A multi-field coupling seepage test device and test method for simulating a tensile-shear combined stress state

Abstract

The application discloses a kind of multi-field coupling seepage experimental device and method simulating pull-shear composite stress state.The experimental device includes top cover, metal cylinder, base, annular upper steel support and annular lower steel support, screw rod, pressurizing device, permeation water collection device, and water inlet and pressure maintaining device of confining pressure chamber and permeation water pressure chamber are also provided, and heating device is also provided in confining pressure chamber.Temperature sensors are provided in confining pressure chamber and permeation water pressure chamber respectively.The method includes device assembly, sample preparation, temperature control, constant water head seepage experiment, and permeability coefficient is obtained by data processing according to experimental data.The device is mainly applied to the research on seepage test related parameters response of new and old concrete interface under the coupling effect of stress field, temperature field and seepage field, and the device is simple to operate and reliable in result.

Description

Technical Field

[0001] This invention relates to a constant head permeability test device and method in the field of civil engineering, specifically to a multi-field coupled permeability test device and method for simulating a tensile-shear composite stress state at the interface of new and old concrete under the coupled effects of temperature field, stress field, and seepage field. Background Technology

[0002] Recently, due to the impacts of climate change and environmental erosion, many dams have undergone heightening and reinforcement measures to increase water storage capacity and repair the dam body. During the dam heightening and repair process, after grinding and other treatments of the existing (old) concrete, fresh concrete is poured, forming a bonding surface with the old concrete, known as the new-old concrete interface. During the service life of these dams, due to the increased water level and concrete shrinkage, the new-old concrete interface at the top of the old dam on the water-facing side is simultaneously subjected to shear and tensile forces, as well as diurnal temperature variations. This makes the interface highly susceptible to penetrating cracks. These penetrating cracks significantly weaken the dam's integrity and seepage resistance, becoming preferential seepage channels, thus exacerbating internal erosion, reducing structural durability, and in severe cases, even threatening the safe operation of the dam. While there is ample research on the permeability characteristics of concrete based on Darcy's law, research on the permeability characteristics of the new-old concrete interface under complex stress states is rarely reported. In order to study in depth the permeability characteristics and permeability coefficient of the interface between new and old concrete under complex stress conditions, it was found that the permeability characteristics and permeability coefficient of the interface between new and old concrete are closely related to the material composition, geometric dimensions and test conditions of the specimen. These parameters not only limit the design of the test device and scheme, but also change under the coupling effect of stress field, temperature field and seepage field, thus causing errors and fluctuations in the measured permeability coefficient.

[0003] To investigate the response of relevant parameters in material seepage tests under the coupled effects of stress, temperature, and seepage fields, precise monitoring and control of changes in these parameters during the test are necessary. Previous tests only considered unidirectional compressive, tensile, or shear stresses, as in Patent Document 1 (CN104458531B, Publication Date 2017.04.12) and Patent Document 2 (CN119124970B, Publication Date 2025.01.21) to obtain stable permeability coefficients. According to GBT50123-1999 standard for geotechnical testing methods, the commonly used specimen size for triaxial compression testing is a cylindrical specimen with a size of 50mm × 100mm. Furthermore, several domestic and international standards (such as EN12390-8) recommend or implicitly specify in different chapters that the specimen should be cubic, cylindrical, or prismatic, with a minimum surface dimension of 150mm and other dimensions of 100mm. Consequently, in current experiments on the determination of concrete permeability coefficient, most scholars choose to use cylindrical specimens to ensure the test object is standardized. Test conclusions can be referenced in patent document 3 (publication number CN120651732A, publication date 2025.09.16). While cylindrical specimens allow for smoother water flow and less resistance on the sidewalls, resulting in more stable permeability coefficients and easier sealing, current technologies, such as patent document 4 (CN206848047U, publication date 2018.01.05), often use geotechnical testing instruments when testing the permeability coefficient of concrete. However, concrete has higher strength and impermeability than geotechnical materials, making it difficult to simultaneously apply force-applying and seepage-proof devices under complex stress conditions. This makes it challenging to measure the permeability coefficient at the interface between new and old concrete, ultimately leading to significant errors in the measured data.

[0004] In summary, the existing devices are insufficient to investigate the permeability characteristics of the interface between new and old concrete under the coupled effects of complex stress, temperature, and seepage fields. Furthermore, the data collected during the experiment is easily affected by various factors and fluctuates, failing to meet the requirements for simulating and analyzing actual engineering environments.

[0005] Therefore, there is an urgent need to design a test device for the seepage characteristics of the interface between new and old concrete that integrates multi-field coupling, precise data acquisition, and temperature control. Summary of the Invention

[0006] The purpose of this invention is to provide a multi-field coupled seepage test device and method for simulating tensile-shear combined stress state. It simulates the water pressure during normal water storage period by using a water pump and a water pressure actuator, and simulates tensile-shear combined stress by using a shear method. At the same time, it changes the tensile-shear stress by adjusting the shear angle, thereby obtaining a permeability coefficient of the interface between new and old concrete that is more in line with engineering practice.

[0007] Therefore, according to the first aspect of the present invention, the present invention adopts the following technical solution:

[0008] A multi-field coupled seepage experimental device for simulating tensile-shear combined stress state, characterized in that:

[0009] The system includes a top cover, a metal cylinder, a base, an annular upper steel support and an annular lower steel support, a screw, a pressurizing device, and a permeable water collection device. The top cover is located above the base, and the outer peripheral surfaces of the top cover and the base are fixedly connected by a screw. The metal cylinder, the upper steel support, and the lower steel support are all installed between the top cover and the base. The upper and lower steel supports are fixedly connected to the top cover and the base, respectively, and are located in the center of the top cover and the base, and are arranged concentrically. The outer diameter of the annular upper steel support is smaller than the inner diameter of the annular lower steel support. The space between the upper and lower steel supports is the position for placing the test block. The metal cylinder, the top cover, and the base form a confining pressure chamber outside the test block, the upper steel support, and the lower steel support. A permeable water pressure chamber is formed between the top cover, the upper steel support, and the test block. The pressurizing device is located in the permeable water pressure chamber and is used to apply pressure to the test block to create a shearing effect.

[0010] The multi-field coupled seepage experimental device is also equipped with a confining pressure chamber water inlet and pressure holding device and a permeation water pressure chamber water inlet and pressure holding device. A heating device is also installed in the confining pressure chamber, and temperature sensors are installed in the confining pressure chamber and the permeation water pressure chamber, respectively.

[0011] Preferably, the top and bottom ends of the metal cylinder are sealed to the top cover and the base, respectively. The top cover and the base are respectively provided with grooves that mate with the metal cylinder, and sealing rings are provided in the grooves. The cylinder is then locked by the connection of a screw and a nut.

[0012] Preferably, the upper end face of the lower steel support has a positioning groove, the wall of the positioning groove tightly protects the lower end of the test block, a silicone pad is placed in the positioning groove, and the lower steel support and the test block are in contact with each other by the annular silicone pad to form a sealing surface; the lower end face of the upper steel support has a positioning groove, the wall of the positioning groove tightly protects the upper end of the test block, a silicone pad is placed in the positioning groove, and the upper steel support and the test block are in contact with each other by the annular silicone pad to form a sealing surface.

[0013] Preferably, the top cover is provided with inlet ports for the infiltration pressure chamber water inlet and pressure holding device and the confining pressure chamber water inlet and pressure holding device. The top cover is also provided with inlet ports for the infiltration pressure chamber water inlet and the confining pressure chamber water inlet. The infiltration pressure chamber water inlet and pressure holding device includes an infiltration pressure actuator and a water storage pump A. The water storage pump A first replenishes the infiltration pressure chamber with constant head test water. After replenishment, the infiltration pressure actuator provides a constant infiltration water pressure. The confining pressure chamber water inlet and pressure holding device includes a confining pressure actuator and a water storage pump B. The water storage pump B replenishes the confining pressure chamber with test confining pressure water. After replenishment, the confining pressure actuator controls the set confining pressure. The temperature sensor, the infiltration pressure actuator, and the confining pressure actuator are respectively connected to a digital signal acquisition instrument.

[0014] Preferably, the heating device uses a spiral copper tube, and the top cover is provided with mounting holes for the spiral copper tube. The inlet and outlet of the spiral copper tube are connected to the water bath circulation system through pipes. Temperature sensors are also installed in the confining pressure chamber and the infiltration water pressure chamber on the top cover.

[0015] Preferably, the base is equipped with a seepage water collection port, which is located within the lower part of the annular steel support. A measuring cylinder and an electronic scale are placed below to collect seepage water volume data.

[0016] The experimental apparatus of this invention is mainly used to study the relevant parameters of seepage tests on new and old concrete under the coupled effects of stress field, temperature field and seepage field, and is used to accurately determine the relevant parameters of seepage tests on the interface of new and old concrete under the coupled effects of stress field, temperature field and seepage field.

[0017] The experimental apparatus of this invention can be used not only to study the relevant parameters of seepage tests at the interface between new and old concrete under constant water pressure and temperature, but also to study the relevant parameters of seepage tests at the interface between new and old concrete under conditions of high water pressure and hot and cold cycles.

[0018] Preferably, the device is more suitable for large-volume concrete and concrete samples with new and old bonding surfaces.

[0019] Preferably, to improve temperature conduction efficiency and reduce heat exchange between the device and the external environment, stainless steel is used as the upper support to ensure that heat can be conducted from the confining pressure chamber to the permeation water pressure chamber in a timely manner, so that the seepage test environment can efficiently reach the predetermined parameter values. The preferred materials and device structure effectively improve the temperature control rate of the test.

[0020] Preferably, the temperature field is simultaneously monitored and recorded by two temperature sensors with an accuracy of one-hundredth. Specifically, the invention includes two temperature sensors, located in the confining pressure chamber and the permeation water pressure chamber, respectively. When the temperature values ​​of the two temperature sensors are stable and equal, it indicates that temperature control is complete. The two temperature sensors transmit temperature data in real time to accurately monitor and record the changes in the temperature of the sample and the test environment under the combined coupling effect of the permeation field and the stress field during the seepage test.

[0021] Preferably, a constant head permeability test is used as a simulation test of the seepage field. That is, the water level at the upstream and downstream is kept constant to ensure that the water seeps in a stable state, thereby obtaining the seepage resistance of concrete materials under fixed conditions. This simulates the internal seepage situation of the interface between new and old concrete in actual engineering when it is affected by a constant head under normal water storage conditions after the height is increased.

[0022] According to a second aspect of the present invention, the present invention adopts the following technical solution:

[0023] The method for designing test blocks for the multi-field coupled seepage experimental device used to simulate the combined tensile-shear stress state is characterized by: firstly, setting the pressure value according to the experimental design requirements; using an inclined plane to decompose the vertical pressure into tensile force perpendicular to the inclined plane and shear force parallel to the inclined plane; and simulating the combined tensile-shear stress state of new and old concrete under any condition by adjusting the inclination angle of the inclined plane and the magnitude of the vertical pressure. This involves prefabricating upper steel supports and annular lower steel supports of corresponding dimensions, as well as the pressure head of the pressure device of corresponding dimensions; utilizing the size difference between the upper steel supports, the annular lower steel supports, and the pressure head of the pressure device to form a compression-shear failure surface or a tensile-shear failure surface according to the design requirements; designing corresponding molds to fabricate cylindrical concrete test blocks; and the specific pouring steps are as follows:

[0024] Step 1:

[0025] When pouring the old concrete part in the shape of a truncated cone, the outer diameter of the upper steel support is used as the upper bottom diameter, and the inner diameter of the lower steel support is used as the lower bottom diameter. The corresponding mold is designed for pouring the old concrete. After the old concrete is poured and formed, the side of the truncated cone will serve as the bonding surface between the new and old concrete.

[0026] Step Two:

[0027] The newly poured concrete section is used to form a cylindrical test block, which eliminates the effects of size effect and edge stress concentration, and facilitates the contact between the test block and the annular silicone gasket between the upper and lower steel supports to form a sealing surface.

[0028] According to a third aspect of the present invention, the present invention adopts the following technical solution:

[0029] The multi-field coupled seepage flow constant head experimental method is characterized by: using the above-mentioned multi-field coupled seepage flow experimental device simulating tensile-shear combined stress state and the above-mentioned method to design and fabricate test blocks.

[0030] The experimental method includes specific operational steps:

[0031] Step 1: Assemble the above-mentioned multi-field coupled seepage experimental apparatus for simulating tensile-shear combined stress state:

[0032] Step Two:

[0033] After closing the outlet valves of the confining pressure chamber and the permeation pressure chamber, and confirming that the device is sealed and the anti-seepage measures for the test block are in place, start water pump A to inject water into the confining pressure chamber. After the water injection is completed, start the confining pressure actuator to apply the target confining pressure. Set the target temperature of the water bath circulation system, and start the water pump to introduce heat transfer oil into the spiral copper tube inside the confining pressure chamber. Set the permeation pressure, and start water pump B to inject water into the permeation pressure chamber. After the water injection is completed and both temperature sensors have measured the target temperature, turn on the permeation pressure actuator to apply the set permeation pressure to the test block.

[0034] Step 3:

[0035] After controlling the water temperature and water pressure to stabilize to meet the requirements of the simulated daily average water temperature and the design water level and head after the dam body is raised, collect the seepage water volume under the test block over time. When the water volume stabilizes, turn on the pressurization device and collect the seepage water volume over time until the water volume stabilizes. Then record the experimental data.

[0036] Open the drain pipes of the permeation pressure chamber and the confining pressure chamber, remove the top cover, replace the test block and repeat the experimental steps until all experiments are completed. Based on the collected water flow and temperature sensor data, calculate the permeability coefficient of the interface between the new and old concrete under the tensile-shear combined stress state according to Darcy's law.

[0037] The permeability coefficient of the concrete sample was calculated as follows:

[0038]

[0039] In the formula:

[0040] K represents the permeability coefficient of the concrete specimen when the water temperature is T ℃ and the seepage pressure is P MPa;

[0041] Q is the volumetric flow rate through the contact area A between the test block and the upper water surface;

[0042] L is the flow path length from the upper water contact surface of the test block to the lower seepage surface;

[0043] A represents the area of ​​the upper part of the test block in contact with water;

[0044] The difference in water head between the top and bottom of the test block.

[0045] This invention utilizes the aforementioned device to conduct temperature-controlled constant head tests and perform permeability measurements. It provides a method for calculating the permeability coefficient based on this device, capable of calculating permeability coefficient values ​​under different temperatures, water pressures, and stress states. This fills the gap in methods for calculating the permeability coefficient at the interface between new and old concrete under complex stress states. Furthermore, it provides a temperature control and monitoring scheme for the confining pressure chamber piping design, enabling more automated and accurate permeability measurements, achieving more automated data acquisition and more precise temperature control. The beneficial effects of this invention are:

[0046] 1. This invention effectively solves the problem of not being able to simultaneously apply and accurately control multiple stress fields, temperature fields, and permeation fields at the interface between new and old concrete.

[0047] 2. This invention effectively solves the problem that when dam concrete stress simulation closely resembles actual engineering conditions, it is impossible to conduct permeability tests simultaneously, and the conclusions drawn lack high-value reference significance.

[0048] 3. This invention effectively solves the problem of fully digital and accurate acquisition of three-field coupled response parameters. Attached Figure Description

[0049] Figure 1 This is a top view of the device of the present invention;

[0050] Figure 2 This is a cross-sectional view of plane A-A';

[0051] Figure 3 This is a cross-sectional view of plane B-B'.

[0052] Figure 4 Configuration diagram of the A-A' plane profile device;

[0053] Figure 5 This is a diagram showing the configuration of the B-B' section device.

[0054] In the diagram: 1. Pressure head; 2. Threaded column; 3. Temperature sensor; 4. Top cover; 5. Upper support; 6. Silicone pad; 7. Test block; 8. Metal cover; 9. Spiral copper tube; 10. Lower support; 11. Base; 12. Inlet of permeate pressure chamber; 13. Inlet of confining pressure chamber; 14. Outlet of confining pressure chamber; 15. Outlet of permeate pressure chamber; 16. Inlet of water bath circulation; 17. Outlet of water bath circulation; 18. Water storage pump A; 19. Water storage pump B; 20. Electronic scale; 21. Measuring cylinder; 22. Water bath circulation system; 24. Digital signal acquisition instrument; 25. Permeate pressure actuator; 26. Confining pressure actuator. Detailed Implementation

[0055] The structural components and specific usage methods of the present invention are described in detail below. Structural diagrams of the device are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar components or components having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0056] like Figures 1-5 As shown, the present invention provides a multi-field coupled seepage experimental device for simulating tensile-shear combined stress state, including a top cover 4, a metal cylinder 8, a base 11, an annular upper steel support 5 and an annular lower steel support 10, a screw 2, a pressurizing device 1, a measuring cylinder 21, and an electronic scale 20; the top cover 4 is located above the base 11, and the outer peripheral end faces of the top cover 4 and the base 11 are fixedly connected by the screw 2; the metal cylinder 8, the upper steel support 5, and the lower steel support 10 are all installed between the top cover 4 and the base 11. The upper steel support 5 and the lower steel support 10 are welded to the top cover 4 and the base 11 respectively, located in the center of the top cover 4 and the base 11, and are arranged concentrically. The outer diameter of the annular upper steel support 5 is smaller than the inner diameter of the annular lower steel support 10. The test block 7 is placed between the upper steel support 5 and the lower steel support 10. The metal cylinder 8, the top cover 4, and the base 11 form a confining pressure chamber outside the test block 7, the upper steel support 5, and the lower steel support 10. A permeable water pressure chamber is formed between the top cover 4, the upper steel support 5, and the test block 7.

[0057] The pressurization device 1 can be a hydraulic device.

[0058] The top and bottom of the metal cylinder 8 are sealed to the top cover 4 and the base 11 respectively, and the test block 7 is sealed to the upper and lower steel support seats 5 and 10. Grooves that mate with the metal cylinder 8 can be set in the top cover 4 and the base 11 respectively, and sealing rings can be set in the grooves. The screw 2 and nut are then used to lock the cylinder.

[0059] A positioning groove is provided on the upper end face of the lower steel support 10. The wall of the positioning groove tightly protects the lower end of the test block 7. A silicone pad 6 is placed in the positioning groove. The lower steel support 10 and the test block 7 are in contact with each other by the annular silicone pad 6 to form a sealing surface.

[0060] The upper steel support 5 and the test block 7 are in contact with an annular silicone pad 6 to form a sealing surface. The lower end face of the upper steel support 5 is also provided with a positioning groove. The wall of the positioning groove tightly protects the upper end of the test block 7, and the silicone pad 6 is placed in the positioning groove.

[0061] The top cover 4 is provided with a permeation water pressure chamber inlet 12, a confining pressure chamber inlet 13, a permeation water pressure chamber drain 15, a confining pressure chamber drain 14, and a spiral copper pipe mounting hole 16. The permeation water pressure inlet 12 corresponds to the permeation water pressure chamber and is connected to the permeation water pressure actuator 25 and the water storage pump A (18) through a steel water pipe. The water storage pump A (18) first replenishes the permeation water pressure chamber with constant head test water. After replenishment, the permeation water pressure actuator 25 provides constant permeation water pressure. The confining pressure inlet 13 corresponds to the confining pressure chamber and is connected to the confining pressure actuator 26 and the water storage pump B (19) through a steel water pipe. The water storage pump B (19) replenishes the confining pressure chamber with test confining pressure water. After replenishment, the confining pressure actuator 26 controls the set confining pressure. The spiral copper pipe mounting hole (16) corresponds to the confining pressure chamber. The inlet and outlet of the spiral copper pipe are connected to the water bath circulation system 22 through pipes. Two temperature sensors 3 are also installed on the 4th chamber. One temperature sensor 3 is located in the confining pressure chamber, and the other temperature sensor 3 is located in the infiltration water pressure chamber. The temperature sensors collect temperature data and control the water bath circulation system. When the temperature in the confining pressure chamber changes, the water bath circulation system 22 is controlled to maintain the temperature in the confining pressure chamber. The spiral copper pipe 9 is installed in the confining pressure chamber. After the heat transfer oil enters the spiral copper pipe 9, it exchanges heat with the water in the confining pressure chamber, causing the temperature in the metal cylinder 8 to approach the target temperature. Then, the heat transfer oil flows out from the outlet 17 of the spiral copper pipe 9 and returns to the water bath circulation system 22. The temperature sensor 3 installed in the infiltration chamber is used to record and monitor the temperature value of the water in the infiltration chamber, which is used to determine whether the viscosity coefficient of the water in the infiltration water pressure chamber reaches the expected value for quantitative analysis of the permeability coefficient of concrete. The drainage interface 15 of the infiltration water pressure chamber is located in the infiltration water pressure chamber and is connected to the outside through a steel water pipe and is equipped with a valve. The drainage interface 14 of the confining pressure chamber is located in the confining pressure chamber and is connected to the outside through an external steel water pipe and is equipped with a valve.

[0062] The base 11 is equipped with a seepage water collection port, which is located within the range of the lower annular steel support 10. A measuring cylinder 21 and an electronic scale 20 are installed below to collect seepage water volume data.

[0063] Temperature sensor 3, permeate pressure actuator 25, and confining pressure actuator 26 are respectively connected to digital signal acquisition instrument (24).

[0064] Twelve threaded posts 2 are arranged circumferentially on the screw 2. The bottom end of the screw 2 is directly fixed to the hole of the base 11 by the thread. The top end of the screw post 2 passes through the twelve screw 2 through holes on the top cover 4 and is connected to the nut.

[0065] The design and fabrication of the test block (7) adopted the following method: First, the pressure value was set according to the experimental design requirements. The vertical pressure was divided into tensile force perpendicular to the inclined plane and shear force parallel to the inclined plane using the inclined plane. The tensile stress was set to 0.0476MPa and the shear stress to 0.3336MPa according to the sensor readings. The tangent angle was calculated to be 8.12°. The upper steel support 5 and the annular lower steel support 10 of the corresponding size were prefabricated, as well as the pressure head of the pressure device 1 of the corresponding size. The ratio of the difference between the outer diameter of the upper steel support 5 and the inner diameter of the lower steel support 10 and the height of the test block corresponded to the ratio of tensile stress and shear stress. The outer diameter of the upper steel support 5 was designed to be 50mm, and the inner diameter of the lower steel support 10 was designed to be 92mm, forming an angle of 8° with an accuracy error of 1.5%. Figures 2-5 As shown, by utilizing the dimensional difference between the upper steel support 5 and the annular lower steel support 10 and the pressure head of the pressurizing device 1, a compression-shear failure surface or a tension-shear failure surface is formed according to the design requirements. Corresponding molds are designed to fabricate cylindrical concrete test blocks 7. Specific pouring steps are as follows:

[0066] Step 1:

[0067] When pouring the old concrete part in the shape of a truncated cone, the outer diameter of the upper steel support 5 is used as the upper bottom diameter, and the inner diameter of the lower steel support 10 is used as the lower bottom diameter. The corresponding mold is designed for pouring the old concrete. After the old concrete is poured and formed, the side of the truncated cone will serve as the bonding surface between the new and old concrete.

[0068] Step Two:

[0069] The newly poured concrete section is used to form a cylindrical test block, which eliminates the effects of size effect and edge stress concentration, and facilitates the contact between the test block 7 and the annular silicone gasket 6 between the upper steel support 5 and the lower steel support 10 to form a sealing surface.

[0070] The specific operating steps of the device of the present invention are as follows:

[0071] Step 1, Assembly of the experimental setup:

[0072] First, place the waterproofed test block 7 on the annular silicone pad 6 of the lower steel support 10, place the annular silicone pad 6 on the upper part of the test block 7, fix the metal cylinder 8 and screw 2 on the base 11, then install the top cover 4, and press the upper steel support 5 welded to the top cover 4 onto the annular silicone pad 6 on the upper part of the sample. At the same time, the spiral copper pipe 9 is installed in the confining pressure chamber, and the temperature sensor 3 is arranged on the top cover 4. Finally, use nuts to fix all the threaded columns 2 to the top cover 4, and connect the corresponding water pipes at each interface to complete the assembly of the device.

[0073] Step Two:

[0074] After closing the valves of the confining pressure chamber outlet pipe and the permeation pressure chamber outlet pipe, and confirming that the device is sealed and the anti-seepage measures of the test block are complete, start the water storage pump A (18) to inject water into the confining pressure chamber. After the water injection is completed, start the confining pressure actuator 26 to apply the target confining pressure. Set the target temperature of the water bath circulation system 22, start the water pump to enter the heat transfer oil into the spiral copper tube 9 in the confining pressure chamber, and let it circulate in the spiral copper tube. The temperature conduction effect is detected by the temperature sensor. Set the permeation pressure, start the water storage pump B (19) to inject water into the permeation pressure chamber. After the water injection is completed and both temperature sensors have measured the target temperature, turn on the permeation pressure actuator 25 to apply the set permeation pressure to the test block 7.

[0075] Step 3:

[0076] The daily average water temperature of 25℃, obtained from temperature measurement, was used as the set value. The water pressure of 78.4 kPa, calculated based on the difference of 8m between the increased water storage height and the original dam crest height, was also used as the set value. After the water temperature and water pressure of the control device stabilized and reached the set requirements, the seepage water volume was collected under test block 7 over time. When the water volume stabilized, the pressurization device 1 was turned on, and the seepage water volume was collected over time until the water volume stabilized. The experimental data was then recorded.

[0077] Open the drain pipes of the permeation pressure chamber and the confining pressure chamber, remove the top cover 4, replace the test block 7 and repeat the experimental steps until all experiments are completed. Based on the collected water flow and the data collected by the temperature sensor 3, calculate the permeability coefficient of the interface between the new and old concrete under the tensile-shear composite stress state according to Darcy's law.

[0078] The permeability coefficient of the concrete sample was obtained by processing the data obtained from the water collection device in the constant head seepage test, and was specifically calculated as follows:

[0079]

[0080] In the formula:

[0081] K represents the permeability coefficient of the concrete specimen when the water temperature is T ℃ and the seepage pressure is P MPa;

[0082] Q is the volumetric flow rate through the contact area A between the test block and the upper water; that is, the amount of water accumulated in the graduated cylinder during the test period.

[0083] L is the flow path length from the upper water contact surface of the test block to the lower seepage surface, which is the distance between the edge of the pressurized head and the edge of the lower support on the same side.

[0084] A represents the area of ​​the upper part of the test block in contact with water; that is, the area of ​​the circle corresponding to the inner diameter of the upper steel support minus the contact area between the pressurizing mechanism and the test block.

[0085] The difference in water head between the top and bottom of the test block is the water pressure in the permeation pressure chamber.

[0086] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any transformations or substitutions that can be conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A multi-field coupled seepage experimental device for simulating tensile-shear combined stress state, characterized in that: The device includes a top cover (4), a metal cylinder (8), a base (11), an annular upper steel support (5) and an annular lower steel support (10), a screw (2), a pressurizing device (1), and a permeable water collection device. The top cover (4) is located above the base (11), and the outer peripheral end faces of the top cover (4) and the base (11) are fixedly connected by the screw (2). The metal cylinder (8), the upper steel support (5), and the lower steel support (10) are all installed between the top cover (4) and the base (11). The upper steel support (5) and the lower steel support (10) are fixedly connected to the top cover (4) and the base (11) respectively. Located in the center of the top cover (4) and the base (11), and arranged concentrically, the outer diameter of the annular upper steel support (5) is smaller than the inner diameter of the annular lower steel support (10), and the space between the upper steel support (5) and the lower steel support (10) is the position for placing the test block; the metal cylinder (8), the top cover (4), and the base (11) form a confining pressure chamber outside the test block, the upper steel support (5), and the lower steel support (10), and a permeable water pressure chamber is formed between the top cover (4), the upper steel support (5), and the test block (7); the working part of the pressurizing device is located in the permeable water pressure chamber, and is used to apply pressure to the test block to form a shearing action; The multi-field coupled seepage experimental device is also equipped with a confining pressure chamber water inlet and pressure holding device and a permeable water pressure chamber water inlet and pressure holding device. A heating device is also provided in the confining pressure chamber, and temperature sensors are respectively provided in the confining pressure chamber and the permeable water pressure chamber (3).

2. The multi-field coupled seepage experimental apparatus as described in claim 1, characterized in that: The top and bottom of the metal cylinder (8) are sealed to the top cover (4) and the base (11) respectively. The top cover (4) and the base (11) are respectively provided with grooves that cooperate with the metal cylinder (8), and a sealing ring is provided in the groove. The cylinder is then locked by the connection of the screw (2) and the nut.

3. The multi-field coupled seepage experimental apparatus as described in claim 1, characterized in that: A positioning groove is provided on the upper end face of the lower steel support (10). The wall of the positioning groove tightly protects the lower end of the test block. A silicone pad (6) is placed in the positioning groove. The lower steel support (10) and the test block (7) are in contact with each other by the annular silicone pad (6) to form a sealing surface. The upper steel support (5) has a positioning groove on its lower end face. The wall of the positioning groove tightly protects the upper end of the test block. A silicone pad (6) is placed in the positioning groove. The upper steel support (5) and the test block (7) are in contact with each other by the annular silicone pad (6) to form a sealing surface.

4. The multi-field coupled seepage experimental apparatus as described in claim 1, characterized in that: The top cover (4) is provided with an inlet (12) for the inlet and pressure-holding device of the permeation water pressure chamber and an inlet (13) for the inlet and pressure-holding device of the confining pressure chamber. The top cover (4) is also provided with an inlet (15) for the inlet and pressure-holding device of the permeation water pressure chamber and an inlet (15) for the confining pressure chamber. The inlet and pressure-holding device of the permeation water pressure chamber includes an inlet water pressure actuator (25) and a water storage pump A (18). The water storage pump A (18) first replenishes the constant head test water in the permeation water pressure chamber. After completion, the constant permeation water pressure is provided by the permeation water pressure actuator (25); the confining pressure chamber water inlet and pressure holding device includes the confining pressure actuator (26) and the water storage pump B (19). The water storage pump B (19) replenishes the test confining pressure water in the confining pressure chamber. After replenishment, the confining pressure actuator (26) controls the set confining pressure; the temperature sensor (3), the permeation water pressure actuator (25), and the confining pressure actuator (26) are respectively connected to the digital signal acquisition instrument (24).

5. The multi-field coupled seepage experimental apparatus as described in claim 1, characterized in that: The heating device uses a spiral copper tube (9), and the top cover is provided with mounting holes (16) for the spiral copper tube (9). The inlet and outlet of the spiral copper tube are connected to the water bath circulation system (22) through pipes. Temperature sensors (3) are also installed in the confining pressure chamber and the infiltration water pressure chamber on the top cover (4).

6. The multi-field coupled seepage experimental apparatus as described in claim 1, characterized in that: The base (11) is equipped with a permeable water collection port, which is located within the range of the lower annular steel support (10). A measuring cylinder (21) and an electronic scale (20) are installed below to collect permeable water data.

7. A method for designing test blocks for a multi-field coupled seepage experimental apparatus for simulating tensile-shear combined stress states as described in any one of claims 1-6, characterized in that: First, set the pressure value according to the experimental design requirements. Use the inclined plane to split the vertical pressure into tensile force perpendicular to the inclined plane and shear force parallel to the inclined plane. Adjust the inclination angle of the inclined plane and the magnitude of the vertical pressure to simulate the tensile-shear composite stress state of new and old concrete under any circumstances. Prefabricate the upper steel support (5) and the annular lower steel support (10) of the corresponding size, as well as the pressure head of the pressure device (1) of the corresponding size. Use the size difference between the upper steel support (5) and the annular lower steel support (10) and the pressure head of the pressure device (1) to form the tensile-shear failure surface according to the design requirements. Design the corresponding mold to make the concrete cylindrical test block (7). Specific pouring steps: Step 1: When pouring the old concrete part in the shape of a truncated cone, the outer diameter of the upper steel support (5) is used as the upper bottom diameter, and the inner diameter of the lower steel support (10) is used as the lower bottom diameter. The corresponding mold is designed for pouring the old concrete. After the old concrete is poured and formed, the side of the truncated cone will serve as the bonding surface between the new and old concrete. Step Two: The new concrete section is poured to form a cylindrical test block, which eliminates the influence of size effect and edge stress concentration, and facilitates the contact between the test block (7) and the annular silicone pad (6) between the upper steel support (5) and the lower steel support (10) to form a sealing surface.

8. A multi-field coupled seepage constant head experimental method, characterized in that: The test block (7) is designed and fabricated using the multi-field coupled seepage experimental apparatus for simulating tensile-shear combined stress state as described in any of claims 1-6 and the method of claim 7. The specific operation steps are as follows: Step 1: Assemble the multi-field coupled seepage experimental apparatus for simulating tensile-shear combined stress state as described in any of claims 1-6; Step Two: After closing the valves of the confining pressure chamber outlet pipe and the permeable pressure chamber outlet pipe, confirming that the device is sealed and the anti-seepage measures of the test block are complete, start the water storage pump A (18) to inject water into the confining pressure chamber. After the water injection is completed, start the confining pressure actuator (26) to apply the target confining pressure. Set the target temperature of the water bath circulation system (22), start the water pump to put the heat transfer oil into the spiral copper tube in the confining pressure chamber; set the osmotic pressure, start the water storage pump B (19) to inject water into the osmotic pressure chamber, and after the water injection is completed and both temperature sensors have measured the target temperature, turn on the osmotic pressure actuator (25) to apply the set osmotic pressure to the test block (7). Step 3: After controlling the water temperature and water pressure to stabilize to meet the requirements of the simulated daily average water temperature and the design water level head after the dam body is raised, collect the seepage water volume under the test block over time. When the water volume reaches a stable level, turn on the pressurization device (1) and collect the seepage water volume over time until the water volume reaches a stable level. Then record the experimental data. Open the drainage pipes of the permeation pressure chamber and the confining pressure chamber, remove the top cover, replace the test block (7) and repeat the experimental steps until all experiments are completed. Based on the collected water flow and the data collected by the temperature sensor (3), calculate the permeability coefficient of the interface between the old and new concrete under the tensile-shear composite stress state according to Darcy's law.

9. The experimental method according to claim 7, characterized in that: The permeability coefficient of the concrete sample was calculated as follows: In the formula: K represents the permeability coefficient of the concrete specimen when the water temperature is T ℃ and the seepage pressure is P MPa; Q is the volumetric flow rate through the contact area A between the test block and the upper water surface; L is the flow path length from the upper water contact surface of the test block to the lower seepage surface; A represents the area of ​​the upper part of the test block in contact with water; The difference in water head between the top and bottom of the test block.

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