A treatment method for the intrusion of bored cast-in-place piles in karst strata

Abstract

The present invention discloses a method for treating the encroachment of bored cast-in-place piles in karst strata. The encroaching part of the encroaching bored cast-in-place pile is chiseled off, including the following steps: when the encroaching part of the encroaching bored cast-in-place pile is greater than 30% of the pile diameter, make measurement marks; break the anchor protection layer of the encroaching bored cast-in-place pile and measure the size of the encroaching bored cast-in-place pile invading the main structure; according to the size of the encroaching bored cast-in-place pile invading the main structure, excavate the rock and soil between the encroaching bored cast-in-place piles to the position of the normal pile's soil-facing side and spray plain concrete with wire mesh for primary support protection; mark the encroaching part of the encroaching bored cast-in-place pile that needs to be broken; at the position upward from the bottom plane of the encroaching bored cast-in-place pile that needs to be broken, break the encroaching bored cast-in-place pile to pre-insert the space for the I-beam; insert the I-beams up and down and implant the double I-beams to form a portal support. The present invention adopts the above method for treating the encroachment of bored cast-in-place piles in karst strata, avoiding the foundation pit safety risks brought about after the treatment of the encroaching bored cast-in-place piles and ensuring the safety of the foundation pit.

Description

Technical Field

[0001] The present invention relates to the technical field of deep foundation pit construction, and in particular to a method for treating the encroachment of bored cast-in-place piles in karst strata. Background Art

[0002] When constructing bored cast-in-place piles in soft upper and hard lower karst strata, it is difficult to control the verticality of the cast-in-place piles, and the verticality of the cast-in-place piles often exceeds the standard, and even a large encroachment problem occurs. The conventional method for treating encroached cast-in-place piles is to chisel off the encroached part of the cast-in-place pile to meet the construction space requirements of the main structure. However, in karst strata, especially when the rock layer is hard, the karst caves are developed and the filling is soft or there is no filling, when using a rotary drilling rig to form a hole, affected by the strata, the drill barrel (bit) is prone to deflect, and its deflection direction is related to the strata; when the cast-in-place pile deflects towards the inside of the station, it will affect the construction of the station structure. If the deflection amount is large and multiple piles deflect, excessive chiseling of the encroached part of the cast-in-place pile will affect the foundation pit safety, and in severe cases, there will be a large risk of foundation pit collapse.

[0003] On the premise that the ground space permits, supplementary piles are made outside the encroached cast-in-place piles. The commonly used rotary drilling rig weighs 85 - 100 tons, and there is a large construction risk when operating at the edge of the foundation pit. Supplementary piles cannot be made when the ground environment does not permit. If the encroached part of the cast-in-place pile that invades the structure is chiseled off, such as continuous chiseling of multiple piles, it will bring a large foundation pit safety risk. If the encroached part is not chiseled off, it is difficult to construct the foundation pit structure. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for treating the encroachment of bored cast-in-place piles in karst strata. Through the underpinning of the support structure, the foundation pit safety risk brought about after the treatment of the encroached cast-in-place piles is avoided, and the safety of the foundation pit is ensured.

[0005] To achieve the above purpose, the present invention provides a method for treating the encroachment of bored cast-in-place piles in karst strata, including the following steps:

[0006] S1. When the encroached part of the encroached cast-in-place pile is greater than 30% of the pile diameter, record the measurement marks and continue to excavate the foundation pit to the design elevation;

[0007] S2. Remove the shotcrete protective layer at the location of the encroached cast-in-place pile, measure the size of the encroached cast-in-place pile invading the main structure, and confirm the geological conditions by horizontally probing holes through the gaps between the cast-in-place piles;

[0008] S3. According to the size of the encroached cast-in-place pile invading the main structure measured in step S2, excavate the rock and soil between the encroached cast-in-place piles to the position of the normal pile's soil-facing side and hang a mesh and spray plain concrete for primary support protection;

[0009] S4. Mark the encroached part of the encroached cast-in-place pile to be removed, and mark the plane position of the encroached cast-in-place pile at the elevation of the bottom slab cushion;

[0010] S5. At the position upward from the bottom plane of the encroaching cast-in-place pile to be demolished, demolish the encroaching cast-in-place pile to create a space for pre-inserting the I-beam. The pre-treated encroaching cast-in-place pile is demolished upward at the same bottom plane position. The radial demolition distance reaches the vertical marking line to be demolished, and the steel bars within the demolition range are cut off. The I-beam is welded to the cut-off bottom steel bars and the pile steel bars in contact.

[0011] S6. Adopt the method described in step S5 to demolish the encroaching cast-in-place pile downward from the upper plane of the encroaching cast-in-place pile to be demolished, and insert the I-beam into the notch formed by the demolition.

[0012] S7. Insert a double-spliced I-beam between the upper and lower inserted I-beams. The double-spliced I-beam is welded to the upper and lower I-beams to form a portal support. The clear distance between the double-spliced I-beams meets the requirements for the installation, grouting, and prestressing construction of the anchor cable and the anchor head.

[0013] Preferably, in step S1, construct the cushion layer of the foundation pit floor according to the design plan, and leave a 0.5 m construction area reserved at the position of the encroaching cast-in-place pile.

[0014] Preferably, in step S4, according to the measured encroaching dimension of the encroaching cast-in-place pile on the main structure, mark the upper position of the encroaching part of the encroaching cast-in-place pile to be demolished, and mark the part of the encroaching cast-in-place pile to be demolished.

[0015] Preferably, in step S5, the outer side of the I-beam is flush with the vertical marking line, and the length of the I-beam is the distance of the outer encroaching cast-in-place pile to be treated + 2 times the clear distance between piles.

[0016] Preferably, in step S5, the inserted I-beam is the lower I-beam.

[0017] Preferably, in step S6, the inserted I-beam is the upper I-beam.

[0018] Preferably, in step S7, the double-spliced I-beam is vertically welded to the inner side of the lower I-beam. After welding, plain concrete is filled below the upper surface of the lower I-beam. The double-spliced I-beam is erected above the lower I-beam, and the length of the double-spliced I-beam is the same as the height of the encroaching cast-in-place pile.

[0019] Preferably, the steps for the clear distance between the double-spliced I-beams to meet the requirements for the installation, grouting, and prestressing construction of the anchor cable and the anchor head in step S7 are as follows:

[0020] S71. After the double-spliced I-beam is fixed, weld the anchor head fixing plate at the position for constructing the anchor cable. The sunken groove faces the soil-facing side, and the groove depth is determined according to the size of the anchor fitting.

[0021] S72. According to the geological conditions and the deviation of the encroaching cast-in-place pile, construct the anchor cable at the position of the I-beam set above the cast-in-place pile to reinforce the upper part of the cast-in-place pile.

[0022] After the cable anchor construction is completed, spray plain concrete not lower than C20 on the exposed formation to complete the initial support protection. Remove the encroaching part of the cast-in-place pile, process the steel bars at the encroaching part, weld the exposed steel bars to the double-rolled I-beams, and then spray plain concrete for protection.

[0023] S74. Roughly chisel the structural surface of the later-constructed part, construct the waterproof structure, tie the steel bars, tie the steel bars of the main structure, erect the formwork, and pour concrete of the same grade. After the steel bar tying is completed and passed the acceptance, erect the formwork and pour concrete of the same grade to complete the construction.

[0024] Therefore, the present invention adopts the above-mentioned method for dealing with the encroachment of bored cast-in-place piles in karst strata, inserts upper and lower I-beams, implants double-rolled I-beams between the upper and lower I-beams to reinforce the structure of the cast-in-place pile, and through the underpinning of the supporting structure, avoids the foundation pit safety risks brought about after the treatment of the encroaching cast-in-place pile, ensuring the safety of the foundation pit.

[0025] The technical solution of the present invention will be further described in detail below with reference to the drawings and embodiments. Brief Description of the Drawings

[0026] Figure 1 An encroaching cast-in-place pile in a karst stratum of a method for dealing with the encroachment of bored cast-in-place piles in karst strata according to the present invention;

[0027] Figure 2 A partial schematic view of the main structure of a subway station of a method for dealing with the encroachment of bored cast-in-place piles in karst strata according to the present invention;

[0028] Figure 3 A schematic view of the part of the cast-in-place pile to be removed of a method for dealing with the encroachment of bored cast-in-place piles in karst strata according to the present invention;

[0029] Figure 4 A schematic cross-sectional view of the insertion of the I-beam of a method for dealing with the encroachment of bored cast-in-place piles in karst strata according to the present invention;

[0030] Figure 5 An enlarged view of the insertion of the I-beam of a method for dealing with the encroachment of bored cast-in-place piles in karst strata according to the present invention;

[0031] Figure 6 A schematic plan view of the insertion of the I-beam of a method for dealing with the encroachment of bored cast-in-place piles in karst strata according to the present invention;

[0032] Figure 7 A schematic view of the anchor head fixing plate structure of a method for dealing with the encroachment of bored cast-in-place piles in karst strata according to the present invention;

[0033] Reference Signs in the Drawings

[0034] 1. Invasive cast-in-place pile; 2. Karst cave; 3. Medium-weathered limestone; 4. Bottom slab cushion; 5. Invasive part; 6. I-beam; 7. Double I-beam; 8. Anchor head fixing plate; 9. Anchor cable and anchor head; 10. Concrete support; 11. Station structure; 12. Cast-in-place pile. Detailed implementation mode

[0035] Embodiment

[0036] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by terms such as "upper", "lower", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship in which the product of the present invention is usually placed during use. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present invention.

[0037] Refer to Figures 1 - 7 , Figure 1 For the invasive situation of the cast-in-place pile after the foundation pit excavation in a certain lava formation, 6 consecutive invasive cast-in-place piles 1 are shown in the figure. According to the stratigraphic profile, the position of the middle plate of the station is the stratigraphic interface. The geological exploration data shows that the bottom of the retaining pile is mainly located in the medium-weathered limestone layer 3. According to the geological exploration, there are many karst caves within the foundation pit range. The karst development is mainly manifested as solution pores, solution fissures and small karst caves 2, belonging to the shallow-covered karst type. The karst development situation of the drilled limestone shows no obvious regularity in the vertical direction. Figure 2 It is a schematic cross-section of the invasive cast-in-place pile and the station structure, including the concrete support 10, the station structure 11, the cast-in-place pile 12 and the bottom slab cushion 4. Figure 3 It is a schematic diagram of the part that needs to be broken of the cast-in-place pile. A treatment method for the invasion of bored cast-in-place piles in a karst formation includes the following steps:

[0038] S1: After the foundation pit grouting construction is completed, the foundation pit is excavated according to the requirements of the construction plan. When the invasive part 5 of the invasive cast-in-place pile 1 during the excavation is greater than 30% of the pile diameter, make measurement marks, continue to excavate the foundation pit to the design elevation, construct the bottom slab cushion 4 of the foundation pit according to the design plan, and leave a 0.5m construction part at multiple invasive cast-in-place piles 1. The main structure construction of other parts is completed according to the normal construction process;

[0039] S2: Remove the shotcrete protective layer at the invasive cast-in-place pile 1, measure the size of the invasive cast-in-place pile 1 invading the main structure, confirm the geological situation by horizontal exploration holes in the gaps between the cast-in-place piles, and if there are non-dense parts in the karst cave or karst filling according to the geological situation checked, carry out reinforcement treatment according to the on-site situation;

[0040] S3: According to the size of the invasive cast-in-place pile invading the main structure measured in step S2, excavate the rock and soil between the invasive cast-in-place piles to the position of the normal pile's soil-facing side and spray plain concrete with wire mesh for primary support protection;

[0041] S4: Mark the encroaching part 5 of the encroaching cast-in-place pile 1. Mark the plane position of the encroaching cast-in-place pile 1 at the elevation of the floor cushion 4. According to the measured size of the encroaching cast-in-place pile into the main structure, mark the upper position of the encroaching cast-in-place pile 1 to be removed, and mark the part of the encroaching cast-in-place pile 1 that needs to be removed, such as Figure 3 shown;

[0042] S5: At the position above the bottom plane of the encroaching cast-in-place pile 1 to be removed, break the encroaching cast-in-place pile 1 to pre-insert the space for the I-beam 6. Multiple pre-treated encroaching cast-in-place piles 1 are broken upward at the same bottom plane position. The radial distance of the break is up to the vertical marking line to be removed, and the space can ensure the insertion of the I-beam 6. As Figure 4 shown in the cross-sectional view of the insertion of the I-beam 6. The outer side of the I-beam 6 is flush with the vertical marking line. Cut off the steel bars within the breaking range. Weld the I-beam 6 to the bottom steel bars to be cut and the pile steel bars in contact. The length of the I-beam 6 is the distance of the encroaching cast-in-place pile on the outer side to be treated + 2 times the clear distance between piles. The I-beam 6 inserted in this step is the lower I-beam;

[0043] S6: Use the method described in step S5 to break the encroaching cast-in-place pile downward from the upper plane of the encroaching cast-in-place pile 1 to be removed and pre-insert the I-beam 6. The inserted I-beam 6 is the upper I-beam;

[0044] S7: Insert a double I-beam 7 between the upper and lower inserted I-beams 6, and reliably weld the double I-beam 7 to the upper and lower I-beams 6. As Figure 5 shown, to form a portal support to reinforce the encroaching cast-in-place pile to be removed. Vertically weld a double I-beam inside the lower I-beam. After welding is completed, fill plain concrete below the upper surface of the lower I-beam. Erect a double I-beam above the lower I-beam. The length of the double I-beam is the same as the height of the encroaching cast-in-place pile. The clear distance between the double I-beams meets the installation, grouting, and prestressing construction of the anchor cable and the anchor head 9.

[0045] The following are the steps for the clear distance between the double I-beams in step S7 to meet the installation, grouting, and prestressing construction of the anchor cable and the anchor head 9:

[0046] S71: After the double I-beam 7 is fixed, weld the anchor head fixing plate 8 at the position of the construction of the anchor cable, as Figure 6 shown. The anchor head fixing plate 8 is made of a 20-mm-thick steel plate, with the sunken groove facing the soil side. The depth of the groove is determined according to the size of the anchor; as Figure 7 shown in the structural diagram of the anchor head fixing plate 8;

[0047] S72: According to the geological conditions and the deviation of the encroaching cast-in-place pile 1, construct the anchor cable at the position of the I-beam set above the cast-in-place pile to further reinforce the upper part of the cast-in-place pile that does not need to be treated;

[0048] S73: After the cable anchor construction is completed, spray plain concrete not lower than C20 on the exposed formation to complete the initial support protection. Demolish the part of the cast-in-place pile that invades the line, process the steel bars at the invaded part. After welding the exposed steel bars to the double-spliced I-beams, spray plain concrete for protection.

[0049] S74: Smoothly chisel the surface of the station structure at the later construction part, construct the waterproof structure and tie the steel bars according to the requirements of the design scheme. Tie the steel bars of the main structure. The steel bars of the later construction part are connected to the steel bars of the previously constructed structure through the reserved straight thread sleeves. After the steel bar tying is completed and passes the acceptance, erect the formwork and pour concrete of the same grade to complete the construction of the station structure.

[0050] Therefore, the present invention adopts the above method for dealing with the invasion of the cast-in-place pile in the karst formation, inserts the upper and lower I-beams, implants the double-spliced I-beams between the upper and lower I-beams to reinforce the cast-in-place pile structure. Through the replacement of the support structure, the foundation pit safety risk brought about after the treatment of the invaded cast-in-place pile is avoided, ensuring the safety of the foundation pit.

[0051] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that: they can still modify or equivalently replace the technical solutions of the present invention, and these modifications or equivalent replacements cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A treatment method for the intrusion of bored cast-in-place piles in karst strata, characterized in that: It includes the following steps: S1. When the encroaching part of the cast-in-place pile is more than 30% of the pile diameter, record the measurement marks and continue to excavate the foundation pit to the designed elevation; S2. Remove the shotcrete protection layer at the location of the encroaching cast-in-place pile, measure the size of the encroaching cast-in-place pile into the main structure, and confirm the geological conditions by horizontally probing holes through the gaps between the cast-in-place piles; S3. According to the size of the encroaching cast-in-place pile into the main structure measured in step S2, excavate the rock and soil between the encroaching cast-in-place piles to the position on the soil-facing side of the normal pile, and hang a mesh and spray plain concrete for primary support protection; S4. Mark the encroaching part of the encroaching cast-in-place pile to be demolished, and mark the plane position of the encroaching cast-in-place pile at the elevation of the bottom slab cushion; S5. At the position above the bottom plane of the encroaching cast-in-place pile to be demolished, break the encroaching cast-in-place pile to pre-insert the space for the I-beam. The pre-treated encroaching cast-in-place pile is broken upward at the same bottom plane position. The radial distance of the break is up to the vertical marked line to be broken, cut off the steel bars within the break range, and weld the I-beam to the bottom steel bars to be cut off and the pile steel bars in contact; S6. Use the method described in step S5 to break the encroaching cast-in-place pile downward from the upper plane of the encroaching cast-in-place pile to be demolished and insert the I-beam into the notch; S7. Insert double I-beams between the upper and lower inserted I-beams, weld the double I-beams to the upper and lower I-beams to form a portal support. The clear distance between the double I-beams meets the requirements for the installation, grouting, and prestressing construction of the anchor cable and the anchor head. After the anchor cable construction is completed, demolish the encroaching part of the cast-in-place pile; 2. The treatment method for the encroachment of bored cast-in-place piles in karst strata according to claim 1, wherein: In step S1, construct the bottom slab cushion of the foundation pit according to the design plan, and leave a 0.5m construction area at the location of the encroaching cast-in-place pile; 3. The treatment method for the intrusion of bored cast-in-place piles in karst strata according to claim 1, characterized in that: In step S4, according to the size of the encroaching cast-in-place pile into the main structure measured, mark the upper position of the encroaching part of the encroaching cast-in-place pile to be demolished, and mark the part of the encroaching cast-in-place pile to be demolished; 4. A method for treating the encroachment of bored cast-in-place piles in karst strata according to claim 1, characterized in that: In step S5, the outside of the I-beam is flush with the vertical marked line, and the length of the I-beam is the distance of the outside encroaching cast-in-place pile to be treated + 2 times the clear distance between piles; 5. The treatment method for the intrusion of bored cast-in-place piles in karst strata according to claim 1, characterized in that: In step S5, the inserted I-beam is the lower I-beam; 6. The treatment method for the encroachment of bored cast-in-place piles in karst strata according to claim 1, characterized in that: In step S6, the inserted I-beam is the upper I-beam; 7. A method for treating the intrusion of bored cast-in-place piles in karst strata according to claim 1, characterized in that, In step S7, vertically weld double I-beams to the inner side of the lower I-beam. After welding is completed, fill plain concrete below the upper surface of the lower I-beam. Erect double I-beams above the lower I-beam, and the length of the double I-beams is the same as the height of the encroaching cast-in-place pile; 8. A method for treating the intrusion of bored cast-in-place piles in karst strata according to claim 1, characterized in that In step S7, the steps for the clear distance between the double I-beams to meet the requirements for the installation, grouting, and prestressing construction of the anchor cable and the anchor head are as follows: S71. After the double I-beams are fixed, weld the anchor head fixing plate at the location of the anchor cable construction. The sunken groove faces the soil-facing side, and the groove depth is determined according to the size of the anchor; S72. According to the geological conditions and the deviation of the encroaching cast-in-place pile, construct the anchor cable at the position of the I-beam above the cast-in-place pile to reinforce the upper part of the cast-in-place pile; S73. After the anchor cable construction is completed, spray plain concrete not less than C20 on the exposed formation to complete the primary support protection, demolish the encroaching part of the cast-in-place pile, process the steel bars at the encroaching part, weld the exposed steel bars to the double I-beams and then spray plain concrete for protection; For the structurally smooth chiseling of the post-construction part, construct the waterproof structure, tie the steel bars, tie the steel bars of the main structure, erect the formwork, and pour the concrete of the same grade. After the steel bar tying is completed and passes the acceptance, erect the formwork and pour the concrete of the same grade to complete the construction.

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