Posterior servo compensation device for foundation pit support and construction method

Abstract

The application discloses a kind of post servo compensation device and construction method of foundation pit support, the inner support body slit of the device is equipped with servo compensation system upper oil cylinder and lower oil cylinder, and two ends of each oil cylinder are abutted with two corbels;Two outer convex parts of left upper corbel are connected into left sleeve hoop by two rows of high-strength bolts with two outer convex parts of left lower corbel, and two outer convex parts of right upper corbel are connected into right sleeve hoop by two rows of high-strength bolts with two outer convex parts of right lower corbel;Each sleeve hoop is sleeved with corresponding segment of inner support body, and a small inside and large outside right wedge block is extruded between each corbel and corresponding segment;The bottom plane of each right wedge block is provided with multiple small inside and large outside racks;The method is key, by high-strength bolt preliminary hoop right wedge block, knock extrusion right wedge block, the mode of oil cylinder positive re-extrusion corbel, steel corbel is completely clamped and extruded with inner support segmentation.The device and method can effectively provide axial force compensation for the poured concrete inner support, to meet the supporting demand of foundation pit under the condition of deepening and increasing.

Description

Technical Field

[0001] This invention relates to the field of foundation pit construction technology, specifically to a post-servo compensation device and construction method for foundation pit support. Background Technology

[0002] When construction companies take on unfinished building projects, they sometimes encounter the following situation: The foundation pit support system is already completed, and the foundation pit is being excavated; that is, the retaining piles and capping beams have been constructed, and the concrete internal supports at the same elevation as the capping beams have been poured. At this point, the developer who took on the project modifies the original project regulations, changing the original residential project to a commercial or industrial project, or adjusts the building structure design, such as changing the location of the elevator shaft. This leads to an increase in the load on the upper part of the building, requiring the foundation slab to be thickened to increase its punching shear resistance. Thickening the foundation slab requires increasing the excavation depth of the foundation pit. For example, if the original foundation pit depth of an unfinished project was 5 meters and the foundation slab thickness was 0.5 to 1 meter, after the regulations are modified, the foundation slab thickness increases to 1.5 to 2 meters, and the foundation pit depth also increases to 6 meters. However, the completed foundation pit support system is designed for a 5-meter excavation depth. After the excavation depth is increased, the old concrete internal supports no longer meet the requirements for resisting the lateral pressure of the soil. Therefore, the conventional approach is to add a new row of concrete internal supports below the existing internal supports at the same elevation. However, pouring an additional row of internal supports is time-consuming, labor-intensive, inefficient, slow, and will delay the construction period. It also requires more steel bars and cement, making it uneconomical. Summary of the Invention

[0003] One technical problem to be solved by the present invention is to provide a post-servo compensation device for foundation pit support that can effectively provide axial force compensation for the cast-in-place concrete internal support, so as to meet the support requirements of the foundation pit under the condition of increased excavation depth, ensure that the lateral displacement deformation of the foundation pit is kept within a safe range, and has a fast and convenient construction process.

[0004] One technical solution of the present invention is to provide a post-servo compensation device for foundation pit support, which includes an inner concrete support body, which is cut into left and right segments by a wire saw; an upper and lower hydraulic cylinder of a servo compensation system are respectively provided above and below the cut of the inner support body, and each hydraulic cylinder is abutted against two brackets at both ends; each bracket has two outward protrusions on both sides, the two outward protrusions of the upper left bracket are connected to the two outward protrusions of the lower left bracket by two rows of high-strength bolts to form a left sleeve, and the two outward protrusions of the upper right bracket are connected to the two outward protrusions of the lower right bracket by two rows of high-strength bolts to form a right sleeve; each sleeve fits over the corresponding segment of the inner support body and a positive wedge block with a smaller inner diameter and a larger outer diameter is squeezed between each bracket and the corresponding segment; the bottom plane of each positive wedge block is provided with multiple toothed racks with a smaller inner diameter and a larger outer diameter.

[0005] Another technical problem to be solved by the present invention is to provide a construction method for a post-servo compensation device for foundation pit support that can effectively provide axial force compensation for the cast-in-place concrete internal support to meet the support requirements of the foundation pit under the condition of increased excavation depth, ensure that the lateral displacement deformation of the foundation pit is kept within a safe range, and has a fast and convenient construction process.

[0006] Another technical solution of the present invention is to provide a construction method for a post-servo compensation device for foundation pit support, the steps of which include:

[0007] a. The upper and lower brackets located on one side of the cut are pulled together by two rows of high-strength bolts to form a hoop, and then fitted into the corresponding segment;

[0008] b. Insert the upper and lower positive wedge blocks into the sleeve, and tighten the nuts of the high-strength bolts so that the upper and lower brackets close synchronously and initially tighten the upper and lower positive wedge blocks. The inner side of the positive wedge blocks is initially tightened while the outer side is outside the sleeve.

[0009] c. Tap the outer ends of the upper and lower wedge blocks to push the two positive wedge blocks back into the gap between the sleeve and the corresponding segment for a certain length; and as the tapping occurs, the rack of the positive wedge block is pressed into the concrete surface of the corresponding segment by the corbel and engages with the contact surface of the segment.

[0010] d. Repeat steps a to c, put the sleeve on the other side of the cut into the corresponding segment, initially tighten the upper and lower positive wedge blocks on the other side, and knock and squeeze the upper and lower positive wedge blocks on the other side.

[0011] e. Place the upper and lower hydraulic cylinders between the corresponding brackets, drive the hydraulic cylinders to push the brackets on both sides outward, while the positive wedge block rack and segment contact surface are engaged and cannot move. The brackets continue to move outward relative to the positive wedge block, squeezing the positive wedge block tighter and tighter until it is completely locked.

[0012] Compared with existing technologies, the above-mentioned post-servo compensation device and construction method for foundation pit support have the following advantages.

[0013] Firstly, from a stress perspective, the internal support is a beam-type structure, with its stress concentrated in the upper and lower regions. Therefore, it is necessary to increase the reinforcement in these areas, forming densely reinforced zones at the top and bottom. The corbel of the hydraulic cylinder must be firmly fixed to the densely reinforced zones at the top and bottom of the internal support segment to fully exert its supporting load function. The industry's conventional approach is to ensure a firm connection between the corbel and the densely reinforced zone of the segment by installing rebar. However, rebar installation is not only laborious but also requires chiseling open the segment concrete to expose the main reinforcement bars for secure installation. However, chiseling open the concrete will inevitably damage the reinforced concrete structure at the top and bottom of the internal support, reducing its performance. Therefore, without rebar installation, it is difficult to achieve a firm connection, while rebar installation is cumbersome, inefficient, laborious, and will also damage the densely reinforced zone, thus creating a dilemma.

[0014] This application solves the aforementioned technical problems by initially tightening the positive wedge block with high-strength bolts, then hammering and counter-pressing the positive wedge block, and finally using a hydraulic cylinder to re-press the corbel in the forward direction. This method thoroughly and tightly clamps the steel corbel and the inner support segments, achieving a firm connection between the steel corbel and the densely reinforced areas of the inner support without installing rebar, chiseling concrete, or significantly damaging the densely reinforced areas of the segments. Furthermore, the rack on the bottom plane of the positive wedge block plays a crucial role. Because the rack is smaller on the inside and larger on the outside, it can be easily squeezed into the gap between the corbel and the segment by manual hammering and counter-pressing. As the hammering, positive wedge block, and corbel continue to tighten, the rack… The steel bracket is also simultaneously engaged with the concrete surface of the segment. Thus, when the hydraulic cylinder pushes the bracket outward, the positive wedge block is firmly engaged with the segment under the action of the rack and pinion, and will not move outward with the bracket. This ensures the relative sliding and lifting range of the bracket and the positive wedge block, further ensuring that it is squeezed tighter and completely locked in place. It is precisely because the steel bracket forms a strong connection with the dense steel reinforcement area of ​​the upper and lower parts of the inner support that the load is transferred stably, so that the hydraulic cylinder can withstand a load of up to 300 tons in the inner support segment when it is officially put into service. This provides sufficient axial force compensation for the already poured concrete inner support, so as to solve the problem of insufficient load support of the existing inner support after the excavation depth of the foundation pit increases.

[0015] It is precisely because of the strong connection between the corbel and the upper and lower stress areas of the segment that the hydraulic cylinder can be placed outside the inner support axis rather than on it. The advantage of placing the hydraulic cylinder externally rather than internally is that there is no need to cut off a section in the middle of the inner support to install the hydraulic cylinder concentrically. In this way, the hydraulic cylinder can intervene in advance before the inner support is cut to compensate for axial force. When cutting the inner support with a wire saw, there is a 4mm kerf. Without the early intervention of the hydraulic cylinder to compensate for axial force, the cross-sections on both sides of the kerf will clamp the wire saw tighter and tighter under the lateral pressure of the soil on both sides, making the cutting difficult, slow and laborious. It is necessary to use a cutting machine with greater power and volume. Moreover, the soil on both sides of the foundation pit may also move laterally by 4mm towards the kerf. Although the above-mentioned 4mm lateral displacement is not large, it is close to or even exceeds the safety requirements of some engineering projects with strict control of foundation pit deformation, such as excavation projects around subways. Therefore, since the hydraulic cylinder of this application is installed outside the inner support, it can intervene in advance before cutting, effectively support the inner support, avoid lateral displacement of the foundation pit and inner support segments during the cutting process, ensure that the wire saw cutting of the inner support is convenient, fast, efficient and labor-saving, and avoid lateral displacement caused by cutting, protect the foundation pit safety, and achieve precise control of lateral displacement, especially suitable for engineering projects with strict control of foundation pit deformation.

[0016] Moreover, compared to existing approaches that require adding an additional internal support to address increased excavation depth, which necessitates tying reinforcing bars to the new internal support and walers, erecting formwork, pouring concrete, and waiting for the concrete to harden; or the conventional approach of chiseling open the concrete of the internal support to install reinforcing bars and waiting for the mortar to harden; the construction process described in this application—tightening high-strength bolts, initially tightening the positive wedge block and internal support via the corbel, hammering the positive wedge block to push it back, and then using a hydraulic cylinder to push the corbel forward—is significantly more convenient, faster, more efficient, and less labor-intensive. For example, the positive wedge block can be manually hammered, and applying 50KN to the hydraulic cylinder is sufficient to push it outward and completely lock the corbel and positive wedge block.

[0017] In summary, this application relies on preliminary clamping, hammering back extrusion, hydraulic cylinder forward re-extrusion, and rack and pinion engagement to achieve a strong connection between the external hydraulic cylinder and the upper and lower densely reinforced areas of the internal support without planting rebar or damaging the densely reinforced areas of the internal support. This allows for early intervention in supporting the internal support, compensating for the shortcomings of insufficient load-bearing capacity of the completed internal support under conditions of increased excavation depth. Furthermore, the entire construction operation is fast, efficient, and labor-saving.

[0018] Preferably, each bracket has an inverted wedge-shaped protrusion on its bottom surface, which is larger on the inside and smaller on the outside. The lower inclined surface of the inverted wedge-shaped protrusion is parallel to and abuts against the upper inclined surface of the corresponding positive wedge-shaped block. This ensures that when the hydraulic cylinder pushes the bracket outward, the inverted wedge-shaped protrusion and the positive wedge-shaped block at the bottom of the bracket are pressed more tightly and firmly, further increasing the connection strength between the bracket and the densely reinforced area of ​​the upper and lower parts of the inner support, and further ensuring the supporting and protective effect of the external hydraulic cylinder on the inner support.

[0019] As a further preferred option, each positive wedge block has an enlarged head at its outer end; this makes it easier for the positive wedge block to be struck and squeezed when it is manually squeezed, ensuring a tighter squeeze and further improving the connection strength between the corbel and the densely reinforced areas of the upper and lower parts of the inner support.

[0020] As a further preferred embodiment, each bracket includes a vertical bearing plate and a horizontal base plate. The lower end of the bearing plate is welded to the inner end of the base plate, and reinforcing ribs are welded between the bearing plate and the base plate. The portions of the base plate that protrude from both sides of the inner support body form two outward protrusions. The portions of the base plate that protrude from the bearing plate form inward protrusions. Two adjusting screws are welded to the inward protrusions of the base plate, each adjusting screw being screwed onto an adjusting nut and a positioning nut. Each cylinder rests on two U-shaped plates at both ends. Each U-shaped plate has two support plates at both ends, which are movably fitted onto the two adjusting screws of the corresponding base plate. Each support plate rests on a corresponding adjusting nut and is pressed down by a corresponding positioning nut. The advantages of this preferred structure are as follows. The bracket, formed by welding the bearing plate, base plate, and ribs, ensures that its strength meets the load transfer requirements of the hydraulic cylinder while being more economical and cost-effective than a solid trapezoidal bracket. The two U-shaped plates, connected to the left and right brackets respectively, meet the installation and support requirements of the hydraulic cylinder. Furthermore, by tightening the adjusting nut and positioning nut, the height of the U-shaped plate, which is the initial position before the hydraulic cylinder is ejected, can be precisely and conveniently adjusted. This allows for precise adjustment of the distance between the hydraulic cylinder and the inner support axis, ensuring balanced and symmetrical force on the upper and lower hydraulic cylinders and precise lever arm, further guaranteeing the support of the external hydraulic cylinder for the two sections of the inner support and the foundation pit. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the structure of the rear servo compensation device for the foundation pit support of the present invention installed inside the foundation pit.

[0022] Figures 2-4 This is a schematic diagram of the structure of the rear servo compensation device for the foundation pit support of the present invention.

[0023] Figure 5 This is a schematic diagram of the bracket structure of the rear servo compensation device for foundation pit support of the present invention.

[0024] Figure 6 This is a schematic diagram of the positive wedge block of the rear servo compensation device for foundation pit support of the present invention.

[0025] The diagram shows: 1. Left segment, 2. Right segment, 3. Cutting slit, 4. Upper cylinder, 5. Lower cylinder, 6. Upper left bracket, 7. Upper right bracket, 8. Lower left bracket, 9. Lower right bracket, 10. Bearing plate, 11. Base plate, 11.1. Outer protrusion, 11.2. Inner protrusion, 12. Reinforcing rib, 13. High-strength bolt, 14. Positive wedge block, 15. Rack, 16. Enlarged head, 17. Inverted wedge protrusion, 18. Adjusting screw, 19. Adjusting nut, 20. Positioning nut, 21. U-shaped plate, 22. Support plate. Detailed Implementation

[0026] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0027] like Figures 1-6 As shown, the post-servo compensation device for foundation pit support of the present invention includes an inner concrete support body, which is cut into a left segment 1 and a right segment 2 by a wire saw. An upper hydraulic cylinder 4 and a lower hydraulic cylinder 5 of the axial force servo compensation system are respectively installed above and below the cut slit 3 of the inner support body. The two ends of the upper hydraulic cylinder 4 are respectively abutted against the upper left bracket 6 and the upper right bracket 7, and the two ends of the lower hydraulic cylinder 5 are respectively abutted against the lower left bracket 8 and the lower right bracket 9.

[0028] Each bracket has two outward protrusions 11.1 on both sides. Specifically, each bracket includes a vertical bearing plate 10 and a horizontal base plate 11. The lower end of the bearing plate 10 is welded to the inner end of the base plate 11. Three reinforcing ribs 12 are welded between the bearing plate 10 and the base plate 11. Each reinforcing rib 12 is perpendicular to the bearing plate 10 and the base plate 11. The portion of the base plate 11 that protrudes from both sides of the inner support body forms two outward protrusions 11.1.

[0029] The two outward protrusions 11.1 of the upper left bracket 6 are connected to the two outward protrusions 11.1 of the lower left bracket 8 via two rows of high-strength bolts 13 to form a left sleeve. The two outward protrusions 11.1 of the upper right bracket 7 are connected to the two outward protrusions 11.1 of the lower right bracket 9 via two rows of high-strength bolts 13 to form a right sleeve. The left sleeve covers the left segment 1 of the inner support body, while the right sleeve covers the right segment 2 of the inner support body. Between the upper left bracket 6 and the upper surface of the left segment 1, between the lower left bracket 8 and the lower surface of the left segment 1, between the upper right bracket 7 and the upper surface of the right segment 2, and between the lower right bracket 9 and the lower surface of the right segment 2, a positive wedge-shaped block 14 with a smaller inner diameter and a larger outer diameter is squeezed tightly; that is, four positive wedge blocks 14 are squeezed tightly between the four brackets and the two segments. Each positive wedge block 14 has multiple toothed racks 15 with a smaller inner diameter and a larger outer diameter welded to its bottom plane. The "inner" refers to the direction closer to the cut 3, and the "outer" refers to the direction away from the cut 3. Each positive wedge block 14 has an enlarged head 16 at its outer end.

[0030] Each cow leg has an inverted wedge-shaped protrusion 17 with a larger inner surface and a smaller outer surface on the bottom surface. The lower inclined surface of the inverted wedge protrusion 17 is parallel to and abuts against the upper inclined surface of the corresponding positive wedge block 14.

[0031] Each base plate 11 protrudes from the welded pressure plate 10, forming an inner protrusion 11.2. Two adjusting screws 18 are welded to the inner protrusion 11.2 of each base plate 11. Each adjusting screw 18 is screwed with an adjusting nut 19 and a positioning nut 20; in other words, the four brackets and four base plates 11 are welded together with a total of eight adjusting screws 18. The upper hydraulic cylinder 4 rests on the upper left and upper right U-shaped plates 21 at both ends; the lower hydraulic cylinder 5 rests on the lower left and lower right U-shaped plates 21 at both ends. Each U-shaped plate 21 has two support plates 22 at both ends. The two support plates 22 are movably fitted onto the two adjusting screws 18 of the corresponding base plate 11. Each support plate 22 rests on the corresponding adjusting nut 19 and is pressed by the corresponding positioning nut 20. The "corresponding" means that the support plate 22, the adjusting nut 19 that rests on the support plate 22, and the positioning nut 20 that presses down on the support plate 22 are all fitted onto the same adjusting screw 18.

[0032] The construction method of the post-servo compensation device for foundation pit support of the present invention includes the following steps.

[0033] a. The upper and lower brackets located on one side of the cut 3 are pulled together by two rows of high-strength bolts 13 to form a ferrule, and then fitted into the corresponding segment; for example, the left ferrule is fitted into the left segment 1.

[0034] In this step, the inner support body has not yet been cut with slit 3, but according to the predetermined position of slit 3, the inner support body is divided into left segment 1 and right segment 2.

[0035] b. Insert two positive wedge blocks 14 into the sleeve. For example, insert two positive wedge blocks 14, one on the upper left and one on the lower left, into the left sleeve. The insertion direction is from the outside to the inside. Insert a section of the positive wedge block 14, about six-tenths of its length, into the sleeve. Then, tighten the nuts of the high-strength bolts 13 until the nuts are tightened. This will cause the two upper and lower brackets of the sleeve to close simultaneously and initially tighten the two positive wedge blocks 14. About six-tenths of the inner length of the positive wedge block 14 will be initially tightened, while about four-tenths of the outer length will be outside the sleeve.

[0036] c. Tap the outer ends of the upper and lower wedge blocks respectively, so that the two positive wedge blocks 14 are pushed back into the gap between the sleeve and the corresponding segment for a certain length. The pushing back length is one-tenth of the total length of the positive wedge blocks 14. As the tapping is performed, the rack 15 of the positive wedge block 14 is pressed into the concrete surface of the corresponding segment by the bracket and engages with the contact surface of the segment. For example, the upper left positive wedge block 14 engages with the upper surface of the left segment 1.

[0037] d. Repeat steps a to c, and put the sleeve on the other side of the cut 3 into the corresponding segment to initially tighten the two upper and lower positive wedge blocks 14 on the other side, and knock and squeeze the two upper and lower positive wedge blocks 14 on the other side.

[0038] e. Place the upper and lower hydraulic cylinders between the corresponding brackets. Specifically, by tightening the two sets of adjusting nuts 19 and positioning nuts 20 on the two adjusting screws 18 of each bracket, lock the initial height of the four U-shaped plates 21 (upper left, lower left, upper right, and lower right) to lock the initial position of the upper and lower hydraulic cylinders, and place the upper and lower hydraulic cylinders on the corresponding four U-shaped plates 21. Then drive the hydraulic cylinders to push the brackets on both sides outward, with each hydraulic cylinder outputting a load of approximately 50KN. Each positive wedge block 14 and rack 15 engages with the segment contact surface and cannot move. The bracket continues to move outward relative to the positive wedge block 14, squeezing the positive wedge block 14 tighter and tighter until it is completely locked.

[0039] f. Subsequently, the upper and lower hydraulic cylinders and the pit servo compensation system began continuous operation, monitoring and compensating for the axial force of the internal support in real time based on the lateral displacement deformation of the pit. The pit servo compensation system itself is a mature technology in the civil engineering industry. It includes hydraulic cylinders, hydraulic pump stations, control cabinets, sensors, etc. The workflow involves real-time monitoring of pit deformation data by sensors, with the control cabinet acting as the main controller receiving the data and determining whether the deformation is abnormal. Based on the determination result, the control cabinet controls the hydraulic pump station to pressurize the hydraulic cylinders to achieve automatic compensation of the axial force and control the deformation of the pit retaining structure.

[0040] Once the foundation pit compensation system is installed and put into service, use a wire saw to cut a slit 3 in the middle of the hydraulic cylinder to cut the inner support body into left and right segments.

[0041] This application also has another function: when the lateral deformation of the foundation pit is too large and it is necessary to add post-deformation control measures, it can also replace the traditional method of pouring a new concrete support. Instead, it can install two sets of hydraulic cylinders and brackets on the already poured inner support to compensate for axial force and cut the groove.

Claims

1. A construction method for a post-servo compensation device for foundation pit support, characterized in that: The rear-mounted servo compensation device includes an inner concrete support body, which is cut into left and right segments by a wire saw. The cut of the inner support body is equipped with an upper and lower hydraulic cylinder of the servo compensation system, with each cylinder's ends abutting against two brackets. Each bracket has two outward protrusions on both sides. The two outward protrusions of the upper left bracket are connected to the two outward protrusions of the lower left bracket via two rows of high-strength bolts to form a left sleeve, and the two outward protrusions of the upper right bracket are connected to the two outward protrusions of the lower right bracket via two rows of high-strength bolts to form a right sleeve. Each sleeve fits over the corresponding segment of the inner support body, and a positive wedge-shaped block with a smaller inner diameter and a larger outer diameter is squeezed between each bracket and the corresponding segment. The bottom plane of each positive wedge-shaped block has multiple toothed racks with a smaller inner diameter and a larger outer diameter. The steps of this construction method include: a. The upper and lower brackets located on one side of the cut are pulled together by two rows of high-strength bolts to form a hoop, and then fitted into the corresponding segment; b. Insert the upper and lower positive wedge blocks into the sleeve, and tighten the nuts of the high-strength bolts so that the upper and lower brackets close synchronously and initially tighten the upper and lower positive wedge blocks. The inner side of the positive wedge blocks is initially tightened while the outer side is outside the sleeve. c. Tap the outer ends of the upper and lower positive wedge blocks to push the two positive wedge blocks back into the gap between the sleeve and the corresponding segment for a certain length; and as the tapping occurs, the rack of the positive wedge block is pressed into the concrete surface of the corresponding segment by the corbel and engages with the contact surface of the segment. d. Repeat steps a to c, put the sleeve on the other side of the cut into the corresponding segment, initially tighten the upper and lower positive wedge blocks on the other side, and knock and squeeze the upper and lower positive wedge blocks on the other side. e. Place the upper and lower hydraulic cylinders between the corresponding brackets, drive the hydraulic cylinders to push the brackets on both sides outward, while the positive wedge block rack and segment contact surface are engaged and cannot move. The brackets continue to move outward relative to the positive wedge block, squeezing the positive wedge block tighter and tighter until it is completely locked.

2. The construction method of the post-servo compensation device for foundation pit support according to claim 1, characterized in that: Each cow leg has an inverted wedge-shaped protrusion on its bottom surface, which is larger on the inside and smaller on the outside. The lower slope of the inverted wedge-shaped protrusion is parallel to and abuts against the upper slope of the corresponding positive wedge-shaped block.

3. The construction method of the post-servo compensation device for foundation pit support according to claim 2, characterized in that: Each positive wedge block has an enlarged head at its outer end.

4. The construction method of the post-servo compensation device for foundation pit support according to claim 1, characterized in that: Each bracket includes a vertical bearing plate and a horizontal base plate. The lower end of the bearing plate is welded to the inner end of the base plate, and a reinforcing rib is welded between the bearing plate and the base plate. The portion of the base plate that protrudes from both sides of the inner support body forms two outward protrusions. The portion of the base plate that protrudes from the bearing plate forms an inward protrusion. Two adjusting screws are welded to the inward protrusions of the base plate. Each adjusting screw is screwed with an adjusting nut and a positioning nut. Each cylinder rests on two U-shaped plates on the left and right. Each U-shaped plate has two support plates at both ends. The two support plates are movably fitted onto the two adjusting screws of the corresponding base plate. Each support plate rests on the corresponding adjusting nut and is pressed by the corresponding positioning nut.

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