A construction method for a large-span cross-section mined tunnel affected by groundwater

Abstract

The present invention provides a construction method for a large-span cross-section mined tunnel affected by groundwater. Specifically, the construction method is as follows: the primary support structure cross-section of the large-span tunnel is divided into two layers, and each layer is horizontally divided into three chambers: left, middle, and right. First, the middle chamber is excavated, and then the two side chambers in the upper layer are excavated. After the upper layer chambers are excavated to a certain length, the space of the upper layer chambers is used to construct a water-stop curtain for the lower layer chambers, and then the lower layer chambers are excavated. Each chamber is first separately closed into a ring, and finally connected into a large cross-section closed ring. The construction of the secondary lining structure is carried out in three parts for backfilling, and the backfilling of each part is carried out alternately with the removal of the primary support temporary support structure. The time-space effect is used to optimize the removal method and time of the temporary support to ensure the smooth transition of the force transfer between the initial support and the secondary lining structure in each stage, and further ensure the construction safety. The construction method for the large-span cross-section mined tunnel affected by groundwater is worthy of popularization and use in the field of subway tunnel construction.

Description

Technical Field

[0001] The present invention relates to the technical field of subway construction, and more particularly to a construction method for a large-span cross-section mined tunnel affected by groundwater. Background Art

[0002] With the development of urban rail transit construction in China, more and more cities are carrying out subway construction. The construction scope of many subways involves above-ground or underground buildings and structures, including municipal roads or numerous municipal pipelines. In order to reduce the impact on municipal roads or pipelines, the subway station passage is constructed by means of mined tunneling under it. At the same time, with the increasing requirements for the protection of underground water resources, and even in some areas, the exploitation of groundwater is restricted. Therefore, dewatering cannot be carried out for mined tunnels affected by groundwater. However, considering the significant impact of groundwater on mined construction, a method of setting up a cut-off curtain to ensure water-free operation in the tunnel excavation area has emerged.

[0003] During the specific construction process, some special situations often occur. For example, the transfer passage of a subway station in Beijing under a road section is constructed by the mined tunneling method. The strata involved in the tunnel excavation are mainly pebble layer and silty clay layer, and the latest exposed stable groundwater level is located at the temporary invert of the mined tunnel. According to the current traffic conditions of this section of the road and the influence of the surrounding environment, combined with the requirements of Beijing for the protection of underground water resources, the groundwater affecting the mined tunnel construction cannot be dewatered. Therefore, a cut-off wall is set along the excavation contour line of the mined tunnel, and a cut-off curtain is formed by combining with the cut-off walls set at certain intervals on the excavation face, so as to cut off the connection between the excavation area of the mined tunnel and the surrounding groundwater, and achieve the condition of water-free operation for the mined tunneling method. The construction of the cut-off curtain for the excavation contour line and the excavation face of the lower chamber is more difficult, the working space is relatively narrow, and the integrity of the cut-off wall formed by the construction of the previous cut-off wall on the excavation face will be damaged during the construction of the subsequent cut-off wall, resulting in the risk of water and sand gushing. Moreover, there are many unpredictable factors during the construction process, and improper treatment of groundwater will pose a greater risk.

[0004] In addition, most of the existing mined tunnels adopt the excavation method of double-sided drift. The two side chambers are excavated first and then the middle chamber is excavated. However, this construction method has problems such as asynchronous longitudinal excavation and inconsistent vertical elevations of the two side chambers. When constructing the middle chamber, it is easy to have misalignment when connecting the reinforcing steel grids of the middle chamber with the reserved connecting plates of the primary support structures of the two side chambers, resulting in non-close contact of the connecting plates, and even major quality problems where they cannot be connected at all. The connecting plate of the reinforcing steel grid is the weak point of the force of the entire primary support structure. Poor construction quality is prone to large deformations, leading to excessive ground settlement, and even the risk of collapse. Moreover, the demolition of the temporary support structure of the initial support corresponding to the stage of building the secondary lining structure of the mined tunnel with a large-span section is also an important factor affecting the overall stability of the tunnel structure. If the demolition time node or the demolition method is inappropriate, large deformations of the overall structure may also occur, and even the phenomenon of tunnel collapse may occur, thus affecting the safety of the municipal roads and municipal pipelines on the top of the tunnel. Therefore, the time node and the demolition method of the temporary support structure of the initial support corresponding to the stage of building the secondary lining structure are the key to ensuring the overall safety of the structure and the key control point of safety risks. Summary of the Invention

[0005] According to the problems existing in the prior art, the present invention provides a construction method for a mined tunnel with a large-span section affected by groundwater. During the construction stage of the primary support structure, the upper chamber is constructed first, and the space of the upper chamber is used to construct a water-stop curtain for the lower chamber, and support reinforcement is carried out by using large-diameter pipe roofs and deep-hole grouting at the crown. During the construction stage of the secondary lining structure, the demolition method and time node of the temporary support structure are optimized, which can solve the disturbance to municipal roads and major pipelines during the mining process, ensure the reliable overall stability of the structure, and reduce construction risks.

[0006] In order to solve the above problems, the present invention provides a construction method for a mined tunnel with a large-span section affected by groundwater. The specific construction steps of the construction method are as follows:

[0007] (1) Determine the excavation contour line of the mined tunnel with a large-span section according to the design drawings. Construct large-diameter pipe roofs within the range of 100 - 300 mm outside the excavation contour line of the arch of the mined tunnel with a large-span section, and then use the deep-hole grouting process to reinforce the strata within the range of 1.5 - 2 m outside the excavation contour line of the arch of the mined tunnel with a large-span section and 0.4 - 0.6 m within the contour line.

[0008] (2) Accurately set out the excavation range of the chambers of the mined tunnel, and divide the excavation surface of the chambers of the mined tunnel into upper and lower layers. Each layer is divided into three areas. The middle area of the upper layer is numbered as Chamber ①, and both sides of Chamber ① are numbered as Chamber ②. The middle area of the lower layer is numbered as Chamber ③, and both sides of Chamber ③ are numbered as Chamber ④.

[0009] (3)Excavate Chamber No. 1, and reserve the core soil in Chamber No. 1. After the excavation is completed, install the steel bar grid, drive the foot-locking anchor pipes, and construct the primary support, the middle partition wall and the temporary inverted arch;

[0010] (4)When the excavation footage of Chamber No. 1 reaches 10 - 15 m, reserve the core soil and excavate Chamber No. 2, and connect the steel bar grid of the primary support of Chamber No. 2 with the reserved steel bar grid in Chamber No. 1, and construct the primary support and the temporary inverted arch of Chamber No. 2;

[0011] (5)When the excavation footage of Chamber No. 2 reaches 7 - 10 m, temporarily seal the faces of Chamber No. 1 and Chamber No. 2, and use the deep-hole grouting process to construct the water-stop walls along the excavation contours and faces of Chambers No. 3 and No. 4 downward from the bottom surfaces of Chambers No. 1 and No. 2, and form a closed water-stop curtain;

[0012] (6)After the construction of the water-stop curtain in step (5) is completed, remove the temporary support on the faces of Chambers No. 1 and No. 2, continue to reserve the core soil and excavate the soil masses of Chambers No. 1 and No. 2, and synchronously reserve the core soil and excavate the soil mass of Chamber No. 3, and construct the primary support and the middle partition wall of Chambers No. 1, No. 2 and No. 3;

[0013] (7)When the excavation footage of Chamber No. 3 in step (6) reaches 10 - 15 m, reserve the core soil and excavate the soil mass of Chamber No. 4, construct the primary support of Chamber No. 4, and integrally close the primary support structures of each chamber into a ring;

[0014] (8)Repeat the above steps (1) - (7) until the construction of the primary support structure of the large-span cross-section mined tunnel is completed;

[0015] (9)Segmentally remove the middle partition wall concrete in the range of 1.2 - 1.8 m above the inverted arch of the large-span cross-section mined tunnel, cut the middle partition wall steel sections in the way of "removing one every other one", construct the secondary lining inverted arch structure and complete the backfill;

[0016] (10)Segmentally remove the temporary inverted arch of Chamber No. 2, construct the secondary lining side wall structure and erect the temporary steel supports;

[0017] (11)Segmentally remove the temporary inverted arch and the middle partition wall of Chamber No. 1, and construct the secondary lining arch crown structure;

[0018] (12)Repeat the above steps (9) - (11) until the secondary lining is all completed. After closing into a ring, remove the temporary steel supports to complete the construction of the large-span cross-section mined tunnel.

[0019] Preferred technical solution of the present invention: The conditions for deep-hole grouting in the excavation contour line area of the arch of the large-span cross-section mined tunnel in step (1) and the deep-hole grouting of the water-stop wall in step (5) are as follows: The grouting pressure is controlled at 0.5-0.8 MPa, and the grouting slurry uses a cement-sodium silicate double-fluid slurry. The water-cement ratio of the cement slurry is 0.8:1-1:1, the concentration of sodium silicate is 35 Be', and the volume ratio of the cement slurry to sodium silicate is 1:1-1:0.6; the soil after deep-hole grouting satisfies that the permeability coefficient is not greater than 1.0×10 - 6 cm / s and the unconfined compressive strength is not less than 0.5 MPa.

[0020] Preferred technical solution of the present invention: The width of the deep-hole grouting in the excavation contour line area of the arch of the large-span cross-section mined tunnel in step (1) is 2-3 m, the width of the grouting in the excavation contour lines of chamber ③ and chamber ④ in step (5) is 3-3.5 m, and the width of the grouting at the heading face is 1.8-2.2 m. The horizontal length of each grouting is 6-8 m.

[0021] Preferred technical solution of the present invention: In the construction of the large pipe shed in step (1), the pipe shed steel pipes use hot-rolled seamless steel pipes with a diameter of 159 mm and a wall thickness of 6 mm; the joints of the pipe shed steel pipes use threaded connections, and the length of the threaded section is greater than 6 cm. When the pipe shed is installed, the adjacent steel pipe joints use different pipe section combination methods to stagger, and the staggered connection length is not less than 1.0 m; the circumferential center spacing of the steel pipes of the pipe shed is 30-40 cm, and the distance from the outer contour line of the initial support of the tunnel is 25-35 cm; the radial construction of the steel pipes is not greater than 20 cm, and the construction along the adjacent steel pipes is not greater than 10 cm; during the construction of the steel pipes, a pipe shed guide pipe with a diameter of 219 mm, a wall thickness of 5 mm, and a length of 1.5 m is embedded; the steel pipes are provided with grouting holes with a diameter of 10 mm in a plum blossom shape, the hole spacing is 15 cm, and the area where the tail of the steel pipe is 2.0 m away from the hole opening is not provided with grouting holes.

[0022] Preferred technical solution of the present invention: When the excavation footage of chamber ② in step (5) reaches 7-10 m, a steel mesh is hung on the headings of chamber ① and chamber ②, dowel bars are driven, the mesh and the dowel bars are spot-welded, and the headings of chamber ① and chamber ② are temporarily sealed by spraying concrete to form a 6-cm-thick slurry-stop wall. Then, a deep-hole grouting process is used to construct a water-stop curtain for the excavation contour lines and headings of chamber ③ and chamber ④ at the bottoms of chamber ① and chamber ②.

[0023] Preferred technical solution of the present invention: In step (5), the construction of the water-stop curtain within the excavation contour line range of chamber ③ and chamber ④ is carried out by grouting with grouting pipes radially arranged on the bottom surfaces of chamber ① and chamber ②. For the places where the slurry fails to reach, supplementary grouting shall be carried out in a timely manner after excavation. The grouting range covers the entire cross-section of the excavation contour line of chamber ③ and chamber ④; the face water-stop wall is directly formed by vertical hole grouting on the bottom surfaces of chamber ① and chamber ②. The grouting is carried out in alternate holes. Before the formal grouting of each cycle, trial grouting shall be carried out first to determine that the grouting radius is within the designed radius range. When the slurry absorption volume is less than 1 L / min, continue grouting for 30 min and then end the grouting.

[0024] Preferred technical solution of the present invention: After the initial support construction in step (8) is completed and the concrete strength reaches the design requirements, the secondary lining construction is started; in step (9), the concrete of the inverted arch structure of the secondary lining is poured in two times, and the length of each section is about 20 m; the cutting height of the middle wall steel section is 1 m. After the steel bars of the inverted arch of the secondary lining are tied, the cut middle wall steel section is connected to the steel bars of the secondary lining. During the removal of the temporary support concrete and the vertical support, the ground settlement and tunnel deformation monitoring shall be strengthened.

[0025] Preferred technical solution of the present invention: In steps (10) and (11), the length of each section during the removal of the temporary support does not exceed 6 m. During the removal of the temporary support and before the structure reaches the design requirements, the ground settlement and tunnel deformation monitoring shall be strengthened.

[0026] The earth excavation, steel bar grid erection, mesh hanging and shotcrete during the initial support construction, and the construction steps such as the steel bar work, formwork work and concrete work of the secondary lining involved in the present invention are all conventional constructions in the cut-and-cover method and do not need to be described in detail separately. The temporary support structure includes a temporary inverted arch and a middle wall.

[0027] In the present invention, the cross-section of the initial support structure of the large-span tunnel is transversely divided into three chambers: left, middle and right. Each chamber is divided into upper and lower layers, forming a total of six small chambers. The cross-sectional structure is the same as that of the double-side drift method. However, different from the double-side drift method, the upper middle chamber is excavated first, and then the upper chambers on both sides are excavated. After the upper chambers are excavated to a certain length, the space of the upper chambers is used to construct the water-stop curtain for the lower chambers. After the groundwater within the excavation range is treated, the lower chambers are excavated. Each chamber is quickly and separately closed into a ring and staggered by a certain safe distance, and finally connected into a large-section closed ring. The construction of the secondary lining structure is carried out in three parts for backfilling, and the backfilling of each part is carried out alternately with the removal of the initial support temporary support structure. The time-space effect is used to optimize the removal method and time of the temporary support to ensure the smooth transition of the force transfer between the initial support and the secondary lining structure in each stage and further ensure the construction safety.

[0028] Advantages of the present invention:

[0029] (1) In the present invention, to ensure overall risk control, ensure excellent quality, and effectively avoid quality problems prone to occur in conventional processes, the advantages of the middle drift method for excavation are borrowed, and the excavation sequence of the double-sided drift method is adjusted. The middle chamber is excavated first, and then the two side chambers are excavated. The steel bar grids of the two side chambers can be effectively connected to the connecting plates reserved for the two side chambers by the middle chamber, solving the major quality problem of the connecting plates of the steel bar grids and avoiding construction risks caused by quality problems.

[0030] (2) In the present invention, to solve the problem that the excavation of the lower chamber of the mined tunnel is affected by groundwater, the excavation sequence of the chambers of the double-sided drift method is adjusted. Generally, the upper chamber is excavated first, and the water-stop curtain of the lower chamber is constructed using the relatively large space formed after the construction of the upper chamber is completed. After the residual groundwater between the strata is pumped and drained, the lower chamber is excavated, so as to achieve the purpose of ensuring water-free operation of the mined method without dewatering, and at the same time protecting water resources.

[0031] (3) Before construction, the present invention uses the advanced support form of "large-diameter pipe shed + deep-hole grouting" to pre-reinforce the strata of the arch part of the mined tunnel, so as to reduce the settlement and deformation of pipelines and municipal roads caused by tunnel excavation. The core soil is left in each chamber and excavated layer by layer in sections, following the principle of "advance pipe, strict grouting, short excavation, strong support, frequent measurement, and early closure", ensuring that the mined passage will not cause disturbance to pipelines and municipal roads when passing under them and ensuring the normal progress of construction.

[0032] (4) The construction structure section of the secondary lining structure in the present invention is constructed in three parts. First, the inverted arch structure of the secondary lining is constructed, then the side wall structure of the secondary lining is constructed, and finally the arch crown structure of the secondary lining is constructed to form a closed loop as a whole. The inverted arch structure is constructed continuously in longitudinal sections. After the temporary support steel profiles within the inverted arch range are cut off in the way of "removing one every other one", they are restored during the construction of the secondary lining structure, ensuring the overall stability of the primary support structure. After the construction and backfilling of the inverted arch structure are completed, the construction of the side wall structure and the arch crown structure is organized. The side wall structure and the arch crown structure are constructed by the longitudinal section and skip-joint method. During the construction process, the removal of the temporary support of the corresponding primary support structure and the erection of the temporary steel support of the secondary lining structure are carried out alternately and continuously, ensuring the reliable overall stability during the force transfer process between the primary support structure and the secondary lining structure and ensuring the structural safety. Description of the Drawings

[0033] Figure 1 It is a schematic diagram of the chamber distribution of the cross-section of the mined tunnel in the embodiment of the present invention;

[0034] Figure 2 It is a construction drawing of the cross-section of the structure of the mined tunnel in the embodiment of the present invention;

[0035] Figure 3 It is the longitudinal section construction drawing of the mined tunnel structure in the embodiment of the present invention;

[0036] Figures 4 to 13 It is the schematic diagram of the construction process of the present invention;

[0037] Figure 14 It is the schematic connection diagram of the steel grids of the primary support structure in the embodiment of the present invention.

[0038] In the figure: 1 - pipe shed support structure, 2 - advanced reinforcement layer, 3 - contour line water stop wall, 4 - upper mined tunnel, 5 - lower mined tunnel, 6 - face water stop wall, 7 - excavation contour line of the arch of the upper mined tunnel, 8 - foot-locking anchor pipe, 9 - primary support structure, 10 - middle partition wall, 11 - reserved core soil, 12 - temporary inverted arch, 13 - steel grid, 14 - connecting plate, 15 - middle partition wall steel section, 16 - secondary lining structure, 17 - temporary steel support, 18 - high-strength bolt. Specific embodiments

[0039] The present invention will be further described below in conjunction with the drawings and embodiments. The attached Figures 1 to 14 All are the drawings of the embodiments, which are drawn in a simplified manner and are only used to clearly and concisely illustrate the purpose of the embodiments of the present invention. The technical solutions shown in the drawings below are the specific solutions of the embodiments of the present invention and are not intended to limit the scope of the present invention to be protected. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0040] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "upper", "lower", "inner", "outer", "left", "right", etc. is based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship in which the product of the invention is usually placed during use, or the orientation or positional relationship commonly understood by those skilled in the art. It is only for the convenience of describing the present invention 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 should not be construed as a limitation of the present invention.

[0041] The mined tunnel in the embodiment is constructed in segments, such as Figure 1 and Figure 2As shown in the figure, each mined tunnel section is divided into the upper mined tunnel 4 constructed first and the lower mined tunnel 5 constructed later. Both the upper mined tunnel 4 and the lower mined tunnel 5 are constructed by dividing them into three chambers. For each layer of mined tunnel, the middle chamber is constructed first, and then the two side chambers are constructed. The construction length of each section of the middle chamber is 10 - 15m, and the construction length of each section of the two side chambers is 7 - 10m. At the arch foot position of the upper mined tunnel 4, there is a DN32X2.75 foot-locking anchor pipe 8, and the length of the foot-locking anchor pipe 8 is 2m - 3m, with a horizontal inclination angle of 30°. To ensure the stability of the construction, an arc-shaped advanced reinforcement layer 2 is formed by advanced grouting for the strata at the arch part of the upper mined tunnel before tunnel excavation. After the construction of the upper mined tunnel 4 of each mined tunnel section is completed, a U-shaped contour water-stop wall 3 is formed by deep-hole grouting along the invert contour line of the lower mined tunnel 5 from the bottom surface of the upper mined tunnel 4. Moreover, the contour water-stop wall 3 and the advanced reinforcement layer 2 are integrally connected in the cross-section to form a reinforcement structure that encloses the mined tunnel. After the construction of the upper mined tunnel 4 of each mined tunnel section is completed, a face water-stop wall 6 is formed by deep-hole grouting from the bottom surface of the upper mined tunnel 4. The bottom surface of the face water-stop wall 6 is integrally connected with the contour water-stop wall 3 to form a closed water-stop curtain, and the width of the face water-stop wall 6 is 1.8 - 2.2m. The width of the advanced reinforcement layer 2 is 2 - 2.5m, the grouting width of the contour water-stop wall 3 is 3 - 3.5m, and the horizontal length of each grouting is 6 - 8m. The pipe shed support structure 1 is constructed within the range of 100 - 300mm from the excavation outline of the upper mined chamber 4. The circumferential spacing of the steel pipes of the pipe shed is 30 - 40cm.

[0042] In the embodiment, the deep-hole grouting pressure of the advanced reinforcement layer 2, the contour water-stop wall 3, and the face water-stop wall 6 is controlled at 0.5 - 0.8MPa. The grouting slurry adopts a cement-sodium silicate double-fluid slurry. The water-cement ratio of the cement slurry is 0.8:1 - 1:1, the concentration of sodium silicate is 35 Be’, and the volume ratio of the cement slurry to the sodium silicate is 1:1 - 1:0.6. The specific ratio is adjusted according to the specific geological conditions during grouting. The soil body after deep-hole grouting satisfies that the permeability coefficient is not greater than 1.0×10 -6 cm / s, and the unconfined compressive strength is not less than 0.5MPa. The steel pipes of the pipe shed support structure 1 adopt hot-rolled seamless steel pipes with a diameter of Φ159mm and a wall thickness of 6mm. The steel pipe joints adopt screw connections, and the length of the screw thread section is greater than 6cm. When the pipe shed is installed, the adjacent steel pipe joints adopt different pipe section combination methods to stagger, and the staggering length is not less than 1.0m. The construction error of the pipe: the radial error is not greater than 20cm, and the error along the direction of adjacent steel pipes is not greater than 10cm. To ensure accurate drilling positioning, a pipe shed guide pipe with a diameter of Φ219, a wall thickness of 5mm, and a length of 1.5m should be pre-buried. The steel pipes are drilled for grouting, with a hole diameter of Φ10mm and a hole spacing of 15cm, arranged in a plum blossom pattern. The tail part (the hole section at the orifice) of 2.0m of the steel pipe is not drilled with flower holes as the grout-stop section.

[0043] The following combines the embodiments to describe the specific construction process of the present invention and the application of the water-stop reinforcement structure in the construction of the mined tunnel. The embodiment is specifically a construction project of the transfer passage of a subway station. The transfer passage of the subway station is constructed by the open-cut method + the mined method. The open-cut part is a two-story, double-column, three-span concrete structure underground, and the mined section is a composite lining structure of primary support and secondary lining, with a horseshoe-shaped cross-section. The length of the mined section is 41.38 m, the maximum span of the cross-section is 13.9 m, the height is 8.07 m, and the overburden depth is 12.38 m. The thickness of the primary support structure is 350 mm, the thickness of the middle wall and the temporary inverted arch is 300 mm, and the thickness of the secondary lining structure is 900 mm. The original design of the primary support structure is to construct by the double-side drift method, and the cross-section is as Figure 1 shown, and it is excavated in six chambers divided into upper and lower layers. The tunnel is located in a cobble stratum, and there is a silty clay layer with a thickness of about 4 m. The temporary inverted arch of the tunnel is 0.2 - 0.3 m above the groundwater level, and the construction of the lower chamber is affected by groundwater.

[0044] The mined section of the transfer passage passes under the west half of the municipal road. The whole road is a two-way 10-lane + 2 non-motor vehicle lanes, with a total road width of 80 m. There are ∅250 medium-pressure gas pipelines, ∅500 high-pressure gas pipelines, ∅1400 water supply pipelines, ∅600 water supply pipelines, 2400×1200 rainwater culverts and several communication line pipelines under the road. The pipeline materials of the gas pipelines and the water supply pipelines are all steel pipes, and the 2400×1200 rainwater culvert is a brick masonry structure. The closest distance to the tunnel vault is about 8 m. At the same time, both the north and east sides of the transfer passage are adjacent to the existing subway operation lines, which belong to the first-level risk sources and pose relatively high risks. During the construction process, protection needs to be strengthened. In order to ensure the safety of the tunnel construction, the construction method in the present invention is adopted, and its specific construction process is as follows:

[0045] (1) Determine the tunnel excavation contour line according to the design drawings, and make marks with spray paint. As Figure 4 shown, construct the large pipe shed 1 100 mm outside the tunnel arch excavation contour line, and then adopt the deep-hole grouting process to conduct advanced grouting reinforcement on the arch stratum. The reinforcement range is 1.5 m outside the excavation contour line and 0.5 m inside the contour line;

[0046] (2) Accurately loft to determine the excavation range of the mined tunnel chambers. As Figure 1 shown, and divide the excavation surface of the mined tunnel chambers into upper and lower layers, and each layer is divided into three areas. The middle area of the upper layer is numbered as chamber ①, and both sides of chamber ① are numbered as chamber ②. The middle area of the lower layer is numbered as chamber ③, and both sides of chamber ③ are numbered as chamber ④;

[0047] (3) As Figure 5As shown in the figure, reserve the soil mass of Chamber ① in the middle of the upper bench excavation of the upper bench excavation tunnel 4 in Chamber ①, erect steel arch frames, drive dowel pipes 8 for foot locking, and construct the primary support structure 9, the middle partition wall 10 and the temporary inverted arch 12;

[0048] (4) When the excavation footage of Chamber ① in step (3) reaches 10 - 15 m, as Figure 6 shown in the figure, reserve the soil mass of Chamber ② in the core soil excavation area adjacent to Chamber ① in Chamber ②, connect the primary support structure 9 and the steel bar grid of Chamber ② with the connecting plate 14 of the steel bar grid 13 reserved in Chamber ① (the connection structure is as Figure 14 shown in the figure), and construct the primary support structure of Chamber ② and the temporary inverted arch of Chamber ②;

[0049] (5) When the excavation footage of Chamber ② in the upper bench excavation tunnel 4 reaches 7 - 10 m, temporarily seal the faces of Chambers ① and ②. As Figure 7 shown in the figure, use the deep hole grouting process to construct the water stop walls 3 on the contour lines of the excavations of Chambers ③ and ④ and the face water stop wall 6 from inside Chambers ① and ② to form a closed water stop curtain;

[0050] (6) After the construction in step (5) is completed, remove the temporary support on the faces of Chambers ① and ②, continue to reserve the core soil to excavate the soil masses of Chambers ① and ②, and simultaneously reserve the core soil to excavate the soil mass of Chamber ③ in the middle of the lower bench excavation tunnel 4. As Figure 8 shown in the figure, construct the primary support, the temporary inverted arch and the middle partition wall of Chambers ①, ② and ③;

[0051] (7) When the excavation footage of Chamber ③ in step (6) reaches 10 - 15 m, reserve the core soil to excavate the soil masses of Chambers ④ on both sides of the lower bench excavation tunnel 4. As Figure 8 shown in the figure, construct the primary support, and the large - section tunnel is integrally closed into a ring;

[0052] (8) Repeat the above steps (1) - (7) until the construction of the primary support 3 is completed;

[0053] (9) As Figure 10 shown in the figure, segmentally remove the middle partition wall concrete within the range of 1.5 m above the inverted arch of the secondary lining of the Ⅰ - section of Chamber ④ in the lower bench excavation tunnel 4, cut the middle partition wall steel section 15 in the way of "removing one every other one", construct the secondary lining inverted arch structure, and complete the backfill;

[0054] (10) As Figure 11 shown in the figure, segmentally remove the temporary inverted arch of Chamber ② in the upper bench excavation tunnel, construct the secondary lining side wall structure and erect the temporary steel support 17;

[0055] (11) As Figure 12As shown, the remaining temporary inverted arch 7 and the middle diaphragm 4 are demolished in sections, and the arch crown structure of the secondary lining is constructed;

[0056] (12) Repeat the above steps (9) to step (11) until the secondary lining 10 is completely completed. As Figure 13 shown, after the closure of the loop, the temporary steel support 11 is demolished.

[0057] The above construction time is calculated based on 12-hour construction. The construction period arrangement: the time for the deep-hole grouting of the advanced support in the arch part is 30 days. For the construction of the water-stop curtain in the lower chamber, the grouting width of the excavation contour line is 3m, the grouting width of the heading face is 2m, and the length of each grouting is 6 - 8m. The construction time for each section is 7 days. During the grouting reinforcement period, closely monitor the ground heave and control the ground settlement.

[0058] In the above embodiment, when the excavation footage of the No. 1 chamber reaches 10 - 15m, first excavate the soil body of the No. 2 chamber according to the reserved core soil method, rather than excavating the soil body of the No. 3 chamber according to the conventional sequence. Affected by groundwater, the No. 4 chamber cannot be directly excavated. It is necessary to first excavate the No. 2 chamber to create a working space for dealing with the groundwater in the lower No. 3 chamber and No. 4 chamber. After the excavation of the soil body in the arch part of the No. 2 chamber is completed, install the initial support steel bar grid and connect it with the connecting plate of the steel bar grid reserved in the No. 1 chamber. As Figure 13 shown, first connect with high-strength bolts, and use steel bars with the same diameter as the grid steel bars to help weld the main grid bars at both ends of the connecting plate. The help welding length is not less than 10d, and the weld height is not less than 8mm. The connecting plate of the grid is subjected to fillet welding treatment, and the weld height is not less than 6mm. After passing the inspection, promptly construct the initial support and temporary support.

[0059] In the above embodiment, when the excavation footage of the No. 2 chamber reaches 7 - 10m, hang the steel bar mesh of HPB300 6mm@150×150 on the headings of the No. 1 and No. 2 chambers, drive the dowel bars at a spacing of 500mm×500mm. The steel bar model is HRB400E 20mm. The mesh and the dowel bars are spot welded and connected, and the headings of the No. 1 and No. 2 chambers are temporarily sealed with sprayed C20 ready-mixed concrete to form a 6cm thick grout-stop wall. Then, use the deep-hole grouting process to construct the water-stop curtain for the excavation contour line and the heading face of the No. 3 and No. 4 chambers in the No. 1 and No. 2 chambers. The construction of the water-stop curtain in the excavation contour range adopts a radial method, and grouting is carried out according to the grouting angles specified in the plan. During the process, the grouting angle and the number of grouting holes can be appropriately adjusted according to the grouting radius. In places where the slurry fails to reach, supplementary grouting should be carried out in a timely manner after excavation to ensure that the grouting range can cover the entire section. The grout-stop wall at the heading face is directly grouted by vertical hole formation in the No. 1 and No. 2 chambers. The grouting is carried out in alternate holes. Before the formal grouting of each cycle, a trial grouting should be carried out first to determine that its grouting radius is within the design radius range. The grouting end standard: when the slurry absorption volume is less than 1L / min, continue grouting for another 30min and then end the grouting.

[0060] In the above embodiments, for the convenience of construction organization, the concrete of the inverted arch structure of the secondary lining is constructed first and completed in two pours, with each section having a length of about 20 m. To ensure the overall stability of the primary support structure, the concrete of the middle wall within a range of 1.5 m above the inverted arch is removed first, and then the middle wall is cut off in the way of "removing one every other one", with the cutting height being 1 m. After the steel bars of the secondary lining inverted arch are tied, the cut-off middle wall is connected to the steel bars of the secondary lining to ensure that the middle wall is inserted into the concrete after the inverted arch concrete is poured. During the removal of the temporary support concrete and the cutting of the vertical support, the ground settlement and tunnel deformation monitoring shall be strengthened. If any abnormality occurs, the removal and cutting shall be stopped immediately and the support shall be restored immediately.

[0061] In the above embodiments, the removal of the temporary support and the structure construction in steps (9) and (10) are carried out alternately. First, the temporary inverted arch of chamber ② is removed in sections, with each section having a length not exceeding 6 m. Then, the side wall structure is constructed using a fixed-type steel formwork, and the temporary steel support is erected in time to prevent the side wall structure from being extruded and deformed into the tunnel by the surrounding rock load. After the side wall structure reaches a certain strength, the middle wall and horizontal support of all the remaining primary support structures are removed, and the arch crown structure is constructed using a full hall scaffold + steel formwork support system. The overall secondary lining structure is closed into a ring. During the removal of the temporary support and before the structure meets the design requirements, the ground settlement and tunnel deformation monitoring shall be strengthened. If any abnormality occurs, the removal shall be stopped immediately and the temporary support shall be restored immediately.

[0062] As mentioned above, this is only one embodiment of the present invention. The above embodiments only express the present invention, and the description is relatively specific and detailed, but it should not be construed as a limitation to the scope of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the appended claims.

Claims

1. A construction method for a large-span cross-section mined tunnel affected by groundwater, characterized in that the specific steps are as follows: (1) Determine the excavation contour line of the large-span cross-section mined tunnel according to the design drawings. Construct large pipe roofs within the range of 100 - 300 mm outside the excavation contour line of the arch part of the large-span cross-section mined tunnel, and then use the deep-hole grouting process to reinforce the strata within the range of 1.5 - 2 m outside the excavation contour line of the arch part of the large-span cross-section mined tunnel and 0.4 - 0.6 m within the contour line; (2) Accurately loft to determine the excavation range of the mined tunnel chamber, and divide the excavation surface of the mined tunnel chamber into upper and lower layers. Each layer is divided into three areas. The middle area of the upper layer is numbered as chamber ①, and both sides of chamber ① are numbered as chamber ②. The middle area of the lower layer is numbered as chamber ③, and both sides of chamber ③ are numbered as chamber ④; (3) Excavate chamber ①, and reserve a core soil within chamber ①. After the excavation is completed, install steel bar grids, drive in lock-foot anchor pipes, and construct the primary support, middle partition wall, and temporary inverted arch; (4) When the excavation footage of chamber ① reaches 10 - 15 m, reserve the core soil and excavate chamber ②, and connect the steel bar grids of the primary support of chamber ② with the reserved steel bar grids of chamber ①, and construct the primary support and temporary inverted arch of chamber ②; (5) When the excavation footage of chamber ② reaches 7 - 10 m, temporarily seal the faces of chamber ① and chamber ②. Use the deep-hole grouting process to construct a water-stop wall for the excavation contour line and the face of chamber ③ and chamber ④ downward from the bottom surfaces of chamber ① and chamber ②, and form a closed water-stop curtain; (6) After the construction of the water-stop curtain in step (5) is completed, remove the temporary support of the faces of chamber ① and chamber ②, continue to reserve the core soil and excavate the soil bodies of chamber ① and chamber ②, and simultaneously reserve the core soil and excavate the soil body of chamber ③, and construct the primary support and middle partition wall of chamber ①, chamber ②, and chamber ③; (7) When the excavation footage of chamber ③ in step (6) reaches 10 - 15 m, reserve the core soil and excavate the soil body of chamber ④, construct the primary support of chamber ④, and integrally close the primary support structures of each chamber into a ring; (8) Repeat the above steps (1) - step (7) until the construction of the primary support structure of the large-span cross-section mined tunnel is completed; (9) Segmentally remove the middle partition wall concrete within the range of 1.2 - 1.8 m above the inverted arch of the large-span cross-section mined tunnel, cut the middle partition wall steel sections in the way of "removing one every other one", construct the secondary lining inverted arch structure and complete the backfill; (10) Segmentally remove the temporary inverted arch of chamber ②, construct the secondary lining side wall structure and erect temporary steel supports; (11) Segmentally remove the temporary inverted arch and middle partition wall of chamber ①, and construct the secondary lining arch crown structure; (12) Repeat the above steps (9) - step (11) until the secondary lining is all completed. After closing into a ring, remove the temporary steel supports to complete the construction of the large-span cross-section mined tunnel.

2. The construction method for a large-span cross-section mined tunnel affected by groundwater according to claim 1, characterized in that The conditions for deep-hole grouting in the excavation contour line area of the arch of the large-span cross-section mined tunnel in step (1) and the deep-hole grouting of the water-stop wall in step (5) are as follows: the grouting pressure is controlled at 0.5-0.8 MPa, and the grouting slurry uses a cement-sodium silicate double-fluid slurry, where the water-cement ratio of the cement slurry is 0.8:1-1:1, the concentration of sodium silicate is 35 Be', and the volume ratio of the cement slurry to sodium silicate is 1:1-1:0.6; the soil after deep-hole grouting meets the requirements that the permeability coefficient is not greater than 1.0×10 -6 cm / s and the unconfined compressive strength is not less than 0.5 MPa.

3. The construction method of a large-span cross-section mined tunnel affected by groundwater according to claim 1, characterized in that: in step (1), the width of the long-hole grouting in the excavation contour line area of the arch of the large-span cross-section mined tunnel is 2-3 m, the width of the grouting in the excavation contour line of chamber ③ and chamber ④ in step (5) is 3-3.5 m, the width of the grouting at the heading face is 1.8-2.2 m, and the horizontal length of each grouting is 6-8 m.

4. The construction method of a large-span cross-section mined tunnel affected by groundwater according to claim 1, characterized in that: in the construction of the large pipe shed in step (1), the pipe shed steel pipes are hot-rolled seamless steel pipes with a diameter of 159 mm and a wall thickness of 6 mm; the joints of the pipe shed steel pipes are connected by screw threads, the length of the screw thread section is greater than 6 cm, and when the pipe shed is driven, the adjacent two steel pipe joints are staggered by different pipe joint combination methods, and the staggered connection length is not less than 1.0 m; the circumferential center distance of the steel pipes of the pipe shed is 30-40 cm, and the distance from the outer contour line of the initial support of the tunnel is 25-35 cm; the radial construction of the steel pipes is not more than 20 cm, and the construction along the adjacent steel pipes is not more than 10 cm; during the construction of the steel pipes, a pipe shed guide pipe with a diameter of 219 mm, a wall thickness of 5 mm, and a length of 1.5 m is embedded; the steel pipes are provided with grouting holes with a diameter of 10 mm in a plum blossom shape, the hole spacing is 15 cm, and the area where the tail of the steel pipe is 2.0 m away from the hole mouth is not provided with grouting holes.

5. The construction method of a large-span cross-section mined tunnel affected by groundwater according to claim 1, characterized in that: when the excavation footage of chamber ② in step (5) reaches 7-10 m, a steel mesh is hung at the headings of chamber ① and chamber ②, dowel bars are driven, the mesh and the dowel bars are spot-welded, and the headings of chamber ① and chamber ② are temporarily sealed with shotcrete to form a grout stop wall with a thickness of 6 cm, and then a long-hole grouting process is used to construct a water-stop curtain for the excavation contour line and the heading face of chamber ③ and chamber ④ at the bottom of chamber ① and chamber ②.

6. The construction method of a large-span cross-section mined tunnel affected by groundwater according to claim 1, characterized in that: the construction of the water-stop curtain in the excavation contour line range of chamber ③ and chamber ④ in step (5) is carried out by grouting in a radial arrangement of grouting pipes on the bottom surface of chamber ① and chamber ②. When the slurry fails to reach a place, supplementary grouting should be carried out in time after excavation. The grouting range covers the entire cross-section of the excavation contour line of chamber ③ and chamber ④; the water-stop wall at the heading face is directly grouted by vertically drilling holes on the bottom surface of chamber ① and chamber ②. The grouting is carried out in alternate holes. Before each cycle of formal grouting, trial grouting should be carried out first to determine that the grouting radius is within the design radius range. When the slurry absorption volume is less than 1 L / min, continuous grouting should be carried out for another 30 min and then the grouting is ended.

7. The construction method of a large-span cross-section mined tunnel affected by groundwater according to claim 1, characterized in that: After the initial support construction in step (8) is completed and the concrete strength reaches the design requirements, the secondary lining construction is started; in step (9), the concrete of the inverted arch structure of the secondary lining is poured in two times, and the length of each section is 20 m; the cutting height of the middle diaphragm steel section is 1 m. After the steel bars of the inverted arch of the secondary lining are tied, the cut middle diaphragm steel section is connected to the steel bars of the secondary lining, and the ground settlement and tunnel deformation monitoring are strengthened during the removal of the temporary support concrete and the vertical support.

8. A construction method for a large-span cross-section mined tunnel affected by groundwater according to claim 1, characterized in that: In steps (10) and (11), the length of each section during the removal of the temporary support does not exceed 6 m, and the ground settlement and tunnel deformation monitoring are strengthened during the removal of the temporary support and before the structure reaches the design requirements.

Images