Water-containing red sandstone stratum deep foundation pit supporting dewatering system

Abstract

The utility model discloses a water-containing red sandstone stratum deep foundation pit supporting dewatering system, which belongs to the technical field of building construction and comprises dewatering wells, top beams, supporting piles, anchor rods, waist beams and plain concrete piles. The supporting piles are arranged in the circumferential direction of the foundation pit at intervals, and the tops are connected into a whole through the top beam. The multiple anchor rods are arranged at equal intervals in the length direction of the edge of the inner wall of the foundation pit, one ends of the anchor rods are embedded into the inner wall of the foundation pit and fixed in a pebble bed through grouting, and the other ends of the anchor rods pull and fix the supporting piles by erecting waist beams. The dewatering well is arranged on the outer side of the foundation pit, penetrates through the red sandstone layer deeply and enters the lower stratum by 5 m. The plain concrete piles are vertically constructed when being excavated to the position 1 m above the red sandstone layer, and the multiple plain concrete piles are matched with one another to form a continuous water interception wall. According to the supporting dewatering system for the deep foundation pit of the water-containing red sandstone stratum, the plain concrete piles are additionally arranged on the inner sides of the supporting piles and the sandstone stratum part, water can be effectively intercepted, and meanwhile the safety of the supporting surface layer at the sandstone part is ensured.

Description

Technical Field

[0001] This utility model belongs to the field of building construction technology, and in particular relates to a deep foundation pit support and dewatering system for water-bearing red sandstone strata. Background Technology

[0002] With the development of high-rise and super high-rise buildings, the demand for large-scale deep foundation pit projects has increased significantly. The unique red sandstone strata in the Lanzhou area, due to their distinctive engineering geological characteristics, pose a major technical challenge in deep foundation pit construction. Exposed red sandstone has a drastically reduced bearing capacity, contains fissure water, has a low permeability coefficient, exhibits significant weathering surface undulations, and is easily softened by water. These characteristics lead to challenges in controlling foundation pit stability, complex groundwater seepage paths, and a high risk of sandstone softening and detachment when carrying out deep foundation pit support and dewatering construction in red sandstone strata. In recent years, with the increasing number of high-rise and super high-rise buildings in Lanzhou, the number of basement levels has generally reached 2-3 stories, corresponding to continuously increasing foundation pit depths. Furthermore, the bottom of the foundation pit is often lower than the red sandstone stratum elevation, further exacerbating the difficulty of support and dewatering construction.

[0003] Existing technologies for deep foundation pit support and dewatering in red sandstone strata mainly employ traditional support measures (such as soil nailing walls and pile support) combined with dewatering wells. In some projects, due to improper support and dewatering methods, safety accidents such as sand inrush, water inrush, and excessive foundation pit deformation are prone to occur, posing a serious threat to the surrounding environment and the safety of people's lives and property. Furthermore, the softening property of red sandstone when exposed to water makes the soil between piles prone to loss, and the support structure is prone to failure.

[0004] Therefore, we propose a deep foundation pit support and dewatering system for water-bearing red sandstone strata. Utility Model Content

[0005] The purpose of this invention is to solve the problems of sand inrush, water inrush, and excessive foundation pit deformation that easily occur in the support and dewatering of deep foundation pits in red sandstone strata in the existing technology, and to propose a deep foundation pit support and dewatering system for water-bearing red sandstone strata.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A deep foundation pit support and dewatering system for water-bearing red sandstone strata includes dewatering wells, capping beams, support piles, anchor bolts, waist beams, and plain concrete piles;

[0008] The support piles are arranged at intervals along the circumference of the foundation pit, and the tops are connected into a whole by a capping beam;

[0009] Multiple anchor rods are equidistantly arranged along the length of the inner wall of the pit. One end is embedded in the inner wall of the pit and fixed by grouting in the pebble layer, and the other end is fixed by traction to the support pile through the erection of waist beam;

[0010] The dewatering wells are located outside the foundation pit and penetrate 5m into the red sandstone layer.

[0011] The plain concrete piles are constructed vertically when the excavation reaches 1m above the red sandstone layer. Multiple plain concrete piles interlock to form a continuous water-cutting wall. The length of the plain concrete pile is twice the height from the top of the pile to the bottom of the pit.

[0012] Preferably, the support piles are reinforced concrete cast-in-place piles with a pile diameter of 800-1200mm and a pile spacing of 1.5-2 times the pile diameter.

[0013] Preferably, the top of the support pile has an extended pile head anchoring steel bar, and the capping beam is erected on top of the support pile through a steel cage and cast integrally with the support pile.

[0014] Preferably, the anchor bolt is inclined, with an inclination angle of 15°-25°.

[0015] Preferably, the waist beam is a steel frame structure, and the waist beam has through holes for anchor rods to pass through. The end of the anchor rod is fitted with a shaped pad, one side of which fits against the waist beam and the other side is perpendicular to the anchor rod axis. The end of the anchor rod is provided with a locking nut.

[0016] Preferably, the waist beam has multiple arc-shaped notches on the side near the support pile, and the arc-shaped notches are adapted to the outer circumference of the support pile.

[0017] Preferably, the well pipe of the dewatering well has a double-layer filter pipe structure, with the outer layer having a diameter of 600mm.

[0018] Preferably, the plain concrete piles include precast piles and cast-in-place piles. The precast piles have two arc-shaped grooves evenly distributed along the circumference. The precast piles and cast-in-place piles are arranged alternately, and the cast-in-place piles fit into the arc-shaped grooves on the adjacent precast piles.

[0019] In summary, this utility model has the following technical effects and advantages:

[0020] This deep foundation pit support and dewatering system for water-bearing red sandstone strata involves constructing plain concrete piles 1m above the sandstone layer during excavation. This ensures that the red sandstone layer remains sealed, reducing the risk of sudden drop in bearing capacity and collapse caused by exposure of red sandstone in traditional methods. By forming a continuous cutoff wall in the red sandstone layer area through plain concrete piles, the system effectively blocks the seepage path of groundwater and avoids soil loss between piles and failure of the support structure due to softening of the sandstone layer caused by water seepage.

[0021] The plain concrete piles extend to a height equal to one meter below the bottom of the foundation pit. Combined with the design of external dewatering wells penetrating 5 meters through the red sandstone layer, a three-dimensional dewatering system of "internal interception and external drainage" is realized, which solves the problem of groundwater being difficult to drain at the junction of the red sandstone layer and the pebble layer.

[0022] Plain concrete piles are constructed by alternating between precast piles and cast-in-place piles. First, precast piles are inserted to maintain the stability of the structure in the foundation pit. Then, cast-in-place piles are poured into the arc-shaped grooves of the precast piles to form a continuous water-cutting wall. Unlike the fully cast-in-place process, which requires interval curing, this method enables continuous operation and shortens the construction period by more than 30%. Attached Figure Description

[0023] Figure 1 This is a cross-sectional structural diagram of the present invention;

[0024] Figure 2 This is a schematic diagram of the overall structure of this utility model;

[0025] Figure 3 for Figure 2 A magnified structural diagram of part A in the middle;

[0026] Figure 4 This is a schematic diagram of the precast pile and cast-in-place pile structures in this utility model.

[0027] In the diagram: 1. Dewatering well; 2. Crown beam; 3. Support pile; 4. Anchor bolt; 41. Irregularly shaped pad; 42. Locking nut; 5. Waist beam; 51. Arc-shaped notch; 6. Plain concrete pile; 61. Precast pile; 611. Arc-shaped groove; 62. Cast-in-place pile; 70. Silty clay layer; 71. Gravel layer; 72. Red sandstone layer; 8. Excavation pit; 81. Inner wall of the excavation pit; 82. Bottom of the excavation pit. Detailed Implementation

[0028] The technical solution of this utility model will now be clearly and completely described in conjunction with the accompanying drawings.

[0029] Reference Figure 1 The unique engineering geological characteristics of the red sandstone strata in the Lanzhou area are generally divided into silty clay layer 70, pebble layer 71, and red sandstone layer 72. Among them, the bearing capacity of red sandstone layer 72 drops sharply after exposure, and it contains fissure water, has a low permeability coefficient, large weathering cross-section undulation, and is easy to soften when exposed to water. These characteristics lead to difficulties in controlling the stability of the foundation pit, complex groundwater seepage paths, and high risk of softening and falling off of the sandstone layer when carrying out deep foundation pit support and dewatering construction in red sandstone strata.

[0030] Reference Figure 1-3 A deep foundation pit support and dewatering system for water-bearing red sandstone strata includes a dewatering well 1, a cap beam 2, support piles 3, anchor bolts 4, a waist beam 5, and plain concrete piles 6.

[0031] Dewatering well 1 is located outside the foundation pit 8, penetrating 72.5 meters into the red sandstone layer. Construction begins outside the foundation pit 8 from the original ground elevation. Dewatering well 1 has a diameter of 600 mm and a spacing of approximately 20 m (the exact spacing will be determined by calculation). The depth of dewatering well 1 is 72.5 meters into the red sandstone layer.

[0032] The support piles 3 are arranged at intervals around the perimeter of the foundation pit 8, and the tops are connected into a whole by the capping beam 2. The support piles 3 provide foundation support for the foundation pit 8.

[0033] Support pile 3 is a reinforced concrete cast-in-place pile with a pile diameter of 800-1200mm and a pile spacing of 1.5-2 times the pile diameter. The pile diameter of support pile 3 is adjusted according to the construction site conditions to adapt to the large undulation of the weathered section of the red sandstone layer 72 in Lanzhou area.

[0034] Reference Figure 1-3 The top of the support pile 3 has extended pile head anchoring steel bars. The cap beam 2 is erected on the top of the support pile 3 through the steel cage 21 and is cast into one piece with the support pile 3. The pile head anchoring steel bars extend into the interior of the cap beam 2, so that the top of the support pile 3 and the cap beam 2 form a double interlocking structure of "steel bar interweaving + concrete wrapping", which improves the shear bearing capacity.

[0035] Reference Figure 1-3 Multiple anchor rods 4 are equidistantly set along the length of the inner wall 81 of the foundation pit. One end is embedded in the inner wall 81 of the foundation pit and fixed by grouting in the pebble layer 71. The other end is fixed by traction to the support pile 3 through the erected waist beam 5. The horizontal tension generated by the anchor rods 4, together with the waist beam 5, acts on the support pile 3 to improve the stability of the support.

[0036] Anchor 4 is installed at an angle of 15°-25°. The anchoring section of the inclined anchor 4 is obliquely engaged with the soil and rock, which increases the friction of the contact surface. Under the same anchoring length, the pull-out bearing capacity of the inclined anchor 4 is effectively improved.

[0037] The waist beam 5 is a steel frame structure. The waist beam 5 has through holes for the anchor rod 4 to pass through. After the anchor rod 4 is installed, the waist beam 5 is installed. The end of the anchor rod 4 is fitted with a special-shaped pad 41. One side of the special-shaped pad 41 fits against the waist beam 5, and the other side is perpendicular to the axis of the anchor rod 4. The end of the anchor rod 4 is provided with a locking nut 42, which fixes the special-shaped pad 41. Under the action of the special-shaped pad 41, the tension at the end of the anchor rod 4 acts perpendicularly on the special-shaped pad 41, ensuring that the force between the anchor rod 4 and the waist beam 5 is more even.

[0038] Reference Figure 1-3The waist beam 5 has multiple arc-shaped notches 51 on the side near the support pile 3. The arc-shaped notches 51 are adapted to the outer circumference of the support pile 3. By fitting the arc-shaped notches 51 to the outer wall of the support pile 3, the contact area is increased, eliminating the stress concentration problem of the straight edge of the waist beam 5 contacting the circular surface of the support pile 3, and improving the overall deformation resistance of the structure.

[0039] Reference Figure 1-4 Plain concrete piles 6 are constructed vertically when excavation reaches 1m above the red sandstone layer 72. Multiple plain concrete piles 6 interlock to form a continuous cutoff wall. The length of the plain concrete piles 6 is twice the height from the pile top to the bottom of the pit 82. That is, the plain concrete piles 6 cut off water from the red sandstone layer 72 from 1m above the red sandstone layer 72 until below the bottom of the pit 82. The exposed length of the plain concrete piles 6 in the pit 8 is the same as the length hidden below the bottom of the pit 82. Because the plain concrete piles 6 are constructed vertically when excavation reaches the sandstone layer 72... Construction was carried out at a depth of 1m to ensure that the red sandstone layer 72 remained in a closed state, reducing the risk of sudden drop in bearing capacity and collapse caused by exposure of the red sandstone layer 72 in traditional processes. A continuous water-cutting wall was formed in the area of ​​the red sandstone layer 72 by plain concrete piles 6, which effectively blocked the seepage path of groundwater and avoided the problem of soil loss between piles and failure of support structure caused by softening of sandstone layer due to seepage. The support piles 3 and the continuous water-cutting wall worked together to control the deformation of the foundation pit 8 within the allowable value of the specification, significantly reducing the incidence of sand and water inrush accidents.

[0040] The well casing of the dewatering well No. 1 has a double-layer filter pipe structure, with the outer layer having a diameter of 600mm.

[0041] The plain concrete pile 6 includes precast piles 61 and cast-in-place piles 62. Each precast pile 61 has two equally spaced arc-shaped grooves 611 along its circumference. The precast piles 61 and cast-in-place piles 62 are alternately arranged, with the cast-in-place piles 62 fitting snugly against the arc-shaped grooves 611 on adjacent precast piles 61. The precast piles 61 are constructed first, leaving space for a single cast-in-place pile 62 in between. After the precast piles 61 are completed, the cast-in-place piles 62 are constructed. The plain concrete pile 6 adopts an alternating combination design of precast piles 61 and cast-in-place piles 62. Through a collaborative approach of "precast piles 61 providing initial support + cast-in-place piles 62 providing interlocking reinforcement," it effectively supports the water interception and shoring of the foundation pit 8. The traditional cast-in-place process requires construction at intervals of 2-3 pile positions, and the area that can be constructed at one time is less than 30% of the total area of ​​the foundation pit 8. After each construction, it is necessary to wait for curing before subsequent construction can be carried out, which results in a long construction period. After the precast piles 61 are driven into the soil layer, the soil strength does not change much. Drilling and grouting between two precast piles 61 to form cast-in-place piles 62 can shorten the construction cycle. Furthermore, during the grouting process of the cast-in-place piles 62, the grout can penetrate into the arc-shaped groove 611 of the precast piles 61 and the surrounding micro-cracks to achieve the filling of gaps.

[0042] Working principle:

[0043] Construction began on the outside of foundation pit 8, starting from the original ground elevation, with the construction of dewatering well 1. The diameter of dewatering well 1 is 600mm, and the dewatering spacing is approximately 20m (the specific spacing will be determined based on calculations). The depth of dewatering well 1 is 72.5 meters through the red sandstone layer.

[0044] Secondly, construct support piles 3, and the spacing between support piles 3 is generally less than twice the pile diameter.

[0045] Next, the top capping beam 2 of the support pile 3 is constructed. The width of the capping beam 2 is the diameter of the support pile 3, and the height is 0.6 times the diameter of the support pile 3.

[0046] Next, the earthwork is excavated to the anchor bolt 4 condition. Steel mesh is hung between the support piles 3 and C20 concrete is sprayed. Anchor bolt 4 is constructed. After the anchor bolt 4 is constructed, a waist beam 5 is erected at the end and the end of the anchor bolt 4 is fixed.

[0047] Finally, construction of plain concrete piles 6 begins 1m above the red sandstone layer 72. Precast piles 61 are constructed first, leaving space for a single cast-in-place pile 62 in the middle. After the precast piles 61 are completed, cast-in-place piles 62 are constructed. The concrete strength of cast-in-place piles 62 is C20. The length of plain concrete piles 6 is twice the height from the top of the pile to the bottom of the pit 82. Each plain concrete pile 6 is parallel to the support piles 3. The arc grooves 611 on the cast-in-place piles 62 and the precast piles 61 interlock to form a water-cutting wall.

Claims

1. A deep foundation pit support and dewatering system for water-bearing red sandstone strata, characterized in that: It includes dewatering wells (1), capping beams (2), support piles (3), anchor bolts (4), waist beams (5) and plain concrete piles (6); The support piles (3) are arranged at intervals around the perimeter of the foundation pit (8), and the tops are connected into a whole by the capping beam (2); Multiple anchor rods (4) are equidistantly arranged along the length of the inner wall (81) of the pit. One end is embedded in the inner wall (81) of the pit and fixed by grouting in the pebble layer (71). The other end is fixed by traction to the support pile (3) through the erected waist beam (5). The dewatering well (1) is located outside the foundation pit (8) and penetrates five meters into the red sandstone layer (72); The plain concrete piles (6) are constructed vertically when excavation reaches 1m above the red sandstone layer (72). Multiple plain concrete piles (6) interlock to form a continuous water-cutting wall. The length of the plain concrete piles (6) is twice the height from the top of the pile to the bottom of the pit (82).

2. The deep foundation pit support and dewatering system for water-bearing red sandstone strata according to claim 1, characterized in that, The support pile (3) is a reinforced concrete cast-in-place pile with a pile diameter of 800-1200mm and a pile spacing of 1.5-2 times the pile diameter.

3. The deep foundation pit support and dewatering system for water-bearing red sandstone strata according to claim 1, characterized in that, The top of the support pile (3) has an extended pile head anchoring steel bar, and the cap beam (2) is erected on the top of the support pile (3) by a steel cage (21) and cast together with the support pile (3).

4. The deep foundation pit support and dewatering system for water-bearing red sandstone strata according to claim 1, characterized in that, The anchor rod (4) is set at an angle of 15°-25°.

5. The deep foundation pit support and dewatering system for water-bearing red sandstone strata according to claim 4, characterized in that, The waist beam (5) is a steel frame structure. The waist beam (5) has a through hole for the anchor rod (4) to pass through. The end of the anchor rod (4) is fitted with a special-shaped pad (41). One side of the special-shaped pad (41) is in contact with the waist beam (5), and the other side is perpendicular to the axis of the anchor rod (4). The end of the anchor rod (4) is provided with a locking nut (42).

6. The deep foundation pit support and dewatering system for water-bearing red sandstone strata according to claim 1, characterized in that, The waist beam (5) has multiple arc-shaped notches (51) on the side near the support pile (3), and the arc-shaped notches (51) are adapted to the outer circumference arc of the support pile (3).

7. The deep foundation pit support and dewatering system for water-bearing red sandstone strata according to claim 1, characterized in that, The well pipe of the precipitation well (1) is a double-layer filter pipe structure with an outer pipe diameter of 600mm.

8. The deep foundation pit support and dewatering system for water-bearing red sandstone strata according to claim 1, characterized in that, The plain concrete pile (6) includes precast piles (61) and cast-in-place piles (62). The precast piles (61) have two arc-shaped grooves (611) evenly distributed along the circumference. The precast piles (61) and cast-in-place piles (62) are arranged alternately, and the cast-in-place piles (62) fit into the arc-shaped grooves (611) on the adjacent precast piles (61).

Images