Test method and device for simulating overloading induced deep karst collapse in dense building group

Abstract

This invention relates to an experimental method and apparatus for simulating deep karst collapse induced by overloading of dense building complexes. The apparatus includes: a model test chamber for placing test soil; a karst channel mechanism with karst channels of different sizes distributed throughout; a loading mechanism for simulating the application of loads to dense urban building complexes and soil consolidation; an intelligent display mechanism; an image acquisition mechanism for observing changes in the overlying soil layer and the underlying karst channels during the loading process; a data analysis mechanism; a karst collapse soil collection mechanism for collecting collapsed soil; and a support mechanism for providing reaction forces to balance the applied load. Compared with existing technologies, this invention can provide technical support for studying deep karst collapse induced by static overloading of dense urban building complexes, reveal the mechanism of deep karst collapse under static overloading of dense urban building complexes, determine the critical disaster-causing and destructive conditions of deep urban karst collapse, and provide reference value for the treatment and prevention of deep urban karst collapse.

Description

Technical Field

[0001] This invention relates to the field of karst collapse technology, and in particular to a test method and apparatus for simulating deep karst collapse induced by overloading of dense building complexes. Background Technology

[0002] Karst collapse refers to the deformation and failure of loose soil covering karst caves under the influence of internal and external forces or human factors. Due to the depth and concealment of deep urban karst, its geological structure is more complex than that of surface karst, and the failure modes of karst collapse vary significantly depending on the soil covering layer. Furthermore, with the continuous increase in urban population and the growing scale of dense building clusters in recent years, it is urgent to clarify the disaster-causing mechanisms of urban karst collapse induced by dense building clusters, determine the critical disaster-causing and failure conditions of karst collapse, and provide a reference for the prevention and control of urban karst collapse.

[0003] CN116859020A discloses a karst collapse experimental device, the technical solution of which includes an installation frame, a high-pressure water tank, a collapse simulation box, a soil dropping box, and a water pipe. The installation frame has upper and lower sides. The collapse simulation box is installed on the lower layer, and the soil dropping box is installed on the upper layer. The high-pressure water tank is installed on the ground at a set distance from the installation frame. The high-pressure water tank is connected to the water pipe, which is connected to the bottom of the collapse simulation box. The bottom of the collapse simulation box is provided with a simulated karst cave opening. The water pipe is connected to the interior of the collapse simulation box through the simulated karst cave opening. The top of the collapse simulation box is provided with a soil dropping box. Soil is filled into the interior of the collapse simulation box using the soil dropping box. The amount and size of the filled soil can be adjusted using the soil dropping box. However, this karst collapse experimental device is not suitable for simulating deep karst collapse induced by overloading of dense building complexes. The main reasons are: (1) It does not simulate the real stress state of the overlying soil in the karst channel. Because the strata of deep karst are deep, and with geological processes, the soil itself has a certain stress. It is necessary to use a loading device to load the soil layer to a specified stress state; (2) The existing devices are basically large-size model boxes, which are difficult to test and have a complicated test process. The test cycle required for different influencing factors is long; (3) The existing devices focus on simulating the structural morphology of karst and do not reveal the disaster mechanism and damage mode of deep karst collapse caused by external factors such as dense building complexes. Summary of the Invention

[0004] The purpose of this invention is to provide a test method and apparatus for simulating deep karst collapse induced by overloading of dense building complexes, in order to solve the above-mentioned problems. This method and apparatus simulates the static overloading of dense urban building complexes to induce deep karst collapse, providing technical support for the study of deep karst collapse caused by static overloading of dense urban building complexes. It can effectively reveal the mechanism of deep karst collapse under static overloading of dense urban building complexes, determine the critical disaster-causing and destructive conditions of deep urban karst collapse, and provide certain reference value for the treatment and prevention of deep urban karst collapse.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] The first objective of this invention is to provide an experimental apparatus for simulating deep karst collapse induced by overload in dense building complexes, comprising: a model test chamber for placing test soil; a karst channel mechanism located at the bottom of the model test chamber for providing karst channels of different sizes, shapes, and numbers; a loading mechanism located at the top of the model test chamber for applying loads from the dense urban building complex and for soil consolidation; an intelligent display mechanism connected to the loading mechanism for displaying the magnitude of the loading values; an image acquisition mechanism located on the side of the model test chamber for observing changes in the overlying soil layer and the underlying karst channels during the loading process; a data analysis mechanism connected to the image acquisition mechanism for analyzing the failure modes of karst collapse; a karst collapse soil collection mechanism located below the karst channel mechanism for collecting soil from karst collapse induced by static overload in the dense urban building complex; and a support mechanism including a model test chamber fixing component connected to the model test chamber and a reaction frame component connected to the loading mechanism, wherein the model test chamber fixing component is used to fix the model test chamber, and the reaction frame component is used as a reaction frame to support the application of the entire load.

[0007] Furthermore, the model test chamber is cylindrical in shape, with a two-lobed structure, the two lobes interlocking at the junction, and has no top or bottom cover.

[0008] Furthermore, the karst channel mechanism includes a karst channel base plate; the karst channel base plate is located at the bottom of the model test chamber; the karst channel base plate has the same diameter as the model test chamber; the karst channel base plate is provided with karst channels of different aperture sizes; the karst channels are in contact with the test soil.

[0009] Furthermore, the loading mechanism includes a hydraulic jack loading mechanism and a circular loader; the hydraulic jack loading mechanism includes a hydraulic jack and a loading head; a separate hydraulic jack and a matching loading head are used for loading; the hydraulic jack is connected to the loading head; the hydraulic jack outputs force, and the loading head can extend to act on the circular loader; the hydraulic jack is connected to a pressure holding valve; the pressure holding valve is used to control the oil in the hydraulic jack.

[0010] Furthermore, the intelligent display mechanism includes a pressure sensor and an intelligent display device; the pressure sensor and the intelligent display device are connected via a data cable; one side of the pressure sensor is disposed on the top of the loading head, and the other side is connected to the intelligent display device.

[0011] Furthermore, the image acquisition mechanism includes an industrial camera arranged on the side, a digital camera and a high-definition video camera arranged on the front and bottom, to capture changes in the overlying soil and the underlying karst channels during the loading process from all directions and multiple angles.

[0012] Furthermore, the data analysis mechanism includes a series of graphics processing software and data analysis software, used to analyze the damage patterns of karst collapse.

[0013] Furthermore, the karst collapse soil collection mechanism includes a plastic basin for collecting soil from deep karst collapses induced by static overload of dense building complexes.

[0014] Furthermore, the model test chamber fixing assembly includes an upper cover plate and a lower cover plate; the upper cover plate is a hollow aluminum alloy cover plate with the same diameter as the model test chamber, facilitating direct contact between the circular loader and the soil; the lower cover plate is a solid aluminum alloy cover plate used as a support during soil consolidation, and can be replaced with a base plate with karst channels during the formal test; the upper and lower cover plates are connected by four bolts.

[0015] Furthermore, the reaction frame assembly includes a reaction frame; the reaction frame includes an upper reaction frame plate, a lower reaction frame plate, a screw, and nuts; the surface of the upper reaction frame plate is flat; the lower reaction frame plate is provided with a lower cave outlet, which is a circular hole with the same diameter as the model test chamber; the upper reaction frame plate and the lower reaction frame plate are connected by a screw, and two nuts are used to fix the junction of the upper reaction frame plate and the screw respectively.

[0016] Furthermore, the entire model test device is placed in a reaction frame and fixed with aluminum alloy upper and lower cover plates, screws, and nuts.

[0017] Furthermore, a circular loader of equal diameter is located at the top of the cylindrical model test chamber. Above the circular loader is a hydraulic jack loading head. After contacting the pressure sensor, the loading head directly contacts the reaction frame. By closing the pressure relief valve and continuously applying pressure, the hydraulic jack can exert force. One end of the loading head is fixed to the reaction frame, while the other end extends directly onto the circular loader, thereby continuously applying the target load. When a certain load value is reached, closing the pressure holding valve stops the flow of oil in the hydraulic jack, maintaining the stability of that load value, thus allowing observation of experimental phenomena. Furthermore, the load value can be displayed on an intelligent display connected to the pressure sensor.

[0018] Furthermore, the soil to be tested is located in the middle of the cylindrical model test box. Depending on the actual engineering background, clay (i.e., the cover layer is cohesive soil layer, a barrier type cover layer), sand (i.e., the cover layer is sandy soil layer, a permeable type cover layer), clay above sand (i.e., the upper cover layer is cohesive soil layer, the lower cover layer is sandy soil layer, a barrier type cover layer), or sand above clay (i.e., the upper cover layer is sandy soil layer, the lower cover layer is cohesive soil layer, a permeable type cover layer) can be selected as the karst upper cover soil layer.

[0019] Furthermore, at the bottom of the cylindrical model test chamber are aluminum alloy plates of equal diameter, used to simulate bedrock. The base plate is processed to approximate karst caves developed on the bedrock. Based on factors such as karst morphology and size, the aluminum alloy plate is processed to create holes that simulate karst channels.

[0020] Furthermore, located below the karst channel is a karst collapse soil collection mechanism, mainly composed of plastic basins, used to collect soil from deep karst collapses induced by static overload of dense building complexes.

[0021] Furthermore, digital cameras and high-definition video cameras are arranged at the front, sides, and bottom of the test chamber to capture the changes in the overlying soil and the underlying karst channels during the loading process from all angles.

[0022] Furthermore, the model test chamber includes two types: one for drainage consolidation, with drainage holes evenly distributed at 2cm intervals on its inner surface, and geotextile glued to the inner surface with strong adhesive to reduce contact between the soil sample and the plexiglass, protecting the integrity of the soil sample surface; the other type is used for formal soil loading tests, with an intact test chamber surface, without drainage holes or geotextile. The test chamber is cylindrical and has no top or bottom cover. The test chamber has a two-part mold structure, with the two parts interlocking at the junction.

[0023] Furthermore, the karst passage mechanism is placed at the bottom of the model test chamber and can be further processed into karst caves of different sizes, numbers, and shapes according to research needs.

[0024] Furthermore, the loading mechanism includes a hydraulic jack, a loading head, and a circular loader. Specifically, a separate hydraulic jack and its matching loading head are used for loading. By closing the pressure relief valve and continuously applying pressure, the jack can exert force, causing the corresponding loading head to extend and act on the circular loader. The average additional stress of the foundation under different dense urban building complexes is converted into a load before loading. When a certain load value is reached, the pressure holding valve is closed, which stops the flow of oil in the hydraulic jack, maintaining the stability of that load value, thereby allowing for observation of experimental phenomena.

[0025] Furthermore, the intelligent display mechanism includes a pressure sensor and an intelligent display device. One end of the pressure sensor is connected to the loading head, and the other end is in contact with the reaction frame, used to display the magnitude change of the value during the loading process.

[0026] Furthermore, the image acquisition equipment includes digital cameras and high-definition video cameras, used to capture changes in the overlying soil and underlying karst channels during the loading process.

[0027] Furthermore, data analysis agencies include various graphics processing software and data processing software, used to analyze the damage patterns and disaster-causing mechanisms of karst collapse.

[0028] Furthermore, the karst collapse soil collection device includes plastic basins for holding the collapsed soil.

[0029] Furthermore, the support mechanism comprises two parts. One part is a fixed model test chamber, with the upper part of the chamber secured by a hollow aluminum alloy cover plate. The diameter of the hollow cover plate is the same as that of the model test chamber, facilitating direct contact between the circular loader and the soil. The lower part of the chamber uses a solid aluminum alloy cover plate for support during soil consolidation. In the formal test, this cover plate can be replaced with a base plate containing karst channels. The upper and lower cover plates are connected by four bolts. The other part is a reaction frame, welded from an iron frame. The upper part of the reaction frame is flat, supporting the pressure sensor and hydraulic jack loading head, while the lower part supports the cylindrical test chamber. The lower part also has holes of the same diameter as the cylindrical test chamber, facilitating the fall of soil from the karst channels.

[0030] The second objective of this invention is to provide a test method for a test apparatus that simulates deep karst collapse induced by overloading in dense building complexes, comprising the following steps:

[0031] S1. Prepare model test boxes, karst channel mechanisms, and overburden soil samples respectively. The model test boxes are divided into two sets: a consolidation drainage model box and a formal loading model box.

[0032] S2. Debug the loading mechanism to pre-load and consolidate the soil sample in the consolidation and drainage model box. Calculate the pre-consolidation pressure of the soil sample based on the soil sampling depth, apply pressure in stages, and load the soil sample according to the load corresponding to each pressure level. The loading mechanism determines the specific loading value based on the intelligent display mechanism. Stabilize the load after loading to the target value, and then observe the consolidation settlement. If the settlement per hour is no more than 0.01 mm after the target pressure is reached, the soil sample is considered to be consolidated and restored to its original stress state.

[0033] S3. Debug the image acquisition mechanism and conduct formal tests. After consolidation is completed, remove the consolidation drainage model box and replace it with the formal loading model box. Apply load and conduct formal loading. Gradually apply load according to the target load value and record the critical load values ​​of cracking and failure of the lower karst channel. Further calculation can then be performed to obtain the critical building volume ratio value and the failure building volume ratio value. At the same time, the collapse failure mode of the upper overburden soil during karst collapse can also be obtained.

[0034] S4. Post-processing and analysis: By recording the failure state of the test soil in the model test chamber and the collapse failure mode of karst channels through the image acquisition mechanism, further analysis is conducted to reveal the mechanism of deep karst collapse induced by static overload in dense urban building clusters, and to determine the critical disaster-causing and failure conditions of deep urban karst collapse.

[0035] Furthermore, the test method includes the following steps:

[0036] S1. Design a cylindrical model test chamber;

[0037] S2. Construct karst passages;

[0038] S3. Based on the actual engineering background, determine the type of overburden soil, prepare soil samples according to the target moisture content, and then fill the test soil in layers into the model test box.

[0039] S4. Debug the loading equipment. First, place the circular loader on top of the model box, and make contact between the loading head and the circular loader, with the other end of the loading head in contact with the pressure sensor. Then, calculate the overburden pressure of the soil based on the actual soil sampling depth, and then consolidate and drain the soil sample until it is completely consolidated. Next, apply Vaseline to the inner wall of another set of plexiglass tubes, then open the two-part mold to change the sample, transferring the consolidated soil column into the plexiglass tube for the formal test.

[0040] S5. After the image acquisition equipment is debugged, conduct the formal test. First, close the pressure relief valve and continue pressurizing to allow the jacks to exert force. Determine the loaded value based on the readings of the intelligent display. Observe the changes in the lower karst channels and the upper overburden soil.

[0041] S6. Post-processing and analysis: The failure state of the test soil in the model box and the collapse failure mode of the karst channel, recorded by the image acquisition mechanism, can be further analyzed.

[0042] Furthermore, the test method includes the following steps:

[0043] S1. Preparation of the cylindrical model test chamber:

[0044] The model test chamber consists of two sets, both made of acrylic glass and are two-part molds with interlocking joints to reduce soil overflow during loading. One set is a consolidation and drainage model chamber for soil consolidation and drainage. Drainage holes are evenly distributed at 2cm intervals on the surface of the chamber, and geotextile is glued to the inner surface with strong adhesive to reduce contact between the soil sample and the acrylic glass and protect the integrity of the soil sample surface. The other set is a formal loading model chamber for formal soil loading tests. The surface of the chamber is intact and has no drainage holes.

[0045] S2. Preparation of karst channels:

[0046] Considering the weight of the overlying load, aluminum alloy is used as the bottom plate material of the model test box to simulate bedrock. The bottom plate is processed to approximate karst caves developed on the bedrock. The size, number and shape of the karst caves can be flexibly adjusted according to research needs.

[0047] S3. Preparation of overburden soil samples:

[0048] Based on the actual engineering background, the type of overburden soil was selected, and soil was taken from the site, dried, crushed, and sieved into soil powder. Soil samples with the same moisture content were prepared according to the site survey report of the taken soil. A certain mass of soil powder and water was weighed according to the target moisture content and mixed with a mixer. The surface of the mixed wet soil was covered with plastic wrap and left to stand for 24 hours to ensure uniform moisture content. Then, the mass and volume of the backfill were controlled, and the soil was filled in layers in a model test box with drainage holes. Each layer was vibrated evenly with a vibrator to continuously remove air bubbles. The surface of the filled model test box was wrapped with plastic wrap and left to stand for another 24 hours to ensure that the moisture content of the soil column was fully uniform.

[0049] S4. Adjust the loading equipment and perform preloading, consolidation, and drainage of the soil sample:

[0050] A circular loader is placed on top of the model test chamber, in direct contact with the soil. The diameter of the circular loader matches that of the cylindrical model test chamber. Further, the loading mechanism is adjusted, the pressure relief valve is closed, and continuous pressure is applied to generate hydraulic jack force. One end of the corresponding loading head extends and acts on the circular loader, while the other end contacts the pressure sensor. The other end of the pressure sensor is then placed against the reaction frame. Based on the soil sampling depth, the preconsolidation pressure of the soil sample is calculated according to the "Standard for Geotechnical Testing Methods" (GB / T). According to the provisions of 50123-2019, pressure is applied in stages. It should be noted that before applying pressure, stainless steel slip-on straps should be used to secure the model test box from top to bottom to prevent the model test box from expanding and soil samples from overflowing during loading. After calculating the preconsolidation pressure and the area of ​​the circular loader, the corresponding load at each pressure level can be obtained. Then, a jack is used to apply the load, and the specific load value is determined by the display instrument. When the target value is reached, the load is stabilized using a pressure holding valve. Then, a dial gauge is used to observe the consolidation settlement. The stabilization standard is specified as consolidation for 24 hours at each pressure level or a change in sample deformation of no more than 0.01 mm per hour. When the target pressure is reached, the settlement per hour is no more than 0.01 mm, which is considered as the soil sample consolidation is complete, that is, the soil sample returns to its original stress state.

[0051] S5. Debug the image acquisition mechanism and conduct the formal test:

[0052] After consolidation is complete, the model test chamber used for consolidation drainage is removed and replaced with the model test chamber for formal loading. Vaseline is first applied to the inner surface of the model test chamber to reduce friction between the sidewalls and the soil. Then, the soil column is placed in the model test chamber. Before the formal test, digital cameras and high-definition video cameras are positioned at the front, sides, and bottom of the model test chamber to capture changes in the overlying soil and underlying karst channels during the loading process from all angles. Simultaneously, supplementary lighting is used to illuminate the test soil to facilitate image capture. Regarding the application of load, the scale of the dense building complex should be considered first. The building volume ratio of a dense building complex is calculated, as different volume ratios can characterize the density of the building complex. Based on the actual engineering background, the dense building complex to be studied and its building volume ratio value are selected. Then, the additional stress on the foundation of individual building loads under different building volume ratios is calculated, converted into the load to be applied, and then formally loaded. The target load value is gradually applied, and the critical load values ​​for cracking and failure of the lower karst channels are recorded. Further conversion yields the critical building volume ratio value and the failure building volume ratio value. At the same time, the collapse failure mode of the upper overburden soil during karst collapse can also be obtained.

[0053] S6. Post-processing and analysis:

[0054] The damage state of the test soil inside the model box and the collapse failure mode of the karst channels, recorded by the image acquisition mechanism, can be further analyzed.

[0055] Compared with the prior art, the beneficial effects of the present invention are reflected in the following aspects:

[0056] 1) The present invention proposes an experimental method and apparatus for simulating deep karst collapse induced by overloading of dense building complexes. It can consider the influence of different overburden soils, karst channels, and different dense building complexes on deep karst collapse in cities. It provides certain technical support for studying deep karst collapse induced by static overloading of dense building complexes in cities. It can also effectively reveal the mechanism of deep karst collapse under static overloading of dense building complexes in cities, determine the critical disaster-causing and damage conditions of deep karst collapse in cities, and provide certain reference value for the treatment and prevention of deep karst collapse in cities.

[0057] 2) Previous considerations on factors influencing karst collapse mainly focused on internal factors (overburden soil properties, bedrock lithology, groundwater activity, etc.) and external factors (drainage, load and gravity, acid and alkali solution erosion, etc.). For cities rich in karst areas, a large number of dense building complexes have been built under human engineering construction activities. However, the impact of overloading of dense building complexes on karst collapse has rarely been considered. Therefore, the experimental method and experimental device in this paper can effectively reveal the disaster-causing conditions and damage modes of urban karst collapse induced by overloading of dense building complexes.

[0058] 3) This invention proposes a test method and apparatus for simulating deep karst collapse induced by overloading of dense building complexes. The test apparatus is simple in overall design, low in cost, and easy to change test sites. It allows for rapid and convenient testing. Furthermore, the size, shape, and number of karst channels in this test apparatus are adjustable, effectively avoiding the drawbacks of traditional apparatuses that can only consider a single influencing factor. Attached Figure Description

[0059] Figure 1 The front view of the overall model test device of the present invention, which simulates the deep karst collapse induced by overloading of dense building complexes.

[0060] Figure 2 This is a schematic diagram of the model test chamber and support mechanism of the present invention.

[0061] Figure 3 This is a schematic diagram of the circular loader of the present invention.

[0062] Figure 4 This is a schematic diagram of the loading head structure of the present invention.

[0063] Figure 5 This is a schematic diagram of the structure of the model test chamber with drainage holes (consolidated drainage model chamber) of the present invention.

[0064] Figure 6 This is a schematic diagram of the structure of the drain-hole-free model test chamber (formal loading model chamber) of the present invention.

[0065] Figure 7 This is a schematic diagram of the reaction frame of the present invention.

[0066] Figure 8 This is the junction of the two valve structures in the model test chamber, as described in an embodiment of the present invention.

[0067] Figure 9 for Figure 1 A schematic diagram of the structure of the upper cover plate of the model test chamber at point A.

[0068] Figure 10 for Figure 1 A schematic diagram of the structure of the first karst cave in the lower cover plate of the model test chamber at point B.

[0069] Figure 11 for Figure 1 A schematic diagram of the structure for opening a second karst cave in the lower cover plate of the model test chamber at point B.

[0070] Figure 12 for Figure 1 A schematic diagram of the structure for opening the third karst cave in the lower cover plate of the model test chamber at point B.

[0071] In the diagram: 1. Model test chamber; 2. Test soil; 3. Karst passage; 311. First karst cave; 312. Second karst cave; 313. Third karst cave; 4. Drainage hole; 5. Lower cover plate of the model test chamber; 6. Upper cover plate of the model test chamber; 7. Circular loader; 8. Loading head; 9. Hydraulic jack; 10. Pressure holding valve; 11. Pressure sensor; 12. Intelligent display instrument; 13. Reaction frame; 14. Image acquisition device; 15. Nut; 16. Screw; 17. Upper plate of the reaction frame; 18. Lower plate of the reaction frame; 19. Lower karst cave outlet. Detailed Implementation

[0072] The present invention will now be described in detail with reference to specific embodiments, but this is by no means a limitation thereof. Any preparation methods, materials, structures, or compositional ratios not explicitly described in this technical solution are considered common technical features disclosed in the prior art.

[0073] This technical solution provides an experimental device for simulating deep karst collapse induced by overloading of dense building complexes. The device includes: a model test chamber for holding the test soil; a karst channel mechanism with karst channels of varying sizes; a loading mechanism for simulating the application of loads and soil consolidation in dense urban building complexes; an intelligent display mechanism for displaying the loading values; an image acquisition mechanism for observing changes in the overlying soil layer and underlying karst channels during loading; a data analysis mechanism for analyzing the failure modes of karst collapse; a karst collapse soil collection mechanism for collecting collapsed soil; and a support mechanism for providing reaction forces to balance the applied load. This technical solution can provide technical support for studying deep karst collapse induced by static overloading of dense urban building complexes, effectively revealing the mechanism of deep karst collapse under static overloading of dense urban building complexes, determining the critical disaster-causing and failure conditions of deep urban karst collapse, and providing valuable reference for the treatment and prevention of deep urban karst collapse.

[0074] In the accompanying drawings, components with the same structure are indicated by the same numerical designation, and components with similar structures or functions are indicated by similar numerical designations. The dimensions and thicknesses of each component shown in the drawings are arbitrary, and the present invention does not limit the dimensions and thicknesses of each component. To make the illustrations clearer and show the mating relationships between the components, some parts in the drawings have been appropriately scaled down, and the distances between the components have been increased or decreased.

[0075] In the description of the embodiments of this application, it should be understood that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly placed when the product of this application is used, or the orientation or positional relationship commonly understood by those skilled in the art. They are only for the convenience of describing this application and simplifying the description, and are not intended to indicate or imply that the device or component referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0076] In the description of the embodiments of this application, it should also be noted that, unless otherwise expressly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0077] Example 1

[0078] This embodiment provides an experimental method for simulating deep karst collapse induced by overloading in dense building complexes, including:

[0079] S1. Design a cylindrical model test chamber 1;

[0080] S2. Construct karst passages 3 according to research needs;

[0081] S3. Based on the actual engineering background, the type of overburden soil was determined. Here, the fifth layer of clay in Xuzhou City is taken as an example. The soil sample was taken from Qiaoshang Village, Xuzhou Metro Line 4, Jiangsu Province. The karst in this area mainly manifests as fissures, pores, and caves, with some beaded caves found locally. The caves are mostly elliptical or circular in shape, belonging to shallow overburden karst, which is relatively well-developed. The karst is mainly unfilled and semi-filled. The filling material of the filled caves is mainly hard to plastic brownish-yellow clay. The soil sampled in this test is brownish-yellow clay. After obtaining the sample from the site, the soil was disturbed, so the mud method was used to prepare the reshaped sample. Then, the soil sample was prepared according to the target moisture content, and after saturation, it was filled into the model test chamber 1 in layers.

[0082] S4. Debug the loading mechanism. First, place the circular loader 7 on the upper part of the model test chamber 1, in direct contact with the soil. Then, place the loading head 8 in contact with the circular loader 7, and the other end of the loading head 8 in contact with the pressure sensor 11, together pressing against the upper plate 17 of the reaction frame. Then, calculate the overburden pressure of the soil based on the actual soil sampling depth, and then consolidate and drain the soil sample until it is completely consolidated. Then, apply Vaseline to the inner wall of another set of plexiglass cylinders, open the consolidated model test chamber 1 (consolidated drainage model chamber) to change the sample, and transfer the consolidated soil column to the glass cylinder model test chamber 1 (formal loading model chamber) for the formal test.

[0083] S5. After the image acquisition mechanism is debugged, conduct the formal test. First, close the pressure relief valve and continue pressurizing to make the hydraulic jack 9 output force. Determine the loaded value based on the reading of the intelligent display instrument 12. Observe and record the changes in the lower karst channel 3 and the changes in the upper overburden soil.

[0084] S6. Post-processing and analysis: The failure state of the test soil in the model box and the collapse failure mode of the karst channel, recorded by the image acquisition mechanism 14, can be further analyzed.

[0085] This invention also provides an experimental apparatus based on the above-described experimental method for simulating deep karst collapse induced by overloading in dense building complexes, such as... Figures 1-12 As shown, it includes:

[0086] like Figure 1-12As shown, the model test chamber 1 is made of plexiglass, cylindrical in shape, and without top or bottom covers. It has a two-part structure, with the two parts interlocking. Model test chamber 1 consists of two sets: one set is used for soil drainage consolidation, with drainage holes 4 evenly distributed at 2cm intervals on its surface. The inner surface of the chamber is covered with geotextile glued with strong adhesive to reduce contact between the soil sample and the plexiglass, protecting the integrity of the soil sample surface; the other set is used for the formal loading test of the soil, with an intact surface and no drainage holes. The entire model test chamber is secured by aluminum alloy top and bottom covers, nuts 15, and screws 16. Model test chamber 1 is used to hold the test soil 2.

[0087] The test soil 2 is located in the cylindrical model test chamber 1. Depending on the actual engineering background, clay (i.e., the cover layer is cohesive soil layer, barrier type cover layer), sand (i.e., the cover layer is sandy soil layer, permeable type cover layer), clay above sand (i.e., the upper cover layer is cohesive soil layer, the lower cover layer is sandy soil layer, barrier type cover layer), or sand above clay (i.e., the upper cover layer is sandy soil layer, the lower cover layer is cohesive soil layer, permeable type cover layer) can be selected as the karst upper cover soil layer.

[0088] Located at the bottom of the cylindrical model test chamber 1 is an aluminum alloy plate of uniform diameter, used to simulate bedrock. Karst channels 3 with different aperture sizes are machined into the circular plate to simulate karst channels of varying sizes. These channels are placed at the bottom of the model test chamber 1, in contact with the test soil 2. Depending on research needs, different sizes and shapes of karst caves can be designed, such as the first cave 311, the second cave 312, and the third cave 313. The difference between the first cave 311, the second cave 312, and the third cave 313 lies in the number and size of the caves, used to simulate karst caves.

[0089] The loading mechanism includes a circular loader 7, a loading head 8, and a hydraulic jack 9. A separate hydraulic jack and its matching loading head are used for loading. Closing the pressure relief valve and continuously pressurizing allows the jack to exert force, causing the corresponding loading head 8 to extend and act on the circular loader 7, loading according to the target value. Once a certain value is reached, closing the pressure holding valve 10 stops the flow of oil in the hydraulic jack, maintaining the stability of that loading value and allowing for observation of experimental phenomena.

[0090] The intelligent display mechanism includes a pressure sensor 11 and an intelligent display 12. One side of the pressure sensor 11 is placed at the loading head 8, and the other side is connected to the intelligent display 12 and in contact with the reaction frame 13 to display the magnitude change of the value during the loading process.

[0091] The image acquisition mechanism includes an image acquisition device 14, specifically including an industrial camera arranged on the side, a digital camera and a high-definition video camera arranged on the front and bottom, which captures the changes of the overlying soil and the underlying karst channels during the loading process from all directions and multiple angles.

[0092] Data analysis agencies utilize a range of graphics processing and data analysis software to analyze the destructive patterns of karst collapses.

[0093] A karst collapse soil collection device is used to collect soil from karst collapses induced by static overload in dense urban building complexes.

[0094] The support mechanism consists of two parts. One part is a fixed model test chamber 1. The upper part of the chamber is fixed with a hollow aluminum alloy cover plate, the diameter of which is the same as the diameter of the model test chamber 1, to facilitate direct contact between the circular loader 7 and the soil. The lower part of the chamber uses a solid aluminum alloy cover plate as support, which is used during the soil consolidation process. In the formal test, it can be replaced with a base plate with karst channels 3. The upper and lower cover plates are connected by four screws 16. The other part is a reaction frame 13, which provides reaction force to the hydraulic jack 9. The upper plate 17 of the reaction frame is flat, and the lower plate 18 of the reaction frame has a circular hole, which is the outlet 19 of the lower karst cave. Its diameter is the same as the diameter of the model test chamber 1. The upper and lower parts of the reaction frame 13 are connected by screws 16, and the junction of the upper plate 17 and the screws 16 is fixed by two nuts 15.

[0095] Example 2

[0096] This embodiment provides an experimental device for simulating deep karst collapse induced by overload in a dense building complex, comprising: a model test chamber 1 for placing test soil 2; a karst channel mechanism located at the bottom of the model test chamber 1 for providing karst channels 3 of different sizes, shapes, and numbers; a loading mechanism located at the top of the model test chamber 1 for applying loads from the dense urban building complex; an intelligent display mechanism connected to the loading mechanism for displaying the magnitude of the loading values; an image acquisition mechanism 14 located on the side of the model test chamber 1 for observing changes in the overlying soil layer and the underlying karst channels 3 during the loading process; a data analysis mechanism connected to the image acquisition mechanism 14 for analyzing the failure modes of karst collapse; a karst collapse soil collection mechanism located below the karst channel mechanism for collecting soil from the static overload-induced karst collapse in the dense urban building complex; and a support mechanism including a model test chamber fixing component connected to the model test chamber 1 and a reaction frame component connected to the loading mechanism. The model test chamber fixing component is used to fix the model test chamber 1, and the reaction frame component is used as a reaction frame 13 to support the application of the entire load.

[0097] The model test chamber 1 is cylindrical in shape, with a two-lobed structure. The two lobes interlock at the junction and have no top or bottom cover.

[0098] The karst channel mechanism includes a karst channel base plate; the karst channel base plate is located at the bottom of the model test chamber 1; the karst channel base plate has the same diameter as the model test chamber 1; the karst channel base plate is provided with karst channels 3 of different aperture sizes; the karst channels 3 are in contact with the test soil 2.

[0099] The loading mechanism includes a hydraulic jack 9 and a circular loader 7; the hydraulic jack 9 includes a hydraulic jack 9 and a loading head 8; a separate hydraulic jack 9 and a matching loading head 8 are used for loading; the hydraulic jack 9 is connected to the loading head 8; the hydraulic jack 9 outputs force, and the loading head 8 can extend to act on the circular loader 7; the hydraulic jack 9 is connected to a pressure holding valve 10; the pressure holding valve 10 is used to control the oil in the hydraulic jack 9.

[0100] The intelligent display mechanism includes a pressure sensor 11 and an intelligent display 12; the pressure sensor 11 and the intelligent display 12 are connected by a data cable; one side of the pressure sensor 11 is located on the top of the loading head 8, and the other side is connected to the intelligent display 12.

[0101] The image acquisition mechanism 14 includes an industrial camera arranged on the side, a digital camera and a high-definition video camera arranged on the front and bottom, to capture the changes of the overlying soil and the underlying karst channel 3 during the loading process from all directions and multiple angles.

[0102] Data analysis agencies include a range of graphics processing and data analysis software used to analyze the destructive forms of karst collapses.

[0103] The karst collapse soil collection device includes plastic basins for collecting soil from deep karst collapses induced by static overload in dense building complexes.

[0104] The model test chamber fixing assembly includes an upper cover plate 6 and a lower cover plate 5. The upper cover plate 6 is a hollow aluminum alloy cover plate with the same diameter as the model test chamber 1, which facilitates direct contact between the circular loader 7 and the soil. The lower cover plate 5 is a solid aluminum alloy cover plate used as a support during the soil consolidation process. During the formal test, it can be replaced with a bottom plate with karst channels 3. The upper cover plate 6 and the lower cover plate 5 are connected by four screws 16.

[0105] The reaction frame assembly includes a reaction frame 13; the reaction frame 13 includes an upper reaction frame plate 17, a lower reaction frame plate 18, a screw 16, and a nut 15; the upper reaction frame plate 17 has a flat surface; the lower reaction frame plate 18 is provided with a lower cave outlet 19, which is a circular hole with the same diameter as the model test chamber 1; the upper reaction frame plate 17 and the lower reaction frame plate 18 are connected by a screw 16, and two nuts 15 are used to fix the junction of the upper reaction frame plate 17 and the screw 16 from top to bottom.

[0106] The test method for the above-mentioned test apparatus includes the following steps:

[0107] S1. Preparation of the cylindrical model test chamber:

[0108] The model test chamber 1 consists of two sets, both made of plexiglass and are two-part molds with interlocking joints at the junction to reduce soil overflow during loading. One set of model test chamber 1 is a consolidation and drainage model chamber for soil drainage and consolidation. Drainage holes 4 are evenly distributed at 2cm intervals on the surface of the test chamber. The inner surface of the chamber is covered with geotextile with strong adhesive to reduce contact between the soil sample and the plexiglass and protect the integrity of the soil sample surface. The other set of model test chamber 1 is a formal loading model chamber for formal soil loading tests. The surface of the test chamber is intact and there are no drainage holes 4.

[0109] S2. Preparation of karst channels:

[0110] Considering the weight of the overlying load, aluminum alloy is used as the base plate material of the model test box 1 to simulate bedrock. The base plate is processed to approximate karst caves developed on the bedrock. The size, number and shape of the karst caves can be flexibly adjusted according to research needs.

[0111] S3. Preparation of overburden soil samples:

[0112] Based on the actual engineering background, the type of overburden soil was selected, and soil was taken from the site, dried, crushed, and sieved into soil powder. Soil samples with the same moisture content were prepared according to the site survey report of the taken soil. A certain mass of soil powder and water was weighed according to the target moisture content and mixed with a mixer. The surface of the mixed wet soil was covered with plastic wrap and left for 24 hours to ensure uniform moisture content. Then, the mass and volume of the backfill were controlled, and the soil was filled in layers in the model test box 1 with drainage holes 4. Each layer was vibrated evenly with a vibrator to continuously remove air bubbles. The surface of the filled model test box 1 was wrapped with plastic wrap and left to stand for another 24 hours to ensure that the moisture content of the soil column was fully uniform.

[0113] S4. Adjust the loading equipment and perform preloading, consolidation, and drainage of the soil sample:

[0114] The circular loader 7 is placed on top of the model test chamber 1, in direct contact with the soil. The diameter of the circular loader 7 is the same as that of the cylindrical model test chamber 1. Further, the loading mechanism is adjusted, the pressure relief valve is closed, and continuous pressure is applied to generate force from the hydraulic jack 9. Then, one end of the corresponding loading head 8 extends and acts on the circular loader 7, while the other end contacts the pressure sensor 11. The other end of the pressure sensor 11 is then placed against the reaction frame 13. Based on the soil sampling depth, the preconsolidation pressure of the soil sample is calculated according to the "Standard for Geotechnical Testing Methods" (GB / T). According to the provisions of 50123-2019, pressure is applied in stages. It should be noted that before applying pressure, stainless steel slip-on straps should be used to secure the model test box 1 at the top, middle and bottom to prevent the model test box 1 from expanding and soil samples from overflowing during loading. After calculating the pre-consolidation pressure and the area of ​​the circular loader 7, the corresponding load under each pressure level can be obtained. Then, the load is applied using a jack, and the specific load value is determined by the display instrument. When the target value is reached, the load is stabilized using the pressure holding valve 10. Then, the consolidation settlement is observed using a dial gauge. The stabilization standard is specified as consolidation for 24 hours under each pressure level or the change in sample deformation per hour not exceeding 0.01 mm. When the target pressure is reached, the settlement per hour is not greater than 0.01 mm, which is considered as the soil sample consolidation is complete, that is, the soil sample returns to its original stress state.

[0115] S5. Debug the image acquisition mechanism and conduct the formal test:

[0116] After consolidation is complete, remove the model test chamber 1 used for consolidation drainage and replace it with the model test chamber 1 for formal loading. First, apply Vaseline to the inner surface of the model test chamber 1 to reduce friction between the sidewalls and the soil. Then, place the soil column in the model test chamber 1. Before the formal test, place digital cameras and high-definition video cameras in front, to the sides, and at the bottom of the model test chamber 1 to capture changes in the overlying soil and the underlying karst channels 3 during the loading process from all angles. Simultaneously, use supplementary lighting to illuminate the test soil 2 to facilitate image capture. Regarding the application of load, it should first be based on the characteristics of the dense building complex. The scale is calculated by determining the building volume ratio of dense building clusters. Different volume ratios can characterize the density of building clusters. Based on the actual engineering background, the dense building clusters to be studied and their building volume ratio values ​​are selected. Then, the additional stress on the foundation of individual building loads under different building volume ratios is calculated. After converting it into the load to be applied, formal loading is carried out. The target load value is gradually applied, and the critical load values ​​for cracking and failure of the lower karst channel 3 are recorded. Further conversion yields the critical building volume ratio value and the failure building volume ratio value. At the same time, the collapse failure mode of the upper overburden soil during karst collapse can also be obtained.

[0117] S6. Post-processing and analysis:

[0118] The damage state of the test soil inside the model box and the collapse failure mode of the karst channels, recorded by the image acquisition mechanism, can be further analyzed.

[0119] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. An experimental device for simulating deep karst collapse induced by overloading in dense building complexes, characterized in that, include: Model test chamber (1), used to place test soil (2); The karst channel mechanism is set at the bottom of the model test box (1) to provide karst channels (3) of different sizes, shapes and quantities. The loading mechanism is located on the upper part of the model test box (1) and is used for the application of loads on dense urban buildings and soil consolidation. An intelligent display mechanism, connected to the loading mechanism, is used to display the magnitude of the loaded value; The image acquisition mechanism (14) is located on the side of the model test box (1) and is used to observe the changes in the overlying soil and the underlying karst channel (3) during the loading process; A data analysis unit, connected to an image acquisition unit (14), is used to analyze the damage patterns of karst collapse; The support mechanism includes a model test box fixing assembly connected to the model test box (1) and a reaction frame assembly connected to the loading mechanism. The model test box fixing assembly is used to fix the model test box (1), and the reaction frame assembly is used as a reaction frame (13) to support the application of the entire load. The model test box (1) is cylindrical in shape, with a two-lobed mold structure. The two lobes interlock at the junction and have no top or bottom cover. The karst passage mechanism includes a karst passage base plate; The karst channel bottom plate is set at the bottom of the model test box (1); The bottom plate of the karst channel has the same diameter as the model test box (1); The bottom plate of the karst channel is provided with karst channels of different aperture sizes (3). The karst channel (3) is in contact with the test soil (2); The loading mechanism includes a hydraulic jack (9) loading mechanism and a circular loader (7); The hydraulic jack (9) loading mechanism includes a hydraulic jack (9) and a loading head (8); The hydraulic jack (9) is connected to the loading head (8); The hydraulic jack (9) outputs force, and the loading head (8) can extend to act on the circular loader (7). The hydraulic jack (9) is connected to a pressure holding valve (10); the pressure holding valve (10) is used to control the oil in the hydraulic jack (9).

2. The experimental apparatus for simulating deep karst collapse induced by overloading of dense building complexes according to claim 1, characterized in that, The data analysis unit includes a series of graphics processing software and data analysis software, used to analyze the damage patterns of karst collapse.

3. The experimental apparatus for simulating deep karst collapse induced by overloading of dense building complexes according to claim 1, characterized in that, The test apparatus also includes a karst collapse soil collection mechanism, which is located below the karst channel mechanism and is used to collect soil from karst collapse induced by static overload in dense urban building complexes.

4. The experimental apparatus for simulating deep karst collapse induced by overloading of dense building complexes according to claim 1, characterized in that, The model test chamber fixing assembly includes an upper cover plate (6) and a lower cover plate (5) of the model test chamber. The upper cover plate (6) of the model test box is made of aluminum alloy with a hollow center. Its diameter is the same as that of the model test box (1), which makes it easy for the circular loader (7) to come into direct contact with the soil. The lower cover plate (5) of the model test box is made of solid aluminum alloy as a support and is used in the soil consolidation process. In the formal test process, it can be replaced with a bottom plate with karst channels (3). The upper cover plate (6) and the lower cover plate (5) of the model test chamber are connected by four screws (16).

5. The experimental apparatus for simulating deep karst collapse induced by overloading of dense building complexes according to claim 1, characterized in that, The reaction frame assembly includes a reaction frame (13). The reaction frame (13) includes an upper plate (17), a lower plate (18), a screw (16), and a nut (15). The surface of the upper plate (17) of the reaction frame is flat; The lower plate (18) of the reaction frame is provided with a lower cave outlet (19), which is a circular hole with the same diameter as the model test box (1). The upper plate (17) and lower plate (18) of the reaction frame are connected by screws (16), and the junction of the upper plate (17) and the screws (16) is fixed by two nuts (15) respectively.

6. A test method using the experimental apparatus for simulating overload-induced deep karst collapse in dense building complexes as described in any one of claims 1-5, characterized in that, Includes the following steps: S1. Prepare model test box (1), prepare karst channel mechanism and prepare overburden soil sample respectively. The model test box (1) is divided into 2 sets, namely the consolidation drainage model box and the formal loading model box. S2. Adjust the loading mechanism to preload and consolidate the soil sample in the consolidated drainage model box for drainage. S3. Debug the image acquisition mechanism (14) and conduct a formal test; S4. Post-processing and analysis: Further analysis is conducted on the damage state of the test soil (2) in the model test box (1) and the collapse failure mode of the karst channel (3) recorded by the image acquisition mechanism (14).

7. The experimental method for simulating deep karst collapse induced by overloading of dense building complexes according to claim 6, characterized in that, The specific process for preparing the overburden soil sample in step S1 is as follows: Choose the type of cover soil, then take soil from the site, and dry, crush and sieve it into soil powder; Prepare soil samples with the same moisture content according to the on-site survey report of the land to be taken; then weigh soil powder and water according to the target moisture content and mix them with a mixer. Cover the surface of the mixed wet soil with plastic wrap and let it sit to make the moisture in the soil uniform. Control the quality and volume of the backfill, fill in layers in the model test box (1) with drainage holes (4), and use a vibrator to vibrate evenly in layers to continuously remove air bubbles from the soil. Wrap the surface of the filled model test box (1) with plastic wrap and let it stand to ensure that the water content of the soil column is fully uniform.

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