CN110318772B - Large-span small-clearance asymmetric section tunnel supporting structure in loess area and construction method - Google Patents
Large-span small-clearance asymmetric section tunnel supporting structure in loess area and construction method Download PDFInfo
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- 238000010276 construction Methods 0.000 title claims abstract description 55
- 239000011435 rock Substances 0.000 claims abstract description 32
- 238000009412 basement excavation Methods 0.000 claims abstract description 27
- 238000000034 method Methods 0.000 claims abstract description 26
- 229910000831 Steel Inorganic materials 0.000 claims description 56
- 239000010959 steel Substances 0.000 claims description 56
- 239000004567 concrete Substances 0.000 claims description 14
- 239000004568 cement Substances 0.000 claims description 9
- 230000002787 reinforcement Effects 0.000 claims description 8
- 239000002002 slurry Substances 0.000 claims description 8
- 239000011150 reinforced concrete Substances 0.000 claims description 4
- 230000003014 reinforcing effect Effects 0.000 claims description 4
- 238000010009 beating Methods 0.000 claims description 2
- 238000005192 partition Methods 0.000 description 3
- 239000002689 soil Substances 0.000 description 3
- 230000009286 beneficial effect Effects 0.000 description 2
- 230000009191 jumping Effects 0.000 description 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 2
- 241000272814 Anser sp. Species 0.000 description 1
- WSNMPAVSZJSIMT-UHFFFAOYSA-N COc1c(C)c2COC(=O)c2c(O)c1CC(O)C1(C)CCC(=O)O1 Chemical compound COc1c(C)c2COC(=O)c2c(O)c1CC(O)C1(C)CCC(=O)O1 WSNMPAVSZJSIMT-UHFFFAOYSA-N 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000005553 drilling Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000005086 pumping Methods 0.000 description 1
- 239000011378 shotcrete Substances 0.000 description 1
- 239000007921 spray Substances 0.000 description 1
- 238000005507 spraying Methods 0.000 description 1
- 239000004575 stone Substances 0.000 description 1
Classifications
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- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21D—SHAFTS; TUNNELS; GALLERIES; LARGE UNDERGROUND CHAMBERS
- E21D11/00—Lining tunnels, galleries or other underground cavities, e.g. large underground chambers; Linings therefor; Making such linings in situ, e.g. by assembling
- E21D11/04—Lining with building materials
- E21D11/10—Lining with building materials with concrete cast in situ; Shuttering also lost shutterings, e.g. made of blocks, of metal plates or other equipment adapted therefor
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- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21D—SHAFTS; TUNNELS; GALLERIES; LARGE UNDERGROUND CHAMBERS
- E21D11/00—Lining tunnels, galleries or other underground cavities, e.g. large underground chambers; Linings therefor; Making such linings in situ, e.g. by assembling
- E21D11/14—Lining predominantly with metal
- E21D11/15—Plate linings; Laggings, i.e. linings designed for holding back formation material or for transmitting the load to main supporting members
- E21D11/152—Laggings made of grids or nettings
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- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21D—SHAFTS; TUNNELS; GALLERIES; LARGE UNDERGROUND CHAMBERS
- E21D11/00—Lining tunnels, galleries or other underground cavities, e.g. large underground chambers; Linings therefor; Making such linings in situ, e.g. by assembling
- E21D11/14—Lining predominantly with metal
- E21D11/28—Longitudinal struts, i.e. longitudinal connections between adjoining arches
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- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21D—SHAFTS; TUNNELS; GALLERIES; LARGE UNDERGROUND CHAMBERS
- E21D19/00—Provisional protective covers for working space
- E21D19/04—Provisional protective covers for working space for use in drifting galleries
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- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21D—SHAFTS; TUNNELS; GALLERIES; LARGE UNDERGROUND CHAMBERS
- E21D9/00—Tunnels or galleries, with or without linings; Methods or apparatus for making thereof; Layout of tunnels or galleries
- E21D9/14—Layout of tunnels or galleries; Constructional features of tunnels or galleries, not otherwise provided for, e.g. portals, day-light attenuation at tunnel openings
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- Geochemistry & Mineralogy (AREA)
- Geology (AREA)
- Architecture (AREA)
- Structural Engineering (AREA)
- Civil Engineering (AREA)
- Environmental & Geological Engineering (AREA)
- Lining And Supports For Tunnels (AREA)
- Excavating Of Shafts Or Tunnels (AREA)
Abstract
The invention discloses a large-span small-clearance asymmetric section tunnel supporting structure in loess areas and a construction method thereof. The invention adopts the construction sequence of firstly excavating a large section and then excavating a small section, wherein the large section is excavated by adopting a double-side-wall pilot pit method, and the small section is excavated by adopting a two-step method. Reasonable excavation sequence and supporting structure are selected, stability of surrounding rock in the tunnel excavation process is ensured, disturbance to the surrounding rock is reduced as much as possible, construction period and engineering cost are greatly shortened, and obvious economic benefit is created.
Description
Technical Field
The invention relates to the field of tunnel construction, in particular to a large-span small-clearance asymmetric section tunnel supporting structure in loess areas and a construction method.
Background
How to ensure the safety of construction and surrounding environment of loess tunnels with large span and small clear distance and asymmetric cross sections is important. The settlement control of tunnel construction is closely related to loess mechanical properties, and is also related to the excavation mode and the selection of a support system. In the limit of land utilization in the urbanization development process, the design scheme of a large-span small-spacing asymmetric section tunnel cannot be avoided, a left line tunnel and a right line tunnel belong to typical asymmetric sections, the distribution of surrounding rock stress is quite complex in the loess area in China, the width of a middle rock pillar between two-hole tunnels is smaller, the surrounding rock stress state is different from that of single tunnel excavation, the phenomenon of stress superposition generally occurs, and the serious subsidence of the earth surface is quite easily caused by improper control of supporting opportunity in the construction of a large span, and the safety of surrounding environment is impacted. The construction difficulty of the tunnel is greatly increased due to the reasons, so that the selection of reasonable excavation sequence and construction parameters is important for the engineering. Because the supporting system is easy to deform in the excavation process of the special bad geological phenomenon of the loess tunnel, the tunnel engineering has larger risk, and if the adopted supporting process is unreasonable, the collapse condition is easy to occur in the construction, thereby threatening the life safety of staff. According to the deformation characteristics of the loess tunnel, what construction method and supporting structure are adopted under the premise of ensuring construction and operation safety have the most economical efficiency, and the problems are needed to be solved at first.
Disclosure of Invention
Aiming at the problems, the invention aims to provide a supporting structure and a construction method for a large-span small-clearance asymmetric-section tunnel in a loess area, wherein a large-section adopts an advanced ramming pipe curtain pre-supporting structure, an initial supporting structure and a secondary lining structure, and a small-section adopts an advanced grouting supporting structure, a first-layer initial supporting structure, a second-layer initial supporting structure and a secondary lining structure, so that the key engineering problem of the large-span small-clearance asymmetric-section loess tunnel construction is solved according to the construction sequence of excavating the large-section first and then excavating the small-section.
In order to achieve the above purpose, the technical scheme adopted by the invention is as follows:
loess area is striden little clear distance asymmetric section tunnel supporting construction, its characterized in that: comprises a first supporting structure, a second supporting structure and a third supporting structure;
The first supporting structure is a supporting structure arranged on surrounding rock between a large section and a small section and comprises ground surface grouting reinforcement performed on the upper surface of the surrounding rock;
The second support structure is a support structure arranged on a large section and comprises an advanced ramming pipe curtain pre-support arranged on the inner surface of the large section, an initial support is covered on the inner surface of the advanced ramming pipe curtain pre-support, and a plurality of foot locking anchor pipes are arranged on the initial support; the large section is divided into six areas by a double-side-wall pilot pit method, namely an upper left area, a lower left area, an upper middle area, a lower middle area, an upper right area and a lower right area, and an intermediate wall is arranged between every two adjacent areas; after the large section is constructed into a ring, a secondary lining is further arranged at the arch wall;
The third supporting structure is a supporting structure arranged on a small section and comprises an advance small-catheter supporting structure arranged on the inner surface of the small section, an initial supporting structure and a second layer of initial supporting structure are covered on the inner surface of the advance small-catheter supporting structure, and a plurality of foot locking anchor pipes are also arranged on the initial supporting structure and the second layer of initial supporting structure; and after the small section is constructed into a ring, a secondary lining is also arranged at the arch wall.
Further, the first supporting structure further comprises two side wall arch supports arranged at the bottom of the surrounding rock, one side wall arch support is arranged along the inner side wall with the large section, the other side wall arch support is arranged along the inner side wall with the small section, and the two side wall arch supports are rigidly connected through at least 3 pull rods.
Preferably, the side wall arch support is no more than 1/4 of the corresponding section circumference.
Further, the primary support comprises a steel bar net paved along a section, concrete is sprayed on the steel bar net, the periphery of the section is supported by arranging a steel frame, the steel frame is connected longitudinally and firmly, and the steel frame is fixed to form an integral stress structure; and a foot locking anchor pipe is arranged on the upper part of the arch foot of the steel frame in a beating mode, and the foot locking anchor pipe is fixedly connected with the steel frame.
Preferably, the secondary lining adopts a reinforced concrete structure.
Further, the construction method of the large-span small-clearance asymmetric section tunnel supporting structure in the loess area is characterized by comprising the following steps of:
Dividing the large cross section into six areas, namely an upper left area, a lower left area, an upper middle area, a lower middle area, an upper right area and a lower right area, according to the structures of the large cross section and the small cross section; dividing the small section into an upper portion and a lower portion;
step two, before tunnel excavation, grouting and reinforcing surrounding rocks between the tunnels with small clear distances on the earth surface;
thirdly, adopting a side wall arch support for the bottom of the surrounding rock between the tunnels with small clear distance;
step four, pre-supporting the large cross section by using an advanced ramming pipe curtain;
excavating an upper left area and an upper right area of a large section, and constructing an initial support and an intermediate wall;
excavating a left lower area and a right lower area of a large section, and constructing an initial support and an intermediate wall;
Step seven, excavating a middle and upper area with a large section, and constructing an initial support and an intermediate wall;
step eight, excavating a middle-lower area with a large section, and constructing an inverted arch primary support;
Step nine, performing secondary lining construction on the arch wall with the large section;
Step ten, carrying out advanced small catheter support on the small section;
step eleven, excavating the upper part of the small section and performing primary support;
twelve, excavating the lower part of the small section, and constructing an inverted arch primary support;
Thirteenth, performing a second layer of primary support on the small section;
fourteen, carrying out secondary lining construction on the small section.
Preferably, in the fifth to eighth steps, when the left upper region, the left lower region, the middle upper region, the middle lower region, the right upper region and the right lower region of the large section are excavated, the excavation surface of each pilot tunnel is staggered for 4-6 m distance, and the excavation footage is not more than 1 steel frame interval at one time.
Preferably, cement slurry is adopted for grouting in the step ten advanced small conduit supporting process, the grouting sequence is from outside to inside, and the grouting method is interval grouting.
Preferably, the cement slurry has a water to cement ratio of 1:1.
Preferably, the distance between the inverted arch primary support and the tunnel face in the tunnel digging process in the eighth step and the twelfth step is not more than 15m, and the distance between the secondary lining and the tunnel face is not more than 40m, so that the stability of the support is ensured.
The beneficial effects of the invention are as follows:
Compared with the prior art, the invention has the advantages that the advanced pre-support is arranged, the primary support with higher rigidity is adopted and is timely closed, the reasonable construction method is adopted, the secondary lining is timely applied, and the like, which are effective measures for controlling deformation and ensuring the construction and operation safety. The supporting structure is suitable for shallow buried small clear distance asymmetric section tunnels in loess areas, can better control primary support deformation and construction risks, and ensures construction safety.
The method adopts the construction sequence of firstly excavating a large section and then excavating a small section, the large section is excavated by adopting a double-side-wall pilot pit method, the small section is excavated by adopting a two-step method, a reasonable excavation sequence is selected, the stability of surrounding rocks in the tunnel excavation process is ensured, the disturbance to the surrounding rocks is reduced as much as possible, the construction period and the engineering cost are greatly shortened, the rapid and safe construction technology of loess tunnels for reducing the disturbance to soil by short excavation and rapid circulation is formed, the construction period is greatly shortened, and obvious economic benefits are created.
Drawings
FIG. 1 is a schematic diagram of a construction support structure of a large-span small-clearance asymmetric section tunnel of the invention;
FIG. 2 is a schematic view of a large-section construction support structure according to the present invention;
FIG. 3 is a schematic view of a small section construction support structure of the present invention;
wherein: 1-large section, 2-small section, 3-surrounding rock, 4-ground grouting reinforcement, 5-advanced ramming pipe curtain pre-support, 6-primary support, 7-foot locking anchor pipe, 8-intermediate wall, 9-advanced small guide pipe support, 10-second layer primary support, 11-secondary lining, 12-side wall arch support and 13-pull rod.
Detailed Description
In order to enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention is further described below with reference to the accompanying drawings and examples.
Referring to fig. 1-3, the loess area large-span small-clearance asymmetric section tunnel supporting structure comprises a supporting structure I, a supporting structure II and a supporting structure III;
The first supporting structure is used for supporting the surrounding rock 3 between the large section 1 and the small section 2 and comprises surface grouting reinforcement 4 which is carried out on the surface of the surrounding rock 3 and two side wall arch supports 12 which are arranged at the bottom of the surrounding rock 3, wherein the two side wall arch supports 12 are rigidly connected by using at least 3 pull rods 13;
Preferably, one of the side wall arch supports 12 is disposed along the inner side wall of the large section 1, and the other of the side wall arch supports 12 is disposed along the side wall of the small section inner section 2;
Preferably, the sidewall arch support 12 is no more than 1/4 the corresponding section perimeter.
The second support structure is a support arranged on the large section 1 and comprises an advanced ramming pipe curtain pre-support 5 arranged on the inner surface of the large section 1, an initial support 6 is covered on the inner surface of the advanced ramming pipe curtain pre-support 5, and a plurality of foot locking anchor pipes 7 are arranged on the initial support 6; the large section 1 is divided into six areas by a double-side-wall pilot pit method, namely an upper left area, a lower left area, an upper middle-upper area, a lower middle area, an upper right area and a lower right area, and an intermediate wall 8 is arranged between every two adjacent areas; after the large section 1 is constructed into a ring, a secondary lining 11 is arranged at the arch wall;
Further, the primary support 6 is positioned at the middle position of the advanced ramming pipe curtain pre-support 5 and the secondary lining 11;
Preferably, the annular length of the pre-support 5 of the advanced ramming pipe curtain is 1/2 of the circumference of the large section 1;
preferably, the length of the primary support 6 is identical to the length of the pre-support 5 of the pre-tamper pipe curtain or the side wall surrounding the whole large section 1.
The third support structure is a support arranged on the small section 3 and comprises a small advance pipe support 9 arranged on the inner surface of the small section 2, the inner surface of the small advance pipe support 9 is covered with an initial support 6 and a second layer of initial support 10, and a plurality of foot locking anchor pipes 7 are also arranged on the initial support 6 and the second layer of initial support 10; after the small section 2 is constructed into a ring, a secondary lining 11 is also arranged at the arch wall.
Furthermore, when the large section 1 is separated, a double-side wall pilot tunnel method is adopted, and the principle is that the whole large section of the tunnel is divided into 3 small sections for construction by using two middle walls, wherein the left pilot tunnel and the right pilot tunnel go first, and the middle section is immediately behind the left pilot tunnel and the right pilot tunnel; and after the primary support inverted arch is looped, removing temporary supports of guide holes at two sides to form a full section. The guide holes on two sides are inverted goose egg-shaped, which is beneficial to controlling the vault sinking.
Furthermore, an up-down step method is adopted when the small sections 2 are separated; the principle is that the section of the whole tunnel is divided into a plurality of layers in the tunnel excavation process, the tunnel is excavated from top to bottom or from bottom to top, and the front-back distance of the excavated surface of each layer is smaller to form a plurality of steps.
Further, the primary support 6 comprises phi 8 steel reinforcement meshes with the spacing of 15cm multiplied by 15cm which are paved immediately after the cavity is excavated, C25 concrete with the thickness of 35cm is sprayed on the steel reinforcement meshes, then I20a steel frames with the spacing of 0.6m are adopted for supporting, two rows of steel frames are connected firmly by phi 22 (with the diameter of 22 mm) steel bar pull rods longitudinally, the circumferential spacing is 1m, and after the steel frames are installed, the steel frames are fixed by anchor rod locks, so that an integral stress structure is formed. And a foot locking anchor pipe 7 is arranged at a position 50cm above the arch foot of the steel frame in a manner of clinging to two sides of the steel frame according to an inclined downward inclination angle of 45 degrees, and the foot locking anchor pipe 7 and the steel frame are firmly welded by adopting U-shaped steel bars.
Furthermore, in the excavation process, the large section 1 adopts a temporary transverse and vertical support system to sequentially support the excavation surface according to the excavation sequence of each part, so that the stability of surrounding rock is improved, and the construction safety is ensured. The middle support system adopts a profile steel horizontal and vertical support and a middle partition wall to spray concrete, and one side of the excavation outline is connected with a profile steel frame of the primary support 6 into a whole. After the primary support 6 is completed, the secondary lining 11 is constructed after the deformation of the surrounding rock 3 and the primary support 6 is substantially stabilized. Under the condition that deformation development of surrounding rock 3 is quickened or can not tend to be stabilized and potential safety hazards appear, measures of secondary lining 11 following and quickening secondary lining 11 are adopted to ensure tunnel structure and construction safety. The secondary lining 11 is constructed by adopting a full-section template trolley integral pouring process, the length of each cycle of the template trolley is 10.5m, concrete adopts a concrete conveying pump, and an inserted tamping tool is used for tamping.
Further, waterproof plates, waterproof cloths and water permeable pipelines are paved between the primary support 6 and the secondary lining 11 to serve as waterproof layers.
Preferably, considering the influence of the small section 2 of the post-construction on the large section 1 of the pre-construction, it is provided that the longitudinal distance between the pre-construction chamber and the post-construction tunnel is kept in the range of 25-40 m.
Further, the whole small section 2 is divided into two parts, and the excavation is performed in two steps. Immediately paving phi 8 steel meshes with the interval of 20cm multiplied by 20cm after the upper part is excavated, spraying C25 concrete with the thickness of 26cm on the steel meshes, arranging I20a steel frame with the interval of 0.6 m/truss, and arranging a foot locking anchor pipe 7 with the length of 6m at 45 degrees of the downward inclined angle of two sides of the steel frame at the arch foot of the steel frame, wherein the foot locking anchor pipe 7 and the steel frame are fixed by adopting U-shaped steel bars. Then the lower part is excavated, and the initial support 2 after the excavation is the same as the above. After the small section 2 is excavated and the primary support 2 is applied, a second layer of primary support 10 is adopted, phi 8 steel reinforcement meshes with the distance of 20cm multiplied by 20cm are paved, C25 concrete with the thickness of 21cm is sprayed on the steel reinforcement meshes, I18 steel frames are paved, the distance is 0.6 m/truss, foot locking anchor pipes 7 with the length of 6m are arranged at arch feet of the steel frames and cling to two sides of the steel frames at an inclined downward inclination angle of 45 degrees, and the foot locking anchor pipes 7 and the steel frames are fixed by adopting U-shaped steel bars.
The construction method of the loess area large-span small-clear-distance asymmetric section tunnel supporting structure comprises the following steps:
Dividing the large cross section into six areas, namely an upper left area, a lower left area, an upper middle area, a lower middle area, an upper right area and a lower right area, according to the structures of the large cross section and the small cross section, and dividing the small cross section into an upper part and a lower part;
And step two, before excavation, grouting and reinforcing the surrounding rock between the tunnels with small clear distance by adopting the earth surface, adopting phi 42 hot-rolled seamless steel pipes as grouting pipes, and arranging quincuncial holes with the wall thickness of 3.2mm and the drilling spacing of 1.2 m. The slurry adopts 1:1 cement-water glass double-slurry, and the grouting pressure is 0.3-0.5 Mpa;
And thirdly, after grouting and reinforcing the earth surface of the surrounding rock, carrying out side arch support on the bottom of the surrounding rock, respectively arranging side wall arch supports on the inner side of the large section and the inner side of the small section, and carrying out support by driving phi 8 steel bar meshes along the sections, wherein the lengths of the side wall arch supports are respectively 1/4 of the circumferences of the large section and the small section, and the two side wall arch supports are connected by 3 pull rods 13 bolts. After each section of tunnel is excavated, the non-excavated part is subjected to side wall arch support, and a pull rod for connecting the two side wall arch supports is required to penetrate through surrounding rock, so that the rock pillar in the middle of the large-section tunnel and the small-section tunnel is prevented from being unstable and collapsed due to the through phenomenon, the constraint force of the arch can be utilized by using the side wall arch support, and the rock pillar in the middle of the section tunnel and the small-section tunnel is ensured to be unstable and deformed even if the rock pillar is in the whole.
Step four, tamping a pipe curtain forepoling, namely sequentially tamping a steel pipe with phi 500mm with a connecting guide device into the longitudinal direction of the tunnel along the contour line of the tunnel; and after the steel pipe is rammed through, the soil in the pipe is pressed out by wind pressure, and then fine stone concrete is injected into the steel pipe in an internal pressure mode to form the horizontal steel pipe concrete pile. Each concrete filled steel tube pile forms a concrete filled steel tube pile curtain under the connection of the guide connecting device;
Excavating an upper left area and an upper middle area of a large section, and constructing an initial support and an intermediate wall; excavating a cavity by adopting a small excavator, excavating soil bodies of an upper left area and an upper middle area, timely constructing an initial support, and excavating a footage of 0.6m;
Excavating a left lower area and a right lower area of a large section, and constructing an initial support and an intermediate wall; mechanically excavating a left lower area and a right lower area, which are timely applied as primary supports, and excavating a footage of 0.6m;
Step seven, excavating a middle upper area with a large section, and constructing an initial support and a middle partition plate; the upper region is excavated mechanically, and the primary support is timely applied. Lengthening the transverse support to the right side to form a complete middle support system with the middle partition wall, and excavating a footage of 0.6m;
step eight, excavating a middle-lower area with a large section, and constructing an inverted arch primary support; mechanically excavating a middle-lower area, mixing an inverted arch and backfilled concrete in a mixing field, pumping by a conveying pump, then tamping by an inserted vibrator, timely constructing an inverted arch primary support, completing filling of the inverted arch concrete after inverted arch construction, and forming a ring early;
Step nine, carrying out secondary lining construction on a large section; the secondary lining adopts a C35 reinforced concrete structure, the circumferential direction of lining steel bars adopts phi 22@20cm (the nominal diameter is 22mm, the distance is 20 cm), the longitudinal direction adopts phi 14@20cm, and the stirrups adopt phi 8@20cm;
Step ten, carrying out advanced small catheter support on the small section; the arch part is provided with a phi 42 advance small guide pipe and pre-grouting cement slurry, the wall thickness of the guide pipe grouting seamless steel pipe is 4mm, the diameter is 42mm, the length is 3.5m, the circumferential spacing is 40cm, and the longitudinal spacing is 1.8 m/ring. Grouting adopts cement slurry with water-cement ratio of 1:1, grouting pressure is set to be 0.5-3MPa, grouting sequence is from outside to inside, and grouting method is interval grouting;
Step eleven, excavating the upper part of the small section and performing primary support; after arch advanced support is completed, small-sized machinery is adopted to excavate the upper part of the small section, the width of an upper step is controlled to be about 3m, the height from a vault is easily controlled to be about 2.5m, primary support is timely applied, and the excavation circulation footage is 1m;
Twelve, excavating the lower part of the small section, and constructing an inverted arch primary support; the distance between the upper step and the lower step is kept at 4-5m, the length of the lower step is controlled at about 9m, when the lower step is excavated, the left and right lower steps are excavated by adopting a middle pulling groove and a horse jumping opening, the horse jumping openings are staggered at the left side and the right side, and the length of the horse opening is controlled at two arch frames. The primary support is timely applied after excavation, channel steel is padded at the bottom of the steel frame, excavation, support and inverted arch lining of the inverted arch are needed to be completed by one-time application, looping is carried out early, and the length of each cycle of excavation footage can be controlled to be 4-6m;
Thirteenth, performing a second layer of primary support on the small section;
Fourteen, performing secondary lining construction on the small section; the reinforced concrete structure is adopted, the circumferential direction of lining reinforced bars is phi 22@20cm, the longitudinal direction is phi 14@20cm, and stirrups are phi 8@20cm.
When the tunnel is supported in the initial stage, the shotcrete is closely filled in time after the steps and parts are followed in the supporting process, the metal net and the steel arch support are closely attached to surrounding rocks, no gap is reserved at the back, arch springing must be placed on a firm foundation and firmly locked by the pin locking anchor rod, and the initial stage supporting should be sealed into a ring in time.
The foregoing has shown and described the basic principles, principal features and advantages of the invention. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, and that the above embodiments and descriptions are merely illustrative of the principles of the present invention, and various changes and modifications may be made without departing from the spirit and scope of the invention, which is defined in the appended claims. The scope of the invention is defined by the appended claims and equivalents thereof.
Claims (7)
1. Loess area is striden little clear distance asymmetric section tunnel supporting construction, its characterized in that: comprises a first supporting structure, a second supporting structure and a third supporting structure;
The first supporting structure is a supporting structure arranged on the surrounding rock (3) between the large section (1) and the small section (2), and comprises earth surface grouting reinforcement (4) carried out on the upper surface of the surrounding rock (3);
The second support structure is a support structure arranged on the large section (1), and comprises an advanced ramming pipe curtain pre-support (5) arranged on the inner surface of the large section (1), an initial support (6) is covered on the inner surface of the advanced ramming pipe curtain pre-support (5), and a plurality of foot locking anchor pipes (7) are arranged on the initial support (6); the large section (1) is divided into six areas by a double-side-wall pilot pit method, namely an upper left area, a lower left area, an upper middle area, a lower middle area, an upper right area and a lower right area, and an intermediate wall (8) is arranged between every two adjacent areas; after the large section (1) is constructed into a ring, a secondary lining (11) is further arranged at the arch wall;
The third supporting structure is a supporting structure arranged on the small section (2) and comprises an advance small-conduit supporting structure (9) arranged on the inner surface of the small section (2), an initial supporting structure (6) and a second-layer initial supporting structure (10) are covered on the inner surface of the advance small-conduit supporting structure (9), and a plurality of foot locking anchor pipes (7) are also arranged on the initial supporting structure (6) and the second-layer initial supporting structure (10); after the small section (2) is constructed into a ring, a secondary lining (11) is also arranged at the arch wall;
The first supporting structure also comprises two side wall arch supports (12) arranged at the bottom of the surrounding rock (3), wherein one side wall arch support (12) is arranged along the inner side wall of the large section (1), the other side wall arch support (12) is arranged along the inner side wall of the small section (2), and the two side wall arch supports (12) are rigidly connected by using at least 3 pull rods (13);
The size of the side wall arch support (12) is not more than 1/4 of the circumference of the corresponding section;
The primary support (6) comprises a steel bar net paved along a section, concrete is sprayed on the steel bar net, the periphery of the section is supported by arranging a steel frame, the steel frame is connected longitudinally and firmly, and the steel frame is fixed to form an integral stress structure; and a foot locking anchor pipe (7) is arranged on the upper part of the arch foot of the steel frame in a beating mode, and the foot locking anchor pipe (7) is fixedly connected with the steel frame.
2. The loess area large-span small-clearance asymmetric section tunnel supporting structure according to claim 1, wherein: the secondary lining (11) adopts a reinforced concrete structure.
3. The construction method of the loess area large-span small-clearance asymmetric section tunnel supporting structure as set forth in claim 1 or 2, characterized by comprising the steps of:
Dividing the large cross section into six areas, namely an upper left area, a lower left area, an upper middle area, a lower middle area, an upper right area and a lower right area, according to the structures of the large cross section and the small cross section; dividing the small section into an upper portion and a lower portion;
step two, before tunnel excavation, grouting and reinforcing surrounding rocks between the tunnels with small clear distances on the earth surface;
thirdly, adopting a side wall arch support for the bottom of the surrounding rock between the tunnels with small clear distance;
step four, pre-supporting the large cross section by using an advanced ramming pipe curtain;
excavating an upper left area and an upper right area of a large section, and constructing an initial support and an intermediate wall;
excavating a left lower area and a right lower area of a large section, and constructing an initial support and an intermediate wall;
Step seven, excavating a middle and upper area with a large section, and constructing an initial support and an intermediate wall;
step eight, excavating a middle-lower area with a large section, and constructing an inverted arch primary support;
Step nine, performing secondary lining construction on the arch wall with the large section;
Step ten, carrying out advanced small catheter support on the small section;
step eleven, excavating the upper part of the small section and performing primary support;
twelve, excavating the lower part of the small section, and constructing an inverted arch primary support;
Thirteenth, performing a second layer of primary support on the small section;
fourteen, carrying out secondary lining construction on the small section.
4. The construction method of the loess area large-span small-clearance asymmetric section tunnel supporting structure according to claim 3, wherein the construction method is characterized by comprising the following steps: and step five to step eight, when the left upper region, the left lower region, the middle upper region, the middle lower region, the right upper region and the right lower region of the large section are excavated, the excavation surfaces of each pilot tunnel are staggered by a distance of 4-6 m, and the excavation footage is not more than 1 steel frame interval at one time.
5. The construction method of the loess area large-span small-clearance asymmetric section tunnel supporting structure according to claim 3, wherein the construction method is characterized by comprising the following steps: cement slurry is adopted for grouting in the ten-lead small-conduit supporting process, the grouting sequence is from outside to inside, and the grouting method is interval grouting.
6. The construction method of the loess area large-span small-clearance asymmetric section tunnel supporting structure according to claim 5, which is characterized by comprising the following steps: the cement slurry has a water-cement ratio of 1:1.
7. The construction method of the loess area large-span small-clearance asymmetric section tunnel supporting structure according to claim 3, wherein the construction method is characterized by comprising the following steps: and step eight and step twelve, the distance between the inverted arch primary support and the tunnel face in the tunnel digging process is not more than 15m, and the distance between the secondary lining and the tunnel face is not more than 40m, so that the stability of the support is ensured.
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