A vacuum supporting excavation method suitable for deep foundation pit of complex stratum adjacent to existing building

Abstract

The application discloses a kind of vacuum support excavation method suitable for existing building complex stratum deep foundation pit nearby, including setting up column pile in foundation pit wall soil;According to the design range, vertical drainage body, vertical reinforced body, peripheral vertical airtight curtain, grouting bag, horizontal drainage body and horizontal airtight layer are set;Through vacuum pressure source, vacuum is extracted and foundation pit is excavated;Slope airtight layer and vacuum nail are laid on the newly excavated foundation pit wall, and internal support system is set in the foundation pit;Slope airtight layer is sealed through slope bottom vertical airtight curtain;Permanent structure construction is carried out, and subsequent demolition, recovery, backfill work is carried out, permanent structure stops vacuum after coming out of ground, and subsequent demolition, recovery work is carried out.The application has the dual role of retaining soil and stopping water, organically combines the internal support support system under the premise of not damaging the slope airtight layer, supports the non-sloping excavation of excavation depth exceeding 10m and the vertical excavation without ground wall, and has obvious advantages in cost and construction period.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of civil engineering foundation pit support technology, in particular to a vacuum support excavation method suitable for deep foundation pit in complex stratum near existing buildings. BACKGROUND

[0002] The vacuum preloading method for ground treatment is a method for reinforcing ground by using atmospheric pressure as preloading load, laying a layer of water-permeable sand cushion on the ground surface, covering a layer of air-tight sealing membrane thereon, sealing the periphery with a sealing wall to isolate it from the atmosphere, burying drainage channels in the sand cushion and soil, then connecting with a vacuum pump to perform vacuum extraction, forming negative pressure in the drainage channels in the sand cushion and soil, gradually extracting pore water and air in the soil, thereby consolidating the soil and improving its strength.

[0003] The vacuum preloading method has also been applied in the field of foundation pit support, and continuous vacuum action is applied to maintain the stability of the pit wall during the entire excavation period.

[0004] Chinese patent CN201210295813.9 discloses a vacuum-acting gravity type foundation pit support system and construction method, which uses a vacuum-acting gravity type pit wall support structure for support, and can achieve greater excavation depth, but the precondition is that sufficient implementation space must be provided outside the excavation range to set up the gravity type retaining wall and slope, which greatly limits its application range due to the small space in modern cities.

[0005] Chinese patent CN200810236142.2 discloses a vacuum curtain water stop and atmospheric pressure support deep foundation pit excavation method, which uses a vacuum curtain water stop and atmospheric pressure for foundation pit support. Although this method is convenient for excavation, it cannot adapt to large excavation depth, and it requires the setting of a side wall solidification wall, which increases the engineering quantity and is not conducive to cost reduction. In addition, this method is essentially a gravity type pit wall support structure, which requires a large implementation space outside the excavation range.

[0006] With the increase of construction projects, the problem of land shortage is increasingly prominent, and it is inevitable to appear existing buildings around the foundation pit. During the construction of the foundation pit, the soil loss and stress state change are often caused, thereby affecting the adjacent existing buildings, for example, the deformation of the surrounding soil during the construction of the foundation pit is easy to cause the inclination deformation of the adjacent houses. Therefore, when the foundation pit adjacent to the existing building is constructed, it is important to reduce the influence on the existing building, especially when the geological conditions of the construction site are complex, such as the existence of a sandy soil layer with a large permeability coefficient under the clay soil layer, the difficulty of supporting and excavating the foundation pit by the existing vacuum action technology will be very great. At this time, how to support and excavate the deep foundation pit by vacuum action under the condition of adjacent existing buildings, limited setting area of supporting structure and existence of permeable sandy stratum in the excavation area to reduce the construction cost becomes a technical problem to be solved. SUMMARY

[0007] The present application aims to provide a vacuum supporting and excavating method suitable for deep foundation pit in complex stratum adjacent to existing buildings to solve the technical problems in the background art.

[0008] To achieve the above technical purpose, the present application adopts the following technical scheme:

[0009] A vacuum supporting and excavating method suitable for deep foundation pit in complex stratum adjacent to existing buildings, comprising the following steps:

[0010] Step S1, a column pile is arranged in the soil inside the pit wall outside the foundation pit excavation range near the excavation face, and the bottom elevation of the column pile is lower than the maximum excavation bottom elevation of the foundation pit;

[0011] Step S2, a vertical drainage body is arranged in the soil of the foundation pit excavation range, and a vertical drainage body and a vertical reinforcement body are arranged in the soil outside the foundation pit excavation range according to the design range in the construction drawing, the top elevation of the vertical drainage body and the vertical reinforcement body is not lower than the top elevation of the column pile, the bottom elevation of the vertical reinforcement body is lower than the maximum excavation bottom elevation of the foundation pit, and the bottom elevation of the vertical drainage body is higher than the elevation of the interface between the clay soil layer and the sandy soil layer;

[0012] Step S3, an outer peripheral vertical airtight curtain is vertically arranged downward from the ground surface of the pit top outside the boundary of the vertical drainage body and the vertical reinforcement body setting range;

[0013] Step S4, a grouting bag is arranged in the foundation between the outer peripheral vertical airtight curtain and the existing building;

[0014] Step S5, a horizontal drainage body is arranged at the top of the vertical drainage body distribution range, the top end of the vertical drainage body is inserted into the horizontal drainage body and communicates with the horizontal drainage body, and a grid-shaped distribution of vacuum filter pipes is arranged inside the horizontal drainage body;

[0015] Step S6, laying a horizontal sealing layer on the top surface of the transverse drainage body, and sealingly connecting the edges of the horizontal sealing layer with the top of the peripheral vertical sealing curtain;

[0016] Step S7, connecting the vacuum filter pipe arranged in step S5 to the vacuum pressure source through a vacuum pipe penetrating the horizontal sealing layer, and sealing the joint between the vacuum pipe and the horizontal sealing layer;

[0017] Step S8, starting the vacuum pressure source, and adding the surcharge on the horizontal sealing layer after the consolidation degree of the ground soil under the horizontal sealing layer meets the surcharge requirement;

[0018] Step S9, continuously drawing vacuum through the vacuum pressure source, removing the surcharge after the consolidation degree of the ground soil meets the excavation requirement, cutting the horizontal sealing layer in the excavation range, sealingly connecting the slope sealing layer on the cut part to the horizontal sealing layer, burying the connected slope sealing layer in the excavation sealing trench, and excavating the foundation pit under the condition of continuous vacuum drawing;

[0019] Step S10, taking the slope sealing layer out of the sealing trench and covering it on the newly excavated foundation pit wall at a certain depth, and then burying the slope sealing layer in the newly excavated sealing trench for storage;

[0020] Step S11, continuously excavating to the design elevation of the internal support system according to the method described in step S10, welding the transfer bar to the column pile at the corresponding elevation, penetrating the transfer bar through the slope sealing layer and sealing the joint between the transfer bar and the slope sealing layer, then setting the enclosing purlin at the cantilever end of each transfer bar and setting the cross brace on the enclosing purlin, wherein the enclosing purlin needs to be separated from the slope sealing layer;

[0021] Step S12, when the excavation depth exceeds the interface between the clay layer and the sandy soil layer, a slope sealing layer needs to be laid on the corresponding pit wall of the exposed sandy soil layer and vacuum nails need to be added, the vacuum nails penetrate the slope sealing layer and extend into the sandy soil layer on the inside of the pit wall, the transverse insertion depth of the vacuum nails does not exceed the horizontal position of the peripheral vertical sealing curtain, the joint between the vacuum nails and the slope sealing layer is sealed, and the outer end of the vacuum nails is connected to the vacuum pressure source through a vacuum pipeline;

[0022] Step S13, continuously excavating according to the method described in step S12, setting the internal support system according to the method described in step S11 when the excavation depth reaches the design elevation of the internal support system, until the maximum excavation depth of the foundation pit, and monitoring the settlement of the existing building during the entire excavation process described in steps S9-S13, when the ground of the existing building deforms greatly, grouting operation needs to be performed on the grouting bag to control the settlement and horizontal deformation of the ground of the surrounding environment and ensure the safety of the surrounding environment;

[0023] Step S14, setting a slope bottom vertical sealing curtain at the slope toe of the foundation pit bottom, and sealing connecting the lower end edge of the slope sealing layer on the top of the slope bottom vertical sealing curtain, wherein the top end elevation of the slope bottom vertical sealing curtain needs to be higher than the elevation of the maximum excavation bottom;

[0024] Step S15, pouring the foundation pit bottom plate, and constructing the underground part of the permanent structure until the height of the permanent structure exceeds the ground surface of the pit top;

[0025] Step S16, with the construction progress of the permanent structure, first removing and recycling the slope bottom vertical sealing curtain, then removing and recycling the slope sealing layer, vacuum nails and each level of internal support system step by step, and backfilling the foundation pit trench until the vacuum is stopped after reaching the ground surface elevation of the pit top, then removing and recycling the horizontal sealing layer, the peripheral vertical sealing curtain and the vertical reinforcement body, and the foundation pit supporting and excavation work is completed.

[0026] Preferably, the surcharge is implemented by filling soil, and the surcharge is added to the horizontal sealing layer in a step-by-step manner.

[0027] Preferably, the horizontal sealing layer and the slope sealing layer are both in the form of double-layer geomembrane, and geotextile is laid on the upper and lower sides of the horizontal sealing layer and the inner and outer sides of the slope sealing layer.

[0028] Preferably, the peripheral vertical sealing curtain and the slope bottom vertical sealing curtain are both in the form of one of a steel sheet pile or a geomembrane.

[0029] Preferably, the vertical reinforcement body is made of threaded steel, the column pile, the surrounding purlin and the cross brace are all made of H-shaped steel, the force transmission rod is made of steel pipe, and the vacuum nail is made of steel pipe with a perforated wall and an outer wrapping filter screen.

[0030] Preferably, the vertical drainage body, the vertical reinforcement body and the vacuum nail are arranged in a rectangular array or a triangular array.

[0031] Compared with the prior art, the application has the advantages that the application is essentially a structural retaining wall, has the dual functions of retaining soil and stopping water, avoids the problem of poor vacuum consolidation of the cohesive soil layer caused by the loss of vacuum pressure after the vertical drainage body penetrates the cohesive soil layer into the sandy soil layer, improves the permanent strength of the soil outside the foundation pit through the vacuum consolidation effect, and improves the temporary strength of the soil through the increase of the effective stress of the soil caused by the negative pressure of the soil pores, the soil with the two properties of permanent strength and temporary strength is tightly combined with the vertical reinforcement body to form a "reinforced soil" with vertical reinforcement, which can greatly improve the self-stability of the side wall of the foundation pit, and organically combines the internal support support system without damaging the slope sealing layer, so that the stability of the pit wall is guaranteed by the synergistic effect of the self-stability of the soil after the improvement and the support force provided by the internal support system, and the non-sloping excavation with an excavation depth of more than 10 m and the vertical excavation without a ground wall are supported, which has obvious cost advantage and construction period advantage compared with the support mode of the bored pile or the ground wall combined with the internal support, and the vacuum pumping and the slope sealing layer also have the function of stopping water, without the need for additional water stopping and dewatering measures, at the same time, the vertical reinforcement body and the load body can effectively offset the inward shrinkage deformation of the soil outside the foundation pit caused by the vacuum effect, prevent the influence of the vacuum support and the excavation process of the foundation pit on the adjacent existing buildings, and the setting of the grouting bag can be used as a further insurance measure, when the foundation of the surrounding existing buildings deforms greatly, the grouting bag is grouted in time to control the settlement and horizontal deformation of the foundation of the surrounding environment, and the safety of the surrounding environment is ensured. BRIEF DESCRIPTION OF DRAWINGS

[0032] The above and / or other aspects and advantages of the present application will become more apparent and more readily appreciated by referring to the following detailed description in conjunction with the accompanying drawings, which are merely exemplary and do not limit the present application, wherein:

[0033] Fig. 1 is a schematic view of the cross-sectional structure of the foundation pit before excavation according to the present application;

[0034] Fig. 2 is a schematic view of the cross-sectional structure of the foundation pit after excavation according to the present application;

[0035] Fig. 3 is a schematic view of the planar arrangement of the local position near the edge of the foundation pit according to the present application.

[0036] Reference signs: 1, ground; 2, existing building; 3, grouting bag; 4, peripheral vertical sealing curtain; 5, horizontal sealing layer; 6, surcharge; 7, transverse drainage body; 8, transfer bar; 9, surrounding purlin; 10, cross brace; 11, slope sealing layer; 12, maximum excavation pit bottom; 13, slope bottom vertical sealing curtain; 14, column pile; 15, vertical drainage body; 16, vertical reinforced body; 17, vacuum nail; 18, cohesive soil layer; 19, sandy soil layer. DETAILED DESCRIPTION

[0037] Hereinafter, an embodiment of a vacuum support excavation method suitable for a deep foundation pit of a complex stratum adjacent to an existing building will be described with reference to the accompanying drawings. The embodiment described herein is a specific, concrete embodiment of the present application, for explaining the concept of the present application, and is all explanatory and illustrative, and should not be construed as limiting the embodiments of the present application and the scope of the present application. In addition to the embodiment described herein, those skilled in the art can employ other technical solutions that are obvious based on the content disclosed in the claims and the specification of the present application, which include technical solutions that make any obvious substitutions and modifications to the embodiment described herein.

[0038] In the description of the present application, it should be noted that the terms "front", "back", "left", "right", "top", "bottom", "up", "down", "in", "out", "horizontal", "vertical", "vertical", "inclined" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application. In addition, the terms "first", "second" and the like are only for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0039] The drawings of the present specification are schematic drawings that assist in explaining the concept of the present application, and schematically represent the shape of each part and its mutual relationship. Please note that in order to clearly show the structure of each component of the embodiment of the present application, the drawings are not drawn according to the same scale. The same reference signs are used to represent the same parts.

[0040] The principles and characteristics of the present application will be described below in conjunction with the drawings, and the examples are only used to explain the present application and are not intended to limit the scope of the present application. The preferred embodiment of the present application will be further described in detail below in conjunction with a certain engineering example and Figs. 1-3 the content shown.

[0041] Brief introduction of example project:

[0042] A foundation pit project, the foundation pit excavation size is 30m*28m*18m, the foundation pit excavation depth is 18m, and there are existing buildings 2 around the foundation pit, the range for setting a horizontal sealing layer 5 to implement vacuum preloading is limited, and large-area slope excavation cannot be carried out;

[0043] The foundation soil layer conditions of the foundation pit site are as follows:

[0044] ① 0-10 meters, gray clay, natural unit weight γ=17.1 kN / m 3 , water content 29%, void ratio 0.91, plasticity index I p =25, undrained shear cohesion C u =8.0 kPa, undrained shear internal friction angle φ u =3.0°, permeability coefficient k≤5*10 -8 m / s, standard penetration blow count 10, basic bearing capacity σ0=70.5 kPa, poor engineering properties;

[0045] ② 10 meters below, yellow-brown fine sand, undrained shear cohesion C u =0.0 kPa, undrained shear internal friction angle φ u =33.0°, dense, standard penetration blow count 38, basic bearing capacity σ0=306 kPa, better engineering properties.

[0046] As shown in Figs. 1-3 , a deep foundation pit supporting structure suitable for being close to existing buildings according to the present application comprises the following parts:

[0047] The setting range of the pit top horizontal sealing layer 5 is 33m*31m, and the outer boundary thereof is sealed and blocked by using the peripheral vertical sealing curtain 4, the peripheral vertical sealing curtain 4 has two setting forms, one of which can be realized by the way of constructing a sealing steel sheet pile, and the other of which can be realized by the way of vertically slotting and laying a geomembrane, in the embodiment, the 3m-deep sealing steel sheet pile vertically set is used as the peripheral vertical sealing curtain 4;

[0048] The grouting bag 3 is arranged in the foundation outside the peripheral vertical sealing curtain 4, in the embodiment, the grouting bag 3 has a diameter of 30cm, a length of 3m, and a buried depth of 2m;

[0049] The vertical drainage body 15 and the vertical reinforcement body 16 arranged in the foundation soil in the setting range of the top horizontal sealing layer 5 are arranged in a rectangular array or a triangular array, the vertical drainage body 15 adopts SPB-B type plastic drainage plate in the embodiment, the depth is 9 m, the rectangular array is arranged, the center distance is 0.6 m, the top elevation is 0.3 m higher than the elevation of the top ground 1 so that it is inserted into the horizontal drainage body 7, the bottom elevation is 1 m higher than the bottom elevation of the cohesive soil layer 18, the vertical reinforcement body 16 adopts φ22 mm screw steel, the depth is 20 m, the rectangular array is arranged and is arranged alternately with the vertical drainage body 15, the center distance is 0.6 m, the top elevation is the same as the elevation of the top ground 1, and the bottom elevation is 3 m lower than the elevation of the maximum excavation bottom 12;

[0050] The stacker 6 is arranged above the top horizontal sealing layer 5, the setting range of the stacker 6 needs to be determined according to the size of the foundation pit, the 3 m high filling is used as the stacker 6 in the embodiment, and only the stacker 6 is arranged in the range of the horizontal sealing layer 5 outside the foundation pit in the embodiment;

[0051] The horizontal drainage body 7 is arranged on the top end of the vertical drainage body 15 and the surface of the foundation soil, the horizontal drainage body 7 is formed by a sand cushion layer composed of 0.5 m thick medium coarse sand, a grid-shaped φ50 mm PVC vacuum filter pipe is horizontally arranged in the middle part of the sand cushion layer, the longitudinal and transverse spacing of the filter pipe is 8 m, the vacuum filter pipe is connected to a vacuum pressure source (such as a vacuum pump) through a vacuum pipe penetrating the horizontal sealing layer 5, and sealing treatment is performed at the joint of the vacuum pipe and the horizontal sealing layer 5;

[0052] Two layers of 0.2 mm thick HDPE geomembrane are laid on the surface of the horizontal drainage body 7 as the horizontal sealing layer 5, the outer edge of the horizontal sealing layer 5 is sealingly connected with the upper end of the peripheral vertical sealing curtain 4, in order to protect the geomembrane, two layers of 200 g / m 2 geotextile are laid on the upper and lower sides of the geomembrane;

[0053] The slope sealing layer 11 is laid on the vertical pit wall of the foundation pit, the slope sealing layer 11 is formed by connecting the horizontal sealing layer 5 on the side of the foundation pit excavation and the reserved part is covered on the newly excavated pit wall, in order to protect the slope sealing layer 11, two layers of 200 g / m 2 geotextile are laid on the inner and outer sides of the slope sealing layer 11, and a protection device such as a wooden board is arranged on the geotextile outside the horizontal sealing layer 5 and the slope sealing layer 11 in the actual construction process to seal and protect the slope sealing layer 11, so as to prevent construction disturbance from causing damage to it;

[0054] The vacuum peg 17 arranged on the pit wall in the range of the sandy soil layer 19 is made of a steel pipe with an outer diameter of 30 mm and a wall thickness of 2 mm, a hole with a diameter of 8 mm is opened on the pipe wall every 15 cm in length of the pipe body inserted into the sandy soil layer 19 and is wrapped with a filter screen, the part of the pipe wall of the vacuum peg 17 exposed to the slope sealing layer 11 is not opened and is sealed and connected to a vacuum pipe with a diameter of 50 mm, the vacuum pipes are connected to a vacuum pressure source after being gathered, and the vacuum peg 17 is arranged on the pit wall in a rectangular array or a triangular array, and in the embodiment, the vacuum peg 17 is arranged on the pit wall in a rectangular array with a center distance of 1.5 m, and the transverse insertion depth does not exceed the horizontal arrangement position of the peripheral vertical sealing curtain 4;

[0055] The slope bottom vertical sealing curtain 13 is arranged at the bottom end boundary of the slope sealing layer 11 and is used for sealing and plugging, and the slope bottom vertical sealing curtain 13 also has two setting forms, one of which is realized by a construction sealing steel sheet pile, and the other of which is realized by vertical slotting and laying a geomembrane, and in the embodiment, the slope bottom vertical sealing curtain 13 is realized by a 2 m deep sealing steel sheet pile arranged vertically at the slope foot position of the pit bottom;

[0056] A column pile 14 formed by 400*400 H-shaped steel with a depth of 24 m and a center distance of 600 mm is arranged along the edge of the foundation pit and is arranged in the soil inside the pit wall and close to the excavation surface;

[0057] A force transmission rod 8 formed by a steel pipe with a length of 20 cm, an outer diameter of 15 cm and a wall thickness of 10 mm, a surrounding purlin 9 formed by 400*400 H-shaped steel, the surrounding purlin 9 on the free surface is connected to the surface of the column pile 14 through the force transmission rod 8 passing through the slope sealing layer 11, the force transmission rod 8 passing through the slope sealing layer 11 is sealed, a cross brace 10 formed by double 400*400 H-shaped steel, the horizontal force borne by the surrounding purlin 9 is borne by the cross brace 10, and the column pile 14, the force transmission rod 8, the surrounding purlin 9 and the cross brace 10 form an internal support system, and the force transmission rod 8, the surrounding purlin 9 and the cross brace 10 are arranged at the same vertical spacing.

[0058] The vacuum support excavation method of the application is suitable for a complex stratum deep foundation pit adjacent to an existing building, and comprises the following steps:

[0059] In step S1, a column pile 14 is arranged in the soil inside the pit wall outside the excavation range and close to the excavation surface, and the bottom of the column pile 14 is lower than the maximum excavation bottom 12 of the foundation pit.

[0060] Step S2, set vertical drainage body 15 in the soil within the foundation pit excavation range, and set vertical drainage body 15 and vertical reinforcement body 16 in the soil outside the foundation pit excavation range according to the design range in the construction drawing, the top elevation of the vertical drainage body 15 and the vertical reinforcement body 16 is not lower than the top elevation of the column pile 14, the bottom elevation of the vertical reinforcement body 16 is lower than the bottom elevation of the maximum excavation depth of the foundation pit 12, and the bottom elevation of the vertical drainage body 15 is higher than the elevation of the interface between the clay layer 18 and the sandy soil layer 19;

[0061] Step S3, vertically set the peripheral vertical airtight curtain 4 from the ground surface 1 to the bottom of the pit outside the boundary of the setting range of the vertical drainage body 15 and the vertical reinforcement body 16;

[0062] Step S4, set the grouting bag 3 in the foundation between the peripheral vertical airtight curtain 4 and the existing building 2;

[0063] Step S5, set the horizontal drainage body 7 at the top of the distribution range of the vertical drainage body 15, ensure that the top end of the vertical drainage body 15 is inserted into the horizontal drainage body 7 and communicates with the horizontal drainage body 7, and arrange the grid-shaped distributed vacuum filter pipe inside the horizontal drainage body 7;

[0064] Step S6, lay the horizontal airtight layer 5 on the top surface of the horizontal drainage body 7, and seal and connect the edge of the horizontal airtight layer 5 with the top of the peripheral vertical airtight curtain 4;

[0065] Step S7, connect the vacuum filter pipe set in step S5 to the vacuum pressure source through the vacuum pipe penetrating the horizontal airtight layer 5, and seal the joint between the vacuum pipe and the horizontal airtight layer 5;

[0066] Step S8, start the vacuum pressure source, and after the consolidation degree of the foundation soil under the horizontal airtight layer 5 meets the requirements of the surcharge (in this embodiment, the consolidation degree is required to reach 50%), set a layer of 400g / m 2 The geotextile protects the horizontal airtight layer 5, and then the surcharge 6 is added in three stages, each stage is 1m high, and the time interval of each stage is 1 week;

[0067] Step S9, continuously vacuumize through the vacuum pressure source, and after the consolidation degree of the foundation soil meets the excavation requirements (in this embodiment, the consolidation degree of the foundation soil reaches 70% under the condition of 3m high surcharge), remove the surcharge 6, cut the horizontal airtight layer 5 in the foundation pit excavation range, seal and connect the slope airtight layer 11 on the cut part to the horizontal airtight layer 5, bury the connected part of the slope airtight layer 11 in the sealed trench for sealing and burying, and excavate the foundation pit under the condition of continuous vacuumization;

[0068] Step S10, every time a certain depth is excavated (in this embodiment, the depth of each excavation is set to 1m, so that the sealing effect can be considered without obvious loss, and the construction efficiency can be considered), the slope sealing layer 11 is taken out from the sealing trench and covered on the newly excavated pit wall, and then the slope sealing layer 11 is buried in the newly excavated sealing trench for storage;

[0069] Step S11, continue to excavate according to the method described in step S10 until the depth reaches the design elevation of the next inner support system, weld the force transmission rod 8 to the column pile 14 at the corresponding elevation position, pass the force transmission rod 8 through the slope sealing layer 11, and seal the connection part of the force transmission rod 8 and the slope sealing layer 11, then set the enclosing purlin 9 at the cantilever end of each force transmission rod 8, and set the cross brace 10 on the enclosing purlin 9, wherein the enclosing purlin 9 needs to be separated from the slope sealing layer 11, the column pile 14, the force transmission rod 8, the enclosing purlin 9 and the cross brace 10 form an inner support system, and form an organic linkage with the vacuum support structure, which provides sufficient safety guarantee for the vertical excavation of the deep foundation pit under the premise of the non-continuous form pit wall solidification wall;

[0070] Step S12, when the excavation depth exceeds the interface between the clay layer 18 and the sandy soil layer 19, the slope sealing layer 11 needs to be laid on the corresponding pit wall of the exposed sandy soil layer 19 and the vacuum nail 17 needs to be added, the vacuum nail 17 penetrates the slope sealing layer 11 and extends into the sandy soil layer 19 inside the pit wall, the horizontal insertion depth of the vacuum nail 17 does not exceed the horizontal setting position of the outer peripheral vertical sealing curtain 4, the connection part of the vacuum nail 17 and the slope sealing layer 11 is sealed, and the outer end of the vacuum nail 17 is connected to the vacuum pressure source through the vacuum pipeline;

[0071] Step S13, continue to excavate according to the method described in step S12, when the excavation depth reaches the design elevation of the inner support system, set the inner support system according to the method described in step S11, until the excavation reaches the maximum excavation depth of the pit bottom 12, and during the whole process of steps S9-S13, the settlement of the existing building 2 is monitored, when the foundation of the existing building 2 deforms greatly, grouting operation needs to be carried out on the grouting bag 3 to control the settlement and horizontal deformation of the surrounding environment foundation, and ensure the safety of the surrounding environment;

[0072] Step S14, set the slope bottom vertical sealing curtain 13 at the slope foot of the pit bottom, and seal and connect the lower end edge of the slope sealing layer 11 to the top of the slope bottom vertical sealing curtain 13, wherein the top elevation of the slope bottom vertical sealing curtain 13 needs to be higher than the elevation of the maximum excavation depth pit bottom 12;

[0073] Step S15, pour the pit bottom plate, and construct the underground part of the permanent structure until the height of the permanent structure exceeds the ground surface 1 of the pit top;

[0074] Step S16, with the construction progress of the permanent structure, first remove and recycle the slope bottom vertical sealing curtain 13, then remove and recycle the slope surface sealing layer 11, vacuum nails 17 and each level of internal support system, and backfill the foundation pit, until the pit top ground 1 elevation is reached, then stop vacuumizing, then remove and recycle the horizontal sealing layer 5, the peripheral vertical sealing curtain 4 and the vertical reinforced body 16, and the foundation pit support and excavation work is completed.

[0075] After the vacuum pressure source works, the ground soil becomes more compacted as the air and water in the ground soil are extracted, but the shrinkage deformation of the ground soil also affects the surrounding soil, causing different degrees of shrinkage settlement of the surrounding soil, which adversely affects the safety of the existing building 2, so it is necessary to reduce this impact as much as possible in actual construction. The present application improves the permanent strength of the soil outside the foundation pit through vacuum consolidation, and improves the temporary strength of the soil through the increase of the effective stress of the soil caused by the negative pressure of the soil pores. The soil with strengthened permanent strength and temporary strength is tightly combined with the vertical reinforced body 16 to form a "reinforced soil" with vertical reinforcement, which can greatly improve the self-stability of the side wall of the foundation pit. At the same time, the internal support support system is organically combined without damaging the slope surface sealing layer 11, so that the stability of the pit wall is guaranteed by the synergistic effect of the self-stability of the soil after strengthening and the support force provided by the internal support system, supporting the non-sloping excavation with an excavation depth of more than 10m and vertical excavation without ground wall. Compared with the support method of bored pile or ground wall with internal support, the cost advantage and time advantage are obvious. Moreover, vacuum water extraction and slope surface sealing layer 11 also have the functions of water stopping and dewatering, without the need for additional water stopping and dewatering measures. At the same time, the setting of the vertical reinforced body 16 and the load body 6 can effectively offset the shrinkage deformation of the soil outside the foundation pit caused by the vacuum effect, preventing the vacuum support and excavation process of the foundation pit from affecting the adjacent existing building 2. The setting of the grouting capsule 3 can be used as a further insurance measure to control the settlement and horizontal deformation of the surrounding environment foundation when the foundation of the surrounding existing building 2 deforms greatly, ensuring the safety of the surrounding environment.

[0076] The original design of this foundation pit project uses the sinking well method for construction, and the cost of the permanent structure that can be combined is 21 million yuan, and the construction period is 12 months. The cost of the present application is only 880,000 yuan, and the construction period is 5.5 months, which is less than half of the original design in terms of cost and construction period, and has very significant economic benefits.

[0077] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A vacuum-supported excavation method suitable for deep foundation pits in complex strata adjacent to existing buildings, characterized in that, Comprising the following steps: Step S1, setting a column pile (14) in the soil near the excavation face in the pit wall outside the foundation pit excavation range, the bottom elevation of the column pile (14) is lower than the maximum excavation bottom (12) elevation of the foundation pit; Step S2, setting a vertical drainage body (15) in the soil of the foundation pit excavation range, and setting a vertical drainage body (15) and a vertical reinforcement body (16) in the soil outside the foundation pit excavation range according to the design range in the construction drawing, the top elevation of the vertical drainage body (15) and the vertical reinforcement body (16) is not lower than the top elevation of the column pile (14), the bottom elevation of the vertical reinforcement body (16) is lower than the maximum excavation bottom (12) elevation of the foundation pit, and the bottom elevation of the vertical drainage body (15) is higher than the elevation of the interface between the cohesive soil layer (18) and the sandy soil layer (19); Step S3, vertically setting an outer peripheral vertical airtight curtain (4) from the ground surface (1) to the bottom of the boundary outside the setting range of the vertical drainage body (15) and the vertical reinforcement body (16); Step S4, setting a grouting bag (3) in the foundation between the outer peripheral vertical airtight curtain (4) and the existing building (2); Step S5, setting a horizontal drainage body (7) at the top of the vertical drainage body (15) distribution range, ensuring that the top end of the vertical drainage body (15) is inserted into the horizontal drainage body (7) and communicates with the horizontal drainage body (7), and a grid-shaped distribution of vacuum filter pipes is arranged inside the horizontal drainage body (7); Step S6, laying a horizontal airtight layer (5) on the top surface of the horizontal drainage body (7), and sealing and connecting the edges of the horizontal airtight layer (5) with the top of the outer peripheral vertical airtight curtain (4); Step S7, connecting the vacuum filter pipes set in step S5 to a vacuum pressure source through vacuum pipes penetrating the horizontal airtight layer (5), and sealing the joint between the vacuum pipes and the horizontal airtight layer (5); Step S8, starting the vacuum pressure source, and after the consolidation degree of the foundation soil below the horizontal airtight layer (5) meets the requirements of the surcharge, adding a surcharge (6) on the horizontal airtight layer (5); Step S9, continuously vacuuming through the vacuum pressure source, and after the consolidation degree of the foundation soil meets the excavation requirements, removing the surcharge (6), cutting the horizontal airtight layer (5) in the foundation pit excavation range, sealing and connecting the slope airtight layer (11) on the cut part to the horizontal airtight layer (5), burying the connected part of the slope airtight layer (11) in the sealed trench for sealing and burying, and excavating the foundation pit under the condition of continuous vacuuming; Step S10, every time a certain depth is excavated, the slope airtight layer (11) is taken out from the sealed trench and covered on the newly excavated foundation pit wall, and then the slope airtight layer (11) is buried in the newly excavated sealed trench for storage; Step S11, continue to excavate to the depth of the inner support system design elevation according to the method of step S10, and weld the force transmission rod (8) to the column pile (14) at the corresponding elevation position, pass the force transmission rod (8) through the slope sealing layer (11), and seal the connection part of the force transmission rod (8) and the slope sealing layer (11), then set the enclosing purlin (9) at the cantilever end of each force transmission rod (8), and set the cross brace (10) on the enclosing purlin (9), wherein the enclosing purlin (9) needs to be separated from the slope sealing layer (11); Step S12, when the excavation depth exceeds the interface between the clay layer (18) and the sandy soil layer (19), the slope sealing layer (11) needs to be laid on the corresponding pit wall of the exposed sandy soil layer (19), and the vacuum nail (17) is additionally arranged, the vacuum nail (17) penetrates through the slope sealing layer (11) and extends into the sandy soil layer (19) on the inner side of the pit wall, the transverse insertion depth of the vacuum nail (17) does not exceed the horizontal arrangement position of the outer vertical sealing curtain (4), the sealing treatment is performed on the combined part of the vacuum nail (17) and the slope sealing layer (11), and the outer end of the vacuum nail (17) is connected to the vacuum pressure source through the vacuum pipeline; Step S13, continue to excavate according to the method of step S12, when the excavation depth reaches the design elevation of the inner support system, set the inner support system according to the method of step S11, until the maximum excavation depth of the foundation pit, and monitor the settlement of the existing building (2) during the whole process of steps S9-S13, when the foundation of the existing building (2) deforms greatly, grouting operation needs to be performed on the grouting bag (3) to control the settlement and horizontal deformation of the surrounding environment foundation, and ensure the safety of the surrounding environment; Step S14, set the slope bottom vertical sealing curtain (13) at the slope foot of the foundation pit bottom, and seal and connect the lower end edge of the slope sealing layer (11) to the top of the slope bottom vertical sealing curtain (13), wherein the top elevation of the slope bottom vertical sealing curtain (13) needs to be higher than the elevation of the maximum excavation depth bottom (12); Step S15, pour the foundation pit bottom plate, and construct the underground part of the permanent structure, until the height of the permanent structure exceeds the ground (1) of the pit top; Step S16, with the construction progress of the permanent structure, first remove and recycle the slope bottom vertical sealing curtain (13), then remove and recycle the slope sealing layer (11), the vacuum nail (17) and the inner support system at each level in sequence, and backfill the foundation pit trench until the elevation of the ground (1) of the pit top, stop vacuumizing, then remove and recycle the horizontal sealing layer (5), the outer vertical sealing curtain (4) and the vertical reinforcing body (16), and the foundation pit supporting and excavating work is completed.

2. The vacuum-supported excavation method suitable for deep foundation pit adjacent to existing building complex stratum according to claim 1, characterized in that: The heap loader (6) is implemented by filling soil, and the heap loader (6) is added to the horizontal sealing layer (5) in a step-by-step manner.

3. The vacuum supported excavation method suitable for deep foundation pit adjacent to existing building complex stratum according to claim 2, characterized in that: The horizontal sealing layer (5) and the slope sealing layer (11) are both in the form of double-layer geomembrane, and the upper and lower sides of the horizontal sealing layer (5) and the inner and outer sides of the slope sealing layer (11) are both paved with geotextile.

4. The vacuum-supported excavation method suitable for deep foundation pit adjacent to existing building complex stratum according to claim 1, characterized in that: The peripheral vertical sealing curtain (4) and the slope bottom vertical sealing curtain (13) are arranged in the form of one of a steel sheet pile and a geomembrane.

5. The method according to claim 1, wherein the method is adapted for deep excavation of a complex ground stratum adjacent to an existing building. The vertical reinforcement body (16) is made of a threaded steel bar, the column pile (14), the surrounding purlin (9) and the cross strut (10) are made of an H-shaped steel, the force transmission rod (8) is made of a steel pipe, and the vacuum nail (17) is made of a steel pipe with a pipe wall punched and wrapped with a filter screen.

6. The method according to claim 1, wherein the method is adapted for deep excavation of a complex ground stratum adjacent to an existing building. The vertical drainage body (15), the vertical reinforcement body (16) and the vacuum nail (17) are arranged in a rectangular array or a triangular array.

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