阅读说明：本技术 一种多段自适应膨胀锚杆施工方法 (Construction method of multi-section self-adaptive expansion anchor rod ) 是由 莫鹏 郝天之 骆俊晖 畅振超 黄海峰 王诗海 秦金喜 廖来兴 曾富权 吴春伟 阳 于 2021-06-24 设计创作，主要内容包括：本发明公开了一种多段自适应膨胀锚杆施工方法,属于边坡加固领域,所述施工方法包括如下步骤：根据膨胀锚杆外壳的长度采用钻头在围岩上钻与膨胀锚杆外壳相适应的锚杆孔；将锚杆膨胀外壳放入锚杆孔内,锚杆头处加固压板,并把拉张装置拧进锚杆膨胀外壳内,转动拉张装置,对锚杆外壳进行加压,使得膨胀段膨胀,与周围岩土贴合,将螺杆取出；将水泥浆浇灌到锚杆膨胀外壳内,水泥浆填充膨胀段的膨胀处,水泥浆凝固后加强锚杆的强度及雨钻孔的侧摩阻力。根据需要拉拔力可以设计相应长度的膨胀锚杆,然后膨胀段可以契合在扩大孔内,使得受力更好,贴合度好,握裹力强,膨胀贴合度好,向内注浆后,相对于摩擦式、扩大式锚杆,抗拔力更强。(The invention discloses a construction method of a multi-section self-adaptive expansion anchor rod, belonging to the field of slope reinforcement, and the construction method comprises the following steps: drilling an anchor rod hole matched with the expansion anchor rod shell on the surrounding rock by adopting a drill bit according to the length of the expansion anchor rod shell; placing the anchor rod expansion shell into the anchor rod hole, reinforcing the pressure plate at the anchor rod head, screwing the tension device into the anchor rod expansion shell, rotating the tension device, pressurizing the anchor rod shell to expand the expansion section, fitting the expansion section with surrounding rock soil, and taking out the screw rod; grout is poured into the anchor rod expansion shell, the expansion part of the expansion section is filled with the grout, and after the grout is solidified, the strength of the anchor rod and the side frictional resistance of the rain drill hole are enhanced. The corresponding length's of drawing force can be designed as required inflation stock, then the inflation section can agree with in expanding the hole for the atress is better, and the laminating degree is good, and the bond stress is strong, and the inflation laminating degree is good, and after inwards slip casting, for friction formula, expansion formula stock, withdrawal resistance is stronger.)

1. A construction method of a multi-section self-adaptive expansion anchor rod is characterized by comprising the following steps:

step 1: drilling an anchor rod hole matched with the expansion anchor rod shell on the surrounding rock by adopting a drill bit according to the length of the expansion anchor rod shell;

step 2: placing the anchor rod expansion shell into the anchor rod hole, reinforcing the pressure plate at the anchor rod head, screwing the tension device into the anchor rod expansion shell, rotating the tension device, pressurizing the anchor rod shell to expand the expansion section, fitting the expansion section with surrounding rock soil, and taking out the screw rod;

and step 3: and pouring cement paste into the anchor rod expansion shell, filling the expansion part of the expansion section with the cement paste, and forming transverse resistance with the soil body after the cement paste is solidified.

2. The construction method of the multi-segment self-adaptive expansion anchor rod according to claim 1, wherein: when the expansion anchor rod needs to be recovered, after the linear hole is drilled in the step 1, large holes are drilled in the drilled linear hole at intervals by using the expansion head type drill bit, and the expansion holes are matched with the expansion section of the expansion anchor rod shell after being expanded.

3. The construction method of the multi-segment self-adaptive expansion anchor rod according to claim 2, wherein: the expansion anchor rod shell in the step 1 comprises an anchor rod shell (1), a hollow structure is arranged inside the anchor rod shell (1), cement slurry is injected into the anchor rod shell (1), the anchor rod shell (1) is arranged in a drill hole of a soil body, the anchor rod shell (1) comprises a plurality of sections of internal thread sections (1.2) and a plurality of sections of expansion sections (1.3), one section of expansion section (1.3) is arranged between the two sections of internal thread sections (1.2), the two ends of the anchor rod shell (1) are both provided with the internal thread sections (1.2), and after the anchor rod shell (1) is installed in the soil body, the expansion sections (1.3) are outwards tensioned and tightly attached to the soil body to be anchored with the soil body.

4. A construction method of a multi-sectional adaptive expansion anchor rod according to claim 3, wherein: the expansion section (1.3) is arranged to be of an empty pipe structure, the side wall is provided with a plurality of grouting holes (1.4), and the grouting holes (1.4) are arranged to be of an oval structure.

5. The construction method of the multi-segment self-adaptive expansion anchor rod according to claim 4, wherein the construction method comprises the following steps: the tension device in step 2 includes front end rotor plate (2.1), front end mobile jib (2.2), front end screw thread (2.3), rear end rotor plate (2.4), rear end rotary rod (2.5), rear end mobile jib (2.6) and rear end screw thread (2.7), front end rotor plate (2.1) sets up the one end at front end mobile jib (2.2), front end screw thread (2.3) sets up on the lateral wall of the front end mobile jib (2.2) other end, the through-hole has been seted up in the middle of front end mobile jib (2.2), rear end rotary rod (2.5) passes the through-hole, rear end rotor plate (2.4) sets up the one end at front end mobile jib (2.2), rear end mobile jib (2.6) sets up the other end at front end mobile jib (2.2), the size of rear end mobile jib (2.6) is the same with the size of front end mobile jib (2.2), rear end screw thread (2.7) sets up on rear end mobile jib (2.6).

6. The construction method of the multi-segment self-adaptive expansion anchor rod according to claim 5, wherein: the interval between the expansion holes is the same as the length of the internal thread section (1.2), and the height of the expansion holes is smaller than the length of the expansion section (1.3).

7. The construction method of the multi-segment self-adaptive expansion anchor rod according to claim 6, wherein: the specific working process of the tension device in the step 2 is as follows: the front end thread (2.3) on the front end main rod (2.2) is in threaded connection with the first internal thread section (1.2) at the inlet of the anchor rod shell (1), then the rear end thread (2.7) on the rear end main rod (2.6) is screwed to be in threaded connection with the second thread section (1.2), then the front end rotating plate (2.1) is fixed, the rear end rotating plate (2.4) is pulled outwards, the expansion section (1.3) between the first internal thread section (1.2) and the second thread section (1.2) expands to be matched with the expansion hole, all the expansion sections (1.3) are pulled to expand in the same way, and the internal thread section (1.2) is accurately pulled between the two expansion holes by measuring and calculating the distance of the rear end rotating plate (2.4) pulled outwards.

8. The construction method of the multi-segment self-adaptive expansion anchor rod according to claim 6, wherein: in step 1, the length process of the expansion anchor rod shell is determined as follows: and calculating the total drawing force required by each expansion anchor rod according to the total drawing force required by the soil body and the quantity of the expansion anchor rods, analyzing the stress of each expansion section, and dividing the drawing force by the stress of each expansion section to obtain the number of the expansion sections so as to obtain the length of the expansion anchor rod shell.

Technical Field

The invention relates to the field of slope reinforcement, in particular to a construction method of a multi-section self-adaptive expansion anchor rod.

Background

Anchor rod support is the most common side slope support mode in slope reinforcement engineering, at present home and abroad relevant technology is comparatively ripe, but the anchor rod only is as a temporary support facility, and after the engineering is accomplished, the anchor rod is abandoned in the soil body in a large number, not only can cause adverse effect to the construction of adjacent engineering, and the wasting of resources, the pollution is serious moreover, with underground space and the more and more nervous trend of building land, therefore country and the local relevant policy regulation building land red line in recent years, the anchor rod leaves the problem to be solved urgently. In order to solve the problem, the concept of recycling the anchor rod is proposed earlier abroad and related products are introduced, and the development speed is higher after the start at home. Most of the existing recoverable anchor rods have the problems of difficult recovery, complex operation, higher cost and the like, and cannot be effectively applied to actual engineering. Simultaneously original stock only friction section or inflation section carry out resistance to plucking alone, and the inflation stock can provide bigger resistance to plucking, according to the resistance to plucking demand, can increase the inflation section, and the demand resistance to plucking is controllable, and need not excessively increase the length of stock.

Disclosure of Invention

The invention aims to provide a construction method of a multi-section self-adaptive expansion anchor rod, and the technical problem of recycling of the existing expansion anchor rod is solved.

A construction method of a multi-section self-adaptive expansion anchor rod comprises the following steps:

step 1: drilling an anchor rod hole matched with the expansion anchor rod shell on the surrounding rock by adopting a drill bit according to the length of the expansion anchor rod shell;

step 2: placing the anchor rod expansion shell into the anchor rod hole, reinforcing the pressure plate at the anchor rod head, screwing the tension device into the anchor rod expansion shell, rotating the tension device, pressurizing the anchor rod shell to expand the expansion section, fitting the expansion section with surrounding rock soil, and taking out the screw rod;

and step 3: and pouring cement paste into the anchor rod expansion shell, filling the expansion part of the expansion section with the cement paste, and forming transverse resistance with the soil body after the cement paste is solidified.

Further, when the expansion anchor rod needs to be recovered, after the linear hole is drilled in the step 1, large holes are drilled in the drilled linear hole at intervals by using the expansion head type drill bit, and the expansion holes are matched with the expansion section of the expansion anchor rod shell after being expanded.

Further, the inflation stock shell in step 1 includes the stock shell, and the stock shell is inside to be set up to hollow structure, injects into grout in the stock shell, and the stock shell sets up in the drilling of soil body, and the stock shell includes a plurality of sections internal thread section and a plurality of section inflation section, is provided with one section inflation section between two sections internal thread sections, and the both ends of stock shell all set up internal thread section, and the stock shell installation is advanced internal back of soil, and the inflation section outwards stretches out and closely laminates with the soil body, and is anchored with the soil body.

Further, the expansion section is set to be a hollow pipe structure, a plurality of grouting holes are formed in the side wall, and the grouting holes are set to be of an oval structure.

Further, the device that draws in step 2 includes the front end rotor plate, the front end mobile jib, the front end screw thread, the rear end rotor plate, the rear end rotary rod, rear end mobile jib and rear end screw thread, the front end rotor plate sets up the one end at the front end mobile jib, the front end screw thread sets up on the lateral wall of the front end mobile jib other end, the through-hole has been seted up in the middle of the front end mobile jib, the rear end rotary rod passes the through-hole, the rear end rotor plate sets up the one end at the front end mobile jib, the rear end mobile jib sets up the other end at the front end mobile jib, the size of rear end mobile jib is the same with the size of front end mobile jib, the rear end screw thread sets up on the rear end mobile jib.

Further, the distance between the enlarged holes is the same as the length of the internal thread section, and the height of the enlarged holes is smaller than the length of the expansion section.

Further, the specific working process of the tensioning device in the step 2 is as follows: the front end screw thread on the front end mobile jib is connected with the first internal thread section threaded connection at the entrance of the anchor rod shell, then the rear end screw thread on the rear end mobile jib is screwed to be connected with the second thread section threaded connection, then the front end rotating plate is fixed, the rear end rotating plate is pulled outwards, the expansion section between the first internal thread section and the second thread section is expanded to be matched with the expansion hole, all the expansion sections are pulled to be expanded in the same way, the distance of the rear end rotating plate pulled outwards is measured and calculated, and the internal thread section is accurately pulled between the two expansion holes.

Further, in step 1, the process of determining the length of the expansion anchor shell is as follows: and calculating the total drawing force required by each expansion anchor rod according to the total drawing force required by the soil body and the quantity of the expansion anchor rods, analyzing the stress of each expansion section, and dividing the drawing force by the stress of each expansion section to obtain the number of the expansion sections so as to obtain the length of the expansion anchor rod shell.

By adopting the technical scheme, the invention has the following technical effects:

according to the invention, the expansion anchor rod with the corresponding length can be designed according to the required drawing force, then the expansion section can be fit in the expansion hole, so that the stress is better, the fitting degree is good, the gripping force is strong, the expansion fitting degree is good, after the grouting is carried out inwards, the pulling resistance is stronger compared with a friction type and expansion type anchor rod, and meanwhile, the expansion anchor rod can be better recovered when being recovered at the later stage, so that the expansion anchor rod can be used for the second time or directly recovered.

Drawings

FIG. 1 is a schematic view of the structure of a large hole drilled and enlarged by the enlarged head drill bit of the present invention.

Fig. 2 is a structural schematic diagram of the anchor rod expansion shell of the invention.

Fig. 3 is a cross-sectional view of the tensioning device of the present invention.

Fig. 4 is a schematic drawing of the structure of the anchor rod shell after being tensioned.

Fig. 5 is a structural schematic diagram of the grouting mechanism of the invention.

Reference numbers in the figures: 1-a bolt housing; 1.1-removable disks; 1.2-internal thread section; 1.3-an expansion section; 1.4-grouting holes; 1.5-pressure sensor; 1.6-bending soft angular displacement sensor; 2-a tension device; 2.1-front rotating plate; 2.2-front end main rod; 2.3-front end thread; 2.4-rear rotating plate; 2.5-rear end rotating rod; 2.6-rear end main rod; 2.7-rear end screw thread 3-grouting mechanism; 3.1-thread protection section; 3.2-grouting section; 3.3-grouting leakage holes.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, preferred embodiments are given and the present invention is described in further detail. It should be noted, however, that the numerous details set forth in the description are merely for the purpose of providing the reader with a thorough understanding of one or more aspects of the present invention, which may be practiced without these specific details.

A construction method of a multi-segment adaptive expansion anchor rod, as shown in fig. 1 to 4, the construction method comprising the steps of:

step 1: and drilling an anchor rod hole matched with the expansion anchor rod shell on the surrounding rock by adopting a drill bit according to the length of the expansion anchor rod shell. When the expansion anchor rod needs to be recovered, after the linear hole is drilled, large holes are drilled at intervals in the drilled linear hole by using the expansion head type drill bit, and the expansion holes are matched with the expansion section of the expansion anchor rod shell after being expanded.

The length process of the expansion anchor rod shell is determined as follows: and calculating the total drawing force required by each expansion anchor rod according to the total drawing force required by the soil body and the quantity of the expansion anchor rods, analyzing the stress of each expansion section, and dividing the drawing force by the stress of each expansion section to obtain the number of the expansion sections so as to obtain the length of the expansion anchor rod shell.

As shown in fig. 2, the expansion anchor rod shell comprises an anchor rod shell 1, the inside of the anchor rod shell 1 is arranged to be a hollow structure, cement slurry is injected into the anchor rod shell 1, the anchor rod shell 1 is arranged in a drill hole of a soil body, the anchor rod shell 1 comprises a plurality of sections of internal thread sections 1.2 and a plurality of sections of expansion sections 1.3, one section of expansion section 1.3 is arranged between the two sections of internal thread sections 1.2, the two ends of the anchor rod shell 1 are both provided with the internal thread sections 1.2, and after the anchor rod shell 1 is installed in the soil body, the expansion section 1.3 is outwards tensioned to be tightly attached to the soil body and anchored with the soil body. The anchor rod shell 1 is made of metal materials and is provided with a metal shell structure. The front end of the anchor rod shell 1 is provided with a detachable disc 1.1 which is connected with the front end of the anchor rod shell 1, and the diameter of the detachable disc 1.1 is larger than that of the anchor rod shell 1. The expansion section 1.3 is arranged to be of an empty pipe structure, a plurality of grouting holes 1.4 are formed in the side wall, and the grouting holes 1.4 are arranged to be of an oval structure.

The expansion anchor rod shell comprises a pressure sensor 1.5 and a bending soft angular displacement sensor 1.6, the pressure sensor 1.5 and the bending soft angular displacement sensor 1.6 are both arranged on the outer side of the expansion section 1.3, the pressure sensor 1.5 detects the pressure of the soil body on the outer side of the expansion section 1.3, and the bending soft angular displacement sensor 1.6 is used for detecting the stretching condition of the expansion section 1.3. Still include data detection device, the last detection interface that is provided with of data detection device, all pressure sensor 1.5 and crooked soft angular displacement sensor 1.6 all stretch out the front end of stock shell 1 through the wire to set up the data acquisition mouth, be provided with waterproof lid on the data acquisition mouth, do not detect time measuring and close the setting with waterproof lid, when the installation with retrieve the inflation stock, use data detection device to detect the atress data of inflation section 1.3 and the condition of stretching out.

Step 2: put into the stock downthehole with stock inflation shell, stock head department consolidates the clamp plate to in screwing into stock inflation shell the tension device, rotate the tension device, pressurize the stock shell, make the inflation section inflation, with the ground laminating on every side, take out the screw rod.

As shown in fig. 3, the tension device includes a front-end rotating plate 2.1, a front-end main rod 2.2, a front-end thread 2.3, a rear-end rotating plate 2.4, a rear-end rotating rod 2.5, a rear-end main rod 2.6 and a rear-end thread 2.7, the front-end rotating plate 2.1 is disposed at one end of the front-end main rod 2.2, the front-end thread 2.3 is disposed on a side wall of the other end of the front-end main rod 2.2, a through hole is disposed in the middle of the front-end main rod 2.2, the rear-end rotating rod 2.5 passes through the through hole, the rear-end rotating plate 2.4 is disposed at one end of the front-end main rod 2.2, the rear-end main rod 2.6 is disposed at the other end of the front-end main rod 2.2, the size of the rear-end main rod 2.6 is the same as that of the front-end main rod 2.2, and the rear-end thread 2.7 is disposed on the rear-end main rod 2.6. The interval between the expanding holes is the same as the length of the internal thread section 1.2, and the height of the expanding holes is smaller than the length of the expansion section 1.3.

The specific working process of the tension device is as follows: the front end thread 2.3 on the front end main rod 2.2 is in threaded connection with the first internal thread section 1.2 at the inlet of the anchor rod shell 1, then the rear end thread 2.7 on the rear end main rod 2.6 is screwed to be in threaded connection with the second thread section 1.2, then the front end rotating plate 2.1 is fixed, the rear end rotating plate 2.4 is pulled outwards, the expansion section 1.3 between the first internal thread section 1.2 and the second thread section 1.2 expands to be matched with the expansion hole, all the expansion sections 1.3 are pulled to expand in the same way, and the internal thread section 1.2 is accurately pulled between the two expansion holes by measuring and calculating the distance of the rear end rotating plate 2.4 pulled outwards.

And step 3: and pouring cement paste into the anchor rod expansion shell, filling the expansion part of the expansion section with the cement paste, and forming transverse resistance with the soil body after the cement paste is solidified. The expansion section 1.3 is arranged to be of an empty pipe structure, a plurality of grouting holes 1.4 are formed in the side wall, and the grouting holes 1.4 are arranged to be of an oval structure. The structure is oval at first, when the tensile appears, can become circular structure for grout better from grouting hole 1.4 outflow outside and the better combination of soil body. The outside of internal thread section 1.2 sets up to enclosed construction, and inside is provided with the internal thread, and the thickness of internal thread section 1.2 is thicker than the thickness of inflation section 1.3. The female thread section 1.2 is provided thicker in order to avoid deformation during installation and stretching.

After the use, when needing to retrieve, put into the expansion drill bit from the centre bore, the expansion drill bit corotation in stock shell 1 breaks intraductal grout, the bottom grout is clear away in the reversal after arriving stock shell 1 bottom, the grout that the bottom was poured is abolished, then it retrieves the screw rod to twist in to screw thread end tail section, strike downwards, use data detection device to detect pressure sensor 1.5 and crooked soft angular displacement sensor 1.6 on one side of strikeing, look over each section inflation section 1.3's bond stress and bending degree data, make the expanded structure resume straight again, extract the stock.

In the embodiment of the invention, as shown in fig. 5, when grouting is performed on an anchor rod shell 1, an arranged grouting mechanism 3 is screwed into the anchor rod shell 1, the inside of the grouting mechanism 3 is of a hollow structure and comprises a thread protection section 3.1 and a grouting section 3.2, the thread protection section 3.1 and the grouting section 3.2 are arranged alternately, a grouting leakage hole 3.2 is formed in the grouting section 3.2, the thread protection section 3.1 and an internal thread section 1.2 of the anchor rod shell 1 are arranged in a threaded manner, the length of the thread protection section 3.1 is the same as that of the internal thread section 1.2, cement slurry is injected from the hollow shell in the grouting mechanism 3, and the cement slurry flows from the grouting leakage hole 3.2 to the inside of an expansion section 1.3 of the anchor rod shell 1 and flows from the grouting hole 1.4 to an external soil body. After grouting, after the cement slurry is changed into solid from slurry, the grouting mechanism 3 is screwed out for 1-2 hours, and then the screw is screwed in. During grouting, a special grouting structure is adopted, the grouting hole is aligned, grouting is conducted outwards, the situation that slurry pollutes internal threads, a tension rod behind the tension rod cannot be twisted in, or a drill bit matched with the threads is adopted is prevented.

The specific process of analyzing the stress of each expansion section in the step 1 is as follows:

the expansion anchor rod transmits the dispersed load by three forms of side wall friction of the middle anchoring section, side wall friction of the expansion section anchoring and resistance of soil body to the end face of the expansion head, and can be divided into n sections for mechanical property analysis, wherein n is a positive integer. Therefore, the section variable cross-section pulling resistance consists of three parts:

T＝T₁+T₂+T_D (1)

in the formula: the T1 provides the pull-out resistance for the side wall friction of the L1 section common non-expansion anchoring section:

T₁＝πD₁L₁τ_f (2)

in the formula: d1 and L1 are the diameter and length of the non-expansion anchoring section of the anchor rod, tau_fThe friction resistance strength between the soil body of the non-expansion anchoring section and the side wall of the anchoring rib is obtained;

t2 is the anti-pulling force that stock inflation anchor section lateral wall friction provided:

T₂＝πD₂L₂τ_fd (3)

wherein D2 and L2 are the diameter and length of the non-expansion anchoring section of the anchor rod, tau_fdThe friction resistance strength between the soil body of the non-expansion anchoring section and the side wall of the anchoring rib is obtained;

TD is the anti-pulling force that the soil body provided to the positive pressure of inflation terminal surface:

in the formula: sigma_DThe strength of positive pressure of soil body acting on the variable cross section is related to the burial depth of the expansion end, the soil body condition in front of the expansion end and the working state of the anchor rod;

the analysis process of the displacement and the axial force of the expansion anchor rod is as follows:

according to a shear displacement method, the deformation of soil around a vertical loaded anchor rod body can be ideally regarded as a concentric cylinder, and a soil body vertical balance differential equation is written according to an elastic theory:

after the anchor rod body is loaded, the shear stress tau is positioned at the anchor rod body_rzIncrease of much more than sigma_zGet it

In the formula, r₀Radius of the anchor rod, τ₀The shear stress of the side edge of the anchor rod,

the solution to the equation is:

from the geometric equation, the shear deformation is:

wherein U is_sIs radial displacement, s is vertical displacement of soil body, omittingThe physical equation is:

to obtain

The solution to the equation is:

namely:

wherein r is_mIn order to effectively influence the radius, G is the shear modulus of the soil body, and tau (z) is the side friction resistance of the anchor rod at the z position; r is₀Is the anchor rod radius; r is_mTo influence the radius; r is_mIn the range of negligible shear deformation of the side soil of the anchor rod, r_m＝χ₁χ₂L₁(1-ν_s)，χ₁、χ₂Is an empirical coefficient of the soil unevenness degree v_sIs the soil body Poisson ratio, r is the distance from the central shaft of the anchor rod,

according to the displacement coordination condition of the anchor rod and the soil contact surface, for the anchor rod with the equal section, the available anchor rod side friction resistance is as follows:

for the differential unit stress static balance condition:

in the formula: u shape_pIs the circumference of the anchor rod, tau_ν(z) frictional resistance at the depth z of the anchor rod side, Q (z) axial force at the depth z of the anchor rod,

the elastic compression of the microcells is:

in the formula, and A_pThe elastic modulus and the cross section area of the anchor rod are respectively obtained by substituting the formula (13)：

Order toWherein k is_vThe rigidity of the anchor rod side soil body spring is provided,

the anchor rod differential equation can be obtained as follows:

the displacement and axial force of the solution are:

s(z)＝Ae^αz+Be^-αz (17)

Q(z)＝-AE_pA_pαe^αz+BE_pA_pαe^-αz (18)

wherein C is₁、C₁Is constant and can be determined by the boundary condition of the anchor rod body, and the above formula is expressed by a matrix:

the anchoring force of the expansion variable cross-section anchor rod is divided into three parts, the first part is the frictional resistance between the section L1 of the thin cross-section rod body and the soil body, the second part is the frictional resistance between the section L2 of the thick cross-section rod body and the soil body, the third part is the end resistance at the variable cross-section position,

for the variable cross-section anchor rod, when the axial force and displacement are deduced by adopting a shear displacement method, the variable cross-section anchor rod is divided into two sections, namely an L1 section and an L2 section, the influence of a soil displacement field around the anchor rod caused by the variable cross section is ignored, the rod body displacement and the rod body axial force solution of the constant cross-section anchor rod are respectively applied, the end resistance and the displacement at the variable cross section are continuously simplified into boundary conditions,

the first segment of boundary conditions is:

when z is 0, P₁(0) P; when z is L1, P₁(L₁)＝T；

In the formula: t is the axial force of the anchor rod at the first end at the variable cross section

The second segment boundary conditions are:

when z is L1, P₂(L₁)＝T-T_D(ii) a When z is L, P₂(L)＝Q；

In the formula: l is L1+ L2 is the length of the anchor rod micro-section, TD is the end resistance of the soil body at the variable cross section,

displacement continuous condition of variable cross-section anchor rod L1 and L2 at variable cross section

s₁(L₁)＝s₂(L₁) (20)

Substituting the first segment of boundary conditions into formula (18)

-E_p1A_p1α₁(A₁-B₁)＝P (21)

Substituting the second segment boundary condition into formula (18)

The continuous conditional expression (20) of the first stage and the second stage can be expressed as:

the coefficients A1, A2, B1 and B2 can be obtained by the united type (21), (22), (23), (24) and (25), the analytic expressions of the displacement and the axial force of the first section of anchor rod can be calculated, and the side friction force of the first section of anchor rod and the second section of anchor rod can be obtained by the united type (12), so that the first and second section of anti-pulling force can be obtained;

and (3) calculating the stress of the expansion end face at the variable cross section of the anchor rod:

taking a soil body micro unit at the upper end of the variable cross section of the anchor rod as an investigation object, taking the axial direction of the anchor rod as a Z axis, a vertical direction and a horizontal direction as X axes respectively, under the limit state that the soil body is compressed,

the stress expression of each direction of the soil body unit under the limit state is as follows:

σ_x＝K₀γL₁+ξσ_T (26)

σ_y＝K₀γL₁+ξσ_T (27)

σ_z＝γL₁+σ_T (28)

in the formula: sigma_TFor the increase in the tension of the anchor in the Z direction of the soil elements, K₀The coefficient of the static soil pressure of the soil at the upper end of the variable cross section can be determined according toCalculating; xi is the lateral pressure coefficient of the variable cross section upper end soil reflecting the soil squeezing effect when the anchor rod is displaced, and can be changed into (0.5-0.95) K according to an empirical formula xi_aCalculation (relating to hardness of soil at variable cross section, 0.95 for harder soil and 0.5 for soft soil), andandrespectively the active and passive soil pressure coefficients of the soil body at the upper end of the variable cross section, wherein c,The cohesive force and the internal friction angle of the soil body;

when the soil body unit reaches the limit state, sigma_zIs the maximum principal stress sigma₁，σ_xIs the minimum principal stress sigma₃According to the molar coulomb strength theory, there are

Combined together to obtain

When the stock variable cross section department soil body each point all reached under the ultimate stress state, the ultimate withdrawal resistance that the vertical compressive stress of variable cross section department provided:

for the whole anchor rod, the boundary condition of the anchor bottom and the anchor head can be obtained according to the continuous condition between each section of anchor rod, the axial force of the anchor bottom is 0, the axial force of the anchor head is known, and the load transfer function of the whole anchor rod is calculated;

therefore, the anti-pulling force calculation formula of the variable cross-section anchor rod is as follows:

T＝T₁+T₂+T_D

the foregoing is only a preferred embodiment of the present invention, and it should be noted that those skilled in the art can make various improvements and modifications without departing from the principle of the present invention, and these improvements and modifications should also be construed as the protection scope of the present invention.