Heavy well guide hole construction method for thick sandy soil interbedded stratum
By calculating the critical self-stabilizing hole depth and performing segmented grouting for wall protection during the construction of the reverse well pilot hole, the problem of easy collapse in thick sandy soil interbedded with soil was solved, thus improving construction safety and efficiency.
Patent Information
- Application Number
- CN202511083605.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-08-04
- Publication Date
- 2025-11-21
Smart Images
Figure CN120990481A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application belongs to the technical field of engineering construction, and particularly relates to a thick sand interbedded stratum reverse well guide hole construction method. BACKGROUND
[0002] In the reverse well guide hole construction, due to the action of land pressure or poor geological conditions, the drilled guide hole is prone to collapse, and the safety of the guide hole drilling process still has great challenges.
[0003] The thick sand interbedded stratum is often prone to collapse of the hole wall due to loose sand particles and low cohesion under the action of drilling disturbance and groundwater soaking, resulting in accidents such as sticking and burying of the drill, increasing construction cost and delaying the construction period.
[0004] The existing technology has mature solutions for the collapse of the guide hole, but there are still deficiencies in the early prevention and avoidance of the collapse of the guide hole in the thick sand interbedded stratum, and how to identify the stratum change in real time and accurately implement the wall protection measures is a technical problem to be solved. SUMMARY
[0005] The purpose of the present application is to provide a thick sand interbedded stratum reverse well guide hole construction method, which prevents the occurrence of guide hole collapse accidents in advance through theoretical calculation and adopts engineering measures to avoid the secondary accidents such as sticking and burying of the drill in the guide hole drilling engineering of the prior art, and solves the problems of increasing construction cost and delaying the construction period.
[0006] To achieve the above purpose, the present application provides the following solutions:
[0007] A thick sand interbedded stratum reverse well guide hole construction method, comprising: dividing a drill hole into one operation section or multiple continuously distributed operation sections according to the mechanical properties of the soil at the drill hole position, determining the critical self-stable hole depth of the operation section and drilling the hole, drilling the guide hole to the critical self-stable hole depth of the operation section, grouting to form a guide hole wall protection, and drilling out the thick sand layer.
[0008] The step of determining the critical self-stable hole depth of the operation section and drilling the hole includes a confirmation step of the critical self-stable hole depth of the first operation section and a confirmation step of the critical self-stable hole depth of the second and subsequent operation sections in sequence.
[0009] Optionally, the mechanical properties of the soil are obtained by collecting soil samples and performing soil mechanical property tests on the collected soil samples.
[0010] The mechanical properties of the soil include cohesion parameters, internal friction angle parameters, permeability coefficient parameters and natural density parameters.
[0011] A stability analysis model of the guide hole is established according to the mechanical property of the soil.
[0012] Optionally, the confirming step of the critical self-stable hole depth of the first operation section comprises:
[0013] The mud wall forms a mud skin to replace the soil in the hole to form a balanced system;
[0014] The active earth pressure outside the mud skin and the mud pressure inside the mud skin are calculated;
[0015] The depth at which the resultant of the active earth pressure and the mud pressure is zero is taken as the critical self-stable hole depth of the first operation section.
[0016] The active earth pressure P α outside the mud skin sw and the mud pressure P j The calculation is as follows:
[0017]
[0018] P sw =-1 / 2γ sw z 2 ;
[0019]
[0020] In the formula, K α is the active earth pressure coefficient; γ sw is the mud density; γ is the soil density; c is the soil cohesion; ψ is the soil internal friction angle; q is the surface load; z is the vertical depth; and r is the radial direction.
[0021] When the resultant P j > 0, it indicates that the soil is unstable in the depth range of z1 < z < z2; when the resultant P j < 0, it indicates that the soil is stable in the depth range of z1 < z < z2; and when the resultant P j = 0, it indicates that the soil is in the limit state at z = z cr , and z = z cr is the critical self-stable hole depth under the action of the mud wall.
[0022] In the formula, z cr1 is the critical self-stable hole depth of the first operation section.
[0023]
[0024] In the formula, γ sw is the mud density; γ is the soil density; c is the soil cohesion; ψ is the soil internal friction angle; q is the surface load; z is the vertical depth; and r is the radial direction.
[0025] Optionally, the confirming step of the critical self-stable hole depth of the second and subsequent work segments in sequence comprises:
[0026] To ensure the safety of drilling construction, the actual work segment depth of construction is
[0027] determining the instability boundary of the work segment; the upper side of the instability boundary is the bottom end of the previous work segment, and the lower side of the instability boundary is the top end of the subsequent work segment; the upper side of the instability boundary is the first instability form, and the lower side of the instability boundary is the second instability form;
[0028] determining the first interface shear stress value and the second interface shear stress value at the instability boundary;
[0029] obtaining the instability depth one value based on the function relationship between the first instability form, the first interface shear stress value and the instability depth one value;
[0030] obtaining the instability depth two value based on the function relationship between the second interface shear stress value and the instability depth two value according to the second instability form;
[0031] comparing the instability depth one value and the instability depth two value, and taking the smaller value as the critical self-stable hole depth of the current work segment.
[0032] The supporting resistance provided by the mortar at different depths is different, and the size of the supporting resistance is in a proportional relationship with the depth z at which it is located. The generation of supporting resistance can be divided into two stages.
[0033] After re-drilling, there is a thin layer of solidified cement mortar on the wall of the guide hole within the grouting segment depth, which plays a stabilizing supporting role for the hole wall. At this time, the calculation of the critical depth of the next stage needs to consider the supporting role of this thin layer of solidified cement mortar. Due to the small thickness, it mainly relies on the arch supporting force, which depends on the compressive strength of the cement mortar, rather than the shear strength of the mortar layer, which is determined by the soil pressure of the soil at the hole wall position and changes with the hole depth.
[0034] Two instability forms are considered:
[0035] The instability of the segment, the destruction of the bottom of the thin layer of mortar, and the mortar supporting force reaching its ultimate compressive strength are the critical instability depth z cri determination basis;
[0036] The instability of the segment, the destruction of the bottom of the thin layer of mortar, and the mortar supporting force reaching its ultimate compressive strength are the critical instability depth z cri determination basis;cri is the critical instability depth.
[0037] drilling depth is the difference between the lateral pressure of the soil and the lateral pressure of the mud, the supporting resistance is 0 at the depth z0, and the supporting resistance increases in a linear function of the drilling depth.
[0038] With the continuous increase of the drilling depth, the additional supporting resistance increases in a positive function of the drilling depth below, but the function relationship cannot be determined, and the additional supporting resistance of the upper thin layer of mud caused by the lower excavation increases with the growth of the excavation depth.
[0039] Now is the boundary, the upper and lower soils are divided into two parts to be considered, and the interaction force of the two parts of soil is analyzed. Considering below, that is, the section without the thin layer of mud, the soil around the hole has a tendency to move into the hole, which will give the upper contacted soil a shear stress into the hole, aggravating the damage of the upper soil, only the size of the interface shear stress between and the two parts of soil is determined, and the size of the additional supporting resistance of the bottom thin layer of mud is determined.
[0040] Optionally, the determination of the instability boundary comprises:
[0041] According to the function relationship of the critical self-stable hole depth value of the previous operation section, the reciprocal of the safety factor, and the instability boundary, the instability boundary is obtained.
[0042] Optionally, the calculation formula of the instability depth value is as follows:
[0043]
[0044] Optionally, the calculation formula of the first interface shear stress value is as follows:
[0045]
[0046]
[0047] σ 界面1 = P 界面1 / 3r0.
[0048] Optionally, when the shear stress of the second and subsequent interfaces is considered, the interface shear stress reaches the limit, and the interface limit shear stress is mainly provided by the friction strength of the soil. When the interface limit shear stress reaches the shear strength of the soil, the drilling depth at which the hole wall is damaged is the critical instability depth, and at this time, the calculation formula of the second interface shear stress value is as follows:
[0049]
[0050] Optionally, the depth of the active earth pressure, the mud side pressure and the resultant of the second interface limit shear stress of the soil body of the section is zero as the critical self-stable hole depth of the second instability form of the soil body.
[0051] The active earth pressure p (z ) of the soil body of the section a (z i ), the mud pressure P sw and the resultant p j (z i ) are calculated as follows:
[0052]
[0053] In the formula: γ sw is the mud weight; γ is the soil weight; c is the soil cohesion; ψ is the internal friction angle of the soil; q is the ground load; r0 is the guide hole radius; z is the vertical depth; and r is the radial direction.
[0054] The instability form analysis of the soil body of the section is the same as the analysis of the first working section, taking the mud skin as the research object, and analyzing the stress conditions on both sides of the mud skin, wherein:
[0055] p a (z i ) is the active earth pressure outside the mud skin of the soil body of the section;
[0056] p j (z i ) is the resultant of the active earth pressure, the mud side pressure and the second interface limit shear stress of the section;
[0057] When the resultant p j (z i ) = 0, it indicates that the limit state is just reached at z = z cr2 / / , and z = z cr2 / / is the critical self-stable hole depth of the second instability form.
[0058] Optionally, the grouting pressure is determined according to the hole depth and the stratum;
[0059] When it is a shallow hole, the grouting pressure is 0.5-1.0 MPa, and when it is a deep hole, the grouting pressure is 1-3 MPa.
[0060] Optionally, the shallow hole depth is less than 50 m.
[0061] Optionally, the step of drilling the pilot hole to the critical self-stable hole depth of the working section comprises determining the drilling operation parameters based on the monitored change value of the pulling force.
[0062] Optionally, the safety factor is F S .
[0063] Optionally, before the step of dividing the drilling hole into one working section or multiple continuous working sections according to the mechanical property of the soil at the drilling hole position, the method further comprises the steps of pouring foundation concrete, installing and debugging the raise boring machine.
[0064] Compared with the prior art, the present application has the following advantages and technical effects:
[0065] The method, through theoretical calculation, drills the pilot hole to the critical self-stable hole depth before the hole collapses, and the hole is self-stable at this time. Then, the drilling hole is formed by grouting after the hole is reinforced by the pilot hole protection wall. The drilling hole is drilled to the critical self-stable hole depth each time. In this way, the drilling hole is always in a self-stable state. The occurrence of the pilot hole collapse accident is prevented in advance, and engineering measures are taken to avoid the accident. The secondary accidents of the pilot hole drilling engineering in the prior art, such as sticking and burying of the drilling hole, are solved, the construction cost is reduced, and the construction period is shortened. BRIEF DESCRIPTION OF DRAWINGS
[0066] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed in the embodiments. Obviously, the drawings described below only show some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor based on these drawings:
[0067] Figure 1 The working flowchart of the present application;
[0068] Figure 2 The critical self-stable hole depth acquisition step diagram of the first working section of the present application;
[0069] Figure 3 The critical self-stable hole depth acquisition step diagram of the second and subsequent working sections of the present application;
[0070] Figure 4 The overall construction flowchart of the present application;
[0071] Figure 5 The lateral pressure distribution diagram before the pilot hole excavation of the present application;
[0072] Figure 6 The lateral pressure distribution diagram after the pilot hole excavation of the present application;
[0073] Figure 7A schematic diagram of the lateral pressure distribution of the re-drilling and excavation of the guide hole of the present application;
[0074] Figure 8 A schematic diagram of the lateral pressure distribution of the re-drilling and excavation of the guide hole of the present application; A schematic diagram of the lateral pressure distribution of the re-drilling and excavation of the guide hole of the present application;
[0075] Figure 9 A schematic diagram of the lateral pressure distribution of the re-drilling and excavation of the guide hole of the present application;
[0076] Figure 10 A schematic diagram of the lateral pressure distribution of the re-drilling and excavation of the guide hole of the present application; A schematic diagram of the lateral pressure distribution of the re-drilling and excavation of the guide hole of the present application. DETAILED DESCRIPTION
[0077] The technical solutions in the embodiments of the present application will be apparently and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application.
[0078] In order to make the above objectives, characteristics and advantages of the present application more apparent, comprehensible and easier to understand, the present application will be further described in detail below with reference to the drawings and specific embodiments.
[0079] With reference to Figures 1 to 10 The present application discloses a construction method of a thick sand soil interbedded stratum counter-bore drilling, comprising: according to the mechanical property characteristics of the soil at the drilling position, dividing the drilling into one operation section or multiple continuous operation sections according to the depth, determining the critical self-stable hole depth of the operation section and drilling, drilling before reaching the critical self-stable hole depth of the operation section, and forming a guide hole protection wall by grouting until the thick sand layer is drilled out.
[0080] The method prevents the drilling from collapsing by drilling before reaching the critical self-stable hole depth through theoretical calculation, and the drilling is self-stable and does not collapse at this time. The drilling is always in a self-stable state by drilling before reaching the critical self-stable hole depth each time, preventing the occurrence of the guide hole collapse accident in advance, avoiding the secondary accidents such as sticking and burying of the drill, increasing the construction cost and delaying the construction period.
[0081] As an optional embodiment, the mechanical property characteristics of the soil are obtained by collecting soil samples and performing soil mechanical property tests on the collected soil samples.
[0082] The soil sample collecting step adopts a PVC pipe with a diameter of 11 cm and a length of 30 cm to collect the soil sample on site, the PVC pipe is vertically placed on the cleaned sampling point, a hammer is used to gently knock the top of the PVC pipe, the PVC pipe is slowly inserted into the soil, when the PVC pipe is inserted to the predetermined depth, a shovel is used to dig the soil around the PVC pipe to separate the bottom of the PVC pipe from the soil, the PVC pipe with the soil sample is timely sealed to prevent the soil sample from being affected by moisture loss, pollution and the like during the transportation and storage process.
[0083] The soil mechanical properties of the collected soil sample are tested by experimental means.
[0084] The cohesion (c) and the internal friction angle (ψ) are measured by the direct shear test.
[0085] The permeability coefficient (K) is obtained by the variable water head permeability test.
[0086] The natural unit weight (γ) is measured by the cutting ring method.
[0087] As an optional implementation, the confirming step of the critical self-stable hole depth of the first operation section includes:
[0088] A guide hole stability analysis model is established.
[0089] The mud skin is formed to replace the soil in the hole to form a balanced system.
[0090] The active earth pressure outside the mud skin and the mud pressure inside the mud skin are calculated.
[0091] The depth at which the resultant of the active earth pressure and the mud pressure is zero is taken as the critical self-stable hole depth of the first operation section.
[0092] The critical unstable depth of the first section of the thick sand layer is determined.
[0093] Before the guide hole drilling of the back drilling machine, the soil layer of the hole wall is in the initial mechanical equilibrium state. During the drilling construction process, the soil is gradually taken out by the drill bit, the lateral pressure of the hole wall is released, the hole wall loses the support of the original soil, the original ground pressure is released freely, the soil appears a large relaxation deformation, the soil stress around the hole is redistributed, and the original soil structure is destroyed. In addition, the soil around the hole is often soaked by the free water in the surrounding mud, thereby weakening some indexes (internal friction angle, cohesion, etc.) of the shear strength of the soil. And under the action of the upper ground pressure, the hole wall rock and soil are forced to move into the hole, causing the hole wall to lose stability and collapse.
[0094] Through soil sampling, the soil related tests are carried out to determine the mechanical indexes of soil. The stability problem of the guide hole is regarded as a plane limit problem on the vertical plane, and a mechanical model of the hole stability is established by using the principle of balance between the Rankine earth pressure, the Coulomb earth pressure and the mud pressure, and the limit hole depth without support, the stability coefficient and the mud bulk density are derived.
[0095] The instability of the guide hole is largely caused by the change of the pressure on both sides of the hole wall before and after the hole is drilled and excavated. The mud protection wall effect is reflected in the mud lateral pressure resisting the lateral stress of the soil, and the gel effect of the mud forms a mud skin. The mud skin is taken as the research object for stress analysis on both sides.
[0096] According to the lateral pressure balance principle, a guide hole stability analysis model is established, wherein: P0, P α are the static earth pressure and the active limit earth pressure respectively; K0, K α are the static earth pressure coefficient and the active earth pressure coefficient respectively; γ sw is the mud bulk density; γ is the soil bulk density; q is the surface load; z is the vertical direction; and r is the radial direction.
[0097] The static lateral pressure before excavation reaches a self-balancing state. The hypothetical film is in a self-balancing state under the static earth pressure P0(z) = 1 / 2K0γz 2 + qK0z on both sides. After excavation, the mud pressure balances the active lateral pressure, the soil in the hole is replaced by mud, the hole wall moves inward to reach the active limit state, the outer side of the mud skin is subjected to the active earth pressure P α (z), and the inner side is subjected to the mud pressure P sw (z) = -1 / 2γ sw z 2 , and reaches a new state under the joint action of the two.
[0098] The active earth pressure of cohesive soil is divided into two parts, including the lateral pressure caused by the self-weight γz of the soil, and the "negative" lateral pressure caused by the cohesion force, which reduces the lateral earth pressure.
[0099] The soil lateral pressure P α (z) acting on the mud skin and the resultant force P j (z) are calculated as follows:
[0100]
[0101] In the formula: K α is the active earth pressure coefficient; γ sw is the mud bulk density; γ is the soil bulk density; c is the soil cohesion; ψ is the internal friction angle of the soil; q is the surface load; z is the vertical depth; and r is the radial direction.
[0102] From the formula, the lateral pressure of mud P sw (z) = -1 / 2γ sw z 2 The lateral pressure generated by cohesion is negative, and both are factors to keep the guide hole stable, while the lateral pressure generated by the self-weight of soil and the lateral pressure generated by the overburden load are positive, which are the factors leading to the instability of the guide hole.
[0103] When the resultant force P j (z1<z<z2) > 0, it means that the soil is unstable in the depth range of z1<z<z2; when the resultant force P j (z1<z<z2) < 0, it means that the soil is stable in the depth range of z1<z<z2; when the resultant force P j (z=z cr ) = 0, it means that it is in the limit state at z=z cr , and z=z cr is the critical self-stable hole depth under the action of mud wall protection.
[0104] The solution is:
[0105]
[0106] In the formula: γ sw is the specific gravity of mud; γ is the specific gravity of soil; c is the cohesion of soil; ψ is the internal friction angle of soil; q is the surface load; z is the vertical depth; r is the radial direction.
[0107] Guide hole wall protection treatment.
[0108] Based on the critical depth of instability obtained by calculation, when the guide hole drilling reaches , the drill is pulled out in advance, and the guide hole is filled by grouting reinforcement measures, and after solidification, drilling is resumed. A thin layer of solidified mortar is formed to stabilize the hole wall, creating conditions for subsequent drilling and reaming, while avoiding accidents such as buried drill caused by collapse, and delaying the construction period.
[0109] Drill pulling and grouting, and drilling after solidification.
[0110] Segmented drill pulling and tool inspection.
[0111] Segmented drill pulling according to the rhythm of "slow pulling-pause-observation". The change of pulling force is closely monitored. If the pulling force suddenly increases, stop pulling immediately, and perform hole cleaning and loosening drill operation. Record the attached rock-soil state of each drill rod during the pulling process to determine the stability of the hole wall at different depths. After pulling, clean the drill and check the drill bit and drill rod wear and bending, repair or replace damaged parts to ensure the safety of subsequent drilling.
[0112] In-hole grouting.
[0113] Slurry pressure: according to the hole depth and stratum, generally 0.5-1.0 MPa for shallow hole (<50 m) and 1-3 MPa for deep hole, with the principle of no slurry return at the hole mouth and no ground uplift.
[0114] Static pressure grouting: slurry is injected into the hole through drill pipe or grouting pipe, which is suitable for the section with concentrated instability of hole wall.
[0115] Segmented grouting: suitable for long distance instability dangerous section, with 0.5-1.0 m interval for each segment.
[0116] As an optional implementation, the confirmation step of the critical self-stable hole depth of the second and subsequent operation sections in sequence of a plurality of continuously distributed operation sections comprises:
[0117] determining the instability boundary of the operation section;
[0118] the bottom end of the previous operation section above the instability boundary and the top end of the subsequent operation section below the instability boundary;
[0119] the first instability mode above the instability boundary and the second instability mode below the instability boundary;
[0120] determining the first interface shear stress value and the second interface shear stress value at the instability boundary;
[0121] when in the first instability mode, obtaining the instability depth one value according to the functional relationship between the first interface shear stress value and the instability depth one value;
[0122] when in the second instability mode, obtaining the instability depth two value according to the functional relationship between the second interface shear stress value and the instability depth two value;
[0123] comparing the instability depth one value and the instability depth two value, and taking the smaller value as the critical self-stable hole depth of the current operation section.
[0124] As an optional implementation, the determination of the instability boundary comprises:
[0125] obtaining the instability boundary according to the functional relationship between the previous critical self-stable hole depth value, the reciprocal of the safety factor and the instability boundary.
[0126] determination of the critical instability depth of the second and subsequent sections.
[0127] After re-drilling, a thin layer of solidified cement mortar remains on the borehole wall within the grouting depth range, providing stable support for the borehole wall. The calculation of the critical depth for the next stage needs to consider the supporting effect of this thin layer of solidified cement mortar. Due to its small thickness, it mainly relies on the arch support force, which depends on the compressive strength of the cement mortar, rather than the shear strength of the mortar layer. The shear strength is determined by the earth pressure on the soil at the borehole wall location and varies with the borehole depth.
[0128] Consider two forms of instability:
[0129] ① The instability of the first segment, the failure of the bottom of the thin mortar layer, and the critical instability depth z of the second segment when the mortar support force reaches its ultimate compressive strength. cr2 The basis for determination;
[0130] ② The instability of the first segment is calculated in the same way as the critical instability depth calculation. Taking the mud skin below the mortar support as the research object, the principle equation of lateral pressure balance on both sides is established, and the resultant force P is taken. j (z=z cr2 Depth z when ) = 0 cr2 This is the critical instability depth for the second segment.
[0131] Specifically:
[0132] ① The method for determining the critical instability depth during segment instability is as follows:
[0133] When the excavation depth z is relatively small, the lateral pressure of the mud slurry inside the borehole will exceed the lateral pressure generated by the soil's own weight and the overlying load, i.e., γ. sw z>Kα(∑γ i z i +q), as the excavation depth increases, γ sw z < K α (∑γ i z i +q), the thin layer of mortar plays a supporting role, resisting the deformation of the borehole wall and generating support resistance, of which γ sw z0 = K α (∑γ i z i The critical point is at z = z0, where the stress direction of the thin mortar layer changes. Due to the thinness of the mortar layer, its shear resistance is poor, and the mortar is brittle, making it prone to fracture at the critical height z = z0. Therefore, in the upper section when z < z0, the thin mortar layer tends to compress the soil, increasing the stability of the borehole wall. Neglecting soil deformation, the earth pressure in this section is passive earth pressure.
[0134] The support resistance provided by mortar at different depths is different, and the magnitude of the support resistance is directly proportional to its depth z. The generation of support resistance can be divided into two stages.
[0135] Drilling depth Within this range, the value represents the difference between the soil lateral pressure and the mud lateral pressure. At a depth of z0, the support resistance is 0, and the support resistance increases as a linear function of the drilling depth.
[0136] As the drilling depth continues to increase, At that time, the additional support resistance increases in a proportional relationship with the drilling depth below, but the functional relationship cannot be determined. The additional support resistance generated by the thin mortar layer above due to the excavation below is difficult to determine as the excavation depth increases.
[0137] Now The soil mass is divided into two parts, with the upper and lower parts serving as the boundary, and the interaction forces between these two parts are analyzed. Considering... Below, in the section without a thin layer of mortar, the soil around the borehole tends to move inwards, exerting a shear stress into the upper soil and exacerbating its failure. It is only necessary to determine... and The magnitude of the interfacial shear stress between the two soil sections can determine the magnitude of the additional support resistance of the bottom mortar thin layer.
[0138] Instability depth - numerical value z cr2 / Calculation:
[0139] Within the range, the bottom mortar layer is the first to fail. Therefore, when the stress of the bottom mortar layer reaches the ultimate compressive strength it can withstand, the drilling depth is the critical instability depth of the borehole wall.
[0140] The calculation of interfacial shear stress should start from... Analysis of the stress equilibrium zone of a portion of the soil, assuming the lower portion of the soil is in... Under the action of interfacial shear stress, it is responsible for preventing the soil around the hole from sliding into the hole.
[0141] When z = z cr2 / At this point, the stress in the bottom mortar thin layer reaches its ultimate bearing capacity. The following analysis considers a range three times the borehole diameter, i.e., the soil bearing capacity within a range three times the borehole diameter after drilling and excavation. Interfacial shear stress generated in part of the soil.
[0142] The interface shear stress is calculated as follows:
[0143]
[0144] σ界面 =P 界面 / 3r0.
[0145] Under uniform radial load, the magnitude of the tangential stress in a thin-walled cylinder is equal to the radial stress, i.e., σ θ =σ r .
[0146] Critical instability depth z cr2 / The calculation is based on the following formula:
[0147]
[0148] In the formula: γ sw γ is the unit weight of mud; c is the unit weight of soil; ψ is the internal friction angle of soil; q is the surface load; r0 is the radius of the borehole; z is the vertical depth; r is the radial direction.
[0149] Due to the compressive strength f of the mortar layer c Given that z can be deduced from this, cr2 / Numerical value.
[0150] When the stress in the thin mortar layer reaches the compressive strength, that is, when the depth z = z satisfies the above formula. cr2 / At this time, z cr2 / This is the critical instability depth of the hole wall.
[0151] Instability depth (two numerical values z) cr2 / / Calculation:
[0152] The critical instability depth at which segmental instability fails is calculated in the same way as z. cr1 The determinations are the same, but need to be considered. Interface ultimate shear stress ( Section of soil to prevent The maximum shear stress that can be provided by the shrinkage and instability of the soil section. The ultimate shear stress at the interface is mainly provided by the frictional strength of the soil. When the ultimate shear stress at the interface reaches the shear strength of the soil, the drilling depth at which the borehole wall fails is the critical instability depth. The following analysis focuses on a range of three times the borehole diameter, that is, the soil within three times the borehole diameter after drilling and excavation bears the ultimate shear stress at the interface and inhibits... The soil shrinkage failure within the affected area. Taking the mud cake as the research object, a stress analysis is performed, where p a (z i )for Active earth pressure on the outer side of the mud skin of the soil segment; p j (z i) is the resultant force of the active earth pressure, the mud side pressure and the second interface limiting shear stress.
[0153]
[0154] wherein: γ sw is the mud weight; γ is the soil weight; c is the soil cohesion; ψ is the soil internal friction angle; q is the surface load; r0 is the guide hole radius; z is the vertical depth; and r is the radial direction.
[0155] When the resultant force P j (z = z cr2 / / ) = 0, z = z cr2 / / is the critical self-stable hole depth under the second drilling and the second instability form.
[0156] The critical instability depth z when the segment is unstable and the critical instability depth z cr2 / is compared with z cr2 / / , and the smaller value is taken as z cr2 . According to this, the depth of the next drilling is determined, and when the drilling reaches the depth z , the drilling is stopped, and the above operation is repeated.
[0157] The drilling and grouting are repeated, and after the solidification, the drilling operation is resumed.
[0158] According to the second segment critical instability depth calculation method, the next critical instability depth z cr3 is determined.
[0159] Real-time monitoring of drilling parameters and rock layer identification In the drilling process, the drilling speed, torque, and vibration frequency are monitored in real time, the drilling speed is controlled according to the rock condition and the return slag and return slurry, the drilling speed is quickly passed when the rock is broken, and the drilling speed is slowed down when the rock is hard, to ensure the drilling accuracy. The rock layer identification condition is set: when the drilling speed drops by ≥30% and the torque increases by ≥20%, it is determined that the drill bit contacts the rock (or boulder), and the drilling is immediately stopped. After stopping, a 219 mm steel casing is lowered, ultra-fine cement slurry (water-cement ratio 0.6:1) is injected, and after 24 h curing, a roller bit is used for secondary drilling.
[0160] Application Example 1:
[0161] As one of the application examples of the case, details are shown in the following steps:
[0162] 1) Drilling rig installation and debugging:
[0163] Water, electric pipeline installation to the working face of the rig, AT3000 reverse drilling rig using water pressure slag removal method, from the water source to the working face, and equipped with a dedicated water pump 40m 3 / h drainage. And in the platform construction of the water tank, water 30-40m 3 / h. The working voltage of the drill is 380V, and the power supply capacity is not less than 300 kilovolt-ampere.
[0164] 2) Foundation concrete pouring:
[0165] According to the reverse drilling positioning position, the reverse drilling rig foundation position is cleaned to the complete bedrock surface, and C30 concrete is poured into a 5.5m x 4m x 0.5m (length x width x height) reverse drilling foundation. The foundation is pre-arranged with a 400x300mm drainage ditch, which has a certain slope, connects the drill hole with the sedimentation tank, and lays 600-900mm tracks, pre-arranges anchor bolt hole positions, and after the concrete final setting, the reverse drilling center point and control line are marked on the concrete surface.
[0166] 3) Reverse drilling installation;
[0167] After the rig is transported to the working face, the equipment is arranged in the specified position according to the arrangement order using a 25t truck crane, the main machine is pushed to the hole center point according to the measured layout position, and the pump station is hoisted near the main machine. According to the distance between the drilling rig center and the center of the walking mechanism axle, the drilling rig position is fixed, the hole midpoint is aligned, the rail clamps are fixed on the tracks. Connect the pump station and the main machine oil pipe, fill the oil tank with hydraulic oil. Then connect the power supply, start the oil pump, then calibrate the perpendicularity of the main machine, connect the inclined struts between the main machine and the frame, adjust the screw jacks, fix the main machine, install the mechanical hand, and connect the air and water pipes.
[0168] 4) Reverse drilling debugging:
[0169] After the rig is installed, check whether the main machine installation is firm, whether the action of each part is accurate, whether the hydraulic system is complete, whether the pressure and flow of the air and water systems are appropriate, and whether the electrical system is normal. After everything is normal, start the main machine, run for 5 minutes, and confirm that everything is correct before drilling.
[0170] 5) Pilot hole drilling;
[0171] The process of pilot hole drilling is also a process of re-prospecting the geological conditions of the shaft. According to the observation of the drilling process and the returned rock debris, a preliminary qualitative analysis and understanding of the geological conditions can be made, which provides a reference for the final expansion to the designed section. In order to control the drilling deviation rate within 1%, it is necessary to ensure the correct installation of the main machine, control the opening speed, and appropriate air volume, water volume, air pressure, and water pressure for slag removal. The drill pipe of the reverse circulation drilling machine is divided into opening drill pipe, ordinary drill pipe, and stabilizing drill pipe. The opening drill pipe is connected with the pilot hole drill bit and constrained by the centralizer. The stabilizing drill pipe has a uniform distribution of steel rib plates on its outer periphery, which serves to bear the radial load, prevent excessive bending and large amplitude of rotation of the drill pipe with increasing depth, ensure the perpendicularity of the drill hole, and protect the contact and wear between the drill pipe and the hole wall.
[0172] 6) Opening drilling;
[0173] With the opening drill pipe, first connect the roller bit with the short rod, and then the mechanical hand grabs the short drill pipe and connects it with the machine head in the rack. The mechanical hand is retracted, the machine head is lowered to the roller bit to contact the concrete foundation, and the drill pipe is supported by the half-clamp ring in the hole of the rack base. First, open the water, use small drilling pressure (1.5-2 MPa) and low speed to open the hole and advance intermittently, and raise and lower the drill bit to sweep the hole and clean the rock debris in the hole in time. At the same time, measurement should be strengthened, and the drill hole deviation should be corrected in time. If the drill hole deviation is too large, another hole should be opened, and it is not allowed to continue drilling in the already deviated drill hole, otherwise the drill tool may be damaged. After the short rod is drilled, the machine is stopped and the water is turned off. According to the program, a drill pipe is installed, supported by the half-clamp ring, and continues to drill at low speed with small drilling pressure. After the drill pipe is fully inserted into the pilot hole, the water is turned off, the drill pipe is removed, the stabilizer is replaced, and it is pushed into the pilot hole. Then install another drill pipe and continue to drill at low speed with small drilling pressure. When the drilling depth exceeds 3m, normal parameters can be used for drilling, and the axial pressure and rotation speed can be gradually increased.
[0174] 7) Pilot hole drilling;
[0175] To control the deviation rate and ensure the verticality of the borehole, the stabilizers should be arranged reasonably. The sequence of installing stabilizers before drilling 10 m is 1, 3, 5, and 10. After that, one stabilizer should be installed every 10-20 m. With the increase of the drilling depth, the interval between stabilizers can be increased appropriately. The speed of the pilot hole drill should be less than 1 m / h. The footage in the strata with serious fissure development and the soft-hard transition layer should be controlled within 0.2-0.5 m / h. When the drill rod is being installed, the special drill rod thread grease should be applied, and the pushing pressure and speed should be controlled strictly. The floating function of the machine head should be used to avoid the damage of the thread. Each drill rod should be screwed with low rotation pressure. The hole mouth should be protected, and no metal or hard objects should be dropped into the hole. If abnormal noise is found in the hole during drilling, the rotation should be stopped for inspection and treatment. If metal objects are dropped into the hole, a magnet or other fishing tool can be used to take them out. The hole mouth should be cleaned in time, and the size and shape of the rock debris should be observed. If the amount of the rock debris is small and the size is fine, the water quantity should be increased. If the rock debris is still not removed, it should be considered that the drill bit has been worn out.
[0176] If the water returning from the hole is very small or even no water returns, it means that geological structures such as faults and fissures are encountered. Or the water does not leak from the hole, but the drill rotates with difficulty and the footage is not obvious, which means that a broken zone or rock layer collapse is encountered. In these two cases, the drilling should be stopped, and the drill rod should be pulled out. The high-grade cement slurry should be poured along the hole wall until the hole is filled. After 2 days, the drilling can be restarted. The water quantity and pressure of the rock debris removal system should be ensured to remove the rock debris in the hole to prevent the drill from being blocked. When the drilling depth exceeds 20 m, the water should be flushed and the rock debris should be removed for 1-2 minutes after each drill rod is drilled. The deeper the hole, the longer the time for removing the rock debris. During the drilling operation, the anchor bolts and the upper top cylinder nut should be checked frequently. The upper top cylinder should be reinforced to keep the machine stable and ensure the angle and level of the machine frame. When the pilot hole drilling is 2-3 m away from the flat hole chamber, the drilling pressure should be gradually reduced, and the drilling speed should be slowed down to make the rock debris in the hole return to the ground surface.
[0177] 8) Rod connecting operation:
[0178] Every 1 m of drilling, a drill rod must be installed. The operator first adjusts the rotation motor speed, rotates the drill rod, and stops the four-square hole of the drill rod at a position that is convenient for inserting the pad fork. The assistant inserts the pad fork → the oil motor reverses, and at the same time, the push cylinder slowly rises accordingly until the thread is disconnected (if the oil motor does not rotate at the beginning, the thread can be loosened first with the auxiliary drill rod remover, and then the oil motor is reversed) → the push cylinder is quickly raised to the maximum height of 100 mm, and then slowly rises to the upper limit. The mechanical hand grabs the drill rod and sends it into the machine head → the rotation pressure is adjusted to the low gear → the oil motor is rotated, and at the same time, the push cylinder slowly descends accordingly until the thread is connected, the machine head and the drill rod are connected → the mechanical hand clamps are loosened, the mechanical arm is returned, the mechanical hand is withdrawn, the oil motor is slowly rotated, and the push cylinder is slowly lowered to connect with the thread below until the thread is tightened. The drill rod is slightly lifted to remove the pad fork. If the operation needs to continue, the rotation pressure is adjusted to the high gear, and the normal work is started again.
[0179] 9) Field sampling of soil samples:
[0180] Unconfined shear test, variable water head permeability test and density test are carried out in the laboratory, and the parameters obtained are substituted into the above formula to obtain the critical depth of different sections, and the minimum value is taken as the threshold value, which is used as the basis for stopping drilling.
[0181] 10) Grouting construction steps:
[0182] Lower the grouting pipe (or original drill pipe) with a grouting hole to a position 0.5-1.0 m above the critical instability depth, with the pipe opening exposed above the ground by more than 0.5 m, and then connect the grouting pump.
[0183] Turn on the pump to inject clean water or thin slurry (pressure 0.2 MPa) to dredge the hole passage.
[0184] Mix the slurry according to the ratio, start the grouting pump, gradually increase the pressure to the design value, and observe the slurry return at the hole opening.
[0185] When the grouting pressure is stable and the slurry suction amount is significantly reduced (<10 L / min), or the slurry is ejected from the ground, stop grouting.
[0186] Pipe pulling and hole sealing: After grouting is completed, pull out the grouting pipe in sections, and supplement the slurry every 1 m to avoid the formation of cavities in the hole; use thick slurry to seal the hole opening to prevent slurry from flowing out.
[0187] Resuming drilling: After the mortar solidifies to the standard, open the hole with low speed and low drilling pressure to ensure the verticality of the pilot hole, and closely observe the drilling parameters such as torque and drilling pressure.
[0188] After grouting the pilot hole, resume drilling and excavation, and divide the soil into and two sections to consider the critical instability depth when the hole wall is damaged, and obtain the critical instability depth z cr2 / and z cr2 / / by calculation, compare their sizes, and take the smaller value as the final critical instability depth z cr2 , and take as the basis for construction, when the drilling depth reaches , stop drilling, and repeat the pipe pulling and grouting operation.
[0189] According to the calculation method of the critical instability depth of the second section, determine the critical instability depth of the next section, and repeat the above operation until the drilling is completed.
[0190] In the description of the present application, it needs to be understood that the terms "longitudinal", "transverse", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship shown in the drawings, which are only for the convenience of describing the present application, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application.
[0191] The above-described embodiments are only to describe the preferred modes of the present application, and not to limit the scope of the present application. Without departing from the design spirit of the present application, various modifications and improvements to the technical solutions of the present application made by those skilled in the art shall fall within the protection scope determined by the claims of the present application.
Claims
1. A method for constructing a reverse well pilot hole in thick sandy soil interbedded with soil, characterized in that, This includes dividing the borehole into one or more continuously distributed working sections based on the soil mechanical properties at the borehole location, determining the critical self-stabilizing depth of the working section and drilling, drilling the pilot borehole before reaching the critical self-stabilizing depth of the working section, and grouting to form a pilot borehole wall until a thick sand layer is drilled out. The step of determining the critical self-stabilizing hole depth of the working section and drilling includes a confirmation step of the critical self-stabilizing hole depth of the first working section and a confirmation step of the critical self-stabilizing hole depth of the second and subsequent working sections, in the order of multiple consecutively distributed working sections.
2. The method for constructing a reverse well pilot hole in a thick sandy soil interbedded strata according to claim 1, characterized in that: The soil mechanical properties are obtained by collecting soil samples and conducting soil mechanical property tests on the collected soil samples. The mechanical properties of the soil include cohesion parameters, internal friction angle parameters, permeability coefficient parameters, and natural unit weight parameters; A guide hole stability analysis model was established based on the aforementioned soil mechanical properties.
3. The method for constructing a reverse well pilot hole in thick sandy soil interbedded with soil, as described in claim 2, is characterized in that... The steps for confirming the critical self-stabilizing hole depth of the first working section include: The mud slurry forms a mud cake that replaces the soil inside the borehole, creating a balanced system. Calculate the active earth pressure on the outer side of the mud cake and the mud pressure on the inner side of the mud cake; The depth at which the combined force of the active earth pressure and the mud pressure is zero is taken as the critical self-stabilizing hole depth of the first working section.
4. The method for constructing a reverse well pilot hole in thick sandy soil interbedded with soil, as described in claim 3, is characterized in that... Taking multiple consecutively distributed work segments as an example, the steps for confirming the critical self-stabilizing hole depth of the second and subsequent work segments include: Determine the instability boundary of the work segment; the area above the instability boundary is the bottom end of the previous work segment, and the area below the instability boundary is the top end of the next work segment; the area above the instability boundary is the first instability state, and the area below the instability boundary is the second instability state. Determine the values of the first interface shear stress and the second interface shear stress at the instability boundary. Based on the first instability mode, the instability depth is obtained by the functional relationship between the first interface shear stress value and the instability depth value. Based on the second instability mode, the second instability depth value is obtained according to the functional relationship between the second interface shear stress value and the second instability depth value. Compare the first value of the instability depth and the second value of the instability depth, and take the smaller value as the critical self-stabilizing hole depth of the current working section.
5. The method for constructing a reverse well pilot hole in a thick sandy soil interbedded strata according to claim 4, characterized in that: The determination of the instability boundary includes: The instability boundary is obtained based on the critical self-stabilizing hole depth value of the previous working section, the reciprocal of the safety factor, and the functional relationship of the instability boundary.
6. The method for constructing a reverse well pilot hole in a thick sandy soil interbedded strata according to claim 1, characterized in that: The grouting pressure is determined based on the hole depth and the formation. When the hole is shallow, the grouting pressure is 0.5 to 1.0 MPa; when the hole is deep, the grouting pressure is 1 to 3 MPa.
7. The method for constructing a reverse well pilot hole in a thick sandy soil interbedded strata according to claim 6, characterized in that: The shallow hole depth is less than 50m.
8. The method for constructing a reverse well pilot hole in a thick sandy soil interbedded strata according to claim 1, characterized in that: The step of drilling before the pilot drill reaches the critical self-stabilizing hole depth of the working section includes determining the drilling operation parameters based on the monitored change value of the lifting force.
9. The method for constructing a reverse well pilot hole in a thick sandy soil interbedded strata according to claim 5, characterized in that: The safety factor is F. S The value should be determined based on the specific safety requirements of the project.
10. The method for constructing a reverse well pilot hole in a thick sandy soil interbedded strata according to claim 1, characterized in that, Before the step of dividing the borehole into one or more consecutive working sections according to the depth based on the soil mechanical properties at the borehole location, the process also includes foundation concrete pouring, and the installation and commissioning of the raise boring machine.