Circular through-hole cave physical model test device and method

Abstract

The present invention provides a circular through-hole karst cave physical model test device and method, which belongs to the field of physical property testing and analysis, and is used to prepare karst foundation model test blocks and conduct simulation experiments. The circular through-hole karst cave physical model test device includes a model frame with an opening at the top and a reinforcement structure arranged on the outer periphery of the model frame; it also includes a cylindrical cavity reservation part, the cavity reservation part is located inside the model frame and passes through the model frame at both ends. Rock-similar materials are poured into the model frame to form a karst foundation model test block. After the pouring is completed, the reservation part forms a through cylindrical cavity in the karst foundation model test block. This device combined with this method not only improves the simulation accuracy of the model test block on the karst foundation, but also facilitates the intuitive analysis of the impact of the cave on the foundation stability, providing a strong experimental basis for the design and treatment of karst foundations.

Description

Technical Field

[0001] The invention belongs to the field of physical property testing and analysis, and in particular relates to a circular through-hole karst cave physical model testing device and method. Background Art

[0002] Karst is a geological phenomenon formed by the long-term dissolution of soluble rocks by groundwater, often resulting in complex underground cave structures. If these caves lie beneath building foundations, they pose a significant threat to the safety and stability of the structure, potentially leading to reduced bearing capacity, uneven settlement, and other issues, posing safety risks to the building.

[0003] Currently, numerical analysis is the primary method used to analyze and treat karst foundations. However, this approach primarily focuses on analyzing a specific cross-section. It is difficult to accurately calculate and analyze the internal deformation patterns of complex three-dimensional karst caves, resulting in certain limitations.

[0004] To gain a deeper understanding of the characteristics and behavior of karst foundations, it is necessary to prepare karst foundation model specimens and conduct simulation experiments using similar principles. Through simulation experiments, we can intuitively observe and analyze the impact of karst caves on foundations, as well as the deformation and failure modes of foundations during loading, providing a more reliable theoretical basis and experimental support for the treatment and design of karst foundations. Summary of the Invention

[0005] In view of the above-mentioned shortcomings of the prior art, the object of the present invention is to provide a circular through-hole cave physical model test device and method for preparing karst foundation model test blocks and conducting simulation experiments.

[0006] To achieve the above-mentioned and other related purposes, the present invention provides a circular through-hole cave physical model test device and method.

[0007] Among them, the circular through-hole karst cave physical model test device includes a model frame with an open top and a reinforcement structure arranged on the periphery of the model frame;

[0008] It also includes a cylindrical cavity reservation part, which is located inside the model frame and passes through the model frame at both ends. Rock-similar materials are poured into the model frame to form a karst foundation model test block. After the pouring is completed, the reservation part forms a penetrating cylindrical cavity in the karst foundation model test block.

[0009] Optionally, the dry material mass ratio of the rock-like material is: 80% sand, 5% cement, and 15% gypsum powder;

[0010] When stirring and mixing, gypsum retarder and water need to be added. The amount of gypsum retarder is 0.3% of the mass of gypsum powder, and the amount of water is determined according to the water-to-solid ratio of 1:7.

[0011] Optionally, a weak interlayer reservation device is further included, wherein the weak interlayer reservation device includes a torsion rod and an interlayer membrane;

[0012] The cylinder of the cavity reserved part is provided with a membrane groove along the axis, and the membrane grooves are grouped into two, and the two groups of membrane grooves are respectively arranged on both sides of the circumference of the cavity reserved part;

[0013] The torsion rod body is located in the cavity reserved part, and the interlayer membrane is grouped in two pieces. The two groups of interlayer membranes are respectively arranged on both sides of the circumference of the torsion rod body. One end of each interlayer membrane is connected to the torsion rod body, and the other end passes through the corresponding membrane groove. The outer end is tightened and fixed. The two interlayer membranes in the same group are in the same direction, and the two interlayer membranes are cast with similar weak interlayer materials.

[0014] The dry material mass ratio of the weak interlayer similar material is: 80% sand, 10% red clay, and 10% gypsum powder;

[0015] When stirring and mixing, gypsum retarder and water need to be added. The amount of gypsum retarder is 0.3% of the mass of gypsum powder, and the amount of water is determined according to the water-to-solid ratio of 1:7.

[0016] Optionally, a strain detection device is further included, wherein the strain detection device includes a first side end cover, a second side end cover, a detection shaft and a driving mechanism;

[0017] During the test, limiting plates are arranged around the casting body, holes are arranged on the limiting plates at positions corresponding to the through-holes, the first side end cover and the second side end cover are respectively arranged on the two side exits of the through-holes through a clamping structure and attached to the limiting plates, the detection shaft is arranged in the through-holes, and both ends of the detection shaft are rotatably supported by the first side end cover and the second side end cover respectively and driven to rotate by the driving mechanism;

[0018] On one section of the detection axis, a row of displacement sensors are arranged along the axial direction, and the probes of the respective displacement sensors point to the wall of the through cave.

[0019] Optionally, it further comprises a tubular film, wherein the tubular film is capable of shrinking, and initially, the tubular film wraps the detection shaft;

[0020] When the detection shaft is placed in the through-hole, both ends of the tubular membrane extend beyond the ends of the through-hole, and the portion extending beyond the through-hole is attached to the limit plate on the end face and is pressed by the first side end cover and the second side end cover to form a sealing interface;

[0021] The first side end cover and the second side end cover are provided with injection holes. When fluid is injected into the interior, the tubular membrane expands and adheres tightly to the wall of the through cave.

[0022] Optionally, a rotation support sleeve is provided on the side of the first side end cover and the second side end cover facing the interior of the through cave, the detection shaft is rotatably installed in the rotation support sleeve, and a first magnet and a second magnet are provided at both ends of the detection shaft respectively;

[0023] The rotating support sleeve forms a sleeve protrusion on the other side of the first side end cover and the second side end cover, and the outer ring of the sleeve protrusion is provided with an annular limit platform, and the driving area is between the sleeve protrusion and the annular limit platform;

[0024] On the first side end cover, there is an electromagnetic coil in a circular array in the driving area, and the electromagnetic coil matches the position of the first magnet to form the driving mechanism;

[0025] On the second side end cover, there is a permanent magnet ring in the annular array in the driving area, the permanent magnet ring matches the position of the second magnet, and a pointer is also provided on the permanent magnet ring. A circular deflection scale is correspondingly provided on the second side end cover.

[0026] Optionally, the clamping structure includes a pressure ring, an air bag and an annular expansion belt;

[0027] The inner circular surface of the pressure ring is connected to the outer circular surface of the rotating support sleeve, the diameter expansion belt is concentrically and spacedly sleeved on the outer ring of the pressure ring, and the plurality of airbags are arranged between the pressure ring and the diameter expansion belt;

[0028] The diameter-expanding belt includes a rubber pad and an elastic membrane, and a plurality of the rubber pads and elastic membranes are alternately connected to form a ring.

[0029] Optionally, a notch is provided in one section of the detection shaft, and pressure blocks are detachably provided on both sides of the notch, and the pressure blocks detachably mount two parallel clamping shafts in the notch area, and the plurality of displacement sensors are arrayed and confined between the clamping shafts;

[0030] The displacement sensor comprises a housing and a probe, wherein the probe points to the wall of the through-hole, and the housing is in sliding cooperation with the two clamping shafts.

[0031] Optionally, the fluid is liquid, and a hydraulic sensor is provided on the first side end cover and / or the second side end cover.

[0032] The circular through-hole karst cave physical model test method uses the circular through-hole karst cave physical model test device as described above, and includes the following steps:

[0033] Casting: Place the weak interlayer pre-installed device into the cylindrical cavity pre-installed part, and pass the interlayer membrane through the membrane slot for later use; fix the cylindrical cavity pre-installed part in the model frame; fill the model frame with the mixed rock-like material, arrange the rock-like material into an inclined surface, then straighten the lower interlayer membrane and cover it on the surface of the casting body, and clamp the end of the interlayer membrane; then cover the weak interlayer material of a certain thickness on this interlayer membrane; then straighten the upper interlayer membrane and cover it on the weak interlayer material and clamp the end; finally, use the rock Similar materials are poured into the remaining space to form a weak interlayer casting area between the upper and lower interlayer membranes. During the casting process, strain gauges are embedded in the similar material of the rock mass above the reserved device, and the matching wires are led to the outside. After completion, the torsion rod is rotated to pull the interlayer membrane out of the casting body and wind it onto the torsion rod. Then, the weak interlayer reserved device is axially pulled out from the cylindrical cavity reserved part. The casting body is patted and compacted. One day after the casting is completed, the mold is removed and the cylindrical cavity reserved part is removed together. The model test block is cured for 14 days.

[0034] Preparation: Set limit plates around the model test block, place pressure plates and pads on the surface of the model test block above the cavity reserved part, set displacement meters around the pressure plates to monitor surface settlement, and set pressure sensors between the pressure plates and pads to monitor load; install the strain detection device to the through-hole cave, inject fluid into the tubular membrane through the pressure injection hole, so that the tubular membrane is stretched and tightly adhered to the through-hole cave wall, rotate the detection shaft, and make all the displacement sensors face horizontally and laterally, then turn on the displacement sensor, rotate the detection shaft again, and let the displacement sensor probe sweep along the arc-shaped top surface of the through-hole cave to the other side. The initial state of the through-hole cave inner wall is established through the detection values of each displacement sensor and the axis data of the detection shaft;

[0035] Test: A loader is used to apply load to the pad. Every time the load increases by a set amount, the inner wall of the through-hole cave is scanned, and the data of the monitoring and measurement units are read and stored at the same time.

[0036] As described above, the circular through-hole cave physical model test device and method of the present invention have at least the following beneficial effects:

[0037] By using cylindrical cavity pre-reserved parts, a cylindrical cavity is precisely constructed within the model block, effectively simulating the karst cave structure found in real karst foundations. This device, combined with experimental methods, not only improves the accuracy of the model block's simulation of karst foundations but also facilitates loading experiments, allowing for intuitive analysis of the impact of caves on foundation stability, providing a strong experimental basis for the design and treatment of karst foundations. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 Shown is a schematic diagram of the appearance of the present invention.

[0039] Figure 2Shown is a schematic diagram of the axial cross-section of the through-cavity of the present invention.

[0040] Figure 3 Shown is a schematic diagram of a radial cross-section of a through-cavity according to the present invention.

[0041] Figure 4 Shown are schematic diagrams of the end covers on both sides of the present invention.

[0042] Figure 5 Shown is a schematic diagram of the outer side of the end cover of the present invention.

[0043] Figure 6 Shown is a schematic diagram of the inner side of the end cover of the present invention.

[0044] Figure 7 Shown is a schematic diagram of the detection axis of the present invention.

[0045] Figure 8 Shown is a schematic diagram of the strain gauge arrangement of the present invention.

[0046] Among them: model frame 1, reinforcement structure 2, cavity reserved part 4, membrane groove 40, torsion rod body 51, interlayer membrane 52, first side end cover 6, injection hole 60, rotation support sleeve 61, sleeve protrusion platform 62, annular limit platform 63, drive area 64, hydraulic sensor 65, second side end cover 7, permanent magnet ring 70, pointer 701, scale 72, electromagnetic coil 32, detection shaft 3, pressure block 30, clamping shaft 31, displacement sensor 33, tubular membrane 9, pressure ring 34, airbag 35, annular expansion belt 36, rubber pad 361, elastic membrane 362, strain gauge 80, pressure plate 81, cushion block 82, displacement meter 83, loader 84. DETAILED DESCRIPTION

[0047] The following describes the implementation of the present invention through specific embodiments. People skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification.

[0048] It should be noted that the structures, proportions, sizes, etc. illustrated in the drawings of this specification are only used to match the contents disclosed in the specification for understanding and reading by those familiar with this technology, and are not used to limit the conditions under which the present invention can be implemented. Therefore, they have no substantial technical significance. Any modification of the structure, change in the proportional relationship, or adjustment of the size should still fall within the scope of the technical content disclosed by the present invention without affecting the efficacy and purpose that can be achieved by the present invention. At the same time, the terms such as "upper", "lower", "left", "right", "middle" and "one" quoted in this specification are only for the convenience of description and are not used to limit the scope of the implementation of the present invention. Changes or adjustments in their relative relationships should also be regarded as the scope of the implementation of the present invention without substantially changing the technical content.

[0049] The following embodiments are for illustration only and can be combined with each other, and are not limited to the contents presented in the following single embodiments.

[0050] See also Figures 1-8 , an embodiment of the circular through-hole cave physical model test device and method provided by the present invention.

[0051] Among them, the circular through-hole cave physical model test device includes a model frame 1 with an opening at the top and a reinforcement structure 2 arranged on the periphery of the model frame 1. The bottom plate of the model frame 1 is made of 30mm thick steel plate, and the four side panels are made of 20mm thick furniture synthetic board bolts. In order to ensure that the test block does not expand and deform during the pouring process, a reinforcement structure 2 with multiple layers of steel pipes is installed on the periphery of the model frame 1.

[0052] It also includes a cylindrical cavity reserved part 4, which is located inside the model frame 1 and passes through the model frame 1 at both ends. Rock-similar materials are poured into the model frame 1 to form a karst foundation model test block. After the pouring is completed, the reserved part forms a penetrating cylindrical cavity in the karst foundation model test block.

[0053] The cylindrical cavity reserved part 4 can be a cylindrical PVC pipe, steel pipe or other tubular component. After pouring is completed, it needs to be pulled out from the casting body to form a cave cavity. In order to reduce the difficulty of pulling out, an oil film can be coated on the surface before pouring. In order to avoid damaging the inner surface of the cast cavity during pulling out, the cylindrical cavity reserved part 4 can be rotated first, and after it is loosened, the cylindrical cavity reserved part 4 can be pulled out along the axis.

[0054] Model specimens are used to simulate the ultimate bearing capacity and failure mechanisms of karst foundations. Karst is a well-known potential geological hazard that can lead to major engineering problems, such as structural collapse, sinkholes swallowing roads, and building disappearance. Research on the stability of karst foundations, both domestically and internationally, primarily utilizes numerical simulation and model testing. With the continuous advancement of numerical methods, limit analysis has become an effective means of calculating the ultimate bearing capacity of karst foundations. However, to reduce computational costs, most karst foundations are simplified as two-dimensional plane strain problems, ignoring the influence of three-dimensional spatial effects. This makes it difficult to simulate the actual conditions of karst foundations. To increase the reliability of the analysis results, comprehensive experimental evaluation of karst foundation stability is necessary. Existing experimental research focuses primarily on cave size, distribution, and cave roof (foundation) thickness. Further technical solutions are lacking for experimental research on the instability modes and processes of karst foundations.

[0055] In the above embodiment, after obtaining the model test block, multiple strain gauges are set in the simulated through-hole cave holes of the model test block, and then a load is applied from the top surface of the model test block to the through-hole cave inside. At the same time, multiple displacement sensors are set in the load application area on the top surface of the model test block to detect the strain of the through-hole cave and the settlement of the top surface during the loading process, which is then used to study the instability mode and process of karst foundation.

[0056] Furthermore, in order to verify the correctness of the numerical simulation results and further study the bearing characteristics and failure mechanism of karst foundation, the similarity theory is used to make a physical model specimen of karst foundation, and model tests are carried out on the model specimen. The karst foundation failure process occurring in the prototype is repeated on the physical model specimen after being reduced under physically similar conditions. The mechanical parameters in the model specimen are measured, recorded, and analyzed, and converted to the prototype based on the similarity relationship, so as to achieve the purpose of studying the mechanical characteristics of the prototype.

[0057] To ensure that the primary mechanical properties of the analog material are similar to those of the prototype rock mass, as well as that the material composition and structure are similar to those of the prototype rock mass, that the physical and mechanical properties of the analog material are stable during the test and not easily affected by external conditions, and that certain physical and mechanical properties of the analog material can be modified accordingly by changing the material ratio to meet the requirements of similar condition screening, the analog material is usually composed of aggregate, binder, and regulator. Currently, domestic and foreign scholars mainly use barite powder, river sand, iron powder, etc. as aggregates, and gypsum, cement, etc. as binders. Because gypsum powder has a relatively short initial setting time, retarders are added as regulating materials.

[0058] Specifically, in this embodiment, the dry material mass ratio of the rock-similar material is: 80% sand, 5% cement, and 15% gypsum powder; during stirring and mixing, gypsum retarder and water are also added, wherein the amount of gypsum retarder is 0.3% of the mass of the gypsum powder, and the amount of water is determined according to a water-to-solid ratio of 1:7.

[0059] Sand is a loose, unbound granular material. In this example, the sand is river sand with a particle size of 0.1-0.6 mm and a density of approximately 1.71 g / cm³. The cement used is P.C42.5 composite Portland cement with a density of approximately 3.0 g / cm³. The density of construction gypsum powder is approximately 2.3 g / cm³, with an initial setting time of 4-6 minutes and a final setting time of 8-10 minutes. In the physical model test, the total mass of the river sand, cement, and gypsum powder is assumed to be 100%, and the water-to-solid ratio is 1:7.

[0060] The mass of river sand, cement, gypsum powder, and tap water for the test blocks is calculated according to the above proportions. The mixture is then mixed evenly to create the mortar used to cast the model test blocks. A gypsum retarder is added during the mixing process to prevent the gypsum powder from solidifying due to prolonged pouring. Due to the low cement content, the final cast product will have a strength far lower than that of concrete, yet stronger than that of ordinary soil and gravel, forming a solidified soil with a certain degree of binding strength. This similar composition of materials greatly simulates the structure and physical properties of rock and soil.

[0061] To simulate karst foundations, the ultimate bearing capacity test selected a karst foundation physical model (the model specimen to be cast) with dimensions of 1000mm (length) × 1000mm (width) × 700mm (height). The corresponding karst foundation prototype (the actual geological structure to be simulated) measured 15m (length) × 15m (width) × 10.5m (height). The internal karst cave of the foundation was circular and continuous. Based on model similarity theory, combining the first, second, and third similarity theorems, the similarity ratio for dimensionless quantities such as Poisson's ratio, strain, and internal friction angle is typically set to 1. Other similarity relationships can be derived by combining equation analysis and dimensional analysis. Specifically, in this scheme, the main controlled similarity parameters include density, compressive strength, elastic modulus, internal friction angle, cohesion, and applied load. Overall, the above ratio, as a material similar to the karst foundation rock mass, combined with the above size ratios, ensures that the cast model specimens meet the similarity relationships well, reflecting the actual geological structure.

[0062] For this example, please refer to Figure 2 , also includes a weak interlayer reservation device, the weak interlayer reservation device includes a torsion rod 51 and an interlayer membrane 52; a membrane groove 40 is opened on the cylinder of the cavity reservation part 4 along the axis, and the membrane groove 40 is grouped into two groups, and the two groups of membrane grooves 40 are respectively arranged on both sides of the circumference of the cavity reservation part 4;

[0063] The torsion rod 51 is located in the cavity reserved part 4. The interlayer membrane 52 is grouped in two pieces. The two groups of interlayer membranes 52 are respectively arranged on both sides of the circumference of the torsion rod 51. One end of each interlayer membrane 52 is connected to the torsion rod 51, and the other end passes through the corresponding membrane groove 40. The outer end is tightened and fixed. The two interlayer membranes 52 in the same group are in the same direction. The two interlayer membranes 52 are cast with a similar weak interlayer material.

[0064] The dry material mass ratio of the weak interlayer analogue is: 80% sand, 10% red clay, and 10% gypsum powder. During mixing, a gypsum retarder and water are added, with the gypsum retarder dosage being 0.3% of the gypsum powder's mass, and the water dosage being determined based on a water-to-solid ratio of 1:7. Red clay refers to highly plastic, reddish-brown, brownish-red, or yellowish-brown clay formed through weathering of carbonate rocks (limestone, dolomite, and argillaceous mudstone). Natural red clay exhibits extremely high shrinkage and porosity. In the model experiment, to increase the strength and setting time of the red clay weak interlayer, a composition of 80% sand, 10% gypsum, and 10% red clay was selected as the analogue for the weak interlayer.

[0065] The orientation of the interlayer membrane 52 in the weak interlayer reserve device can be adjusted as needed. To simulate the orientation of weak interlayer zones in actual rock mass, it is generally set according to the target rock mass structure. In rock mass, weak interlayers primarily manifest as thin, layered or banded weak layers. Generally, weak interlayers are thinner than adjacent rock layers, and their mechanical strength and deformation modulus are also lower, with saturated compressive strength being only half or less of the dry compressive strength. Some disintegrate in contact with water.

[0066] In this embodiment, the weak interlayer belt runs through the cave obliquely. During casting, the weak interlayer reservation device is first placed inside the cylindrical cavity reservation part 4, and the free end of the interlayer membrane 52 is passed through the membrane groove 40 on the cavity reservation part 4 to the outside for standby. The weak interlayer reservation device is then fixed in the model frame 1 together with the cylindrical cavity reservation part 4. Next, the rock mass-similar material is used to cast the lower rock mass of the weak interlayer, and then the lower interlayer membrane 52 is straightened to cover the surface of the casting body, and the end of the interlayer membrane 52 is clamped and fixed; then a certain thickness of weak interlayer-similar material is covered on this layer of interlayer membrane 52, and the specific thickness depends on the actual thickness of the simulation target and the similarity ratio; then the upper interlayer membrane 52 is straightened to cover the weak interlayer-similar material and the end is clamped and fixed. Considering that the interlayer membrane 52 needs to withstand a certain degree of tension during the above process, the interlayer membrane 52 needs to have a certain strength, and cloth or high-strength plastic film can be used. Finally, a material similar to the rock mass is used to cast the upper rock mass of the weak interlayer, forming a weak interlayer casting area between the upper and lower layers of the interlayer membrane 52. At this time, by rotating the torsion rod 51, the interlayer membrane 52 can be pulled out of the casting body and wound onto the torsion rod 51, and then the weak interlayer reservation device is axially pulled out from the cylindrical cavity reservation part 4. Finally, the casting body is patted and compacted, and the mold is removed 24 hours after the casting is completed. The model frame 1 and the peripheral reinforcement structure 2 are removed, and the model test block is obtained by curing at room temperature for 14 days.

[0067] In the above embodiment, during the initial pouring, Figure 2As shown, the interlayer membrane 52 is used to separate the rock-like material 88 and the weak interlayer-like material 99. After the initial pouring is completed, the top of the pouring body is first patted and compacted, but it should not be compacted too tightly; then the interlayer membrane 52 is removed and the final patting and compaction are performed again from the top of the pouring body. Retaining the interlayer membrane 52 during the initial tapping and tamping can effectively ensure that the weak interlayer-like material 99 can maintain its original continuous layer structure during the tapping and tamping process, so that the rock-like material 88 on both sides of the weak interlayer-like material 99 will not pass through the weak interlayer-like material 99 to form a connection or even destroy the layer structure formed by the weak interlayer-like material 99; after the initial tapping and tamping is completed, the rock-like material 88 and the weak interlayer-like material 99 become tight to a certain extent, and after removing the interlayer membrane 52 and tapping and tamping again, the structure inside the casting body will not have too much dislocation and change, but in the process of tapping and tamping again, the rock-like material 88 and the weak interlayer-like material 99 can be embedded in each other's surface to a certain extent, and gradually solidify and embed in the later maintenance process, simulating the situation of weak interlayers in real rock and soil to the greatest extent.

[0068] After the model test block is prepared, the strain of the cave inside the model can be measured by applying a load from above the model test block to simulate the weight of the building. Then, based on the similarity theory, it can be inferred that in real scenarios, when there are caves in the lower soil of the building foundation, the bearing and mechanical conditions of the foundation and caves can be inferred, providing basic information for building design and construction safety.

[0069] In order to observe and measure the response of the model to the load, the existing technology often performs measurements by pasting multiple strain gauges inside the through-hole. However, in actual operation, due to the long length and small diameter of the through-hole, it is difficult to install multiple strain gauges inside. Due to the limited installation angle and installation space, the installation position, quantity and status are often inaccurate, affecting the accuracy of subsequent measurement results.

[0070] Therefore, in this embodiment, the circular through cave physical model test device also includes a strain detection device, see Figure 3 , the strain detection device includes a first side end cover 6, a second side end cover 7, a detection shaft 3 and a driving mechanism;

[0071] During the test (at this time, the torsion rod 51 and the interlayer membrane 52 of the weak interlayer reservation device have been removed), limit plates are set around the casting body, which are equivalent to support plates in four directions, and are used to simulate the soil around the simulation test block. Otherwise, when the top of the simulation test block is loaded, there is a lack of support on all sides, which does not conform to the actual working conditions. Holes are set on the limit plates at positions corresponding to the through-holes, and the first side end cover 6 and the second side end cover 7 are respectively set at the two side exits of the through-hole through a clamping structure and attached to the limit plates. The two end covers can support the detection shaft 3 and set it at the axis center of the through-hole. Specifically, the detection shaft 3 is set in the through-hole, and the two ends of the detection shaft 3 are respectively supported by the first side end cover 6 and the second side end cover 7 for rotation and driven to rotate by the driving mechanism;

[0072] A row of displacement sensors 33 are arranged along one section of the detection axis 3, with the probes of each displacement sensor 33 pointing toward the wall of the cave. This section of the detection axis 3 corresponds to the simulated loading area of the simulated test block soil surface.

[0073] During the test, in the initial state, the array of displacement sensors 33 can detect the position of each point on a line extending along the axial direction through the cave wall (equivalent to the distance from a point on a generatrix extending through the cave wall to the axis). When the detection shaft 3 rotates an angle under the action of the drive mechanism, the array of displacement sensors 33 can detect the position of each point on another generatrix extending through the cave wall along the axial direction. Repeating this process multiple times can scan the dot-matrix three-dimensional structural profile of the cave wall (i.e., the angle and distance from each point on the wall to the axis). During the test, the strain detection device can detect the three-dimensional shape changes of the cave by pressing down on the top of the model through the loading system. Based on the magnitude of the loading force and the deformation of the physical model of the cave, the mechanical load-bearing conditions associated with the presence of caves in the soil beneath a building foundation in a real-world scenario can be estimated based on the principle of similarity.

[0074] In the above embodiments, the displacement sensor can be a non-contact photoelectric type or a contact mechanical type. The photoelectric type uses the wave emitted by the probe and received back, and calculates the distance based on the wave velocity and the time difference between emission and reception. The probe does not need to be in contact with the through-hole cave wall. The contact type usually has a potentiometer inside. When the probe / probe is pressed, it slides to change the potentiometer position, thereby converting the displacement change into an electrical signal. The probe needs to be against the through-hole cave wall.

[0075] For this example, please refer to Figure 4 , further comprising a tubular membrane 9, the tubular membrane 9 being capable of shrinking, and initially, the tubular membrane 9 wraps the detection shaft 3;

[0076] When the detection shaft 3 is placed in the through-hole, both ends of the tubular membrane 9 extend beyond the through-hole end, and the portion extending beyond the through-hole is attached to the limit plate on the end face ( Figure 4(not shown) and is pressed by the first side end cover 6 and the second side end cover 7 to form a sealing interface (sealing rings are provided on the end covers);

[0077] The first side end cover 6 and the second side end cover 7 are provided with injection holes 60. When fluid is injected into the interior, the tubular membrane 9 expands and adheres tightly to the wall of the through-hole.

[0078] In order to achieve the sealing effect of the first side end cover 6 and the second side end cover 7 on the two ends of the tubular membrane 9, the first side end cover 6 and the second side end cover 7 are provided with a rotation support sleeve 61 on the side facing the interior of the through cave. The detection shaft 3 is rotatably installed in the rotation support sleeve 61, and the two ends of the detection shaft 3 are respectively provided with a first magnet and a second magnet;

[0079] like Figure 5 and Figure 6 As shown, the rotation support sleeve 61 forms a sleeve protrusion 62 on the other side of the first side end cover 6 and the second side end cover 7. The outer ring of the sleeve protrusion 62 is provided with an annular limit platform 63. Between the sleeve protrusion 62 and the annular limit platform 63 is a driving area 64. The driving component in the driving area 64 can drive the detection shaft 3 to rotate through the housing of the sleeve protrusion 62.

[0080] Specifically, on the first side end cover 6, there is an electromagnetic coil 32 in a circular array in the drive area 64. The electromagnetic coil 32 matches the position of the first magnet to form a driving mechanism, and the alternating magnetic field change of the electromagnetic coil 32 is used to drive the detection shaft 3 to rotate; as another driving method, the electromagnetic coil 32 can also be replaced with an ordinary permanent magnet, which is pushed to rotate manually or by other external mechanisms, and the mutual magnetic force between the permanent magnet and the first magnet and the second magnet at the end of the detection shaft 3 in the sleeve protrusion 62 is used to achieve locking, thereby driving the detection shaft 3 to rotate. For example, a force-bearing column 991 is set on the permanent magnet, and the force-bearing column 991 is inserted into a slide groove 9920 of a strip groove part 992. The width of the slide groove 9920 matches the diameter of the force-bearing column 991, and the length of the slide groove 9920 matches the maximum rotation range of the force-bearing column 991 relative to the permanent magnet. When a telescopic part such as a cylinder is used to push the strip groove part 992 in the vertical direction along the slide groove 9920, the reciprocating translational motion of the strip groove part 992 will be able to drive the permanent magnet to rotate reciprocally, thereby driving the detection shaft 3 to rotate reciprocally, so that the displacement sensor can measure the busbars at different angles on the wall of the cave.

[0081] On the second side end cover 7, as shown Figure 4As shown, a ring array of permanent magnets 70 is located within the drive zone 64. The permanent magnets 70 match the positions of the second magnets. A pointer 701 is also provided on the permanent magnets 70, and a corresponding circumferential deflection scale 72 is provided on the second end cap 7. When the drive mechanism on the first end cap 6 drives the detection shaft 3 to rotate, the electromagnetic coil 32 on this side and the magnet at the end of the detection shaft 3 are driven magnetically without direct mechanical contact. This allows the tubular membrane 9 between the end caps to contain fluid, making leakage less likely. However, contactless drive can also result in low position control accuracy. It can even lead to situations where the detection shaft 3 does not rotate despite the external electromagnetic coil 32's drive, due to internal jamming of the detection shaft 3. Therefore, on the second end cap 7, the detection shaft 3 serves as the active axis. Through magnetic locking, the permanent magnets 70 drive the pointer 701 to deflect, and in conjunction with the deflection scale 72, precise positioning of the measurement point is achieved.

[0082] In summary, the main beneficial effect of the above-described embodiment is that the tubular membrane 9 and the fluid (such as water or gas) within it provide a certain degree of support for the through-hole wall of the cave. The fluid pressure should not be too high, so that the tubular membrane 9 can be tightly attached to the through-hole wall of the cave. It is necessary to ensure that the support force of the tubular membrane 9 on the through-hole wall of the cave is much smaller than the load acting on the through-hole wall of the cave when the model is loaded. This is because the model test block is cast from sand, and the through-hole is formed by removing the reserved tubular parts after the model is formed. The sand and soil used are mainly sand and have a relatively low content of cement. During the removal of the tubular parts and the loading process, the through-hole wall may be damaged, resulting in localized sand shedding and the formation of sand pits.

[0083] Defects in the through-hole cave wall formed when the tubular member is removed can be compensated by adjusting the initial values of the displacement sensors at the corresponding locations (for example, when no load is applied, the initial values of the displacement sensors at each location are recorded as 0, and the changes in the readings during the loading process are used as the deformation of the through-hole cave wall). However, during the loading process, if the tubular membrane 9 of this embodiment is not used to support the through-hole cave wall, once the through-hole cave is compressed and deformed, sand particles may fall off the wall or even collapse locally. In this case, the values measured by the displacement sensors within the through-hole cave cannot reflect the deformation of the cave wall under the corresponding load (theoretically, the local deformation caused by collapse is much greater than the overall deformation caused by loading). In this embodiment, after the tubular membrane 9 is installed to support the through-hole cave wall, the tubular membrane 9 adheres closely to the wall, effectively limiting local collapse of the wall. However, the supporting force of the tubular membrane 9 on the wall is much smaller than the loading force. This ensures that the load applied to the through-hole cave is accurate, and further improves the accuracy of the overall load deformation of the through-hole cave detected by the detection unit (displacement sensor).

[0084] This embodiment can be found in Figure 6, the clamping structure includes a pressure ring 34, an air bag 35 and an annular expansion belt 36;

[0085] The inner surface of the pressure ring 34 is connected to the outer surface of the rotating support sleeve 61, and the expansion belt is concentrically and spaced apart on the outer ring of the pressure ring 34. A plurality of air bags 35 are provided between the pressure ring 34 and the expansion belt.

[0086] The diameter-expanding belt includes a rubber pad 361 and an elastic membrane 362 , and a plurality of rubber pads 361 and elastic membranes 362 are alternately connected to form a ring.

[0087] When the first side end cap 6 or the second side end cap 7 needs to be installed at the end of the through-hole, the air bag 35 is first released to shrink the annular expansion band 36. The annular expansion band 36 is then inserted into the hole at the end of the through-hole. The air bag 35 is then pressurized. The air bag 35 expands, causing the annular expansion band 36 to expand and contact the wall of the through-hole. The clamping structure of this embodiment is characterized by easy assembly and disassembly.

[0088] For this example, please refer to Figure 7 A notch is provided in one section of the detection shaft 3, and pressure blocks 30 are detachably provided on both sides of the notch. The pressure blocks 30 detachably mount two parallel clamping shafts 31 in the notch area, and a plurality of displacement sensors 33 are arrayed and confined between the clamping shafts 31;

[0089] The displacement sensor 33 includes a shell and a probe. The probe points to the wall of the cave. The shell slides with the two clamping shafts 31. Multiple displacement sensors can be installed in an array from the side of the clamping shaft 31, but the displacement sensor cannot be taken out from between the clamping shafts 31 along the probe direction.

[0090] A mechanical displacement sensor can be used, with the probe pointing toward the through-hole wall and the tail of the displacement sensor pointing toward the axis of detection axis 3. The distance from the probe tip to the axis of detection axis 3 can be determined using the displacement sensor reading (considering the sensor's dimensions). When detection axis 3 is positioned at a certain angle, the array of sensors can measure the distance from the through-hole wall to the axis center along the axis. By rotating detection axis 3, the distance from the entire through-hole wall to the axis center can be measured, allowing the 3D contour of the through-hole wall to be constructed. The load can then be varied and the measurement repeated to obtain the 3D shape of the through-hole wall under the new load.

[0091] like Figure 6As shown, the fluid is liquid, and a hydraulic sensor 65 is provided on the first side end cap 6 and / or the second side end cap 7 to detect the pressure inside the tubular membrane 9. During the test, once the fluid is injected into the tubular membrane 9, the injection hole 60 can be closed, and the internal pressure remains relatively stable. During the test, when the load is too large, exceeding the elastic deformation range of the model specimen, the soil above the through-hole may collapse and fall into the cave. The tubular membrane 9 is compressed, and the internal pressure fluctuates greatly. The hydraulic sensor 65 detects the beginning of the signal fluctuation and sends a signal to the controller. The controller controls the rotation of the detection shaft 3 to point the probe of the displacement sensor toward the bottom or side of the through-hole to prevent damage by the fallen soil.

[0092] This embodiment is an embodiment of a circular through-hole karst cave physical model test method, using the above circular through-hole karst cave physical model test device, including the following steps:

[0093] Casting: Place the weak interlayer reservation device into the cylindrical cavity reservation part 4, and pass the interlayer membrane 52 through the membrane groove 40 for standby use; fix the cylindrical cavity reservation part 4 in the model frame 1; fill the model frame 1 with the stirred rock-like material, and arrange the rock-like material into an inclined surface (simulating the lower rock mass of the weak interlayer zone), then straighten the lower interlayer membrane 52 and cover it on the surface of the casting body, and clamp the end of the interlayer membrane 52; then cover this layer of interlayer membrane 52 with a certain thickness of weak interlayer similar material, and the specific thickness needs to be calculated according to the thickness of the interlayer in the actual rock mass to be simulated with reference to the model similarity ratio; then straighten the upper interlayer membrane 52 and cover it on the weak interlayer similar material The similar material is placed on the material and the end is clamped and fixed; finally, the remaining space is cast with a rock-like material (simulating the upper rock of the weak interlayer zone), and a weak interlayer casting area is formed between the upper and lower interlayer membranes 52; during the casting process, a strain gauge 80 is embedded in the rock-like material above the reserved device, and the matching wires are led to the outside; after completion, the torsion rod 51 is rotated, the interlayer membrane 52 is pulled out of the casting body and wound onto the torsion rod 51, and then the weak interlayer reserved device is axially pulled out from the cylindrical cavity reserved part 4; the casting body is patted and compacted, and the mold is removed one day after the casting is completed, and the cylindrical cavity reserved part 4 is removed together, and the model test block is obtained by curing for 14 days;

[0094] Preparation: Set limit plates around the model test block, place a pressure plate 81 and a pad 82 on the surface of the model test block above the cavity reserved part 4, and set displacement meters 83 around the pressure plate 81 to monitor surface settlement. The displacement meter 83 can use the same device as the displacement sensor 33. A pressure sensor is set between the pressure plate 81 and the pad 82 to monitor the load; install the strain detection device to the through-hole, inject fluid into the tubular membrane 9 through the pressure injection hole 60, so that the tubular membrane 9 is stretched and tightly attached to the wall of the through-hole; rotate the detection shaft 3 to make all the displacement sensors 33 face horizontally, then open the displacement sensor 33, and rotate the detection shaft 3 again to let the probe of the displacement sensor 33 sweep along the arc-shaped top surface of the through-hole to the other side. During the process, record the detection value of each position, and establish the initial state (the distance and angle from multiple points on the wall to the axis) profile of the inner wall of the through-hole through the cave through the detection value of each displacement sensor 33 and the axis position data of the detection shaft 3;

[0095] Test: Loader 84 applies a load to pad 82. Each time the load increases by a set amount, the inner wall of the through-hole cave is scanned (detection axis 3 rotates, and each displacement sensor 33 measures the distance from the axis to the wall at the corresponding angle). Simultaneously, data from the monitoring and measurement units is read and stored. By superimposing the load data and wall deformation data, the response of the through-hole cave in the model test block to the load (simulating buildings on the rock surface, etc.) can be determined. Based on similarity theory, the mechanical properties of the actual rock mass can be inferred.

[0096] In summary, the present invention effectively overcomes various shortcomings in the prior art, can produce beneficial technical effects, and has significant progress.

[0097] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Anyone skilled in the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by one of ordinary skill in the art without departing from the spirit and technical principles disclosed herein are intended to be covered by the claims of the present invention.

Claims

1. A circular through-hole cave physical model test device, characterized by: It includes a model frame with an opening at the top and a reinforcement structure arranged on the periphery of the model frame; The invention also includes a cylindrical cavity reserved part, which is located inside the model frame and has both ends passing through the model frame. A rock-like material is poured into the model frame to form a karst foundation model test block. After the pouring is completed, the reserved part forms a cylindrical cavity passing through the karst foundation model test block. It also includes a weak interlayer reservation device, which includes a torsion rod and an interlayer membrane; The cylinder of the cavity reserved part is provided with a membrane groove along the axis, and the membrane grooves are grouped into two, and the two groups of membrane grooves are respectively arranged on both sides of the circumference of the cavity reserved part; The torsion rod body is located in the cavity reserved part, and the interlayer membrane is grouped in two pieces. The two groups of interlayer membranes are respectively arranged on both sides of the circumference of the torsion rod body. One end of each interlayer membrane is connected to the torsion rod body, and the other end passes through the corresponding membrane groove. The outer end is tightened and fixed. The two interlayer membranes in the same group are in the same direction, and similar weak interlayer materials are cast inside the two interlayer membranes.

2. The circular through-hole cave physical model test device according to claim 1, characterized in that: The dry material mass ratio of the rock mass similar material is: 80% sand, 5% cement, and 15% gypsum powder; When stirring and mixing, gypsum retarder and water need to be added. The amount of gypsum retarder is 0.3% of the mass of gypsum powder, and the amount of water is determined according to the water-to-solid ratio of 1:

7.

3. The circular through-hole cave physical model test device according to claim 1, characterized in that: The dry material mass ratio of the weak interlayer similar material is: 80% sand, 10% red clay, and 10% gypsum powder; When stirring and mixing, gypsum retarder and water need to be added. The amount of gypsum retarder is 0.3% of the mass of gypsum powder, and the amount of water is determined according to the water-to-solid ratio of 1:

7.

4. The circular through-hole karst cave physical model test device according to claim 1, characterized in that: Also included is a strain detection device, the strain detection device including a first side end cover, a second side end cover, a detection shaft and a drive mechanism; During the test, limiting plates are arranged around the casting body, holes are arranged on the limiting plates at positions corresponding to the through-holes, the first side end cover and the second side end cover are respectively arranged on the two side exits of the through-holes through a clamping structure and attached to the limiting plates, the detection shaft is arranged in the through-holes, and both ends of the detection shaft are rotatably supported by the first side end cover and the second side end cover respectively and driven to rotate by the driving mechanism; On one section of the detection axis, a row of displacement sensors are arranged along the axial direction, and the probes of the respective displacement sensors point to the wall of the through cave.

5. The circular through-hole cave physical model test device according to claim 4, characterized in that: The apparatus further comprises a tubular film, wherein the tubular film is capable of shrinking and initially wraps the detection shaft; When the detection shaft is placed in the through-hole, both ends of the tubular membrane extend beyond the ends of the through-hole, and the portion extending beyond the through-hole is attached to the limit plate on the end face and is pressed by the first side end cover and the second side end cover to form a sealing interface; The first side end cover and the second side end cover are provided with injection holes. When fluid is injected into the interior, the tubular membrane expands and adheres tightly to the wall of the through cave.

6. The circular through-hole karst cave physical model test device according to claim 5, characterized in that: The first side end cover and the second side end cover are provided with a rotation support sleeve on the side facing the interior of the through cave, the detection shaft is rotatably installed in the rotation support sleeve, and the two ends of the detection shaft are respectively provided with a first magnet and a second magnet; The rotating support sleeve forms a sleeve protrusion on the other side of the first side end cover and the second side end cover, and the outer ring of the sleeve protrusion is provided with an annular limit platform, and the driving area is between the sleeve protrusion and the annular limit platform; On the first side end cover, there is an electromagnetic coil in a circular array in the driving area, and the electromagnetic coil matches the position of the first magnet to form the driving mechanism; On the second side end cover, there is a permanent magnet ring in the annular array in the driving area, the permanent magnet ring matches the position of the second magnet, and a pointer is also provided on the permanent magnet ring. A circular deflection scale is correspondingly provided on the second side end cover.

7. The circular through-hole karst cave physical model test device according to claim 6, characterized in that: The clamping structure includes a pressure ring, an air bag and an annular expansion belt; The inner circular surface of the pressure ring is connected to the outer circular surface of the rotating support sleeve, the diameter expansion belt is concentrically and spacedly sleeved on the outer ring of the pressure ring, and the plurality of airbags are arranged between the pressure ring and the diameter expansion belt; The diameter-expanding belt includes a rubber pad and an elastic membrane, and a plurality of the rubber pads and elastic membranes are alternately connected to form a ring.

8. The circular through-hole karst cave physical model test device according to claim 4, characterized in that: A notch is provided in one section of the detection shaft, and pressure blocks are detachably provided on both sides of the notch. The pressure blocks detachably mount two parallel clamping shafts in the notch area, and a plurality of the displacement sensors are arrayed and confined between the clamping shafts. The displacement sensor comprises a housing and a probe, wherein the probe points to the wall of the through-hole, and the housing is in sliding cooperation with the two clamping shafts.

9. The circular through-hole cave physical model test device according to claim 5, characterized in that: The fluid is liquid, and a hydraulic sensor is provided on the first side end cover and / or the second side end cover.

10. A physical model test method for a circular through-hole cave, characterized in that: The circular through-hole cave physical model test device according to claim 8 comprises the following steps: Casting: Place the weak interlayer pre-installed device into the cylindrical cavity pre-installed part, and pass the interlayer membrane through the membrane slot for later use; fix the cylindrical cavity pre-installed part in the model frame; fill the model frame with the mixed rock-like material, arrange the rock-like material into an inclined surface, then straighten the lower interlayer membrane and cover it on the surface of the casting body, and clamp the end of the interlayer membrane; then cover the weak interlayer material of a certain thickness on this interlayer membrane; then straighten the upper interlayer membrane and cover it on the weak interlayer material and clamp the end; finally, use the rock Similar materials are poured into the remaining space to form a weak interlayer casting area between the upper and lower interlayer membranes. During the casting process, strain gauges are embedded in the similar material of the rock mass above the reserved device, and the matching wires are led to the outside. After completion, the torsion rod is rotated to pull the interlayer membrane out of the casting body and wind it onto the torsion rod. Then, the weak interlayer reserved device is axially pulled out from the cylindrical cavity reserved part. The casting body is patted and compacted. One day after the casting is completed, the mold is removed and the cylindrical cavity reserved part is removed together. The model test block is cured for 14 days. Preparation: Set limit plates around the model test block, place pressure plates and pads on the surface of the model test block above the cavity reserved part, set displacement meters around the pressure plates to monitor surface settlement, and set pressure sensors between the pressure plates and pads to monitor load; install the strain detection device to the through-hole cave, inject fluid into the tubular membrane through the pressure injection hole, so that the tubular membrane is stretched and tightly adhered to the through-hole cave wall, rotate the detection shaft, and make all the displacement sensors face horizontally and laterally, then turn on the displacement sensor, rotate the detection shaft again, and let the displacement sensor probe sweep along the arc-shaped top surface of the through-hole cave to the other side. The initial state of the through-hole cave inner wall is established through the detection values of each displacement sensor and the axis data of the detection shaft; Test: A loader is used to apply load to the pad. Every time the load increases by a set amount, the inner wall of the through-hole cave is scanned, and the data of the monitoring and measurement units are read and stored at the same time.

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