Device for loading test of pile foundation crossing karst cave and preparation method thereof

Abstract

The application discloses a device for carrying out a loading test on a pile foundation crossing a karst cave and a preparation method thereof, and has the advantages that the cave roof rock mass and the pile bearing rock mass are mutually buckled and are completely wrapped by the pile bearing platform rock mass, and a completely closed karst cave structure is simulated; the pile bearing rock mass, the cave roof rock mass, the post-cast solid pile layer and the pile bearing platform rock mass constituting the rock mass model are all made of the same rock stratum similar material, the integrity is better, the mechanical properties of the material of the contour of the karst cave are consistent; the pile bearing platform rock mass completely wraps the whole pile bearing rock mass from all directions downwards, the shear resistance of the top surface of the pile bearing rock mass is good, the integrity of the rock mass model is further improved, and the adverse influence of the secondary pouring is reduced; in conclusion, the pile foundation in the strong karst development area is more truly simulated, the reduction degree is high, the parameters measured after loading various loads are more accurate, the indoor model test research on the karst cave type pile foundation is more rigorous, and the design and construction of the pile foundation in the karst area can be better guided.

Description

Technical Field

[0001] This invention relates to the field of pile foundation bearing mechanics model testing, and in particular to a device for conducting loading tests on pile foundations passing through karst caves and a method for preparing the device. Background Technology

[0002] To study the mechanical properties of pile foundations, technicians often use indoor simulation methods. PVC pipes, proportionally scaled-down concrete columns, and aluminum alloy pipes are used as model piles to simulate various pile types, such as PC / PHC pipe piles, bored piles, and steel pipe piles. Stress plates are installed at different depths on the model piles. Soil-like materials are constructed using a mixture of quartz sand, talc powder, and bentonite to simulate soil layers, while rock-like materials are constructed using a mixture of quartz sand, barite powder, gypsum, cement, and water in specific proportions to simulate rock layers. The rock-like materials are then poured, and the lower section of the model pile is pre-embedded within them to form… A rock mass model with model piles is then hoisted into a model box using a crane. A soil-like material is then applied to the rock mass model inside the model box to create a complete model of the pile, soil, and rock layers. Various loads are applied to the model piles, and parameters such as the vertical and horizontal displacements of the model piles under different load modes, as well as the stress and strain values ​​at different depths of the piles, are measured to comprehensively analyze the working mechanism and stress performance of the pile foundation. This provides a basis for the subsequent design and application of pile foundations and actual construction.

[0003] When constructing pile foundations in areas with highly developed karst topography, hollow karst caves are often encountered within the rock strata. If the bearing capacity of the rock strata above the cave is sufficient, construction proceeds normally. However, if the cave roof is insufficient to bear the pile foundation load, the pile foundation must penetrate the cave, using the stable rock strata below as the bearing layer. Because this type of pile foundation penetrates karst caves, its bearing form and failure mode are more complex than those where the entire pile body is supported by ordinary rock strata. Therefore, a model of a pile foundation penetrating karst caves is constructed, and indoor loading simulation tests are conducted on this model. Various loads are applied, and stress-strain data at different heights under various loads are collected. This allows for the establishment of a mathematical model and corresponding research, clarifying the bearing mechanism of pile foundations penetrating karst caves. This clarifies the design and construction of pile foundations in areas with highly developed karst topography, thus possessing significant engineering and economic value.

[0004] In existing technologies, researchers have tried various methods to simulate pile foundations passing through karst caves for loading tests, but the results have not been ideal.

[0005] One type of indoor model simulates a karst cave using a tunnel-like design. For example, the Chinese utility model patent CN214883927U, "Indoor Model Test Device for Simulating the Stress and Deformation of Foundation Piles in Karst Caves," first erects four side plates and a base plate. A rectangular mold core extending laterally is fixed between the front and rear side plates. Then, concrete (a material similar to rock strata) is poured into the space between the four side plates and the base plate. After hardening, the front and rear side plates are removed, and the transverse mold core is extracted, thus forming a simulated karst cave with open ends. However, this karst cave is essentially a tunnel running from front to back, not a real karst cave. This model differs greatly from the mechanical properties, load distribution, and failure modes of a completely enclosed karst cave in a real karst development area. Its simulation accuracy and reproduction are low, and the data obtained has low reference value, making it difficult to accurately guide the design and construction of pile foundations in karst development areas.

[0006] Another type of indoor model simulates a karst cave using a box-shaped structure. This indoor model includes a hollow wooden box, model piles that penetrate and are fixed to the wooden box, and a rock mass model cast from a material similar to the rock strata surrounding the wooden box. The idea is to use a hollow wooden box to construct a hollow karst cave, insert and fix the model piles to the wooden box, and then cast a rock mass model from the outside. However, the wooden box in the above-mentioned indoor model is not removed after casting and remains inside the rock mass model. Therefore, it can be understood that the interface of the karst cave in this indoor model has a layer of wood, which is quite different from a completely hollow karst cave in reality. Objectively speaking, the structure of the pile foundation sealed with the wooden box essentially constructs an irregularly shaped pile with a hollow wooden mold. Its mechanical properties, load distribution, and specific structure are inconsistent with a completely hollow karst cave in the rock strata. The degree of reproduction is low, the data obtained is weak for reference, and it is far from the real situation. Similarly, it is difficult to guide the practical application of pile foundation design and construction in areas with strong karst development.

[0007] Another type of indoor model simulates a cave using a flow-through method. This indoor model includes a rock mass model cast from materials similar to rock strata, and a cave formed inside by the flow of phase change materials. For example, Chinese invention patent application number CN202011358359.8 uses magnetorheological materials as phase change materials. When electricity is applied, a magnetic field is applied to make it solid, and when the electricity is cut off, it becomes liquid and flows out, thus forming a hollow cave inside the rock mass model. Of course, there is a more common method, such as pre-embedding ice blocks as phase change materials when casting the rock mass model. After the rock mass model hardens, the ice blocks melt into water and flow out, thus forming a hollow cave. All of the above methods suffer from the same major flaw: how to drain the liquid phase change material after the rock model hardens and the cave is formed. Generally, holes are left to drain water or magnetorheological fluid. However, regardless of the hole size, there are problems. If the hole for draining the phase change material is too small, water or magnetorheological fluid will have difficulty draining, inevitably leaving a considerable amount of phase change material adhering to the cave wall, which is difficult to remove. This disrupts the uniformity and integrity of the surrounding materials, resulting in inconsistencies in the density, strength, viscosity, and other mechanical properties between the surrounding layer and similar rock strata, similar to the situation with the wooden box mentioned above, reducing the accuracy of the reconstruction. However, if the hole size for draining the phase change material is increased, it becomes the tunnel-shaped cave situation described earlier. Even if a cylinder is used to plug the drain hole later, the cylinder and the ordinary rock model are completely independent and unconnected entities, not a unified structure. Their mechanical properties, load distribution, and failure modes differ greatly from reality, resulting in low accuracy and reference value, urgently requiring improvement.

[0008] Furthermore, after preparing the rock mass model of the pile foundation with the karst cave, it needs to be hoisted into a model box that is one person tall, and a soil-like material is covered on the rock mass model inside the box to establish a complete model of the pile, soil, and rock layers, so that various loads can be applied to it. After the test is completed, the soil in the model box needs to be dug out, and then the rock mass model needs to be hoisted out. The rock mass model is very thick and heavy, and a special crane is required to hoist it, so the operation is cumbersome and laborious. Summary of the Invention

[0009] One of the technical problems to be solved by the present invention is to provide a device for loading tests on pile foundations that pass through karst caves. The karst cave structure simulated inside the rock mass model of the device is completely hollow, which is closer to the real situation and can more accurately simulate the rock mass conditions in areas with strong karst development, so as to better carry out indoor model test research on pile foundations that pass through karst caves.

[0010] One technical solution of the present invention is: a device for conducting loading tests on pile foundations passing through karst caves, comprising mutually fixed model piles and a rock mass model, wherein the rock mass model has a simulated karst cave inside, and the model pile passes through the simulated karst cave; the rock mass model is covered by a soil-like material; the rock mass model includes a pile-bearing rock mass made of a rock-like material to support the model pile, a cave roof rock mass made of a rock-like material, and a foundation rock mass cast from a rock-like material; the pile-bearing rock mass has a karst cave cavity in the middle, the upper part of the karst cave cavity has an opening, and the bottom surface of the karst cave cavity has a pile-embedding hole; The bottom of the convex rock mass at the top of the cave fits into the opening of the cave cavity. A pile hole is provided in the middle of the rock mass at the top of the cave. The model pile passes through the pile hole, and the lower section of the model pile is inserted into the pile hole. A layer of post-cast solid pile layer made of a rock-like material is poured on the bottom surface of the cave cavity to bond the lower section of the model pile to the wall of the pile hole. The post-cast solid pile layer, the side wall of the cave cavity, and the bottom surface of the rock mass at the top of the cave together construct the simulated cave. The cross-section and height of the foundation rock mass are greater than the cross-section and height of the pile bearing rock mass. The foundation rock mass wraps around the middle section of the model pile, the top surface of the cave ceiling rock mass, and the pile bearing rock mass.

[0011] Another technical problem to be solved by the present invention is to provide a method for preparing the above-mentioned device for loading tests on pile foundations passing through karst caves. The method is simple to construct and the prepared rock mass model has a completely hollow internal karst cave structure, which is closer to the real situation and can more accurately simulate the geological conditions of karst strongly developed areas, so as to better carry out indoor model test research on pile foundations passing through karst caves.

[0012] Another technical solution of the present invention is: a method for preparing a device for loading tests on pile foundations passing through karst caves, specifically including the following steps:

[0013] S1. Prepare model piles, as well as pile-bearing rock masses and tunnel roof rock masses molded from materials similar to rock strata;

[0014] S2. Insert the bottom end of the model pile into the pile hole of the bearing rock mass. Pour a layer of rock-like material on the bottom surface of the karst cavity and the periphery of the model pile. Some of the rock-like material flows into the gap between the model pile and the wall of the pile hole. When the rock-like material solidifies to form a post-cast pile layer, fix the lower section of the model pile to the wall of the pile hole through the post-cast pile layer.

[0015] S3. Place the rock mass at the top of the cave onto the model pile, and make the bottom of the convex rock mass at the top of the cave match the opening of the cave cavity;

[0016] S4. Place the model pile, the interlocking tunnel roof rock mass, and the pile bearing rock mass into a square mold. The cross-sectional area of ​​the square mold is larger than that of the pile bearing rock mass. Pour a rock stratum-like material into the square mold, making the pouring height higher than that of the tunnel roof rock mass, thereby forming a pile cap rock mass that surrounds the middle section of the model pile, the tunnel roof rock mass, and the top and sides of the pile bearing rock mass. Demold after the pile cap rock mass has solidified.

[0017] Compared with the prior art, the advantages of the device and preparation method for performing loading tests on pile foundations passing through karst caves in this invention are as follows.

[0018] The cave roof rock mass and the pile-bearing rock mass interlock and are completely encased by the secondary casting of the foundation rock mass, thus simulating a completely sealed karst cave structure. Furthermore, the pile-bearing rock mass, cave roof rock mass, foundation rock mass, and the post-cast reinforced pile layer on the bottom surface of the karst cave cavity, all constituting the rock mass model, are made of the same rock stratum-like material. There is no use of existing wooden boards or residual phase change material corrosion, so the material around the karst cave has consistent density, strength, viscosity, and other mechanical properties, resulting in better connection and overall integrity. The lower section of the pile is bonded to the pile hole a second time through the post-cast reinforced pile layer grout, while the middle section is tightly encased by the secondary casting of the foundation rock mass. Therefore, the connection and anchoring between the middle and lower sections of the pile and the rock stratum-like material is firm, more closely resembling the actual load-bearing conditions of the pile penetrating the karst cave and entering the rock. The post-cast foundation rock mass extends downwards from all sides... The entire rock mass supporting the pile is completely enclosed, resulting in good shear resistance at the interface between the two, i.e., the top surface of the rock mass supporting the pile. This further improves the integrity of the rock mass model and reduces the adverse effects of secondary casting. In summary, because this application more realistically simulates the situation of pile foundations in areas with strong karst development, it truly achieves a situation where the karst cave is completely empty, without the wooden boards, phase change materials, etc. of existing technologies. The surrounding rock strata are all similar materials of the same and uniform type. Its mechanical properties, load distribution, and specific structure are closer to the actual situation after the pile foundation construction in areas with strong karst development. The simulation and reproduction are high. Therefore, the parameters measured by this model after loading various loads are more accurate, which enables more rigorous indoor model test research on pile foundations that traverse karst caves and better guides the design and construction of pile foundations in karst areas.

[0019] Preferably, the upper opening of the cave cavity has a gradually tapering lower conical surface, and the lower edge of the cave roof rock mass has a gradually tapering upper conical surface. The upper conical surface rests on the lower conical surface, and the gap between the two conical surfaces forms a conical annular joint. Furthermore, the lower end of the upper conical surface has a ring of eaves to seal the lower opening of the conical annular joint. In this way, when pouring the foundation rock mass, some grout will flow into the conical annular joint. Due to the obstruction of the convex eaves of the upper conical surface, this grout can be prevented from flowing into the simulated cave. Moreover, the upper load of the cave roof rock mass will support the upper conical surface of the cave roof rock mass and the lower conical surface of the cave cavity. Dynamic compaction is used to compress the grout flowing into the gap between the two conical surfaces, thereby forming a whole, or as close as possible to a whole, between the rock mass at the top of the tunnel and the rock mass supporting the pile under the action of the grout and the upper load pressure. This compensates for the shortcomings, because the two components at the conical ring joint abut against each other, unlike other parts that are connected by secondary casting when in contact with the pile cap rock mass, so the strength and connection are relatively weak. Therefore, the upper pressure is used to compress the flowing grout and seal the upper opening of the karst cave, simulating the actual situation of the pile passing through the karst cave as much as possible.

[0020] As an enhancement, the device also includes a model box comprising a rectangular frame with four side walls and openings at the top and bottom, on which a loading device is mounted; the rectangular frame rests on the top surface of the pier rock mass; the rectangular frame is filled with a soil-like material, and most of the pile segments of the model piles extending from the top surface of the rock mass model are embedded in the soil-like material while the top of the model piles extends beyond the top of the soil-like material.

[0021] As a matching process, the preparation method also includes: S5. placing the rectangular frame of the model box on the top surface of the foundation rock mass, filling the rectangular frame with a soil-like material to bury the upper section of the model pile, and making the top of the model pile protrude, and installing a loading device on the rectangular frame.

[0022] The advantages of the aforementioned gain structure and method are as follows: It creatively proposes using a widened rock mass model as the base for the rectangular frame of the model box, and after removing the bottom plate and halving the height of the model box, it is placed on top of the rock mass model and covered with soil. This eliminates the need to transport the rock mass model into a one-person-high model box as in existing technologies, simplifying operation and eliminating the need for a dedicated crane to lift the rock mass model. Furthermore, during disassembly, only the soil inside the model box needs to be excavated, again without the need to lift the rock mass model, making assembly and disassembly convenient, saving time and effort. Moreover, these features are combined and mutually reinforcing with the aforementioned features. Because the pier rock mass widens the top area of ​​the rock mass model, it provides sufficient space to place the rectangular frame of the model box, ensuring that the area of ​​the rectangular frame, i.e., the cross-section of the soil-like material, is large enough to ensure that the model pile is not affected by the boundary effect of the rectangular frame, thus improving the accuracy of data from subsequent loading tests. Attached Figure Description

[0023] Figure 1 This is an exploded view of the model pile, the rock mass supporting the pile, and the rock mass at the top of the tunnel, taken from above.

[0024] Figure 2 This is an exploded view of the model pile, the rock mass supporting the pile, and the rock mass at the top of the tunnel, taken from below.

[0025] Figure 3 This is a cross-sectional view of the model pile of the present invention after assembly with the pile-bearing rock mass and the rock mass at the top of the tunnel.

[0026] Figure 4 This is a bottom-view perspective view of the model pile and rock mass model of this invention.

[0027] Figure 5 This is a cross-sectional view of the model pile and rock mass model of the present invention.

[0028] Figure 6 for Figure 5 An enlarged schematic diagram of region A.

[0029] Figure 7 This is a perspective view of the device of the present invention.

[0030] Figure 8 This is a cross-sectional view of the device of the present invention.

[0031] As shown in the diagram: 1. Model pile,

[0032] 2. Rock mass model; 21. Piling rock mass; 22. Cave cavity; 22-1. Lower cone surface; 23. Post-cast pile layer; 24. Pile hole; 25. Cave top rock mass; 25-1. Through-pile hole; 25-2. Upper cone surface; 25-3. Eaves platform; 26. Piling rock mass.

[0033] 3. Rectangular frame;

[0034] 41. Horizontal tension loading mechanism; 42. Vertical pressure loading mechanism;

[0035] 5. Soil layers with similar materials. Detailed Implementation

[0036] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0037] This implementation example Figures 1 to 8The diagram shows a device for conducting a loading test on a pile foundation passing through a karst cave. It includes a model pile 1 and a rock mass model 2 fixed to each other. The rock mass model 2 contains a simulated karst cave, through which the model pile 1 passes. The rock mass model 2 is covered with a soil-like material 5. The rock mass model 2 includes a pile-bearing rock mass 21 made of the soil-like material to support the model pile 1, a cave roof rock mass 25 made of the soil-like material, and a foundation rock mass 26 cast from the soil-like material. The pile-bearing rock mass 21 has a karst cave cavity 22 in its middle, with an opening at the top and a pile-embedding hole 24 at its bottom. The convex bottom of the cave roof rock mass 25 matches the opening of the karst cave cavity 22, and a through-hole 25-1 is provided in the middle of the cave roof rock mass 25 through which the model pile 1 passes. Through the through-hole 25-1, the outer wall of the model pile 1 fits against the wall of the through-hole 25-1. The lower section of the model pile 1 is inserted into the embedded pile hole 24, and the bottom surface of the model pile 1 fits against the bottom surface of the embedded pile hole 24. A layer of post-cast solid pile layer 23, made of a rock-like material, is poured on the bottom surface of the cave cavity 22 and around the model pile 1 to bond the lower section of the model pile 1 to the wall of the embedded pile hole 24. The outer wall of the model pile 1, the post-cast solid pile layer 23, the side wall of the cave cavity 22, and the bottom surface of the cave roof rock mass 25 together construct a sealed hollow simulated cave. The cross-section and height of the foundation rock mass 26 are greater than the cross-section and height of the bearing rock mass 21. The foundation rock mass 26 wraps around the top of the cave roof rock mass 25 and the top surface and surroundings of the bearing rock mass 21. The foundation rock mass 26 wraps around the middle section of the model pile 1.

[0038] Preferably, the upper opening of the cavern 22 has a gradually tapering lower conical surface 22-1, and the lower edge of the cave roof rock mass 25 has a gradually tapering upper conical surface 25-2. The upper conical surface 25-2 rests on the lower conical surface 22-1, and the gap between the two conical surfaces forms a conical annular joint. The lower end of the upper conical surface 25-2 has a ring of eaves 25-3 that seals the lower opening of the conical annular joint, and the outer ring of the eaves 25-3 fits against the sidewall of the cavern 22. Furthermore, the upper surface of the cave roof rock mass 25 is a conical surface. The slope of the conical surface is 15°~35°, that is, the angle between the conical line of the conical surface and the axis of the pile hole 25-1 is 55°~75°.

[0039] In this embodiment, the device further includes a model box, which comprises a rectangular frame 3 consisting of four side walls. The rectangular frame 3 has openings at the top and bottom. The rectangular frame 3 also includes four vertical angle steels located at the four outer corners between the four side walls, horizontal bars connected between two vertical angle steels and arranged vertically, and two horizontal beam angle steels located on the left and right sides. The two ends of the horizontal beam angle steels are respectively fixed to the two vertical angle steels on the same side. The vertical angle steels are detachably fixed to the corresponding side walls by bolts (not shown in the figure) or other means. The rectangular frame 3 is equipped with loading devices such as a horizontal tension loading mechanism 41 and a vertical pressure loading mechanism 42. The horizontal tension loading mechanism 41 is installed on the two horizontal bars on the left side, and the vertical pressure loading mechanism 42 is installed on the two horizontal beam angle steels. The horizontal tension loading mechanism 41 and the vertical pressure loading mechanism 42 are mature prior art and are not the inventive point of this application, so they will not be described in detail here. In addition, other loading mechanisms for loads required for the test can be installed on the rectangular frame 3.

[0040] The cross-section of the rectangular frame 3 is smaller than that of the foundation rock mass 26. The rectangular frame 3 rests on the middle of the top surface of the foundation rock mass 26. The distance between the axis of the model pile 1 and the inner wall of the rectangular frame 3 is the same. The soil-similar material 5 is filled inside the rectangular frame 3. Most of the pile segments of the model pile 1 that protrude from the top surface of the rock mass model 2 are buried in the soil-similar material 5, while the top of the model pile 1 protrudes from the top of the soil-similar material 5. Here, the distance between the outer perimeter of the foundation rock mass 26 and the outer perimeter of the pile-bearing rock mass 21 is greater than five times the diameter of the model pile 1. The distance between the outer edge of the rectangular frame 3 and the boundary of the foundation rock mass 26 is preferably twice the diameter of the model pile 1. That is, there is enough distance between the rectangular frame 3 and the model pile 1 so that the setting of the rectangular frame 3 does not affect the stress condition of the model pile 1 in the soil-similar material 5.

[0041] The preparation method of the above-mentioned device for loading tests on pile foundations passing through karst caves specifically includes the following steps:

[0042] S1. Prepare model pile 1, and pile-bearing rock mass 21 and tunnel roof rock mass 25 molded from rock strata-like materials respectively;

[0043] S2. Insert the lower section of the model pile 1 into the pile hole 24 of the bearing rock mass 21. Pour a layer of rock-like material at the bottom of the karst cavity 22 and around the model pile 1. Some of the rock-like material flows into the gap between the model pile 1 and the hole wall of the pile hole 24. When the rock-like material solidifies to form the post-cast pile layer 23, fix the lower section of the model pile 1 to the hole wall of the pile hole 24 through the post-cast pile layer 23.

[0044] S3. Set the rock mass 25 on the model pile 1, and make the bottom of the rock mass 25 convex downward fit with the opening of the cave cavity 22, and the bottom surface of the edge of the rock mass 25 fits with the upper surface of the supporting rock mass 21; that is, the upper conical surface 25-2 of the bottom of the rock mass 25 rests on the lower conical surface 22-1 of the opening of the cave cavity 22, and the outer ring of the eaves 25-3 at the lower end of the upper conical surface 25-2 fits with the side wall of the cave cavity 22.

[0045] S4. Place the model pile 1 and the interlocking tunnel roof rock mass 25 and pile bearing rock mass 21 into a square mold. The cross-sectional area of ​​the square mold is larger than the cross-sectional area of ​​the pile bearing rock mass 21. Pour a rock stratum-like material into the square mold and make the pouring height higher than the tunnel roof rock mass 25, thereby forming a pile cap rock mass 26 that surrounds the middle section of the model pile 1, the tunnel roof rock mass 25 and the pile bearing rock mass 21. After the pile cap rock mass 26 solidifies, demold it.

[0046] S5. Place the rectangular frame 3 of the model box on the top surface of the foundation rock mass 26, fill the rectangular frame 3 with soil-like material 5 to bury the upper section of the model pile 1, and make the top of the model pile 1 protrude, and install the loading device on the rectangular frame 3.

Claims

1. A device for loading test of a pile foundation crossing a karst cave, comprising a model pile (1) and a rock mass model (2) fixed to each other, the inside of the rock mass model (2) being provided with a simulated karst cave, the model pile (1) crossing the simulated karst cave; and a similar material (5) of overburden on the rock mass model (2), characterized in that, The rock mass model (2) comprises a pile-bearing rock mass (21) made of rock stratum similar material for supporting the model pile (1), a cave roof rock mass (25) made of rock stratum similar material, and a pile cap rock mass (26) cast from rock stratum similar material; the pile-bearing rock mass (21) is provided with a cave cavity (22) in the middle, the upper part of the cave cavity (22) is provided with an opening, and the bottom surface of the cave cavity (22) is provided with a pile-embedding hole (24); the bottom of the cave roof rock mass (25) is concave and fits the opening of the cave cavity (22), the middle of the cave roof rock mass (25) is provided with a pile-penetrating hole (25-1), the model pile (1) penetrates through the pile-penetrating hole (25-1), the lower section of the model pile (1) is inserted into the pile-embedding hole (24), and a layer of post-cast pile layer (23) made of rock stratum similar material for bonding the lower section of the model pile (1) and the hole wall of the pile-embedding hole (24) is cast on the bottom surface of the cave cavity (22); the post-cast pile layer (23), the side wall of the cave cavity (22) and the bottom surface of the cave roof rock mass (25) jointly form the simulated cave; the cross section and height of the pile cap rock mass (26) are greater than those of the pile-bearing rock mass (21), and the pile cap rock mass (26) wraps downward the middle section of the model pile (1), the cave roof rock mass (25) and the top surface and surrounding of the pile-bearing rock mass (21).

2. The apparatus for conducting a load test on a pile penetrating a cavern according to claim 1, wherein: The opening of the cave cavity (22) is provided with a gradually converging lower taper surface (22-1), the lower edge of the cave roof rock mass (25) is provided with a gradually converging upper taper surface (25-2), the upper taper surface (25-2) is placed on the lower taper surface (22-1) and the gap between the two taper surfaces forms a tapered annular gap, and the lower end of the upper taper surface (25-2) is provided with a ring of eave platform (25-3) closing the lower opening of the tapered annular gap.

3. Apparatus for conducting a loading test on a pile passing through a solution cavity according to claim 1 or claim 2, wherein: It also comprises a model box comprising a rectangular frame (3) with four side walls and an upper and lower opening, and the rectangular frame (3) is provided with a loading device; the rectangular frame (3) is placed on the top surface of the pile cap rock mass (26); the rectangular frame (3) is filled with soil layer similar material (5), and most of the pile section of the model pile (1) extending out of the top surface of the rock mass model (2) is embedded in the soil layer similar material (5) while the top end of the model pile (1) extends out of the top of the soil layer similar material (5).

4. The method of claim 3, wherein the device is prepared by the steps of: Specifically comprising the following steps: S1. respectively preparing the model pile (1), and the pile-bearing rock mass (21) and the cave roof rock mass (25) molded from rock stratum similar material; S2. inserting the lower section of the model pile (1) into the pile-embedding hole (24) of the pile-bearing rock mass (21), casting a layer of rock stratum similar material on the bottom surface of the cave cavity (22) and the periphery of the model pile (1), part of the rock stratum similar material flowing into the gap between the model pile (1) and the hole wall of the pile-embedding hole (24), and fixing the lower section of the model pile (1) to the hole wall of the pile-embedding hole (24) through the post-cast pile layer (23) when the rock stratum similar material is solidified to form the post-cast pile layer (23); S3. sleeving the cave roof rock mass (25) onto the model pile (1) and fitting the concave bottom of the cave roof rock mass (25) to the opening of the cave cavity (22); S4. Put the model pile (1) and the hole top rock mass (25) and the pile bearing rock mass (21) which are mutually clamped into a square mold, the cross-sectional area of which is larger than that of the pile bearing rock mass (21), pour the rock layer similar material into the square mold and make the pouring height higher than the hole top rock mass (25), so as to form the pile bearing rock mass (26) which wraps the middle section of the model pile (1), the top surface and the surrounding of the hole top rock mass (25) and the pile bearing rock mass (21), and after the pile bearing rock mass (26) is solidified, demold.

5. The method of claim 4, wherein the method further comprises: S5. Put the rectangular frame (3) of the model box on the top surface of the pile bearing rock mass (26), fill the soil layer similar material (5) into the rectangular frame (3), bury the upper section of the model pile (1), and make the top end of the model pile (1) protrude, and install the loading device on the rectangular frame (3).

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