Disaster mode and active support system of horizontal thin-layer weakly cemented expansive rock tunnel

Abstract

The invention provides a catastrophe mode and active support system of a horizontal thin-layer weak cementation expansive rock tunnel, and relates to the technical field of tunnel and underground engineering disaster prevention and control, and the catastrophe mode and active support system comprises the following steps: carrying out geological investigation on a tunnel engineering area, obtaining geological investigation parameters, and determining a chain catastrophe evolution mode according to the geological investigation parameters; based on the chain catastrophe evolution mode and geological survey parameters, predicting the total floor heave displacement of the tunnel through a quantitative calculation model; according to the total floor heave displacement, construction parameters of an active supporting system composed of a structure strengthening subsystem, a rock mass strengthening subsystem and a waterproof source blocking subsystem are determined; and according to the construction parameters, the structure strengthening subsystem, the rock mass strengthening subsystem and the waterproof source blocking subsystem are constructed in sequence, an active supporting system of the horizontal thin-layer weakly-cemented expansive rock tunnel is formed, and a monitoring system is established for the active supporting system. The method can effectively treat the heaving floor disease, and long-term operation safety is guaranteed.

Description

Technical Field

[0001] This invention relates to the field of disaster prevention and control technology for tunnels and underground engineering, and more specifically, to disaster modes and active support systems for horizontal thin-layer weakly cemented expansive rock tunnels. Background Technology

[0002] In the construction and operation of tunnels and underground engineering projects, severe tunnel floor heave, also known as floor bulge, is frequently encountered when traversing horizontal, thin-layered, weakly cemented expansive rock strata. Currently, the engineering community's understanding of this type of disaster is generally simplistic, attributing its main cause to the volume expansion of the rock mass upon contact with water. Existing prevention and control measures primarily rely on rigid reinforcement methods such as increasing the thickness of the invert arch and raising the reinforcement ratio. This approach is not only costly but also often results in recurrence within a short period of operation because it does not address the root cause of the disaster. Furthermore, existing measures lack a systematic approach, with waterproofing and reinforcement being disconnected. In particular, conventional drainage designs only focus on draining water from the tunnel, failing to effectively prevent water from seeping back into the surrounding rock, leading to continuous water-rock interaction and poor treatment results. Summary of the Invention

[0003] The purpose of this invention is to provide a disaster mode and active support system for horizontal thin-layer weakly cemented expansive rock tunnels to improve the aforementioned problems. To achieve the above objective, the technical solution adopted by this invention is as follows:

[0004] In a first aspect, this application provides a disaster mode and active support system for a horizontal thin-layer weakly cemented expansive rock tunnel, including:

[0005] Geological surveys were conducted in the tunnel engineering area to obtain geological survey parameters consisting of rock mass physical and mechanical parameters, structural surface characteristics, and in-situ stress parameters.

[0006] Based on the geological exploration parameters, the chain-like catastrophe evolution mode of tunnel floor heave in horizontal thin-layered weakly cemented expansive rock strata was determined.

[0007] Based on the aforementioned chain-like disaster evolution model and geological exploration parameters, the total floor heave displacement of the tunnel is predicted through a quantitative calculation model.

[0008] Based on the total heave displacement, the construction parameters of the active support system, consisting of a structural reinforcement subsystem, a rock mass reinforcement subsystem, and a waterproofing and source-blocking subsystem, are determined.

[0009] Based on the construction parameters, the structural reinforcement subsystem, rock mass reinforcement subsystem, and waterproofing and source-blocking subsystem are constructed in sequence to form an active support system for a horizontal thin-layer weakly cemented expansive rock tunnel, and a monitoring system is established for the active support system.

[0010] The beneficial effects of this invention are as follows:

[0011] This invention decomposes the total heave displacement into multiple quantitative prediction models, thereby elevating support design from reliance on empirical estimation to theoretical calculation and quantitative analysis. Furthermore, this application constructs a three-in-one active support system integrating structural reinforcement, rock mass consolidation, and waterproofing, achieving the blocking and suppression of the source. Utilizing this active support system for protection can effectively control heave defects and ensure long-term operational safety.

[0012] Other features and advantages of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing embodiments of the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures particularly pointed out in the written description, claims, and drawings. Attached Figure Description

[0013] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0014] Figure 1 This is a schematic diagram of the disaster mode and active support system of the horizontal thin-layer weakly cemented expansive rock tunnel described in the embodiments of the present invention.

[0015] Figure 2 This is a schematic diagram of the disaster mode evolution process described in the embodiments of the present invention;

[0016] Figure 3 A schematic diagram of a composite thick plate formed by reinforcing the inverted arch with anchor bolts at the bottom of the tunnel;

[0017] Figure 4 Schematic diagram of a fully enclosed waterproof layer for drainage ditches. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0019] It should be noted that similar reference numerals and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. Furthermore, in the description of this invention, terms such as "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0020] Example 1:

[0021] This embodiment provides a disaster mode and active support system for a horizontal thin-layer weakly cemented expansive rock tunnel.

[0022] See Figure 1 The figure shows that this includes:

[0023] S1. Conduct geological surveys of the tunnel engineering area to obtain geological survey parameters consisting of rock mass physical and mechanical parameters, structural surface characteristics, and in-situ stress parameters;

[0024] Specifically, the physical and mechanical parameters of the rock mass include the uniaxial compressive strength of the rock mass, the cohesion of the rock mass, the internal friction angle, the elastic modulus of the rock mass, Poisson's ratio, and the rock mass fragmentation coefficient, etc.

[0025] The structural features include the thickness of a single rock layer and the reduction factor of interlayer cementation;

[0026] The geostress parameters include the initial geostress.

[0027] Based on the above embodiments, this method further includes:

[0028] S2. Based on the geological exploration parameters, determine the chain-like catastrophe evolution mode of tunnel floor heave in horizontal thin-layered weakly cemented expansive rock strata;

[0029] Specifically, the floor heave of horizontally thin-layered, weakly cemented expansive rock tunnels is a multi-stage, progressively advancing chain evolution process. This evolution process is divided into four stages, each of which exists independently yet influences each other, jointly driving the formation of the floor heave disaster. For example... Figure 2 As shown, Figure 2 (a) illustrates the crack initiation stage. Figure 2 (b) illustrates the infiltration, softening, and expansion stages. Figure 2 (c) illustrates the peeling and buckling stage. Figure 2 (d) shows the stage of deformation accumulation.

[0030] The first stage is the fissure initiation stage. Tunnel excavation disrupts the original rock stress balance, leading to radial stress release and tangential stress concentration in the rock mass at the tunnel bottom. Since the bedding planes of the horizontal thin rock mass are natural weak points, and the cement is mostly argillaceous, under the action of tangential stress concentration, the rock mass is prone to initiating vertical fissures along the bedding planes or primary micro-fissures.

[0031] Furthermore, the cyclic dynamic load generated by train traffic during operation will accelerate the expansion and connection of microcracks, eventually forming vertical seepage channels and providing a path for subsequent water intrusion.

[0032] The second stage is the seepage, softening, and expansion stage, in which water within the tunnel seeps into the surrounding rock at the tunnel floor through gaps in the drainage system or the existing network of vertical fissures. Water infiltrates the tunnel mainly through two pathways: one is through defects in the drainage system, specifically including failure of the sealing of drainage ditch joints and cracking of the side ditch concrete; the other is through the vertical fissures formed in the first stage.

[0033] When the seepage reaches a certain level, the rock mass enters a critical softening state. When the water comes into contact with the clay minerals in the rock mass, it softens the muddy cement between the layers, resulting in a significant reduction in the interlayer bond strength. At the same time, it reduces the internal friction angle and shear strength of the rock mass.

[0034] Furthermore, moisture diffuses laterally along the bedding planes, forming a softened zone, which is a key factor in the development of tunnel floor heave disaster.

[0035] After the weakly cemented expansive rock at the bottom of the tunnel absorbs enough water, the hydrophilic minerals undergo hydration, causing the rock mass to expand and generating expansion stress.

[0036] Due to the differences in permeability of the rock mass, the expansion effect is unevenly distributed. The shallow rock mass expands first, forming a difference in expansion stress, which causes the deep, unexpanded rock mass to shift towards the free face of the tunnel bottom. The cracks further expand, forming a positive feedback loop of expansion-crack expansion-intensified seepage, which accelerates the evolution of the bottom heave disaster.

[0037] The third stage is the stripping and buckling stage. Under the action of continuous expansion stress, the horizontal thin-layer rock mass has extremely low interlayer cementation strength and thin single-layer thickness, and cannot form an overall structure to resist the upward bulging deformation. Therefore, interlayer shear failure and relative slip occur from the weakest bedding plane, that is, interlayer stripping.

[0038] Furthermore, after being stripped, the single or several thin rock slabs, under axial pressure, lose their lateral restraint and undergo longitudinal buckling, i.e., folding failure, just like thin wooden boards that are bent and stacked together, undergoing upward folding deformation, and the deformation increases with the number of layers.

[0039] The fourth stage is the deformation accumulation stage, where the deformation of each layer of rock mass will be superimposed upwards, causing the vertical load borne by the tunnel bottom arch structure to far exceed the design value, ultimately leading to the overall upward bulging of the tunnel bottom and the formation of a bottom bulge.

[0040] When the cumulative heave exceeds the standard limit, it will cause the track structure smoothness to seriously exceed the standard, affecting the safety and comfort of train operation.

[0041] If the volume of the drum continues to increase, it will be necessary to suspend operations for emergency rectification, resulting in huge economic losses and social impact.

[0042] Based on the above embodiments, this method further includes:

[0043] S3. Based on the chain-like disaster evolution model and geological exploration parameters, the total floor heave displacement of the tunnel is predicted through a quantitative calculation model;

[0044] Specifically, step S3 includes:

[0045] S31. The total bottom drum displacement is decomposed into five sub-displacements: elastoplastic displacement, expansion displacement, expansion displacement, flexural buckling displacement, and damage rheological displacement.

[0046] S32. Based on the rock mass elastic modulus, Poisson's ratio, cohesion, internal friction angle, fragmentation coefficient, free expansion rate, interlayer cementation strength, single-layer rock mass thickness and initial in-situ stress in the geological exploration parameters, the displacement of each component is calculated respectively.

[0047] Specifically, step S32 includes:

[0048] S321. Based on the initial ground stress, rock mass elastic modulus, Poisson's ratio, cohesion, and internal friction angle, the elastoplastic displacement caused by tunnel excavation unloading is calculated. The specific calculation formula is as follows:

[0049] ;

[0050] In the formula, Indicates elastic-plastic displacement. E The elastic modulus of the rock mass. μ Poisson's ratio of the rock mass r 0 Where is the tunnel radius. The friction angle within the rock mass. P 0 For initial ground stress, c For rock mass cohesion, σ c It represents the uniaxial compressive strength of the rock mass.

[0051] S322. Based on the fragmentation coefficient and initial in-situ stress, the expansion displacement caused by volumetric fragmentation after rock mass shear failure is calculated. The specific calculation formula is as follows:

[0052] ;

[0053] In the formula, Indicates expansion displacement. ξ The rock mass fragmentation coefficient is... A , BTo determine the correlation coefficient of expansion stress, indoor triaxial compression tests were conducted under different confining pressures. A linear regression was performed with the ratio of the test confining pressure to the corresponding peak strength as the abscissa and the characteristic length of the plastic zone obtained through experimental analysis as the ordinate. The slope of the resulting straight line is then calculated. A The intercept is B .

[0054] S323. Based on the free expansion rate and tunnel geometry, the expansion displacement caused by the hydration reaction of the rock mass upon contact with water is calculated. The specific calculation formula is as follows:

[0055] ;

[0056] In the formula, K s The free expansion rate of the rock mass. α Where is the expansion effect coefficient, and C is the tunnel width.

[0057] S324. Based on the thickness of a single rock layer, initial in-situ stress, and interlayer cementation strength, the flexural buckling displacement caused by longitudinal buckling after rock mass stripping is calculated. The specific calculation formula is as follows:

[0058] ;

[0059] In the formula, σ x This represents the axial compressive stress in the rock mass, calculated from the initial geostress. For the span of thin rock slabs, the tunnel width is usually taken as the reference. C , t The thickness of a single rock layer. k b The buckling coefficient, β This is the interlayer bond reduction factor, calculated from the interlayer bond strength. This represents the elastic modulus of the rock mass.

[0060] S325. Based on the rock mass rheological parameters and the tunnel's design and operation time, the damage rheological displacement caused by rock mass damage, softening, and rheology is calculated. The specific calculation formula is as follows:

[0061] ;

[0062] In the formula, E 1 For rheological modulus, η 1 The viscoelastic coefficient, η 2 The viscosity coefficient, σ d The long-term effective stress of the rock mass is determined by the results of in-situ stress testing and the calculation of support reaction force. The operating time refers to the critical operating period or design reference period of the tunnel, such as 100 years for high-speed railway tunnels. α d The damage development coefficient ranges from 0.001 to 0.005. k It is a geometric factor, equivalent to the tunnel radius r0.

[0063] S33. The five individual displacements are superimposed to obtain the final value of the total tunnel floor heave displacement. :

[0064] ;

[0065] In response to the aforementioned chain-like disaster model, this embodiment constructs a three-in-one active support system of "structural reinforcement - rock mass consolidation - waterproofing and source blocking". Each subsystem targets the key links in the disaster chain, and at the same time, it forms an overall protective capability through spatiotemporal and mechanical coordination mechanisms to ensure that the measures support and complement each other, thereby achieving full-chain prevention and control of bottom heave disasters.

[0066] Based on the above embodiments, this method further includes:

[0067] S4. Based on the total heave displacement, determine the construction parameters of the active support system, which consists of a structural reinforcement subsystem, a rock mass reinforcement subsystem, and a waterproofing and source-blocking subsystem;

[0068] Specifically, the structural reinforcement subsystem resists flexural buckling displacement caused by the peeling and buckling of thin rock layers through high stiffness. u bend and share the initial elastoplastic displacement caused by excavation. u ep .

[0069] The rock mass reinforcement subsystem suppresses dilatational displacement by enhancing interlayer shear strength. u dil Furthermore, by forming composite thick plates, the risk of buckling is reduced, thereby controlling bending buckling displacement. u bend .

[0070] The waterproofing and source-blocking subsystem cuts off the water infiltration path at the source, reducing external factors that induce surrounding rock expansion, thereby reducing expansion displacement. u exp Simultaneously, by maintaining the surrounding rock in a relatively dry state, its long-term rheological softening is slowed down, thus mitigating the damage rheological displacement. u creep Its development has been inhibited.

[0071] Specifically, step S4 includes:

[0072] S41. Calculate the proportions of bending buckling displacement, expansion displacement, and dilatation displacement in the total heel displacement, respectively:

[0073] S42. When the proportion of bending buckling displacement exceeds the first preset threshold, it indicates that the stripping and longitudinal buckling of the thin rock mass are the main causes of bottom heave, and it is necessary to improve the invert arch rise-span ratio and the reinforced concrete strength grade in the structural strengthening subsystem.

[0074] Specifically, the rise-to-span ratio of the invert arch structure is set to 1 / 6, and the design strength grade of the concrete for the invert arch lining is set to C35 or higher. For sections with particularly large predicted displacements, C40 reinforced concrete can be used, with an expansion agent added to compensate for shrinkage and enhance the overall structural integrity.

[0075] S43. When the proportion of expansion displacement exceeds the second preset threshold, it indicates that the expansion caused by water-rock interaction is the main cause, and the thickness of the waterproof membrane in the waterproof source blocking subsystem should be increased.

[0076] Preferably, a fully enclosed waterproof structure design for the drainage ditch is also required, ensuring that the waterproof layer extends upward along the side wall of the drainage ditch to a sufficient distance above the design elevation of the invert arch, covering all areas that may be flooded.

[0077] S44. When the proportion of expansion displacement exceeds the third preset threshold, it indicates that the rock mass shear failure and fragmentation effect are significant. The circumferential and longitudinal spacing of the anchor bolts in the rock mass reinforcement subsystem should be reduced, or the anchor bolt length should be increased.

[0078] Specifically, in sections with high expansion pressure or low interlayer strength, the circumferential and longitudinal spacing of the anchor bolts is set to 1.0m x 1.0m.

[0079] In this embodiment, the first preset threshold, the second preset threshold, and the third preset threshold need to be set based on engineering experience, specification requirements, and tunnel safety level.

[0080] Based on the above embodiments, this method further includes:

[0081] S5. Based on the construction parameters, the structural reinforcement subsystem, rock mass reinforcement subsystem, and waterproofing and source-blocking subsystem are constructed in sequence to form an active support system for a horizontal thin-layer weakly cemented expansive rock tunnel, and a monitoring system is established for the active support system.

[0082] Specifically, the construction of the structural reinforcement subsystem includes:

[0083] S51a. Construct a reinforced concrete inverted arch structure with a predetermined rise-to-span ratio at the bottom of the tunnel;

[0084] Specifically, based on the rise-to-span ratio parameters, a custom-made, integral steel formwork is used for installation. Before installation, the centerline, arch foot elevation, and arch crown elevation of the invert arch structure must be determined. The formwork installation should be firm and smooth, and rubber strips should be used to seal the joints to prevent grout leakage.

[0085] S52a. Add reinforcing steel bars to the stress concentration areas at the arch foot and arch crown of the inverted arch structure;

[0086] S53a. Concrete is poured into the inverted arch structure using a layered pouring method;

[0087] Specifically, the thickness of each layer should be controlled between 30 and 50 centimeters to ensure compaction. Use an immersion vibrator for thorough compaction, ensuring even distribution of vibration points to avoid under-vibration or over-vibration, until cement slurry appears on the concrete surface, no longer significantly settles, and no air bubbles escape. After the concrete is poured, cover the surface with geotextile or a film for insulation and moisture retention to prevent early cracking.

[0088] S54a. When the concrete strength reaches the preset strength, the rock mass is reinforced.

[0089] Preferably, before constructing the invert arch structure, the following steps are also included:

[0090] Based on the total heave displacement, tunnel segments whose bending buckling displacement ratio exceeds a fourth preset threshold are identified, and these tunnel segments are designated as easily deformable segments. In this embodiment, the fourth preset threshold should be determined comprehensively based on the engineering safety level, allowable structural deformation, and expert experience, and is usually higher than the first preset threshold, in order to screen out the local areas where the risks are most concentrated.

[0091] A polyurethane elastic buffer layer is installed between the surface of the tunnel bottom rock mass and the invert arch structure in the easily deformable section; then, the joints of the polyurethane elastic buffer layer are sealed by hot-melt welding.

[0092] Specifically, the construction of the rock mass reinforcement subsystem includes:

[0093] S51b. Drill anchor bolt holes in the horizontal thin rock mass below the inverted arch structure, and install hollow grouting anchor bolts in the anchor bolt holes; preferably, the anchor bolt holes are arranged in a quincunx pattern.

[0094] S52b. Pressure grouting is performed on the hollow grouting anchor rod using cement grout until grout returns from the anchor rod orifice;

[0095] Specifically, grouting is carried out in stages and by gradually increasing the pressure. When the grout with a concentration similar to that of the incoming grout continues to return from the orifice, the design pressure is maintained for a certain period of time, and then grouting is stopped and the grouting valve is closed.

[0096] S53b. Lay a pad and a steel mesh in sequence above the grouting anchor, and weld the pad and the steel mesh together to fix them in place;

[0097] S54b. A fiber-reinforced concrete cushion layer is sprayed onto the reinforcing mesh to form a thick composite rock plate covering the anchor bolts, such as... Figure 3 As shown.

[0098] Preferably, before drilling the anchor bolt hole, the procedure further includes:

[0099] In water-rich strata, grouting holes are arranged circumferentially along the outer contour of the tunnel bottom excavation, with a hole depth not less than the depth of the tunnel bottom disaster impact.

[0100] Pre-grouting is carried out into the grouting holes to form a reinforcement ring of a predetermined depth, thereby pre-sealing the groundwater channel and reinforcing the weak rock mass before excavation; preferably, the grout is diffused and cemented in the rock mass fissures by segmented grouting.

[0101] Specifically, the construction of the waterproof and source-blocking subsystem includes:

[0102] S51c. A composite protective layer is formed by laying a polymer waterproof membrane and geotextile on the outer surface of the central drainage ditch and the longitudinal drainage ditches on both sides of the tunnel. Figure 4 As shown;

[0103] First, a geotextile is laid as a protective layer on the sidewalls and base of the drainage ditch. Then, a polymer waterproof membrane, which can be PVC or EVA, is laid on top of the geotextile. The membrane should completely cover the outer surface of the drainage ditch structure and extend upwards along the sidewalls to an area at least 30 cm above the design elevation of the invert arch, to cover all potential flooding areas. During installation, the membrane should be laid flat, wrinkle-free, and in close contact with the substrate.

[0104] S52c. The joints of the polymer waterproof membrane are sealed using a hot-melt welding process, and the airtightness of the weld is tested. Specifically, one end of the weld is sealed, and compressed air is injected into the other end and pressure is maintained. The sealing performance of the weld is judged by observing whether the pressure gauge reading drops within a set time.

[0105] S53c. Install water-swellable waterstop strips and fill them with sealant at the joint between the drainage ditch and the tunnel lining.

[0106] Specifically, a monitoring system is established for the active support system, including:

[0107] Settlement monitoring points are set up along the longitudinal direction of the tunnel at preset intervals, and high-precision total station is used to monitor the deformation data of the tunnel bottom. Preferably, the preset interval is 20-50 meters.

[0108] Sensors are installed on the inverted arch reinforcement and anchor bolts to monitor the stress state of the support system in real time;

[0109] Infrared thermal imagers were used to monitor the waterproof structure of the drainage ditch and the seepage-proof layer at the bottom of the roadbed in real time to evaluate the waterproofing effect.

[0110] In summary, this embodiment, through a high-span-to-rise inverted arch, a systematic inverted arch anchor bolt, and a fully enclosed drainage ditch for waterproofing, achieves source blocking, process suppression, and outcome resistance of the disaster chain. It can effectively eradicate tunnel bottom heave and greatly improve the stability and safety of long-term tunnel operation. It is particularly suitable for tunnel projects such as high-speed railways and heavy-haul railways that have extremely high requirements for track smoothness.

[0111] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

[0112] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A disaster mode and active support system for a horizontal thin-layer weakly cemented expansive rock tunnel, characterized in that, include: Geological surveys were conducted in the tunnel engineering area to obtain geological survey parameters consisting of rock mass physical and mechanical parameters, structural surface characteristics, and in-situ stress parameters. Based on the geological exploration parameters, the chain-like catastrophe evolution mode of tunnel floor heave in horizontal thin-layered weakly cemented expansive rock strata was determined. Based on the aforementioned chain-like disaster evolution model and geological exploration parameters, the total floor heave displacement of the tunnel is predicted through a quantitative calculation model. Based on the total heave displacement, the construction parameters of the active support system, consisting of a structural reinforcement subsystem, a rock mass reinforcement subsystem, and a waterproofing and source-blocking subsystem, are determined. Based on the construction parameters, the structural reinforcement subsystem, rock mass reinforcement subsystem, and waterproofing and source-blocking subsystem are constructed in sequence to form an active support system for a horizontal thin-layer weakly cemented expansive rock tunnel, and a monitoring system is established for the active support system.

2. The disaster mode and active support system for horizontal thin-layer weakly cemented expansive rock tunnels according to claim 1, characterized in that, Based on the aforementioned chain-like catastrophe evolution model and geological exploration parameters, the total floor heave displacement of the tunnel is predicted using a quantitative calculation model, including: The total bottom drum displacement is decomposed into five sub-displacements: elastoplastic displacement, expansion displacement, dilatation displacement, flexural buckling displacement, and damage rheological displacement. Based on the rock mass elastic modulus, Poisson's ratio, cohesion, internal friction angle, fragmentation coefficient, free expansion rate, interlayer cementation strength, single-layer rock mass thickness, and initial in-situ stress in the geological exploration parameters, the displacement of each component is calculated. The final value of the total tunnel floor displacement is obtained by superimposing the five sub-displacements.

3. The disaster mode and active support system for horizontal thin-layer weakly cemented expansive rock tunnels according to claim 2, characterized in that, Based on the rock mass elastic modulus, Poisson's ratio, cohesion, internal friction angle, fragmentation coefficient, free expansion rate, interlayer cementation strength, single-layer rock mass thickness, and initial in-situ stress from the geological exploration parameters, the displacements of each component are calculated, including: Based on the initial ground stress, rock mass elastic modulus, Poisson's ratio, cohesion and internal friction angle, the elastoplastic displacement caused by tunnel excavation unloading is calculated. Based on the fragmentation coefficient and initial in-situ stress, the expansion displacement caused by volume fragmentation after rock mass shear failure was calculated. Based on the free expansion rate and tunnel geometry, the expansion displacement caused by the hydration reaction of the rock mass upon contact with water was calculated. Based on the thickness of a single rock layer, the initial geostress, and the interlayer cementation strength, the flexural buckling displacement caused by longitudinal buckling after rock mass stripping is calculated. Based on the rock mass rheological parameters and the tunnel's design and operation time, the damage rheological displacement caused by rock mass damage, softening, and rheology was calculated.

4. The disaster mode and active support system for horizontal thin-layer weakly cemented expansive rock tunnels according to claim 1, characterized in that, Based on the total heave displacement, the construction parameters of the active support system, consisting of a structural reinforcement subsystem, a rock mass reinforcement subsystem, and a waterproofing and source-blocking subsystem, are determined, including: Calculate the proportions of bending buckling displacement, expansion displacement, and volumetric displacement in the total heave displacement, respectively: When the proportion of bending buckling displacement exceeds the first preset threshold, the rise-to-span ratio of the invert arch and the strength grade of reinforced concrete in the structural strengthening subsystem are increased. When the proportion of expansion displacement exceeds the second preset threshold, the thickness of the waterproof membrane in the waterproof source blocking subsystem is increased. When the proportion of expansion displacement exceeds the third preset threshold, reduce the circumferential and longitudinal spacing of the anchor bolts in the rock mass reinforcement subsystem, or increase the anchor bolt length.

5. The disaster mode and active support system for horizontal thin-layer weakly cemented expansive rock tunnels according to claim 1, characterized in that, Construction of the structural reinforcement subsystem includes: A reinforced concrete inverted arch structure with a predetermined rise-to-span ratio is constructed at the bottom of the tunnel; Reinforcing steel bars are added to the stress concentration areas at the arch foot and arch crown of the inverted arch structure; The concrete was poured into the inverted arch structure using a layered pouring method. Once the concrete reaches the preset strength, the rock mass is reinforced.

6. The disaster mode and active support system for horizontal thin-layer weakly cemented expansive rock tunnels according to claim 1, characterized in that, Construction of the rock mass reinforcement subsystem includes: Anchor bolt holes are drilled in the horizontal thin rock mass below the inverted arch structure, and hollow grouting anchor bolts are installed in the anchor bolt holes; Cement grout is used to pressure grout the hollow grouting anchor until grout returns from the anchor hole. A pad and a steel mesh are laid sequentially above the grouting anchor, and the pad and the steel mesh are welded and fixed together. A fiber-reinforced concrete cushion layer is sprayed onto the reinforcing mesh to form a thick composite rock plate covering the anchor bolts.

7. The disaster mode and active support system for horizontal thin-layer weakly cemented expansive rock tunnels according to claim 1, comprising the construction of the waterproofing and source-blocking subsystem, including: On the outer surfaces of the central drainage ditch and the longitudinal drainage ditches on both sides of the tunnel, a composite protective layer is formed by laying polymer waterproof membrane and geotextile. The joints of the polymer waterproof membrane were sealed using a hot-melt welding process, and the welds were tested for air tightness. Water-swellable waterstop strips are installed at the joints between the drainage ditch and the tunnel lining, and then filled with sealant.

8. The disaster mode and active support system for horizontal thin-layer weakly cemented expansive rock tunnels according to claim 5, further comprising, before constructing the invert arch structure: Based on the total heave displacement, tunnel segments whose bending buckling displacement ratio exceeds a fourth preset threshold are identified, and these tunnel segments are classified as easily deformable segments. A polyurethane elastic buffer layer is provided between the surface of the tunnel bottom rock mass and the invert arch structure in the easily deformable section; The joints of the polyurethane elastic buffer layer are sealed using a hot-melt welding process.

9. The disaster mode and active support system for horizontal thin-layer weakly cemented expansive rock tunnels according to claim 6, further comprising, before drilling anchor bolt holes: In water-rich strata, grouting holes are arranged circumferentially along the outer contour of the tunnel bottom excavation. Pre-grouting of the tunnel floor is carried out into the grouting holes to form a reinforcement ring of a predetermined depth.

10. The disaster mode and active support system for horizontal thin-layer weakly cemented expansive rock tunnels according to claim 1, characterized in that, Establish a monitoring system for the active support system, including: Settlement monitoring points are set up along the longitudinal direction of the tunnel at preset intervals to monitor the deformation data of the tunnel bottom; Sensors are installed on the inverted arch reinforcement and anchor bolts to monitor the stress state of the support system in real time; Real-time monitoring of the waterproof structure of the drainage ditch and the seepage-proof layer at the bottom of the roadbed to assess the waterproofing effect.

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