CN111395332B

CN111395332B - Rotary excavating and anchor cable construction method for hard rock stratum

Info

Publication number: CN111395332B
Application number: CN202010238145.0A
Authority: CN
Inventors: 胡美玲
Original assignee: Xiangyang Geological Foundation Engineering Co ltd
Current assignee: Xiangyang geological foundation engineering Co.,Ltd.
Priority date: 2020-03-30
Filing date: 2020-03-30
Publication date: 2021-08-31
Anticipated expiration: 2040-03-30
Also published as: CN111395332A

Abstract

The invention provides a rotary drilling and anchor cable construction method for a hard rock stratum, belonging to a foundation pit supporting engineering, comprising the working procedures of rotary drilling, side wall filling and anchor cable construction; in the rotary drilling process, a plurality of small drill holes are drilled on a circle with a designed aperture by using small drill cylinders with smaller diameters, and the designed holes are drilled on the whole by using large drill cylinders; in the side wall filling process, a sealing cylinder consisting of all concrete cylinders with the height of H can be formed in the designed hole wall by using the side wall sleeve and the concrete conveying pipe; the problem of current construction method need with the drill bit of installing multiple specification, cause the work progress loaded down with trivial details to during the slip casting step, the thick liquid can permeate in the clearance of this geology fast, lead to serious mud to run off is solved.

Description

Rotary excavating and anchor cable construction method for hard rock stratum

Technical Field

The invention relates to a foundation pit supporting engineering, in particular to a rotary excavating and anchor cable construction method for a hard rock stratum.

Background

At present, a foundation pit support is a retaining, reinforcing and protecting measure adopted for a side wall of a foundation pit and a surrounding environment in order to ensure the safety of the construction of an underground structure and the surrounding environment of the foundation pit.

The construction steps of the conventional foundation pit support comprise a rotary drilling hole and anchor cable installation, wherein the rotary drilling hole is used for drilling a hole on the side wall of the foundation pit by using a rotary drilling rig, and the anchor cable is installed in the modes of conventional anchor cable construction, single-liquid rotary spraying anchor cable construction, double-liquid rotary spraying anchor cable construction and the like after the hole is drilled.

However, for a stratum with a lot of hard rocks and hard stones, the problems that a rotary drilling machine cannot drill in the step of drilling holes in a rotary mode and the required torque is too large easily occur, and at present, a grading rotary drilling mode is adopted, namely, drill bits with diameters being enlarged continuously are used for drilling in sequence, but the mode needs and installs drill bits with various specifications, so that the construction process is complicated.

In addition, after the hole is drilled in the hard rock and the hard stone in a rotary drilling mode, the hole wall is usually drilled broken stones and non-drilled broken stone blocks, the two stone blocks form geology during anchor cable construction, and slurry can rapidly permeate into gaps of the geology during a grouting step, so that serious slurry loss is caused.

In conclusion, the existing construction method is not suitable for the stratum with hard rocks and a lot of hard rocks, and a stratum construction method suitable for the geology is urgently needed.

Disclosure of Invention

Therefore, the invention aims to provide a rotary excavating and anchor cable construction method for a hard rock stratum so as to solve the technical problem.

The technical purpose of the invention is realized by the following technical scheme:

a rotary drilling and anchor cable construction method for hard rock stratum comprises the working procedures of rotary drilling, side wall filling and anchor cable construction; the rotary drilling process comprises the following steps:

s11, preparing a large drill barrel with the diameter D and a small drill barrel with the diameter D, wherein the diameter D of the large drill barrel is larger than the diameter D of the small drill barrel;

s12, determining the drilling direction and the design aperture, wherein the design aperture is the same as the diameter D of the large drill cylinder;

s13, positioning the rotary drilling rig, adjusting the drilling angle of the rotary drilling rig, and fixing the angle;

s14, mounting the small drill cylinders on the rotary drilling rig, and sequentially drilling at least four small drill holes in a circle with the designed hole diameter;

s15, mounting the large drill cylinder on the rotary drilling rig, and integrally drilling a designed hole;

the sidewall filling process comprises the following steps:

s21, preparing a side wall sleeve with the diameter smaller than the designed aperture, and installing the side wall sleeve on a rotary drilling rig;

s22, mounting the output end of a concrete conveying pipe on the outer wall of the side wall sleeve, and conveying the concrete conveying pipe to the bottom end of the designed hole by a rotary drilling rig;

s23, injecting concrete between the outer wall of the side wall sleeve and the inner wall of the design hole by using the concrete delivery pipe until a concrete cylinder with the height of H is formed;

s24, withdrawing the side wall sleeve from the design hole by a height H;

and S25, alternately repeating the steps S23 and S24, and forming a sealing cylinder consisting of all concrete cylinders with the height H on the inner wall of the design hole after the side wall sleeve completely exits the design hole.

By adopting the technical scheme, in the rotary drilling process, a plurality of small drill holes are drilled on the circle where the designed aperture is located by using the small drill cylinders with smaller diameters, and the designed holes are drilled integrally by using the large drill cylinders, so that compared with the existing construction method of drilling the designed holes by directly drilling the large drill cylinders, the method greatly reduces the maximum torque required by the rotary drilling rig, reduces the power loss of the rotary drilling rig, and particularly reduces the foundation pit supporting engineering constructed in a hard rock stratum; in addition, compared with a construction method for gradually drilling designed holes by stage reaming, the number of the drill cylinders and the steps of mounting the drill cylinders on a rotary drilling rig can be reduced, and the construction steps during hole forming are greatly reduced;

in the side wall filling process, a sealing cylinder consisting of all concrete cylinders with the height of H can be formed in the designed hole wall by using the side wall sleeve and the concrete conveying pipe, and the density of the sealing cylinder is greatly improved compared with the hole wall of the designed hole, so that the serious slurry loss caused by the fact that slurry quickly permeates into gaps of the geology in the grouting step is effectively avoided after the hole is formed in the hard rock and the hard stone in a rotary drilling mode.

Preferably, in step S14, the circle where one of the small holes is located has an intersection area with the circle where the other small hole is located.

By adopting the technical scheme, the circle where each small drill hole is located and the circles where other small drill holes are located have the intersection area, so that when the second small drill hole is drilled, the circle where each small drill hole is located and the circle where the first small drill hole is located have a free surface (namely, the free surface is drilled), and the maximum torque required by the rotary drilling rig is further reduced.

Preferably, when the compressive strength of the stratum is less than 55MPa, four small drill holes are drilled in the circle with the designed hole diameter by the small drill cylinder in the step S14, and D is more than D and less than 2D; and when the compressive strength of the stratum is greater than or equal to 55MPa, five small drill holes are drilled in the circle with the designed hole diameter by the small drill cylinder in the step S14, and D is greater than 2D and less than 3D.

By adopting the technical scheme, the condition of four small drill holes is suitable for the geological condition of the hard rock stratum with smaller compressive strength, and the condition of five small drill holes is suitable for the geological condition of the hard rock stratum with larger compressive strength.

Preferably, when four small drill holes need to be drilled, the circles of the four small drill holes are tangent to the circle of the design hole, and the four generated tangent points are located on four vertexes of an inscribed square of the circle of the design hole; when five small drill holes need to be drilled, the circle center of one of the small drill holes coincides with the circle center of the circle where the design hole is located, and the circle centers of the other four small drill holes are respectively located on two vertical diameters of the circle where the design hole is located.

By adopting the technical scheme, the construction steps of the four small drilling conditions are as follows: firstly, drilling a first small drill hole tangent to the designed hole by using a small drill cylinder, then drilling a second small drill hole by using the small drill cylinder, wherein the circle center of a circle where the second small drill hole is located and the circle center of the circle where the first small drill hole is located are located on the diameter of the designed hole, and then drilling a third small drill hole and a fourth small drill hole by using the same method, wherein the circle centers of the circles where the third small drill hole and the fourth small drill hole are located on the other diameter of the designed hole, the two diameters are mutually vertical, and D is less than 2D, so that when the second small drill hole is drilled, the second small drill hole and the first small drill hole must have a free surface, and the torque required by the rotary drilling rig can be reduced due to the free surface;

the construction steps for the case of five small boreholes are as follows: the method comprises the steps of firstly drilling a first small drill hole which is coincident with the circle center of a circle where a design hole is located by using a small drill cylinder, then roughly drawing two mutually perpendicular diameters of the design hole, digging a second small drill hole and a third small drill hole which are tangent to the design hole on one diameter, digging a fourth small drill hole and a fifth small drill hole which are tangent to the design hole on the other diameter, wherein the two small drill holes and the first small drill hole can generate a free surface when the second small drill hole and the third small drill hole are drilled because the distance between the two small drill holes is more than 2D and less than 3D.

Preferably, the side wall sleeve is hollow with two open ends, a reinforcing ring is arranged on the outer wall of the side wall sleeve, the diameter of the reinforcing ring is the same as that of the designed hole, the distance between the reinforcing ring and the bottom end of the side wall sleeve is 50 cm-100 cm, a pouring hole is formed in the reinforcing ring, and the output end of the concrete conveying pipe penetrates through the pouring hole.

Through adopting above-mentioned technical scheme, be the space that a section height is H below the reinforcement ring, utilize the concrete conveyer pipe can carry the concrete to this space in, when waiting to the concrete and will fill up this space soon, can receive the extrusion of reinforcement ring, thereby reach the effect of fastening, improve the intensity of concrete drum, when waiting that the preliminary setting appears in last section concrete drum, can withdraw from the boundary wall sleeve slowly, the height of withdrawing from is H, later continue to let in the concrete, form second section concrete drum, cycle operation in proper order, withdraw from in the design hole completely until the boundary wall sleeve, from this at the design downthehole wall formed one by all highly be the sealed section of thick bamboo that the concrete drum of H constitutes.

Preferably, in the steps S23 and S24, H is 80cm, and the rate of withdrawal of the sidewall sleeve is 50 cm/min.

Through adopting above-mentioned technical scheme, the concrete cylinder has not condensed completely yet when the boundary wall sleeve withdraws from, therefore the speed of withdrawing from should not be too big, avoids producing the extrusion to the concrete cylinder and takes place deformation.

Preferably, the difference between the outer diameter of the reinforcing ring and the outer diameter of the sidewall sleeve is 5 cm.

Through adopting above-mentioned technical scheme, the external diameter of reinforcing ring and the external diameter difference of boundary wall sleeve also are the thickness of concrete cylinder, when controlling thickness at 5cm, reduce the loss of material on the one hand, on the other hand can satisfy required intensity.

Preferably, in step S22, when the sidewall sleeve is delivered to the bottom end of the design hole by the rotary drilling rig, there is a space between the sidewall sleeve and the bottom end of the design hole, and the space is 5 cm.

Through adopting above-mentioned technical scheme, can let the bottom in design hole also can produce the concrete layer that a 5cm is thick, further avoid the condition that the thick liquid runs off from the bottom in design hole.

Preferably, the anchor cable construction process includes the following steps:

s31, preparing an anchor cable body, a grouting pipe and a grouting sleeve with the same diameter as the designed hole, and lowering the grouting sleeve to the end part of the designed hole by using a rotary drilling rig;

s32, lowering the anchor cable body and the grouting pipe into the designed hole to the end part of the designed hole through the grouting sleeve;

s33, introducing cement paste into the end part of the designed hole by using a grouting pipe, and finishing primary grouting after the cement paste overflows from the orifice of the designed hole;

s34, gradually withdrawing the grouting sleeve from the designed hole, continuously supplementing the grouting by using the grouting pipe in the process, and completing the slurry supplementing when the grouting sleeve is completely withdrawn from the designed hole;

and S35, after the primary grouting and grout supplementing slurry is formed and solidified to form an anchoring section and a free section, performing third grouting by using a grouting pipe to reinforce the anchoring section.

Preferably, after the anchor cable construction process is completed, the anchor cable body is subjected to tension test.

By adopting the technical scheme, the process only needs to use a common tension tester to apply tension to the free end of the anchor cable so as to determine the maximum tension value which can be borne by the anchor cable under the limit condition.

The rotary excavating and anchor cable construction method for the hard rock stratum provided by the invention has the following advantages:

1. the maximum torque of the rotary drilling rig required by rotary drilling operation in hard rock and hard stone geology can be greatly reduced, and the loss of the rotary drilling rig is reduced;

2. the anchor cable is particularly suitable for anchor cable installation work in hard rock and hard stone geology, and slurry is effectively prevented from permeating into gaps among the hard rocks under the capillary effect, so that the loss of the slurry can be effectively avoided;

3. the sealing layer is generated, so that the tensile strength of the anchor cable can be greatly improved, and the length of the anchor cable is smaller under the condition that the formed tensile values are the same, so that the supporting work can be completed under the condition that the length of the anchor cable is limited.

Drawings

FIG. 1 is a schematic distribution diagram of four small drill holes required to be drilled in a rotary drilling process in the invention;

FIG. 2 is a schematic distribution diagram of a rotary drilling process in the invention when no small drill hole needs to be drilled;

FIG. 3 is a schematic view of the structure of the sidewall sleeve located in the design hole during the sidewall filling process of the present invention;

FIG. 4 is an enlarged view of a portion of FIG. 3 at A;

FIG. 5 is a partial schematic view of a sidewall sleeve according to the present invention.

The reference numerals in the figures are explained below:

1. designing a hole; 2. a first small bore hole; 3. a second small bore hole; 4. a third small borehole; 5. a fourth small borehole; 6. a fifth small drill hole; 7. a sidewall sleeve; 8. a reinforcing ring; 9. injecting holes;

Detailed Description

The technical solutions of the present invention will be described clearly and completely with reference to the accompanying drawings, and it should be understood that the described embodiments are some, but not all embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, and are only for convenience of description and simplicity of description, but do not indicate or imply that the device or element being referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, should not be construed as limiting the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.

In the description of the present invention, it should be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.

A rotary excavating and anchor cable construction method for a hard rock stratum, as shown in figures 1 to 5, sequentially comprises the following four procedures:

firstly, the rotary drilling process S1 includes the following steps:

and S15, mounting the large drill cylinder on the rotary drilling rig, and drilling the designed hole 1 integrally.

Second, the sidewall filling process S2 includes the steps of:

s21, preparing a side wall sleeve 7 with the diameter smaller than the designed aperture, and installing the side wall sleeve on a rotary drilling rig;

s22, mounting the output end of a concrete conveying pipe on the outer wall of the side wall sleeve 7, and conveying the concrete conveying pipe to the bottom end part of the design hole 1 by a rotary drilling rig;

s23, injecting concrete between the outer wall of the side wall sleeve 7 and the inner wall of the design hole 1 by using a concrete delivery pipe until a concrete cylinder with the height of H is formed;

s24, withdrawing the side wall sleeve 7 from the design hole 1 by a height H;

and S25, alternately repeating the steps S23 and S24, and forming a sealing cylinder consisting of all concrete cylinders with the height H on the inner wall of the design hole 1 after the side wall sleeve 7 completely exits the design hole 1.

Thirdly, an anchor cable construction process S3 includes the following steps:

s31, preparing an anchor cable body, a grouting pipe and a grouting sleeve with the diameter the same as that of the designed hole 1, and lowering the grouting sleeve to the end part of the designed hole 1 by using a rotary drilling rig;

s32, lowering an anchor cable body and a grouting pipe into the designed hole 1 to the end part of the designed hole 1 through the grouting sleeve;

s33, introducing cement paste into the end part of the designed hole 1 by using a grouting pipe, and finishing primary grouting after the cement paste overflows from the orifice of the designed hole 1;

s34, gradually withdrawing the grouting sleeve from the designed hole 1, continuously supplementing grout by using the grouting pipe in the process, and completing grout supplementation when the grouting sleeve is completely withdrawn from the designed hole 1;

And fourthly, a tension testing procedure S4, wherein the procedure only needs to use a common tension tester to apply tension to the free end of the anchor cable so as to determine the maximum tension value which can be borne by the anchor cable under the limit condition.

The present invention solves the first technical problem mentioned in the background art: for the stratum with a lot of hard rocks and hard stones, the problems that a rotary drilling machine cannot drill and the required torque is too large are easily caused in the step of drilling holes in a rotary drilling manner, the rotary drilling machine can adopt the grading rotary drilling manner at present, namely, drill bits with continuously enlarged diameters are used for drilling in sequence, but the mode needs and installs the drill bits with various specifications, so that the construction process is complicated.

The working principle for solving the first technical problem is as follows: in the rotary drilling process, a plurality of small drill holes are drilled on the circle of the designed aperture by using the small drill cylinders with smaller diameters, and the designed hole 1 is drilled by using the large drill cylinder as a whole, so that compared with the existing construction method of directly drilling the designed hole 1 by using the large drill cylinder as a whole, the maximum torque required by the rotary drilling rig is greatly reduced, the power loss of the rotary drilling rig is reduced, and particularly the foundation pit supporting engineering constructed in a hard rock stratum is adopted; in addition, compared with a construction method for gradually drilling the design hole 1 by stage reaming, the number of the drill cylinders and the steps of mounting the drill cylinders on a rotary drilling rig can be reduced, and the construction steps during hole forming are greatly reduced.

The present invention also solves the second technical problem mentioned in the background art: after the holes are drilled in the hard rock and the hard stone in a rotary drilling mode, broken stones which are drilled and broken blocks which are not drilled are usually arranged on the hole wall, the two kinds of stones form the geology when the anchor cable is constructed, and during the grouting step, slurry can quickly permeate into gaps of the geology to cause serious slurry loss.

The working principle for solving the second technical problem is as follows: in the side wall filling process, a sealing cylinder consisting of all concrete cylinders with the height of H can be formed on the inner wall of the design hole 1 by utilizing the side wall sleeve 7 and the concrete conveying pipe, and the density of the sealing cylinder is greatly improved compared with the hole wall of the design hole 1, so that after a hole is dug in a rotary manner on hard rock and hard stone, the serious slurry loss caused by the fact that slurry rapidly permeates into the gap of the geology in the grouting step is effectively avoided.

In summary, the present invention solves two technical problems mentioned in the background art.

Besides, the invention further optimizes and sets up as follows.

In step S14, a circle in which one of the small drill holes is located and a circle in which the other small drill hole is located have a crossing region; each of the small drill holes has an intersection area with the other small drill hole, so that when the second small drill hole 3 is drilled, the circle with the first small drill hole 2 has a free surface (i.e. the surface is drilled), and the maximum torque required by the rotary drilling rig is further reduced.

When the compressive strength of the stratum is less than 55MPa, four small drill holes are drilled in the circle where the designed aperture is located by the small drill cylinders in the step S14, and D is more than D and less than 2D; when the compressive strength of the stratum is greater than or equal to 55MPa, five small drill holes are drilled in the circle where the designed aperture is located by the small drill cylinder in the step S14, and D is greater than 2D and less than 3D; the situation of four small drill holes is suitable for the geological situation of the hard rock stratum with low compressive strength, and the situation of five small drill holes is suitable for the geological situation of the hard rock stratum with high compressive strength.

When four small drill holes need to be drilled, circles where the four small drill holes are located are tangent to a circle where the design hole 1 is located, and four generated tangent points are located on four vertexes of an inscribed square of the circle where the design hole 1 is located; when five small drill holes need to be drilled, the circle center of the circle where one small drill hole is located coincides with the circle center of the circle where the design hole 1 is located, and the circle centers of the other four small drill holes are respectively located on two vertical diameters of the circle where the design hole 1 is located.

The construction steps for the case of four small boreholes are as follows: firstly, a first small drill hole tangent to the designed hole 1 is drilled by using a small drill cylinder, then a second small drill hole 3 is drilled by using the small drill cylinder, the circle center of the circle where the second small drill hole 3 is located and the circle center of the circle where the first small drill hole 2 is located are located on the diameter of the designed hole 1, then a third small drill hole 5 and a fourth small drill hole 5 are drilled by using the same method, the circle centers of the circles where the third small drill hole 5 and the fourth small drill hole 5 are located on the other diameter of the designed hole 1, the two diameters are mutually perpendicular, and since D is less than D and less than 2D, when the second small drill hole 3 is drilled, the second small drill hole 3 and the first small drill hole 2 must have a free surface, and the torque required by a rotary drilling rig can be reduced due to the free surface.

The construction steps for the case of five small boreholes are as follows: firstly, a small drill cylinder is used for drilling a first small drill hole which is coincident with the circle center of a circle where the design hole 1 is located, then two mutually perpendicular diameters of the design hole 1 are roughly drawn, a second small drill hole 3 and a third small drill hole 4 which are tangent to the design hole 1 are dug on one diameter, a fourth small drill hole 5 and a fifth small drill hole 6 which are tangent to the design hole 1 are dug on the other diameter, and since 2D is more than or equal to D and less than 3D, when the second small drill hole 3 and the third small drill hole 4 are drilled, the two small drill holes and the first small drill hole 2 can generate a free surface.

The side wall sleeve 7 is hollow with two open ends, the outer wall of the side wall sleeve is provided with a reinforcing ring 8, the diameter of the reinforcing ring 8 is the same as that of the design hole 1, the distance between the reinforcing ring 8 and the bottom end of the side wall sleeve 7 is 50 cm-100 cm, the reinforcing ring 8 is provided with an injection hole 9, and the output end of the concrete conveying pipe penetrates through the injection hole 9.

The following space that is a section height for H that is of reinforcement ring 8, utilize the concrete conveyer pipe to carry the concrete to this space in, when waiting to the concrete and will fill up this space soon, can receive the extrusion of reinforcement ring 8, thereby reach the effect of fastening, improve the intensity of concrete drum, when waiting that last section concrete drum appears preliminary setting, can slowly withdraw from boundary wall sleeve 7, the height of withdrawing from is H, later continue to let in the concrete, form second section concrete drum, cycle operation in proper order, withdraw from in design hole 1 completely until boundary wall sleeve 7, from this at design hole 1 inner wall formed a sealed section of thick bamboo of constituteing by all concrete drums that highly is H.

In the S23 step and the S24 step, H is 80cm, and the rate of withdrawal of the sidewall sleeve 7 is 50 cm/min; when the side wall sleeve 7 is withdrawn, the concrete cylinder is not completely condensed, so that the withdrawal speed is not too high, and the concrete cylinder is prevented from being extruded and deformed.

The difference between the outer diameter of the reinforcing ring 8 and the outer diameter of the sidewall sleeve 7 is 5 cm; the difference between the outer diameter of the reinforcing ring 8 and the outer diameter of the sidewall sleeve 7 is also the thickness of the concrete cylinder, and when the thickness is controlled to 5cm, on the one hand, the loss of material is reduced, and on the other hand, the required strength can be satisfied.

In the step S22, when the side wall sleeve 7 is delivered to the bottom end of the design hole 1 by the rotary drilling rig, a space is formed between the side wall sleeve 7 and the bottom end of the design hole 1, and the space is 5 cm; can let the bottom of design hole 1 also can produce a concrete layer of 5cm thick, further avoid the condition that the thick liquid runs off from the bottom of design hole 1.

It should be understood that the above examples are only for clarity of illustration and are not intended to limit the embodiments. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. And obvious variations or modifications therefrom are within the scope of the invention.

Claims

1. A rotary drilling and anchor cable construction method for a hard rock stratum is characterized by comprising the working procedures of rotary drilling, side wall filling and anchor cable construction; the rotary drilling process comprises the following steps:

the sidewall filling process comprises the following steps:

s24, withdrawing the side wall sleeve from the design hole by a height H;

2. The rotary excavation and anchor rope construction method for the hard rock formation as claimed in claim 1, wherein in the step S14, a circle in which one of the small drill holes is located and a circle in which the other small drill hole is located have an intersection region.

3. The rotary excavating and anchor cable construction method for the hard rock stratum as claimed in claim 1, wherein when the compressive strength of the stratum is less than 55MPa, four small drill holes are drilled in the circle where the designed aperture is located by the small drill cylinder in the step S14, and D is more than D and less than 2D; and when the compressive strength of the stratum is greater than or equal to 55MPa, five small drill holes are drilled in the circle with the designed hole diameter by the small drill cylinder in the step S14, and D is greater than 2D and less than 3D.

4. The rotary excavating and anchor cable construction method for the hard rock formation according to claim 3, wherein when four small drill holes need to be drilled, the circles of the four small drill holes are all tangent to the circle of the design hole, and the four generated tangent points are located at four vertexes of an inscribed square of the circle of the design hole; when five small drill holes need to be drilled, the circle center of one of the small drill holes coincides with the circle center of the circle where the design hole is located, and the circle centers of the other four small drill holes are respectively located on two vertical diameters of the circle where the design hole is located.

5. The rotary excavating and anchor rope construction method for the hard rock formation according to claim 1, wherein the sidewall sleeve is hollow with openings at both ends, a reinforcing ring is arranged on the outer wall of the sidewall sleeve, the diameter of the reinforcing ring is the same as that of the design hole, the distance between the reinforcing ring and the bottom end of the sidewall sleeve is 50cm to 100cm, an injection hole is formed in the reinforcing ring, and the output end of the concrete conveying pipe penetrates through the injection hole.

6. The rotary excavation and anchor rope construction method for the hard rock formation as claimed in claim 5, wherein in the steps S23 and S24, H is 80cm, and the withdrawal rate of the sidewall sleeve is 50 cm/min.

7. The method for rotary excavation and anchor cable construction of a hard rock formation as claimed in claim 5, wherein the difference between the outer diameter of the reinforcing ring and the outer diameter of the sidewall sleeve is 5 cm.

8. The method for rotary excavation and anchor rope construction of a hard rock formation as claimed in claim 1, wherein in step S22, when the sidewall sleeve is delivered to the bottom end of the design hole by the rotary excavation drilling machine, there is a space between the sidewall sleeve and the bottom end of the design hole, and the space is 5 cm.

9. The rotary excavating and anchor rope construction method for the hard rock formation according to claim 1, wherein the anchor rope construction process comprises the following steps:

10. The method for rotary excavation and anchor cable construction of a hard rock formation of claim 9, wherein the anchor cable body is subjected to a tensile test after the anchor cable construction process is completed.