Karst foundation model test block preparation device and test method

Abstract

The present invention provides a karst foundation model test block preparation device and test method, which belongs to the field of physical property testing and analysis technology, and is used to solve the problem that the traditional model test block preparation technology in the prior art is difficult to cast a karst model with a hollow structure inside. Specifically, it includes a model frame with an opening on the top and a reinforcement structure arranged on the periphery of the model frame; it also includes a cavity reservation device, the cavity reservation device is located inside the model frame and does not contact the wall of the model frame, and the rock-similar material is poured in the model frame to form a karst foundation model test block. After the pouring is completed, the reservation device forms a cavity with an arc-shaped top surface in the karst foundation model test block. The present invention constructs a cavity space simulating karst holes inside the model test block, which effectively solves the problem that the traditional preparation technology is difficult to form a hollow structure inside, and provides strong support for in-depth research on the instability mode and process of karst foundation.

Description

Technical Field

[0001] The invention belongs to the technical field of physical property testing and analysis, and particularly relates to a karst foundation model test block preparation device and a test method. Background Art

[0002] Karst is a special geological phenomenon formed by the long-term dissolution of soluble rocks by groundwater, which often leads to the appearance of underground cavities, caves and other structures. These cavities pose a serious threat to the safety and stability of building structures, and may cause catastrophic events such as structural collapse and ground collapse, bringing huge risks to people's lives and property safety.

[0003] In order to study the mechanical performance of karst foundation (karst under the foundation), similar models and similar principles are usually used to conduct simulation tests. However, the traditional model test block preparation technology makes it difficult to cast a karst model with a hollow structure inside, which limits the research on the internal stress distribution and deformation mechanism of the karst foundation and makes it difficult to truly reflect the actual situation of the karst foundation.

[0004] Therefore, it is necessary to develop a device that can cast simulated karst holes inside the model test block in order to more accurately simulate the mechanical performance of the karst foundation. Summary of the invention

[0005] In view of the above-mentioned shortcomings of the prior art, the purpose of the present invention is to provide a karst foundation model test block preparation device and test method, which are used to solve the problem that the traditional model test block preparation technology in the prior art is difficult to cast a karst model with a hollow structure inside.

[0006] To achieve the above-mentioned and other related purposes, the present invention provides a karst foundation model test block preparation device and a test method.

[0007] The karst foundation model test block preparation device comprises a model frame with an opening at the top and a reinforcement structure arranged on the periphery of the model frame;

[0008] It also includes a cavity reservation device, which is located inside the model frame and does not contact the wall of the model frame. Rock-similar materials are poured into the model frame to form a karst foundation model block. After the pouring is completed, the reservation device forms a cavity with an arc-shaped top surface in the karst foundation model block.

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

[0010] 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.

[0011] Optionally, 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;

[0012] During pouring, the spherical foam block and the conduit are poured into the karst foundation model test block;

[0013] After the pouring is completed, gasoline is injected from the conduit, and the spherical foam block is dissolved under the action of gasoline, forming a cavity with an arc-shaped top surface in the karst foundation model test block.

[0014] Optionally, the cavity preserving device includes a base, a first spherical shell and a second spherical shell;

[0015] The base is provided with a spherical cavity opening upward, the outer surfaces of the first spherical shell and the second spherical shell are in contact with the inner surface of the spherical cavity and are slidably matched, the first spherical shell and the second spherical shell are arranged opposite to each other on both sides of the spherical cavity, and are controlled by the retracting mechanism to slide in opposite directions or reverse directions;

[0016] When the first spherical shell and the second spherical shell slide toward each other and the end faces are in contact, the first spherical shell and the second spherical shell are connected to the base to form a spherical shape;

[0017] The first spherical shell and the second spherical shell can be received into the base when sliding in opposite directions, and a cavity with an arc-shaped top surface is formed on the upper side of the base.

[0018] Optionally, the retracting and expanding mechanism includes a force arm and a driver;

[0019] Two support seats are arranged on the inner bottom surface of the base, the two support seats face the center of the spherical cavity of the base, and a driving shaft is rotatably arranged on each of the two support seats, which are defined as a first shaft and a second shaft;

[0020] The bottom of the first spherical shell and the bottom of the second spherical shell each have a force arm, and the two force arms are fixedly connected to the first shaft and the second shaft respectively;

[0021] The opposite surfaces of the two force arms connected to the drive shaft are both provided with gear discs;

[0022] The driver is also arranged on the inner bottom surface of the base and located between the two support seats. The output shaft of the driver faces the center of the spherical cavity of the base. A gear is arranged on the output shaft of the driver, and the gear is meshed with the two gear discs at the same time.

[0023] Optionally, the first spherical shell and / or the second spherical shell includes an arc sheet body and an arc strip body;

[0024] The arc piece body is a part that contacts and slides with the base;

[0025] The arc strip body is in the shape of an arc strip, one end of the plurality of arc strip bodies is fixedly connected to the inner side of the arc sheet body, and the other end is bent and extended according to the arc surface of the arc sheet body, and the plurality of arc strip bodies are arranged at intervals;

[0026] The outer arc surface radius of the arc strip body is smaller than the inner arc surface radius of the first spherical shell and the second spherical shell;

[0027] When the first spherical shell and the second spherical shell are both provided with arcuate bodies, the arcuate bodies on the first spherical shell and the second spherical shell are staggered with each other;

[0028] When the first spherical shell and the second spherical shell slide toward each other and the end faces of the arc sheet bodies are in contact, the respective arc strip bodies are respectively inserted into the inner sides of the other arc sheet bodies;

[0029] When the first spherical shell and the second spherical shell slide in opposite directions to store the arc-shaped body into the base, the respective arc-shaped bodies are respectively located in the gaps between the arc-shaped bodies of the other party.

[0030] Optionally, the arcuate body is provided with a groove facing the outer side of the arc surface, and a plurality of groups of displacement measuring units are arranged at intervals in the groove;

[0031] The probe of the displacement measuring unit faces the outside of the arc surface, and the bottom of the displacement measuring unit and the bottom of the groove of the arc strip body are connected through a flexible lifting structure.

[0032] Optionally, the flexible lifting structure is an arc-shaped strip airbag laid at the bottom of the arc-shaped strip groove, and the airbag expands in the arc-shaped strip groove to form lifting when pressurized.

[0033] Optionally, a flexible cover is connected to the opening of the spherical cavity of the base, and the flexible cover is connected to the base to form a sphere, and gas can be filled inside to maintain the shape, and the first spherical shell and the second spherical shell are covered by the flexible cover.

[0034] Optionally, the karst foundation model test block test method, using the karst foundation model test block preparation device as described above, comprises the following steps:

[0035] Casting: Fill the model frame with the stirred rock-like material to a preset height, let the first spherical shell and the second spherical shell of the cavity pre-reserved device slide towards each other and fit the end faces to form a spherical shape as a whole and put it into the model frame, continue to load the rock-like material to embed the cavity pre-reserved device into the karst foundation model test block, embed the strain gauge 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 to the outside, pat and tamp the casting body, remove the mold one day after the casting is completed, and cure for 14 days to obtain the model test block;

[0036] Preparation: When the first spherical shell and the second spherical shell of the cavity reservation device slide in opposite directions to store the arc sheet body into the base, the arc strip body enters the top surface of the cavity at the same time, and the airbag is pressurized and expanded to raise the height of the displacement measuring unit in the upper groove of the arc strip body. After the readings of each displacement measuring unit have changed, the probes of each displacement measuring unit have abutted against the cavity wall of the arc-shaped top surface in the model test block, and the pressurization is stopped and the readings of the displacement measuring unit are cleared; limit plates are set around the model test block, and a pressure plate and a cushion block are placed on the surface of the model test block above the cavity reservation device. Displacement meters are set around the pressure plate to monitor surface settlement, and a pressure sensor is set between the pressure plate and the cushion block to monitor load;

[0037] Test: Use a loading machine to apply load to the pad, and read and store the data of the monitoring and measuring unit at the same time.

[0038] As described above, the karst foundation model test block preparation device and test method of the present invention have at least the following beneficial effects:

[0039] Through the cavity reservation device, a cavity space simulating karst holes was constructed inside the model test block, which effectively solved the problem that traditional preparation technology is difficult to form a hollow structure inside. The device ensures the stability of the test block during casting, guarantees the shape and size of the cavity, and improves the simulation accuracy of the model test block on the real karst foundation. In addition, combined with the setting of strain gauges and displacement sensors, it can monitor the strain of the cavity cave and the top surface settlement during loading in real time, providing strong support for in-depth research on the instability mode and instability process of karst foundation. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 Shown is an overall schematic diagram of the present invention.

[0041] Figure 2 Shown is a cross-sectional schematic diagram of the present invention.

[0042] Figure 3 Shown is a schematic diagram of the cavity reservation device of the present invention.

[0043] Figure 4 Shown is a schematic cross-sectional view of the cavity reservation device of the present invention.

[0044] Figure 5 Shown as the present invention Figure 4 A partial enlarged schematic diagram in the middle.

[0045] Figure 6 Shown is a schematic diagram of the first spherical shell and the second spherical shell of the present invention.

[0046] Figure 7 Shown is a schematic diagram of the explosion assembly of two spherical shells and a base according to the present invention.

[0047] Figure 8Shown is the arc sheet body of the spherical shell of the present invention.

[0048] Fig. 9 Shown as the present invention Figure 8 The schematic diagram is a partial enlargement of point B in the middle.

[0049] Fig.10 It is a schematic diagram of the cross section inside the arc plate groove of the present invention.

[0050] Fig.11 Shown is a schematic diagram of the base and the flexible cover of the present invention.

[0051] Fig.12 Shown is a schematic diagram of the strain gauge arrangement of the present invention.

[0052] Among them: model frame 1, reinforcement structure 2, model test block 4, arc top surface 40, base 5, spherical cavity 50, support seat 51, first axis 52, second axis 53, flexible cover 54, first spherical shell 6, arc sheet body 60, arc strip body 61, airbag 611, displacement measurement unit 62, probe 621, second spherical shell 7, force arm 70, gear disc 701, driver 71, gear 711, strain gauge 80, pressure plate 81, cushion block 82, displacement meter 83, loader 84. DETAILED DESCRIPTION

[0053] 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.

[0054] See also Figures 1 to 12 . 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 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 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. 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.

[0055] 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.

[0056] See also Figure 1The embodiment of the karst foundation model test block preparation device provided by the present invention comprises 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 a 30 mm thick steel plate, and the surrounding side plates are made of 20 mm 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.

[0057] It also includes a cavity reservation device, which is located inside the model frame 1 and does not contact the wall of the model frame 1. Rock-similar materials are poured in the model frame 1 to form a karst foundation model block 4. After the pouring is completed, the reservation device forms a cavity with an arc-shaped top surface 40 in the karst foundation model block 4.

[0058] After pouring, a cavity space is formed at the cavity reserved device inside the model test block to simulate the cave. 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. They will 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 of the karst foundation is simplified to a two-dimensional plane strain problem for analysis, ignoring the influence of three-dimensional space effects, and it is difficult to simulate the real situation of karst foundation. In order to increase the reliability of the analysis results, it is also necessary to combine experiments to comprehensively evaluate the stability of karst foundation. The existing research content mainly focuses on the influence of cave size, distribution location and cave roof (foundation) thickness on mechanical properties. There are no more technical solutions for experimental research on the instability mode and process of karst foundation.

[0059] In the above embodiment, after obtaining the model test block, a plurality of strain gauges are arranged in the cavity cave holes of the model test block, and then a load is applied from the top surface of the model test block to the internal cavity cave area to simulate the weight of the building. At the same time, a plurality of displacement sensors are arranged in the load application area on the top surface of the model test block to detect the strain of the cavity cave and the settlement of the top surface during the loading process, thereby forming a corresponding curve of load and deformation, which is then used to study the instability mode and process of karst foundation.

[0060] 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.

[0061] In order to ensure that the main mechanical properties of similar materials are similar to those of the prototype rock layer soil and the material composition structure is similar to that of the prototype rock mass, the physical and mechanical properties of the simulated materials are stable during the test and are not easily affected by external conditions, and 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, gypsum, cement, etc. as binder materials, because the initial setting time of gypsum powder is relatively short, and retarders are added as regulating materials.

[0062] 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.

[0063] 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.

[0064] 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 and water 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.

[0065] 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 cave of the foundation is an arc-top cavity. 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 load during the test. 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.

[0066] In this embodiment, the cavity reservation device includes a spherical foam block and a conduit, the conduit connects the spherical foam block and the outside of the model frame 1, and multiple conduits can be provided, connected to the 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 gasoline, forming a cavity with an arc-shaped top surface 40 in the karst foundation model test block 4. Multiple conduits are more likely to form a loop, and gasoline is more likely to be injected into the foam block and flow out after dissolving.

[0067] The cavity reservation device in this embodiment is cleverly designed. Through the spherical foam block and the conduit, the purpose of flexibly constructing the cavity in the karst foundation model test block is achieved. Multiple conduits can ensure that gasoline can be injected quickly, thereby effectively promoting the dissolution of the spherical foam block and exporting the dissolved fluid material. The operation process of this method is simple and fast, and the cost is relatively low. More importantly, by adjusting the shape of the foam block, various complex cavity structures, including domes and special-shaped tops, etc., can be easily formed. The foam block can be changed in the corresponding shape, thereby simulating the shape and characteristics of the real cave to the maximum extent, providing strong support for the research of karst foundations.

[0068] On the other hand, this method also has its shortcomings. For example, when foam blocks are used as cavity pre-reservation devices, the patting and tamping of similar materials to the rock mass during the pouring process may cause their deformation, and the final shape does not match the designed shape. At the same time, by dissolving the foam blocks with gasoline as the cavity, it is difficult to set up sensors such as strain gauges inside to detect the deformation of the cavity during loading.

[0069] As an alternative to the above embodiment, please refer to Figure 3 The cavity pre-reserved device includes a base 5, a first spherical shell 6 and a second spherical shell 7;

[0070] 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 oppositely on both sides of the spherical cavity 50, and are controlled by the retracting mechanism to slide oppositely or reversely, thereby opening or closing the top of the spherical cavity 50;

[0071] When the first spherical shell 6 and the second spherical shell 7 slide toward each other and the end faces are in contact, Figure 4 As shown, the first spherical shell 6 and the second spherical shell 7 are connected to the base 5 to form a spherical shape;

[0072] The first spherical shell 6 and the second spherical shell 7 can be received into the base 5 when they slide in opposite directions. Figure 3 As shown, a cavity with an arc-shaped top surface 40 is formed on the upper side of the base 5, and the cavity is located inside the model test block.

[0073] During pouring, the first spherical shell 6 and the second spherical shell 7 slide in opposite directions and the end faces fit together, and the entire cavity reservation device is spherical. Then, the cavity reservation device is embedded in the rock-like material for pouring. In order to prevent the rock-like material from being connected to the first spherical shell 6 and the second spherical shell 7 as a whole, an oil film can be applied on the surface of the first spherical shell 6 and the second spherical shell 7. After the pouring is completed, when the model test block is solidified and formed, when the loading test is carried out, the first spherical shell 6 and the second spherical shell 7 are controlled to slide in the opposite direction and be collected into the base 5, so as to form a cavity space with an arc-shaped top surface 40 inside the model test block. At the same time, sensors are arranged in the base 5. During the loading process, these sensors can be used to measure the arc-shaped top surface 40 of the cavity space, obtain the cavity deformation under different loading forces, and reversely infer the mechanical characteristics of the real foundation according to the model similarity theory.

[0074] In the above embodiment, the controllable opening and closing of the spherical cavity reservation device is realized by the sliding cooperation of the first spherical shell and the second spherical shell in the spherical cavity of the base, which is convenient for constructing a cavity structure in a rock-like material. Applying an oil film effectively prevents the adhesion of the casting material to the shell, ensures the smooth sliding of the first spherical shell 6 and the second spherical shell 7 and the smooth formation of the cavity. In addition, the sensor integrated in the base can monitor the deformation of the cavity in real time during the loading test, providing test data for the accurate reverse calculation of the real foundation mechanical characteristics.

[0075] Furthermore, in this embodiment, the retracting mechanism includes a lever arm 70 and a driver 71;

[0076] like Figure 4As shown, two support seats 51 are arranged on the inner bottom surface of the base 5, and the two support seats 51 face the central area of ​​the spherical cavity 50 of the base 5. 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 contact parts between the first shaft 52 and the second shaft 53 can slide against each other to form respective rotations. The two shafts are coaxial, but the rotation directions are different.

[0077] The first spherical shell 6 and the second spherical shell 7 each have a force arm 70 at the bottom, and the two force arms 70 are fixedly connected to the first shaft 52 and the second shaft 53 respectively;

[0078] The opposite surfaces of the two force arms 70 connected to the drive shaft are both provided with toothed discs 701;

[0079] 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 central area of ​​the spherical cavity 50 of the base 5. A gear 711 is arranged on the output shaft of the driver 71. The gear 711 is meshed with the two toothed discs 701 at the same time. The gear 711 and the toothed disc 701 can use conical teeth.

[0080] When the driver 71 drives the toothed disc 701 to rotate, the two force arms 70 are driven to rotate in different directions, thereby driving the first spherical shell 6 and the second spherical shell 7 to open and close. This structure can save space and ensure that there is enough space in the base 5 to set up the controller, etc. If the pre-buried base 5 is connected to the outside through wireless instead of pre-buried wiring harness, Bluetooth or other wireless modules, batteries, etc. need to be set in the base 5.

[0081] In this embodiment, the first spherical shell 6 and / or the second spherical shell 7 includes an arc sheet body 60 and an arc strip body 61;

[0082] The arc piece 60 is a part that contacts and slides with the base 5;

[0083] The arc strip body 61 is in the shape of an arc strip, one end of the arc strip body 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. The arc strip bodies 61 are arranged at intervals, and the arc sheet body 60 and the arc strip body 61 form a hemispherical structure;

[0084] The outer arc surface radius of the arc strip body 61 is smaller than the inner arc surface radius of the first spherical shell 6 and the second spherical shell 7;

[0085] When the first spherical shell 6 and the second spherical shell 7 are both provided with arc strips 61, the arc strips 61 on the first spherical shell 6 and the second spherical shell 7 are laterally staggered with each other, such as Figure 8 As shown;

[0086] When the first spherical shell 6 and the second spherical shell 7 slide toward each other and the end faces of the arc sheet body 60 fit together, that is, the two spherical shells are closed and form a sphere with the base 5, at this time, the first spherical shell 6 and the second spherical shell 7 have a supporting effect on the cavity wall, and the respective arc strip bodies 61 are respectively inserted into the inner side of the other arc sheet body 60;

[0087] When the first spherical shell 6 and the second spherical shell 7 slide in opposite directions to put the arc strip body 60 into the base 5, that is, the two spherical shells are opened and the cavity wall loses support, the respective arc strip bodies 61 are respectively located in the gap between the arc strip bodies 61 of the other party, and each arc strip body 61 is located on the lower side of the wall of the spherical cavity 50, as shown in FIG. Figure 8 At this time, the arc strip body 61 does not contact the wall surface of the cavity, and there is still a distance between them. The arc strip body 61 has no supporting effect on the wall surface of the spherical cavity 50.

[0088] Furthermore, in this embodiment, the arc strip body 61 is provided with a groove facing the outer side of the arc surface, and a plurality of groups of displacement measuring units 62 are arranged at intervals in the groove. Figure 8 and 9 Only three groups of displacement measurement units 62 are shown;

[0089] The probe 621 of the displacement measuring unit 62 faces the outer side 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 through a flexible lifting structure.

[0090] The displacement measuring units 62 can be arranged at intervals on all the arc strips 61, and radially toward the wall in a dot matrix manner to detect the displacement of each point on the wall, thereby depicting the spatial shape of the spherical cavity 50. During the load loading process, the displacement changes of each point under various loads are measured, and then the overall deformation of the spherical cavity 50 is reflected. In this embodiment, since the arc strips 61 do not contact the wall and have no supporting function, the wall deformation of the spherical cavity 50 is entirely derived from the test load, and the test conclusion is more accurate.

[0091] The displacement measurement unit 62 includes a housing and a probe (mechanical) / probe (photoelectric). The photoelectric type is non-contact, while the mechanical type is contact. The photoelectric type uses the waves emitted by the probe and received by the probe, 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 cave wall, but is susceptible to interference. The contact type usually has a potentiometer inside. When the probe is pressed, it slides to change the position of the potentiometer, thereby converting the change into an electrical signal. The probe needs to support the measured wall and automatically adjust its own expansion and contraction according to the deformation of the wall.

[0092] Preferably, a mechanical displacement sensor is used, the probe of the displacement sensor points to the wall of the cave hole, and the tail points to the center of the cave. The distance from the position of the probe tip to the center of the cave can be obtained by the reading of the displacement sensor, for example, by adding the distance from the displacement sensor housing to the center of the cave to the extension amount of the probe. Each sensor can measure the distance of the cave wall relative to the hole center, forming a spherical distribution of points, which can depict the spatial shape of the entire cave and construct the 3D shape of the cave wall. Then, the load size is changed, and the measurement is repeated to obtain the 3D shape of the cave wall under the new load.

[0093] Furthermore, this embodiment Fig.10 As shown, 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. The displacement measuring unit 62 is installed on the arc-shaped strip airbag 611, and the expansion state of the arc-shaped strip airbag 611 is used to adjust the initial distance of the probe / probe relative to the wall of the spherical cavity 50. Before starting the measurement, the probe / probe of the displacement measuring unit 62 needs to be located inside the spherical first spherical shell 6 and the second spherical shell 7, so that the first spherical shell 6 and the second spherical shell 7 can slide and close normally; when performing a load test, the first spherical shell 6 and the second spherical shell 7 are opened, and the probe / probe of the displacement measuring unit 62 needs to be against the wall of the spherical cavity 50 to perform the measurement, especially for the contact displacement measuring unit 62, the probe needs to be in contact with the wall to accurately measure the position changes of each point on the wall. In the later stage of the loading test, the load is already very large, and the local casting body on the upper side of the spherical cavity 50 may be compressed and collapsed, resulting in a large displacement. These gravity forces act on the probe / probe, which may cause damage to the displacement measuring unit 62. However, since the bottom is supported by a flexible arc-shaped strip air bag 611, the probe / probe of the displacement measuring unit 62 can be retracted into the groove structure of the arc strip body 61 by changing (unloading) the air pressure, and the compressed and collapsed simulation block is supported by the top surface of the arc strip body 61, thereby protecting the displacement measuring unit 62 and devices such as the controller located on the inner side of the first spherical shell 6 and the second spherical shell 7. At the same time, since the arc-shaped strip airbag 611 is flexible, even if the pressure is not unloaded, when the displacement measuring unit 62 is under greater pressure, the arc-shaped strip airbag 611 can also deform, allowing the displacement measuring unit 62 to have space to move downward without having a large rigid contact with the wall of the spherical cavity 50. However, in order to ensure the measurement accuracy, the extension and retraction elastic force of the probe of the displacement measuring unit 62 should be smaller than the elasticity of the arc-shaped strip airbag 611. In this way, when the probe contacts the wall of the spherical cavity 50 and is subjected to force, it is the probe rather than the arc-shaped strip airbag 611 that extends and retracts, so that the displacement measuring unit 62 can accurately sense the change.

[0094] In this embodiment, Fig.11As shown, a flexible cover 54 is connected to the opening of the spherical cavity 50 of the base 5. The flexible cover 54 is connected to the base 5 to form a sphere, and gas can be filled inside to maintain the shape. The first spherical shell 6 and the second spherical shell 7 are covered by the flexible cover 54. The surface of the flexible cover 54 can be coated with an oil film and then pre-embedded and cast together with the pre-embedded device. The oil film makes it easy to remove from the damaged model test block after the test is completed. The flexible cover 54 can prevent the spherical cavity 50 from being deformed under load during the test, resulting in local mud and sand falling into the device, affecting its normal operation. The flexible cover 54 can use a flexible rubber film.

[0095] The more important function of the flexible cover 54 is to avoid the need to demold the spherical cavity 50 after the casting is completed. For example, in the embodiment without the flexible cover 54, the first spherical shell 6 and the second spherical shell 7 need to be rotated into the base 5 to form a cavity, which may cause damage to the cavity wall, local sand and soil falling off, and the appearance of sand pits. As a result, the probe of the local displacement measurement unit 62 may reach the defect, resulting in the measured local deformation being inconsistent with the deformation caused by the actual force. The flexible cover 54 is supported by the first spherical shell 6 and the second spherical shell 7 during casting. After casting, the interior is bulged by appropriate air pressure and fits tightly with the wall of the spherical cavity 50 to form a supporting effect, but the supporting force (determined by the internal air pressure) is much smaller than the loading force on the wall of the spherical cavity 50, and does not affect the accuracy of the test. During the loading test, even if the wall of the spherical cavity 50 is partially detached due to the force, the sand remains in place due to the support of the flexible cover 54, thereby improving the accuracy of the overall load deformation of the wall of the spherical cavity 50 detected by the detection unit (displacement sensor).

[0096] This embodiment is an embodiment of a test method for a karst foundation model test block 4, using the above karst foundation model test block 4 preparation device, including the following steps:

[0097] Casting: Fill the model frame 1 with the stirred rock-like material to a preset height, let the first spherical shell 6 and the second spherical shell 7 of the cavity pre-reserved device slide towards each other and fit the end faces to form a spherical shape as a whole and put it into 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 the strain gauge 80 in the rock-like material above the cavity pre-reserved device, lead the matching wires or air pipes of the cavity pre-reserved device and the strain gauge 80 to the outside, pat and tamp the casting body, remove the mold one day after the casting is completed, and cure for 14 days to obtain the model test block 4;

[0098] Preparation: When the first spherical shell 6 and the second spherical shell 7 of the cavity reservation device slide in opposite directions to receive 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 airbag 611 is pressurized and expanded to raise the height of the displacement measuring unit 62 in the 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 of the arc-shaped top surface 40 in the model test block 4, and the pressurization is stopped and the reading of the displacement measuring unit 62 is cleared; limit plates are set around the model test block 4 (to simulate the squeezing effect of the surrounding soil), and a pressure plate 81 and a cushion block 82 are placed on the surface of the model test block 4 above the cavity 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. The displacement meter 83 and the displacement measuring unit 62 can use the same components;

[0099] Test: Use the loader 84 to apply load to the pad 82, and read and store the data of the monitoring and measuring unit at the same time. By superimposing the load data and the wall deformation data, the response of the spherical cavity 50 (simulating the cave area in the rock mass) and the soil above it to the load (simulating the building on the rock surface, etc.) in the model test block can be obtained, so as to reversely infer the mechanical working conditions of the actual rock mass based on the similarity theory.

[0100] In summary, the present invention effectively overcomes various shortcomings in the prior art, can produce beneficial technical effects, and has significant progress.

[0101] 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 includes a cavity reservation device, the cavity reservation device is located inside the model frame (1) and does not contact the wall surface of the model frame (1), and 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) in the karst foundation model test block (4); 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).

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 2, 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.

4. The karst foundation model test block (4) preparation device according to claim 3, 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 part 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).

5. The karst foundation model test block (4) preparation device according to claim 4, 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.

6. The karst foundation model test block (4) preparation device according to claim 5, 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.

7. The karst foundation model test block (4) preparation device according to claim 6, 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).

8. A method for testing a karst foundation model test block (4), characterized in that the method comprises using the karst foundation model test block (4) preparation device as claimed in claim 7, and comprising 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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