Double-side-wall pilot tunnel excavation method for shallow-buried extremely-soft rock tunnel and tunnel supporting structure

Abstract

The invention relates to a double-side-wall pilot tunnel excavation method for a shallow-buried extremely-soft rock tunnel and a tunnel supporting structure, the cross section of the tunnel is divided into a first part, a second part, a third part, a fourth part, a fifth part, a sixth part, a seventh part and an eighth part, regional small-range excavation is carried out, different regions are alternately and sequentially excavated, and the tunnel supporting structure is formed. The influence on the stability of a stratum soil body can be minimized, disturbance to surrounding rocks is reduced as much as possible, the peripheral contour is smooth, and stress concentration is avoided; therefore, landslide and even collapse of the stratum soil body are effectively prevented, tunnel construction safety is guaranteed, and personal injury to constructors and potential property loss hidden dangers to equipment are eliminated.

Description

Technical Field

[0001] The present application relates to the technical field of tunnel construction, and in particular to a double-side wall pilot pit excavation method and a tunnel support structure for a shallow buried extremely soft rock tunnel. Background Art

[0002] Tunnels are engineering structures buried in the ground, and are a form of human use of underground space. According to their uses, tunnels can be divided into traffic tunnels, municipal tunnels, military tunnels, etc. In an environment with complex geological conditions, the surface of the tunnel is Quaternary volcanic deposited clay soil, with a thick soil layer, relatively loose soil, high water content, and a large porosity. The original soil layer has a certain structural strength. After the soil is exposed to water and disturbed, its properties deteriorate significantly, and it has special characteristics. After the excavation of the expansive mudstone tunnel, the surrounding rock excavation stress release process, exposure to air and saturation state will cause the surrounding rock cohesion, internal friction angle and strength to decrease sharply, which is manifested in cracking and disintegration after water loss. If it encounters water seepage, it will soften into mud. The above two situations will cause the surrounding rock to lose stability. During the construction process, it is mainly manifested in face collapse, arch settlement, cracking of the initial support, and large deformation.

[0003] For large-span tunnels with great surrounding rock pressure and unstable strata, if conventional tunnel excavation methods are used, the lack of effective support for the stratum soil will easily cause large deformation and collapse of the tunnel, posing a huge safety hazard to tunnel construction and threatening the personal safety of construction workers and the safety of equipment and property. Summary of the invention

[0004] Based on this, it is necessary to provide a double-side wall pilot pit excavation method and tunnel support structure for shallow buried extremely soft rock tunnels in order to address the safety hazards of conventional tunnel excavation methods.

[0005] In a first aspect of the present application, a double-sidewall pilot pit excavation method for a shallow extremely soft rock tunnel is provided, wherein the cross section of the tunnel is divided into a first part, a second part, a third part, a fourth part, a fifth part, a sixth part, a seventh part and an eighth part, comprising the following steps:

[0006] Excavate the first part, advance one frame per cycle, and close the side wall, primary arch frame and temporary cross brace in time after excavation;

[0007] The first and second parts are excavated alternately, and two frames are excavated in each cycle of the second part. After excavation, the primary arch frame is connected with the steel pipe pile, and the side wall, primary arch frame and temporary invert are closed in time. After closing, the corresponding temporary cross brace in the first part is removed;

[0008] After the first part has advanced 3.6m and has been excavated normally, the third and fourth parts will be constructed. The construction sequence is the same as that of the first and second parts.

[0009] After the third section is 3.6m advanced, the fifth section middle trench is excavated, one frame per cycle, and the primary arch frame connecting plates are arranged in a staggered manner. After the fifth section is excavated for 3m, the sixth section is excavated on steps, and a temporary invert is constructed at the bottom of the sixth section. After the temporary invert is closed with the primary arch frame, the corresponding pilot pit side wall is dismantled 3m behind the closed loop position of the sixth section;

[0010] The seventh part of the lower step is excavated 9m after the closed loop of the temporary inverted arch. The left and right sides are alternately excavated at the bottom of the temporary inverted arch. The arch foot is welded with a bracket structure. The primary arch frame is connected to the steel pipe pile through the bracket structure. The temporary inverted arch of the corresponding mileage is dismantled according to the settlement situation.

[0011] After 3m of the seventh part, the eighth part is excavated manually with the cooperation of machinery. The initial arch frame is closed into a ring and each cycle is constructed for 3m. After 2 cycles of construction, the invert lining and filling construction are carried out in time.

[0012] When the excavation method of this scheme is used to construct a shallow buried extremely soft rock tunnel, the first part is excavated, and the advance is 1 frame per cycle. After excavation, the side wall, primary arch frame and temporary cross brace are closed in time; the first part and the second part are excavated alternately, and 2 frames are excavated per cycle of the second part. After excavation, the primary arch frame is connected with the steel pipe pile, and the side wall, primary arch frame and temporary invert are closed in time. After closing, the corresponding temporary cross brace in the first part is removed; after the first part advances 3.6m and is excavated normally, the third and fourth parts are started, and the construction sequence is the same as the first and second parts; after the third part advances 3.6m, five middle slots are excavated, and 1 frame per cycle is opened. The connecting plates of the primary arch frame are arranged alternately. A temporary invert is constructed at the bottom of the sixth part 3m after the fifth part. After the temporary invert is closed with the primary arch frame, the corresponding side wall of the pilot pit is removed 3m after the sixth part is closed. The seventh part of the lower step is excavated 9m after the closed loop of the temporary invert. Slots are dug alternately at the lower part of the temporary invert. The corbel structure is welded to the arch foot. The primary arch frame is connected to the steel pipe pile through the corbel structure. The temporary invert of the corresponding mileage is removed according to the settlement situation. 3m after the seventh part, the eighth part is excavated manually with the cooperation of machinery. The primary arch frame is closed into a ring and 3m is constructed each cycle. After 2 cycles of construction, the invert lining and filling construction are carried out in time. By excavating in small areas in different areas and excavating different areas alternately in sequence, the tunnel excavation section can be reduced, the impact on the stability of the stratum soil can be minimized, the disturbance to the surrounding rock can be minimized, the surrounding contour is smooth, and stress concentration is avoided; the addition of the steel pipe pile corbel structure increases the vertical bearing capacity and lateral earth pressure of the initial support arch foot; thereby effectively preventing the stratum soil from settling, deforming, or even collapsing, ensuring the safety of tunnel construction, and eliminating the risk of personal injury to construction personnel and potential property loss to equipment.

[0013] The technical solution of this application is further described below:

[0014] In one of the embodiments, in the step of excavating the first portion, advancing one frame per cycle, and closing the loop of the side wall, primary support arch frame and temporary cross brace after excavation, three longitudinally arranged I-beams are set between two adjacent primary support arch frames.

[0015] In one of the embodiments, the first part and the second part are excavated alternately, and two frames are excavated in each cycle of the second part. After excavation, the primary arch frame is connected to the steel pipe pile, and the side wall, the primary arch frame and the temporary invert are closed in time. After the closing, in the step of removing the corresponding temporary cross brace in the first part, two adjacent primary arch frame supports are provided with two longitudinally arranged I-beams.

[0016] In one embodiment, after the first part has advanced 3.6m and has been excavated normally, the construction of the third and fourth parts begins. The construction sequence is the same as that of the first and second parts. The step distance between the right guide pit formed by excavating the first and second parts and the left guide pit formed by excavating the third and fourth parts is controlled at 3m~5m.

[0017] In a second aspect of the present application, a tunnel support structure is further provided, which is applied to the construction of the double-sidewall pilot pit excavation method of the shallow buried extremely soft rock tunnel as described above, and the tunnel support structure comprises:

[0018] A first steel pipe pile and a second steel pipe pile, wherein the first steel pipe pile and the second steel pipe pile are arranged side by side and spaced apart in a transverse direction parallel to the ground, and the first steel pipe pile and the second steel pipe pile are arranged to extend vertically;

[0019] A primary steel arch, the primary steel arch being arranged between the first steel pipe pile and the second steel pipe pile;

[0020] A first connecting mechanism, which is disposed on a side of the first steel pipe pile facing the second steel pipe pile and is connected and fixed to one side of the primary supporting steel arch;

[0021] A second connecting mechanism, which is disposed on the side of the second steel pipe pile facing the first steel pipe pile and is connected and fixed to the other side of the primary supporting steel arch; and

[0022] A first supporting mechanism and a second supporting mechanism, wherein the first supporting mechanism is detachably disposed inside the primary supporting steel arch and arranged close to the first steel pipe piles, and the second supporting mechanism is detachably disposed inside the primary supporting steel arch and arranged close to the second steel pipe piles.

[0023] In one of the embodiments, the primary supporting steel arch is provided with a plurality of mounting holes along its arc-shaped extension direction, and each of the mounting holes is used for passing and installing an advance small conduit.

[0024] In one embodiment, the first connecting mechanism and the second connecting mechanism both include a first corbel structure, and the first corbel structure is connected and fixed to the arc-shaped outer wall of the primary supporting steel arch.

[0025] In one embodiment, the first connecting mechanism and the second connecting mechanism also include a second corbel structure, the second corbel structure is arranged below the first corbel structure at intervals, and the second corbel structure is connected and fixed to the arc-shaped outer wall of the primary supporting steel arch.

[0026] In one embodiment, the first supporting mechanism and the second supporting mechanism both include an arc-shaped support, a temporary cross brace and an inverted arch support, the opposite ends of the temporary cross brace are respectively connected to the primary supporting steel arch and the arc-shaped support, the opposite ends of the arc-shaped support are respectively connected to the primary supporting steel arch and the inverted arch support, and one end of the inverted arch support is connected to the primary supporting steel arch.

[0027] In one of the embodiments, the tunnel supporting structure further comprises a temporary invert, and the temporary invert is connected between two of the invert supports. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The drawings constituting a part of the present application are used to provide a further understanding of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application.

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0030] FIG1 is a flowchart showing the steps of a double-sidewall pilot pit excavation method for a shallow buried extremely soft rock tunnel according to an embodiment of the present invention.

[0031] FIG. 2 is a schematic structural diagram of a cross section of a tunnel excavation.

[0032] Description of reference numerals:

[0033] 100. Tunnel; 10a. First part; 10b. Second part; 10c. Third part; 10d. Fourth part; 10e. Fifth part; 10f. Sixth part; 10g. Seventh part; 10h. Eighth part; 20. First steel pipe pile; 30. Second steel pipe pile; 40. Primary steel arch; 50. First connecting mechanism; 50a. First corbel structure; 50b. Second corbel structure; 60. Second connecting mechanism; 70. First supporting mechanism; 70a. Arc support; 70b. Temporary cross brace; 70c. Inverted arch support; 80. Second supporting mechanism; 90. Temporary inverted arch. DETAILED DESCRIPTION

[0034] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are described in detail below in conjunction with the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present application. However, the present application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present application, so the present application is not limited by the specific embodiments disclosed below.

[0035] In the description of the present application, it should be understood that if the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. appear, the orientation or position relationship indicated by these terms is based on the orientation or position relationship shown in the accompanying drawings, which is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application.

[0036] In addition, if the terms "first" or "second" appear, these terms are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of the features. In the description of this application, if the term "plurality" appears, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0037] In this application, unless otherwise clearly specified and limited, if the terms "installed", "connected", "connected", "fixed" and the like appear, these terms should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integrated connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to the specific circumstances.

[0038] In the present application, unless otherwise clearly specified and limited, if there is a description that a first feature is "above" or "below" a second feature, etc., or similar descriptions appear, it may mean that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediate medium. Moreover, the first feature being "above", "above" and "above" the second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. The first feature being "below", "below" and "below" the second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0039] It should be noted that if an element is referred to as being "fixed to" or "disposed on" another element, it may be directly on the other element or there may be a central element. If an element is considered to be "connected to" another element, it may be directly connected to the other element or there may be a central element at the same time. If any, the terms "vertical", "horizontal", "upper", "lower", "left", "right" and similar expressions used in this application are for illustrative purposes only and do not represent the only implementation method.

[0040] Referring to FIG. 1 and FIG. 2 , a double-sidewall pilot pit excavation method for a shallow extremely soft rock tunnel 100 is shown in one embodiment of the present application. The cross section of the tunnel 100 is divided into a first part 10a, a second part 10b, a third part 10c, a fourth part 10d, a fifth part 10e, a sixth part 10f, a seventh part 10g and an eighth part 10h, and includes the following steps:

[0041] S10: Excavate the first part 10a, advance one frame per cycle, and close the side wall, primary arch frame and temporary cross brace 70b in time after excavation.

[0042] S20: The first part 10a and the second part 10b are excavated alternately, and two frames of the second part 10b are excavated in each cycle. After excavation, the primary arch frame is connected with the steel pipe piles, and the side wall, the primary arch frame and the temporary invert 90 are closed in time. After closing, the corresponding temporary cross brace 70b in the first part 10a is removed.

[0043] S30: After the first part 10a has been excavated to a depth of 3.6 m and is excavated normally, the third part 10c and the fourth part 10d are started to be constructed. The construction sequence is the same as that of the first part 10a and the second part 10b.

[0044] S40: After the third part 10c advances 3.6m, the middle trench is excavated, one frame per cycle, the primary support arch connecting plates are arranged alternately, and a temporary invert 90 is constructed at the bottom of the sixth part 10f. After the temporary invert 90 and the primary support arch form a loop of 3m, the corresponding pilot pit side wall is removed.

[0045] S50: Excavate the seventh part 10g of the lower step 9m after the closed loop of the temporary invert 90, dig grooves and excavate alternately at the lower part of the temporary invert 90, weld the corbel structure to the arch foot of the primary support steel frame, connect the primary support arch frame and the steel pipe pile through the corbel structure, and dismantle the temporary invert 90 of the corresponding mileage according to the settlement situation.

[0046] S60: After the seventh part is delayed by 10g3m, the eighth part is excavated manually with mechanical excavation for 10h. The initial arch frame is closed into a ring and 3m is constructed per cycle. After 2 cycles of construction, the invert lining and filling construction are carried out in time.

[0047] In summary, the implementation of the technical solution of this embodiment will achieve the following beneficial effects: when the excavation method of this solution is used to construct the shallow buried extremely soft rock tunnel 100, the first part 10a is excavated, and one frame is advanced in each cycle. After excavation, the side wall, the primary arch frame and the temporary cross brace 70b are closed in time; the first part 10a and the second part 10b are excavated alternately, and two frames are excavated in each cycle of the second part 10b. After excavation, the primary arch frame is connected with the steel pipe pile, and the side wall, the primary arch frame and the temporary invert 90 are closed in time. After closing, the corresponding temporary cross brace 70b in the first part 10a is removed; after the first part 10a has advanced 3.6m and is excavated normally, the third part 10c and the fourth part 10d are started to be constructed, and the construction sequence is the same as that of the first part 10a and the second part 10d. b is the same; after the third part 10c advances 3.6m, the middle trench is excavated, one frame per cycle, the primary arch frame connecting plates are arranged alternately, and a temporary invert 90 is constructed at the bottom of the sixth part 10f. After the temporary invert 90 and the primary arch frame are closed in a loop for 3m, the corresponding pilot pit side wall is removed; 9m after the temporary invert 90 is closed, the seventh part 10g of the lower step is excavated, and the grooves are alternately excavated at the lower part of the temporary invert 90. The primary steel frame arch foot is welded with a corbel structure, and the primary arch frame is connected to the steel pipe pile through the corbel structure. The temporary invert 90 of the corresponding mileage is removed according to the settlement situation; 3m after the seventh part 10g, the eighth part is excavated by manual and mechanical means for 10h, the primary arch frame is closed into a loop and constructed 3m per cycle. After 2 cycles of construction, the invert lining and filling construction are carried out in time. By excavating in small areas in different areas and excavating different areas alternately in sequence, the tunnel excavation section can be reduced, the impact on the stability of the stratum soil can be minimized, the disturbance to the surrounding rock can be minimized, the surrounding contour is smooth, and stress concentration is avoided; the addition of the steel pipe pile corbel structure increases the vertical bearing capacity and lateral earth pressure of the initial arch foot; thereby effectively preventing the stratum soil from settling, deforming, or even collapsing, ensuring the safety of Tunnel 100 construction, and eliminating the risk of personal injury to construction personnel and potential property loss to equipment.

[0048] In one embodiment, during the excavation of the first portion 10a, one frame is advanced per cycle, and the side wall, primary support arch frame and temporary cross brace 70b are closed in time after excavation, three longitudinally arranged I-beams are set between two adjacent primary support arch frames. The additional I-beams can effectively increase the connection strength of adjacent primary support arch frames to improve the overall support performance.

[0049] In one embodiment, the first part 10a and the second part 10b are excavated alternately, and the second part 10b is excavated 2 frames per cycle. After excavation, the primary arch frame is connected to the steel pipe pile, and the side wall, the primary arch frame and the temporary invert 90 are closed in time. After closing, in the step of removing the corresponding temporary cross brace 70b in the first part 10a, two adjacent primary arch frame brackets are provided with two longitudinally arranged I-beams. The additional I-beams can effectively increase the connection strength of adjacent primary arch frames to improve the overall support performance.

[0050] In one embodiment, after the first part 10a is excavated normally with a length of 3.6m, the third part 10c and the fourth part 10d are constructed, and the construction sequence is the same as that of the first part 10a and the second part 10b. The step distance between the right pilot pit formed by excavating the first part 10a and the second part 10b and the left pilot pit formed by excavating the third part 10c and the fourth part 10d is controlled to be 3m~5m. By controlling the step distance within the range of 3m~5m, the depth and spatial size of the excavated left and right pilot pits can be controlled to avoid excessive step distances in the pilot pits.

[0051] Please continue to refer to Figure 2. In the second aspect of the present application, a tunnel 100 support structure is also provided, which is applied to the construction of the double-side wall pilot pit excavation method of the shallow buried extremely soft rock tunnel 100 as described above. The tunnel 100 support structure includes a first steel pipe pile 20, a second steel pipe pile 30, a primary support steel arch 40, a first connecting mechanism 50, a second connecting mechanism 60, a first supporting mechanism 70 and a second supporting mechanism 80.

[0052] The first steel pipe piles 20 and the second steel pipe piles 30 are arranged side by side and spaced apart in a transverse direction parallel to the ground, and the first steel pipe piles 20 and the second steel pipe piles 30 are arranged to extend along the vertical direction.

[0053] According to actual needs, the cross-sections of the first steel pipe pile 20 and the second steel pipe pile 30 can be any one of circular, square and the like.

[0054] The lower ends of the first steel pipe pile 20 and the second steel pipe pile 30 should be inserted into the soil layer at the bottom of the tunnel to a sufficient depth, for example, a depth of 5 m to 8 m, to ensure the structural stability of the first steel pipe pile 20 and the second steel pipe pile 30 .

[0055] The primary support steel arch 40 is arranged between the first steel pipe pile 20 and the second steel pipe pile 30; the first connecting mechanism 50 is arranged on the side of the first steel pipe pile 20 facing the second steel pipe pile 30 and is connected and fixed to one side of the primary support steel arch 40; the second connecting mechanism 60 is arranged on the side of the second steel pipe pile 30 facing the first steel pipe pile 20 and is connected and fixed to the other side of the primary support steel arch 40; the first supporting mechanism 70 is detachably arranged inside the primary support steel arch 40 and arranged close to the first steel pipe pile 20, and the second supporting mechanism 80 is detachably arranged inside the primary support steel arch 40 and arranged close to the second steel pipe pile 30.

[0056] The tunnel 100 support structure formed by the cooperation of the first steel pipe pile 20, the second steel pipe pile 30, the primary support steel arch 40, the first connecting mechanism 50, the second connecting mechanism 60, the first supporting mechanism 70 and the second supporting mechanism 80 can be adapted to the construction needs of large deformation tunnels in expansive mudstone formations, and effectively support the stratum soil and tunnel structure of the side wall of the tunnel 100, thereby ensuring effective control of tunnel settlement and large deformation risks.

[0057] In another embodiment, the primary support steel arch 40 is provided with a plurality of mounting holes along its arc extension direction, and each mounting hole is used to penetrate and install an advance small conduit. The advance small conduit is a very effective auxiliary construction method for stabilizing the excavation working surface. In the construction of soft and broken rock formations, the advance small conduit plays a reinforcing role on the loose rock formations, and after grouting, the stability of the loose and weak surrounding rock is enhanced, which is conducive to the stability of the surrounding rock after the excavation is completed and during the initial support time, so as to prevent the surrounding rock from becoming unstable and damaged until it collapses.

[0058] Please continue to refer to FIG. 2 . In addition, based on any of the above embodiments, the first connecting mechanism 50 and the second connecting mechanism 60 both include a first corbel structure 50a, and the first corbel structure 50a is connected and fixed to the arc-shaped outer wall of the primary supporting steel arch 40. Further, the first connecting mechanism 50 and the second connecting mechanism 60 both include a second corbel structure 50b, and the second corbel structure 50b is arranged below the first corbel structure 50a at intervals, and the second corbel structure 50b is connected and fixed to the arc-shaped outer wall of the primary supporting steel arch 40.

[0059] By simultaneously connecting the primary steel arch 40 through the first corbel structure 50a and the second corbel structure 50b arranged at intervals up and down, two upper and lower connection limits can be formed, providing structural strength and position stability for the primary steel arch 40, and avoiding displacement of the primary steel arch 40 during soil excavation, thereby affecting construction accuracy.

[0060] Specifically, the first corbel mechanism is composed of a corbel, an enlarged arch foot and other components welded together. One end of the corbel is welded to the side walls of the first steel pipe pile 20 and the second steel pipe pile 30, and the end of the enlarged arch foot away from the corbel is welded and fixed to the outer wall of the primary supporting steel arch 40. The welded connection has high strength and good reliability, which helps to obtain better overall structural performance.

[0061] Please continue to refer to Figure 2. Both the first support mechanism 70 and the second support mechanism 80 include an arc support 70a, a temporary cross brace 70b and an inverted arch support 70c. The opposite ends of the temporary cross brace 70b are respectively connected to the primary steel arch 40 and the arc support 70a. The opposite ends of the arc support 70a are respectively connected to the primary steel arch 40 and the inverted arch support 70c. One end of the inverted arch support 70c is connected to the primary steel arch 40. The arc support 70a is respectively connected to the primary steel arch 40 and the inverted arch support 70c to form a vertical support function; the temporary cross brace 70b connects the primary steel arch 40 with the arc support 70a to form a lateral support function, thereby being able to form a reliable support and reinforcement for the stratum soil around the tunnel 100 to prevent collapse.

[0062] Furthermore, the tunnel 100 support structure further includes a temporary inverted arch 90, which is connected between the two inverted arch supports 70c. The installed temporary inverted arch 90 can form a lateral support reinforcement for the first support mechanism 70 and the second support mechanism 80 on the left and right sides, thereby further improving the overall structural stability of the tunnel 100 support structure.

[0063] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0064] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be construed as limiting the scope of the patent application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent application shall be subject to the attached claims.

Claims

1. A double-sidewall pilot pit excavation method for a shallow buried extremely soft rock tunnel, wherein the cross section of the tunnel is divided into a first part, a second part, a third part, a fourth part, a fifth part, a sixth part, a seventh part and an eighth part, characterized in that: The steps include: Excavate the first part, advance one frame per cycle, and close the side wall, primary arch frame and temporary cross brace in time after excavation; After the first part has advanced 3m, the second part is excavated. The first and second parts are excavated alternately. Two frames are excavated in each cycle of the second part. After excavation, the primary arch frame is connected with the steel pipe piles. The side wall, primary arch frame and temporary invert are closed in time. After closing, the corresponding temporary cross brace in the first part is removed. After the first part has advanced 3.6m and has been excavated normally, the third and fourth parts will be constructed. The construction sequence is the same as that of the first and second parts. After the third section is 3.6m advanced, the fifth section middle trench is excavated, one frame per cycle, and the primary support arch connecting plates are arranged alternately. After the fifth section is excavated for 3m, the sixth section is excavated on steps. A temporary invert is constructed at the bottom of the sixth section. After the temporary invert is closed with the primary support arch, the corresponding pilot pit side wall is removed 3m later. The seventh part of the lower step is excavated 9m after the closed loop of the temporary inverted arch. The left and right sides are alternately excavated at the bottom of the temporary inverted arch. The arch foot is welded with a bracket structure. The primary arch frame is connected to the steel pipe pile through the bracket structure. The temporary inverted arch of the corresponding mileage is dismantled according to the settlement situation. After 3m of the seventh part, the eighth part is excavated manually with the cooperation of machinery. The initial arch frame is closed into a ring and each cycle is constructed for 3m. After 2 cycles of construction, the invert lining and filling construction are carried out in time.

2. The double-sidewall pilot pit excavation method for a shallow buried extremely soft rock tunnel according to claim 1, characterized in that: In the step of excavating the first part, advancing one frame per cycle, and closing the loop of the side wall, primary support arch frame and temporary cross brace in time after excavation, three longitudinally arranged I-beams are set between two adjacent primary support arch frames.

3. The double-sidewall pilot pit excavation method for a shallow buried extremely soft rock tunnel according to claim 1, characterized in that: The first part and the second part are excavated alternately, and two frames are excavated in each cycle of the second part. After excavation, the primary arch frame is connected to the steel pipe pile side wall, the primary arch frame and the temporary invert are closed in time, and in the step of removing the corresponding temporary cross brace in the first part after closing the loop, two adjacent primary arch frame supports are provided with two longitudinally arranged I-beams.

4. The double-sidewall pilot pit excavation method for a shallow buried extremely soft rock tunnel according to claim 1, characterized in that: After the first part had a progress of 3.6m and was excavated normally, the construction of the third and fourth parts began. The construction sequence was the same as that of the first and second parts. The step distance between the right guide pit formed by excavating the first and second parts and the left guide pit formed by excavating the third and fourth parts was controlled at 3m~5m.

5. A tunnel support structure, applied to the construction of the double-sidewall pilot pit excavation method of a shallow buried extremely soft rock tunnel as claimed in any one of claims 1 to 4, characterized in that: The tunnel support structure comprises: The first steel pipe pile and the second steel pipe pile have a diameter of 609 mm and are arranged at a longitudinal spacing of 1.8 m. The distance between the steel pipe pile and the primary support excavation edge of the tunnel is 50 cm. The wall thickness of the steel pipe is 12 mm. C30 concrete is poured into the steel pipe and the side wall. The first steel pipe pile and the second steel pipe pile are arranged side by side in a horizontal direction parallel to the ground, and the first steel pipe pile and the second steel pipe pile are arranged along the vertical extension with equal pressure. A primary steel arch, the primary steel arch being arranged between the first steel pipe pile and the second steel pipe pile; A first connecting mechanism, which is disposed on a side of the first steel pipe pile facing the second steel pipe pile and is connected and fixed to one side of the primary supporting steel arch; A second connecting mechanism, which is disposed on the side of the second steel pipe pile facing the first steel pipe pile and is connected and fixed to the other side of the primary supporting steel arch; and A first supporting mechanism and a second supporting mechanism, wherein the first supporting mechanism is detachably disposed inside the primary supporting steel arch and arranged close to the first steel pipe piles, and the second supporting mechanism is detachably disposed inside the primary supporting steel arch and arranged close to the second steel pipe piles.

6. The tunnel support structure according to claim 5, characterized in that: The primary supporting steel arch is provided with a plurality of mounting holes along its arc-shaped extending direction, and each mounting hole is used for passing and installing an advance small conduit.

7. The tunnel support structure according to claim 5, characterized in that: The first connecting mechanism and the second connecting mechanism both include a first corbel structure, and the first corbel structure is connected and fixed to the arc-shaped outer wall of the primary supporting steel arch.

8. The tunnel support structure according to claim 7, characterized in that: The first connecting mechanism and the second connecting mechanism also include a second corbel structure, which is arranged below the first corbel structure at intervals, and the second corbel structure is connected and fixed to the arc-shaped outer wall of the primary supporting steel arch.

9. The tunnel support structure according to claim 5, characterized in that: The first supporting mechanism and the second supporting mechanism both include an arc-shaped support, a temporary cross brace and an inverted arch support, the opposite ends of the temporary cross brace are respectively connected to the primary supporting steel arch and the arc-shaped support, the opposite ends of the arc-shaped support are respectively connected to the primary supporting steel arch and the inverted arch support, and one end of the inverted arch support is connected to the primary supporting steel arch.

10. The tunnel support structure according to claim 9, characterized in that: The tunnel support structure further comprises a temporary invert arch, and the temporary invert arch is connected between two of the invert arch supports.

Images