A method for predicting the bearing capacity of main cables of composite tunnel anchor structures

Abstract

The present invention discloses a method for predicting the bearing capacity of the main cable of a composite tunnel anchor structure. The main cable tension of the composite tunnel anchor structure is calculated under the conditions of moment balance, vertical force balance, and horizontal force balance according to the geometric dimensions and burial depth of the composite tunnel anchor structure and the angle between the slope sliding surface and the horizontal plane. The calculation method of the present invention can predict the bearing capacity of the main cable of the composite tunnel anchor structure. The composite tunnel anchor structure will not overturn under the predicted bearing capacity of the main cable. The predicted bearing capacity of the main cable is compared with the main cable tension required by the design. If the predicted bearing capacity of the main cable is greater than the main cable tension required by the design, the composite tunnel anchor structure will not overturn under the main cable tension required by the design.

Description

Technical Field

[0001] The present invention belongs to the field of geotechnical engineering technology, and more specifically relates to a composite tunnel anchor main cable bearing capacity prediction method, which is suitable for surrounding rock conditions such as soft rock and loose accumulation slopes that are extremely susceptible to engineering disturbances and do not meet bearing design requirements, and is used to evaluate the bearing capacity of the tunnel anchor main cable. Background Art

[0002] In view of the defects of the existing tunnel anchor and gravity anchor technologies, the prior art proposes to construct a new type of suspension bridge anchor, namely the gravity tunnel anchor, whose mechanical model is as follows Figure 1 . The gravity-type tunnel anchor has a conceptual structural design of two anchor sections, the upper anchor is the front anchor body 3, and the lower anchor is the rear anchor body 4. The front anchor body 3 is intended to replace the function of the original tunnel anchor's scattered cable saddle, and evenly distribute the main cable steel cable to the anchor cross section; the rear anchor body 4 is designed to have a wedge-shaped central axis that intersects the horizontal line at a large angle, and its gravity can resist part of the vertical component of the main cable force. Its wedge-shaped appearance can form a clamping effect on the surrounding rock to resist the remaining vertical component of the main cable force. The horizontal component of the main cable force is designed to resist sliding by referring to the base friction sliding failure mode of the gravity anchor; furthermore, if the failure mode of the anchor being pulled out along the main cable force direction is considered, the anchor burial depth can be adjusted until the pull-out design requirements are met. This new anchor combines the advantages of both gravity anchors and tunnel anchors, and is suitable for steep slopes and areas with broken rock masses. Preferably, the front anchor body 3 and the rear anchor body 4 can be connected by a connecting section.

[0003] According to the research results of many scholars on the failure mode of tunnel anchors, the potential fracture surface of the tunnel anchor when the load reaches the limit is Figure 3 Based on the above basic mechanical analysis of gravity tunnel anchors, it can be predicted that when the tunnel anchors are in two possible failure modes, namely, overall overturning and horizontal sliding, the following may occur in the surrounding rock mass: Figure 3 The middle dotted line ② represents the fracture surface.

[0004] According to searches on the China Patent Network and related paper websites, there is currently no solution for predicting the bearing capacity of the main cable of a composite tunnel anchor. If the bearing capacity of the main cable of a composite tunnel anchor can be accurately predicted, the burial depth of the composite tunnel anchor and the maximum bearing limit of the main cable can be known. Summary of the invention

[0005] Aiming at the problem that the bearing capacity of main cables in current gravity anchor and tunnel anchor engineering applications is difficult to predict, a method for predicting the bearing capacity of main cables of composite tunnel anchors is provided.

[0006] A method for predicting the bearing capacity of a main cable of a composite tunnel anchor structure, wherein the composite tunnel anchor structure is arranged in a rock layer on a slope sliding surface, and comprises a main cable access hole parallel to the incident direction of the main cable, a cable-scattering chamber for accommodating a front anchor body, a connecting chamber for accommodating a connecting section, and a wedge-shaped chamber for accommodating a rear anchor body, which are sequentially excavated through the main cable access hole. After the main cable passes through the main cable access hole and is dispersed into steel strands arranged side by side at intervals equal to the number of main cables, all the steel strands are evenly dispersed into the cross section of the cable-scattering chamber through a guide piece and pass through the front anchor body, and then are diverted through a diverting piece and evenly dispersed into the cross sections of the connecting chamber and the wedge-shaped chamber, and finally pass through the connecting body and the rear anchor block and are respectively fixed to the base surface of the wedge-shaped chamber through anchors;

[0007] The front anchor body is a rounded rectangular structure with equal cross-section and coincides with the central axis direction of the main cable access hole. The rear anchor body is a rounded rectangular structure with a cross-section that gradually increases from top to bottom. The two sides of the rear anchor body facing and facing away from the slope sliding surface are rectangular, and the two sides of the rear anchor body perpendicular to the slope sliding surface are trapezoidal. The connector is a triangular prism structure with equal cross-section. The two side edges of the triangular prism structure are connected to the lower end of the front anchor body and the upper end of the rear anchor body respectively. The angle between the other side edge of the connector and the horizontal plane is d. The thickness of the front anchor body, the rear anchor body, and the connector in the direction perpendicular to the rock mass compressive stress and the main cable is equal from top to bottom and is S. The sides of the composite tunnel anchor structure that are in contact with the upper rock mass and the lower rock mass of the main cable access hole are the outer bending side and the inner bending side respectively. The edge O of the connector that is in contact with both the front anchor body and the rear anchor body is the moment balance center axis of the composite tunnel anchor structure.

[0008] The main cable bearing capacity prediction method comprises:

[0009] Step 1: collect the buried depth h4 of the rear anchor body in the slope sliding surface, collect the dimensions and geometric characteristics of the front anchor body, connector body and rear anchor body of the composite tunnel anchor structure: the inner and outer curved length L1 of the front anchor body, the outer curved length L2 of the connector body, the inner and outer curved length L3 of the rear anchor body, the distance L between the central axis of the front anchor body and O, T , the distance between the center axis of the rear anchor body and O is L G , the distance between the outer curved side of the front anchor and O is L F1 , the distance L between the external curved side and O F3 , the distance between the outer bending side of the rear anchor and O is L F2 , the angle c between the slope sliding surface and the horizontal plane, the angles β, d, and α between the outer curved sides of the front anchor body, the connector, and the rear anchor body and the horizontal plane, respectively, and the distance L between the load concentration direction of the rock mass compressive stress N′1 acting vertically on the inner curved side of the front anchor body and O N1 , calculate the distance L between the load concentration direction of the rock mass compressive stress N2 acting vertically on the outer bending side of the rear anchor and O N2 , L N1 =(1-2 / 3)L1,L N2=(2 / 3)L2;

[0010] Step 2, the top of the rear anchor body is buried at a depth h3 relative to the slope sliding surface, the lower outer curved side edge of the front anchor body is buried at a depth h2 relative to the slope sliding surface, the upper outer curved side edge of the front anchor body is buried at a depth h1 relative to the slope sliding surface, and the upper inner curved side edge of the front anchor body is buried at a depth h5 relative to the slope sliding surface;

[0011] Step 3, calculate the rock mass compressive stresses on the outer curved sides of the front anchor body, the connector, and the rear anchor body and the inner curved sides of the front anchor body and the rear anchor body by the following formulas: N1, N3, N2, N′1, N′2, and the friction shear stresses F1, F3, F2, F1', F2' corresponding to the rock mass compressive stresses;

[0012] N1=[(h1+h2)×S×(cosβ+kγsinβ)]×0.5×L1;

[0013] N3=[(h2+h3)×S×(cosd+kγsind)]×0.5×L3;

[0014] N2=[(h3+h4)×S×(cosα+kγsinα)]×0.5×L2;

[0015] N′1=[(h5+h3)×S×(cosβ+kγsinβ)]×0.5×L1;

[0016] N′2=[(h3+h4)×S×(cosα+kγsinα)]×0.5×L2;

[0017] γ is the weight of rock and soil, k is the lateral pressure coefficient;

[0018] Step 4, according to the moment balance of the composite tunnel anchor structure at O ​​and the force balance of the composite tunnel anchor structure in the vertical and horizontal directions, calculate the upper limit value of the main cable bearing capacity: T1, T2, T3, and take the minimum value of T1, T2, T3 as the main cable bearing capacity;

[0019] T1<(G×L G +N1×μ×L F1 +N2×μ×L F2 +N3×μ×L F3 ) / L T ;

[0020] T2<(G+N1×μ×sinβ+N2×μ×sinα×2+N3×μ×sind+N1×cosβ+N3×cosd) / sinβ;

[0021] T3<(N′2×μ+N′1×sinβ+N′1×μ×cosβ) / cosβ;

[0022] μ is the friction coefficient.

[0023] In step 2

[0024] h3=h4-L2sinα-L2cosαtanc;

[0025] h2=h3-L3sind-L3cosdtanc=h4-L2sinα-L2cosαtanc-L3sind-L3cosdtanc;

[0026] h1=h2-L1sinβ-L1cosβtanc=h4-L2sinα-L2cosαtanc-L3sind-L3cosdtanc-L1sinβ-L1cos

[0027] βtanc;

[0028] h5=h3-L1sinβ-L1cosβtanc=h4-L2sinα-L2cosαtanc-L1sinβ-L1cosβtanc.

[0029] By using the calculation method of the present invention, the main cable bearing capacity of the composite tunnel anchoring structure can be predicted. The composite tunnel anchoring structure will not overturn under the predicted main cable bearing capacity. The predicted main cable bearing capacity is compared with the main cable tension required by the design. If the predicted main cable bearing capacity is greater than the main cable tension required by the design, the composite tunnel anchoring structure will not overturn under the main cable tension required by the design.

[0030] The method of the invention is convenient for scientifically estimating whether the designed composite tunnel anchoring structure meets the design requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a layout diagram of a composite tunnel anchor structure in the prior art;

[0032] Figure 2 This is a layout diagram of the composite tunnel anchor structure in Example 1;

[0033] Figure 3 This is a schematic diagram of the failure mode of the composite tunnel anchor structure in Example 1;

[0034] Figure 4 is the moment balance diagram of the composite tunnel anchor structure in Example 1;

[0035] Figure 5 It is the vertical force balance diagram of the composite tunnel anchor structure in Example 1;

[0036] Figure 6This is the horizontal force balance diagram of the composite tunnel anchor structure in Example 1. DETAILED DESCRIPTION

[0037] The method of the present invention is further described in detail below in conjunction with engineering examples, with the aim of enabling those skilled in the art to have a more detailed understanding and knowledge of the method of the present invention. The following embodiments should not be understood in any way as limiting the scope of protection claimed for the present invention.

[0038] Embodiment 1:

[0039] like Figure 6 A composite tunnel anchor structure is arranged in a rock layer 6 of a slope sliding surface 1, including a main cable access hole 2 parallel to the incident direction of the main cable, a loose cable chamber for accommodating a front anchor body 3, a connecting chamber for accommodating a connecting section 5, and a wedge-shaped chamber for accommodating a rear anchor body 4, which are sequentially excavated through the main cable access hole 2. After the main cable access hole 2, the loose cable chamber, the connecting chamber, and the wedge chamber are excavated, a cavern surrounding rock support layer is prepared by anchor spraying and the like, a loose cable saddle is installed in the main cable access hole 2, and a guide is installed at one end of the loose cable chamber close to the main cable access hole 2, the guide comprising a plurality of casings A honeycomb structure or a rigid pad with dense holes, a steering member is arranged at the interface between the cable room, the connecting room and the wedge-shaped room, and the steering member includes a rigid pad with dense holes, a front anchor body 3 is arranged in the cable room, a connecting body 5 is arranged in the connecting room, and a rear anchor body 4 is arranged in the wedge-shaped room. The angle between the slope sliding surface 1 and the horizontal plane is c, the front anchor body 3 is a rounded rectangular structure with equal cross-section, and coincides with the central axis direction of the main cable access hole 2, and the angle between the central axis of the main cable access hole 2 and the horizontal plane is β, and the rear anchor body 4 is a rounded rectangular structure with a cross-section that gradually increases from top to bottom. The two sides of the rear anchor body 4 facing and facing away from the slope sliding surface 1 are rectangular, the two sides of the rear anchor body 4 perpendicular to the slope sliding surface 1 are trapezoidal, and the angle between the inner or outer curved side of the rear anchor body 4 and the horizontal plane is α, the connector 5 is a triangular prism structure with equal cross-section, the two side edges of the triangular prism structure are connected with the lower end of the front anchor body 3 and the upper end of the rear anchor body 4 respectively, the angle between the other side edge of the connector 5 and the horizontal plane is d, α is greater than d, d is greater than the incident angle β of the main cable, the supporting layers of the main cable access hole 2, the cable room, the connecting room and the wedge-shaped room are attached to the front anchor body 3, the connecting room The front anchor body 3, the connector and the rear anchor body 4 and the surrounding supporting layer form a tunnel / gravity anchor wrapped in the rock layer 6 under the tensile stress of the main cable. The main cable is dispersed from the main cable access hole 2 through the cable saddle into steel strands arranged side by side with the same number of intervals as the main cables. All the steel strands are evenly dispersed into the cross-section of the cable chamber through the guide and pass through the front anchor body 3, and then are diverted through the steering member and evenly dispersed into the cross-sections of the connecting chamber and the wedge-shaped chamber, and finally pass through the connector 5 and the rear anchor block 4 and are fixed to the base surface of the wedge-shaped chamber by anchors respectively.

[0040] The main cable bearing capacity of the composite tunnel anchorage structure is calculated according to the following scheme:

[0041] like Figure 2 , the composite tunnel anchor structure is subjected to the following forces, including:

[0042] The main cable stress T is parallel to the main cable and acts on the central axis of the front anchor body;

[0043] The rock mass compressive stress N′1 acts vertically on the inner curved side of the front anchor;

[0044] The rock mass compressive stress N1 acts vertically on the external bending side of the front anchor body;

[0045] The rock mass compressive stress N2 acts vertically on the outer bending side of the rear anchor;

[0046] The rock mass compressive stress N′2 acts vertically on the inner curved side of the rear anchor;

[0047] Rock mass compressive stress N3 acts vertically on the external bending side of the connector;

[0048] The friction shear stress F1, perpendicular to the rock mass compressive stress N1, acts on the outer bending side of the front anchor body;

[0049] The friction shear stress F1′, perpendicular to the rock mass compressive stress N′1, acts on the inner curved side of the front anchor;

[0050] The friction shear stress F2, perpendicular to the rock mass compressive stress N2, acts on the outer bending side of the rear anchor;

[0051] The friction shear stress F2, perpendicular to the rock mass compressive stress N′2, acts on the inner curved side of the rear anchor;

[0052] The friction shear stress F3, perpendicular to the rock mass compressive stress N3, acts on the external bending side of the connector;

[0053] The outer bending side refers to the side where the composite tunnel anchoring structure contacts the rock mass 6 on the upper side of the main cable access hole 2, and the inner bending side refers to the side where the composite tunnel anchoring structure contacts the rock mass 6 on the lower side of the main cable access hole 2. The edge O where the connector 5 contacts both the front anchor body 3 and the rear anchor body 4 is the moment balance center axis of the composite tunnel anchoring structure.

[0054] As the rock mass compressive stress N1, N′1, N2, and N′2 increase with the depth of the rock mass 6, when the rock mass pressure acts on the front anchor body 3 and the rear anchor body 4, the rock mass pressure is distributed in a trapezoidal shape from top to bottom. After the rock mass pressure distribution load is converted into a concentrated load, the action point is approximately at two-thirds of the top of the action surface. In addition, due to the dimensions of the front anchor body 3, the connector, and the rear anchor body 4: the inner and outer bending length L1 of the front anchor body, the outer bending length L2 of the connector body, the inner and outer bending length L3 of the rear anchor body, and the distance L between the center axis of the front anchor body and O T , the distance between the center axis of the rear anchor body and O is L G , the distance between the outer curved side of the front anchor and O is LF1 , the distance L between the external curved side and O F3 , the distance between the outer bending side of the rear anchor and O is L F2 , and the angle c between the slope sliding surface 1 and the horizontal plane is known, so the distance L between the point of action of the rock mass compressive stress N′1 and N2 and O is N1 , L N2 It is also known that when the buried depth h4 of the bottom surface of the rear anchor body relative to the slope sliding surface 1 is known, the following can be calculated based on the angle α between the inner or outer curved side of the rear anchor body 4 and the horizontal plane, the angle d between the outer curved side of the connector 5 and the horizontal plane, the incident angle β of the main cable access hole 2, and the dimensions of the front anchor body 3, the connector 5, and the rear anchor body 4: the buried depth h3 of the top of the rear anchor body 4 relative to the slope sliding surface 1, the buried depth h2 of the outer curved side edge of the lower end of the front anchor body 3 relative to the slope sliding surface 1, the buried depth h1 of the outer curved side edge of the upper end of the front anchor body 3 relative to the slope sliding surface 1, and the buried depth h5 of the inner curved side edge of the upper end of the front anchor body 3 relative to the slope sliding surface 1.

[0055] In order to calculate the bearing capacity of the main cable of the composite tunnel anchor structure, the composite tunnel anchor structure is taken as the load-bearing object and the following equations are established: Figure 2 The mechanical model shown in the figure is used to calculate the rock pressure on the inner and outer curved sides of the front anchor body 3, the rear anchor body 4 and the connector 5. It is assumed that the thickness of the front anchor body 3, the rear anchor body 4 and the connector 5 in the direction perpendicular to the rock compressive stress and perpendicular to the main cable is equal from top to bottom. The composite tunnel anchor structure with a thickness of 1 meter is used as the minimum unit for calculation. In the minimum unit, the area S1 of the front anchor body 3 subjected to the rock compressive stress N1 is (1+1)×0.5×L1, and the area S1 of the inner curved side of the front anchor body 3 subjected to the rock compressive stress N′1 is ’ =(1+1)×0.5×L1, the area S3 of the connector 5 bearing the rock mass compressive stress N3 is (1+1)×0.5×L2, the area S2 of the rear anchor 4 bearing the rock mass compressive stress N2 is (1+1)×0.5×L3, and the area S2 of the rear anchor 4 bearing the rock mass compressive stress N′2 is (1+1)×0.5×L3.

[0056] Then, a balance analysis is performed to obtain the following calculation formula:

[0057] 1) Moment balance centered at point O

[0058]

[0059] Where: M G Calculate the moment of gravity on point O for the anchor body, M F1O is the moment of friction shear stress F1 on point O, M F2O is the moment of friction shear stress F2 on point O, M F3O is the moment of friction shear stress F3 on point O.

[0060] 2) Vertical force balance

[0061] T2sinβ<G+F1sinβ+F2sinα×2+F3sind+N1cosβ+N3cosd (2)

[0062] 3) Horizontal force balance

[0063] T3cosβ<N′2+N′1sinβ+F′1cosβ (3)

[0064] 4) Finally: The bearing capacity of the tunnel anchor is the minimum value of the results calculated by the three formulas. T = min (T1, T2, T3);

[0065] M G =G×L G ;

[0066] M F1O =F1×L F1 =N1×μ×L F1

[0067] M F2O =F2×L F2 =N2×μ×L F2 ;

[0068] M F3O =F3×L F3 =N3×μ×L F3 ;

[0069] N1, N2, and N3 are the integrals of the rock mass pressure on areas S1, S2, and S3, respectively. Areas S1, S2, and S3 are divided from top to bottom into several rows perpendicular to the rock mass compressive stress and the direction of the main cable. The rock mass pressure in each row is N h =1m×γhcosθ+1m×kγhsinθ, θ is the angle β, α, d between the outer curved sides of the front anchor body 3, the rear anchor body 4, and the connector 5 and the horizontal plane, 1m is the thickness of the minimum unit body, h is the depth of each row relative to the slope sliding surface 1, γ is the weight of the rock and soil, k is the lateral pressure coefficient, k=0.30.

[0070] Therefore, N1 is the area of ​​a trapezoidal region with an upper base of h1×1m×(cosβ+kγsinβ), a lower base of h2×1m×(cosβ+kγsinβ), and a height of L1, measured in units of force;

[0071] N3 is the area of ​​a trapezoidal region measured in units of force, with an upper base of h2×1m×(cosd+kγsind), a lower base of h3×1m×(cosd+kγsind), and a height of L3;

[0072] N2 is the area of ​​a trapezoidal region measured in units of force, with an upper base of h3×1m×(cosα+kγsinα), a lower base of h4×1m×(cosα+kγsinα), and a height of L2;

[0073] N′1 is the area of ​​a trapezoidal region measured in units of force, with an upper base of h5×1m×(cosβ+kγsinβ), a lower base of h3×1m×(cosβ+kγsinβ), and a height of L1;

[0074] N′2 is the area of ​​a trapezoidal region measured in units of force, with an upper base of h3×1m×(cosα+kγsinα), a lower base of h4×1m×(cosα+kγsinα), and a height of L2;

[0075] Finally, the bearing capacity of the main cable is obtained by multiplying the number of the minimum unit bodies n of the composite tunnel anchorage structure by T.

[0076] According to engineering geological conditions, relevant geological data, and the example dimensions of composite tunnel anchoring structures, it can be known that:

[0077] Actual deadweight of composite tunnel anchorage structure:

[0078] G overall = 69.9 MN;

[0079] The calculation is based on the minimum unit cross section with a unit thickness of 1m. The calculated deadweight of the anchor body is: G = 0.1G overall = 6.99MN;

[0080] The outer bending lengths of the front anchor body, connector body and rear anchor body are

[0081] L1=8.01m, L2=10.01m, L3=10.14m;

[0082] L N1 =(1-2 / 3)L1=2.67m, L N2 =(2 / 3)L2=6.67m;

[0083] The main cable tension T, anchor body calculated deadweight G, friction shear stress F1, F2, F3 to O distance L respectively T , L G , L F1 , L F2 , L F3 ;

[0084] L T =6.22m, L G =5.92m, L F1 =10.88m(L F1 Approximate L F3)、L F2 =11.99m, L F3 =10.88m

[0085] Rock mass compressive stress N h =1m×γhcosθ+1m×kγhsinθ(I)

[0086] The weight of rock and soil is γ=28kN / m 2 ; α=87°,β=40°,d=65°;friction coefficient μ=0.50,lateral pressure coefficient k=0.30;h1=47.8m,h2=55.8m,h3=67.1m,h4=77.4m,h5=52.79m;

[0087] γcosβ+kγsinβ=26.84668(I)

[0088] γcosd+kγsind=19.44572

[0089] γcosα+kγsinα=9.8

[0090] The rock mass compressive stress at each corresponding point can be obtained by formula (I):

[0091] N1=[(h1+h2)×1m×(cosβ+kγsinβ)]×0.5×L1=(47.8+55.8)×1×26.84668×0.5×8.01=11139.17kN

[0092] N3=[(h2+h3)×1m×(cosd+kγsind)]×0.5×L3=(55.8+67.1)×1×19.44572×0.5×10.14=12116.68kN

[0093] N2=[(h3+h4)×1m×(cosα+kγsinα)]×0.5×L2=(67.1+77.4)×1×9.8×0.5×10.01=7087.58kN

[0094] N′1=[(h5+h3)×1m×(cosβ+kγsinβ)]×0.5×L1=(52.79+67.1)×1×26.84668×0.5×8.01=12890.69kN

[0095] N′2=[(h3+h4)×1m×(cosα+kγsinα)]×0.5×L2=(67.1+77.4)×1×9.8×0.5×10.01=7087.58kN

[0096] F1=N1×μ=11139.17×0.50=5569.585kN

[0097] F2=N2×μ=7087.58×0.50=3543.79kN

[0098] F3=N3×μ=12116.68×0.50=6058.34kN

[0099] M G =G×L G =41380kN·M

[0100] M F1O =F1×L F1 =N1×μ×L F1 =5569.585×10.88=60597.0848kN·M

[0101] M F2O =F2×L F2 =N2×μ×L F2 =3543.79×11.99=42490.0421kN·M

[0102] M F3O =F3×L F3 =N3×μ×L F3 =6058.34×10.88=65914.7392kN·M

[0103] M′1=N′1×L N1 =12890.69×2.67=34418.1423kN·M

[0104] M2=N2×L N2 =7087.58×6.67=47,274.1586kN·M

[0105] Moment balance centered on O

[0106]

[0107] T1<(41380+60597.0848+42490.0421+65914.7392)÷6.22=33823.4511kN

[0108] Balanced vertical force

[0109] T2sinβ<G+F1sinβ+F2sinα×2+F3sind+N1cosβ+N3cosd

[0110] sinα=0.99≈1, sinβ=0.64, cosβ=0.77, cosd=0.42, sind=0.91

[0111] T2<(6.99×10 3 +5569.585×0.64+3543.79×1×2+6058.34×0.91+11139.17×0.77+12116.68×0.42)÷0.64=57533.39kN

[0112] Balanced by horizontal forces

[0113] T3cosβ<N′2+N′1sinβ+F′1cosβ

[0114] F′1=N′1×μ=12890.69×0.50=6445.345kN

[0115] T3<(7087.58+12890.69×0.64+6445.345×0.77)÷0.77=26364.33kN

[0116] Finally: The tunnel anchor bearing capacity is the minimum value of the results calculated by the three formulas.

[0117] T=min(T1, T2, T3)=26364.33kN

[0118] The main cable bearing capacity of the smallest unit body of the composite tunnel anchor structure is 26364.33 kN. Finally, the bearing capacity of the main cable is obtained by multiplying the number n of the smallest unit body of the composite tunnel anchor structure by T.

[0119] In the above embodiment 1:

[0120] h3=h4-L2sinα-L2cosαtanc;

[0121] h2=h3-L3sind-L3cosdtanc=h4-L2sinα-L2cosαtanc-L3sind-L3cosdtanc;

[0122] h1=h2-L1sinβ-L1cosβtanc=h4-L2sinα-L2cosαtanc-L3sind-L3cosdtanc-L1sinβ-L1cosβtanc;

[0123] h5=h3-L1sinβ-L1cosβtanc=h4-L2sinα-L2cosαtanc-L1sinβ-L1cosβtanc.

Claims

1. A method for predicting the bearing capacity of a main cable of a composite tunnel anchor structure, wherein the composite tunnel anchor structure is arranged in a rock layer on a slope sliding surface, characterized in that: It includes a main cable access hole parallel to the incident direction of the main cable, a cable sling chamber for accommodating the front anchor body, a connecting chamber for accommodating the connecting section, and a wedge-shaped chamber for accommodating the rear anchor body, which are sequentially excavated through the main cable access hole. After the main cable passes through the main cable access hole and is dispersed into steel strands arranged side by side at intervals equal to the number of main cables, all the steel strands are evenly dispersed into the cross section of the cable sling chamber through guides and pass through the front anchor body, and then are diverted through diverters and evenly dispersed into the cross sections of the connecting chamber and the wedge-shaped chamber, and finally pass through the connecting body and the rear anchor block and are respectively fixed to the base surface of the wedge-shaped chamber through anchors; The front anchor body is a rounded rectangular structure with equal cross-section and coincides with the central axis direction of the main cable access hole. The rear anchor body is a rounded rectangular structure with a cross-section that gradually increases from top to bottom. The two sides of the rear anchor body facing and facing away from the slope sliding surface are rectangular, and the two sides of the rear anchor body perpendicular to the slope sliding surface are trapezoidal. The connector is a triangular prism structure with equal cross-section. The two side edges of the triangular prism structure are connected to the lower end of the front anchor body and the upper end of the rear anchor body respectively. The angle between the other side edge of the connector and the horizontal plane is d. The thickness of the front anchor body, the rear anchor body, and the connector in the direction perpendicular to the rock mass compressive stress and the main cable is equal from top to bottom and is S. The sides of the composite tunnel anchor structure that are in contact with the upper rock mass and the lower rock mass of the main cable access hole are the outer bending side and the inner bending side respectively. The edge O of the connector that is in contact with both the front anchor body and the rear anchor body is the moment balance center axis of the composite tunnel anchor structure. The main cable bearing capacity prediction method comprises: Step 1: collect the buried depth h4 of the rear anchor body in the slope sliding surface, collect the dimensions and geometric characteristics of the front anchor body, connector body and rear anchor body of the composite tunnel anchor structure: the inner and outer curved length L1 of the front anchor body, the outer curved length L2 of the connector body, the inner and outer curved length L3 of the rear anchor body, the distance L between the center axis of the front anchor body and the edge O T , the distance L between the center axis of the rear anchor body and the edge O G , the distance L between the outer curved side of the front anchor and the edge O F1 , the distance L between the external curved side and the edge O F3 , the distance L between the outer bending side of the rear anchor and the edge O F2 , the angle c between the slope sliding surface and the horizontal plane, the angles β, d, and α between the outer curved sides of the front anchor body, the connector, and the rear anchor body and the horizontal plane respectively, and the distance L between the load concentration direction of the rock mass compressive stress N′1 acting vertically on the inner curved side of the front anchor body and the edge O N1 , calculate the distance L between the load concentration direction of the rock mass compressive stress N2 acting vertically on the outer bending side of the rear anchor body and the edge O N2 , L N1 =(1-2 / 3)L1,L N2 =(2 / 3)L2; Step 2, the top of the rear anchor body is buried at a depth h3 relative to the slope sliding surface, the lower outer curved side edge of the front anchor body is buried at a depth h2 relative to the slope sliding surface, the upper outer curved side edge of the front anchor body is buried at a depth h1 relative to the slope sliding surface, and the upper inner curved side edge of the front anchor body is buried at a depth h5 relative to the slope sliding surface; Step 3, calculate the rock mass compressive stresses on the outer curved sides of the front anchor body, the connector, and the rear anchor body and the inner curved sides of the front anchor body and the rear anchor body by the following formulas: N1, N3, N2, N′1, N′2, and the friction shear stresses F1, F3, F2, F1', F2' corresponding to the rock mass compressive stresses; N1=[(h1+h2)×S×(cosβ+kγsinβ)]×0.5×L1; N3=[(h2+h3)×S×(cosd+kγsind)]×0.5×L3; N2=[(h3+h4)×S×(cosα+kγsinα)]×0.5×L2; N′1=[(h5+h3)×S×(cosβ+kγsinβ)]×0.5×L1; N′2=[(h3+h4)×S×(cosα+kγsinα)]×0.5×L2; γ is the weight of rock and soil, k is the lateral pressure coefficient; Step 4, according to the moment balance of the composite tunnel anchor structure at the edge O and the force balance of the composite tunnel anchor structure in the vertical and horizontal directions, calculate the upper limit value of the main cable bearing capacity: T1, T2, T3, and take the minimum value of T1, T2, T3 as the main cable bearing capacity; T1<(G×L G +N1×μ×L F1 +N2×μ×L F2 +N3×μ×L F3 ) / L T ; T2<(G+N1×μ×sinβ+N2×μ×sinα×2+N3×μ×sind+N1×cosβ+N3×cosd) / sinβ; T3<(N′2×μ+N′1×sinβ+N′1×μ×cosβ) / cosβ; μ is the coefficient of friction.

2. The prediction method according to claim 1, characterized in that: in step 2 h3=h4-L2sinα-L2cosαtanc; h2=h3-L3sind-L3cosdtanc=h4-L2sinα-L2cosαtanc-L3sind-L3cosdtanc; h1=h2-L1sinβ-L1cosβtanc=h4-L2sinα-L2cosαtanc-L3sind-L3cosdtanc-L1sinβ-L1cos βtanc; h5=h3-L1sinβ-L1cosβtanc=h4-L2sinα-L2cosαtanc-L1sinβ-L1cosβtanc。

Images