Method for Deformation Control of Large-span Tunnel in Chlorite Schist Stratum

Abstract

A method for deformation control of large-span tunnel in chlorite schist stratum. The method divides the large deformation of large-span tunnel in chlorite schist stratum into five deformation grades according to the surrounding rock conditions of the tunnel. In response to each deformation grade, the deformation control of large-span tunnel is determined so as to ensure the safety and stability of the tunnel support structure and to avoid the clearance intrusion caused by tunnel deformation.

Claims

1. A method for deformation control of large-span tunnel in chlorite schist stratum, comprising; dividing a deformation of a large-span tunnel in chlorite schist stratum into five deformation grades according to surrounding rock conditions of the tunnel, wherein the five large deformation grades are extremely serious large-deformation, serious large-deformation, medium large-deformation, slight large-deformation, and zero large-deformation; and controlling a deformation of the large-span tunnel corresponding to one of the five deformation grades, wherein the extremely serious large-deformation comprises the tunnel surrounding rock being composed of single chlorite schist, having a saturated uniaxial compressive strength Rc<5 MPa, and being in a powder or granular structure; wherein the serious large-deformation comprises the tunnel surrounding rock being composed of chlorite schist and contains 20% of quartz veins, containing underground water, having a saturated uniaxial compressive strength Rc of rock mass of 5-10 MPa, and having a rock mass integrity coefficient Kv0.15, and being in a cataclastic or granular structure; wherein the medium large-deformation comprises the tunnel surrounding rock being composed of chlorite schist and containing less than 20% quartz veins, having no underground water, having a saturated uniaxial compressive strength Rc of rock mass of 10-20 MPa, having a rock mass integrity coefficient Kv of 0.15-0.35, and being in a thin stratified structure with a layer thickness less than 10 cm or a cataclastic structure; wherein the slight large-deformation comprises the tunnel surrounding rock being composed of chlorite schist and contain-sing large quartz veins with particle size greater than 5 cm, having no underground water, having a saturated uniaxial compressive strength Rc of rock mass of 20-25 MPa, having a rock mass integrity coefficient Kv of 0.35-0.55, and being in a thick stratified structure with a layer thickness greater than 10 cm or a blocky structure; and wherein the zero large-deformation comprises the tunnel surrounding rock being chlorite albite schist or other stratum with chlorite as a main part, having no underground water, having a saturated uniaxial compressive strength Rc of rock mass of equal or greater than 25 MPa, having a rock mass integrity coefficient Kv of 0.55-0.75, and being in a blocky structure.

2. The method for deformation control of large-span tunnel in chlorite schist stratum according to claim 1, wherein the large-span tunnel is single-hole highway tunnel with three lanes, or another tunnel with a same span as the single-hole highway tunnel with three lanes.

3. (canceled)

4. The method for deformation control of large-span tunnel in chlorite schist stratum according to claim 1, wherein controlling deformation comprises constructing advance support, setting reserved deformation, excavating the tunnel, constructing primary support, and constructing secondary lining.

5. The method for deformation control of large-span tunnel in chlorite schist stratum according to claim 4, wherein controlling deformation of large-span tunnel with different deformation grades is realized by controlling a row number of advance grouting pipes, a value of reserved deformation, a distance from a bottom of the tunnel invert to a top surface of invert backfill during the excavation process, a model of and the space between the steel frames, a value of reserved deformation, a diameter and quantity of feet-lock pipes, and a thickness of shotcrete and secondary lining concrete of each layer of steel frames.

6. The method for deformation control of large-span tunnel in chlorite schist stratum according to claim 4, wherein controlling the extremely serious large-deformation of the large-span tunnel comprises: constructing advance support using double-row advance grouting pipe; setting reserved deformation to be 90-120 cm; excavating the tunnel using a method of three steps with reserving core soil, wherein, when a tunnel invert is excavated, a distance from the bottom of the tunnel invert to a top surface of invert backfill is 3-4 m, which can improve a stress condition of the tunnel invert and effectively prevent cracking and heave of the tunnel invert; constructing primary support, wherein double-layer primary supports are carried out in turn for the arch, side wall and invert of the tunnel, wherein the reserved deformation for the first-layer primary support is 90-120 cm, and the second-layer primary support is carried out when the reserved deformation has a remaining of 45-60 cm; and each layer of primary support uses HK200b-type steel frame with an interval of 50-60 cm and shotcrete with a thickness of 26-30 cm, and each layer of steel frame is installed with a double-layer steel mesh; and the arch foot and the wall foot of the upper, middle and lower steps of the first-layer steel frame are set with small-diameter double-row feet-lock pipes with a diameter 50 mm; and a large-diameter feet-lock pipe with a diameter 89 mm is set for each steel frame of the second layer at the arch foot and the wall foot of the middle and lower steps, and the installation angle of the feet-lock pipe is 20-50; and constructing secondary lining, wherein the secondary lining uses reinforced concrete with a thickness of 70-90 cm at the arch and the side wall, and reinforced concrete with a thickness of 70-100 cm in the tunnel invert.

7. The method for deformation control of large-span tunnel in chlorite schist stratum according to claim 4, wherein controlling the serious large-deformation of the large-span tunnel comprises: constructing advance support by using double-row advance grouting pipe; setting reserved deformation to be 50-90 cm; excavating the tunnel using a method of three steps with reserving core soil, wherein the distance from the bottom of the tunnel invert to the top surface of invert backfill is 3-4 m; constructing primary support, wherein double-layer primary supports are carried out in turn for the arch and side wall of the tunnel, wherein the reserved deformation for the first-layer primary support is 50-90 cm, and the second-layer primary support is carried out when the reserved deformation has a remaining of 25-45 cm; and single-layer primary support is applied to the tunnel invert; and each layer of primary support uses HK200b-type steel frame with an interval of 60-70 cm and shotcrete with a thickness of 26-30 cm, and each layer of steel frame is installed with a double-layer steel mesh; and the arch foot and the wall foot of the upper, middle and lower steps of the first-layer steel frame are set with small-diameter double-row feet-lock pipes with a diameter 50 mm; and a large-diameter feet-lock pipe with a diameter 89 mm is installed for every two steel frames of the second layer at the arch foot and the wall foot of the middle and lower steps; and the installation angle of the feet-lock pipe is 20-50; when the second-layer primary support is finished, the grouting pipe is used to carry out radial grouting reinforcement to the surrounding rock; and constructing secondary lining using reinforced concrete with a thickness of 70-90 cm at the arch and the side wall, and reinforced concrete with a thickness of 70-100 cm in the tunnel invert.

8. The method for deformation control of large-span tunnel in chlorite schist stratum according to claim 4, wherein controlling the medium large-deformation of the large-span tunnel comprises: constructing advance support by using double-row advance grouting pipe; setting reserved deformation to be 30-50 cm; excavating the tunnel using a method of three steps with reserving core soil, wherein the distance from the bottom of the tunnel invert to the top surface of invert backfill is 3-4 m; constructing primary support, wherein double-layer primary supports are carried out in turn for the arch and side wall of the tunnel, wherein the reserved deformation for the first-layer primary support is 30-50 cm, and the second-layer primary support is carried out when the reserved deformation has a remaining of 15-25 cm; and single-layer primary support is applied to the tunnel invert; and each layer of primary support uses HW175-type steel frame with an interval of 70-80 cm and shotcrete with a thickness of 26-30 cm, and each layer of steel frame is installed with a double-layer steel mesh; and the arch foot and the wall foot of the upper, middle and lower steps of the first-layer steel frame are set with small-diameter double-row feet-lock pipes with a diameter 50 mm; and a large-diameter feet-lock pipe with a diameter 89 mm is installed for every two steel frames of the second layer at the arch foot and the wall foot of the middle and lower steps; and the installation angle of the feet-lock pipe is 20-50; when the second-layer primary support is finished, the grouting pipe is used to carry out radial grouting reinforcement to the surrounding rock; and constructing secondary lining using reinforced concrete with a thickness of 70-90 cm at the arch, the side wall and the invert of the tunnel.

9. The method for deformation control of large-span tunnel in chlorite schist stratum according to claim 4, wherein controlling the slight large-deformation of the large-span tunnel comprises: constructing advance support using double-row advance grouting pipe; setting reserved deformation to be 20-30 cm; excavating the tunnel using a method of three steps with reserving core soil, wherein the distance from the bottom of the tunnel invert to the top surface of invert backfill is 2.5-3 m; constructing primary supports, wherein the arch, single-layer primary support is carried out for the arch, side wall and invert of the tunnel, wherein the primary support uses HK200b-type steel frame with an interval of 80-90 cm and shotcrete with a thickness of 26-30 cm, and the steel frame is set with a double-layer steel mesh; and the arch foot and the wall foot of the upper, middle and lower steps of the steel frame are set with small-diameter double-row feet-lock pipes with a diameter 50 mm, and the installation angle of the feet-lock pipe is 20-50; as for the replaced or twisted part of the steel frame, the grouting pipe is used to carry out radial grouting reinforcement to the surrounding rock; and constructing secondary lining using reinforced concrete with a thickness of 60-80 cm at the arch, the side wall and the invert of the tunnel.

10. The method for deformation control of large-span tunnel in chlorite schist stratum according to claim 4, wherein controlling the zero large-deformation of the large-span tunnel comprises: constructing advance support using double-row advance grouting pipe; setting reserved deformation to be 10-20 cm; excavating the tunnel using a method of three steps with reserving core soil; constructing primary support, wherein single-layer primary support is carried out for the arch, side wall and invert of the tunnel, wherein the primary support uses HW175-type steel frame with an interval of 90-100 cm and shotcrete with a thickness of 26-28 cm, and the steel frame is set with a double-layer steel mesh; and the arch foot and the wall foot of the upper, middle and lower steps of the steel frame are set with small-diameter double-row feet-lock pipes with a diameter 50 mm, and the installation angle of the feet-lock pipe is 20-50; and constructing secondary lining using reinforced concrete with a thickness of 60-80 cm at the arch, the side wall and the invert of the tunnel.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0050] FIG. 1 is a diagram of corresponding tunnel support structure of extremely serious large-deformation grade;

[0051] FIG. 2 is the arrangement diagram of 108 mm feet-lock pipe in extremely serious large-deformation grade;

[0052] FIG. 3 is a diagram of corresponding tunnel support structure of serious large-deformation grade;

[0053] FIG. 4 is the arrangement diagram of 108 mm feet-lock pipe in serious large-deformation grade;

[0054] FIG. 5 is a diagram of corresponding tunnel support structure of medium large-deformation grade;

[0055] FIG. 6 is the arrangement diagram of 89 mm feet-lock pipe in medium large-deformation grade;

[0056] FIG. 7 is a diagram of corresponding tunnel support structure of slight large-deformation grade;

[0057] FIG. 8 is a diagram of corresponding tunnel support structure of zero large-deformation grade.

[0058] Drawing References: 1. advance grouting pipe; 2. HK200b-type steel frame; 3. C25 shotcrete; 4. 50 mm feet-lock pipe; 5. 108 mm feet-lock pipe; 6. connection steel plate; 7. C35 reinforced concrete; 8. HW175-type steel frame; 9. 89 mm feet-lock pipe; 10. C30 reinforced concrete.

DETAILED DESCRIPTION OF THE FIGURES

[0059] In order to make the purpose, technical solution and advantages of the present invention clearer, the present invention is further described in detail through the drawings and the embodiments. It should be understood that the concrete embodiments as described herein are only used to explain the present invention instead of defining the present invention.

[0060] To the contrary, the present invention covers any substitute, modification, equivalent method, and solution that are defined by the claims within the essence and scope of the present invention. Further, in order to make the public have a better understanding of the present invention, some specific details are described in the details in the present invention described below. And those skilled in the art can completely understand the present invention even if there is no description of these details.

Example 1

[0061] The present example provides a method for deformation control of large-span tunnel in chlorite schist stratum, and said method divides the large deformation of large-span tunnel in chlorite schist stratum into five deformation grades according to the surrounding rock conditions of the tunnel (including the main mineral components of chlorite schist, density, rock mass strength, rock mass integrity, rock mass discontinuity occurrence and underground water condition, etc.) in combination with the large deformation grades and the controlling effects of the large deformation under different conditions of the surrounding rock in the tunnel site. The five large deformation grades are listed from the highest to the lowest degree of deformation: extremely serious large-deformation, serious large-deformation, medium large-deformation, slight large-deformation, and zero large-deformation. And the present invention determines corresponding method for the deformation control of large-span tunnel in response to each deformation grade so as to ensure the safety and stability of the tunnel support structure and to avoid the clearance intrusion caused by tunnel deformation.

[0062] The tunnel surrounding rock condition of the extremely serious large-deformation is: the tunnel surrounding rock is composed of single chlorite schist, and its saturated uniaxial compressive strength Rc<5 MPa, and it is in a powder or granular structure.

[0063] The tunnel surrounding rock condition of the serious large-deformation is: the tunnel surrounding rock is composed of chlorite schist and contains a small amount of quartz veins with the content less than 20%; it also has underground water, and its saturated uniaxial compressive strength of rock mass Rc=5-10 MPa, and its rock mass integrity coefficient Kv0.15, and it is in a cataclastic or granular structure.

[0064] The tunnel surrounding rock condition of the medium large-deformation is: the tunnel surrounding rock is composed of chlorite schist and contains a small amount of quartz veins with the content less than 20%; it has no underground water, and its saturated uniaxial compressive strength of rock mass Rc=10-20 MPa, and its rock mass integrity coefficient Kv is 0.15-0.35, and it is in a thin stratified structure with a layer thickness less than 10 cm or a cataclastic structure.

[0065] The tunnel surrounding rock condition of the slight large-deformation is: the tunnel surrounding rock is composed of chlorite schist and contains large quartz veins with particle size greater than 5 cm; it has no underground water, and its saturated uniaxial compressive strength of rock mass Rc=20-25 MPa, and its rock mass integrity coefficient Kv is 0.35-0.55, and it is in a thick stratified structure with a layer thickness greater than 10 cm or a blocky structure.

[0066] The tunnel surrounding rock condition of the zero large-deformation is: the tunnel surrounding rock is chlorite albite schist or other stratum with chlorite as its main part; it has no underground water, and its saturated uniaxial compressive strength of rock mass Rc25 Pa, and its rock mass integrity coefficient Kv is 0.55-0.75, and it is in a blocky structure.

[0067] Further, the large-span tunnel is single-hole highway tunnel with three lanes, or other tunnels with the same span.

[0068] When the large deformation grade of large-span tunnel in chlorite schist stratum is extremely serious large-deformation, as shown in FIG. 1, the corresponding control measure for extremely serious large-deformation is:

[0069] Construct advance support: carrying out advance support by using 50 double-row advance grouting pipe 1 with a length of 3.5 m and a circumferential space of 40 cm;

[0070] Set reserved deformation: set the value of reserved deformation to be 90-120 cm;

[0071] Excavate the tunnel: excavating the tunnel by the method of three steps with reserving core soil; in order to improve the stress condition of the tunnel invert, the distance from the bottom of the tunnel invert to the top surface of invert backfill is 3-4 m;

[0072] Construct primary support: double-layer primary supports are carried out in turn for the arch, side wall and invert of the tunnel, that is, carry out the first-layer primary support and then the second-layer primary support when the reserved deformation has a remaining of 45-60 cm; and the first-layer steel frame and the second-layer steel frame in the double-layer primary supports use HK200b-type steel frame 2 with an interval of 50 cm, and each layer of steel frame is installed with a double-layer 8 steel mesh with the mesh space of 2020 cm; and the first layer of shotcrete and the second layer of shotcrete are made of C25 shotcrete 3 with a thickness of 28 cm; and double-row 50 feet-lock pipes 4 with a length of 4 m are installed at the arch foot and the wall foot of the upper, middle and lower steps for the first-layer steel frame, and each truss of steel frame is installed with 24 feet-lock pipes; 108 feet-lock pipe 5 with a length of 6 m is set for each steel frame of the second layer at the arch foot and the wall foot of the middle and lower steps, as shown in FIG. 2 for the specific arrangement diagram, and a connection steel plate 6 with a thickness of 20 mm is welded firmly with the two neighboring steel frames so as to support the second-layer steel frame by 108 feet-lock pipe 5; and the installation angle of the aforesaid feet-lock pipe is 20-50;

[0073] Construct secondary lining: the secondary lining is made of C35 reinforced concrete 7 with a thickness of 80 cm at the arch and the side wall, and the thickness of the secondary lining in the tunnel invert is 100 cm, and the rebar in the reinforced concrete uses 28 rebar as the main reinforcement, and the space is 20 cm.

[0074] When the large deformation grade of large-span tunnel in chlorite schist stratum is extremely serious large-deformation, the aforesaid control measure can be used to avoid the clearance intrusion caused by tunnel deformation and to ensure the safety and stability of the tunnel support structure, and the cost is controllable.

[0075] When the large deformation grade of large-span tunnel in chlorite schist stratum is serious large-deformation, as shown in FIG. 3, the corresponding control measure for serious large-deformation is:

[0076] Construct advance support: carrying out advance support by using 50 double-row advance grouting pipe 1 with a length of 3.5 m and a circumferential space of 40 cm;

[0077] Set reserved deformation: set the value of reserved deformation to be 50-90 cm;

[0078] Excavate the tunnel: excavating the tunnel by the method of three steps with reserving core soil; in order to improve the stress condition of the tunnel invert, the distance from the bottom of the tunnel invert to the top surface of invert backfill is 3-4 m;

[0079] Construct primary support: double-layer primary supports are carried out in turn for the arch and side wall of the tunnel, that is, carry out the first-layer primary support and then the second-layer primary support when the reserved deformation has a remaining of 25-45 cm; and the single-layer primary support is used in the tunnel invert; the first-layer steel frame and the second-layer steel frame at the arch and side wall in the double-layer primary supports use HK200b-type steel frame 2 with an interval of 60 cm, and each layer of steel frame is installed with a double-layer 8 steel mesh with the mesh space of 2020 cm; and the first layer of shotcrete and the second layer of shotcrete at the arch and side wall are made of C25 shotcrete 3 with a thickness of 28 cm; and the parameters of primary support in the tunnel invert are the same with the parameters of the single-layer primary support at the arch and the side wall; and double-row 50 feet-lock pipes 4 with a length of 4 m are installed at the arch foot and the wall foot of the upper, middle and lower steps for the first-layer steel frame, and each truss of steel frame is installed with 24 feet-lock pipes; 108 mm feet-lock pipe 5 with a length of 6 m is installed for every two steel frames of the second layer at the arch foot and the wall foot of the middle and lower steps, as shown in FIG. 4 for the specific arrangement diagram, and a connection steel plate 6 with a thickness of 20 mm is welded firmly with the two neighboring steel frames so as to support the second-layer steel frame by 108 feet-lock pipe 5; and the installation angle of the aforesaid feet-lock pipe is 20-50; when the second-layer primary support is done, 50 grouting pipe with a length of 4 m and a space of 1.51.5 m is used to carry out radial grouting reinforcement to the surrounding rock;

[0080] Construct secondary lining: the secondary lining is made of C35 reinforced concrete 7, and the thickness of the secondary lining at the arch and side wall is 80 cm, and the secondary lining 22 in the tunnel invert is made of C35 reinforced concrete with a thickness of 100 cm, and the rebar in the secondary lining uses 28 rebar as the main reinforcement, and the space is 20 cm.

[0081] When the large deformation grade of large-span tunnel in chlorite schist stratum is serious large-deformation, the aforesaid control measure can be used to avoid the clearance intrusion caused by tunnel deformation and to ensure the safety and stability of the tunnel support structure, and the cost is controllable.

[0082] When the large deformation grade of large-span tunnel in chlorite schist stratum is medium large-deformation, as shown in FIG. 5, the corresponding control measure for medium large-deformation is:

[0083] Construct advance support: carrying out advance support by using 50 double-row advance grouting pipe 1 with a length of 3.5 m and a circumferential space of 40 cm;

[0084] Set reserved deformation: set the value of reserved deformation to be 30-50 cm;

[0085] Excavate the tunnel: excavating the tunnel by the method of three steps with reserving core soil; in order to improve the stress condition of the tunnel invert, the distance from the bottom of the tunnel invert to the top surface of invert backfill is 3-4 m;

[0086] Construct primary support: double-layer primary supports are carried out in turn for the arch and side wall of the tunnel, that is, carry out the first-layer primary support and then the second-layer primary support when the reserved deformation has a remaining of 15-25 cm; and the single-layer primary support is used in the tunnel invert; the first-layer steel frame and the second-layer steel frame at the arch and side wall in the double-layer primary supports use HW175-type steel frame 8 with an interval of 80 cm, and each layer of steel frame is installed with a double-layer 8 steel mesh with the mesh space of 2020 cm; and the first layer of shotcrete and the second layer of shotcrete at the arch and side wall are made of C25 shotcrete 3 with a thickness of 28 cm; and the parameters of primary support in the tunnel invert are the same with the parameters of the single-layer primary support at the arch and the side wall; and double-row 50 feet-lock pipes 4 with a length of 4 m are installed at the arch foot and the wall foot of the upper, middle and lower steps for the first-layer steel frame, and each truss of steel frame is installed with 24 feet-lock pipes; 89 feet-lock pipe 9 with a length of 6 m is installed for every two steel frames of the second layer at the arch foot and the wall foot of the middle and lower steps, as shown in FIG. 6 for the specific arrangement diagram, and a connection steel plate 6 with a thickness of 20 mm is welded firmly with the two neighboring steel frames so as to support the second-layer steel frame by 89 feet-lock pipe 9; when the second-layer primary support is done, 50 grouting pipe with a length of 4 m and a space of 1.51.5 m is used to carry out radial grouting reinforcement to the surrounding rock;

[0087] Construct secondary lining: the secondary lining is made of C35 reinforced concrete 7, and the thickness of the secondary lining at the arch, side wall and tunnel invert is 80 cm, and the rebar in the secondary lining uses 28 rebar as the main reinforcement, and the space is 20 cm.

[0088] When the large deformation grade of large-span tunnel in chlorite schist stratum is medium large-deformation, the aforesaid control measure can be used to avoid the clearance intrusion caused by tunnel deformation and to ensure the safety and stability of the tunnel support structure, and the cost is controllable.

[0089] When the large deformation grade of large-span tunnel in chlorite schist stratum is slight large-deformation, as shown in FIG. 7, the corresponding control measure for slight large-deformation is:

[0090] Construct advance support: carrying out advance support by using 50 double-row advance grouting pipe 1 with a length of 3.5 m and a circumferential space of 40 cm;

[0091] Set reserved deformation: set the value of reserved deformation to be 20-30 cm;

[0092] Excavate the tunnel: excavating the tunnel by the method of three steps with reserving core soil; in order to improve the stress condition of the tunnel invert, the distance from the bottom of the tunnel invert to the top surface of invert backfill is 2.5-3 m;

[0093] Construct primary support: the arch, single-layer primary support is carried out for the arch, side wall and invert of the tunnel, wherein the primary support uses HK200b-type steel frame 2 with an interval of 80 cm and C25 shotcrete 3 with a thickness of 28 cm, and the steel frame is set with a double-layer 8 steel mesh with the mesh space of 2020 cm; and double-row 50 feet-lock pipes 4 with a length of 4 m are installed at the arch foot and the wall foot of the upper, middle and lower steps, and each truss of steel frame is installed with 24 feet-lock pipes; as for the replaced or twisted part of the steel frame, 50 grouting pipe with a length of 4 m and a space of 1.51.5 m is used to carry out radial grouting reinforcement to the surrounding rock;

[0094] Construct secondary lining: the secondary lining is made of C35 reinforced concrete 7, and the thickness of the secondary lining at the arch, side wall and tunnel invert is 70 cm, and the rebar in the secondary lining uses 25 rebar as the main reinforcement, and the space is 20 cm.

[0095] When the large deformation grade of large-span tunnel in chlorite schist stratum is slight large-deformation, the aforesaid control measure can be used to avoid the clearance intrusion caused by tunnel deformation and to ensure the safety and stability of the tunnel support structure, and the cost is controllable.

[0096] When the large deformation grade of large-span tunnel in chlorite schist stratum is zero large-deformation, as shown in FIG. 8, the corresponding control measure for zero large-deformation is:

[0097] Construct advance support: carrying out advance support by using 50 double-row advance grouting pipe 1 with a length of 3.5 m and a circumferential space of 40 cm;

[0098] Set reserved deformation: set the value of reserved deformation to be 10-20 cm;

[0099] Excavate the tunnel: excavating the tunnel by the method of three steps with reserving core soil;

[0100] Construct primary support: the arch, single-layer primary support is carried out for the arch, side wall and invert of the tunnel, wherein the primary support uses HW175-type steel frame 8 with an interval of 100 cm and C25 shotcrete 3 with a thickness of 28 cm, and the steel frame is set with a single-layer 8 steel mesh with the mesh space of 2020 cm; and double-row 50 feet-lock pipes 4 with a length of 4 m are installed at the arch foot and the wall foot of the upper, middle and lower steps, and each truss of steel frame is installed with 24 feet-lock pipes;

[0101] Construct secondary lining: the secondary lining is made of C35 reinforced concrete 10, and the thickness of the secondary lining at the arch, side wall and tunnel invert is 60 cm, and the rebar in the secondary lining uses 25 rebar as the main reinforcement, and the space is 20 cm.

[0102] When the large deformation grade of large-span tunnel in chlorite schist stratum is zero large-deformation, the aforesaid control measure can be used to avoid the clearance intrusion caused by tunnel deformation and to ensure the safety and stability of the tunnel support structure, and the cost is controllable.