Precast pile stress release hole for soft soil foundation and construction method

Abstract

The invention discloses a precast pile stress release hole for a soft soil foundation and a construction method, and the method comprises the following steps: S100, drawing a plane layout diagram of the stress release hole according to the field condition, and carrying out hole site lofting on the plane layout diagram; s200, a site hole site is determined according to the plane layout diagram, after a drilling machine is in place, hole guiding is conducted through the drilling machine, construction is conducted in cooperation with a punching and pulling machine, and a pile casing is buried into the site hole site; s300, a drilling machine is used for conducting rotary excavating and drilling operation in the sequence from slow to fast till the drilled hole reaches the preset depth, and hole completion of the soil hole is achieved; s400, the structure of the stress release unit is optimized according to the hole completion size of the soil hole, and the specific size suitable for the field actual engineering geology is determined; s500, the punching and pulling machine is used for being aligned with the center of the soil hole to hoist the stress releasing unit into the soil hole, and the stress releasing unit is controlled not to float upwards; and S600, the steel casing is slowly pulled out through vibration of a beating and pulling machine, and a cover plate is manufactured through a formwork batten to protect the hole opening of the stress release hole. And the problem of soil squeezing effect of the soft soil foundation is solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of pile column construction, and more specifically, relates to a prefabricated pile stress release hole for soft soil foundation and a construction method thereof. Background Art

[0002] The Code for Design of Foundations (GB50007-2011) stipulates: "The impact of the soil squeezing effect on the surrounding environment of the pile foundation during pile foundation construction should be considered; large and dense pile foundations with soil squeezing effect should not be used in deep saturated soft soil." Because sensitive clay will soften during precast pile construction, the soil will be squeezed out from the surrounding area of ​​the pile and the surface will rise to a large height; the soil uplift of non-sensitive clay (such as hard clay, fine sand, coarse sand and other soil layers) is relatively small; soft soil foundation has high natural water content, strong soil compressibility, low bearing capacity, and has thixotropic, rheological, low permeability and low shear strength characteristics, so the soil squeezing effect of soft soil will be more obvious than other soil types.

[0003] With the development of the industry and the advancement of technology, as well as the low cost and high construction efficiency of precast piles, more and more projects are trying to use precast piles in soft soil foundations. The soil squeezing effect of precast piles in the soft soil foundation is more obvious, and may even affect other precast piles that have been constructed in the surrounding area. As an effective measure to combat the soil squeezing effect, stress relief holes do not have clear structures and practices in current specifications and atlases.

[0004] In order to solve a series of problems caused by the soil squeezing effect, Chinese patent CN216360739U discloses a stress release structure to prevent soil squeezing effect. The foundation is divided into a construction area and a non-construction area. An anti-squeezing groove is provided between the areas. A number of stress release holes are opened at the bottom of the anti-squeezing groove. Two rows are arranged in a plum blossom shape, with a row spacing of 800mm, a spacing of 1000mm between adjacent stress release holes, and a stress release hole diameter of 300 to 500mm. The stress release holes can reduce the uneven settlement, cracking and damage to existing buildings in the non-construction area caused by pile sinking in the construction area. However, the stress release structure of this patent is limited by its own structure and layout. It can protect the non-construction area, but cannot solve the problems of pile position deviation and pile gushing caused by the soil squeezing effect.

[0005] Chinese patent CN219568866U discloses a stress release mechanism during static pressure pile construction, including: a stress release hole, which is arranged between the construction area and the non-construction area; a cover plate, which is adapted to the position of the stress release hole and covered on the construction ground, the cover plate is provided with a mounting hole aligned with the stress release hole up and down, and a downwardly protruding baffle portion is arranged around the mounting hole, the baffle portion is inserted into the stress release hole, and prevents the side wall at the opening of the stress release hole from collapsing into the hole; a steel cage assembly, which is inserted into the stress release hole from the mounting hole downward. A preferred stress release mechanism during static pressure pile construction, by setting a stress release hole and effectively supporting the stress release hole, enables the stress release hole to fully play the role of reducing the soil squeezing effect. However, the stress release structure of the patent is a structure with relatively large rigidity, which is mainly used to eliminate pore water pressure, and has poor effect on eliminating stress caused by soil movement, and cannot solve the problems of pile position deviation and pile gushing caused by the soil squeezing effect. At the same time, due to its structural limitations, it is difficult to arrange deeper stress release holes to eliminate deep stress.

[0006] Therefore, a precast pile stress release hole and construction method for soft soil foundation is needed to reduce the impact of the soil squeezing effect on adjacent areas and underground pipelines when using precast piles on soft soil foundation, and at the same time solve the impact of the soil squeezing effect on the constructed precast piles during the construction of dense precast pile groups. Summary of the invention

[0007] In view of the above defects or improvement needs of the prior art, the present invention provides a prefabricated pile stress relief hole and construction method for soft soil foundation. By arranging the stress relief holes between piles, between large caps and around protected buildings, the soil squeezing effect caused by stress is reduced during the pipe column construction process, thereby achieving the purpose of protecting adjacent buildings and underground pipelines. While playing a protective role, it can effectively solve the problems of pile gushing and pile position displacement caused by the soil squeezing effect of soft soil foundation, thereby achieving the purpose of improving construction quality.

[0008] To achieve the above objectives, according to a first aspect of an embodiment of the present invention, a construction method for a prefabricated pile stress relief hole for a soft soil foundation is provided, comprising the following steps:

[0009] S100, drawing a plan layout of stress relief holes according to the on-site conditions, and performing hole position setting on the plan layout;

[0010] S200, determine the on-site hole position according to the plan layout, and after the drilling rig is in place, the drilling rig will be used to guide the hole, and the drilling machine will be used to carry out construction, and the casing will be buried in the on-site hole position;

[0011] S300, using a drilling machine to perform rotary drilling operations in a sequence of first slow and then fast, until the drilling hole reaches a preset depth, thereby completing the soil hole;

[0012] S400, optimizing the structure of the stress release unit according to the completed hole size of the soil hole, and determining a specific size suitable for the actual engineering geology on site;

[0013] S500, use a pulling machine to align the stress release unit with the center of the soil hole and hoist it into the soil hole, and control the stress release unit not to float up;

[0014] S600, use a pull-out machine to slowly pull out the steel casing by vibration, and use a template wooden plank to make a cover plate to protect the stress release hole.

[0015] Further, in step S100, the drawing of the plan layout of the stress release holes is performed according to the layout principle;

[0016] The arrangement principle is to arrange the stress release holes mainly in places where piles are densely packed, between pedestals and in the direction of the protected area outside the construction site, and to arrange them densely near the protection positions.

[0017] Furthermore, in step S200, when the casing is buried, its deviation angle needs to be evaluated to control the verticality of the controller, and its average deviation angle for:

[0018]

[0019] Where Δh(z) is the horizontal deviation distance between the top and bottom of the casing at depth z,

[0020] L is the height of the casing,

[0021] is the deviation rate of the casing at depth z.

[0022] Further, in step S300, the drilling speed change rate during drilling is:

[0023]

[0024] Where r(z) is the rate of change of drilling speed

[0025] k is the proportionality coefficient,

[0026] H(z) is the formation hardness at depth z,

[0027] W(z) is the wear degree of the drill bit at depth z,

[0028] w m is the maximum allowable wear of the drill bit,

[0029] P(z) is the groundwater pressure at depth z,

[0030] p m is the maximum allowable value of groundwater pressure.

[0031] Furthermore, the rate of change of the formation hardness with depth H(z) is:

[0032] H(z)=H 0 ·e kz ;

[0033] Among them, H 0 is the ground hardness at the surface,

[0034] k is the hardness growth coefficient,

[0035] e is the base of natural logarithm;

[0036] The wear degree W(z) of the drill bit at the depth z is:

[0037] W(z)=W 0 +m·z;

[0038] Among them, W 0 is the initial drill wear degree,

[0039] m is the wear growth coefficient,

[0040] z is the current depth of the drilling;

[0041] The groundwater pressure P(z) at the depth z is:

[0042] P(z)=P 0 +ρ·g·z;

[0043] Among them, P 0 is the initial groundwater pressure, i.e. the pressure at the surface, calculated according to atmospheric pressure,

[0044] ρ is the density of groundwater,

[0045] g is the acceleration due to gravity,

[0046] z is the current depth of drilling.

[0047] Furthermore, in step S400, the stability of the stress release unit needs to be checked, specifically:

[0048]

[0049] Among them, F s (z) is the safety factor for depth variation,

[0050] F c (z) is the bearing capacity of the stress release unit as it changes with depth,

[0051] F a (z) is the actual load of the stress release unit that varies with depth.

[0052] Furthermore, the load-bearing capacity F of the stress release unit varies with depth. c (z) is:

[0053]

[0054] Among them, σ c (z) is the compressive strength of the stress release unit varying with depth,

[0055] A(z) is the cross-sectional area of ​​the stress release unit as it changes with depth;

[0056] The actual load F of the stress release unit varies with depth. a (z) is:

[0057]

[0058] Among them, σ t (z) is the soil pressure that varies with depth,

[0059] τ(z) is the groundwater pressure that varies with depth,

[0060] C(z) is the lateral area of ​​the stress release unit that varies with depth,

[0061] A(z) is the cross-sectional area of ​​the stress release unit that varies with depth.

[0062] Furthermore, in step S500, when the stress release unit is vertically placed in the soil hole, the verticality of the stress release unit needs to be controlled, and the inclination angle is:

[0063]

[0064] Where θ(z) is the inclination angle of the stress release unit at depth z,

[0065] Δg(z) is the horizontal offset of the stress release unit at depth z.

[0066] Furthermore, in step S600, the bearing capacity of the protection of the stress release hole opening needs to be verified, specifically:

[0067] F r =∑F c (i) = ∑(A i ·σ c (i)·φ(i));

[0068] Among them, F r The bearing capacity of the cave entrance protection,

[0069] F c(i) is the bearing capacity of the ith part,

[0070] A i is the cross-sectional area of ​​the ith part,

[0071] σ c (i) is the material compressive strength of the i-th part,

[0072] φ(i) is the effective utilization coefficient of the i-th part.

[0073] According to a second aspect of an embodiment of the present invention, there is provided a prefabricated pile stress release hole for soft soil foundation, comprising a soil hole and a stress release unit arranged in the soil hole;

[0074] The soil holes are formed by drilling with a drilling rig and are arranged between a plurality of precast piles, between large caps, and around the protected buildings;

[0075] The main body of the stress release unit is a plurality of vertically arranged bamboo main bars, which are arranged along the circumference and fixed on the periphery by steel reinforcement hoops and bamboo reinforcement hoops. The steel reinforcement hoops and bamboo reinforcement hoops are both multiple and arranged at intervals on the outer circle of the bamboo main bars. The bottom end of the bamboo main bar is closed inward to form a cone, and its tip is fixed with bamboo binding wire;

[0076] The periphery of the stress release unit is also provided with an outer wrapping gauze.

[0077] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects compared with the prior art:

[0078] 1. The present invention provides a construction method for prefabricated pile stress release holes for soft soil foundations, which solves the problem that prefabricated pile stress release holes for soft soil foundations have no specific structure and construction method, reduces the soil squeezing effect caused by stress during the pipe pile construction process, and achieves the purpose of protecting adjacent buildings (structures) and underground pipelines.

[0079] 2. The present invention provides a construction method for prefabricated pile stress release holes for soft soil foundations. By setting the stress release holes between piles, between large abutments and around protected buildings (structures), it can effectively solve the problems of pile gushing and pile position displacement caused by the soil squeezing effect of soft soil foundation while playing a protective role, thereby achieving the purpose of improving construction quality.

[0080] 3. The construction method of the precast pile stress release holes for soft soil foundation of the present invention can ensure the construction progress of the project while ensuring the safety of nearby buildings (structures) and underground pipelines and the construction quality of the precast pile project by adopting a method of reasonably setting stress release holes suitable for soft soil foundation.

[0081] 4. The construction method of the prefabricated pile stress release holes for soft soil foundation of the present invention, the component materials and construction machinery involved are all easily obtained at the construction site, which solves the problem that the threshold of new technology is high and difficult to use during the promotion process, and achieves the purpose of easy on-site construction, easy processing of related components and good construction effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0082] Figure 1 This is a schematic structural diagram of a prefabricated pile stress release hole for soft soil foundation according to an embodiment of the present invention;

[0083] Figure 2 This is a schematic structural diagram of a stress release unit of a prefabricated pile stress release hole for a soft soil foundation according to an embodiment of the present invention;

[0084] Figure 3 A top view of a stress release unit structure of a prefabricated pile stress release hole for a soft soil foundation according to an embodiment of the present invention;

[0085] Figure 4 A schematic diagram of the steps of a construction method for a prefabricated pile stress release hole for a soft soil foundation according to an embodiment of the present invention;

[0086] Figure 5 A schematic diagram of a construction method for a prefabricated pile stress release hole for a soft soil foundation according to an embodiment of the present invention;

[0087] Figure 6 The present invention is a schematic diagram of the arrangement positions of stress release holes in a construction method of prefabricated pile stress release holes for soft soil foundation according to an embodiment of the present invention.

[0088] In all the drawings, the same reference numerals represent the same technical features, specifically: 1-soil hole, 2-stress release unit, 21-bamboo main reinforcement, 22-steel reinforcement hoop, 23-bamboo reinforcement hoop, 24-bamboo bundle wire, 25-outer covering mesh. DETAILED DESCRIPTION

[0089] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0090] Example 1

[0091] like Figure 1-3As shown, an embodiment of the present invention provides a prefabricated pile stress release hole for soft soil foundation, comprising: a soil hole 1 and a stress release unit 2 arranged in the soil hole 1. The soil hole 1 is formed by drilling a hole by a drilling rig, and is arranged between a plurality of prefabricated piles, between large caps, and around protected buildings. The stress release unit 2 comprises a bamboo main reinforcement 21, a steel reinforcement hoop 22, a bamboo reinforcement hoop 23, a bamboo binding wire 24, and an outer gauze 25. The soil squeezing effect caused by stress is reduced during the construction of the pipe column, so as to achieve the purpose of protecting adjacent buildings and underground pipelines. While playing a protective role, it can effectively solve the problems of pile surging and pile position displacement caused by the soil squeezing effect of the soft soil foundation, thereby achieving the purpose of improving the construction quality.

[0092] The main body of the stress release unit 2 is a plurality of vertically arranged bamboo main bars 21, which are arranged along the circumference and fixed by steel reinforcement hoops 22 and bamboo reinforcement hoops 23 on the periphery. The steel reinforcement hoops 22 and bamboo reinforcement hoops 23 are both multiple and are arranged at intervals on the outer ring of the bamboo main bars 21. The bottom end of the bamboo main bar 21 is closed inward to form a cone, and its tip is fixed by a bamboo binding wire 24. The bamboo main bar 21, the steel reinforcement hoop 22, the bamboo reinforcement hoop 23 and the bamboo binding wire 24 together form a cage structure, which is a flexible structure. When it is subjected to radial stress, it bends and deforms to offset the stress. The steel reinforcement hoop 22 added to the cage structure enhances rigidity, making it a flexible structure with a certain rigidity. When it is not in the construction state, the rigidity brought by the steel reinforcement hoop 22 resists the soil extrusion, and when it is in the construction state, it releases the direct stress generated by the soil extrusion through deformation.

[0093] The outer gauze 25 is wrapped around the periphery of the cage structure to discharge water in the soil when the soil is squeezed, so as to release the generated pore water pressure.

[0094] Preferably, the main bamboo reinforcement 21 and the steel reinforcement hoop 22, the main bamboo reinforcement 21 and the bamboo reinforcement hoop 23, and the outer gauze 25 and the main bamboo reinforcement 21 are all fixed by binding with wire.

[0095] The stress release unit 2 is a columnar structure with a pointed bottom and an opening at the top. When the depth of the soil hole 1 is large, multiple stress release units 2 are connected together by socketing, that is, the bottom pointed mouth of the upper stress release unit 2 is placed in the top opening of the lower stress release unit 2, so that under deeper construction conditions, deeper stress release holes can be arranged to eliminate deep stress.

[0096] Example 2

[0097] like Figure 1 , 2As shown, an embodiment of the present invention provides a construction method for a prefabricated pile stress release hole for a soft soil foundation, which specifically includes the following steps:

[0098] S100, drawing a plan layout of stress relief holes according to the on-site conditions, and performing hole position setting on the plan layout;

[0099] S200, determine the on-site hole position according to the plan layout, and after the drilling rig is in place, the drilling rig will be used to guide the hole, and the drilling machine will be used to carry out construction, and the casing will be buried in the on-site hole position;

[0100] S300, using a drilling machine to perform rotary drilling operations in a slow-first-faster-later order until the drilling hole reaches a preset depth, thereby completing the soil hole 1;

[0101] S400, optimizing the structure of the stress release unit 2 according to the completed hole size of the soil hole 1, and determining a specific size suitable for the actual engineering geology on site;

[0102] S500, using a pulling machine to align with the center of the soil hole 1 to hoist the stress release unit 2 into the soil hole 1, and controlling the stress release unit 2 not to float;

[0103] S600, use a pull-out machine to slowly pull out the steel casing by vibration, and use a template wooden plank to make a cover plate to protect the stress release hole.

[0104] like Figure 6 As shown, in step S100, the plan layout of the stress release holes is drawn according to the layout principle. The layout principle is different from the traditional arrangement of stress release measures between the construction area and the protected area. The stress release holes are mainly arranged in the direction of the protected area outside the construction site where the piles are densely located, between the caps, and near the protected position. In addition to protecting the adjacent buildings, it can also effectively reduce the impact of excessive stress on the soft soil foundation on the displacement and gushing of the prefabricated piles that have been constructed.

[0105] In step S200, the method of burying the casing is the method of drilling + vibration driving. The casing is a steel casing, and its length is determined by the actual address and construction requirements. It is made of a steel plate not less than 8 mm thick. The diameter of the casing is consistent with the aperture of the stress release hole to prevent the empty hole from collapsing. The drilling rig is a crawler rotary drilling rig, and the hole depth during drilling is 0.5m-1m. When burying the casing, its deviation angle must also be evaluated to control the verticality of the controller, and its average deviation angle for:

[0106]

[0107] Where Δh(z) is the horizontal deviation distance between the top and bottom of the casing at depth z,

[0108] L is the height of the casing,

[0109] is the deviation rate of the casing at depth z.

[0110] The deviation rate of the casing at depth z for:

[0111]

[0112] In step S300, the preset depth is determined by the depth of the precast pile. Specifically, the preset depth is 1 / 3 to 1 / 2 of the depth of the precast pile, and the diameter of the drilled soil hole 1 is greater than the diameter of the stress release unit 2 by 180-220 mm. The soil hole 1 is drilled by casing + rotary drilling process. When drilling, the initial footage is 40-50 cm each time. During the drilling process, confirm whether the underground is an unfavorable stratum. If a lone rock is encountered, change the hole position nearby and keep a record. After drilling is normal, increase the footage to 70-90 cm. After the hole reaches the designed depth, check the hole depth and hole diameter. The hole depth and hole diameter are not less than the design requirements.

[0113] In step S300, the drilling speed change rate during drilling is:

[0114]

[0115] Where r(z) is the rate of change of drilling speed

[0116] k is the proportionality coefficient,

[0117] H(z) is the formation hardness at depth z,

[0118] W(z) is the wear degree of the drill bit at depth z,

[0119] w m is the maximum allowable wear of the drill bit,

[0120] P(z) is the groundwater pressure at depth z,

[0121] p m is the maximum allowable value of groundwater pressure.

[0122] The rate of change of the formation hardness with depth H(z) is:

[0123] H(z)=H 0 ·e kz ;

[0124] Among them, H 0 is the ground hardness at the surface,

[0125] k is the hardness growth coefficient,

[0126] e is the base of natural logarithms.

[0127] The wear degree W(z) of the drill bit at the depth z is:

[0128] W(z)=W 0 +m·z;

[0129] Among them, W 0 is the initial drill wear degree,

[0130] m is the wear growth coefficient,

[0131] z is the current depth of drilling.

[0132] The groundwater pressure P(z) at the depth z is:

[0133] P(z)=P 0 +ρ·g·z;

[0134] Among them, P 0 is the initial groundwater pressure, i.e. the pressure at the surface, calculated according to atmospheric pressure,

[0135] ρ is the density of groundwater,

[0136] g is the acceleration due to gravity,

[0137] z is the current depth of drilling.

[0138] In step S400 , the specific dimensions of the stress release unit 2 include the overall length, the diameters and spacings of the steel reinforcement hoop 22 and the bamboo reinforcement hoop 23 .

[0139] In step S400, the stability of the stress release unit 2 needs to be checked, specifically:

[0140]

[0141] Among them, F s (z) is the safety factor for depth variation,

[0142] F c (z) is the bearing capacity of the stress release unit as it changes with depth,

[0143] F a (z) is the actual load of the stress release unit that varies with depth.

[0144] More specifically, the load capacity F of the stress release unit varies with depth. c (z) is:

[0145]

[0146] Among them, σ c(z) is the compressive strength of the stress release unit varying with depth,

[0147] A(z) is the cross-sectional area of ​​the stress release unit as it changes with depth;

[0148] The compressive strength σ of the stress release unit varies with depth c (z) is:

[0149] σ c (z)=σ c0 exp(-k·P(z));

[0150] Among them, σ c0 is the initial compressive strength,

[0151] k is the compressive strength reduction coefficient,

[0152] z is the current depth of drilling,

[0153] exp(x) is e x .

[0154] The actual load F of the stress release unit varies with depth. a (z) is:

[0155]

[0156] Among them, σ t (z) is the soil pressure that varies with depth,

[0157] is the groundwater pressure that varies with depth,

[0158] C(z) is the lateral area of ​​the stress release unit that varies with depth,

[0159] A(z) is the cross-sectional area of ​​the stress release unit that varies with depth.

[0160] The earth pressure σ that varies with depth t (z) and groundwater pressure varying with depth Determined according to geological survey data; the cross-sectional area A(z) of the stress release unit that varies with depth and the lateral area C(z) of the stress release unit that varies with depth are measured when the stress release unit is manufactured.

[0161] Preferably, in step S400, since the bamboo pieces are relatively irregular natural materials, they are affected by natural grains, natural curvatures, and the material itself is small at the top and large at the bottom. It is difficult to cut the whole bamboo piece evenly when processing it. The quality of bamboo piece processing is controlled by the average width, and the processing quality of the bamboo cage is controlled by the total width of the main bamboo ribs in the cross section. Before the stress release unit 2 is made, the bent bamboo pieces should be removed.

[0162] The stress release unit 2 is provided with a reinforcement hoop, which is divided into a steel reinforcement hoop 22 and a bamboo reinforcement hoop 23. The steel reinforcement hoop 22 is formed by bending a steel bar suitable for the on-site working conditions, and the overlap is welded, and the overlap length is not less than 100mm; the bamboo reinforcement hoop 23 is formed by bending a bamboo piece, and is fixed by binding with no less than two strands of wire, and the overlap length is not less than 300mm.

[0163] After the stress relief unit 2 is tied, the side and the cone section need to be wrapped with a gauze 25 and fixed with a tie wire. After the stress relief unit 2 is formed, it needs to be inspected and can be used only after passing the inspection.

[0164] In step S500, the stress release unit 2 is placed vertically into the soil hole 1. It should be placed gently and slowly to avoid collision with the hole wall, rotation to the left and right, and deformation. If there is an obstacle, the lowering should be stopped, the cause should be found out, and it should be handled. It is strictly forbidden to drop it violently or forcefully. In order to reduce the floating degree of the bamboo cage and prevent stones from damaging the bamboo cage, fillers are placed at the bottom of the bamboo cage to press the bamboo cage before hoisting it into the hole.

[0165] In step S500, when the stress release unit 2 is vertically placed in the soil hole 1, the verticality of the stress release unit 2 needs to be controlled, and the inclination angle is:

[0166]

[0167] Where θ(z) is the inclination angle of the stress release unit at depth z,

[0168] Δg(z) is the horizontal offset of the stress release unit at depth z.

[0169] The horizontal offset of the stress release unit at depth z is:

[0170]

[0171] Among them, F h (z) is the horizontal force that varies with depth,

[0172] E(z) is the stiffness of the stress release unit that varies with depth.

[0173] The horizontal force F that varies with depth h (z) is:

[0174]

[0175] Among them, σ h (z) soil resistance varying with depth,

[0176] A(z) is the cross-sectional area of ​​the stress release unit that varies with depth.

[0177] The stiffness E(z) of the stress release unit that varies with depth is:

[0178]

[0179] Among them, σ E (z) is the elastic modulus of the stress release unit that changes with depth,

[0180] I(z) is the moment of inertia that varies with depth.

[0181] In step S600, when pulling out the steel casing, it needs to be pulled out slowly to reduce the impact of silt on the bamboo cage; the edge of the cover plate extends 300mm out of the hole, and a soil covering mark is set on the top.

[0182] In step S600, the bearing capacity of the protection of the stress release hole opening needs to be verified, specifically:

[0183] F r =∑F c (i) = ∑(A i ·σ c (i)·φ(i));

[0184] Among them, F r The bearing capacity of the cave entrance protection,

[0185] F c (i) is the bearing capacity of the ith part,

[0186] A i is the cross-sectional area of ​​the ith part,

[0187] σ c (i) is the material compressive strength of the i-th part,

[0188] φ(i) is the effective utilization coefficient of the i-th part.

[0189] The effective utilization coefficient φ(i) of the i-th part is:

[0190] φ(i)=φ 0 +k φ ·σ c (i);

[0191] Among them, φ 0 is the initial effective utilization coefficient,

[0192] k φ is the coefficient of effective utilization coefficient varying with compressive strength.

[0193] The material compressive strength σ of the i-th part c (i)

[0194] σc (i) = σ c0 +kσ·z i ;

[0195] Among them, σ c0 is the initial compressive strength,

[0196] k σ is the coefficient of compressive strength variation with depth,

[0197] z i is the depth position of the ith part.

[0198] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A construction method for prefabricated pile stress release holes for soft soil foundation, characterized in that: The following steps are involved: S100, drawing a plan layout of stress relief holes according to the on-site conditions, and performing hole position setting on the plan layout; S200, determine the on-site hole position according to the plan layout, and after the drilling rig is in place, the drilling rig will be used to guide the hole, and the drilling machine will be used to carry out construction, and the casing will be buried in the on-site hole position; S300, using a drilling machine to perform rotary drilling operations in a sequence of first slow and then fast, until the drilling hole reaches a preset depth, thereby completing the soil hole (1); S400, optimizing the structure of the stress release unit (2) according to the completed hole size of the soil hole (1), and determining a specific size suitable for the actual engineering geology on site; S500, using a pulling machine to align the stress release unit (2) with the center of the soil hole (1) and hoisting it into the soil hole (1), and controlling the stress release unit (2) to prevent it from floating up; S600, use a pull-out machine to slowly pull out the steel casing by vibration, and use a template wooden plank to make a cover plate to protect the stress release hole.

2. The construction method of a prefabricated pile stress release hole for soft soil foundation according to claim 1, characterized in that: In step S100, the plan layout diagram of the stress release holes is drawn according to the layout principle; The arrangement principle is to arrange the stress release holes mainly in places where piles are densely packed, between pedestals and in the direction of the protected area outside the construction site, and to arrange them densely near the protection positions.

3. The construction method of a prefabricated pile stress release hole for soft soil foundation according to claim 1, characterized in that: In step S200, when the casing is buried, the deviation angle needs to be evaluated to control the verticality of the controller, and the average deviation angle for: Where Δh(z) is the horizontal deviation distance between the top and bottom of the casing at depth z, L is the height of the casing, is the deviation rate of the casing at depth z.

4. The construction method of a prefabricated pile stress release hole for soft soil foundation according to claim 1, characterized in that: In step S300, the drilling speed change rate during drilling is: Where r(z) is the rate of change of drilling speed k is the proportionality coefficient, H(z) is the formation hardness at depth z, W(z) is the wear degree of the drill bit at depth z, w m is the maximum allowable wear of the drill bit, P(z) is the groundwater pressure at depth z, p m is the maximum allowable value of groundwater pressure.

5. The construction method of a prefabricated pile stress release hole for soft soil foundation according to claim 4, characterized in that: The rate of change of the formation hardness with depth H(z) is: <h2 style=";text-align:left;direction:ltr">H(z) = H0·e<h2 style=";text-align:left;direction:ltr"> kz <h2 style=";text-align:left;direction:ltr"> ; Where H0 is the ground hardness at the surface, k is the hardness growth coefficient, e is the base of natural logarithm; The wear degree W(z) of the drill bit at the depth z is: W(z)=W0+m·z; Among them, W0 is the initial drill wear degree, m is the wear growth coefficient, z is the current depth of the drilling; The groundwater pressure P(z) at the depth z is: P(z)=P0+ρ·g·z; Where P0 is the initial groundwater pressure, that is, the pressure at the surface, calculated according to atmospheric pressure, ρ is the density of groundwater, g is the acceleration due to gravity, z is the current depth of drilling.

6. A construction method for prefabricated pile stress release holes for soft soil foundation according to any one of claims 1-5, characterized in that: In step S400, the stability of the stress release unit (2) needs to be checked, specifically: Among them, F s (z) is the safety factor for depth variation, F c (z) is the bearing capacity of the stress release unit as it changes with depth, F a (z) is the actual load of the stress release unit that varies with depth.

7. The construction method of a prefabricated pile stress release hole for soft soil foundation according to claim 6, characterized in that: The load capacity F of the stress relief unit varies with depth c (z) is: Among them, σ c (z) is the compressive strength of the stress release unit varying with depth, A(z) is the cross-sectional area of ​​the stress release unit as it changes with depth; The actual load F of the stress release unit varies with depth. a (z) is: Among them, σ t (z) is the soil pressure that varies with depth, τ(z) is the groundwater pressure that varies with depth, C(z) is the lateral area of ​​the stress release unit that varies with depth, A(z) is the cross-sectional area of ​​the stress release unit that varies with depth.

8. A construction method for prefabricated pile stress release holes for soft soil foundation according to any one of claims 1-5, characterized in that: In step S500, when the stress release unit (2) is vertically placed in the soil hole (1), the verticality of the stress release unit (2) needs to be controlled, and the inclination angle is: Where θ(z) is the inclination angle of the stress release unit at depth z, △y(z) is the horizontal offset of the stress release unit at depth z.

9. A construction method for prefabricated pile stress release holes for soft soil foundation according to any one of claims 1 to 5, characterized in that: In step S600, the bearing capacity of the protection of the stress release hole opening needs to be verified, specifically: F r =∑F c (i)=∑(A i ·σ c (i)·φ(i)); Among them, F r The bearing capacity of the cave entrance protection, F c (i) is the bearing capacity of the ith part, A i is the cross-sectional area of ​​the ith part, σ c (i) is the material compressive strength of the i-th part, φ(i) is the effective utilization coefficient of the i-th part.

10. A prefabricated pile stress relief hole for soft soil foundation, used to implement a construction method of a prefabricated pile stress relief hole for soft soil foundation as claimed in any one of claims 1 to 9, characterized in that: It comprises a soil hole (1) and a stress release unit (2) arranged in the soil hole (1); The soil holes (1) are formed by drilling with a drilling machine and are arranged between a plurality of prefabricated piles, between large caps, and around the protected buildings; The main body of the stress release unit (2) is a plurality of vertically arranged bamboo main bars (21), the plurality of bamboo main bars (21) are arranged along the circumference, and the periphery is fixed by a steel reinforcement hoop (22) and a bamboo reinforcement hoop (23), the steel reinforcement hoop (22) and the bamboo reinforcement hoop (23) are both in plurality and are arranged at intervals on the outer circle of the bamboo main bars (21); The bottom end of the main bamboo rib (21) is closed toward the center to form a cone, and the tip thereof is fixed by a bamboo binding wire (24); The outer periphery of the stress release unit (2) is also provided with an outer covering gauze (25).

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