Underground composite lining cavern structure and construction method

Abstract

The invention provides an underground composite lining cavern structure and a construction method.The underground composite lining cavern structure comprises a reinforced concrete lining layer, a ceramsite foam concrete lining layer and a rock surrounding layer from inside to outside, and graded anchor rod assemblies are arranged between the rock surrounding layer and the ceramsite foam concrete lining layer to achieve a multi-stage energy dissipation mechanism; the reinforced concrete lining layer can exert the characteristic of high bearing capacity, and the problem that the shear strength and the overall stability are insufficient when ceramsite foam concrete is independently used is solved; the ceramsite foam concrete lining layer can utilize the energy absorption characteristic of the ceramsite foam concrete lining layer to relieve the problems that traditional reinforced concrete is insufficient in toughness and prone to crack expansion under dynamic loads; according to the graded anchor rod assembly, graded energy consumption can be achieved through cooperation of the multi-stage reducing sleeve, the anchoring rod body and the sliding sleeves with different diameters, and the situation that a conventional anchor rod is prone to anchoring failure or fracture when surrounding rock is greatly deformed is avoided. According to the structure, the advantages of all the layers and the progressive energy dissipation mechanism of the graded anchor rods are combined, and the anti-explosion, anti-seismic and deformation adaptive capacity of the cavern under the action of strong dynamic loads is improved.

Description

Technical Field

[0001] This invention relates to the field of underground engineering protection technology, and in particular to an underground composite lining cavern structure and construction method. Background Technology

[0002] With the rapid development of underground engineering construction, deep geotechnical engineering, national defense protection engineering, and urban underground space development have placed higher demands on the blast resistance, earthquake resistance, and large deformation adaptability of structures. Traditional underground cavern protection structures mostly use single reinforced concrete linings or ordinary anchor bolt supports. However, under earthquake, blast impact, or large deformation of surrounding rock conditions, they are prone to brittle failure, cracking, or even overall instability, making it difficult to meet the safety and durability requirements of modern engineering. Currently, ceramsite foam concrete, due to its lightweight, high strength, and good energy absorption characteristics, has been gradually applied in protection engineering. However, its shear strength and overall stability are insufficient when used alone. While traditional reinforced concrete linings have high load-bearing capacity, their toughness is insufficient, and crack propagation is prone to occur under dynamic loads. In addition, conventional anchor bolt support systems are prone to anchorage failure or breakage under large deformation of surrounding rock, failing to achieve graded energy dissipation, thus limiting the overall deformation resistance of the support structure.

[0003] To address the aforementioned issues, there is an urgent need for a novel composite protective structure in existing technologies that can combine the energy absorption advantages of expanded clay foam concrete, the high load-bearing characteristics of reinforced concrete, and the progressive energy dissipation mechanism of graded large deformation anchors. This would enable multi-level protection under conditions of explosion, impact, or large deformation of surrounding rock, ensuring the overall stability and safety of underground caverns. Summary of the Invention

[0004] The purpose of this invention is to provide an underground composite lining cavern structure and construction method to solve the problem that existing underground protective structures are prone to brittle failure under strong dynamic loads such as explosions and earthquakes.

[0005] The present invention provides an underground composite lining cavern structure, comprising a reinforced concrete lining layer, a ceramsite foam concrete lining layer and a surrounding rock layer arranged sequentially from the inside to the outside, wherein a multi-component hierarchical anchor bolt assembly is arranged at intervals between the surrounding rock layer and the ceramsite foam concrete lining layer along the contour direction of the cavern. The graded anchor bolt assembly includes a multi-stage variable diameter sleeve, an anchor bolt body, and multiple sliding sleeves of different diameters. The multi-stage variable diameter sleeve is sleeved on the outside of the anchor bolt body. Each variable diameter area of ​​the anchor bolt body is fixedly provided with a sliding sleeve corresponding to its diameter. The end of the multi-stage variable diameter sleeve is pressed with a fixing plate by a spiral anchor.

[0006] Furthermore, the reinforced concrete lining layer is formed by a skeleton consisting of cubic steel mesh and arched steel mesh, and is formed by spraying concrete.

[0007] Furthermore, the expanded clay foam concrete lining layer is constructed by splicing segmented arched test blocks and cubic test blocks.

[0008] Furthermore, the arched test block and the cube test block are cast using a circular arch mold and a cube mold, respectively, with an opening at the top of the mold.

[0009] Furthermore, the graded anchor bolt assembly is fixed in the anchor bolt hole of the surrounding rock by anchoring grout, and its end is connected to the lining layer by a fixing plate and a spiral anchor.

[0010] Furthermore, the outer circumferential surface of each of the sliding sleeves abuts against the inner wall of the corresponding position of the multi-stage variable diameter sleeve.

[0011] Furthermore, the outer side of the sliding sleeve is provided with a friction coating that contacts the inner wall of the multi-stage variable diameter sleeve, with a friction coefficient of 0.3-0.5.

[0012] A construction method for an underground composite-lined cavern structure, comprising the aforementioned underground composite-lined cavern structure, includes the following specific steps: S1: Drill a variable-diameter borehole in the surrounding rock layer and inject grout into the borehole to implant graded anchor bolt components; S2: After the test blocks of the ceramsite foam concrete lining layer are poured in sections, they are spliced ​​together along the outline of the cavern. S3: Install the steel mesh framework and spray concrete to form a reinforced concrete lining layer.

[0013] Furthermore, the test blocks of the expanded clay foam concrete lining layer are spliced ​​using cement mortar, and the joint thickness does not exceed 5mm.

[0014] Furthermore, the concrete spraying of the reinforced concrete lining layer is carried out in two layers, with the thickness of the first spraying being 60%-70% of the total thickness.

[0015] The technical solution of this invention establishes a multi-stage energy dissipation mechanism by setting up a reinforced concrete lining layer, a ceramsite foamed concrete lining layer, and a surrounding rock layer from the inside out, and arranging graded anchor bolt assemblies between the surrounding rock layer and the ceramsite foamed concrete lining layer. The reinforced concrete lining layer can exert high load-bearing characteristics, compensating for the insufficient shear strength and overall stability of ceramsite foamed concrete when used alone. The ceramsite foamed concrete lining layer can utilize its energy absorption characteristics to alleviate the problems of insufficient toughness and easy crack propagation under dynamic loads in traditional reinforced concrete. The graded anchor bolt assembly, through the cooperation of multi-stage variable diameter sleeves, anchor rods, and sliding sleeves of different diameters, can achieve graded energy dissipation, avoiding the easy anchoring failure or breakage of conventional anchor bolts under large deformation of the surrounding rock. The overall structure combines the advantages of each layer with the progressive energy dissipation mechanism of the graded anchor bolts, significantly improving the underground cavern's resistance to blasting, earthquakes, and large deformations under strong dynamic loads such as explosions and earthquakes, effectively avoiding brittle failure, cracking, or overall instability, and ensuring the safety and durability of the structure. Attached Figure Description

[0016] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the composite lining structure of the present invention.

[0018] Figure 2 This is a schematic diagram of the installation of the graded anchor bolt assembly in this invention.

[0019] Figure 3 This is a schematic diagram of the overall structure of the graded anchor bolt assembly in this invention.

[0020] Figure 4 This is a schematic diagram of the installation of the sliding sleeve on the anchor rod body in this invention.

[0021] Figure 5 This is a schematic diagram of the sleeve structure in this invention.

[0022] Figure 6 This is a schematic diagram of the arched mold and test block for the ceramsite foam concrete lining layer of the present invention.

[0023] Figure 7 This is a schematic diagram of the cube mold and test block of the expanded clay foam concrete of the present invention.

[0024] Figure 8 This is a schematic diagram of the steel mesh structure in this invention.

[0025] Figure 9 This is a schematic diagram of the reinforced concrete fixing mold in this invention.

[0026] Explanation of reference numerals in the attached drawings: 1-Reinforced concrete lining layer, 101-Cube steel mesh, 102-Arch steel mesh, 2-Lightweight foamed concrete lining layer, 3-Graded anchor bolt assembly, 301-Anchor bolt body, 302-Sleeve, 303-Spiral anchor, 304-Fixing plate, 305-Sliding sleeve, 4-Surrounding rock layer, 5-Anchor bolt hole, 6-Anchoring grout, 7-Circular arch mold, 8-Arch test block, 9-Cube mold, 10-Cube test block, 11-Fixing mold. Detailed Implementation

[0027] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0029] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the stated features. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified. Furthermore, the terms "installed," "connected," and "linked" should be interpreted broadly; for example, they may refer to a fixed connection, a detachable connection, or an integral connection; they may refer to a mechanical connection or an electrical connection; they may refer to a direct connection or an indirect connection through an intermediate medium; and they may refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0030] Example 1 like Figures 1-9As shown, the present invention provides an underground composite lining cavern structure and construction method. The composite lining structure adopts a three-layer composite system design, which includes, from the center of the cavern to the outside, a reinforced concrete lining layer 1: as the main load-bearing structural layer; a ceramsite foam concrete lining layer 2: as an energy absorption buffer layer; and a surrounding rock layer 4: as an outer support structure.

[0031] The reinforced concrete lining layer 1 is located on the innermost side of the structure and consists of a cubic steel mesh 101 and an arched steel mesh 102 forming the main framework. During construction, the steel mesh frame is first installed on the outside of the expanded clay foam concrete lining layer 2, with the cubic steel mesh 101 used for the straight walls and the arched steel mesh 102 used for the arched top. After installation, a fixed mold 11 is set on the outermost side, and then shotcrete is applied. The shotcrete is used to form an integral shell; after the concrete has cured to the design strength, the fixed mold 11 is removed, forming the complete reinforced concrete lining layer 1. Under impact loads, the steel mesh absorbs energy through plastic deformation, and the concrete dissipates energy through controlled fragmentation.

[0032] The expanded clay foam concrete lining layer 2 is located outside the reinforced concrete lining layer 1. It is cast in sections using specially made molds. The straight wall section uses a cubic mold 9, and the arched top section uses a circular arch mold 7. The molds are made of steel plates spliced ​​together, with openings at the top for demolding. After the cast arched test blocks 8 and cubic test blocks 10 are cured, they are spliced ​​together with cement mortar to form the complete expanded clay foam concrete lining layer 2.

[0033] A graded anchor bolt assembly 3 is arranged at intervals along the contour direction of the cavern between the surrounding rock layer 4 and the ceramsite foam concrete lining layer 2. In this embodiment, the graded anchor bolt assembly 3 includes a three-stage variable diameter sleeve 302, an anchor rod body 301, and three sliding sleeves 305 of different diameters. The three-stage variable diameter sleeve 302 is sleeved on the outside of the anchor rod body 301. A sliding sleeve 305 corresponding to the diameter of each variable diameter area of ​​the three-stage variable diameter sleeve 302 is fixed on the anchor rod body 301. The sliding sleeve 305 can be welded to the anchor rod body 301 as a whole and installed into the sleeve 302. The outer diameter of the sliding sleeve 305 is slightly larger than the inner diameter of the sleeve 302. The sliding sleeve 305 needs to be pre-extruded into the sleeve 302 by a pressure device. The end of the three-stage variable diameter sleeve 302 is pressed with a fixing plate 304 by a spiral anchor 303. The spiral anchor 303 and the fixing plate 304 ensure the overall stability of the system. The fixing plate 304 is a steel plate. Under strong earthquakes or impacts, the three-stage variable diameter sleeve 302 and the three sliding sleeves 305 will slide relative to each other to achieve staged energy dissipation.

[0034] The expanded clay foam concrete lining layer 2 is prefabricated in sections using specially made cubic molds 9 and arch molds 7 to form arched test blocks 8 and cubic test blocks 10, which are then assembled on site. Energy absorption is achieved through the compression deformation of the porous foam matrix and the displacement of the lightweight expanded clay particles. The directional propagation of microcracks further dissipates the impact energy.

[0035] The graded anchor bolt assembly 3 is fixed in the surrounding rock layer 4 by anchoring grout 6; the three-stage variable diameter sleeve 302 and the sliding sleeve 305 form a sliding pair; under load, the three-stage variable diameter sleeve 302 and the sliding sleeve 305 undergo graded sliding, specifically: the energy absorption process of the graded anchor bolt assembly 3 is divided into three stages of sliding. Here, for easy distinction, the three sliding sleeves 305 with different diameters are named large sliding sleeve, medium sliding sleeve and small sliding sleeve respectively. The three are fixed to the threaded rod by threads and are spaced at a set distance; the three parts of the three-stage variable diameter sleeve 302 are named large sleeve, medium sleeve and small sleeve respectively. First-stage sliding: The large sliding sleeve slides in the large sleeve, while the medium and small sliding sleeves are in an unloaded state until the medium sliding sleeve contacts the medium sleeve. Second-stage sliding: The large sliding sleeve and the medium sliding sleeve slide simultaneously in the large sleeve and the medium sleeve respectively, while the small sliding sleeve remains unloaded until the small sliding sleeve contacts the small sleeve. Third-stage slippage: The large, medium and small sliding sleeves 305 simultaneously slip in the large, medium and small sleeves 302 respectively, until the small sliding sleeve slips to the end of the small sleeve and gets stuck. At this time, the threaded rod begins to provide tension. When the rock mass deformation stress exceeds the maximum tensile strength of the inner rod, the anchor rod fails and is destroyed.

[0036] This composite structure achieves multi-level protection through the following methods: First-level protection: The graded anchor bolt assembly 3 absorbs the initial impact energy through the sliding of the sleeve 302; Second-level protection: The ceramsite foam concrete lining layer 2 dissipates the remaining energy through material deformation and failure; Third-level protection: The reinforced concrete lining layer 1 provides the final load-bearing guarantee. The load transfer path is: surrounding rock layer 4 → anchor bolt assembly → ceramsite concrete layer → reinforced concrete layer.

[0037] The specific installation process of the graded anchor bolt assembly 3 of the present invention is as follows: Drilling operation stage: Use a hydraulic rock drill to drill anchor holes 5 at the designed positions on the surface of the surrounding rock cavern; control the diameter of the drill hole to be 10-15mm larger than the diameter of the graded anchor assembly 3; use an inclinometer to monitor the drilling angle to ensure that the inclination deviation does not exceed ±2°; after drilling is completed, use a high-pressure air pipe to thoroughly clean the hole and remove rock powder and debris inside the hole.

[0038] Grouting construction stage: Prepare micro-expansion cement-based anchoring grout 6 with a water-cement ratio controlled at 0.38-0.42; inject the anchoring grout 6 into the anchor hole 5 through a grouting pump, and insert the grouting pipe to the bottom of the hole; maintain the grouting pressure at 0.3-0.5MPa to ensure that the grout fully fills the hole; control the grouting volume to exceed the theoretical calculation value by 10%-15%.

[0039] Anchor bolt insertion stage: Slowly insert the pre-assembled graded anchor bolt assembly 3 into the anchor bolt hole 5; keep the graded anchor bolt assembly 3 rotating at a uniform speed during insertion to promote uniform distribution of grout; control the insertion speed at 0.5-1.0 m / min to avoid grout segregation.

[0040] During the installation phase of the fixing system: accurately locate the installation position of the fixing plate 304 on the outer wall of the tunnel; fix the fixing plate 304 tightly against the lining surface using temporary supports; apply prestress through the spiral anchor 303, loading in three stages; finally tighten the spiral anchor 303 with a torque wrench to ensure reliable locking.

[0041] Quality inspection stage: Check the exposed length of the anchor rod, and control the deviation within ±20mm; conduct a pull-out test to check the anchoring force, which should not be less than 95% of the design value; check the contact density between the 304 fixing plate and the lining, and ensure that the local gap does not exceed 1mm; record the installation parameters of each anchor rod and establish a complete quality file.

[0042] Subsequent treatment phase: Corrosion protection treatment is applied to the exposed parts of the anchor bolts; the perimeter of the 304 fixing plate is sealed; the construction site is cleaned and excess materials and equipment are removed; necessary deformation monitoring points are set up.

[0043] The construction method for the expanded clay foam concrete lining layer 2 is as follows: According to the structural size requirements, thick steel plates are used to make cubic mold 9 and arch mold 7. The cubic mold 9 is designed to be detachable and consists of side plates, end plates and bottom plates. The arch mold 7 is assembled from segmented arc-shaped steel plates and is equipped with an adjustable support frame. All molds have pre-reserved openings at the top to facilitate concrete pouring and vibration.

[0044] Prepare expanded clay foam concrete according to the mix proportion. Soak the expanded clay for 24 hours in advance and control the moisture content to 15%-20%. After diluting the foaming agent, mechanically foam the concrete. The cube mold 9 is poured in layers, with each layer not exceeding 300mm in thickness. The arch mold 7 is poured symmetrically from the arch foot to the arch top. Control the pouring speed and use an immersion vibrator to vibrate. Vibrate for 20-30 seconds at each point. Stop pouring when the concrete is 50mm away from the top surface of the mold to leave room for curing.

[0045] After pouring, smooth the surface to ensure accurate geometric dimensions. Before initial setting, perform a second troweling to eliminate surface air bubbles and cover with plastic film to prevent moisture from evaporating too quickly.

[0046] After standing for 24 hours, begin watering and curing, maintaining a curing temperature of 20±5℃ and a relative humidity of ≥90%. Demolding can only be performed after the strength reaches 60% of the design strength.

[0047] Clean the installation base surface, removing laitance and debris. Moisten the contact surface with water 24 hours in advance. Position the specimen according to the design, controlling the error within ±5mm. Use mechanical hoisting for placement. First, install the lower cubic specimen block 10, then symmetrically install the arch-shaped specimen blocks 8 from the two arch feet towards the arch crown. Control the joint width to 10-15mm, fill with micro-expansion cement mortar, compact in layers, and smooth the joint surface to make it flush with the specimen block surface.

[0048] The construction method for reinforced concrete lining layer 1 is as follows: After the ceramsite foam concrete lining layer 2 is poured and installed, the cubic steel mesh 101 is installed first. Φ12mm HRB400 grade steel bars are tied at 150mm×150mm intervals. The mesh panels in the straight wall sections are welded together, with an overlap length of not less than 150mm. Then, the arched steel mesh 102 is installed. Pre-bent Φ14mm steel bars are arranged at 120mm×120mm intervals and reliably connected to the cubic steel mesh 101 using special connectors. All steel bar intersections must be firmly tied, and a 40mm thick concrete spacer is placed between the steel mesh and the base layer.

[0049] After the steel mesh is erected, a detachable fixed mold 11 is set up on the outermost side. The mold is made of 5mm thick steel plate. Flat molds are used for straight wall sections and segmented arc molds are used for arched sections. Before the mold is installed, a release agent is applied and rubber waterstops are added at the joints. The mold is fixed by an adjustable steel support system to ensure the overall rigidity and stability of the mold. The verticality deviation of the mold installation is controlled within 3mm and the height difference of the joints does not exceed 1mm.

[0050] Wet spraying technology is adopted, with concrete strength grade C30. The spraying operation is carried out in two layers. The thickness of the first layer is controlled at 80-100mm, the spraying angle is kept perpendicular to the sprayed surface, the spraying distance is 0.8-1.0m, and the air pressure is controlled at 0.4-0.6MPa. The second layer is sprayed after an interval of 2-3 hours, and the total thickness reaches the design requirement of 200mm. During the spraying process, the density and thickness of the concrete are checked at any time, and local depressions are repaired in time. After the spraying is completed, the surface is leveled with a screed immediately.

[0051] Curing should begin within 12 hours of spraying, using geotextile covering and regular watering to keep the concrete surface moist, with a curing period of no less than 14 days; when the ambient temperature is below 5℃, insulation measures should be taken, and external impacts are strictly prohibited during the curing period, with daily records of curing conditions and ambient temperature and humidity; strength tests should be conducted regularly during the curing period, and subsequent work can only proceed when the strength of the test blocks cured under the same conditions reaches more than 80% of the design value.

[0052] After the concrete strength reaches 75% of the design strength, the fixed formwork is removed in the order of first the arch top and then the straight walls, and first the non-load-bearing parts and then the load-bearing parts. Special tools are used during removal to avoid damage to the concrete edges and corners caused by rough construction. After the formwork is removed, the surface quality of the lining is thoroughly inspected. Local defects such as air bubbles and pitting are treated with special repair mortar. Finally, the dimensions are checked and the appearance quality is inspected to ensure that all indicators meet the design requirements.

[0053] When the structure is subjected to strong dynamic loads such as explosions or earthquakes, the protection system operates according to the following mechanism: First-level energy dissipation mechanism: When the structure is subjected to strong dynamic loads such as explosions or earthquakes, the anchor rod 301 provides radial restraint and suspension. Unlike traditional anchor rods that rely solely on the material's own strength to bear external loads, the graded anchor rod assembly 3 is fixed by the helical anchor 303 and the fixing plate 304. Under external impact, the sliding sleeve 305 and the sleeve 302 slip relative to each other. The impact load is absorbed through the material's elastic-plastic deformation and friction, combining the surrounding rock with the ceramsite foam concrete lining layer 2 and the reinforced concrete lining layer 1 into an integral load-bearing structure.

[0054] The second-level energy conversion mechanism: The remaining energy, buffered by the anchor system, is transferred to the expanded clay foam concrete lining layer 2. This layer achieves energy conversion through three physical mechanisms: the pore compression deformation of the porous foam matrix under pressure consumes approximately 45% of the transferred energy; the displacement and breakage of the lightweight expanded clay absorb energy; and the directional propagation of microcracks within the material dissipates the remaining energy. The splicing structure of the arched test block 8 and the cubic test block 10 ensures that energy is transferred in an orderly manner along a predetermined path, avoiding localized damage caused by stress concentration.

[0055] The third-level ultimate protection mechanism: The energy ultimately reaching the reinforced concrete lining layer 1 is absorbed through a dual mechanism: the cubic steel mesh 101 and the arched steel mesh 102 absorb some of the remaining energy through plastic deformation, and their yielding process effectively prolongs the load application time; the concrete matrix consumes some of the remaining energy through controlled fragmentation, and the fragmentation pattern exhibits an orderly distribution characteristic under the constraint of the fixed mold 11. This energy dissipation method, combining rigidity and flexibility, ensures the integrity of the structure while minimizing the vibration energy transmitted into the cavity.

[0056] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An underground composite-lined cavern structure, characterized in that, It includes a reinforced concrete lining layer, a ceramsite foamed concrete lining layer and a surrounding rock layer arranged sequentially from the inside to the outside. The surrounding rock layer and the ceramsite foamed concrete lining layer are provided with multiple sets of graded anchor bolt assemblies at intervals along the outline of the cavern. The graded anchor bolt assembly includes a multi-stage variable diameter sleeve, an anchor bolt body, and multiple sliding sleeves of different diameters. The multi-stage variable diameter sleeve is sleeved on the outside of the anchor bolt body. Each variable diameter area of ​​the anchor bolt body is fixedly provided with a sliding sleeve corresponding to its diameter. The end of the multi-stage variable diameter sleeve is pressed with a fixing plate by a spiral anchor.

2. The underground composite lining cavern structure according to claim 1, characterized in that, The reinforced concrete lining layer is formed by a skeleton consisting of cubic steel mesh and arched steel mesh, and is shaped by sprayed concrete.

3. The underground composite lining cavern structure according to claim 1, characterized in that, The expanded clay foam concrete lining layer is constructed by splicing arched test blocks and cubic test blocks cast in sections.

4. The underground composite lining cavern structure according to claim 3, characterized in that, The arched test block and the cube test block are formed by casting using a circular arch mold and a cube mold, respectively, with an opening at the top of the mold.

5. The underground composite lining cavern structure according to claim 1, characterized in that, The graded anchor bolt assembly is fixed in the anchor bolt hole of the surrounding rock by anchoring grout, and the end is connected to the lining layer by a fixing plate and a spiral anchor.

6. The underground composite lining cavern structure according to claim 1, characterized in that, The outer circumferential surface of each of the sliding sleeves abuts against the inner wall of the corresponding position of the multi-stage variable diameter sleeve.

7. The underground composite lining cavern structure according to claim 6, characterized in that, The outer side of the sliding sleeve is provided with a friction coating that contacts the inner wall of the multi-stage variable diameter sleeve, and the friction coefficient is 0.3-0.

5.

8. A construction method for an underground composite lining cavern structure, characterized in that, The underground composite lining cavern structure according to any one of claims 1-7 includes the following specific steps: S1: Drill a variable-diameter borehole in the surrounding rock layer and inject grout into the borehole to implant graded anchor bolt components; S2: After the test blocks of the ceramsite foam concrete lining layer are poured in sections, they are spliced ​​together along the outline of the cavern. S3: Install the steel mesh framework and spray concrete to form a reinforced concrete lining layer.

9. The construction method for the underground composite lining cavern structure according to claim 8, characterized in that, The test blocks of the expanded clay foam concrete lining layer are spliced ​​using cement mortar, and the joint thickness does not exceed 5mm.

10. The construction method of the underground composite lining cavern structure according to claim 8, characterized in that, The concrete spraying of the reinforced concrete lining layer is carried out in two layers, with the first spraying thickness being 60%-70% of the total thickness.

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