Circular through karst cave physical model test device and method

Abstract

The invention provides a circular through karst cave physical model test device and method, belongs to the field of physical property test analysis, and is used for preparing a karst foundation model test block and carrying out a simulation experiment. The circular through karst cave physical model test device comprises a model frame with an opening in the top and a reinforcing structure arranged on the periphery of the model frame. The device further comprises a cylindrical cavity reserved part, the cavity reserved part is located in the model frame, the two ends of the cavity reserved part penetrate through the model frame, rock mass similar materials are poured into the model frame to form a karst foundation model test block, and after pouring is completed, the reserved part forms a penetrating cylindrical cavity in the karst foundation model test block. The device is combined with the method, so that the simulation precision of the model test block on the karst foundation is improved, the influence of the karst cave on the stability of the foundation is conveniently and intuitively analyzed, and a powerful experimental basis is provided for design and treatment of the karst foundation.

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 long-term dissolution of soluble rocks by groundwater, which often leads to complex cave structures underground. If these caves are located under the foundation of a building, they will pose a great threat to the safety and stability of the building structure, and may cause problems such as reduced foundation bearing capacity and uneven settlement, posing safety hazards to the building.

[0003] At present, the processing and analysis of karst foundations are mainly carried out by numerical analysis. However, this method mainly focuses on the analysis of a certain cross section. It is difficult to accurately calculate and analyze the internal deformation mode of caves with complex three-dimensional structures, and there are certain limitations.

[0004] In order to gain a deeper understanding of the characteristics and behavior of karst foundations, it is necessary to prepare karst foundation model test blocks and conduct simulation experiments using similar principles. Through simulation experiments, we can intuitively observe and analyze the impact of caves on the foundation, as well as the deformation and failure mode of the foundation 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 karst 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 karst 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 opening at the top and a reinforcement structure arranged on the periphery of the model frame; 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 block. After the pouring is completed, the reservation part forms a penetrating cylindrical cavity in the karst foundation model block.

[0008] Optionally, the dry material mass ratio of the rock-like material is: 80% sand, 5% cement, and 15% gypsum powder; During stirring and mixing, gypsum retarder and water need to be added, wherein 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.

[0009] Optionally, it further comprises a weak interlayer reservation device, wherein the weak interlayer reservation device comprises a torsion rod body and an interlayer membrane; The cylinder of the cavity reserved part is provided with film grooves along the axis, and the film grooves form a group of two, and the two groups of film 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, and one end of each interlayer membrane is connected to the torsion rod body, and the other end passes through the corresponding membrane groove, and 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 materials of weak interlayers; The dry material mass ratio of the weak interlayer similar material is: 80% sand, 10% red clay, and 10% gypsum powder; During stirring and mixing, gypsum retarder and water need to be added, wherein 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.

[0010] Optionally, it further comprises a strain detection device, wherein the strain detection device comprises a first side end cover, a second side end cover, a detection shaft and a driving mechanism; During the test, a limit plate is arranged around the casting body, and a hole is arranged on the limit plate at a position corresponding to the through cave. The first side end cover and the second side end cover are respectively arranged at the two side exits of the through cave through a clamping structure and attached to the limit plate. The detection shaft is arranged in the through cave, and the two ends of the detection shaft are respectively supported by the first side end cover and the second side end cover for rotation 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 displacement sensors point to the hole wall of the through cave.

[0011] Optionally, it further comprises a tubular film, wherein the tubular film is capable of shrinking, and initially, the tubular film wraps the detection shaft; When the detection shaft is placed in the through cave, both ends of the tubular membrane extend beyond the end of the through cave, and the portion extending beyond the through cave is attached to the limit plate on the end surface 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-hole.

[0012] Optionally, the first side end cover and the second side end cover are provided with a rotation support sleeve on the side facing the inside of the through cave, the detection shaft is rotatably installed in the rotation support sleeve, and the first magnet and the second magnet are respectively provided at both ends of the detection shaft; 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, a pointer is also arranged on the permanent magnet ring, and a circular deflection amount scale is correspondingly arranged on the second side end cover.

[0013] Optionally, 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 a plurality of airbags are arranged between the pressure ring and the diameter expansion belt; The diameter expansion belt comprises a rubber pad and an elastic membrane, and a plurality of the rubber pads and the elastic membrane are alternately connected to form a ring.

[0014] 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 a plurality of the displacement sensors are restricted between the clamping shafts by an array; The displacement sensor comprises a housing and a probe, wherein the probe points to the wall of the cave and penetrates the cave, and the housing is slidably matched with the two clamping shafts.

[0015] Optionally, the fluid is liquid, and a hydraulic sensor is provided on the first side end cover and / or the second side end cover.

[0016] The circular through-hole karst cave physical model test method adopts the circular through-hole karst cave physical model test device as described above, and 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 groove for use; fix the cylindrical cavity pre-installed part in the model frame; fill the model frame with the stirred rock-like material, arrange the rock-like material into an inclined surface, and then straighten the lower interlayer membrane to cover the surface of the casting body, and clamp the end of the interlayer membrane to fix it; then cover a certain thickness of weak interlayer-like material on this interlayer membrane; then straighten the upper interlayer membrane to cover the weak interlayer-like material and clamp the end to fix it; finally use the rock The remaining space is cast with similar materials 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 materials of the rock mass above the reserved device, and the matching wires are led out to the outside; after completion, the torsion rod body is rotated to pull the interlayer membrane out of the casting body and wind it onto the torsion rod body, and then the weak interlayer reserved device is axially pulled out from the cylindrical cavity reserved part; 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 is removed together, and the model test block is obtained after curing 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 plate to monitor surface settlement, and set pressure sensors between the pressure plate and the 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, let the tubular membrane open and close to the hole wall of the through-hole cave, rotate the detection shaft, let all the displacement sensors face horizontally, then turn on the displacement sensor, let the detection shaft rotate again, let the displacement sensor probe sweep along the arc top surface of the through-hole cave to the other side, and establish the initial state of the inner wall of the through-hole cave through the detection values ​​of each displacement sensor and the axis data of the detection shaft; Test: Use a loader 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 once, and the data of the monitoring and measurement units are read and stored at the same time.

[0017] As described above, the circular through-hole karst cave physical model test device and method of the present invention have at least the following beneficial effects: The cylindrical cavity is precisely constructed in the model test block through the cylindrical cavity reservation, effectively simulating the cave structure in the real karst foundation. The device combined with the experimental method not only improves the simulation accuracy of the model test block on the karst foundation, but also facilitates the loading experiment and intuitively analyzes the impact of the cave on the foundation stability, providing a strong experimental basis for the design and treatment of karst foundations. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Shown is a schematic diagram of the appearance of the present invention.

[0019] Figure 2 Shown is a schematic diagram of the axial section of the through-hole cave of the present invention.

[0020] Figure 3 Shown is a schematic diagram of a radial cross-section of a through-hole cave according to the present invention.

[0021] Figure 4 Shown are schematic diagrams of the end covers on both sides of the present invention.

[0022] Figure 5 Shown is a schematic diagram of the outer side of the end cover of the present invention.

[0023] Figure 6 Shown is a schematic diagram of the inner side of the end cover of the present invention.

[0024] Figure 7 Shown is a schematic diagram of the detection axis of the present invention.

[0025] Figure 8 Shown is a schematic diagram of the strain gauge arrangement of the present invention.

[0026] 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

[0027] The following is a description of the implementation of the present invention by means of specific embodiments. Those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification.

[0028] 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 people familiar with this technology to understand and read, and are not used to limit the limiting conditions for the implementation of the present invention, so they have no substantial technical significance. Any modification of the structure, change in the proportion relationship, or adjustment of the size should still fall within the scope of the technical content disclosed by the present invention without affecting the effects and purposes 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. The change or adjustment of their relative relationship should also be regarded as the scope of the implementation of the present invention without substantially changing the technical content.

[0029] The following embodiments are only for illustration purposes and can be combined with each other, and are not limited to the contents presented in the following single embodiments.

[0030] See also Figure 1-Figure 8 , an embodiment of a circular through cave physical model test device and method provided by the present invention.

[0031] Among them, the circular through-hole cave physical model test device includes a model frame 1 with an opening on 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 surrounding side plates are made of 20mm thick furniture synthetic board bolts. In order to ensure that the test block does not expand and deform during the casting process, a reinforcement structure 2 with multiple layers of steel pipes is installed on the periphery of the model frame 1.

[0032] It also includes a cylindrical cavity reserved part 4, which is located inside the model frame 1 and penetrates the model frame 1 at both ends. Rock-similar materials are poured in the model frame 1 to form a karst foundation model block. After the pouring is completed, the reserved part forms a penetrating cylindrical cavity in the karst foundation model block.

[0033] 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.

[0034] The model test block is used to simulate the ultimate bearing capacity and failure mechanism of karst foundation. Karst is a well-known potential geological disaster. It can cause major engineering problems such as structural collapse, collapse pits swallowing roads, and disappearance of buildings. For the study of karst foundation stability, numerical simulation and model test are mainly used at home and abroad. With the continuous development of numerical methods, the limit analysis method has become an effective means to calculate the ultimate bearing capacity of karst foundation. However, in order to reduce the calculation cost, most karst foundations are simplified as two-dimensional plane strain problems for analysis, ignoring the influence of three-dimensional space effects, and it is difficult to simulate the real situation of karst foundations. In order to increase the reliability of the analysis results, it is also necessary to combine experiments to comprehensively evaluate the stability of karst foundations. The existing experimental research content mainly focuses on the size, distribution location and thickness of the cave roof (foundation). There are no more technical solutions for the experimental study of the instability mode and process of karst foundation.

[0035] In the above embodiment, after obtaining the model test block, a plurality of strain gauges are set in the simulated through-cavity holes of the model test block, and then a load is applied from the top surface of the model test block to the internal through-cavity. At the same time, a plurality of 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-cavity 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.

[0036] 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 test block of karst foundation, and model tests are carried out on the model test block. The karst foundation destruction process occurring in the prototype is repeated on the physical model test block after being reduced under physically similar conditions. The mechanical parameters in the model test block are measured, recorded, and analyzed, and converted to the prototype according to the similarity relationship, so as to achieve the purpose of studying the mechanical properties of the prototype.

[0037] In order to ensure that the main mechanical properties of similar materials are similar to those of the prototype rock mass and that they are similar to the prototype rock mass in terms of material composition and structure, that the physical and mechanical properties of the simulated materials are stable during the test and are not easily affected by external conditions, and that some physical and mechanical properties of the simulated materials can be changed accordingly by changing the material ratio to meet the screening requirements of similar conditions, similar materials are usually composed of aggregates, binders and regulators. At present, domestic and foreign scholars mainly use barite powder, river sand, iron powder, etc. as aggregates, and gypsum, cement, etc. as binder materials. Because the initial setting time of gypsum powder is relatively short, retarders are added as regulating materials.

[0038] Specifically, in this embodiment, the dry material mass ratio of the rock-similar material is: 80% sand, 5% cement, and 15% gypsum powder; when 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.

[0039] Sand is a loose, unbound granular material. In this embodiment, the sand is river sand with a particle size of 0.1-0.6 mm and a density of about 1.71 g per cubic centimeter. The cement is P.C42.5 composite silicate cement with a density of about 3.0 g per cubic centimeter. The density of building gypsum powder is about 2.3 g per cubic centimeter, the initial setting time is 4-6 minutes, and the final setting time is 8-10 minutes. In the physical model test, the total mass of river sand, cement, and gypsum powder is determined to be 100%, and the water-solid ratio is 1:7.

[0040] According to the above ratio, the mass of river sand, cement, gypsum powder and tap water of the test block is calculated, and then mixed evenly to obtain the mortar for casting the model test block. Gypsum retarder is added during the mixing process to prevent the gypsum powder from coagulating due to long casting time. Due to the low amount of cement used, the final casting product will be much lower than the strength of concrete, but stronger than the strength of ordinary soil sand and gravel, forming a solidified soil body with a certain bonding force. Through this component similar material, the structure and physical properties of rock and soil are greatly simulated.

[0041] In order to simulate the karst foundation, the ultimate bearing capacity test selected a karst foundation physical model (model test block to be cast) with a size of 1000mm (length) × 1000mm (width) × 700mm (height), and the corresponding karst foundation prototype (real geological structure to be simulated) size is 15m (length) × 15m (width) × 10.5m (height); the shape of the internal karst cave of the foundation is circular and through. According to the model similarity theory, combined with the first, second and third similarity theorems, for dimensionless physical quantities such as Poisson's ratio, strain, and internal friction angle, the similarity ratio is usually set to 1, and other similarity relationships can be derived by combining equation analysis method and dimensional analysis method. Further, in this scheme, the main controlled similarity parameters include density, compressive strength, elastic modulus, internal friction angle, cohesion and the size of the loaded load. In summary, the above ratio is used as a similar material for the karst foundation rock mass, and with the above size ratio, the cast model test block can well meet the similarity relationship and reflect the real geological structure.

[0042] For this example, please refer to Figure 2 , and also includes a weak interlayer reservation device, which 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 grooves 40 are grouped into two, and the two groups of membrane grooves 40 are respectively arranged on both sides of the circumference of the cavity reservation part 4; The torsion rod body 51 is located in the cavity reserved part 4, and 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 body 51. One end of each interlayer membrane 52 is connected to the torsion rod body 51, and the other end passes through the corresponding membrane groove 40, and the outer end is tightened and fixed. The two interlayer membranes 52 in the same group are in the same direction, and the two interlayer membranes 52 are cast with similar materials of weak interlayer. The dry material mass ratio of similar materials for weak interlayer is: 80% sand, 10% red clay, and 10% gypsum powder; when mixing, gypsum retarder and water need to be added, of which 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-solid ratio of 1:7. Red clay refers to carbonate rocks (limestone, dolomite, mudstone, etc.), which are residual, slope or residual-slope deposits formed by weathering. The reddish brown, reddish brown or yellowish brown high plasticity clay, natural red clay has extremely strong shrinkage and porosity. In the model experiment, in order to increase the strength and setting time of the red clay weak interlayer, 80% sand, 10% gypsum and 10% red clay were selected as the similar ratio of the weak interlayer.

[0043] The direction of the interlayer membrane 52 of the weak interlayer reservation device can be set as needed. In order to simulate the direction of the weak interlayer belt in the actual rock mass, it is generally set according to the explored target rock mass structure. In the rock mass, the weak interlayer is mainly manifested as a layered or banded weak thin layer in the rock mass. Generally, the thickness of the weak interlayer is smaller than that of the adjacent rock layer, and the mechanical strength and deformation modulus are also lower. The saturated compressive strength is only half of the dry compressive strength or lower. Some disintegrate when exposed to water.

[0044] In this embodiment, the weak interlayer belt runs through the cave obliquely. During casting, first place the weak interlayer reservation device inside the cylindrical cavity reservation part 4, and let the free end of the interlayer membrane 52 pass through the membrane groove 40 on the cavity reservation part 4 to the outside for standby. Then fix the weak interlayer reservation device together with the cylindrical cavity reservation part 4 in the model frame 1. Then use rock-like materials to cast the lower rock mass of the weak interlayer, and then straighten the lower interlayer membrane 52 to cover 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, the specific thickness depends on the actual thickness of the simulation target and the similarity ratio; then straighten the upper interlayer membrane 52 to cover the weak interlayer similar material and clamp the end. Considering that the interlayer membrane 52 needs to withstand a certain degree of tension in 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 rock-like material is used to cast the upper rock mass of the weak interlayer, and a weak interlayer casting area is formed between the upper and lower interlayer membranes 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 reserved device is axially pulled out from the cylindrical cavity reserved part 4. Finally, the casting body is patted and compacted, and the mold is removed 24 hours after the casting is completed, and 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.

[0045] In the above embodiment, during the initial pouring, Figure 2As shown, the interlayer membrane 52 is used to separate the rock mass-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 lamellar 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 lamellar structure formed by the weak interlayer-like material 99; after the initial tapping and tamping, the rock-like material 88 and the weak interlayer-like material 99 become tight to a certain extent, and after the interlayer membrane 52 is removed and tapping and tamping are performed 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 fit in the later maintenance process, simulating the situation of weak interlayers in real rock and soil to a greater extent.

[0046] After the model test block is prepared, the strain of the cave inside the model can be measured by loading 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 mechanics of the foundation and caves can be inferred, providing basic information for building design and construction safety.

[0047] In order to observe and measure the response of the model to the load, in the prior art, multiple strain gauges are often pasted in the through-hole for measurement. 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.

[0048] 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; During the test (at this time, the torsion rod body 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 simulated test block. Otherwise, when the top of the simulated 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 caves, 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 cave through a clamping structure and attached to the limit plates. The two end covers can support the detection shaft 3 to be set at the axis center of the through cave. Specifically, the detection shaft 3 is set in the through cave, and the two ends of the detection shaft 3 are rotatably supported by the first side end cover 6 and the second side end cover 7 respectively and driven to rotate by the driving mechanism; On one section of the detection axis 3, a row of displacement sensors 33 are arranged along the axial direction, and the probes of each displacement sensor 33 point to the hole wall penetrating the cave. This section of the detection axis 3 corresponds to the simulated loading area of ​​the soil surface of the simulated test block.

[0049] During the test, in the initial state, this row of displacement sensors 33 can detect the position of each point on a line along the axis direction on the hole wall of the karst cave (equivalent to the distance from the point on a busbar on the hole wall of the karst cave to the axis). When the detection shaft 3 rotates an angle under the action of the driving mechanism, this row of displacement sensors 33 can detect the position of each point on another busbar on the hole wall of the karst cave along the axis direction. Repeating the above process many times can scan the dot matrix three-dimensional structure contour of the hole wall of the karst cave (that is, the angle and distance from each point on the hole wall to the axis). During the test, the strain detection device can detect the three-dimensional shape change process of the karst cave by pressing down the top of the model through the loading system. Therefore, according to the size of the loading force and the deformation of the physical model of the karst cave, according to the similarity principle, the relevant mechanical bearing conditions when there is a karst cave in the lower soil of the building foundation in the real scene are inferred.

[0050] 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 by the reflected wave, and uses the wave speed and the time difference between emission and reception to calculate the distance. The probe does not need to contact the wall of the through-hole cave. The contact type usually has a potentiometer inside. When the probe / probe is pressed, it slides to change the position of the potentiometer, thereby converting the displacement change into an electrical signal. The probe needs to support the wall of the through-hole cave.

[0051] For this example, please refer to Figure 4 , further comprising a tubular film 9, the tubular film 9 can shrink, and initially, the tubular film 9 wraps the detection shaft 3; When the detection shaft 3 is placed in the through-hole, both ends of the tubular membrane 9 extend beyond the through-hole, and the portion extending beyond the through-hole is attached to the stopper plate ( 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); 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 inside, the tubular membrane 9 expands and adheres tightly to the wall of the through-hole.

[0052] 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 rotating support sleeve 61 on the side facing the inside of the through cave, the detection shaft 3 is rotatably installed in the rotating support sleeve 61, and the first magnet and the second magnet are respectively provided at both ends of the detection shaft 3; like Figure 5 and Figure 6 As shown, the rotation support sleeve 61 forms a sleeve protruding platform 62 on the other side of the first side end cover 6 and the second side end cover 7, and the outer ring of the sleeve protruding platform 62 is provided with an annular limiting platform 63, and a driving area 64 is between the sleeve protruding platform 62 and the annular limiting platform 63. The driving component in the driving area 64 can drive the detection shaft 3 to rotate through the housing of the sleeve protruding platform 62; Specifically, on the first side end cover 6, there is an electromagnetic coil 32 in a circular array in the driving area 64, and 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 by an ordinary permanent magnet, and the permanent magnet 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 member 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 member such as a cylinder is used to push the strip groove member 992 in the vertical direction along the slide groove 9920, the reciprocating translational motion of the strip groove member 992 will be able to drive the permanent magnet to reciprocate, thereby driving the detection shaft 3 to reciprocate, so that the displacement sensor can measure the busbars at different angles passing through the wall of the cave.

[0053] On the second side end cover 7, as Figure 4As shown, the ring array in the driving area 64 has a permanent magnet ring 70, which matches the position of the second magnet, and a pointer 701 is also arranged on the permanent magnet ring 70, and a circular deflection scale 72 is correspondingly arranged on the second side end cover 7. In the process of the driving mechanism on one side of the first side end cover 6 driving 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 by magnetic force without direct mechanical contact, so that the inner side of the tubular membrane 9 between the end covers can contain fluid, and it is not easy to leak. However, contactless driving may also lead to low position control accuracy, and even due to the reasons such as the internal jamming of the detection shaft 3, the detection shaft 3 does not rotate under the drive of the external electromagnetic coil 32. Therefore, on the side of the second side end cover 7, the detection shaft 3 is taken as the active shaft, and the permanent magnet ring 70 is driven to drive the pointer 701 to deflect through magnetic locking, and the deflection scale 72 is used to achieve accurate positioning of the measurement point.

[0054] In summary, the main beneficial effect of the above embodiment is that the tubular membrane 9 and the fluid (such as water or gas) inside it are used to support the hole wall of the through-hole cave to a certain extent. The pressure of the fluid should not be too high, so that the tubular membrane 9 can be closely attached to the hole wall of the through-hole cave. It should be ensured that the support force of the tubular membrane 9 on the hole wall of the through-hole cave is much smaller than the load force on the hole wall of the through-hole cave when the model is loaded. This is because the model test block is cast by sand and soil, and the through-hole cave is obtained by removing the reserved tubular parts after the model is formed. The sand and soil raw materials used are mainly sand and soil, with less cement. During the removal of the tubular parts and the loading process, the wall surface of the through-hole cave may be damaged, and local sand and soil may fall off, and sand pits may appear.

[0055] The defects of the through-hole cave wall formed when the tubular member is removed can also be compensated by adjusting the initial value of the displacement sensor at the corresponding position (for example, when no load is applied, the initial value of the displacement sensor at each position is recorded as 0, and the reading change during the loading process is used as the deformation of the through-hole cave wall); however, during the loading process, if there is no tubular membrane 9 in this embodiment to support the through-hole cave hole wall, once the through-hole cave is compressed and deformed, the hole wall is likely to have sand falling off or even local collapse. In this case, the numbers measured by the displacement sensor in 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 set to support the through-hole cave hole wall, the tubular membrane 9 is close to the wall surface, which can effectively limit the local collapse of the wall surface, but the supporting force of the tubular membrane 9 on the wall surface is much smaller than the loading force, which ensures that the load loaded on 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).

[0056] This embodiment can be found in Figure 6The clamping structure includes a pressure ring 34, an air bag 35 and an annular expansion belt 36; The inner circumference of the pressure ring 34 is connected to the outer circumference of the rotating support sleeve 61, the expansion belt is concentrically and spacedly sleeved on the outer ring of the pressure ring 34, and a plurality of air bags 35 are arranged between the pressure ring 34 and the expansion belt; 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.

[0057] When the first side end cap 6 or the second side end cap 7 needs to be installed at the end of the through cave, the air bag 35 is first released to shrink the annular diameter expansion belt 36, and then inserted into the hole at the end of the through cave, and then pressurized to expand the air bag 35, the air bag 35 expands and drives the annular diameter expansion belt 36 to abut against the wall of the through cave. The clamping structure of this embodiment has the characteristic of easy disassembly and assembly.

[0058] 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 install two parallel clamping shafts 31 in the notch area, and a plurality of displacement sensors 33 are arrayed and restricted between the clamping shafts 31; The displacement sensor 33 includes a shell and a probe. The probe points to the wall of the cave. The shell is slidably matched 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.

[0059] A mechanical displacement sensor can be used, with the probe of the displacement sensor pointing to the wall of the through-hole cave, and the tail of the displacement sensor pointing to the axis of the detection axis 3. The distance from the position of the probe tip to the axis of the detection axis 3 can be obtained using the reading of the displacement sensor (also combined with the size of the displacement sensor). When the detection axis 3 is at a certain angle, at this angle, this row of sensors can measure the distance from the through-hole cave wall to the axis center along the axial direction; by rotating the detection axis 3, the distance from the entire through-hole cave wall to the axis center can be measured, and the 3D contour shape of the through-hole cave wall can be constructed. Then, change the load size, repeat the measurement, and obtain the 3D shape of the through-hole cave wall under the new load.

[0060] like Figure 6As shown, the fluid is liquid, and a hydraulic sensor 65 is provided on the first side end cover 6 and / or the second side end cover 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 test block, the soil above the through-hole may collapse and fall into the cave directly, the tubular membrane 9 is compressed, and the internal pressure fluctuates greatly. The hydraulic sensor 65 detects the beginning moment of the signal fluctuation and gives the signal to the controller. The controller controls the detection shaft 3 to rotate and points the probe of the displacement sensor toward the bottom or side of the through-hole to prevent damage from the fallen soil.

[0061] 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: 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, arrange the rock-like material into an inclined surface (simulating the lower rock mass of the weak interlayer zone), and then straighten the lower interlayer membrane 52 to cover the surface of the casting body, and clamp the end of the interlayer membrane 52; then cover the weak interlayer similar material of a certain thickness on this interlayer membrane 52, and the specific thickness needs to be calculated according to the thickness of the interlayer in the actual rock mass to be simulated and refer to the model similarity ratio; then straighten the upper interlayer membrane 52 and cover it on the weak interlayer The similar material is placed on the casting body and the end is clamped and fixed; finally, the rock-like material is used to cast the remaining space (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 body 51 is rotated, the interlayer membrane 52 is pulled out of the casting body and wound onto the torsion rod body 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 after curing for 14 days; Preparation: Set limit plates around the model test block, place a pressure plate 81 and a cushion block 82 on the surface of the model test block above the cavity reserved part 4, set displacement meters 83 around the pressure plate 81 to monitor surface settlement, and the displacement meter 83 can use the same device as the displacement sensor 33. Set a pressure sensor between the pressure plate 81 and the cushion block 82 to monitor the load; install the strain detection device to the through-hole cave, inject fluid into the tubular membrane 9 through the injection hole 60, so that the tubular membrane 9 is stretched and closely attached to the hole wall of the through-hole cave, rotate the detection shaft 3, let the displacement sensor 33 all face horizontally, then turn on the displacement sensor 33, let the detection shaft 3 rotate again, let the probe of the displacement sensor 33 scan along the arc-shaped top surface of the through-hole cave to the other side, record the detection value of each position in the process, 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 cave through the detection value of each displacement sensor 33 and the axis position data of the detection shaft 3; Test: Use the loader 84 to apply load to the pad 82. Every time the load increases by a set amount, the inner wall of the through-hole cave is scanned once (the detection shaft 3 rotates, and each displacement sensor 33 obtains the distance from the axis to the wall at the corresponding angle), and the data of the monitoring and measurement unit are read and stored. By superimposing the load data and the wall deformation data, the response of the through-hole cave in the model test block to the load (simulating the building on the rock surface, etc.) can be obtained, so as to reversely infer the mechanical working conditions of the actual rock mass based on the similarity theory.

[0062] In summary, the present invention effectively overcomes various shortcomings in the prior art, can produce beneficial technical effects, and has significant progress.

[0063] 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 familiar with 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 a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A karst foundation model test block (4) preparation device, comprising a model frame (1) with an opening at the top and a reinforcement structure (2) arranged on the periphery of the model frame (1), characterized in that: It also comprises a cavity reservation device, which is located inside the model frame (1) and does not contact the wall surface of the model frame (1). A rock mass-similar material is poured into the model frame (1) to form a karst foundation model test block (4). After the pouring is completed, the reservation device forms a cavity with an arc-shaped top surface (40) inside the karst foundation model test block (4).

2. The karst foundation model test block (4) preparation 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; During stirring and mixing, gypsum retarder and water need to be added, wherein 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 karst foundation model test block (4) preparation device according to claim 1, characterized in that: The cavity preserving device comprises a spherical foam block and a conduit, wherein the conduit connects the spherical foam block and the outside of the model frame (1); During pouring, the spherical foam block and the conduit are poured into the karst foundation model test block (4); After the pouring is completed, gasoline is injected from the conduit, and the spherical foam block is dissolved under the action of the gasoline, forming a cavity with an arc-shaped top surface (40) in the karst foundation model test block (4).

4. The karst foundation model test block (4) preparation device according to claim 1, characterized in that: The cavity preserving device comprises a base (5), a first spherical shell (6) and a second spherical shell (7); The base (5) is provided with a spherical cavity (50) opening upward, the outer surfaces of the first spherical shell (6) and the second spherical shell (7) are in contact with the inner surface of the spherical cavity (50) and are slidably matched, the first spherical shell (6) and the second spherical shell (7) are arranged on two sides of the spherical cavity (50) facing each other, and are controlled by a retracting mechanism to slide in opposite directions or reverse directions; When the first spherical shell (6) and the second spherical shell (7) slide towards each other and their end faces are in contact, the first spherical shell (6) and the second spherical shell (7) are connected to the base (5) to form a spherical shape; The first spherical shell (6) and the second spherical shell (7) can be retracted into the base (5) when sliding in opposite directions, and a cavity with an arc-shaped top surface (40) is formed on the upper side of the base (5).

5. The karst foundation model test block (4) preparation device according to claim 4, characterized in that: The retracting mechanism comprises a lever arm (70) and a driver (71); Two support seats (51) are arranged on the inner bottom surface of the base (5), the two support seats (51) face the center of the spherical cavity (50) of the base (5), and a driving shaft is rotatably arranged on each of the two support seats (51), which are defined as a first shaft (52) and a second shaft (53); The bottom of each of the first spherical shell (6) and the second spherical shell (7) is provided with a force arm (70), and the two force arms (70) are respectively fixedly connected to the first shaft (52) and the second shaft (53); The opposite surfaces of the two force arms (70) connected to the drive shaft are both provided with toothed discs (701); The driver (71) is also arranged on the inner bottom surface of the base (5) and is located between the two support seats (51). The output shaft of the driver (71) faces the center of the spherical cavity (50) of the base (5). A gear (711) is arranged on the output shaft of the driver (71), and the gear (711) is meshed with the two toothed discs (701) at the same time.

6. The karst foundation model test block (4) preparation device according to claim 4, characterized in that: The first spherical shell (6) and / or the second spherical shell (7) comprises an arc sheet body (60) and an arc strip body (61); The arc piece body (60) is a portion that contacts and slidably fits with the base (5); The arc strip body (61) is in the shape of an arc strip, one end of a plurality of the arc strip bodies (61) is fixedly connected to the inner side of the arc sheet body (60), and the other end is bent and extended according to the arc surface of the arc sheet body (60), and the plurality of the arc strip bodies (61) are arranged at intervals; The radius of the outer arc surface of the arc strip body (61) is smaller than the radius of the inner arc surfaces of the first spherical shell (6) and the second spherical shell (7); When the first spherical shell (6) and the second spherical shell (7) are both provided with arcuate bodies (61), the arcuate bodies (61) on the first spherical shell (6) and the second spherical shell (7) are staggered with each other; When the first spherical shell (6) and the second spherical shell (7) slide towards each other and the end surfaces of the arc-shaped sheet body (60) are in contact with each other, the respective arc-shaped strip bodies (61) are respectively inserted into the inner side of the other arc-shaped sheet body (60); When the first spherical shell (6) and the second spherical shell (7) slide in opposite directions to store the arc-shaped body (60) into the base (5), the respective arc-shaped body (61) is located in the gap between the other arc-shaped body (61).

7. The karst foundation model test block (4) preparation device according to claim 6, characterized in that: The arcuate body (61) is provided with a groove facing the outside of the arc surface, and a plurality of groups of displacement measuring units (62) are arranged at intervals in the groove; The probe (621) of the displacement measuring unit (62) faces the outside of the arc surface, and the bottom of the displacement measuring unit (62) and the bottom of the groove of the arc strip body (61) are connected via a flexible lifting structure.

8. The karst foundation model test block (4) preparation device according to claim 7, characterized in that: The flexible lifting structure is an arc-shaped strip airbag (611) laid at the bottom of the groove of the arc-shaped body (61); when the airbag (611) is pressurized, it expands in the groove of the arc-shaped body (61) to form lifting.

9. The karst foundation model test block (4) preparation device according to claim 4, characterized in that: A flexible cover (54) is connected to the opening of the spherical cavity (50) of the base (5), and the flexible cover (54) is connected to the base (5) to form a spherical shape. Gas can be filled inside to maintain the shape, and the first spherical shell (6) and the second spherical shell (7) are covered by the flexible cover (54).

10. A test method for a karst foundation model test block (4), characterized in that the test method comprises the following steps: Casting: Fill the model frame (1) with the stirred rock-like material to a preset height, allow the first spherical shell (6) and the second spherical shell (7) of the cavity pre-reserved device to slide towards each other and fit their end faces together to form a spherical shape and place it in the model frame (1), continue to load the rock-like material to embed the cavity pre-reserved device into the karst foundation model test block (4), embed a strain gauge (80) in the rock-like material above the cavity pre-reserved device, lead the wires or air pipes matching the cavity pre-reserved device and the strain gauge (80) to the outside, pat and compact the cast body, remove the mold one day after the casting is completed, and cure for 14 days to obtain the model test block (4); Preparation: When the first spherical shell (6) and the second spherical shell (7) of the cavity pre-reservation device slide in opposite directions to store the arc sheet body (60) into the base (5), the arc strip body (61) enters the top surface of the cavity at the same time, and the air bag (611) is pressurized and expanded to raise the height of the displacement measuring unit (62) in the upper groove of the arc strip body (61). After the readings of each displacement measuring unit (62) have changed, the probe (621) of each displacement measuring unit (62) has abutted against the cavity wall surface of the arc-shaped top surface (40) inside the model test block (4), and the pressurization is stopped and the readings of the displacement measuring unit (62) are cleared; a limit plate is set around the model test block (4), and a pressure plate (81) and a cushion block (82) are placed on the surface of the model test block (4) above the cavity pre-reservation device. Displacement meters (83) are set around the pressure plate (81) to monitor surface settlement, and a pressure sensor is set between the pressure plate (81) and the cushion block (82) to monitor load; Test: A load is applied to the pad (82) using a loading machine (84), while the data of the monitoring and measuring unit are read and stored.

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