Reinforcing pile with shear key permanent steel casing combined with bottom bag grouting expanded head and construction method of reinforcing pile

Abstract

The invention discloses a reinforced pile with a shear key and a permanent steel casing combined with a bottom bag grouting expanded head and a construction method thereof. The reinforced pile comprises the permanent steel casing with the shear key, the permanent steel casing with the shear key comprises an inner cylinder body and a plurality of trapezoidal shear keys and rectangular shear keys which are arranged on the outer peripheral side and the inner peripheral side of the inner cylinder body respectively; sawtooth blade feet are arranged at the bottom of the inner cylinder body and connected with the bag interlocking grooves in a locked mode, and the inner cylinder body can design a shear ring according to the length of the inner cylinder body so as to enhance the bearing capacity. The bag grouting system is connected with the inner cylinder body and comprises a bag body, a high-pressure grouting pipe, an anchoring chassis and flow guide ribs, the upper end of the bag body is fixed to the inner cylinder body through a hoop, the anchoring chassis is connected with the bag interlocking groove in a sealed mode through a flange plate, and the high-pressure grouting pipe is connected with the inner cylinder body. Compared with the traditional technology, the problems of hole collapse, necking and pile sliding are solved fundamentally, and the friction force around the pile and the bearing capacity of the pile bottom and the pile end can be enhanced.

Description

Technical Field

[0001] The invention relates to the technical field of beaded-type high-speed railway roadbed construction in medium-strong karst areas, and in particular to a permanent steel casing with a shear key combined with a bottom bag grouting enlarged head reinforced pile and a construction method thereof. Background Art

[0002] High-speed railway deformation control is strict (≤15mm). In areas with densely developed beaded karst caves in deep overburden (≥30m), pile foundations find it difficult to find a suitable bearing layer. Pile lengths may reach 80-90m or even exceed 100m and still fail to reach the bedrock layer. There may also be undiscovered karst caves underneath. High-speed railway subgrade diseases are frequent in karst areas (for example, the Guizhou section of the Shanghai-Kunming High-Speed ​​Railway has over 2,000 kilometers of karst-prone sections). The beaded karst cave geology poses many difficulties for bored pile construction, which is prone to problems such as hole collapse, slurry leakage, and ground subsidence. Conventional grouting in thick overburden is also difficult to handle deep karst caves. The traditional method of grouting, filling, solidification, and then excavation with cement and water glass slurry is difficult to adapt to such geological conditions. It has defects such as large investment in equipment, materials, and labor, extremely high requirements for exploration, time-consuming layer-by-layer grouting, casing material problems affecting the segmentation effect, and difficulty in controlling grouting pressure. In addition, ultra-long piles are expensive and construction faces huge challenges such as borehole collapse.

[0003] Based on the above technical problems, the present invention provides a permanent steel casing with shear keys combined with a bottom bag grouting enlarged head reinforced pile and a construction method thereof. Summary of the Invention

[0004] The purpose of the present invention is to provide a permanent steel casing with shear keys combined with a bottom bag grouting enlarged head reinforced pile and a construction method thereof, so as to solve the problems existing in the prior art.

[0005] To achieve the above object, the present invention provides the following solution: The present invention provides a permanent steel casing with shear keys combined with a bottom bag grouting and enlarged head reinforced pile, comprising:

[0006] A permanent steel casing with shear keys comprises an inner tube body and a plurality of trapezoidal shear keys and rectangular shear keys respectively arranged on the outer and inner circumferences of the inner tube body; the bottom of the inner tube body is provided with serrated blades, which are locked and connected with the interlocking grooves of the bag; the inner tube body can be designed with shear rings according to its own length to enhance the bearing capacity;

[0007] The bladder bag grouting system is connected to the inner tube body, and includes a bladder bag body, a high-pressure grouting pipe, an anchoring chassis and a guide rib, wherein the upper end of the bladder bag body is fixed to the inner tube body by a clamp, the anchoring chassis is tightly connected to the bladder bag interlocking groove through a flange, and the high-pressure grouting pipe is connected to the inner tube body.

[0008] According to the permanent steel casing with shear keys combined with the bottom bag grouting enlarged head reinforced pile provided by the present invention, the size of the trapezoidal shear keys is 80×12mm, four are arranged circumferentially, the spacing between two adjacent ones is 90°, the longitudinal spacing is 500mm, and the longitudinal spacing in the cave section is 300mm; the height of the rectangular shear keys is 100mm, the bottom width is 100mm, and the top width is 60mm, four are arranged circumferentially, the spacing between two adjacent ones is 90°, and the longitudinal spacing is 1000mm; the trapezoidal shear keys and the rectangular shear keys are respectively welded by K-shaped groove welds, the weld penetration is ≥15mm, and the verticality deviation of the steel casing is ≤1% of the pile diameter.

[0009] According to the permanent steel casing with shear key combined with the bottom bag grouting enlarged head reinforced pile provided by the present invention, in the bag grouting system, the bag body is a prefabricated folded rubber bag, the outer layer is a high-strength polyester fiber woven layer, the inner lining is a chloroprene rubber film with a pressure resistance of more than 10MPa, and has an annular grouting cavity; the guide ribs are a number of radial reinforcing ribs for controlling the expansion shape, ensuring that the slurry diffuses into a pear-shaped profile and accelerates the diffusion; the high-pressure grouting pipe includes a grouting inner sleeve, a type I grouting outer sleeve, a connector and a type II grouting outer sleeve, and grouting is achieved by alternatingly connecting the type I grouting outer sleeve, the connector and the type II grouting outer sleeve, and the grouting pipe outlet and the slurry outlet are used for grouting into the bag body.

[0010] According to the reinforced piles provided by the present invention, the permanent steel casing with shear keys combined with the bottom bladder grouting enlarged head, the permanent steel casing with shear keys is subjected to full-length anti-corrosion treatment, the galvanized layer is ≥80μm or epoxy coating is adopted, and the diameter is 20cm larger than the designed pile diameter; the arrangement and quantity of the trapezoidal shear keys and the rectangular shear keys, the segment length of the permanent steel casing with shear keys and the size of the bottom bladder grouting enlarged head system are all adjusted according to geological exploration data.

[0011] A construction method for reinforced piles with a permanent steel casing with shear keys and bottom bag grouting and enlarged heads includes the following steps:

[0012] S1, processing the inner tube body and grouting bag, obtaining the beaded karst distribution according to geological survey data, processing trapezoidal shear keys in different areas on the outer surface of the inner tube body, anti-corrosion treatment of the entire length of the inner tube body, and pre-installing the bag grouting system at the bottom of the inner tube body;

[0013] S2, design and process the outer casing, which provides temporary support;

[0014] S3: Positioning and initial sinking of the outer casing. Measure and stake out the pile position with a deviation of ≤3cm. Clamp the first section of casing with a vibratory hammer and press it vertically in. After the outer casing is in place, connect the drill pipe to the drilling rig, connect the rotary drill to the drill pipe, and drill the soil in the casing until it reaches the roof of the second cavern.

[0015] S4: The outer casing is laid in sections and welded until the top of the cave is reached. After that, the bottom drill bit is replaced. A vibratory hammer is used to assist in sinking the casing and the verticality is monitored in real time. The deviation is ≤1%.

[0016] S5, repeating steps S3 and S4 until the outer casing sinks to the designed elevation;

[0017] S6, clearing obstacles and taking soil inside the barrel. The rotary drill takes soil inside the outer casing to the designed elevation. If there are isolated rocks, high-pressure water jetting is used inside the barrel to break them.

[0018] S7, hoist the inner cylinder to the bottom of the hole;

[0019] S8, drilling the inner barrel to the bearing layer with a rotary drill;

[0020] S9, pouring concrete for the inner tube;

[0021] S10, after the concrete has initially set and the strength is ≥5MPa, the outer casing is pulled out in sections, and then the fluidized solidified soil is injected into the gaps in the hole wall simultaneously, and the bag body constrains the grouting to form an enlarged head;

[0022] S11, the outer casing is pulled out layer by layer, and fluidized solidified soil is injected section by section through the gaps between the trapezoidal shear keys to permanently retain the permanent steel casing with shear keys.

[0023] According to the construction method of a permanent steel casing with shear keys combined with bottom bag grouting and enlarged head reinforced pile provided by the present invention, step S1 includes the following steps:

[0024] S11. Determine the beaded karst distribution area based on geological survey data, and process rectangular shear keys and trapezoidal shear keys in the corresponding areas of the inner tube body to ensure that the arrangement and quantity of the rectangular shear keys and trapezoidal shear keys are adapted to the karst distribution characteristics;

[0025] S12, the inner barrel is treated with full-length anti-corrosion treatment, using zinc plating or epoxy coating;

[0026] S13, pre-install the bag grouting system at the bottom of the inner barrel.

[0027] According to the construction method of the reinforced pile with permanent steel casing with shear key combined with bottom bag grouting and enlarged head provided by the present invention, step S2 includes the following steps:

[0028] S21, select Q345 steel plate as the outer casing material, and determine its wall thickness to be 12-20mm;

[0029] S22, determine the outer casing diameter according to the designed pile diameter, making it 40 cm larger than the designed pile diameter;

[0030] S23, annular cutting teeth are welded on the bottom of the outer casing, and the blade angle is controlled to 30°-45° to enhance the soil cutting ability.

[0031] According to the construction method of the reinforced pile with permanent steel casing with shear key combined with bottom bag grouting and enlarged head provided by the present invention, step S3 includes the following steps:

[0032] S31, determine the pile position by measuring and setting out, ensuring that the pile position deviation is ≤3cm;

[0033] S32: Use a vibratory hammer to clamp the first section of outer casing and press it vertically into the formation. For soft formations, keep the water head inside the casing 2m above the groundwater level.

[0034] S33, after the outer casing is in place, use a rotary drill to extract soil from the casing until the top of the second cave is reached and drilling is stopped.

[0035] According to the construction method of the reinforced pile with permanent steel casing with shear key combined with bottom bag grouting and enlarged head provided by the present invention, step S10 includes the following steps:

[0036] S101: After the concrete in the inner tube has initially set and its strength is ≥5MPa, the outer casing is pulled out in sections. After each section is pulled out, fluidized solidified soil is immediately injected into the gaps in the hole wall to fill the gap between the outer casing and the inner tube and form preliminary support.

[0037] S102, synchronously constraining grouting is performed on the bag body to form an enlarged head. The grouting process is carried out in the following stages:

[0038] The first stage uses 1.5MPa low-pressure grouting to slowly expand the folded bladder body to a preliminary diameter of 1.8D, avoiding uneven deformation of the bladder body due to instantaneous excessive force;

[0039] The second stage uses 4.0MPa medium-pressure grouting to squeeze the surrounding soil through the radial force generated by the further expansion of the bag body, thereby achieving compaction and reinforcement of the pile bottom and surrounding soil;

[0040] The third stage uses 6.0MPa high-pressure grouting to allow the slurry to penetrate into the cracks and pores of the surrounding soil under high pressure, thereby strengthening the bonding strength between the bag body and the surrounding strata.

[0041] In the fourth stage, a constant pressure of 2.5 MPa is applied for 30 minutes to ensure that the slurry is fully solidified and hardened under the pressure, fix the shape of the enlarged head, and form the bearing layer at the end of the enlarged head pile;

[0042] S103, the slurry used for grouting the bag body is composed of 73% ultrafine silicate cement, 15% silica fume, 2% steel fiber, and 10% expansion agent, with a water-binder ratio of 0.38; the diameter of the enlarged head and the expanded body formed is ≥2.5D, and the height is ≥1.2D.

[0043] The present invention discloses the following technical effects:

[0044] The shear keys arranged circumferentially and longitudinally inside and outside the casing can be customized in distribution density according to geological survey results, effectively enhancing the shear friction resistance between the casing and the surrounding soil / concrete. Especially in beaded karst formations, the friction around the pile is significantly improved through the embedding effect of the shear keys and the karst top and bottom plates.

[0045] The serrated blade design at the bottom of the casing enhances its ability to penetrate hard layers, forming a mechanical bite with the interlocking groove of the bladder bag to avoid displacement of the bladder bag during grouting and ensure the molding accuracy of the enlarged head.

[0046] The fiber-reinforced rubber bag expands through high-pressure grouting to form an enlarged head with controllable diameter at the bottom of the pile, thereby increasing the bearing area of ​​the pile end, similar to the effect of an expanded bottom pile. It effectively addresses the problems of no suitable bearing layer in beaded karst areas, insufficient bearing capacity at the pile end, and excessive settlement at the pile end.

[0047] The guide ribs optimize the slurry diffusion path, avoid local bulging of the bag, ensure the grouting body is uniform and dense, and improve the collaborative working performance of the enlarged head and the casing.

[0048] The outer casing is sunk in sections to provide temporary support for the hole wall during the drilling process, avoiding the risk of cave roof collapse in the karst area. The rotary drill is used to extract soil layer by layer to achieve simultaneous advancement of "casing-drilling" and reduce the rate of hole collapse accidents.

[0049] During vibratory hammer-assisted sinking, verticality is monitored in real time (deviation ≤ 1%) to ensure the accuracy of the casing axis and reduce the cost of subsequent correction.

[0050] To address the distribution of beaded karst, shear keys are machined into different areas of the inner barrel to match the strength of different karst layers and avoid pile slippage. High-pressure water jetting is used to break up isolated boulders, replacing blasting to reduce the impact of construction vibration on the stability of the beaded karst. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0052] Figure 1 This is a cross-sectional view of a permanent steel casing with shear keys;

[0053] Figure 2 This is the structural diagram of the bottom bladder grouting expansion head;

[0054] Figure 3 Detailed structural diagram of the grouting pipe, barrel wall and bag node;

[0055] Figure 4 This is a schematic diagram of the outer temporary steel casing structure;

[0056] Figure 5 This is a schematic diagram of the outer casing positioning and initial sinking construction;

[0057] Figure 6 This is a schematic diagram of the outer casing sinking construction in sections and relays;

[0058] Figure 7 This is a construction diagram of the outer casing passing through the first cave;

[0059] Figure 8 This is a construction diagram of the outer casing passing through the second cave;

[0060] Figure 9 This is a schematic diagram of the construction of the outer casing approaching the third cave;

[0061] Figure 10 This is a construction diagram of sinking the outer casing to the designed elevation;

[0062] Figure 11 This is a schematic diagram of the construction work for clearing obstacles and taking soil inside the cylinder;

[0063] Figure 12 This is a schematic diagram of the inner casing hoisting and steel cage lowering construction;

[0064] Figure 13 This is a schematic diagram of the underwater concrete pouring construction of the inner casing;

[0065] Figure 14 A construction diagram for pulling out the outer casing and enlarging the bladder grouting head;

[0066] Figure 15 This is a schematic diagram of the outer casing being pulled out layer by layer and the composite load-bearing structure being formed.

[0067] Among them, 1. rectangular shear key; 2. inner tube body; 3. trapezoidal shear key; 4. clamp; 5. bladder body; 6. bladder interlocking groove; 7. serrated blade foot; 8. diversion rib; 9. grouting pipe; 10. grouting pipe inner casing; 11. Type I grouting outer casing; 12. connector; 13. Type II grouting outer casing; 14. anchoring chassis; 15. grouting pipe outlet; 16. slurry outlet; 17. outer temporary steel casing; 18. drill rod; 19. covering soil; 20. sizing drill bit; 21. first cave roof; 22. first cave; 23. second cave roof; 24. second cave; 25. third cave roof; 26. third cave; 27. bottom expansion drill bit; 28. steel cage; 29. ​​permanent steel casing with shear key; 30. pouring concrete; 31. pouring fluidized solidified soil. DETAILED DESCRIPTION

[0068] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0069] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0070] Reference Figures 1-15 The invention provides a permanent steel casing with shear keys combined with bottom bag grouting and enlarged head reinforced pile, comprising:

[0071] A permanent steel casing 29 with shear keys, comprising an inner tube body 2 and a plurality of trapezoidal shear keys 3 and rectangular shear keys 1 respectively arranged on the outer circumference and inner circumference of the inner tube body 2;

[0072] The bottom of the inner tube body 2 is provided with a serrated blade foot 7, and the serrated blade foot 7 is locked and connected with the bag interlocking groove 6. The inner tube body 2 can be designed with a shear ring according to its own length to enhance the bearing capacity;

[0073] The bladder bag grouting system is connected to the inner tube body 2, and includes a bladder bag body 5, a high-pressure grouting pipe 9, an anchoring chassis 14 and a guide rib 8, wherein the upper end of the bladder bag body 5 is fixed to the inner tube body 2 through a clamp 4, the anchoring chassis 14 is sealed with the bladder bag interlocking groove 6 through a flange, and the high-pressure grouting pipe 9 is connected to the inner tube body 2.

[0074] Further optimization plan, the size of trapezoidal shear key 3 is 80×12mm, four are arranged circumferentially with the spacing between adjacent two at 90°, the longitudinal spacing is 500mm, and the longitudinal spacing in the cave section is 300mm; the height of rectangular shear key 1 is 100mm, the bottom width is 100mm, and the top width is 60mm, four are arranged circumferentially with the spacing between adjacent two at 90°, and the longitudinal spacing is 1000mm; the trapezoidal shear key 3 and the rectangular shear key 1 are welded by K-shaped groove welds respectively, the weld penetration is ≥15mm, and the verticality deviation of the steel casing is ≤1% of the pile diameter.

[0075] Further optimization scheme, the bag body 5 is a prefabricated folded rubber bag in the bag grouting system, the outer layer is a high-strength polyester fiber woven layer, the inner lining is a chloroprene rubber film and the pressure resistance is more than 10MPa, and the bag body 5 has an annular grouting cavity; the guide rib 8 is a plurality of radial reinforcing ribs for controlling the diameter expansion mode and ensuring that the slurry diffusion is pear-shaped and accelerates the diffusion; the high-pressure grouting pipe 9 comprises a grouting inner sleeve, an I-shaped grouting outer sleeve 11, a connecting head 12 and a II-shaped grouting outer sleeve 13, and the grouting is realized by the alternative connection of the I-shaped grouting outer sleeve 11, the connecting head 12 and the II-shaped grouting outer sleeve 13; the grouting pipe outlet 15 and the grouting hole 16 are used for grouting into the bag body 5.

[0076] Further optimization scheme, the permanent steel casing 29 with shear keys is treated with full-length corrosion protection, the zinc plating layer is greater than or equal to 80μm or an epoxy coating is used, and the diameter is 20cm larger than the designed pile diameter; the arrangement and number of the trapezoidal shear keys 3 and the rectangular shear keys 1, the segment length of the permanent steel casing 29 with shear keys and the size of the bottom bag grouting expansion head system are adjusted according to the geological exploration data.

[0077] A construction method of a permanent steel casing with shear keys combined with a bottom bag grouting expansion head enhanced pile comprises the following steps:

[0078] S1, processing the inner cylinder body 2 and the grouting bag, obtaining the string bead type karst distribution according to the geological exploration data, processing the trapezoidal shear keys 3 on the outer circumferential surface of the inner cylinder body 2 in regions, treating the inner cylinder body 2 with full-length corrosion protection, and preinstalling the bag grouting system at the bottom of the inner cylinder body 2;

[0079] S2, designing and processing the outer casing, the outer casing provides temporary support;

[0080] S3, positioning and initial sinking of the outer casing, measuring and laying out the pile position with a deviation of less than or equal to 3cm, vertically pressing the first section of the casing into the vibration hammer, after the outer casing is in place, connecting the drill rod 18 to the drilling machine, connecting the rotary drill to the drill rod 18, and stopping drilling at the second cave roof 23 by taking soil in the cylinder;

[0081] S4, segmented relay sinking of the outer casing, welding the segmented steel casing until the expansion bottom drill bit 27 is replaced after drilling into the cave roof, sinking the casing with the assistance of the vibration hammer and monitoring the verticality in real time, and the deviation is less than or equal to 1%;

[0082] S5, repeatedly performing steps S3 and S4 until the outer casing is sunk to the designed elevation;

[0083] S6, obstacle removal and soil taking in the cylinder, taking soil in the outer casing by the rotary drill to the designed elevation, and crushing the boulders by high-pressure water jet in the cylinder;

[0084] S7, hoisting the inner cylinder body 2 to the hole bottom;

[0085] S8, drilling to the bearing layer by the rotary drill in the inner cylinder body 2;

[0086] S9, pouring concrete into the inner cylinder body 2;

[0087] S10, after the concrete has initially set and the strength is ≥5MPa, the outer casing is pulled out in sections, and then the fluidized solidified soil is injected into the gaps in the hole wall simultaneously, and the bag body 5 constrains the grouting to form an enlarged head;

[0088] S11, the outer casing is pulled out layer by layer, and fluidized solidified soil is injected section by section through the gaps between the trapezoidal shear keys 3 to permanently retain the permanent steel casing with shear keys.

[0089] Further optimizing the scheme, step S1 includes the following steps:

[0090] S11, based on the geological survey data, determine the beaded karst distribution area, and process the rectangular shear key 1 and the trapezoidal shear key 3 in the corresponding area of ​​the inner cylinder body 2, ensuring that the arrangement and number of the rectangular shear key 1 and the trapezoidal shear key 3 are adapted to the karst distribution characteristics;

[0091] S12, performing anti-corrosion treatment on the entire length of the inner barrel body 2, using a zinc coating or epoxy coating;

[0092] S13, pre-installing the bag grouting system at the bottom of the inner barrel body 2.

[0093] Further optimizing the scheme, step S2 includes the following steps:

[0094] S21, select Q345 steel plate as the outer casing material, and determine its wall thickness to be 12-20mm;

[0095] S22, determine the outer casing diameter according to the designed pile diameter, making it 40 cm larger than the designed pile diameter;

[0096] S23, annular cutting teeth are welded on the bottom of the outer casing, and the blade angle is controlled to 30°-45° to enhance the soil cutting ability.

[0097] Further optimizing the scheme, step S3 includes the following steps:

[0098] S31, determine the pile position by measuring and setting out, ensuring that the pile position deviation is ≤3cm;

[0099] S32: Use a vibratory hammer to clamp the first section of outer casing and press it vertically into the formation. For soft formations, keep the water head inside the casing 2m above the groundwater level.

[0100] S33, after the outer casing is in place, use a rotary drill to take soil from the casing until it reaches the top plate 23 of the second cave and stops drilling.

[0101] Further optimizing the solution, step S10 includes the following steps:

[0102] S101: After the concrete in the inner tube body 2 has initially set and its strength is ≥5 MPa, the outer casing is pulled out in sections. After each section is pulled out, fluidized solidified soil is immediately injected into the gaps in the hole wall to fill the gap between the outer casing and the inner tube body 2 and form a preliminary support.

[0103] S102, synchronously performing constrained grouting on the bag body 5 to form an enlarged head, the grouting process is carried out in the following stages:

[0104] The first stage uses 1.5MPa low-pressure grouting to slowly expand the folded bladder body 5 to initially expand it to a diameter of 1.8D, thereby preventing the bladder body 5 from deforming unevenly due to excessive instantaneous force.

[0105] The second stage uses 4.0MPa medium-pressure grouting to squeeze the surrounding soil through the radial force generated by the further expansion of the bag body 5, thereby achieving compaction and reinforcement of the pile bottom and surrounding soil;

[0106] The third stage uses 6.0MPa high-pressure grouting to allow the slurry to penetrate into the cracks and pores of the surrounding soil under high pressure, thereby strengthening the bonding strength between the bag body 5 and the surrounding strata;

[0107] In the fourth stage, a constant pressure of 2.5 MPa is applied for 30 minutes to ensure that the slurry is fully solidified and hardened under the pressure, fix the shape of the enlarged head, and form the bearing layer at the end of the enlarged head pile;

[0108] S103, the slurry used for grouting the bag body 5 is composed of 73% ultrafine silicate cement, 15% silica fume, 2% steel fiber, and 10% expansion agent, with a water-binder ratio of 0.38; the diameter of the enlarged head and the enlarged body formed is ≥2.5D, and the height is ≥1.2D.

[0109] Example:

[0110] A high-speed railway subgrade section passes through a deep overburden layer (about 30m thick). Geological surveys revealed the presence of string-like moderately to strongly developed karst, with three caves distributed from top to bottom:

[0111] The first cave 22: average burial depth 32-35m, height 2.5m, half filled with soft clay;

[0112] The second cave 24: average burial depth 41-45m, height 4.0m, fully filled with loose sand and gravel;

[0113] The third cave 26: average burial depth 51-54m, height 3.0m, empty and unfilled.

[0114] The designed pile diameter is 1.5m and the pile length is 55m. The deformation control requirement of high-speed railway should be ≤15mm. The reinforced pile scheme of the present invention is used for construction.

[0115] 2. Strengthen the pile construction parameters;

[0116] Permanent steel casing with shear keys29;

[0117] Diameter 1.7m (20cm larger than the designed pile diameter), full-length anti-corrosion treatment (epoxy coating, thickness ≥80μm);

[0118] Outer shear key: trapezoidal ribs (80×12mm), four circumferential ribs (90° spacing), longitudinal spacing 500mm, increased to 300mm in the cave section;

[0119] Inboard shear key: height 100mm, bottom width 100mm, top width 60mm, four circumferential joints (90° spacing), longitudinal spacing 1000mm, welded by K-groove weld (penetration ≥15mm);

[0120] The bottom of the tube is provided with a serrated blade foot 7 (angle 35°), which is locked with the bag interlocking groove 6, and a matching shear ring is designed to enhance the bearing capacity (one is provided every 10m).

[0121] Bag grouting system;

[0122] The bag body 5 has a high-strength polyester fiber braided outer layer, lined with a neoprene rubber membrane (pressure resistance 12 MPa), and a ring-shaped grouting cavity design. The bag 5 is customized for the size of the third cave 26. After expansion, the diameter of the bag 5 is ≥3.8m (2.5D, D=1.5m), and the height is ≥1.8m (1.2D).

[0123] High-pressure grouting pipe 9: It is alternately connected by grouting inner casing 10, type I grouting outer casing 11, and type II grouting outer casing 13 (total length 55m), and the matching anchor chassis 14 is sealed with the bag interlocking groove 6 through the flange;

[0124] Guide ribs 8: 8 radial reinforcement ribs to control the slurry diffusion into a pear-shaped profile.

[0125] Outer temporary steel casing 17;

[0126] The material is Q345 steel plate, with a wall thickness of 16mm and a diameter of 1.9m (40cm larger than the designed pile diameter). The bottom of the cylinder is welded with an annular cutting tooth (edge ​​foot angle 35°).

[0127] 3. Construction steps (combined with Figures 1-15 )

[0128] The inner tube body and the bladder are processed in 5 systems;

[0129] According to the distribution of the three caves, the outer shear keys are increased in the sections of 32-35m (first cave 22), 45-49m (second cave 24), and 51-54m (third cave 26);

[0130] The bladder bag 5 system is pre-installed at the bottom of the inner tube: the clamp 4 fixes the fiber reinforced rubber bladder bag 5, the bladder bag interlocking groove 6 is locked with the serrated blade foot 7, the dual-channel grouting pipe 9 (including type I grouting outer sleeve 11 and type II grouting outer sleeve 13) is arranged along the tube body, and the grouting pipe outlet 15 and the slurry outlet 16 are aligned with the annular cavity of the bladder bag 5.

[0131] Outer casing processing;

[0132] The outer casing is processed in sections (8m per section), the interface is made of CO2 shielded welding + submerged arc welding filling, and the welds are 100% ultrasonically tested.

[0133] Positioning and initial sinking of outer casing;

[0134] The pile position was measured and staked out, with the deviation controlled within 2 cm. A vibratory hammer was used at a high frequency and low amplitude of 1200 times per minute to vertically press the first section of the outer casing into the soft formation 19, keeping the water head in the casing 2 m above the groundwater level.

[0135] After the outer casing is in place, the rotary drill (diameter drill bit 20) takes soil in the tube to the second cave roof 23 (buried depth 35m) and stops drilling.

[0136] The outer casing passes through the first and second caves in sections;

[0137] Weld the second section of outer casing, sink it to the first cave roof 21 (30m) with the help of a vibratory hammer, replace the bottom drill bit 27 to pass through the cave, and monitor the verticality in real time (deviation ≤ 0.8%);

[0138] Continue welding the third section of outer casing, sink it to the second cave roof 23 (35m), expand the bottom drill bit 27 to crush the loose sand and gravel in the cave, and take soil to the second cave floor (45m).

[0139] The outer casing passes through the third cave 26 and reaches the design elevation

[0140] Repeat the segmented welding and sinking. When crossing the third cave 26 (51-54m), the bottom drill bit 27 enlarges the hole diameter to 1.9m to ensure that the casing sinks close to the cave wall.

[0141] It eventually sank to the designed elevation (55m), with the bottom entering the stable rock layer 1.0m deep.

[0142] Obstacle removal and soil removal inside the barrel

[0143] The rotary drill (diameter drill bit 20) takes soil to the bottom of the hole in the outer casing. When encountering isolated rocks in the cave, 28MPa high-pressure water jet is used to break them, and the sediment thickness is controlled within 4cm.

[0144] Inner tube hoisting and steel cage 28 sinking

[0145] The full-rotation equipment is pressed into the inner cylinder in sections, with a verticality deviation of ≤0.8% and the bottom embedded in the stabilization layer of 1.0m;

[0146] The diameter of the steel cage 28 is 1.6m (90mm smaller than the inner diameter of the inner cylinder), a conical guide cap is provided at the bottom of the cage, and an adjustable cross positioning frame is installed on the top, and the center deviation is controlled within 40mm.

[0147] Underwater concrete pouring 30

[0148] The initial filling volume of the conduit ensures a buried depth of 2.5m, an overfilling height of 1.2m (covering the top of the inner tube), and a concrete strength grade of C35.

[0149] Outer casing is pulled out and bag 5 is grouting to enlarge the head

[0150] After the concrete has initially set (strength reaches 6 MPa), the outer casing is pulled out in sections, and fluidized solidified soil is injected into the voids of the hole wall simultaneously.

[0151] Grouting of pile bottom bag 5:

[0152] 1) Low-pressure support bladder (1.5 MPa): The diameter of the bladder is 2.7 m (1.8D), covering the third cave 26;

[0153] 2) Medium pressure soil compaction (4.0MPa): compacting the soil around the cave;

[0154] 3) High-pressure penetration (6.0 MPa): Slurry (73% ultrafine Portland cement + 15% silica fume + 2% steel fiber + 10% expansion agent, water-binder ratio 0.38) penetrates into the cave fissures through the slurry outlet 16;

[0155] 4) Steady pressure molding (2.5 MPa × 30 min): Finally, a pear-shaped enlarged head with a diameter of 4.0 m (2.7D) and a height of 1.8 m (1.2D) is formed (corresponding to the size of the third cave 26).

[0156] Final shape

[0157] After all outer casings are pulled out, fluidized solidified soil 31 is injected through the gaps of the trapezoidal shear keys 3 in the inner tube to form a composite bearing structure of "steel tube-shear key-fluidized solidified soil 31-soil body";

[0158] The permanent steel casing is retained as the anti-seepage and anti-corrosion layer of the inner tube reinforced concrete pile and bears the load in coordination with the fluidized solidified soil 31.

[0159] In the description of the present invention, it should be understood that the terms "longitudinal", "transverse", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention, 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 on the present invention.

[0160] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A permanent steel casing with shear keys combined with bottom bag grouting and enlarged head reinforced pile, characterized by: include: A permanent steel casing (29) with shear keys, comprising an inner tube body (2) and a plurality of trapezoidal shear keys (3) and rectangular shear keys (1) respectively arranged on the outer circumference and inner circumference of the inner tube body (2); The bottom of the inner cylinder body (2) is provided with a serrated blade foot (7), and the serrated blade foot (7) is locked and connected with the bag interlocking groove (6). The inner cylinder body (2) can be designed with a shear ring according to its own length to enhance the bearing capacity; A bag grouting system is connected to the inner tube body (2), comprising a bag body (5), a high-pressure grouting pipe (9), an anchoring chassis (14) and a guide rib (8), wherein the upper end of the bag body (5) is fixed to the inner tube body (2) via a clamp (4), the anchoring chassis (14) is tightly connected to the bag interlocking groove (6) via a flange, and the high-pressure grouting pipe (9) is connected to the inner tube body (2).

2. A permanent steel casing with shear key combined with bottom bag grouting and enlarged head reinforced pile according to claim 1, characterized in that: The size of the trapezoidal shear key (3) is 80×12 mm, four of them are arranged in a circumferential direction, the spacing between two adjacent ones is 90°, the longitudinal spacing is 500 mm, and the longitudinal spacing in the cave section is 300 mm; the height of the rectangular shear key (1) is 100 mm, the bottom width is 100 mm, and the top width is 60 mm, four of them are arranged in a circumferential direction, the spacing between two adjacent ones is 90°, and the longitudinal spacing is 1000 mm; the trapezoidal shear key (3) and the rectangular shear key (1) are respectively welded by K-shaped groove welds, the weld penetration is ≥15 mm, and the verticality deviation of the steel casing is ≤1% of the pile diameter.

3. A permanent steel casing with shear key combined with bottom bag grouting and enlarged head reinforced pile according to claim 1, characterized in that: In the bag grouting system, the bag body (5) is a prefabricated folded rubber bag, the outer layer of which is a high-strength polyester fiber woven layer, the inner lining of which is a chloroprene rubber film with a pressure resistance exceeding 10 MPa, and has an annular grouting cavity; the guide ribs (8) are a plurality of radial reinforcement ribs for controlling the diameter expansion shape, ensuring that the slurry diffuses into a pear-shaped profile and accelerates the diffusion; the high-pressure grouting pipe (9) comprises a grouting inner sleeve, a type I grouting outer sleeve (11), a connector (12) and a type II grouting outer sleeve (13), and grouting is achieved by alternately connecting the type I grouting outer sleeve (11), the connector (12) and the type II grouting outer sleeve (13); the grouting pipe outlet (15) and the slurry outlet (16) are used for grouting into the bag body (5).

4. A permanent steel casing with shear key combined with bottom bag grouting and enlarged head reinforced pile according to claim 1, characterized in that: The permanent steel casing (29) with shear keys is subjected to full-length anti-corrosion treatment, has a galvanized layer ≥80 μm or an epoxy coating, and has a diameter 20 cm larger than the designed pile diameter; the arrangement and number of the trapezoidal shear keys (3), the rectangular shear keys (1), the segment length of the permanent steel casing (29) with shear keys, and the size of the bottom bag grouting enlargement head system are all adjusted according to geological survey data.

5. A construction method for a reinforced pile with a permanent steel casing and a bottom bag grouting enlarged head with a shear key, based on the reinforced pile with a permanent steel casing and a bottom bag grouting enlarged head with a shear key according to any one of claims 1 to 4, characterized in that: The steps include: S1, processing the inner tube body (2) and the grouting bag, obtaining the beaded karst distribution according to the geological survey data, processing the trapezoidal shear keys (3) in different areas on the outer peripheral surface of the inner tube body (2), performing anti-corrosion treatment on the entire length of the inner tube body (2), and pre-installing the bag grouting system at the bottom of the inner tube body (2); S2, design and process the outer casing, which provides temporary support; S3, positioning and initial sinking of the outer casing, measuring and setting out the pile position with a deviation of ≤3cm, clamping the first section of the casing with a vibrating hammer and pressing it vertically, after the outer casing is in place, connecting the drill rod (18) to the drilling rig, connecting the rotary drill to the drill rod (18), and stopping the rotary drill to take soil from the barrel to the second cave roof (23); S4, the outer casing is laid in sections, and the steel casing is welded until the top of the cave is drilled. The bottom drill bit (27) is replaced and the casing is lowered with the aid of a vibrating hammer and the verticality is monitored in real time. The deviation is ≤1%; S5, repeating steps S3 and S4 until the outer casing sinks to the designed elevation; S6, clearing obstacles and taking soil inside the barrel. The rotary drill takes soil inside the outer casing to the designed elevation. If there are isolated rocks, high-pressure water jetting is used inside the barrel to break them. S7, hoisting the inner cylinder body (2) to the bottom of the hole; S8, drilling the inner barrel body (2) to the bearing layer; S9, pouring concrete into the inner barrel (2); S10, after the concrete has initially set and the strength is ≥5MPa, the outer casing is pulled out in sections, and then the fluidized solidified soil is injected into the gaps in the hole wall simultaneously, and the bag body (5) constrains the grouting to form an enlarged head; S11, the outer casing is pulled out layer by layer, and fluidized solidified soil is injected section by section through the gaps of the trapezoidal shear keys (3), so as to permanently retain the steel casing with shear keys.

6. The construction method of a permanent steel casing with shear key combined with bottom bag grouting and enlarged head reinforced pile according to claim 5 is characterized in that: Step S1 includes the following steps: S11, determining the beaded karst distribution area based on geological survey data, processing rectangular shear keys (1) and trapezoidal shear keys (3) in the corresponding area of ​​the inner cylinder body (2), ensuring that the arrangement and number of the rectangular shear keys (1) and the trapezoidal shear keys (3) are adapted to the karst distribution characteristics; S12, performing anti-corrosion treatment on the entire length of the inner barrel (2) by using a zinc coating or epoxy coating; S13, pre-installing a bag grouting system at the bottom of the inner barrel body (2).

7. The construction method of a permanent steel casing with shear keys combined with bottom bag grouting and enlarged head reinforced pile according to claim 5 is characterized in that: Step S2 includes the following steps: S21, select Q345 steel plate as the outer casing material, and determine its wall thickness to be 12-20mm; S22, determine the outer casing diameter according to the designed pile diameter, making it 40 cm larger than the designed pile diameter; S23, annular cutting teeth are welded on the bottom of the outer casing, and the blade angle is controlled to 30°-45° to enhance the soil cutting ability.

8. The construction method of a permanent steel casing with shear keys combined with bottom bag grouting and enlarged head reinforced pile according to claim 5 is characterized in that: Step S3 includes the following steps: S31, determine the pile position by measuring and setting out, ensuring that the pile position deviation is ≤3cm; S32: Use a vibratory hammer to clamp the first section of outer casing and press it vertically into the formation. For soft formations, keep the water head inside the casing 2m above the groundwater level. S33, after the outer casing is in place, a rotary drill is used to extract soil from the casing until the second cave roof (23) is reached and the drilling is stopped.

9. The construction method of a permanent steel casing with shear keys combined with bottom bag grouting and enlarged head reinforced pile according to claim 5, characterized in that: Step S10 includes the following steps: S101, after the concrete in the inner tube body (2) has initially set and the strength is ≥5MPa, the outer casing is pulled out in sections, and after each section is pulled out, fluidized solidified soil is immediately injected into the gaps in the hole wall to fill the gap between the outer casing and the inner tube body (2) and form a preliminary support; S102, synchronously performing constrained grouting on the bag body (5) to form an enlarged head, the grouting process is carried out in the following stages: The first stage uses 1.5MPa low-pressure grouting, the purpose of which is to slowly expand the folded bladder body (5) to initially expand it to a diameter of 1.8D, thereby preventing the bladder body (5) from deforming unevenly due to excessive instantaneous force; In the second stage, 4.0 MPa medium pressure grouting is used to squeeze the surrounding soil through the radial force generated by the further expansion of the bag body (5), thereby achieving compaction and reinforcement of the pile bottom and surrounding soil; The third stage uses 6.0MPa high-pressure grouting to allow the slurry to penetrate into the cracks and pores of the surrounding soil under high pressure, thereby enhancing the bonding strength between the bag body (5) and the surrounding strata; In the fourth stage, a constant pressure of 2.5 MPa is applied for 30 minutes to ensure that the slurry is fully solidified and hardened under the pressure, fix the shape of the enlarged head, and form the bearing layer at the end of the enlarged head pile; S103, the slurry used for grouting the bag body (5) is composed of 73% ultrafine silicate cement, 15% silica fume, 2% steel fiber, and 10% expansion agent, with a water-binder ratio of 0.38; the enlarged head and enlarged body formed have a diameter ≥2.5D and a height ≥1.2D.

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