Construction method of small super-deep foundation pit using pre-steel support system

Abstract

The application discloses a construction method of a small-sized super-deep foundation pit using a front-arranged steel support system, and adopts a front-arranged steel support system which comprises a plurality of lattice columns, a plurality of connecting devices, a front-arranged steel support, a plurality of steel strands, a plurality of through-type jacks, a plurality of jack foundations, a plurality of steel strand guide frames, a plurality of servo oil cylinders and a hydraulic system. The front-arranged steel support system can realize the construction method of front-arranging concrete support or steel support and lowering and supporting simultaneously with excavation, effectively shortens the construction period and the time of over-excavation without support, and can effectively transfer the self-weight of the front-arranged steel support and the self-weight of the upper cast-in-place concrete to the ground and keep the front-arranged steel support horizontal through the adjustable angle support arranged on the steel support, and can guarantee that the servo oil cylinder is not subjected to vertical torsional force when supporting the underground continuous wall in the horizontal direction, thereby improving the construction safety and the rationality of equipment stress.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of construction machinery, and particularly relates to a construction method of a small super-deep foundation pit using a front-located steel support system. BACKGROUND

[0002] The small super-deep foundation pit (such as a subway end well) has the characteristics of small area, large depth, high deformation control requirement, etc., and usually adopts a support scheme of an underground continuous wall plus a steel support (or a concrete support).

[0003] However, the simple use of the traditional steel support (or concrete support) to support the underground continuous wall has the disadvantages and shortcomings of too long over-excavation time without support, inability to actively control the deformation of the underground continuous wall, and influence on the construction period due to the need to wait for the strength of the concrete support to reach the standard before excavation. SUMMARY

[0004] The present application aims to provide a construction method of a small super-deep foundation pit using a front-located steel support system, to solve the problems of too long over-excavation time without support, inability to actively control the deformation of the underground continuous wall, and influence on the construction period due to the need to wait for the strength of the concrete support to reach the standard before excavation in the prior art.

[0005] To solve the above technical problems, the present application provides the following technical scheme:

[0006] A construction method of a small super-deep foundation pit using a front-located steel support system, which adopts a front-located steel support system, the front-located steel support system comprising a plurality of lattice columns, a plurality of connecting devices, a front-located steel support, a plurality of steel strands, a plurality of through-type jacks, a plurality of jack foundations, a plurality of steel strand guide frames, a plurality of servo oil cylinders, and a hydraulic system, the front-located steel support comprising a steel enclosing purlin and a plurality of corner horizontal diagonal braces arranged at four corner portions of the steel enclosing purlin, a lattice column is correspondingly arranged on the inner side of the corner horizontal diagonal brace at each corner portion of the steel enclosing purlin, the lattice column is pre-pressed into the soil layer at the designed position, the corner horizontal diagonal brace at each corner portion of the steel enclosing purlin is connected to the corresponding lattice column through the corresponding connecting device, and the plurality of jack foundations are arranged at the four corner portion positions of the first layer ring beam of the continuous wall, respectively; the through-type jacks are arranged on the corresponding jack foundations; the steel strand guide frames are arranged on the corresponding jack foundations or the first layer ring beam of the continuous wall; the steel strands are arranged on the corresponding steel strand guide frames; the inner side surface of the steel enclosing purlin and the two side surfaces of the corner horizontal diagonal brace are respectively arranged with a plurality of adjustable struts at equal intervals by means of bolt connection; the hydraulic system is arranged on the first layer ring beam of the continuous wall, the ground, or the front-located steel support, the plurality of servo oil cylinders are arranged on the outer side surface of the steel enclosing purlin along the circumferential direction of the steel enclosing purlin, and the method comprises the following steps:

[0007] Step 1: Complete the pouring construction of the underground continuous wall and the first-floor ring beam of the continuous wall, press the lattice columns into the soil layer according to the design position, excavate the soil layer to a certain depth, pour a concrete pad layer on the soil layer, set up jack foundations on the first-floor ring beam of the continuous wall, and install through-hole jacks and steel strand guide frames.

[0008] Step 2: The components of the pre-positioned steel support are hoisted onto the concrete pad through the gap in the first-floor ring beam of the diaphragm wall, and the assembly of the pre-positioned steel support is completed. Steel strand anchors are distributed at the four corners of the steel waler of the pre-positioned steel support. Each through-hole jack is connected to the corresponding steel strand anchor on the pre-positioned steel support through the corresponding steel strand. The servo cylinders and the through-hole jacks are connected to the hydraulic system. The adjustable support feet are adjusted so that they extend and support the concrete pad. The adjustable support feet are finely adjusted to make the pre-positioned steel support horizontal. The servo cylinders are driven to extend through the hydraulic system to apply a certain pressure to the diaphragm wall and actively control the deformation of the diaphragm wall.

[0009] Step 3: Install concrete or steel supports above the pre-positioned steel supports at the designed positions, while continuing to excavate the soil layer. The pre-positioned steel supports enable simultaneous support and excavation, improving the efficiency of foundation pit construction.

[0010] Step 4: Excavate the soil layer to a certain depth and pour a concrete cushion layer on top of the soil layer;

[0011] Step 5: Drive the servo cylinder to retract via the hydraulic system, check the descent path of the front steel support to ensure it is unobstructed, drive the through-hole jack via the pressure system to lower the front steel support to a certain distance above the current concrete cushion, level the front steel support via the through-hole jack, adjust the adjustable support foot 54 to support it on the concrete cushion, and drive the servo cylinder to extend via the hydraulic system to apply a certain pressure to the diaphragm wall 1 to actively control the deformation of the diaphragm wall. Connect each lattice column to the corresponding corner horizontal diagonal brace via the connecting device to achieve support as excavation progresses, improve the construction efficiency of foundation pit excavation and support, reduce the time of over-excavation without support, and thus improve the safety of foundation pit construction.

[0012] Step 6: Repeat steps 3 to 5 until the excavation and support construction of the small ultra-deep foundation pit is completed, and dismantle the pre-positioned steel support at the bottom and lift its components away from the foundation pit.

[0013] Preferably, in the above-mentioned construction method for small ultra-deep foundation pits using a pre-installed steel support system, the connecting device includes a load-bearing triangular frame, a triangular frame support plate, two connecting angle steels, several welded nuts, several adjusting bolts, an adjusting support plate, two lattice column U-bolts, two lattice column connecting plates, four lattice column connecting nuts, a horizontal diagonal brace connecting plate, two horizontal diagonal brace U-bolts, and four horizontal diagonal brace connecting nuts. The load-bearing triangular frame is a right-angled triangular structure, having a horizontal plane and a vertical plane. The horizontal diagonal brace connecting plate is fixedly installed on the horizontal plane, and the triangular frame support plate is fixedly installed on the vertical plane. The horizontal diagonal brace connecting plate is perpendicular to the triangular frame support plate. The two connecting angle steels are respectively vertically installed on the left and right sides of the triangular frame support plate. The upper and lower parts of the two connecting angle steels are respectively provided with first through holes for the U-bolts of the lattice columns to pass through. After the two U-bolts of the lattice columns are clamped, they are connected by corresponding lattice column connecting plates and lattice column connecting nuts. The two sides of the horizontal brace connecting plate are respectively provided with a row of second through holes for the corresponding horizontal brace U-bolts to pass through. The two horizontal brace U-bolts are connected to the horizontal brace connecting plate and the corner horizontal brace by the corresponding horizontal brace connecting nuts. The upper and lower parts of the tripod support plate are respectively provided with a third through hole, and a threaded hole matching the adjusting bolt is provided at the third through hole. One end of the adjusting bolt passes through the corresponding threaded hole on the tripod support plate and is hinged to the adjusting support plate by ball joint. Rotating the adjusting bolt can move the corresponding adjusting support plate so that the adjusting support plate fits against the side of the lattice column.

[0014] Preferably, in the above-mentioned construction method for small ultra-deep foundation pits using a pre-installed steel support system, the load-bearing tripod includes two vertical members, two horizontal members, two diagonal members, and three horizontal members. The vertical members, horizontal members, and diagonal members are connected to form a triangular structure. The ends of the two triangular structures are connected by the three horizontal members. A horizontal diagonal brace connecting plate is placed on the upper part of the load-bearing tripod. The horizontal diagonal brace connecting plate is rigidly connected to the horizontal members and horizontal members of the tripod, respectively. The vertical members and horizontal members of the tripod are rigidly connected to the tripod support plate, so that the load-bearing tripod is supported on the tripod support plate.

[0015] Preferably, in the above-mentioned construction method for small ultra-deep foundation pits using a pre-positioned steel support system, each adjustable support plate is hinged to three adjusting bolts, and the three adjusting bolts are set at equal intervals along the horizontal direction.

[0016] Preferably, in the above-mentioned construction method for small ultra-deep foundation pits using a pre-positioned steel support system, the steel waler of the pre-positioned steel support includes several straight steel beams and four L-shaped corner steel beams. The several straight steel beams are assembled into four strip steel beams by bolt connection. The ends of the four strip steel beams are connected by L-shaped corner steel beams to form a rectangular steel waler. The strip steel beams and the corresponding L-shaped corner steel beams are connected by bolt connection. The two ends of the corner horizontal bracing are respectively connected to the inner wall of the steel waler through corner horizontal bracing connecting sections. Several parallel corner horizontal bracings are set at each corner of the steel waler. Several connecting beams are set on the two parallel corner horizontal bracings located on the inner side. Scaffold boards are laid on the corner horizontal bracings as working platforms.

[0017] Preferably, in the above-mentioned construction method for small ultra-deep foundation pits using a pre-installed steel support system, the connecting beam includes a connecting beam steel beam and two connecting beam end connecting plates. The two connecting beam end connecting plates are fixedly installed at both ends of the connecting beam steel beam. The two connecting beam end connecting plates are provided with through holes for connecting beam U-bolts to pass through. The corner horizontal diagonal bracing corresponding to the connecting beam U-bolt clamp is then fixed to the corresponding connecting beam end connecting plate by connecting beam connecting nuts.

[0018] Preferably, in the above-mentioned construction method for small ultra-deep foundation pits using a pre-installed steel support system, the corner horizontal bracing includes a corner bracing steel beam, two corner bracing end connecting plates, and several corner bracing foot connecting channel steels. The two corner bracing end connecting plates are respectively fixedly installed at both ends of the corner bracing steel beam. The corner bracing foot connecting channel steels are symmetrically arranged in pairs at equal intervals on both sides of the corner bracing steel beam along the longitudinal direction of the corner bracing steel beam. Bolt holes for connecting corresponding corner horizontal bracing connecting sections are opened on the two corner bracing end connecting plates. Several bolt holes for connecting corresponding adjustable corner braces are spaced apart on the corner bracing foot connecting channel steels.

[0019] Preferably, in the above-mentioned construction method for small ultra-deep foundation pits using a pre-installed steel support system, the corner horizontal brace connection section includes a connecting section steel beam, a connecting section corner brace connection plate, and a connecting section steel waler connection plate. The connecting section corner brace connection plate and the connecting section steel waler connection plate are respectively rigidly connected to both ends of the connecting section steel beam. The connecting section steel waler connection plate is obliquely arranged, and the connecting section corner brace connection plate is vertically arranged. Bolt holes for connecting the steel waler are opened on the connecting section steel waler connection plate, and bolt holes for connecting the corresponding corner horizontal brace are opened on the connecting section corner brace connection plate.

[0020] Preferably, in the above-mentioned construction method for small ultra-deep foundation pits using a pre-installed steel support system, the cross-section of the straight steel beam is H-shaped with double webs, formed by fixing the web of the straight steel beam to the flanges of the straight steel beams on both sides; the cross-section of the L-shaped corner steel beam is H-shaped with double webs, formed by fixing the web of the L-shaped corner steel beam to the flanges of the L-shaped corner steel beams on both the inner and outer sides; the web of the L-shaped corner steel beam has openings, and the steel strand anchors are installed at the openings, with stiffening plates installed on both sides of the steel strand anchors.

[0021] Preferably, in the above-mentioned construction method for small ultra-deep foundation pits using a pre-positioned steel support system, the servo cylinder includes a cylinder housing, an adjusting pad, a housing hook roller, and a cylinder body. The cylinder body is disposed within the cylinder housing. A vertical end plate is disposed at one end of the cylinder housing. An adjusting pad for adjusting the total elongation of the servo cylinder is disposed within the cylinder housing. The adjusting pad is located between the vertical end plate and the cylinder body. A downward-opening housing hook for attaching to the steel waler is disposed at the upper end of the vertical end plate. Several housing hook rollers are disposed between the vertical end plate and the housing hook. Bolt holes for connecting to the steel waler are opened on the vertical end plate.

[0022] As can be seen from the above-disclosed technical solutions, the beneficial effects of the present invention compared with the prior art are as follows:

[0023] This invention discloses a construction method for small-scale ultra-deep foundation pits using a pre-positioned steel support system. The pre-positioned steel support system includes several lattice columns, several connecting devices, pre-positioned steel supports, several steel strands, several through-hole jacks, several jack foundations, several steel strand guide frames, several servo cylinders, and a hydraulic system. The pre-positioned steel supports include a steel waler and several corner horizontal braces located at the four corners of the steel waler. At each corner of the steel waler, a lattice column is correspondingly installed on the inner side of the innermost corner horizontal brace. The lattice columns are pre-pressed into the soil at the designed positions. At each corner of the steel waler... The innermost corner horizontal bracing is connected to the corresponding lattice column via corresponding connecting devices. Several jack foundations are respectively set at the four corners of the first-floor ring beam of the diaphragm wall; through-hole jacks are set on the corresponding jack foundations; steel strand guide frames are set on the corresponding jack foundations or on the first-floor ring beam of the diaphragm wall; steel strands are laid on the corresponding steel strand guide frames; several adjustable bracing angles are equally spaced on the inner side of the steel waler and on both sides of the corner horizontal bracing via bolt connections; the hydraulic system is set on the first-floor ring beam of the diaphragm wall, the ground, or a front-mounted steel support; several servo cylinders are spaced along the circumference of the steel waler. On the outer side, the method includes the following steps: Step 1, complete the pouring construction of the underground continuous wall and the first-floor ring beam of the continuous wall, press the lattice column into the soil layer according to the design position, excavate the soil layer to a certain depth, and pour a concrete pad layer on the soil layer, and set up jack foundations on the first-floor ring beam of the continuous wall; and install through-hole jacks and steel strand guide frames; Step 2, hoist the components of the pre-positioned steel support to the concrete pad layer through the gap of the first-floor ring beam of the continuous wall, and complete the assembly of the pre-positioned steel support. Steel strand anchors are distributed at the four corners of the steel waler of the pre-positioned steel support, and each through-hole jack is connected to the pre-positioned steel support through the corresponding steel strand. The corresponding steel strand anchorages are connected, and the servo cylinders and the through-hole jacks are respectively connected to the hydraulic system. The adjustable support feet are adjusted so that they extend and support the concrete cushion layer. The adjustable support feet are finely adjusted to make the front-mounted steel support horizontal. The servo cylinders are extended through the hydraulic system to apply a certain pressure to the diaphragm wall and actively control the deformation of the diaphragm wall. Step 3: Concrete supports or steel supports are set above the front-mounted steel supports at the designed position. At the same time, the soil layer is excavated. The front-mounted steel supports enable excavation while supporting, which improves the construction efficiency of the foundation pit. Step 4: The soil layer is excavated to a certain depth, and a concrete cushion layer is poured on the top of the soil layer.Step 5: The servo cylinder is retracted via the hydraulic system, and the through-hole jack is driven by the pressure system to lower the front-mounted steel support to a certain distance above the current concrete cushion. The front-mounted steel support is leveled by the through-hole jack, and the adjustable support feet 54 are adjusted to support it on the concrete cushion. The servo cylinder is extended via the hydraulic system to apply a certain pressure to the diaphragm wall 1, thereby actively controlling the deformation of the diaphragm wall. Each lattice column is connected to the corresponding corner horizontal brace via a connecting device. Step 6: Steps 3 to 5 are repeated until the excavation and support construction of the small ultra-deep foundation pit is completed. The front-mounted steel support is then dismantled at the bottom layer, and its components are lifted out of the foundation pit. By adopting the front-mounted... The steel support system enables a construction method of excavation, lowering, and supporting simultaneously with the concrete or steel supports, effectively shortening the construction period and reducing the time spent without support during over-excavation. It boasts advantages such as high mechanization, strong construction safety, and high reusability. By employing a through-hole jack in conjunction with steel strands to raise and lower the front-mounted steel support as a whole, it offers advantages such as stable descent, safety, reliability, and good synchronization. Adjustable angle braces on the steel supports effectively transfer the self-weight of the front-mounted steel support and the self-weight of the poured concrete above to the ground, maintaining the front-mounted steel support horizontally. This also ensures that the servo cylinders are not subjected to vertical torsional forces when horizontally supporting the diaphragm wall, thereby improving construction safety and the rationality of equipment stress distribution. Attached Figure Description

[0024] Figure 1 This is a three-dimensional diagram of the construction status of the front-mounted steel support system in this invention.

[0025] Figure 2 This is a plan view of the construction status of the front-mounted steel support system in this invention.

[0026] Figure 3 This is a three-dimensional diagram of the front-mounted steel support system in this invention.

[0027] Figure 4 This is a three-dimensional diagram of the lattice column in this invention.

[0028] Figure 5 This is a front view of the connecting device in this invention.

[0029] Figure 6 This is a top view of the connecting device in this invention.

[0030] Figure 7 This is a side view of the connecting device in this invention.

[0031] Figure 8 This is a three-dimensional diagram of the connecting device in this invention.

[0032] Figure 9 This is a three-dimensional diagram of the straight section of the steel beam in this invention.

[0033] Figure 10This is a three-dimensional diagram of the L-shaped corner steel beam in this invention.

[0034] Figure 11 This is a three-dimensional diagram of the servo hydraulic cylinder in this invention.

[0035] Figure 12 This is a three-dimensional diagram of the adjustable support legs in this invention.

[0036] Figure 13 This is a three-dimensional diagram of the horizontal diagonal brace connection section at the corner of the present invention.

[0037] Figure 14 This is a plan view of the horizontal diagonal brace connection section at the corner in this invention.

[0038] Figure 15 This is a three-dimensional diagram of the horizontal diagonal brace at the corner of the present invention.

[0039] Figure 16 Three-dimensional diagram of the connecting beam in this invention.

[0040] Figure 17 This is a structural diagram of step 1 of a construction method for a small, ultra-deep foundation pit using a pre-installed steel support system.

[0041] Figure 18 This is a structural diagram of step 2 of a construction method for a small, ultra-deep foundation pit using a pre-installed steel support system.

[0042] Figure 19 This is a structural diagram of step 3 of a construction method for a small, ultra-deep foundation pit using a pre-installed steel support system.

[0043] Figure 20 This is a structural diagram of step 4 of a construction method for a small, ultra-deep foundation pit using a pre-installed steel support system.

[0044] Figure 21 This is a structural diagram of step 5 of a construction method for a small, ultra-deep foundation pit using a pre-installed steel support system.

[0045] Figure 22 This is a structural diagram of step 6 of a construction method for a small, ultra-deep foundation pit using a pre-installed steel support system.

[0046] In the picture:

[0047] 1. Diaphragm wall,

[0048] 2. First-floor ring beam of diaphragm wall,

[0049] 3. Lattice column; 31. Lattice column angle steel; 32. Angle steel connecting plate;

[0050] 4. Connection device between horizontal diagonal brace and lattice column; 401. Triangular frame support plate; 402. Connecting angle steel; 403. Welding nut; 404. Adjusting bolt; 405. Adjusting support plate; 406. Lattice column U-bolt; 407. Lattice column connecting plate; 408. Lattice column connecting nut; 409. Triangular frame vertical bar; 410. Triangular frame horizontal bar; 411. Triangular frame diagonal bar; 412. Triangular frame horizontal bar; 413. Horizontal diagonal brace connecting plate; 414. Horizontal diagonal brace U-bolt; 415. Horizontal diagonal brace connecting nut.

[0051] 5. Front-mounted steel support,

[0052] 51. Straight steel beam section; 511. Straight steel beam section web; 512. Straight steel beam section flange plate.

[0053] 52. L-shaped corner steel beam, 521. L-shaped corner steel beam web, 522. L-shaped corner steel beam flange, 523. Steel strand anchor, 524. Stiffening plate.

[0054] 53. Servo cylinder; 531. Cylinder housing; 532. Adjusting pad; 533. Housing hook roller; 534. Cylinder body; 534. Vertical end plate; 535. Housing hook.

[0055] 54. Adjustable support legs; 541. Support leg connecting plate; 542. Support legs;

[0056] 55. Corner horizontal diagonal brace connection section; 551. Connecting section steel beam; 552. Connecting section corner brace connection plate; 553. Connecting section steel waler connection plate.

[0057] 56. Corner horizontal diagonal brace; 561. Corner brace steel beam; 562. Corner brace end connecting plate; 563. Corner brace support leg connecting channel steel.

[0058] 57. Tie beam; 571. Tie beam steel beam; 572. Tie beam end connecting plate;

[0059] 58. Connecting beam U-bolts,

[0060] 59. Connecting nut for connecting beam

[0061] 510. Scaffold boards,

[0062] 6. Steel strand,

[0063] 7. Through-type jack,

[0064] 8. Jack foundation,

[0065] 9. Steel strand guide frame,

[0066] 10. Concrete or steel supports

[0067] 11. Soil layers

[0068] 12. Concrete foundation. Detailed Implementation

[0069] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The technical content and features of the present invention will be described in detail below with reference to the listed embodiments and the accompanying drawings. It should be noted that the drawings are all in a very simplified form and use non-precise proportions, and are only used to facilitate and clarify the illustration of the embodiments of the present invention. For ease of description, the terms "upper" and "lower" used below are consistent with the upper and lower directions in the accompanying drawings, but this should not be construed as a limitation of the technical solution of the present invention.

[0070] Please see Figures 1 to 22 This embodiment discloses a construction method for a small ultra-deep foundation pit using a pre-positioned steel support system. The pre-positioned steel support system includes several lattice columns 3, several connecting devices 4, pre-positioned steel supports 5, several steel strands 6, several through-hole jacks 7, several jack foundations 8, several steel strand guide frames 9, several servo cylinders 53, and a hydraulic system. The pre-positioned steel supports 5 include a steel waler and several corner horizontal braces 56 located at the four corners of the steel waler. At each corner of the steel waler, a lattice column 3 is correspondingly installed on the innermost corner horizontal brace 56. The lattice column 3 is pre-pressed into the soil layer 11 according to the design position. At each corner of the steel waler, the innermost corner horizontal brace 56... The diagonal brace 56 is connected to the corresponding lattice column 3 via the corresponding connecting device 4. The plurality of jack foundations 8 are respectively set at the four corner positions of the first-floor ring beam 2 of the continuous wall; the through-type jack 7 is set on the corresponding jack foundation 8; the steel strand guide frame 9 is set on the corresponding jack foundation 8 or the first-floor ring beam 2 of the continuous wall; the steel strand 6 is erected on the corresponding steel strand guide frame 9; the inner side of the steel waler and the two sides of the corner horizontal diagonal brace 56 are respectively set with a plurality of adjustable bracing angles 54 at equal intervals by bolt connection; the hydraulic system is set on the first-floor ring beam 2 of the continuous wall or on the ground or on the front-mounted steel support 5, and the plurality of servo cylinders 53 are set at intervals along the circumference of the steel waler on the outer side of the steel waler. The method includes the following steps:

[0071] Step 1, please refer to it carefully. Figure 17The construction of the diaphragm wall 1 and the first-floor ring beam 2 was completed. The lattice columns 3 were then driven into the soil layer 11 according to the design position. The soil layer 11 was excavated to a certain depth, and a concrete pad 12 was poured on top of it. A jack foundation 8 was installed on the first-floor ring beam 2 of the diaphragm wall. A through-type jack 7 and a steel strand guide frame 9 were also installed. Furthermore, during the excavation of the soil layer 11 to a certain depth, the earthwork was excavated in the order of first the center and then the surrounding areas. More excavation was carried out at the location of the lattice columns 3 to facilitate the installation of the horizontal bracing and the connection device 4 between the lattice columns 3 and the horizontal bracing. This increased the amount of earthwork excavation and improved the safety of the foundation pit construction.

[0072] Step 2, please refer to it carefully. Figure 18 The components of the pre-positioned steel support 5 are hoisted onto the concrete pad 12 through the gap in the first-layer ring beam 2 of the diaphragm wall, and the assembly of the pre-positioned steel support 5 is completed. Steel strand anchors 523 are distributed at the four corners of the steel waler of the pre-positioned steel support 5. Each through-hole jack 7 is connected to the corresponding steel strand anchor 523 on the pre-positioned steel support 5 through the corresponding steel strand 6. The servo cylinders 53 and the through-hole jacks 7 are connected to the hydraulic system. The adjustable support feet 54 are adjusted so that they extend and support the concrete pad 12. The adjustable support feet 54 are finely adjusted to make the pre-positioned steel support 5 horizontal. The servo cylinders 53 are driven by the hydraulic system to extend and apply a certain pressure to the diaphragm wall 1 to actively control the deformation of the diaphragm wall 1. The adjustable support feet 54 make the overall leveling of the steel support more convenient and reliable, and can effectively transfer the weight of the front-mounted steel support 5 to the ground, avoiding the servo cylinder 53 from being subjected to vertical force and torsional damage when horizontally supporting the underground continuous wall 1, thus ensuring construction safety and reasonable equipment stress.

[0073] Step 3, please refer to it carefully. Figure 19 Concrete or steel supports 10 are installed above the pre-positioned steel support 5 at the designed position, while the soil layer 11 is excavated. The pre-positioned steel support 5 enables excavation while supporting, thus improving the construction efficiency of the foundation pit.

[0074] Step 4, please refer to it carefully. Figure 20 Excavate the soil layer 11 to a certain depth, and pour a concrete cushion layer 12 on top of the soil layer 11.

[0075] Please refer to step 5 carefully. Figure 21The hydraulic system drives the servo cylinder 53 to retract, checks the descent path of the front steel support 5 to ensure it is unobstructed, drives the through-hole jack 7 through the pressure system to lower the front steel support 5 to a certain distance above the current concrete cushion 12, levels the front steel support 5 through the through-hole jack 7, adjusts the adjustable support feet 54 to support it on the concrete cushion 12, and extends the servo cylinder 53 through the control hydraulic system to apply a certain pressure to the underground continuous wall 11, actively controlling the deformation of the underground continuous wall 1. Connect each lattice column 3 to the corresponding corner horizontal diagonal brace 56 through the connecting device 4. The front steel support 5 is used to support as it is excavated, improving the construction efficiency of the foundation pit excavation and support, reducing the time of over-excavation without support, and thus improving the safety of foundation pit construction.

[0076] Please refer to step 6 carefully. Figure 22 Repeat steps 3 to 5 until the excavation and support construction of the small ultra-deep foundation pit is completed, and dismantle the front-mounted steel support 5 at the bottom and lift its components away from the foundation pit.

[0077] The present invention provides a construction method for small ultra-deep foundation pits using a pre-positioned steel support system. This system allows for simultaneous excavation, lowering, and support of the pre-positioned concrete or steel supports 10, effectively shortening the construction period and reducing the time spent without support during over-excavation. It offers advantages such as high mechanization, strong construction safety, and high reusability. The pre-positioned steel support 5 is raised and lowered as a whole using a through-type jack 7 and steel strands 6, providing advantages such as stable descent, safety, reliability, and good synchronization. Adjustable angle braces 54 on the steel supports effectively transfer the weight of the pre-positioned steel support 5 and the weight of the upper poured concrete to the ground, maintaining the pre-positioned steel support 5 horizontally. This also ensures that the servo cylinder 53 is not subjected to vertical torsional force when horizontally supporting the underground continuous wall 1, thereby improving construction safety and the rationality of equipment stress distribution.

[0078] Preferably, in the above-mentioned construction method for small ultra-deep foundation pits using a pre-installed steel support system, please refer to the following: Figures 5 to 8The connecting device 4 includes a load-bearing triangular frame, a triangular frame support plate 401, two connecting angle steels 402, several welding nuts 403, several adjusting bolts 404, an adjusting support plate 405, two lattice column U-bolts 406, two lattice column connecting plates 407, four lattice column connecting nuts 408, a horizontal diagonal brace connecting plate 413, two horizontal diagonal brace U-bolts 414, and four horizontal diagonal brace connecting nuts 415. The load-bearing triangular frame is a right-angled triangular structure with a horizontal plane and a vertical plane. The horizontal diagonal brace connecting plate 413 is fixedly installed on the horizontal plane, and the triangular frame support plate is fixedly installed on the vertical plane. The horizontal diagonal brace connecting plate 413 is perpendicular to the triangular frame support plate 401. The two connecting angle steels 402 are respectively vertically installed on the left and right sides of the triangular frame support plate 401. The upper and lower parts of the two connecting angle steels 402 are respectively provided with lattice support. The first through hole through which the U-bolt 406 of the column passes, and the two U-bolts 406 of the lattice column 3 are connected by the corresponding lattice column connecting plate 407 and lattice column connecting nut 408. The two sides of the horizontal diagonal brace connecting plate 413 are respectively opened with a row of second through holes along its own longitudinal direction for the corresponding horizontal diagonal brace U-bolt 414 to pass through. The two horizontal diagonal brace U-bolts 414 are connected to the horizontal diagonal brace connecting plate 413 and the corner horizontal diagonal brace 56 by the corresponding horizontal diagonal brace connecting nut 415. The upper and lower parts of the tripod support plate 401 are respectively opened with a third through hole, and a threaded hole matching the adjusting bolt 404 is provided at the third through hole. One end of the adjusting bolt 404 passes through the corresponding threaded hole on the tripod support plate 401 and is hinged to the adjusting support plate 405 by ball joint. Rotating the adjusting bolt 404 can move the corresponding adjusting support plate 405, so that the adjusting support plate 405 fits against the side of the lattice column 3. Considering the possibility of torsion and vertical deflection of the lattice column 3, preliminary positioning is first performed during connection to ensure that the bottom surface of the horizontal brace connecting plate 413 is in contact with the corner horizontal brace 56. Then, the connecting device 4 is rotated, and the adjusting bolt 404 is rotated to ensure that the two adjusting support plates 405 are in contact with the side of the lattice column 3. Then, the lattice column U-bolt 406, the lattice column connecting plate 407, and the lattice column connecting nut 408 are used to connect and fix the connecting device 4 and the lattice column 3. Finally, the two horizontal brace U-bolts 414 are used to clamp the corner horizontal brace 56 and are tightened with the horizontal brace connecting nut 415, thereby realizing the connection between the corner horizontal brace 56 and the lattice column 3.

[0079] On the one hand, since the corner horizontal brace 56 and the connecting device 4 are connected by the horizontal brace U-bolt 414, when the horizontal brace connecting plate 413 is in contact with the bottom surface of the corner horizontal brace 56, the connection between the lattice column 3 and the connecting device 4 is ensured by rotating the connecting device 4 when there is torsional deviation and horizontal position deviation of the lattice column 3. Since multiple openings, namely two rows of second through holes, are provided on the horizontal brace connecting plate 413, even if the connecting device 4 is rotated, the appropriate second through hole can still be selected to insert the corresponding horizontal brace U-bolt 414 to realize the connection between the corner horizontal brace 56 and the connecting device 4.

[0080] On the other hand, since the two ends of the U-bolt of the lattice column can rotate freely in the corresponding first through hole of the corresponding connecting angle steel, and by setting the adjusting bolt 404 and the adjusting support plate 405, one end of the adjusting bolt 404 passes through the corresponding threaded hole on the tripod support plate 401 and is hinged to the adjusting support plate 405 by ball joint. Therefore, by rotating the adjusting bolt 404, the two adjusting support plates 405 can be made to fit against the side of the lattice column 3, ensuring that the lattice column 3 and the horizontal diagonal brace have an effective force transmission connection, i.e., an effective support connection, when there is a verticality deviation of the lattice column 3. The connecting device 4 can always have an effective support connection with the lattice column 3 with the help of the adjusting support plate 405, so that the connecting device 4 has high adaptability and can adapt to the horizontal distance deviation, planar torsion, vertical tilt and other embedment errors of the lattice column 3.

[0081] Furthermore, since the adjusting support plate 405 is in close contact with the side of the lattice column 3, the vertical force of the corner horizontal brace 56 of the steel support can be effectively transferred to the lattice column 3. Moreover, since the connection between the connecting device 4 and the corner horizontal brace 56 is made by U-bolt clamping, and the connecting device 4 is not subject to horizontal constraint, the corner horizontal brace 56 can be effectively prevented from transferring the horizontal force to the lattice column 3, thus ensuring safety.

[0082] To improve the rigidity and load-bearing capacity of the load-bearing tripod, the load-bearing tripod includes two vertical rods 409, two horizontal rods 410, two diagonal rods 411, and three horizontal rods 412. The vertical rods 409, horizontal rods 410, and diagonal rods 411 are connected to form a triangular structure. The ends of the two triangular structures are connected by the three horizontal rods 412. A horizontal diagonal brace connecting plate 413 is placed on the upper part of the load-bearing tripod. The horizontal diagonal brace connecting plate 413 is rigidly connected to the horizontal rods 410 and the horizontal rods 412. The vertical rods 409 and the horizontal rods 412 are both rigidly connected to the tripod support plate 401, so that the load-bearing tripod is supported on the tripod support plate 401.

[0083] Preferably, in the above-mentioned construction method for small ultra-deep foundation pits using a pre-installed steel support system, each adjustable support plate 405 is hinged to three adjusting bolts 404, and the three adjusting bolts 404 are set at equal intervals along the horizontal direction, so that the adjustable support plate 405 is tightly attached to the side of the lattice column 3, thereby improving the force transmission performance between the two.

[0084] Please see Figure 4 The lattice column 3 is formed by connecting four lattice column angle steels 31 through several angle steel connecting plates 32.

[0085] Preferably, in the above-mentioned construction method for small ultra-deep foundation pits using a pre-positioned steel support system, the steel waler of the pre-positioned steel support 5 includes several straight steel beams 51 and four L-shaped corner steel beams 52. The several straight steel beams 51 are assembled into four strip steel beams by bolt connection. The ends of the four strip steel beams are connected by L-shaped corner steel beams 52 to form a rectangular steel waler. The strip steel beams and the corresponding L-shaped corner steel beams 52 are connected by bolt connection. The two ends of the corner horizontal brace 56 are respectively connected to the inner wall of the steel waler through corner horizontal brace connecting sections 55. Several parallel corner horizontal braces 56 are provided at each corner of the steel waler. Several connecting beams 57 are provided on the two parallel corner horizontal braces 56 located on the inner side to improve the overall stability of the pre-positioned steel support 5. Scaffold boards 510 are laid on the corner horizontal braces 56 as a working platform to facilitate construction workers to carry out construction work.

[0086] Preferably, in the above-mentioned construction method for small ultra-deep foundation pits using a pre-installed steel support system, please refer to the following: Figures 5 to 8 The adjustable support leg 54 includes a support leg connecting plate 541 and a support leg body 542. The support leg connecting plate 541 is fixedly disposed on the upper part of the support leg body 542. The support leg connecting plate 541 is vertically disposed, and a plurality of bolt holes for adjusting the height of the adjustable support leg 54 are arranged vertically at intervals on the support leg connecting plate 541 so as to realize the support height of the adjustable support leg 54.

[0087] Preferably, in the above-mentioned construction method for small ultra-deep foundation pits using a pre-installed steel support system, please refer to the following: Figure 9 The cross-section of the straight steel beam 51 is H-shaped with double webs, and it is formed by the fixed connection between the web 511 of the straight steel beam and the flanges 512 of the straight steel beams on both sides; please refer to the following for details. Figure 10The L-shaped corner steel beam 52 has a double-web H-shaped cross-section and is formed by the L-shaped corner steel beam web 521 and the L-shaped corner steel beam flange plates 522 on the inner and outer sides. The L-shaped corner steel beam web 521 has holes and steel strand anchors 523 are installed at the holes to form an effective connection between the through-hole jack 7 and the steel waler, so as to achieve stable lifting and lowering of the steel waler and improve construction safety. In addition, stiffening plates 524 are installed on both sides of the steel strand anchors 523 to further improve the stability and safety of the lifting and lowering of the steel waler.

[0088] Preferably, in the above-mentioned construction method for small ultra-deep foundation pits using a pre-installed steel support system, please refer to the following: Figure 11 The servo cylinder 53 includes a cylinder housing 531, an adjusting pad 532, a housing hook roller 533, and a cylinder body 534. The cylinder body 534 is disposed inside the cylinder housing 531. A vertical end plate 535 is disposed at one end of the cylinder housing 531. An adjusting pad 532 for adjusting the total extension of the servo cylinder 53 is disposed inside the cylinder housing 531. The adjusting pad 532 is located between the vertical end plate 535 and the cylinder body 534. A downward-opening housing hook 536 for attaching to a steel waler is disposed at the upper end of the vertical end plate 535. A plurality of housing hook rollers 533 are disposed between the vertical end plate 535 and the housing hook 536. Bolt holes for connecting to the steel waler are opened on the vertical end plate 535. By setting the sleeve hook roller 533, the servo cylinder 53 can easily move along the steel waler, reducing the friction between the two. When the servo cylinder 53 reaches the predetermined position, it can be fixedly connected to the steel waler by bolt holes opened on the vertical end plate 535.

[0089] Preferably, in the above-mentioned construction method for small ultra-deep foundation pits using a pre-installed steel support system, please refer to the following: Figures 13 to 14 The corner horizontal brace connecting section 55 includes a connecting section steel beam 551, a connecting section corner brace connecting plate 552, and a connecting section steel waler connecting plate 553. The connecting section corner brace connecting plate 552 and the connecting section steel waler connecting plate 553 are respectively rigidly connected to both ends of the connecting section steel beam 551. The connecting section steel waler connecting plate 553 is obliquely arranged, and the connecting section corner brace connecting plate 552 is vertically arranged. Bolt holes for connecting the steel waler are opened on the connecting section steel waler connecting plate 553, and bolt holes for connecting the corresponding corner horizontal brace 56 are opened on the connecting section corner brace connecting plate 552. This realizes a detachable connection between the corner horizontal brace connecting section 55, the corner horizontal brace 56, and the steel waler, improving the convenience of installation and dismantling and the turnover rate.

[0090] Preferably, in the above-mentioned construction method for small ultra-deep foundation pits using a pre-installed steel support system, please refer to the following: Figure 15The corner horizontal brace 56 includes a corner brace steel beam 561, two corner brace end connecting plates 562, and several corner brace support foot connecting channel steels 563. The two corner brace end connecting plates 562 are respectively fixedly installed at both ends of the corner brace steel beam 561. The corner brace support foot connecting channel steels 563 are symmetrically arranged in pairs at equal intervals along the longitudinal direction of the corner brace steel beam 561 on both sides of the corner brace steel beam 561. Bolt holes for connecting the corresponding corner horizontal brace connecting sections 55 are opened on the two corner brace end connecting plates 562. Several bolt holes for connecting the corresponding adjustable corner brace 54 are arranged at intervals on the corner brace support foot connecting channel steels 563.

[0091] Preferably, in the above-mentioned construction method for small ultra-deep foundation pits using a pre-installed steel support system, please refer to the following: Figure 16 The connecting beam 57 includes a connecting beam steel beam 571 and two connecting beam end connecting plates 572. The two connecting beam end connecting plates 572 are fixedly installed at both ends of the connecting beam steel beam 571. The two connecting beam end connecting plates 572 are provided with through holes for connecting beam U-bolts 58 to pass through. The connecting beam U-bolts 58 clamp the corresponding corner horizontal brace 56 and are then fixed to the corresponding connecting beam end connecting plate 572 by connecting beam connecting nuts 59. This realizes a detachable connection between the connecting beam 57 and the corner horizontal brace 56, improving the convenience of installation and dismantling and the turnover rate.

[0092] Preferably, in the above-mentioned construction method for small ultra-deep foundation pits using a pre-positioned steel support system, an integral platform plate (not shown) can be set on the pre-positioned steel support 5. This platform can serve as a working platform to support workers, engineering materials, and the side formwork for concrete support, as well as as the bottom formwork for the upper concrete pouring support. This avoids frequent installation and dismantling of the formwork, effectively improves the turnover efficiency of the formwork, and thus improves the construction efficiency of the foundation pit and shortens the construction period.

[0093] The principle and effects of the construction method for small ultra-deep foundation pits using a pre-installed steel support system of the present invention are as follows: The pre-installed steel support 5, together with the diaphragm wall 1 and traditional concrete supports or steel supports 10, forms the support system for small ultra-deep foundation pits; the pre-installed steel support 5 is arranged before the traditional concrete supports or steel supports 10, allowing for simultaneous excavation, lowering, and support, which can shorten the time without support during over-excavation and enhance construction safety; the pre-installed steel support 5 integrates a servo hydraulic cylinder 53, which can apply pressure to the inner wall of the diaphragm wall 1, realizing active control of foundation pit deformation; the pre-installed... The steel support 5 uses a through-hole jack 7 in conjunction with steel strands 6 for overall descent, which can improve the stability and safety of the descent. The corner horizontal braces 56 of the front-mounted steel support 5 are connected by a detachable and highly adaptable connecting device 4, which improves the overall stability and construction efficiency. The front-mounted steel support 5 is equipped with adjustable support feet 54, which can improve the overall stability. The upper part of the front-mounted steel support 5 is equipped with a working platform, which enhances the convenience of construction. All components of the front-mounted steel support 5 adopt a standard modular design and are assembled, which can effectively improve the convenience of installation and dismantling and the efficiency of component turnover.

[0094] In summary, this invention achieves active control of the deformation of the underground continuous wall 1 by setting servo cylinders 53 around the steel waler of the front-mounted steel support 5, improves the turnover rate by adopting a modular assembly design, and shortens the construction period and over-excavation time by adopting the construction method of excavating, lowering and supporting as the concrete support or steel support 10 is placed in front, which has the advantages of high mechanization, strong construction safety and high turnover rate. In addition, (1) the corner horizontal support of the front-mounted steel support 5 is connected to the lattice column 3 by a special connecting device 4. The connecting device 4 can adapt to the position error of the lattice column 3, can follow the front-mounted steel support 5 to descend, and can be quickly installed and dismantled; (2) the front-mounted steel support 5 is raised and lowered as a whole by using a through-hole jack 7 and steel strand 6, which has the advantages of stable descent, safety and reliability and good synchronization; (3) the steel support is equipped with an adjustable corner brace 54, which can effectively transfer the self-weight of the front-mounted steel support 5 and the self-weight of the upper concrete to the ground. , and keep the front steel support 5 horizontal, and ensure that the servo cylinder 53 is not subjected to vertical torsional force when supporting the underground continuous wall 1 in the horizontal direction, thereby improving construction safety and equipment stress rationality; (4) The front steel support 5 is equipped with an integral platform plate, which can be used as a working platform to carry the side formwork of workers, engineering materials and concrete support, and can also be used as the bottom formwork for the upper concrete pouring support, thereby avoiding frequent installation and dismantling of the formwork, effectively improving the turnover efficiency of the formwork, thereby improving the construction efficiency of the foundation pit and shortening the construction period.

[0095] The above description is merely a description of preferred embodiments of the present invention and is not intended to limit the scope of the present invention in any way. Any changes or modifications made by those skilled in the art based on the above disclosure shall fall within the protection scope of the claims.

Claims

1. A construction method for a small-scale ultra-deep foundation pit using a pre-installed steel support system, characterized in that, A pre-installed steel support system is adopted, characterized in that the pre-installed steel support system includes several lattice columns, several connecting devices, pre-installed steel supports, several steel strands, several through-hole jacks, several jack foundations, several steel strand guide frames, several servo cylinders, and a hydraulic system. The pre-installed steel supports include steel walers and several corner horizontal braces set at the four corners of the steel walers. A lattice column is correspondingly installed on the inner side of the innermost corner horizontal brace at each corner of the steel walers. The lattice columns are pre-pressed into the soil layer according to the design position. The innermost corner horizontal brace at each corner of the steel walers is connected to the... The corresponding lattice column connection includes several jack foundations respectively set at the four corners of the first-floor ring beam of the continuous wall; through-type jacks are set on the corresponding jack foundations; steel strand guide frames are set on the corresponding jack foundations or on the first-floor ring beam of the continuous wall; steel strands are laid on the corresponding steel strand guide frames; several adjustable support feet are set at equal intervals on the outer side of the steel waler and the two sides of the corner horizontal diagonal braces by bolt connection; the hydraulic system is set on the first-floor ring beam of the continuous wall, the ground, or the front-mounted steel support; several servo cylinders are set at intervals along the circumference of the steel waler on the outer side of the steel waler. The method includes the following steps: Step 1: Complete the pouring construction of the underground continuous wall and the first-floor ring beam of the continuous wall, press the lattice columns into the soil layer according to the design position, excavate the soil layer to a certain depth, pour a concrete pad layer on the soil layer, set up jack foundations on the first-floor ring beam of the continuous wall, and install through-hole jacks and steel strand guide frames. Step 2: The components of the pre-positioned steel support are hoisted onto the concrete pad through the gap in the first-floor ring beam of the diaphragm wall, and the assembly of the pre-positioned steel support is completed. Steel strand anchors are installed at the four corners of the steel waler of the pre-positioned steel support. Each through-hole jack is connected to the corresponding steel strand anchor on the pre-positioned steel support through the corresponding steel strand. The servo cylinders and the through-hole jacks are connected to the hydraulic system. The adjustable support feet are adjusted so that they extend and support the concrete pad. The adjustable support feet are finely adjusted to make the pre-positioned steel support horizontal. The servo cylinders are driven to extend through the hydraulic system to apply a certain pressure to the diaphragm wall and actively control the deformation of the diaphragm wall. Step 3: Install concrete or steel supports above the pre-positioned steel supports at the designed positions, while continuing to excavate the soil layer downwards, using the pre-positioned steel supports to achieve excavation while supporting. Step 4: Excavate the soil layer to a certain depth and pour a concrete cushion layer on top of the soil layer; Step 5: The servo cylinder is retracted via the hydraulic system, and the through-hole jack is driven by the hydraulic system to lower the front steel support to a certain distance above the current concrete pad. The through-hole jack is used to level the front steel support, and the adjustable support feet are adjusted to support it on the concrete pad. The servo cylinder is extended via the hydraulic system to apply a certain pressure to the diaphragm wall, thus actively controlling the deformation of the diaphragm wall. Each lattice column is connected to its corresponding corner horizontal brace via a connecting device. The connecting device includes a load-bearing triangular frame, a triangular frame support plate, two connecting angle steels, several welded nuts, several adjusting bolts, an adjusting support plate, two lattice column U-bolts, two lattice column connecting plates, four lattice column connecting nuts, a horizontal brace connecting plate, two horizontal brace U-bolts, and four horizontal brace connecting nuts. The load-bearing triangular frame is a right-angled triangular structure with a horizontal plane and a vertical plane. The horizontal brace connecting plate is fixedly set on the horizontal plane, and the triangular frame support plate... Fixedly installed on the vertical surface, the horizontal diagonal brace connecting plate is perpendicular to the tripod support plate. The two connecting angle steels are respectively vertically installed on the left and right sides of the tripod support plate. The upper and lower parts of the two connecting angle steels are respectively opened with first through holes for the U-shaped bolts of the lattice column to pass through. The two U-shaped bolts of the lattice column are connected by corresponding lattice column connecting plates and lattice column connecting nuts after clamping the lattice column. The two sides of the horizontal diagonal brace connecting plate are respectively opened with a row of second through holes for the corresponding horizontal diagonal brace U-shaped bolts to pass through. The two horizontal diagonal brace U-shaped bolts are connected to the horizontal diagonal brace connecting plate and the corner horizontal diagonal brace by the corresponding horizontal diagonal brace connecting nuts. The upper and lower parts of the tripod support plate are respectively opened with a third through hole, and a threaded hole matching the adjusting bolt is provided at the third through hole. One end of the adjusting bolt passes through the corresponding threaded hole on the tripod support plate and is hinged to the adjusting support plate by ball joint. Rotating the adjusting bolt can move the corresponding adjusting support plate so that the adjusting support plate fits against the side of the lattice column. Step 6: Repeat steps 3 to 5 until the excavation and support construction of the small ultra-deep foundation pit is completed, and dismantle the pre-positioned steel support at the bottom and lift its components away from the foundation pit.

2. The construction method for small-scale ultra-deep foundation pits using a pre-installed steel support system as described in claim 1, characterized in that, The load-bearing tripod includes two vertical members, two horizontal members, two diagonal members, and three horizontal members. The vertical members, horizontal members, and diagonal members are connected to form a triangular structure. The ends of the two triangular structures are connected by the three horizontal members. A horizontal diagonal brace connecting plate is placed on the upper part of the load-bearing tripod. The horizontal diagonal brace connecting plate is rigidly connected to the horizontal members and horizontal members of the tripod. The vertical members and horizontal members of the tripod are rigidly connected to the tripod support plate, so that the load-bearing tripod is supported on the tripod support plate.

3. The construction method for small-scale ultra-deep foundation pits using a pre-installed steel support system as described in claim 1, characterized in that... Each adjustment support plate is hinged to three adjustment bolts, which are evenly spaced along the horizontal direction.

4. The construction method for small-scale ultra-deep foundation pits using a pre-installed steel support system as described in claim 1, characterized in that... The front-mounted steel support waler includes several straight steel beams and four L-shaped corner steel beams. The several straight steel beams are assembled into four strip steel beams by bolt connection. The ends of the four strip steel beams are connected by L-shaped corner steel beams to form a rectangular steel waler. The strip steel beams and the corresponding L-shaped corner steel beams are connected by bolt connection. The two ends of the corner horizontal bracing are respectively connected to the inner wall of the steel waler through corner horizontal bracing connecting sections. Several parallel corner horizontal bracings are set at each corner of the steel waler. Several connecting beams are set on the two parallel corner horizontal bracings located on the inner side. Scaffold boards are laid on the corner horizontal bracings as a working platform.

5. The construction method for small-scale ultra-deep foundation pits using a pre-installed steel support system as described in claim 4, characterized in that... The connecting beam includes a connecting beam steel beam and two connecting beam end connecting plates. The two connecting beam end connecting plates are fixedly installed at both ends of the connecting beam steel beam. The two connecting beam end connecting plates are provided with through holes for connecting beam U-bolts to pass through. The corresponding corner horizontal diagonal bracing of the connecting beam U-bolt clamp is fixed to the corresponding connecting beam end connecting plate by connecting beam connecting nuts.

6. The construction method for small-scale ultra-deep foundation pits using a pre-installed steel support system as described in claim 1, characterized in that, The corner horizontal bracing includes a corner bracing steel beam, two corner bracing end connecting plates, and several corner bracing foot connecting channel steels. The two corner bracing end connecting plates are respectively fixedly installed at both ends of the corner bracing steel beam. The corner bracing foot connecting channel steels are symmetrically arranged in pairs at equal intervals on both sides of the corner bracing steel beam along the longitudinal direction of the corner bracing steel beam. Bolt holes for connecting corresponding corner horizontal bracing connecting sections are opened on the two corner bracing end connecting plates. Several bolt holes for connecting corresponding adjustable support feet are provided at intervals on the corner bracing foot connecting channel steels.

7. The construction method for small-scale ultra-deep foundation pits using a pre-installed steel support system as described in claim 4, characterized in that... The corner horizontal brace connection section includes a connecting section steel beam, a connecting section corner brace connection plate, and a connecting section steel waler connection plate. The connecting section corner brace connection plate and the connecting section steel waler connection plate are respectively rigidly connected to both ends of the connecting section steel beam. The connecting section steel waler connection plate is obliquely arranged, and the connecting section corner brace connection plate is vertically arranged. Bolt holes for connecting the steel waler are opened on the connecting section steel waler connection plate, and bolt holes for connecting the corresponding corner horizontal brace are opened on the connecting section corner brace connection plate.

8. The construction method for small-scale ultra-deep foundation pits using a pre-installed steel support system as described in claim 4, characterized in that... The cross-section of the straight steel beam is H-shaped with double webs, and is formed by fixing the web of the straight steel beam to the flanges of the straight steel beams on both sides; the cross-section of the L-shaped corner steel beam is H-shaped with double webs, and is formed by fixing the web of the L-shaped corner steel beam to the flanges of the L-shaped corner steel beams on both the inner and outer sides; the web of the L-shaped corner steel beam has an opening, and the steel strand anchor is installed at the opening, with stiffening plates installed on both sides of the steel strand anchor.

9. The construction method for small-scale ultra-deep foundation pits using a pre-installed steel support system as described in claim 1, characterized in that, The servo cylinder includes a cylinder housing, an adjusting pad, a housing hook roller, and a cylinder body. The cylinder body is housed within the cylinder housing. A vertical end plate is provided at one end of the cylinder housing. An adjusting pad for adjusting the total extension of the servo cylinder is provided inside the cylinder housing. The adjusting pad is located between the vertical end plate and the cylinder body. A downward-opening housing hook for attaching to a steel waler is provided at the upper end of the vertical end plate. Several housing hook rollers are provided between the vertical end plate and the housing hook. Bolt holes for connecting to the steel waler are provided on the vertical end plate.

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