Large-diameter pile foundation construction method under string bead type karst cave condition

Abstract

The invention discloses a construction method of a large-diameter pile foundation under the condition of a bead type karst cave, which comprises the following steps of: adopting a plurality of sections of equal-diameter steel casings with stiffening ribs on the peripheries, welding in sections in the construction process, and simultaneously drilling in cooperation with double drill bits and expanding the bottom of a karst cave top plate, so that the steel casings smoothly sink to a preset position. Therefore, the construction task of the pile foundation can be realized by only one layer of steel casing, and the steel casing serving as a permanent pile foundation structure has the advantages of simplicity and convenience in construction process, high pile foundation strength and capability of saving steel casing materials and reinforcement cages, and has obvious economic benefits.

Description

Technical Field

[0001] The invention relates to the technical field of underground pile foundation karst cave treatment, in particular to a large-diameter pile foundation construction method under bead-type karst cave conditions. Background Art

[0002] When constructing pile foundations in karst areas, cave strata treatment is a recognized technical problem in the engineering community. Especially when encountering multi-layer beaded caves, there are the following technical difficulties: First, the wall protection structure of the cave section is missing or weak during the drilling process, which can easily cause mud leakage and lead to hole collapse; second, during the concrete pouring stage, due to the poor stability of the hole wall in the cave area, concrete leakage is likely to occur, affecting the quality of pile body forming.

[0003] There are two main mainstream solutions:

[0004] The first is the cave filling and wall building method, which uses composite materials such as stone flakes, clay, and cement to fill and reinforce the cave to form an artificial wall structure. Although this solution has the advantages of convenient construction and low cost, it has significant defects in the implementation process: the stability of the filling structure is easily destroyed by fluid pressure during concrete pouring, there is a risk of secondary collapse, and the continuous reinforcement effect of multi-layer beaded caves is difficult to guarantee.

[0005] The second is the multi-layer steel casing protection method, which adopts the hierarchical nested steel casing technology. According to the karst layer determined by geological exploration, steel casings with decreasing diameters are set layer by layer from the surface to form a continuous rigid protective wall. Although this technology can effectively control the collapse and leakage of slurry, there are three major technical bottlenecks: ① The gradual enlargement of the casing diameter leads to a doubling of the amount of steel used, and the temporary support structure cannot be recycled, resulting in a waste of resources; ② The construction accuracy requirements are strict, and the distribution level of the karst cave needs to be accurately predicted; ③ The multi-level casing nesting process is complicated, and the construction period is extended by about 30%-50%. According to engineering statistics, the cost of this solution is 2-3 times higher than that of conventional processes. Summary of the invention

[0006] In view of the above problems, the present invention proposes a large-diameter pile foundation construction method under beaded cave conditions, aiming to reduce engineering costs under the premise of controlling hole collapse and slurry leakage.

[0007] In order to solve the above technical problems, the technical solution of the present invention is as follows:

[0008] A large diameter pile foundation construction method under beaded cave conditions comprises the following steps:

[0009] Step 1, according to the geological exploration results, a plurality of steel casings of equal diameter are processed in sections, wherein the outer circumference of the steel casings is provided with radially uniformly arranged stiffening ribs;

[0010] Step 2, passing the first section of steel casing through the soft soil layer and installing a drilling rig, the drilling rig uses a sizing drill bit that matches the inner diameter clearance of the steel casing, and after the sizing drill bit passes through the first section of steel casing, it starts rotary drilling until it reaches the bottom plate of the topmost cave;

[0011] Step 3, replacing the sizing drill bit with a bottom expansion drill bit to expand the top plate of the topmost cave;

[0012] Step 4, after welding the second section of steel casing to the top open end of the first section of steel casing, an extended steel casing is formed, the extended steel casing is sunk into the bottom plate of the topmost cave, and the bottom expansion drill bit is replaced with a sizing drill bit to drill into the top plate of the second layer of cave;

[0013] Step 5, repeat steps 3 and 4, drill the sizing drill bit into the stable rock formation, then replace the bottom expansion drill bit to expand the top plate of all rock caves and the stable rock formation, gradually weld to increase the length of the steel casing to form a new extended steel casing, until the length of the extended steel casing reaches the stable rock formation, and finally pour micro-expansive concrete into the extended steel casing to form a steel tube concrete composite pile.

[0014] In some embodiments, the bottom of the stiffening rib is processed into a wedge-shaped edge angle.

[0015] In some embodiments, after the first section of the steel casing passes through the soft soil layer, it is exposed above the ground for at least 1 meter.

[0016] In some embodiments, in steps 3-5, the size of the hole drilled by the bottom expansion drill bit is D+2h, where D is the diameter of the steel casing and h is the height of the stiffening rib.

[0017] In some embodiments, the length of the second section of the steel casing is greater than the distance from the top surface of the roof of the topmost cave to the top surface of the bottom plate of the topmost cave.

[0018] In some embodiments, before pouring the micro-expansive concrete, the debris in the lengthened steel casing is removed, the inner pipe wall is cleaned with a high-pressure water gun, and the muddy water in the lengthened steel casing is drained.

[0019] The beneficial effects of the present invention are as follows: by adopting multiple sections of steel casings with equal diameters and stiffening ribs arranged on the outer periphery, the steel casings are welded in sections during the construction process, and the double drill bits are used for drilling and bottom expansion of the cave roof, so that the steel casings can be smoothly sunk to the predetermined position. Therefore, the construction task of the pile foundation can be achieved with only one layer of steel casings, and the steel casings, as permanent pile foundation structures, have the advantages of simple construction process, high pile foundation strength, and saving steel casing materials and steel cages, and have obvious economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1A schematic cross-sectional view of a steel casing disclosed in an embodiment of the present invention;

[0021] Figure 2 This is a construction diagram of step 2 disclosed in an embodiment of the present invention;

[0022] Figure 3 This is a construction diagram of step 3 disclosed in an embodiment of the present invention;

[0023] Figure 4 This is a construction diagram of step 4 disclosed in an embodiment of the present invention;

[0024] Figure 5 This is a construction diagram of step 501 disclosed in an embodiment of the present invention;

[0025] Figure 6 This is a construction diagram of step 502 disclosed in an embodiment of the present invention;

[0026] Figure 7 This is a construction diagram of step 503 disclosed in an embodiment of the present invention;

[0027] Figure 8 This is a construction diagram of step 504 disclosed in an embodiment of the present invention;

[0028] Fig. 9 This is a construction diagram of step 505 disclosed in an embodiment of the present invention;

[0029] Among them: 1-steel casing, 2-stiffening ribs, 3-micro-expansive concrete, 4-drill rod, 5-diameter drill bit, 6-bottom expansion drill bit, 7-soft soil layer, 801-top layer cave, 802-second layer cave, 803-bottom layer cave, 9-stable rock layer. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solution and advantages of the present invention clearer and more specific, the content of the present invention is further described in detail below in conjunction with the accompanying drawings and specific implementation methods. It is understood that the specific embodiments described herein are only used to explain the present invention, rather than to limit the present invention. It should also be noted that, for the convenience of description, only the parts related to the present invention are shown in the accompanying drawings, rather than all the contents.

[0031] This embodiment proposes a large diameter pile foundation construction method under beaded cave conditions, comprising the following steps:

[0032] Step 1: According to geological exploration results, several steel casings 1 with equal diameters are processed in sections, and the outer circumference of the steel casing 1 is provided with radially uniformly arranged stiffening ribs 2.

[0033] In one example, if Figure 1As shown, the steel tube concrete composite pile is composed of a steel casing 1, a stiffening rib 2, and an injected micro-expansive concrete 3. In this embodiment, the steel casing 1 provides a temporary wall protection for the pile foundation passing through the cave range during the construction drilling and pouring process to prevent hole collapse and slurry leakage. After the pile foundation is poured, the steel casing 1 forms a hoop effect on the micro-expansive concrete 3, which enhances the strength of the micro-expansive concrete 3 in the steel tube and improves the bending resistance of the pile, and the steel cage required for the ordinary concrete pile foundation can be eliminated. In addition, since the steel casing 1 has a too large diameter, the hoop effect on the micro-expansive concrete 3 will be weakened and local instability may occur. Therefore, the uniformly distributed stiffening ribs 2 are used to improve the local compressive stability of the steel casing 1 and the restraining effect on the micro-expansive concrete 3 in the tube, so that the steel cage required for the general concrete pile foundation can be eliminated. In addition, by using the micro-expansive concrete 3 as the concrete filled in the steel casing 1, the compactness between the micro-expansive concrete 3 and the steel casing 1 can be increased to avoid cracks caused by the shrinkage of the concrete in the later stage.

[0034] It should be noted that the total length of the extended steel casing described below is determined according to the geological exploration results, that is, the total length of the extended steel casing needs to reach the stable rock layer 9 required by the design.

[0035] More preferably, the bottom of the stiffening rib 2 is processed into a wedge-shaped edge angle to reduce the sinking resistance of the steel casing 1.

[0036] Step 2, such as Figure 2 As shown, the first section of steel casing 1 is passed through the soft soil layer 7 (for example, a vibrating hammer is used to drive the first section of steel casing 1 into the soft soil layer 7), and a drilling rig is installed. The drilling rig uses a sizing drill bit 5 that matches the inner diameter clearance of the steel casing 1. The sizing drill bit 5 is installed at the end of the drill rod 4 of the drilling rig. After the sizing drill bit 5 passes through the first section of steel casing 1, rotary drilling begins until it reaches the bottom plate of the topmost cave 801. More preferably, after the first section of steel casing 1 passes through the soft soil layer 7, it is exposed at least 1m above the ground to prepare for the subsequent welding of the remaining sections of the steel casing.

[0037] Step 3, such as Figure 3 As shown, the sizing drill bit 5 is replaced with a bottom expansion drill bit 6 to expand the top plate of the topmost cave 801.

[0038] In step 3, the size of the hole drilled by the bottom expansion drill bit is D+2h, where D is the diameter of the steel casing 1 and h is the height of the stiffening rib 2. In subsequent steps 4 and 5, the size of the hole expansion can refer to the above dimensions.

[0039] Step 4, such as Figure 4 As shown, after the second section of steel casing 1 is welded to the top open end of the first section of steel casing 1, an extended steel casing is formed, the extended steel casing is sunk into the bottom plate of the topmost cave 801, and the bottom expansion drill bit 6 is replaced with a sizing drill bit 5 to drill into the top plate of the second layer of cave 802.

[0040] Optionally, the length of the second section of the steel casing 2 is greater than the distance from the top surface of the roof of the topmost cave 801 to the top surface of the bottom plate of the topmost cave 801, ensuring that the extended steel casing protrudes above the ground during construction.

[0041] Step 5, repeat steps 3 and 4, drill the sizing drill bit into the stable rock layer 9, then replace the bottom expansion drill bit 6 to expand the top plate of all the rock caves and the stable rock layer 9, gradually weld to increase the length of the steel casing 1, and form a new extended steel casing until the length of the extended steel casing reaches the stable rock layer 9, and finally pour micro-expansive concrete 3 into the extended steel casing to form a steel tube concrete composite pile.

[0042] In one example, taking a three-layer cave structure as an example, the construction process of the second layer cave 802 and the bottom layer cave 803 is described:

[0043] Step 501, such as Figure 5 As shown, for the second layer of cave 802 , the sizing drill bit 5 is replaced with a bottom expansion drill bit 6 to expand the top plate of the second layer of cave 802 .

[0044] Step 502, then weld the third section of steel casing 1 to the top of the extended steel casing, and sink the extended steel casing to the bottom plate of the second layer of cave 802, as shown in FIG. Figure 6 Position shown.

[0045] Step 503, repeat steps 3 and 4, lengthen the steel casing through the lowest cave 803, sink to the bottom of the lowest cave 803, and drill the sizing drill bit 5 to the stable rock layer 9 to meet the designed pile bottom elevation and reach the predetermined pile length, such as Figure 7 shown.

[0046] Step 504, such as Figure 8 As shown, the sizing drill bit 5 is replaced with the bottom expansion drill bit 6 for the last time, and the expansion is stopped after the hole expansion range reaches about 1 times the pile diameter of the steel casing 1, and then the steel casing is sunk and lengthened to the expanded hole range.

[0047] Step 505, before pouring the micro-expansive concrete, remove the slag in the extended steel casing, use a high-pressure water gun to clean the inner wall, and drain the mud and water in the extended steel casing. Finally, pour the micro-expansive concrete 3 into the extended steel casing to form a steel tube concrete composite pile. Fig. 9 shown.

[0048] The above construction methods can be referred to for cave structures with more layers.

[0049] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable ordinary technicians in the field to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made based on the essence of the content of the present invention should be included in the protection scope of the present invention.

Claims

1. A large diameter pile foundation construction method under beaded cave conditions, characterized in that: The following steps are involved: Step 1, according to the geological exploration results, a plurality of steel casings of equal diameter are processed in sections, wherein the outer circumference of the steel casings is provided with radially uniformly arranged stiffening ribs; Step 2, passing the first section of steel casing through the soft soil layer and installing a drilling rig, the drilling rig uses a sizing drill bit that matches the inner diameter clearance of the steel casing, and after the sizing drill bit passes through the first section of steel casing, it starts rotary drilling until it reaches the bottom plate of the topmost cave; Step 3, replacing the sizing drill bit with a bottom expansion drill bit to expand the top plate of the topmost cave; Step 4, after welding the second section of steel casing to the top open end of the first section of steel casing, an extended steel casing is formed, the extended steel casing is sunk into the bottom plate of the topmost cave, and the bottom expansion drill bit is replaced with a sizing drill bit to drill into the top plate of the second layer of cave; Step 5, repeat steps 3 and 4, drill the sizing drill bit into the stable rock formation, then replace the bottom expansion drill bit to expand the top plate of all rock caves and the stable rock formation, gradually weld to increase the length of the steel casing to form a new extended steel casing, until the length of the extended steel casing reaches the stable rock formation, and finally pour micro-expansive concrete into the extended steel casing to form a steel tube concrete composite pile.

2. The large diameter pile foundation construction method under beaded cave conditions as claimed in claim 1, characterized in that: The bottom of the stiffening rib is processed into a wedge-shaped edge angle.

3. The large diameter pile foundation construction method under beaded cave conditions as claimed in claim 1, characterized in that: After the steel casing described in the first section passes through the soft soil layer, it is exposed on the ground for at least 1m.

4. The large diameter pile foundation construction method under beaded cave conditions as claimed in claim 1, characterized in that: In step 3-5, the size of the hole drilled by the bottom expansion drill bit is D+2h, where D is the diameter of the steel casing and h is the height of the stiffening rib.

5. The large diameter pile foundation construction method under beaded cave conditions as claimed in claim 1, characterized in that: The length of the steel casing described in the second paragraph is greater than the distance from the top surface of the roof of the topmost cave to the top surface of the bottom plate of the topmost cave.

6. The large diameter pile foundation construction method under beaded cave conditions as claimed in claim 1, characterized in that: Before pouring the micro-expansive concrete, the slag in the lengthened steel casing is removed, the inner pipe wall is cleaned with a high-pressure water gun, and the muddy water in the lengthened steel casing is drained.

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