Construction method for rapid excavation of shallow tunnel in strong swelling soft rock

Abstract

The present application relates to the technical field of tunnel construction, in particular to a rapid tunneling construction method for strong swelling soft rock shallow-buried tunnel. In view of the problems of high risk of deformation and collapse of surrounding rock and low construction efficiency of strong swelling soft rock shallow-buried tunnel caused by water-rock coupling degradation effect, the tunnel section is divided into upper, middle and lower three steps by three-step full-face dynamic construction system, and mechanical cooperative operation is adopted to realize multi-process parallel advancement (excavation, slag removal, stand, simultaneous spraying), combined with "process negative connection" technology to reduce construction interruption. The hydraulic inverted arch trestle is used to ensure the continuous construction of the inverted arch and the center water channel, shorten the exposure time of the surrounding rock, and improve the efficiency by using the sub-site wet spraying concrete process. The method significantly improves the monthly footage (from 20m to more than 80m), reduces the risk of collapse, saves the construction period and cost, and is suitable for tunnel engineering with high V-grade surrounding rock ratio and strong swelling soft rock geology.

Description

Technical Field

[0001] This invention relates to the field of tunnel construction technology, specifically to a method for rapid excavation of shallow-buried tunnels in highly expansive soft rock. Background Technology

[0002] Tunnels in highly expansive soft rock are prone to damage due to the periodic expansion and contraction deformation of the water-sensitive soft rock caused by groundwater. This can lead to asymmetric stress concentration in the initial support structure, steel arch twisting, and circumferential cracking of the lining. Simultaneously, the water-rock coupling degradation effect in water-rich strata significantly reduces the shear strength of the soft rock, exacerbating the risk of extrusion deformation and sudden water inrush at the tunnel face. The secondary stress field imbalance caused by construction disturbance further tightens the requirements for the step-by-step advance distance in the bench method. Therefore, conducting relevant research is of significant engineering guiding importance for ensuring the construction safety of shallow-buried tunnels in highly expansive soft rock. The tunnel faces complex geological conditions, primarily traversing sandstone, mudstone, and basalt strata. New loess is distributed on the gentle slopes and old terraces of the low-to-medium mountainous area near the tunnel section. Its age and origin are mostly Quaternary Holocene alluvial-diluvial deposits and Upper Pleistocene colluvial-diluvial deposits, generally yellowish-brown, hard to stiff plastic, with well-developed vertical joints and large pores. The mudstone sandstone within the tunnel body is weakly expansive rock, while the completely weathered mudstone layer is strongly expansive soil. Therefore, how to break away from the traditional assembly-line model and achieve high efficiency in the dynamic construction of the three-stage full-section tunnel through mechanical collaboration and process interleaving in shallowly buried areas of strongly expansive soft rock is a technical problem that needs to be solved. Summary of the Invention

[0003] The problem to be solved by this invention is to achieve high efficiency in three-stage full-section dynamic construction in shallow buried areas of strongly expansive soft rock through mechanical coordination and process interleaving.

[0004] To address the shortcomings of existing technologies, the technical solution adopted by this invention is a rapid excavation construction method for shallow-buried tunnels in highly expansive soft rock, comprising the following steps: S1: A three-stage system that divides the tunnel cross-section into an upper stage, a middle stage, and a lower stage; S2: While the upper bench is excavating and removing slag, the middle bench is also excavated and removed slag. Two excavators work together. The first excavator performs the excavation of the upper bench and moves the slag to the middle bench, while the second excavator simultaneously performs the slag removal and excavation of the lower bench. S3: The construction of the scaffolding, shotcreting and invert arch is carried out in a staggered manner through the negative connection technology of the process: the scaffolding is erected on the upper and middle steps while the slag is excavated and removed from the lower steps; the scaffolding is erected on the upper and middle steps while the shotcreting is carried out on the lower steps. S4: After the scaffolding is erected on the lower step, spray concrete; continue to repeat S1~S4; S5: Tunnel bottom excavation; S6: Construction of the central water ditch; a hydraulic inverted arch trestle bridge is used in conjunction with a liftable approach bridge to keep the trestle bridge fixed during the construction of the inverted arch and the central water ditch, and to complete the section work in one go; S7: Tunnel bottom closed; S8: Construction of the invert arch; continue repeating S5~S8.

[0005] Preferably, the hydraulic arch trestle includes a base plate, a trestle body is installed on the upper surface of the base plate, a walking component is provided on the upper surface of the trestle body, a number of movable outriggers are installed on the surface of the base plate, and a bridge lifting and folding component is provided on one side of the trestle body. The hydraulic arch trestle triggers a lifting command according to the construction progress.

[0006] Preferably, the negative connection technology for the process further includes: Erecting the scaffolding immediately after the upper step excavation is completed, with a time interval of ≤0.5 hours; Start shotcreting when 50% of the scaffolding is erected, with a time difference of ≤1 hour; When 70% of the shotcreting on the lower step is completed, start the excavation at the bottom of the tunnel, with a time difference of ≤2 hours. The ratio of personnel between the shotcrete team and the scaffolding team is 1:1.5.

[0007] Preferably, the height of the upper step is ≤4.5m and a core soil is reserved. The width of the core soil is ≥1 / 2 of the excavation width and ≥6.5m, and the height is ≥3.0m, serving as a platform for erecting the frame. The height of the middle step is ≤4m, and the height of the lower step is dynamically adjusted according to the stability of the surrounding rock.

[0008] Preferably, the process parameters for shotcrete include shotcrete pressure, spraying distance, rebound rate control, and C25 shotcrete mix proportion; specifically as follows: The shotcrete pressure is 0.5-0.8 MPa; Spraying distance: 1.5-2m; Rebound rate should be controlled at ≤18%; The mix proportion of C25 shotcrete is cement:sand:aggregate:water = 1:2:2:0.45, with 3% quick-setting agent added.

[0009] Preferably, the safe step distance for tunnel bottom excavation is ≤40m, the safe step distance for invert arch construction is ≤45m, and the safe step distance for three-stage construction is ≤70m.

[0010] The beneficial effects of this invention are as follows: By using three-stage full-section dynamic construction and negative process connection technology, the construction efficiency was achieved, increasing the monthly progress from 20m to more than 80m and shortening the construction period by about 56 months. Reducing the exposure time of the surrounding rock lowers the risk of collapse and ensures construction safety; mechanized collaborative operations reduce the exposure of dangerous areas to manual labor, and anchor pipes and advanced support enhance structural stability; Three-dimensional laser scanning precisely controls over- and under-excavation, reducing ineffective earthwork and waste stockpiling; centralized equipment scheduling reduces unit energy consumption and meets construction environmental protection requirements; The hydraulic inverted arch trestle and the modular platform are designed to flexibly cope with complex geological conditions and are highly adaptable to tunnels with strong expansion soft rock and a high proportion of Class V surrounding rock. Attached Figure Description

[0011] Figure 1 This is a flowchart of the construction process of the present invention; Figure 2 This is a diagram showing the machinery layout for the three-stage excavation operation in this invention; Figure 3 This is a schematic diagram of the parameters of the three-step work platform in this invention; Figure 4 This is a schematic diagram of the arch excavation in this invention; Figure 5 This is a schematic diagram of the construction of the central drainage ditch in this invention; Figure 6 This is a schematic diagram of the hydraulic inverted arch trestle structure in this invention; Explanation of reference numerals in the attached drawings: 1. Base plate; 2. Trestle body; 3. Approach bridge lifting and folding assembly; 4. Traveling assembly; 5. Movable outriggers; 6. Excavator; 7. Loader; 8. Hydraulic inverted arch trestle; 10. Upper step; 20. Middle step; 30. Lower step; 40. Inverted arch; 50. Central ditch. Detailed Implementation

[0012] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. The embodiments of the present invention are given for illustrative and descriptive purposes only, and are not intended to be exhaustive or to limit the invention to the forms disclosed. Many modifications and variations will be apparent to those skilled in the art. The embodiments were chosen and described to better illustrate the principles and practical application of the invention, and to enable those skilled in the art to understand the invention and design various embodiments with various modifications suitable for a particular purpose.

[0013] Addressing the issues raised in the background section, our unit used a tunnel entrance as the primary research subject and summarized a large-scale mechanized construction method. Utilizing a modular operating platform for dynamic adjustment, this method breaks away from the traditional assembly line model, achieving dynamic three-stage full-section construction through mechanical collaboration and process interleaving. By simultaneously excavating and erecting the scaffolding in three stages, the initial support closure loop is formed promptly, reducing the exposure time of the surrounding rock and lowering the risk of collapse. The shotcreting, scaffolding erection, and muck removal processes employ negative linkage, significantly improving construction efficiency. Through on-site research and development practice, we summarized and refined a rapid excavation construction method for shallow-buried tunnels in highly expansive soft rock.

[0014] The construction method of this invention has the following characteristics: Balancing safety and efficiency: Breaking away from the traditional assembly line model, dynamic three-stage full-section construction is achieved through mechanical collaboration and interleaved processes. By simultaneously carrying out three-stage excavation and scaffolding erection, the initial support loop is formed promptly, reducing the exposure time of the surrounding rock and lowering the risk of collapse. The shotcreting, scaffolding erection, and muck removal processes utilize negative linkage, significantly improving construction efficiency.

[0015] The system combines mechanization and intelligentization: Excavators 6, wet spraying trolleys, and hydraulic arch bridges 8 operate in tandem, enabling multi-machine collaborative work, reducing reliance on manual labor and improving mechanization levels. The hydraulic arch bridge 8 incorporates features such as a liftable approach bridge and a modular platform, including a base plate 1, bridge body 2, approach bridge lifting and folding components 3, walking components 4, and movable outriggers 5. For details, refer to the utility model application document for a liftable tunnel arch bridge with approach bridge application number 2025208945830. This allows for flexible adaptation to complex geological conditions and construction interference.

[0016] Strong capacity for intensive resource allocation and dynamic adjustment: The 10-meter-high scaffolding erection and the 30-meter-high slag removal are carried out in parallel on the upper bench, while the invert arch construction is interspersed within the excavation gaps. Space is reused in shifts, enabling multi-process collaboration within a limited space. Mechanical excavation dominates rough excavation, while manual finishing ensures both efficiency and quality.

[0017] This invention is primarily applicable to the construction of shallow-buried tunnels in highly expansive soft rock. Based on a multi-stage parallel operation system, the tunnel cross-section is divided into an upper stage 10, a middle stage 20, and a lower stage 30. Two excavators 6 work collaboratively to achieve simultaneous excavation and muck removal. A "negative process connection" technology is employed to interleave processes such as frame erection and shotcreting, reducing construction interruptions. An adjustable hydraulic trestle ensures continuous construction of the invert arch and central drainage ditch 50, while segmented wet shotcreting improves efficiency. Simultaneously, the rapid closure of the invert arch into a ring, the coordinated action of anchor bolts and advanced support, and the formation of a dynamically balanced surrounding rock support system ultimately achieve safe and efficient excavation and structural stability control under mechanized collaboration. The specific process principle is as follows: 1. Construct a multi-stage parallel operation system and dynamically adjust and optimize the work space: Based on the core principle of tunnel cross-section segmented excavation and support, the tunnel cross-section is divided into upper, middle and lower stages. A combination of mechanical collaborative operation and manual assistance is adopted to achieve the synchronous advancement of excavation, slag removal, frame erection and shotcreting of each stage.

[0018] 2. Innovative working platform, expanded equipment functions: The upper step 10 adopts a pre-reserved core soil, stone chips trimming or modular frame to flexibly adapt to various surrounding rock conditions; the hydraulic inverted arch trestle 8 is modified into a liftable approach bridge to ensure uninterrupted transportation channel during the construction of the central buried water ditch. The hydraulic inverted arch trestle 8 serves as both a passageway and a construction platform, enabling one-time long-distance construction of the inverted arch and water ditch, avoiding frequent movement of equipment from affecting continuous operation at the working face.

[0019] 3. Mechanized and coordinated operations across different sections, innovative processes and refined management: The shotcrete operation is divided into four parts: upper, middle, and lower steps (30 sections) and the initial support at the tunnel floor. A vehicle-mounted wet shotcrete trolley replaces the traditional robotic arm, avoiding obstruction issues. Shotcreting of the lower step (30 sections) can begin immediately after the upper and middle steps (20 sections) are completed. Large-section construction (each section's length matched to the trolley) is employed, combined with a hydraulic trestle to ensure simultaneous passage and construction, reducing waiting time between procedures.

[0020] Construction process flow chart as follows Figure 1 As shown, it includes the following steps: S1: The tunnel cross-section is divided into a three-step system: upper step 10, middle step 20, and lower step 30; S2: After the upper bench 10 is excavated and the slag is removed, the middle bench 20 is also excavated and the slag is removed. Two excavators 6 work together. The first excavator 6 performs the excavation of the upper bench 10 and moves the slag to the middle bench 20. The second excavator 6 simultaneously performs the slag removal and excavation of the lower bench 30. S3: The construction of the scaffolding, shotcreting, and invert arch 40 is carried out in a staggered manner through the negative process connection technology: scaffolding is erected on the upper step 10 and the middle step 20 while excavation and slag removal are carried out on the lower step 30; after the scaffolding is erected on the upper step 10 and the middle step 20, shotcreting is carried out while the scaffolding is erected on the lower step 30; the negative process connection technology also includes: scaffolding erection begins immediately after the excavation of the upper step 10 is completed, with a time interval of ≤0.5 hours; Shotcreting begins when 50% of the scaffolding is erected, with a time difference of ≤1 hour; tunnel bottom excavation begins when 70% of the shotcreting at the lower step is completed, with a time difference of ≤2 hours; the ratio of shotcreting team to scaffolding team personnel is 1:1.5.

[0021] The upper step (10) has a height of ≤4.5m and a reserved core soil. The width of the core soil is ≥1 / 2 of the excavation width and ≥6.5m, and the height is ≥3.0m, serving as a platform for erecting the frame. The middle step (20) has a height of ≤4m, and the lower step (30) has a height that is dynamically adjusted according to the stability of the surrounding rock.

[0022] The height of the three steps is dynamically adjusted based on the surrounding rock stability coefficient K. (Safety threshold); Where: c is the rock mass cohesion, φ is the internal friction angle, and γ is the rock mass unit weight. Parameter value verification: Upper step height ≤ 4.5m → K=1.52 > 1.5; Middle step height ≤ 4.0m → K=1.48 ≈ 1.5 (requires core soil).

[0023] S4: After setting up the scaffold 30 meters down the step, spray concrete; continue repeating S1~S4, with a safe step distance ≤70m; the process parameters for spray concrete include spraying pressure, spraying distance, rebound rate control, and C25 spray concrete mix proportion; specifically as follows: spraying pressure 0.5-0.8MPa; spraying distance 1.5-2m; rebound rate control ≤18%; C25 spray concrete mix proportion is cement:sand:stone:water = 1:2:2:0.45, with 3% quick-setting agent added.

[0024] S5: Tunnel bottom excavation; safety step distance ≤ 40m; S6: Construction of the central ditch 50; a hydraulic inverted arch trestle bridge 8 is used in conjunction with a liftable approach bridge to keep the trestle bridge fixed during the construction of the inverted arch 40 and the central ditch 50, so as to complete the section operation in one go; S7: Tunnel bottom closed; S8: Invert arch construction; safe step distance ≤ 45m, continue to repeat S5~S8.

[0025] The main technical parameters of the stepped construction method are as follows: (1) Step height: For the three-step construction method, the height of the upper step 10 shall not exceed 4.5 meters (considering the allowance for settlement); the height of the middle step 20 shall not exceed 4 meters; the height of the lower step 30 shall be determined according to the convenience of operation and construction method conversion; the core soil shall be reserved according to 1 / 2 to 2 / 3 of the excavation width. The width of the reserved core soil for Shangshan Tunnel shall not be less than 6.5 meters, the length shall not be less than 3 meters, and the height shall not be less than 3.0 meters. (2) Step length: The length of the upper step 10 shall not exceed 10 meters, the middle and lower steps 303 meters, and the left and right sides shall be staggered by 3 to 4 steel frames. The distance from the lower step 30 to the initial support at the bottom of the tunnel shall not exceed 12 meters. The total length of the steps (distance between the working faces of the upper and lower steps 30) shall not exceed 23 meters.

[0026] (3) Cyclic advance: The upper bench 10 is generally controlled by 2 advances, and when the self-stabilizing ability of the face is poor, it can be controlled by 1 advance; the middle and lower benches 30 should generally not be controlled by more than 3 advances.

[0027] (4) Closure loop index: In order to ensure that the initial support of the tunnel bottom does not exceed 35m, according to the on-site construction situation, the invert arch needs to be excavated in time 2-3 days after the excavation of the upper bench 10, and the central deep buried water ditch and the initial support of the tunnel bottom need to be constructed. Considering the most unfavorable factors, the initial support of the tunnel bottom is constructed 2 days after the excavation of the upper bench 10. The advance of the upper bench 10 on the same day is considered to be 1.2m, that is, the excavation advance is 6m in 3 days. Therefore, the closure loop time of the initial support of the tunnel bottom is no more than 18 days.

[0028] Before construction, the process design should be carried out according to the characteristics of the construction method, the operation method and process organization should be refined, and process control requirements and safety precautions should be formulated.

[0029] The parallel operation of slag removal on the upper, middle, and lower steps (10 arches) is the core of the rapid construction organization for tunnels in weak surrounding rock. The tunnel face must be managed meticulously to ensure that each process is tightly connected, synchronized, and forms an organic whole, achieving order and efficiency.

[0030] Strictly control the length of each step and ensure that each step is completed simultaneously.

[0031] Strict quality control must be maintained during construction, especially regarding the length of the anchor pipes, welding quality, and arch frame connection quality; voids behind the initial support are strictly prohibited, and any voids discovered must be promptly repaired by spraying or grouting.

[0032] Strictly control the safe step distance: the step distance of the initial support at the tunnel bottom should be controlled within the range of 35 to 40m, the step distance of the invert arch should be controlled within the range of 40 to 45m, and the step distance of the secondary lining should be controlled within 70m.

[0033] A foreman coordination mechanism was established inside the tunnel. Four foremen were assigned to each work face inside the tunnel (two from the project department and two from the work team), working 24 hours a day to coordinate the work of all work groups in the excavation and support, invert arch, and arch wall lining processes. They recorded the work process connection status and ensured "zero delay and negative connection" between each process.

[0034] Mechanical configuration Excavation work line: 2 narrow-body excavators, 1.99m wide.

[0035] Loading line: 72 loaders, 3m 3 3 dump trucks (to be added as the transport distance increases).

[0036] Support operation line: 10 YT28 pneumatic drills (including 5 spares); 1 grouting pump, 5m... 3 / h; several water pumps.

[0037] Shotcrete production line: 1 wet concrete shotcrete unit, 30m diameter 3 / h; 3 concrete mixer trucks, ≥10m 3 .

[0038] Lining work line: 1 concrete pump with a pumping power of not less than 80kw; 4 concrete mixer trucks, ≥10m 3 .

[0039] Each opening is equipped with one hydraulic inverted arch trestle, one rebar waterproofing membrane hanging trolley, one lining formwork trolley, one concrete curing platform, and one drainage ditch / cable trough formwork trolley. The effective length of the self-propelled hydraulic inverted arch trestle must be twice the length of one lining section; the rebar waterproofing membrane hanging trolley and curing platform must be fabricated or purchased independently; the lining formwork trolley must be equipped with intelligent systems such as a concrete pouring flow monitoring system, a concrete pouring temperature monitoring system, a concrete pouring pressure monitoring system, a pouring status display system, a video monitoring system, a void monitoring system, an immersion vibrator, and an intelligent layered and compartmentalized pouring system.

[0040] The core of excavation and support process control is organizing parallel operations both above and below. Each process is interdependent and mutually restrictive. Through meticulous management of the excavation and support process, the goal of safe and efficient construction organization can be achieved. The main operational points are as follows: Mechanical excavation was used for the upper, middle, and lower steps of S1 and S2, with details provided. Figure 2 The excavation machinery layout diagram shows that two excavators (6) are deployed. During excavation, one excavator (6) first excavates the middle bench 20 to create a road. Excavator (6) then moves to the upper bench 10 and uses a ripper to excavate the upper bench 10, while manual trimming is used to remove the excavated soil to the middle bench 20. While the upper bench 10 is being excavated, the second excavator excavates the lower bench 30 and removes slag from the upper bench 10. After the upper bench 10 is excavated, the first excavator (6) reverses, and a loader (7) promptly transports engineering materials to the upper bench 10 to begin erecting the arch. The second excavator continues removing slag and excavating the lower bench 30. On-site construction is carried out in parallel with the erection of the arch and slag removal on the upper, middle, and lower benches 30. The three-bench method construction frame erection is completed in two stages: the upper and middle benches 20 and the lower bench 30. The erection of the scaffolding on the upper and middle steps (20) and the removal of slag on the lower step (30) are carried out simultaneously. After the erection of the scaffolding on the middle step (20) is completed, the removal of slag on the lower step (30) is finished, and the workers are moved to the lower step (30), with the scaffolding erection work carried out simultaneously on both sides. The organization method of erecting the scaffolding on the upper step (10) and removing slag on the lower step (30) in parallel is adopted. During the scaffolding erection process, when conditions permit for installing anchor bolts, the pneumatic drill crew is promptly arranged to carry out the construction.

[0041] like Figure 3 As shown, the work platform is being repaired: the height of the upper step 10 is about 4.5m. The core soil reserved in the upper step 10 can be used as the work platform; or a part of the stone rubble in the upper step 10 can be reserved and repaired into a platform for convenient operation; or a simple and lightweight on-site assembled work platform can be used, and the work platform can be manually positioned.

[0042] During the excavation of the tunnel bottom and construction of the central drainage ditch 50 in tunnels S5 and S6, a deep-buried central drainage ditch 50 was installed at the tunnel bottom. The bottom of the deep-buried central drainage ditch 50 is located 233.7cm below the bottom surface of the initial arch support, which is quite deep. In the early stages of construction, it was necessary to lift the front approach bridge of the hydraulic invert arch trestle bridge 8 to excavate the invert arch and the deep-buried central drainage ditch 50, which blocked the transportation channel. By modifying the front approach bridge of the hydraulic invert arch trestle bridge 8, setting a lifting mode, and extending the approach bridge to 12m, as follows... Figure 5 As shown. After the trestle bridge is in place, the approach bridge can be raised and lowered at any time according to the traffic conditions on site. The construction center deep-buried water ditch, the excavation of the invert arch, and the initial support can be carried out in the on-site construction intervals. With the trestle bridge remaining stationary, the invert arch and the center deep-buried water ditch can be constructed in one go for 9 meters, thus ensuring continuous operation at the working face.

[0043] Shotcrete work was divided into four sections: upper bench 10, middle bench 20, lower bench 30, and the initial support of the tunnel floor. The erection of the scaffolding for upper bench 10 and the removal of slag for lower bench 30 were carried out in parallel. Shotcrete work was performed on upper and middle benches 20, while scaffolding work was carried out on lower bench 30. Once shotcrete work on upper and middle benches 20 was completed, lower bench 30 was ready for shotcrete work. This avoided the need to complete the scaffolding for all three benches 30 before shotcrete work began. This transformed the work from a continuous flow to parallel operations, achieving a seamless transition between shotcrete and scaffolding processes, thus accelerating the construction progress. Simultaneously, the initial support of the tunnel floor was manually shotcreted using a GHP20G truck-mounted wet shotcrete trolley. The wet shotcrete trolley was positioned between the hydraulic invert arch trestle 8 and the steel reinforcement waterproofing membrane laying trolley, avoiding obstruction of the path when using a wet shotcrete robot to spray concrete for the initial support of the tunnel floor. This reduced shotcrete work time by 2-3 hours and improved construction efficiency.

[0044] The construction of the invert arch in S8 mainly includes tunnel lining construction, which comprises the invert arch (including its filling layer), arch wall lining, and ancillary works. The invert arch is a prerequisite for arch wall lining construction, and timely invert arch construction helps control surrounding rock deformation. Therefore, from the perspective of all tunnel construction procedures, "the invert arch is crucial." Invert arch construction inevitably affects excavation and support operations. To achieve the goal of "excavation being the leading factor" and to ensure that excavation and support operations effectively drive tunnel construction, invert arch construction should be carried out during the intervals between excavation and support operations. Waterproofing layer, reinforcement, and arch wall lining concrete should be installed immediately after the invert arch to achieve the goal of "lining being the guarantee." Tunnel lining construction should follow the principle of corresponding construction joints for the invert arch and its filling layer, circumferential construction joints for the arch wall lining, and construction joints for drainage ditches and cable trenches (i.e., "three joints combined").

[0045] The construction of the invert arch should follow the principle of "rapid closure of the initial support into a ring, followed by construction of the secondary lining invert arch and large sections of invert arch filling." The length of each invert arch and filling layer should correspond to the length of the trolley. To allow vehicle access during invert arch construction, a hydraulic invert arch trestle 8 should be installed above the invert arch. The length of the trestle should correspond to the effective construction length of the invert arch and the arch wall lining. The structure of the hydraulic invert arch trestle 8 is shown in [details omitted]. Figure 6 The hydraulic arch bridge 8 includes a base plate 1, a bridge body 2 is installed on the upper surface of the base plate 1, a walking component 4 is provided on the upper surface of the bridge body 2, a number of movable support legs 5 are installed on the surface of the base plate 1, and a bridge lifting and folding component 3 is provided on one side of the bridge body 2. The hydraulic arch bridge 8 triggers lifting commands according to the construction progress.

[0046] Construction sequence of the invert arch: Construction preparation → Surveying and setting out → Removal of loose debris from the top surface of the initial support invert arch → Advancement of hydraulic invert arch trestle 8 → Construction joint treatment and structural waterproofing and drainage construction → Installation of invert arch reinforcement → Installation of invert arch side wall formwork, end formwork and circumferential construction joint waterstop (installation of inspection well formwork) → Invert arch concrete construction → Invert arch filling layer concrete construction → Formwork removal and curing → Next cycle.

[0047] The arch wall lining should be constructed after the initial support deformation has stabilized. The arch wall lining concrete should be centrally mixed, pumped into the formwork in layers, and vibrated, then poured continuously in one go using a monolithic steel formwork trolley. During construction, a complete set of lining construction techniques, including layered material placement and grouting with formwork, should be implemented to ensure the arch crown concrete is fully and densely poured. To reduce the risk of concrete falling off at the construction joints of the arch wall lining, the installation of the embedded waterstop should employ a combination of trolley steel end formwork clamps and positioning reinforcement, and the waterstop should be at least 20cm from the inner surface of the lining. The formwork trolley end molds should preferably use a combination of steel end molds and rubber plates.

[0048] Secondary lining construction sequence: construction preparation → initial support surface treatment → waterproof layer construction → reinforcement installation → trolley positioning, circumferential waterstop and end formwork installation → arch grouting pipe installation → concrete pouring → formwork removal and curing → next cycle.

[0049] The labor force organization is shown in Table 1.

[0050] Table 1 Labor Force Organization Table 1 Chief Engineer Responsible for overall construction plan 1 person 2 Technical Director Responsible for overall work of construction organization and technical guidance for the project. 2 people 3 technician Responsible for technical tracking during the construction process 4 people 4 Safety officer Safety management during construction 4 people 5 surveyor Monitoring and measurement 2 people 6 electrician Power supply guarantee during equipment electrical installation, construction and operation 1 person 7 Excavation Team Excavation of the tunnel 6 people 8 Transport Team Outbound transport of slag 8 people 9 Frame erection team Steel frame and steel mesh installation, and welding of anchor pipes to the steel frame. 18 people 10 Air Force Squad The pneumatic drill team is mainly responsible for the construction of anchor pipes and advanced support. 14 people 11 shotcrete team Shotcrete construction 6 people 12 Lining Team Lining construction 32 people 13 total 98 people (1) The excavation team is mainly responsible for the excavation of the tunnel body. The tunnel excavation method adopts mechanical excavation, with 3 people per shift, namely 1 foreman and 2 excavator drivers. A total of 2 shifts are equipped, with a total of 6 people.

[0051] (2) The transport team is mainly responsible for transporting the slag from the tunnel. Each team is mainly equipped with 1 loader driver and 3 transport vehicle drivers, with a total of 2 teams and 8 people.

[0052] (3) The scaffolding erection team is mainly responsible for the installation of the steel frame and steel mesh, as well as the welding of the anchor pipes to the steel frame. The scaffolding erection for the three-stage construction is completed in two stages: the upper middle stage 20 and the lower stage 30. There are 12 scaffolding erection workers per shift. The scaffolding erection for the upper middle stage 20 and the slag removal for the lower stage 30 are carried out simultaneously. Among them, 9 people are arranged for the upper stage 10 and 3 people are arranged for the middle stage 20. After the middle stage 20 is erected and the slag removal for the lower stage 30 is completed, the workers are transferred to the lower stage 30 to carry out the scaffolding erection work simultaneously. In actual construction, considering the rest and rotation of the workers, the staff is equipped with 1.5 shifts.

[0053] (4) The pneumatic gun team is mainly responsible for the construction of anchor pipes and advanced support. The pneumatic gun team is set up with 3 groups, each with 3 people. One group is assigned to the middle step 20 and two groups are assigned to the upper step 10, for a total of 9 people. After the construction of the upper and middle steps 20 is completed, the personnel will be adjusted to the lower step 30. In actual construction, considering the rest and rotation of the workers, the personnel are allocated according to 1.5 shifts.

[0054] (5) The shotcrete team consists of 4 people per shift, including 1 shotcrete operator; 1 person to direct the concrete mixer truck to position and unload the concrete; and 2 people on the work platform to assist the shotcrete operator in moving the spray pipe and removing the shotcrete from the arch ribs. The shotcrete operator is solely responsible for shotcreting and leaves immediately after finishing. The remaining work is completed by other personnel. In actual construction, considering the rest and rotation of the workers, the team is equipped with 1.5 shifts.

[0055] (6) The lining team is generally configured with 32 people, 6 people for drainage and waterproofing, 12 people for steel reinforcement, 8 people for concrete, 4 people for formwork, and 2 people for concrete pump truck drivers.

[0056] The main materials involved in the construction method of this invention are as follows: The materials used in this construction method include C30 / C35 concrete, C20 / C25 / C35 shotcrete, mortar anchors, steel mesh, steel pipes, reinforcing bars, structural steel, EVA waterproof membrane, geotextile, waterstop, corrugated pipe, etc. For specific model requirements, please refer to the design drawings.

[0057] The main mechanical equipment involved in the construction method of this invention is shown in Table 2: Table 2. Main Machinery and Equipment Configuration Table 1 excavator 1m³ tower 2 2 Loader 3m³ tower 1 3 pneumatic drill YT28 tower 10 4 Concrete wet spraying unit 30m³ / h tower 1 5 Tanker ≥10 vehicle 7 6 Concrete pump ≥80kW tower 2 7 arched pier / tower 1 8 Reinforcing steel waterproofing board hanging trolley / tower 1 9 Intelligent lining trolley / tower 1 10 Concrete curing platform / tower 1 11 Water ditch cable trough template trolley / tower 1 total / / / 38 The construction method of this invention complies with the current national and Ministry of Railways railway engineering construction specifications and acceptance standards. Code for Acceptance of Construction Quality of Concrete Structures (GB50204-2015); Standard for Acceptance of Construction Quality of High-Speed ​​Railway Tunnel Engineering (TB / 10753-2018); Technical Specification for Rock and Soil Anchors and Shotcrete Support Engineering (GB50084-2015); Technical Specification for Construction of Railway Concrete Engineering (Q / CR9027-2017); Standard for Acceptance of Construction Quality of Railway Concrete Engineering (TB / 10424-2018); Technical Specification for Construction of High-Speed ​​Railway Tunnel Engineering (Q / CR9604-2015); Standard for Durability Design of Concrete Structures (GB / T50474-2019); Construction Technology and Management of High-Speed ​​Railways (TB / T1853-2018); Code for Winter Construction of Building Engineering (JGJ / T104-2011); Technical Specification for Temporary Power Supply Safety at Construction Sites (JGJ44-2012).

[0058] Before construction, a process design should be developed based on the characteristics of the construction method, detailing the work methods and process organization, and formulating process control requirements and safety precautions. Before the waterproofing lining is installed, the initial support surface should be inspected to determine the extent of over-excavation or under-excavation. Three-dimensional laser scanning should be used for cross-sectional inspection to achieve comprehensive, blind-spot-free inspection, ensuring zero under-excavation of the lining and guaranteeing that the thickness of the lining concrete meets design requirements. Positioning reinforcement bars should be installed to ensure that the layer spacing and interval of the arch wall reinforcement meet requirements. Concrete spacers of the same grade should be placed on the inner and outer main reinforcement bars to ensure that the thickness of the arch wall reinforcement protective layer meets design requirements. Before positioning the lining trolley, the electrical, hydraulic, and walking systems should be checked, and the trolley template surface should be cleaned and coated with a release agent. The plane position and elevation of the lining trolley should be measured and positioned strictly according to the design geometric dimensions. After the dimensions and position meet the requirements, the trolley template support should be fixed, the end templates should be firmly installed, and the joints should be tightly sealed to prevent grout leakage. An automatic diversion device should be used for concrete pouring to achieve layered and compartmentalized pouring, ensuring that the concrete is poured continuously and symmetrically from bottom to top. Below the arch, immersion vibrators are used for layered compaction, while the arch section is compacted using a combination of attached vibrators and immersion vibrators to prevent any omissions and ensure the concrete is dense.

[0059] During construction, a safety production organization and a robust safety production guarantee system will be established. Emergency response plans for the four-stage construction of the large-section tunnel will be formulated, and adequate reserves of emergency materials and supplies will be maintained. On-site technicians and dedicated safety officers must work in shifts day and night to monitor and ensure the implementation of all safety and quality measures. A comprehensive safety management system centered on the safety production responsibility system will be established, including safety production responsibility systems for all levels and types of personnel, safety inspection systems, safety education systems, safety technical measures planning systems, safety briefing systems, special operations personnel management systems, safety acceptance systems, team safety activity systems, accident reporting and handling systems, and safety reward and punishment systems. Safety production responsibility targets will be broken down layer by layer and assigned to specific individuals. Strict quality control will be maintained during construction, especially regarding the length of the anchor pipes, welding quality, and arch frame connection quality. Voiding behind the initial support is strictly prohibited; any voids discovered will be promptly repaired with spraying or grouting. Safe step distances will be strictly controlled: the initial support step distance at the tunnel bottom will be controlled within the range of 35–40m, the invert arch step distance within the range of 40–45m, and the secondary lining step distance within the range of 70m. Electrical equipment must use dedicated switch boxes. Strictly adhere to the "one machine, one switch, one leakage protector, one box" rule, ensuring the leakage protection device is compatible with the equipment. Do not use a single switch to directly control two or more electrical devices. Distinguish between high-voltage and low-voltage power outlets to prevent accidents caused by misoperation. Power switches, control boxes, and other facilities should be uniformly arranged, locked, and protected to prevent haphazard wiring. Assign dedicated personnel for management to prevent leakage and electric shock. Do not arbitrarily adjust the setting current of automatic switch trip units or the fuse specifications in switches and fuses. The electrical safety supervisor is responsible for the layout, organization, and inspection of wiring.

[0060] During construction, environmental protection and civilized construction management methods were formulated, a reward and punishment system was established, and these were conscientiously implemented. Employees were educated to raise their environmental awareness. Environmental management was strengthened by establishing an environmental protection leading group headed by the project manager. Strict control was exercised over all channels that could easily cause environmental pollution during construction, and key environmental protection priorities were clearly defined. Environmental protection and civilized construction signs were set up on site, responsibility areas were demarcated, and responsibilities were assigned to specific individuals. Materials on the construction site were stacked neatly and orderly, without obstructing construction access roads or fire safety facilities, and kept away from transformers, high-voltage power lines, etc. Environmental awareness among construction personnel was strengthened through enhanced environmental education, dissemination of relevant environmental policies and knowledge, and promotion of environmental regulations through various means. Construction noise was strictly controlled to reduce its impact on construction personnel.

[0061] Through comparative research and analysis of traditional construction methods during the project construction, our unit improved equipment, adopted new construction technologies using large-scale equipment, and combined these with the actual construction of the project, summarizing and forming a rapid excavation construction method for tunnels in highly expansive soft rock. All efficiency indicators have been significantly improved. For a certain tunnel with rapidly changing geology and extremely poor surrounding rock stability, the monthly advance was initially less than 20 meters. After adopting the new method, the monthly advance increased to 80 meters. Based on the application length of 1500m using the new method, approximately 56 months of construction time were saved.

[0062] This construction method, through parallel operations of upper, middle, and lower steps (30mm), enables simultaneous advancement of multiple work faces, reducing waiting time between processes, accelerating construction speed while ensuring safety, and alleviating regional traffic pressure. Simultaneously, reserving core soil and staggered excavation ensures face stability, reducing the risk of collapse, and mechanized collaborative operations reduce the time workers spend exposed to hazardous areas, improving construction safety. The use of mechanical excavation also reduces construction noise and vibration disturbances to residents' lives.

[0063] This construction method utilizes three-dimensional laser scanning to control over- and under-excavation, precisely excavating to reduce the amount of ineffective earthwork, decrease the amount of waste, and mitigate the damage to mountain vegetation caused by waste dumping. Simultaneously, centralized scheduling of mechanized equipment reduces energy consumption per unit of earthwork, minimizes overall energy consumption, and minimizes environmental pollution, demonstrating significant environmental advantages. A tunnel in the JDYZQ-1 section of the newly built Jining-Datong-Yuanping Railway is located in a village in Fengzhen City, Ulanqab City. This is a single-bore, double-track tunnel. The geology is mainly composed of weak surrounding rock, with Class V surrounding rock accounting for 74.53%. The tunnel entrance is 13.3 m wide and 9.6 m high. The strata within the tunnel are mudstone and sandstone, completely weathered, relatively soft, and nearly soil-like. The rock mass is relatively intact, exhibiting a layered structure. The completely weathered mudstone has strong expansibility. Construction revealed that the surrounding rock at the tunnel face is distributed in gently dipping thin layers with well-developed joints and fissures. After excavation, stress release is rapid, making collapse and rockfalls likely. The surrounding rock has poor self-stability, resulting in high construction safety risks. The monthly progress was approximately 20 m. After the improvement of the trestle bridge and the adoption of a new construction method in March 2023, the monthly progress gradually increased, reaching a maximum of 80 m, providing technical support for the timely completion of the tunnel and ensuring its opening to traffic.

[0064] A tunnel in the JDYZQ-1 section of the newly built Jining-Datong-Yuanping Railway is located in a village in Fengzhen City, Ulanqab City, with an exit mileage of DK39+903. The tunnel entrance is 13.3 m wide and 9.6 m high. The tunnel has a large cross-section. The working face reveals completely weathered basalt, with extremely broken rock containing large, isolated boulders and a loose structure. The working face is moist, with localized water seepage, mixed with mud and sand, and well-developed joints and fissures. The tunnel body strata are mudstone and sandstone, completely weathered, relatively soft, and nearly soil-like. The rock mass is relatively intact, exhibiting a layered structure. The completely weathered mudstone has strong expansibility. Construction revealed that the surrounding rock at the working face is distributed in gently dipping thin layers with well-developed joints and fissures. After excavation, stress release is rapid, making it prone to collapse and rockfall. The surrounding rock has poor self-stability, resulting in high construction safety risks. With a monthly advance of only 18 m, this presents a severe challenge to the timely completion of the tunnel. After the trestle bridge was improved and a new construction method was adopted in April 2023, the monthly progress gradually increased, reaching a maximum of 85m, which provided technical support for the timely completion of the tunnel and ensured its opening to traffic.

[0065] This invention provides a rapid excavation method for shallow-buried tunnels in highly expansive soft rock. Through three-stage excavation and coordinated mechanical operations, multiple processes are advanced in parallel. Combined with core technologies such as a hydraulic inverted arch trestle, negative connection between processes, and segmented wet spraying, the method effectively shortens the exposure time of the surrounding rock and improves construction efficiency. In the application of this method in the Shangshan Tunnel of the Jida Railway (74.53% of the surrounding rock is Class V), the monthly advance increased to over 80 meters, significantly reducing the risk of collapse and saving time and costs. Its innovative design combining mechanization and intelligent technology provides a safe and efficient technical solution for tunnel engineering under similar geological conditions, and has broad application value.

Claims

1. A method for rapid excavation of shallow-buried tunnels in highly expansive soft rock, characterized in that: Includes the following steps: S1: The tunnel cross-section is divided into a three-step system consisting of an upper step (10), a middle step (20), and a lower step (30); S2: While the upper step (10) is excavating and excavating the middle step (20), two excavators (6) work together. The first excavator (6) excavates the upper step (10) and moves the slag to the middle step (20), while the second excavator (6) simultaneously excavates and excavates the lower step (30). S3: The construction of the frame erection, shotcreting and inverted arch (40) is carried out in a staggered manner through the negative connection technology of the process: the frame erection of the upper step (10) and the middle step (20) is carried out at the same time as the lower step (30) is excavated and the slag is removed; the frame erection of the upper step (10) and the middle step (20) is carried out and the concrete is shotcreted at the same time as the lower step (30) is erected. S4: After the scaffolding is erected at the bottom of the step (30), spray concrete; continue to repeat S1~S4; S5: Tunnel bottom excavation; S6: Construction of the central ditch (50); a hydraulic inverted arch trestle (8) is used in conjunction with a liftable approach bridge to keep the trestle fixed during the construction of the inverted arch (40) and the central ditch (50) and complete the section operation in one go; S7: Tunnel bottom closed; S8: Construction of the invert arch; Continue to repeat S5~S8; The hydraulic arch bridge (8) includes a base plate (1), the upper surface of the base plate (1) is equipped with a bridge body (2), the upper surface of the bridge body (2) is provided with a walking component (4), the surface of the base plate (1) is equipped with several movable legs (5), and a bridge lifting and folding component (3) is provided on one side of the bridge body (2). The hydraulic arch bridge (8) triggers lifting commands according to the construction progress. The process negative connection technology also includes: After the excavation of the upper step (10) is completed, the scaffolding should be erected immediately, with a time interval of ≤0.5 hours; Shotcreting should begin when 50% of the scaffolding is complete, with a time difference of ≤1 hour. When 70% of the shotcreting on the lower step (30) is completed, start the excavation at the bottom of the tunnel, with a time difference of ≤2 hours; The ratio of personnel between the shotcrete team and the scaffolding team is 1:1.

5.

2. The rapid excavation method for shallow-buried tunnels in highly expansive soft rock according to claim 1, characterized in that: The upper step (10) has a height of ≤4.5m and a reserved core soil. The width of the core soil is ≥1 / 2 of the excavation width and ≥6.5m, and the height is ≥3.0m, serving as a platform for erecting the frame. The middle step (20) has a height of ≤4m, and the lower step (30) has a height that is dynamically adjusted according to the stability of the surrounding rock.

3. The rapid excavation method for shallow-buried tunnels in highly expansive soft rock according to claim 1, characterized in that: The process parameters for shotcrete include shotcrete pressure, spraying distance, rebound rate control, and C25 shotcrete mix proportions; specifically as follows: The shotcrete pressure is 0.5-0.8 MPa; Spraying distance: 1.5-2m; Rebound rate should be controlled at ≤18%; The mix proportion of C25 shotcrete is cement:sand:aggregate:water = 1:2:2:0.45, with 3% quick-setting agent added.

4. The rapid excavation method for shallow-buried tunnels in highly expansive soft rock according to claim 1, characterized in that: The safe step distance for tunnel bottom excavation is ≤40m, the safe step distance for invert arch construction is ≤45m, and the safe step distance for three-stage construction is ≤70m.

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