Arch support supporting structure of large-span foundation pit, design method and construction method

Abstract

The invention relates to the technical field of foundation pit excavation and slope supporting engineering, and particularly discloses a large-span foundation pit skewback supporting structure, a design method and a construction method.The structure comprises a waterproof curtain, row piles, supporting piles, supporting beams, inner inclined struts, inclined throwing struts, support piers, top beams, waist beams and anti-floating pressure top beams; the straight edge of the large-span foundation pit adopts densely-arranged row piles or underground diaphragm walls for retaining soil, and multi-span arched sparse-arranged supporting piles are arranged on the inner side of the foundation pit to support the row piles or the underground diaphragm walls. The top beams and the waist beams of the row piles are linear sections, and the top beams and the waist beams of the supporting piles are arc-shaped; the inclined throwing supports transfer arch foot supporting force of the arc arch to the support piers; when the pit bottoms of the row piles and the supporting piles are silt, full-space-shaped or lattice-shaped stirring piles are arranged for reinforcement; internal force calculation and stability analysis are carried out according to a model with the row piles as the active side of the supporting structure and the multi-span skewback as the passive side. The method has the advantages that a large-span inner support is replaced by the multi-span arched support, materials are saved, and the construction period is shortened.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of foundation pit excavation and support engineering, and particularly relates to an arch support structure of a large-span foundation pit, a design method and a construction method. BACKGROUND

[0002] The problems of foundation pit excavation and support exist in building engineering basement, municipal and rail transit, road and bridge engineering, the support retaining structure usually adopts row piles or underground continuous walls, and anchor cables or internal supports are used to provide support reaction force. Due to the complex and variable shape of the land, basically irregular polygon, the design generally uses angle support at the corner and support structure form of counter support in the middle, but for large-span foundation pit, the counter support often has large span, and a plurality of columns need to be arranged on each support to bear, in addition to causing material waste, when high temperature and low temperature and other temperature mutations occur, the support structure shrinks or expands due to temperature stress, causing the foundation pit to collapse.

[0003] For large-span foundation pit, if the approximate square design scheme can adopt large circular arch + truss type inner support mode, rectangular can adopt double circular or multi-circular + truss type inner support mode, for irregular polygon, there is also local circular arch or curved arch + truss type inner support mode. The problem is that the large circular arch + truss type inner support mode has the advantages of no support inside the large circular arch, easy earth excavation, and the disadvantages of the support beam arrangement between the foundation pit side and the large circular arch being longitudinal and horizontal interlaced, and the number of vertical piles being more, the stress being complex, and the basement structure construction being greatly disturbed; there is another support form, which changes the straight line side of the large-span foundation pit into a curved arch side, for example, the invention patent (publication number CN10515554A) discloses a deep foundation pit of an arch support system, each side wall of the surrounding foundation pit is composed of a plurality of arch structure units, and inner support beams are arranged between the supports of the arch. The advantage is that the earth pressure of the side wall of the foundation pit is converted into the support reaction force of the support of the arch, and the disadvantage is that a large number of support rows of piles are increased on the arch side than on the straight line side, which not only increases the engineering quantity, but also increases the number of joints between the rows of piles, and increases the risk of water gushing; the invention patent (publication number CN107740426A) discloses a fabricated multi-arch wall foundation pit support structure and construction process, the structure includes a prefabricated concrete arch piece and a special-shaped "mountain" steel pile, when the foundation pit is shallow, a cantilever pile support system is adopted, when the foundation pit is deep, a pull anchor or an inner support can be added, the advantage is to utilize the arch structure, and the disadvantage is that the joints between the prefabricated concrete arch pieces have the risk of leakage, and the arch shape is towards the non-trench side, which increases the earthwork excavation amount, the earth pressure of the foundation pit is all transferred to the arch foot, the support force of the arch foot is all borne by the earth reaction force when cantilevered, the deformation is too large, when the inner support is adopted, the earth pressure is all applied to the support or a anchor cable, if one support loses stability or the anchor cable is pulled out, the foundation pit has the risk of collapse; the invention patent (publication number CN109235447A) discloses a horizontal arch shell foundation pit support device, which is composed of a wall column pile wall, two ends of adjacent two arc shapes share a support pier, and a plurality of layers of arch frame beams are arranged longitudinally between adjacent two support piers, which has the problems of CN10515554A and CN109235447A. As for the invention patent (publication number CN110387889A) discloses a multi-arch foundation pit support method for long strip foundation pit, the support span is small, and it is more unnecessary to do so, the straight line side of the long strip side is intentionally changed into a multi-arch side, which greatly increases the engineering quantity of the support row of piles compared with the support beam engineering quantity of the short side, which is really unnecessary. The common problem of the above methods is that the design calculation method has not been solved. SUMMARY

[0004] In view of the problems in the prior art, the present application provides an arch support structure, a design method and a construction method for a large-span foundation pit.

[0005] In a first aspect, the application provides an arch support structure and design method for a large-span foundation pit, comprising a water stop curtain (103), a row pile (1), a support pile (2), a support beam (3), an inner diagonal brace (4), an inclined throw brace (5), a support pier (802), an anti-floating pressure roof beam (9);

[0006] The row pile (1) is arranged densely and comprises a first crown beam (101) and a first waist beam (102), and is arranged on a straight side of the large-span foundation pit. The first waist beam (102) is arranged on the side of the pile.

[0007] The support pile (2) is arranged sparsely and comprises a second crown beam (201) and a second waist beam (202). The second crown beam (201) and the second waist beam (202) are circular arc arches and are connected with the inclined throw brace (5). The inclined throw brace (5) transfers the arch foot support force to the support pier (802). The second waist beam (202) intersects with the support pile (2).

[0008] The intersection of two adjacent circular arc arches is the arch foot. The upper end of the inclined throw brace (5) is connected with the arch foot of the circular arc arch, and the lower end is connected with the support pier (802). The inclined throw brace anchoring rib (501) and the support pier closure hoop (803) are anchored in the bottom plate (801) of the basement.

[0009] The support beam (3) is arranged between the row pile (1) and the support pile (2) to connect them.

[0010] Optionally, the row pile (1) or the underground continuous wall arranged on one side of the large-span foundation pit is arranged in a straight line. The first crown beam (101) and the first waist beam (102) of the row pile (1) or the underground continuous wall are straight line segments.

[0011] Optionally, the span of the circular arc arch is not less than 10.0 m. When the distance between the basement outer wall (8) and the site building red line is sufficient to arrange the support pile (2), the support pile (2) is arranged outside the basement outer wall (8), and the arch foot is close to the basement outer wall (8). After the completion of the basement construction, the support pile (2) is not removed and serves as part of the basement anti-floating structure. When the distance between the basement outer wall (8) and the site building red line is insufficient to arrange the support pile (2), part of the support pile (2) is arranged inside the basement. After the completion of the basement construction, the support pile (2) located inside the basement is removed.

[0012] Optionally, the inner diagonal brace (4) is arranged between the row pile (1) and the support pile (2) and is connected with the first waist beam (102) of the row pile (1) and the second waist beam (202) of the support pile (2).

[0013] Optionally, the width of the counterpressure soil (602) reserved at the bottom of the large-span foundation pit is such that the horizontal included angle of the inclined throw brace (5) is not greater than 60°.

[0014] Optionally, the support pile (2) is a reinforced concrete structure or a combination structure of steel and concrete, and the cross section is rectangular, and the long side of the rectangle is perpendicular to the foundation pit side of the row pile (1).

[0015] Optionally, when the basement outer wall is close to the arch foot support pile (2) of the circular arc, the basement outer wall and the support (2) pile of the circular arc arch foot are reliably connected through the anti-floating pressure roof beam (9) and the anchoring rib (901).

[0016] In a second aspect, the embodiments of the present application provide a design method of an arch support structure of a large-span foundation pit, which is suitable for an arch support structure of a large-span foundation pit. Internal force calculation is performed according to a model in which the row pile (1) is the active side and the support pile (2) of the multi-span arch is the passive side. The passive earth pressure of the support pile (2) and the counterforce of the support pier (802) are in a balanced state with the active earth pressure of the row pile (1). The row pile (1) transmits horizontal force to the support pile (2) through the support beam (3). The arch foot force is transmitted to the support pier (802) and the bottom plate of the basement through the inclined throw support (5).

[0017] Optionally, in combination with the second aspect, in some embodiments, the arch support structure system of one span is regarded as a unit to perform anti-sliding stability checking and anti-overturning stability checking.

[0018] In a third aspect, the present application provides a construction method of an arch support structure of a large-span foundation pit, which includes the following steps:

[0019] S1: construction of the water stop curtain (103), the row pile (1), the support pile (2), the first crown beam (101) of the row pile, and the second crown beam (201) of the support pile;

[0020] If the foundation pit bottom (601) is silt, the foundation between the row pile (1) and the support pile (2) is reinforced to form a reinforced area (10) of the foundation;

[0021] S2: excavation of earthwork to the bottom surface (6) of the -1 layer, construction of the first waist beam (102) of the row pile, the second crown beam (201) of the support pile, and the first support beam (3);

[0022] S3: excavation to the bottom surface (6) of the -2 layer, construction of the second first waist beam (102), the support beam (3), and the inner inclined brace (4);

[0023] S4: middle excavation to the bottom surface (601) of the -3 layer, reservation of the counterpressure soil (602) between the row pile (1) and the support pile (2), pouring of the central area bottom plate (801), and installation of the inclined throw support (5) of the arch foot;

[0024] S5: excavate counter-pressure soil (602), the first waist beam (102), the support beam (3) and the inner inclined brace (4) corresponding to the construction bottom plate;

[0025] S6: pour the bottom plate cushion layer (7), the bottom plate (801), the outer wall structure (801) and the anti-floating pressure top beam (9) of the construction basement periphery;

[0026] S7: remove the support pile (2) located in the basement;

[0027] S8: the foundation pit side wall is backfilled with soil in layers and compacted, if the basement is more than 3 layers, repeat S3 and S4 until the bottom plate and backfill earthwork are completed.

[0028] Compared with the prior art, the beneficial effects of the present application are:

[0029] 1) For sites with large foundation pit span and strict environmental protection requirements, the present application uses a multi-span arch support structure to replace a large-span internal support structure, which can greatly reduce the amount of internal support and supporting column pile materials and save engineering costs.

[0030] 2) Compared with the arch-shaped support on the side of the foundation pit, the linear side arrangement of support row piles or underground continuous walls greatly reduces the engineering quantity compared with the curved side arch-shaped dense row piles or arch-shaped underground continuous walls, thereby reducing the engineering cost.

[0031] 3) The multi-span arch support structure of the present application is only arranged on the periphery of the large-span foundation pit, and the large area in the middle of the foundation pit is a non-supporting area, so the excavator operation is convenient when excavating earthwork, and the earthwork period is shortened.

[0032] 4) The support structure on the periphery of the foundation pit is connected with the outer wall of the basement, becoming part of the anti-floating structure of the basement, thereby reducing the number of anti-floating engineering piles. BRIEF DESCRIPTION OF DRAWINGS

[0033] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and those skilled in the art can obtain other drawings according to these drawings without creative labor.

[0034] Figure 1 A circular arc arch support structure plan view in an arch support structure of a large-span foundation pit according to an embodiment of the present application;

[0035] Figure 2 A first layer support section view in an arch support structure of a large-span foundation pit according to an embodiment of the present application;

[0036] Figure 3 A second layer support sectional view in an arch support structure of a large-span foundation pit according to an embodiment of the present application;

[0037] Figure 4 A diagonal throw support and support base sectional view in an arch support structure of a large-span foundation pit according to an embodiment of the present application;

[0038] Figure 5 A counter-pressure soil excavation and support sectional view in an arch support structure of a large-span foundation pit according to an embodiment of the present application;

[0039] Figure 6 A basement structure and support connection sectional view in an arch support structure of a large-span foundation pit according to an embodiment of the present application;

[0040] Figure 7 A foundation pit side wall backfilling view in an arch support structure of a large-span foundation pit according to an embodiment of the present application;

[0041] Figure 8 An abutment structure general view of an arch in an arch support structure of a large-span foundation pit according to an embodiment of the present application;

[0042] Figure 9 An arch-shaped support pile and waist beam, connecting beam, and anchoring bar general view in an arch support structure of a large-span foundation pit according to an embodiment of the present application;

[0043] Figure 10 A diagonal throw support and support base connection general view in an arch support structure of a large-span foundation pit according to an embodiment of the present application

[0044] Figure 11 A soft soil base reinforcement sectional view in an arch support structure of a large-span foundation pit according to an embodiment of the present application

[0045] Figure 12 A soft soil base reinforcement mixing pile arrangement general view in an arch support structure of a large-span foundation pit according to an embodiment of the present application;

[0046] Figure 13 A calculation unit stress plane view in an arch support structure of a large-span foundation pit according to an embodiment of the present application;

[0047] Figure 14 A calculation unit stress sectional view in an arch support structure of a large-span foundation pit according to an embodiment of the present application;

[0048] Figure 15 An overall stability checking schematic view in an arch support structure of a large-span foundation pit according to an embodiment of the present application.

[0049] Wherein, the reference signs are as follows: 1-pile row, 101-first crown beam, 102-first waist beam, 103-water stop curtain, 2-support pile, 201-second crown beam, 202-second waist beam, 203-waist beam anchoring steel bar, 3-support beam, 301-continuous beam anchoring steel bar, 4-inner diagonal brace, 5-inclined throw brace, 501-inclined throw brace anchoring steel bar, 6-excavation surface, 601-bottom surface of foundation pit, 602-counterpressure soil, 7-bottom plate cushion layer, 8-basement outer wall, 801-bottom plate of basement, 802-supporting pier, 803-supporting pier closed hoop, 9-anti-floating pressure roof beam, 901-anchoring steel bar of anti-floating pressure roof beam, 10-reinforcement area of pile row and support pile bottom. DETAILED DESCRIPTION

[0050] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0051] The arch support structure and design method of the large-span foundation pit in the embodiment of the present application are shown in the drawings as follows, Figures 1 to 15 The straight edge of the large-span foundation pit adopts the pile row 1 or the underground continuous wall to stop soil, and the inner side of the foundation pit is provided with multi-span arch-shaped support piles 2 to support the pile row or the underground continuous wall. The crown beam 101 and the waist beam 102 of the pile row are straight segments, and the crown beam 201 and the waist beam 202 of the support pile are circular arc arches. The inclined throw brace 5 transfers the support force of the arch foot of the circular arc arch to the supporting pier 802. When the pit bottom is silt soft soil, the pit bottom of the pile row and the support pile is arranged with full-tower type or lattice type mixing pile reinforcement.

[0052] In the embodiment of the present application, the pile row 1 is densely arranged, the support pile 2 is sparsely arranged, the top of the pile row and the support pile is provided with a crown beam, the waist beam 102 of the pile row is arranged on the side of the pile, and the waist beam 202 of the support pile intersects with the support pile.

[0053] In the embodiment of the present application, the intersection of the two adjacent circular arc arches is the arch foot, the upper end of the inclined throw brace 5 is connected to the arch foot of the circular arc arch, the lower end is connected to the supporting pier 802, and the inclined throw brace anchoring steel bar 501 and the supporting pier closed hoop 803 are anchored in the bottom plate 801 of the basement.

[0054] In the embodiment of the present application, the active side soil and water pressure of the pile row 1 is transferred to the support of the arch and the support pile 2, and the horizontal load is shared by the bottom plate under the supporting pier and the support pile.

[0055] Specifically, asFigure 1 and Figure 8 As shown, the piles 1 or diaphragm wall on one side of the foundation pit are arranged in a straight line, and the capping beam 101 and waist beam 102 of the piles or diaphragm wall are straight segments; the capping beam 201 and waist beam 202 of the support piles are circular arches, and the support piles 2 are arranged on the circular arches. The spacing of the support piles is determined by the horizontal bearing capacity calculation, and the support beams 3 are set between the piles and the support piles.

[0056] Optionally, the piles (1) or underground continuous wall on the straight edge of the foundation pit are arranged in a straight line, and the capping beam (101) and waist beam (102) are straight segments; the arched structure span of the support piles (2) is not less than the conventional design value. When site conditions permit, the support piles (2) are arranged on the outside of the basement exterior wall (8) and connected to the anti-buoyancy pressure beam (9) as an anti-buoyancy structure; when the site is limited, the support piles (2) are partially arranged in the basement and can be removed.

[0057] Optionally, the angle between the inclined bracing (5) and the horizontal plane is controlled by the pre-reserved counterweight soil (602) at the bottom of the foundation pit. The width of the counterweight soil is not less than a reasonable multiple of the distance between the pile (1) and the support pile (2) to ensure that the angle of the inclined bracing meets the mechanical transmission requirements.

[0058] The embodiments of the present invention do not limit the span of the circular arch, but preferably, such as Figure 8 As shown, the span of the circular arch is not less than 10.0m. When the distance between the basement exterior wall 8 and the site building boundary line is sufficient to accommodate the support piles 2, the span of the circular arch is taken as the larger value. The support piles 2 are arranged on the outside of the basement exterior wall 8, with the arch foot close to the basement exterior wall 8. After the basement construction is completed, the support piles 2 are not removed and are used as part of the basement's anti-buoyancy structure. When the distance between the basement exterior wall 8 and the site building boundary line is insufficient to accommodate the support piles 2, the span of the circular arch is taken as the smaller value. The support piles 2 are partially arranged inside the basement. After the basement construction is completed, the support piles 2 located inside the basement are removed.

[0059] Furthermore, as one implementation method, the traditional circular arch can be optimized into a variable cross-section parabolic arch, resulting in a more uniform distribution of bending moment within the arch body and reducing stress concentration at the cross-section compared to a circular arch. The support piles can also employ a composite structure of "steel frame + fiber reinforced concrete," with prestressed steel strands arranged on the tension side of the support pile. Taking a support pile with a cross-section of 500mm × 800mm as an example, after prestressing, the initial compressive stress in the pile body reaches 5MPa, which can resist 80% of the tensile stress during the excavation stage, reducing crack width to below 0.1mm. The steel frame uses Q355B hot-rolled H-beams (H400×300×10×16), working in conjunction with the concrete to increase bending stiffness by 40%.

[0060] Specifically, such as Figures 3 to 8As shown, the inner diagonal brace 4 is set between the pile 1 and the support pile 2, and is connected to the waist beam 102 of the pile and the waist beam 202 of the support pile, transforming the rectangular support structure into a triangular support system, making the support structure more stable.

[0061] Preferred, such as Figure 4 As shown, the width of the pre-reserved counterweight soil 602 at the bottom of the foundation pit ensures that the horizontal angle of the inclined brace 5 is no greater than 60°. Preferably, the angle between the inclined brace (5) and the horizontal plane is 45° to reduce the vertical component of the load on the inclined brace.

[0062] Specifically, the support pile 2 is a reinforced concrete structure or a steel and concrete composite structure along its entire length, with a rectangular cross-section and its long side perpendicular to the edge of the foundation pit of pile 1, thereby improving the bending resistance of the support pile. The steel and concrete composite structure can also adopt a "steel skeleton + fiber concrete" composite structure, with prestressed steel strands arranged on the tension side of the support pile to improve the bending resistance of the composite section.

[0063] Preferred, such as Figure 6 As shown, when the basement exterior wall 8 is close to the arch support pile, the basement exterior wall 8 and the arch support pile 2 are reliably connected through the anti-buoyancy pressure top beam 9 and the anchoring bar 901, so that the pile and support pile become part of the basement anti-buoyancy structure.

[0064] Optionally, the support pile (2) adopts a composite structure, and its cross-sectional shape is designed as a rectangle with the long side perpendicular to the edge of the foundation pit to improve the bending resistance; the basement exterior wall (8) and the arch foot support pile (2) are connected by an anti-buoyancy pressure top beam (9) and anchoring bars (901) to form an anti-buoyancy integrated system.

[0065] Optionally, the piles (1) or underground continuous wall on the straight edge of the foundation pit are arranged in a straight line, and the capping beam (101) and waist beam (102) are straight segments; the arched structure span of the support piles (2) is not less than the conventional design value. When site conditions permit, the support piles (2) are arranged on the outside of the basement exterior wall (8) and connected to the anti-buoyancy pressure beam (9) as an anti-buoyancy structure; when the site is limited, the support piles (2) are partially arranged in the basement and can be removed.

[0066] In this embodiment of the invention, specifically, the internal forces are calculated using a model with pile 1 as the active side and multi-span arched support piles as the passive side. The passive earth pressure of the support piles 2 and the reaction force of the support piers are in equilibrium with the active earth pressure of the piles. The piles transmit the horizontal force to the support piles through the support beams, and the arch foot force is transmitted to the support piers 802 and the bottom plate 801 through the inclined bracing 5, satisfying the static equilibrium condition. The internal forces of the support structure are then calculated.

[0067] (1) Calculation model of internal forces of arched support structure and retaining piles in deep foundation pit

[0068] like Figure 13 ,Figure 14 As shown, the passive earth pressure of the support piles and the active earth pressure of the retaining piles are in equilibrium. The retaining piles transfer the horizontal force to the support piles through the support beams and internal diagonal braces, and the arch foot force is transferred to the abutment and base plate through the diagonal braces, satisfying the following equilibrium conditions:

[0069]

[0070] In the formula, F ij N represents the horizontal force (kN) at each support point within the range of a single supporting arch, and the supporting force of the j-th connecting beam in the horizontal direction is equal; N is the axial force (kN) of the inclined brace; p ak p bk E represents the standard value (kPa) of earth pressure acting on the active and passive zones of the retaining piles. ak E pk , respectively, represent the standard values ​​(kN / m) of the total active earth pressure and the total passive earth pressure acting on the support piles; L is the horizontal span (m) of a single support arch, L = xs; x is the number of connecting beams within the range of a single support arch; s is the horizontal spacing (m) of the connecting beams within the range of the support arch; α is the angle (°) between the inclined brace and the horizontal plane. n is a constant.

[0071] The retaining piles are considered as a vertical elastic foundation beam, and the calculated support force of the connecting beam is applied in reverse to the internal support system as a load. The retaining piles and the support structure are calculated separately and independently, and the deformation coordination conditions are met.

[0072] The reaction force of the connecting beam support obtained by the elastic method is applied to the support system. The support stiffness is based on the actual length (l0) of the inclined brace and takes into account the influence of the vertical angle.

[0073] 1) The bending capacity of the support pile and the shear capacity of the inclined section are calculated according to the bending and shear stress of the circular section concrete.

[0074] 2) The capping beam of the support piles can be reinforced according to structural requirements. Its web beams are calculated based on the reaction forces at the support points as an elastic multi-span continuous beam, with uniform distribution satisfying the following formula:

[0075] q = F ij / s(4)

[0076] 3) The embedment depth of the support piles shall be verified according to the vertical bearing capacity of the piles to meet the self-weight load of the support arch, connecting beam and internal diagonal bracing. The vertical pull-out bearing capacity of the piles shall meet the bearing requirements of the upward vertical component of the diagonal bracing.

[0077]

[0078] In the formula: R a R is the characteristic value (kN) of the vertical compressive bearing capacity of a single pile supporting the structure. atThe characteristic value of the pull-out bearing capacity of a single support pile (kN); N k G represents the standard value of the axial force of the inclined propeller (kN); kh +G k To support the self-weight (kN) of the arch, connecting beam, and internal diagonal bracing.

[0079] 4) The supporting pile ring crown and waist beam are subjected to stress analysis and calculation of cross-section and reinforcement according to the arch structure. The horizontal component of the arch foot (parallel to the support edge) is transmitted to the side wall of the foundation pit through the multi-arch structure, and the vertical component of the arch foot is transmitted to the lower support pier and the bottom plate of the central area set at the bottom of the foundation pit.

[0080] 5) The cross-section and reinforcement of the coupling beam are calculated based on the support reaction force as an axially compressed member.

[0081] In specific embodiments of the present invention, such as... Figure 15 As shown,

[0082] The anti-slip stability calculation is performed by treating a single-span arched support structure system as a single unit. The overturning stability calculation is also performed by treating a single-span arched support structure system as a single unit.

[0083] The present invention also includes an embodiment of an arch support structure for a large-span foundation pit, comprising the following construction steps:

[0084] S1: Construction of water-stop curtain 103, pile 1, support pile 2, first capping beam 101, second pile capping beam 201; if the bottom of the foundation pit 601 is silt, the base between pile 1 and support pile 2 is reinforced to form a reinforced area 10 of the base.

[0085] S2: Excavate the earthwork to the bottom surface of the -1 layer 6, and construct the first waist beam 102, the second pile cap beam 201 and the first support beam 3;

[0086] S3: Excavate to the bottom surface 6 of the -2 level, and construct the second waist beam 102, support beam 3 and inner diagonal brace 4;

[0087] S4: Excavate the middle section to the bottom surface 601 of the -3 level, reserve counter-pressure soil 602 between the pile and the support pile, pour the bottom plate 801 of the central area, and install the inclined bracing 5 of the arch foot.

[0088] S5: Excavate 602 of the counter-pressure soil, and construct the bottom slab waist beam 102, support beam 3 and internal diagonal brace 4;

[0089] S6: Pour the foundation slab cushion layer 7, construct the foundation slab 801 around the basement, the external wall structure 8, and the anti-buoyancy pressure top beam 9;

[0090] S7: Remove support pile 2 located in the basement;

[0091] S8: Backfill the sidewalls of the foundation pit with soil in layers and compact it.

[0092] If the basement is above the third floor, repeat steps S3 and S4 until the foundation slab and backfill are completed.

[0093] The present invention has been further described above with reference to specific embodiments. However, it should be understood that the specific description herein should not be construed as limiting the nature and scope of the present invention. Various modifications made to the above embodiments by those skilled in the art after reading this specification are all within the scope of protection of the present invention.

Claims

1. An arch support structure for a large-span foundation pit, characterized in that, Including water-stop curtain (103), piles (1), support piles (2), support beams (3), internal diagonal bracing (4), diagonal bracing (5), support piers (802), and anti-buoyancy pressure top beams (9); The piles (1) are arranged in a close arrangement, including a first cap beam (101) and a first waist beam (102), and are set on the straight side of the large span foundation pit. The first waist beam (102) is set on the side of the pile. The support piles (2) are sparsely arranged, including a second crown beam (201) and a second waist beam (202). The second crown beam (201) and the second waist beam (202) are circular arches and are connected to the inclined bracing (5). The inclined bracing (5) transfers the arch foot support force to the support pier (802). The second waist beam (202) intersects with the support piles (2). The intersection of two adjacent circular arches is the arch foot. The upper end of the inclined brace (5) is connected to the arch foot of the circular arch, and the lower end is connected to the support pier (802). The inclined brace anchor bar (501) and the support pier closing hoop (803) are both anchored in the basement floor slab (801). A support beam (3) is provided between the pile group (1) and the support pile (2) to connect them.

2. The arch support structure for a large-span foundation pit according to claim 1, characterized in that, The piles (1) or diaphragm wall on one side of the large-span foundation pit are arranged in a straight line, and the first cap beam (101) and the first waist beam (102) of the piles (1) or the diaphragm wall are straight segments.

3. The arch support structure for a large-span foundation pit according to claim 2, characterized in that, The span of the circular arch is not less than 10.0m. When the distance between the underground exterior wall (8) and the site building boundary line is sufficient to arrange support piles (2), the span of the circular arch is taken as the larger value. The support piles (2) are arranged on the outside of the basement exterior wall (8), and the arch foot is close to the basement exterior wall (8). After the basement construction is completed, the support piles (2) are not removed and are used as part of the basement anti-buoyancy structure. When the distance between the underground exterior wall (8) and the site building boundary line is insufficient to arrange support piles (2), the span of the circular arch is taken as the smaller value. The support piles (2) are partially arranged in the basement. After the basement construction is completed, the support piles (2) located in the basement are removed.

4. The arch support structure for a large-span foundation pit according to claim 3, characterized in that, The inner diagonal brace (4) is disposed between the pile group (1) and the support pile (2) and is connected to the first waist beam (102) of the pile group (1) and the second waist beam (202) of the support pile (2).

5. The arch support structure for a large-span foundation pit according to claim 4, characterized in that, The width of the counter-pressure soil (602) reserved at the bottom of the large-span foundation pit ensures that the horizontal angle of the inclined support (5) is no greater than 60°.

6. The arch support structure for a large-span foundation pit according to claim 5, characterized in that, The supporting pile (2) is a reinforced concrete structure or a combination of steel and concrete, and its cross-section is rectangular, with the long side of the rectangle perpendicular to the pit edge of the pile (1).

7. The arch support structure for a large-span foundation pit according to claim 6, characterized in that, When the basement exterior wall (8) is close to the support pile (2) of the arch foot of the arc, the basement exterior wall (8) and the support pile (2) of the arch foot of the arc are reliably connected by the anti-buoyancy top beam (9) and the anchor bar (901).

8. A design method for an arch support structure for a large-span foundation pit, applicable to the arch support structure for a large-span foundation pit as described in claim 1, characterized in that, The internal forces are calculated based on the model where the pile (1) is the active side and the multi-span arched support pile (2) is the passive side. The passive earth pressure of the support pile (2) and the reaction force of the support pier (802) are in equilibrium with the active earth pressure of the pile (1). The pile (1) transmits the horizontal force to the support pile (2) through the support beam (3), and the arch foot force is transmitted to the support pier (802) and the basement floor slab (801) through the inclined brace (5).

9. The design method for an arch support structure for a large-span foundation pit as described in claim 8, characterized in that, The arched support structure system of one span is treated as a single unit for anti-slip stability calculation and anti-overturning stability calculation.

10. A construction method for an arch support structure for a large-span foundation pit, characterized in that, Includes the following steps: S1: Construction of water-stop curtain (103), pile (1), support pile (2), first capping beam of pile (101), second capping beam of support pile (201); If the bottom of the foundation pit (601) is silt, the base between the pile (1) and the support pile (2) is reinforced to form a reinforced area (10) of the base; S2: Excavate the earthwork to the bottom surface of the -1 layer (6), construct the first waist beam (102) of the pile foundation, the second crown beam (201) of the support pile foundation and the first support beam (3); S3: Excavate to the bottom surface (6) of the -2 level, and construct the second first waist beam (102), the support beam (3) and the inner diagonal brace (4); S4: Excavate the bottom surface (601) of the middle section to the -3 level, reserve counter-pressure soil (602) between the pile (1) and the support pile (2), pour the bottom plate (801) of the central area, and install the inclined bracing (5) of the arch foot; S5: Excavate the counter-pressure soil (602), and construct the first waist beam (102), the support beam (3), and the inner diagonal brace (4) corresponding to the base plate; S6: Pour the base slab cushion layer (7), construct the base slab (801) around the basement, the external wall structure and the anti-buoyancy pressure top beam (9); S7: Remove the support piles located in the basement (2); S8: Backfill the foundation pit sidewalls in layers and compact the soil. If the basement has more than 3 floors, repeat S3 and S4 until the bottom slab and backfill are completed.

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