the foundation pit construction method above the existing underground structure of the present invention.

[0041] Figure 2 Schematic top view of multiple segments of the longitudinal distribution of the target area of ​​the present invention.

[0042] Figure 3 This is a schematic diagram of the excavation sequence of prefabricated back pressure blocks on the first slope surface of the present invention and multiple units in a section.

[0043] Figure 4 for Figure 3 Schematic diagram of the flexible packaging in the section being ballasted into place.

[0044] Figure 5 for Figure 4 Schematic diagram of flipping the back pressure block onto the flexible package and squeezing the flexible package.

[0045] In the figure: 10-first row of engineering piles; 20-second row of engineering piles; 30-tunnel; 40-target foundation pit bottom; 50-pile foundation reinforcement; 60-first slope; 70-second slope; 80-counter pressure block; 81-concrete strip; 82-first lifting piece; 83-second lifting piece; 84-first anchor; 85-second anchor; 86-first winch; 87-rotating shaft; 88-steel formwork; 90-flexible packaging. DETAILED DESCRIPTION

[0046] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0047] like Figure 1 The method for constructing a foundation pit above an existing underground structure shown includes the following steps:

[0048] A first row of engineering piles 10 and a second row of engineering piles 20 are constructed on opposite sides of an existing underground structure. The existing underground structure of this embodiment includes a tunnel 30, especially an already-operated subway tunnel 30.

[0049] like Figure 2 、 3 As shown, before constructing the first and second rows of engineering piles 10, 20, it is necessary to first locate the outline of the tunnel 30 on the original ground (i.e., the ground before the foundation pit excavation). Then, according to the design requirements, the distribution area of ​​the first and second rows of engineering piles 10, 20 should be determined. When setting the distribution area of ​​the first and second rows of engineering piles 10, 20, the tunnel 303m keep-out line should be taken into consideration, so that the first and second rows of engineering piles 10, 20 are constructed outside this keep-out line.

[0050] like Figure 2 As shown, the first row of engineering piles 10 and the second row of engineering piles 20 are arranged along the longitudinal direction of the tunnel 30, and the first row of engineering piles 10 and the second row of engineering piles 20 are arranged on both sides of the tunnel 30 opposite to each other. Figure 2 Reference numeral A represents the longitudinal center line of the tunnel 30. The first row of engineering piles 10 includes a plurality of first engineering piles arranged at intervals of 4m along the longitudinal direction of the tunnel 30, and the second row of engineering piles 20 includes a plurality of second engineering piles arranged at intervals of 4m along the longitudinal direction of the tunnel 30. The pile diameters of the first engineering piles 10 and the second row of engineering piles 20 are 1.2m. The first row of engineering piles 10 and the second row of engineering piles 20 are constructed and cast to at least 0.5m above the design bottom plate elevation according to the design depth. The design bottom plate elevation is the design bottom plate elevation of the foundation pit to be constructed, and the design bottom plate elevation can also be understood as the target foundation pit bottom surface 40 in this embodiment. Pile foundation steel bars 50 are respectively reserved at the tops of the first engineering piles and the second engineering piles. The pile foundation steel bars 50 extend above the target foundation pit bottom surface 40, and concrete is not poured at the pile foundation steel bars 50 to facilitate the connection of the pile foundation steel bars 50 with the back pressure block 80 at a later stage.

[0051] The soil in the target area is divided into a plurality of sections distributed longitudinally along the existing underground structure. The soil in the target area includes the soil between the first row of engineering piles 10 and the second row of engineering piles 20 and above the existing underground structure.

[0052] like Figure 2 As shown, the soil in the target area is divided into ten sections distributed longitudinally along the tunnel 30. The ten sections are numbered longitudinally as I, II, III, IV, V, VI, VII, VIII, IX, and X. The length of each section along the longitudinal direction is 6 to 8 meters.

[0053] The soil in the target area is excavated according to a preset excavation sequence, so that the soil in the target area is excavated one by one to the target foundation pit bottom surface 40.

[0054] According to the first excavation sequence, the soil in ten sections within the target area is excavated.

[0055] Specifically: multiple sections within the target area are divided into multiple groups along the longitudinal distribution direction, and each group includes at least two sections distributed along the longitudinal direction; based on the skipping method, the soil of all units in the first section along the longitudinal direction of each group is excavated to the bottom surface 40 of the target foundation pit, and then the soil of all units in the second section along the longitudinal direction of each group is excavated to the bottom surface 40 of the target foundation pit, until the soil of all units in the last section along the longitudinal direction of each group is excavated to the bottom surface 40 of the target foundation pit.

[0056] One possible excavation method is to divide sections I and II into the first group, sections III and IV into the second group, sections V and VI into the third group, and so on, dividing the ten sections into five groups, each consisting of two sections. After excavating the first section of each of the five groups, excavate the soil in the first section of each group to 40° below the target pit bottom. Then, excavate the soil in the second section of each group until the soil in the second section of each group reaches 40° below the target pit bottom. That is, first excavate odd-numbered sections I, III, V, VII, and IX, then excavate even-numbered sections II, IV, VI, VIII, and X. After excavating each section, wait 2-3 days before excavating the next section. For example, after excavating section I, wait 2 days before excavating section III.

[0057] Another possible excavation method is to divide the sections numbered I, II, III, IV, and V into the first group, and the sections numbered VI, VII, VIII, IX, and X into the second group. First, excavate the section numbered I in the first group. After a 2-3 day delay, excavate the section numbered VI in the second group. After another 2-3 day delay, excavate the section numbered II in the first group, and so on until the section numbered X is excavated.

[0058] The above examples are merely illustrative of the sequence of excavation sections and do not require that all sections be excavated before proceeding to the next step in the foundation pit. In practice, excavation of one section can be completed while the subsequent construction of that section is underway, simultaneously with the excavation of the next section. This can achieve higher construction efficiency and shorten the construction period.

[0059] like Figure 3 As shown in FIG, the soil in each section is divided into multiple units distributed laterally along the existing underground structure. For example, in this embodiment, Figure 3 The soil in the section shown is divided into 6 units from left to right (transversely of the tunnel 30), and each unit is numbered, that is, the 6 units are marked with numbers 1, 2, 3, 4, 5, and 6 respectively.

[0060] According to the second excavation sequence, soil in a plurality of units in each section is excavated.

[0061] Specifically, along the lateral distribution direction of the multiple units in the section, after the soil in one unit is excavated to the target foundation pit bottom surface 40, the soil in the next adjacent unit is excavated to the target foundation pit bottom surface 40, and the soil in all the units in the section is excavated to the target foundation pit bottom surface 40. Based on the 6 numbers of the 6 units mentioned above, it can be understood that the excavation order of the 6 units in the section is 1→2→3→4→5→6. That is, the soil in the unit numbered 1 is excavated first, and after the soil in the unit is excavated to the designed depth / height of the target foundation pit bottom surface 40, the excavation work of the soil in the unit numbered 1 is completed, and the excavation work of the soil in the unit numbered 2 is carried out, and this process is carried out in sequence until the excavation of the soil in the unit numbered 6 is completed. At this point, the target foundation pit bottom surface 40 of the 6 units in the section is fully formed.

[0062] The flexible packaging member 90 is placed on the first excavated target foundation pit bottom 40, and a fluid medium is injected into the flexible packaging member 90. This causes the ballast surface and pressure of the flexible packaging member 90 on the target foundation pit bottom 40 to increase synchronously with the excavation of the soil within the target area. In this embodiment, the flexible packaging member 90 comprises a water bag, and the fluid medium comprises water. In some embodiments, the flexible packaging member 90 may also be a rubber bag or other flexible, soft, deformable, and sealed film structure.

[0063] Combine Figure 3 、 Figure 4 As shown, after the soil in unit number 1 is excavated to the target foundation pit bottom 40, a water bag is placed on the target foundation pit bottom 40 where unit number 1 is located, and water is injected into the water bag. The injected water is used to ballast the target foundation pit bottom 40, thereby replacing the soil excavated from unit number 1. Then, the soil in unit number 2 is excavated. After the soil in unit number 2 is excavated to the target foundation pit bottom 40, water is injected into the water bag again. Due to the fluidity of the water and the deformation of the water bag, the ballast surface of the water bag on the target foundation pit bottom 40 is simultaneously increased. That is, the water bag continues to ballast the target foundation pit bottom 40 of unit number 1 as well as the target foundation pit bottom 40 of unit number 2. Due to the additional water injection, the pressure exerted by the water bag on the target foundation pit bottom 40 of unit number 1 and the target foundation pit bottom 40 of unit number 2 can be guaranteed. This is done sequentially until the bottom surface 40 of the target foundation pit of unit number 6 is also ballasted with water bags, such as Figure 4As shown, in this state, the ballast of the tunnel 30 by the soil in the units numbered 1-6 in the section is replaced by the ballast of the tunnel 30 by the water bags. Compared with the traditional method of excavating all the soil in the units numbered 1-6 and then constructing the counter-pressure structure, the buoyancy of the tunnel 30 can be effectively controlled. In particular, in the traditional method, after the soil in the section is excavated and before the counter-pressure structure in the section is constructed, the tunnel 30 is very easy to float. The present invention can effectively solve this problem.

[0064] Since the flexible packaging member 90 is only a temporary ballast structure, it is necessary to use the counter-pressure block 80 to replace the flexible packaging member 90 so that the tunnel 30 has permanent ballast.

[0065] like Figure 5 As shown, the back pressure block 80 is set on the flexible packaging member 90, and the back pressure block 80 is used to squeeze the flexible packaging member 90 to discharge the fluid medium in the flexible packaging member 90. Of course, the fluid medium in the flexible packaging member 90 can also be actively discharged.

[0066] Connect the back pressure block 80 with the first row of engineering piles 10 and the second row of engineering piles 20 to form a portal frame.

[0067] When the remaining amount of the fluid medium in the flexible packaging member 90 reaches a preset range, the flexible packaging member 90 is removed. It can be understood that when the water in the water bag is about to be emptied or is about to be emptied, the water bag can be drawn out.

[0068] In some embodiments, the flexible packaging member 90 is a degradable plastic bag. Therefore, the flexible packaging member 90 may not be removed and may be permanently loaded under the counter-pressure block 80 until it degrades.

[0069] Using the lifting and flipping assembly, the counter-pressure block 80 is pressed down on the target foundation pit bottom surface 40;

[0070] The first anchor 84 preset on the back pressure block 80 is connected to the pile foundation steel bar 50 preset on the top of the first row of engineering piles 10, and concrete is poured; the second anchor 85 preset on the back pressure block 80 is connected to the pile foundation steel bar 50 preset on the top of the second row of engineering piles 20, and concrete is poured; the first row of engineering piles 10, the back pressure block 80 and the second row of engineering piles 20 are connected to form a portal frame.

[0071] It should be noted that each section corresponds to a back pressure block 80 and a water bag. After a section is excavated and ballasted with a water bag, the back pressure block 80 corresponding to the section is ballasted on the water bag. Finally, after the water in the water bag is drained, the back pressure block 80 of the section is ballasted on the target foundation pit bottom 40 of the section, and the back pressure block 80 is connected to the first engineering pile and the second engineering pile corresponding to the section to form a portal frame of the section. At this point, the construction of the section is completed. The construction of the next section is then carried out, and a portal frame of the same structure is finally formed in the next section, until all sections are formed with a portal frame. In some embodiments, the portal frames of all sections can be connected as a whole, and the connection method can be a combination of steel bar connection and concrete pouring.

[0072] In addition, before excavating the soil in the target area according to the preset excavation sequence, it also includes:

[0073] The soil above the first row of engineering piles 10 and the second row of engineering piles 20 is excavated and sloped to form a first slope 60 extending from the bottom of the slope to the top of the first row of engineering piles 10 and a second slope 70 extending from the bottom of the slope to the top of the second row of engineering piles 20. The slopes of the first slope 60 and the second slope 70 are 0-20 degrees.

[0074] Before the counter-pressure block 80 is placed on the flexible package 90, the method further includes:

[0075] A counter-pressure block 80 is prefabricated on the first slope 60. The counter-pressure block 80 includes a concrete strip 81 and a first lifting member 82, a second lifting member 83, a first anchoring member 84 and a second anchoring member 85 provided on the concrete strip 81.

[0076] The back pressure block 80 is placed on the flexible package 90, and the steps of discharging the fluid medium in the flexible package 90 include:

[0077] The back pressure block 80 on the first slope 60 is flipped onto the flexible packaging 90 using the lifting and flipping assembly. The back pressure block 80 is then slowly pressed downward to squeeze the flexible packaging 90. Simultaneously, a valve on the flexible packaging 90 is opened, allowing the fluid medium in the flexible packaging 90 to be discharged through the valve. The valve is located at the bottom of the flexible packaging 90, and the discharged fluid medium can be connected to a storage device, such as a water reservoir.

[0078] The injection amount of the fluid medium in the flexible package 90 is controlled according to the rebound amount δ of the target foundation pit bottom surface 40 caused by the pressure of the flexible package 90 on the target foundation pit bottom surface 40 offsetting the weight of the excavated soil on the target foundation pit bottom surface 40 to be less than 8mm.

[0079] Among them, after the soil in each unit is excavated to the target foundation pit bottom surface 40, the calculation formula of the rebound amount δ of the target foundation pit bottom surface 40 corresponding to the unit is:

[0080]

[0081] Where, is the rebound empirical coefficient; p c E is the deadweight pressure of the soil above the bottom of the foundation pit, and the buoyancy should be deducted below the groundwater level; ci is the modulus of resilience of the i-th soil layer. Zi is the distance from the bottom of the i-th soil layer to the bottom of the foundation pit, and αi is the average additional stress coefficient from the bottom of the foundation pit to the bottom of the i-th soil layer.

[0082] Assuming that the length of the foundation pit corresponding to a strip unit is l, the width is b, and the excavation depth is z, the additional stress coefficient αi is selected according to Table 1 below.

[0083] Table 1 Selection table of additional stress coefficient αi

[0084]

[0085] Based on the above-mentioned calculation formula for the buoyancy of foundation pit excavation of each unit (i.e., the rebound amount δ), the present invention proposes to achieve regulation and control of the buoyancy by means of dynamic water injection and ballasting.

[0086] Based on the same inventive concept, the present invention also proposes a foundation pit construction system above an existing underground structure, comprising: a first row of engineering piles 10 , a second row of engineering piles 20 , a flexible packaging member 90 and a back pressure block 80 .

[0087] The first row of engineering piles 10 and the second row of engineering piles 20 are respectively arranged on opposite sides of the existing underground structure.

[0088] The flexible package 90 is ballasted on the bottom surface 40 of the first excavated target foundation pit in the target area. Fluid medium is injected into the interior of the flexible package 90, so that the ballasting surface and pressure of the flexible package 90 on the bottom surface 40 of the target foundation pit increase synchronously with the excavation of the soil in the target area one by one; wherein, the soil in the target area includes the soil located between the first row of engineering piles 10 and the second row of engineering piles 20, and located above the existing underground structure.

[0089] The back pressure block 80 is provided on the flexible packaging member 90 and is used to squeeze the flexible packaging member 90 to discharge the fluid medium in the flexible packaging member 90 ; the back pressure block 80 is also connected to the first row of engineering piles 10 and the second row of engineering piles 20 to form a portal frame.

[0090] The system also includes a lifting and flipping assembly for lifting and flipping the back pressure block 80 onto the flexible package 90, and adjusting the pressure applied by the back pressure block 80 on the flexible package 90 to replace the pressure applied by the fluid medium discharged from the flexible package 90 on the target foundation pit bottom surface 40.

[0091] After the soil above the first row of engineering piles 10 was excavated and sloped, a first slope 60 was formed, and the bottom of the first slope 60 extended to the top of the first row of engineering piles 10; after the soil above the second row of engineering piles 20 was excavated and sloped, a second slope 70 was formed; the bottom of the second slope 70 extended to the top of the second row of engineering piles 20; the slopes of the first slope 60 and the second slope 70 are 0-20°.

[0092] The back pressure block 80 is prefabricated on the first slope surface 60; the back pressure block 80 includes a concrete strip 81 and a first lifting member 82, a second lifting member 83, a first anchor 84 and a second anchor 85 arranged on the concrete strip 81; the first lifting member 82 is arranged on the end surface of the concrete strip 81 facing the first slope surface 60, and the second lifting member 83 is arranged on the end surface of the concrete strip 81 facing away from the first slope surface 60; the first anchor 84 is arranged on the end surface of the concrete strip 81 close to the bottom of the first slope surface 60, and the second anchor 85 is arranged on the end surface of the concrete strip 81 away from the bottom of the first slope surface 60.

[0093] The first anchor 84 is connected to the pile foundation steel bar 50 at the top of the first row of engineering piles 10 , and the second anchor 85 is connected to the pile foundation steel bar 50 at the top of the second row of engineering piles 20 .

[0094] In some embodiments, the concrete strip 81 is further provided with a steel formwork 88 on the end face facing the first slope 60 and the end face provided with the first anchor 84, so that when the concrete strip 81 rotates, the concrete strip 81 does not directly contact the first slope 60, thereby avoiding damage to the concrete strip 81.

[0095] In some embodiments, a horizontal rotating shaft 87 is provided at the edge where the end face of the concrete strip 81 facing the first slope 60 intersects with the end face provided with the first anchor 84. The rotating shaft 87 can be a pre-buried roller. When the concrete strip 81 is flipped over, it rotates around the axis of the rotating shaft 87, which not only facilitates rotation and positioning, but also further protects the concrete strip 81 and prevents it from being damaged at the edge. In some embodiments, an angle measuring device is provided at the end of the rotating shaft 87. The angle measuring device is used to measure the rotation angle of the rotating shaft 87, thereby obtaining the rotation angle of the concrete strip 81, so as to more accurately control the tilt angle of the concrete strip 81 when it is loaded on the flexible packaging 90. The remaining amount of fluid medium in the flexible packaging 90 can also be determined by the angle value.

[0096] In this embodiment, the lifting and flipping assembly includes a first winch 86 and a truck crane; the first winch 86 is arranged at the top of the first slope 60, and the truck crane is arranged on the ground outside the target area. The truck crane is connected to the second lifting component 83, and is used to lift and flip the concrete strip 81 on the first slope 60 to the flexible packaging component 90; the wire rope of the first winch 86 is connected to the first lifting component 82, and the pressure applied by the concrete strip 81 to the flexible packaging component 90 is adjusted by adjusting the tightness of the wire rope.

[0097] like Figure 5 As shown, a truck crane is used to lift the concrete strip 81 on the first slope 60 and tilt it away from the first slope 60. The steel wire rope of the first hoist 86 is used to pull the concrete strip 81 to limit its tilting speed. A certain tension can also be applied to it to adjust the pressure exerted by the concrete strip 81 on the flexible packaging member 90. Figure 5 As shown, when the concrete strip 81 is tilted and loaded onto the flexible packing member 90, the side of the flexible packing member 90 near the first slope 60 first contacts the concrete strip 81 and is squeezed, causing the fluid medium within the flexible packing member 90 to flow toward the second slope 70. Once the concrete strip 81 is fully loaded onto the flexible packing member 90, the truck crane can be removed, and the first hoist 86 can be used to slowly lower the concrete strip 81. The pressure exerted by the concrete strip 81 on the flexible packing member 90 can be adjusted by adjusting the tension of the steel wire rope. Once the fluid medium within the flexible packing member 90 is empty or nearly empty, the flexible packing member 90 can be removed and the concrete strip 81 can be lowered again until it is fully loaded onto the target foundation pit floor 40.

[0098] In some embodiments, the lifting and flipping assembly includes a first winch 86 and a second winch; the first winch 86 is arranged at the top of the first slope 60, and the wire rope of the first lifting member 82 is connected to the first lifting member 82; the second winch is arranged at the top of the second slope 70, and the wire rope of the second winch is connected to the second lifting member 83; the first winch 86 and the second winch flip the concrete strip 81 on the first slope 60 to the flexible packaging member 90 by adjusting the retraction and extension of their respective wire ropes, and the first winch 86 and the second winch adjust the pressure applied by the concrete strip 81 on the flexible packaging member 90 by adjusting the retraction and extension and tightness of their respective wire ropes.

[0099] In some embodiments, a first guide rail is further provided at the top of the first slope 60. The first guide rail is arranged along the longitudinal direction of the tunnel 30. The first hoist 86 is arranged on the first guide rail and can move along the first guide rail. When the construction of one section is completed, the first hoist 86 is pushed along the first guide rail to move to the top of the first slope 60 corresponding to the next section. Similarly, when the lifting and flipping assembly in some embodiments includes a first hoist 86 and a second hoist, a second guide rail is also provided at the top of the second slope 70. The second guide rail is arranged along the longitudinal direction of the tunnel 30, and the second hoist is arranged on the second guide rail and can move along the second guide rail.

[0100] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiment. All technical solutions based on the concept of the present invention are within the scope of protection of the present invention. It should be noted that for those skilled in the art, various improvements and modifications that do not depart from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A method for constructing a foundation pit above an existing underground structure, characterized in that: The following steps are involved: Construct the first row of engineering piles and the second row of engineering piles on opposite sides of the existing underground structure; Excavating the soil in the target area according to a preset excavation sequence, so that the soil in the target area is excavated one by one to the bottom surface of the target foundation pit; wherein the soil in the target area includes the soil located between the first row of engineering piles and the second row of engineering piles and above the existing underground structure; placing a flexible package on the bottom surface of the first excavated target foundation pit, and injecting a fluid medium into the flexible package so that the ballast surface and pressure of the flexible package on the bottom surface of the target foundation pit increase synchronously with the excavation of soil in the target area one by one; placing a back pressure block on the flexible package to discharge the fluid medium in the flexible package; The back pressure block is connected to the first row of engineering piles and the second row of engineering piles to form a portal frame.

2. The method for constructing a foundation pit above an existing underground structure according to claim 1, wherein: Before excavating the soil in the target area according to the preset excavation sequence, the method further includes: Dividing the soil in the target area into a plurality of sections distributed longitudinally along the existing underground structure, and dividing the soil in each section into a plurality of units distributed transversely along the existing underground structure; The step of excavating the soil in the target area according to a preset excavation sequence includes: excavating soil in a plurality of sections within the target area according to a first excavation sequence; According to the second excavation sequence, soil in a plurality of units in each of the sections is excavated.

3. The method for constructing a foundation pit above an existing underground structure according to claim 2, wherein: The step of excavating soil in multiple sections within the target area according to the first excavation sequence includes: The multiple sections within the target area are divided into multiple groups along the longitudinal distribution direction, and each group includes at least two sections distributed along the longitudinal direction; based on the skipping method, after the soil of all units in the first section along the longitudinal direction of each group is excavated to the bottom surface of the target foundation pit, the soil of all units in the second section along the longitudinal direction of each group is excavated to the bottom surface of the target foundation pit, until the soil of all units in the last section along the longitudinal direction of each group is excavated to the bottom surface of the target foundation pit.

4. The method for constructing a foundation pit above an existing underground structure according to claim 2, wherein: The step of excavating the soil in the plurality of units in each section according to the second excavation sequence includes: Along the lateral distribution direction of the multiple units in the section, after excavating the soil in one unit to the bottom surface of the target foundation pit, the soil in the next adjacent unit is excavated to the bottom surface of the target foundation pit, until the soil in all units in the section is excavated to the bottom surface of the target foundation pit.

5. The method for constructing a foundation pit above an existing underground structure according to claim 1, wherein: Before excavating the soil in the target area according to the preset excavation sequence, the method further includes: The soil above the first row of engineering piles and the second row of engineering piles is excavated, and slope treatment is performed to form a first slope surface with the bottom of the slope extending to the top of the first row of engineering piles and a second slope surface with the bottom of the slope extending to the top of the second row of engineering piles.

6. The method for constructing a foundation pit above an existing underground structure according to claim 5, characterized in that: Before the back pressure block is arranged on the flexible packaging member, the method further comprises: The counter-pressure block is prefabricated on the first slope surface; the counter-pressure block includes a concrete strip and a first lifting member, a second lifting member, a first anchor and a second anchor arranged on the concrete strip.

7. The method for constructing a foundation pit above an existing underground structure according to claim 6, wherein: The step of placing the back pressure block on the flexible package to discharge the fluid medium in the flexible package comprises: The back-pressure block on the first slope is flipped onto the flexible package by using a lifting and flipping assembly, and the back-pressure block is slowly pressed down and squeezed by using the lifting and flipping assembly, while the valve provided on the flexible package is opened to discharge the fluid medium in the flexible package through the valve.

8. The method for constructing a foundation pit above an existing underground structure according to claim 6, wherein: The step of connecting the back pressure block with the first row of engineering piles and the second row of engineering piles to form a portal frame comprises: When the remaining amount of the fluid medium in the flexible packaging reaches a preset range, removing the flexible packaging; Using a lifting and flipping assembly to press the counter-pressure block downward on the bottom surface of the target foundation pit; The first anchoring piece preset on the counter-pressure block is connected to the pile foundation steel bar preset on the top of the first row of engineering piles, and concrete is poured; the second anchoring piece preset on the counter-pressure block is connected to the pile foundation steel bar preset on the top of the second row of engineering piles, and concrete is poured; a portal frame is formed.

9. A foundation pit construction system above an existing underground structure, characterized in that: include: The first row of engineering piles, the second row of engineering piles, flexible packaging and counter-pressure blocks; The first row of engineering piles and the second row of engineering piles are respectively arranged on opposite sides of the existing underground structure; The flexible package is loaded onto the bottom surface of a first excavated target foundation pit within the target area, and a fluid medium is injected into the interior of the flexible package so that the loading surface and pressure of the flexible package on the bottom surface of the target foundation pit increase synchronously with the excavation of soil within the target area. The soil within the target area includes soil located between the first row of engineering piles and the second row of engineering piles and above the existing underground structure. The back pressure block is arranged on the flexible packaging member and is used for squeezing the flexible packaging member to discharge the fluid medium in the flexible packaging member; the back pressure block is also connected to the first row of engineering piles and the second row of engineering piles to form a portal frame.

10. The foundation pit construction system above an existing underground structure according to claim 9, characterized in that: The system also includes a lifting and flipping assembly for lifting and flipping the back-pressure block onto the flexible package and adjusting the pressure applied by the back-pressure block on the flexible package to displace the pressure applied by the fluid medium discharged from the flexible package on the bottom surface of the target foundation pit.

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