Device and method for simulating three-dimensional crustal stress environment through prestressed reinforcement

Abstract

The invention belongs to the technical field of deep ground environment mechanical testing, and discloses a device and a method for simulating a three-dimensional ground stress environment through prestressed reinforcements. The device comprises a test piece main body part, a prestress applying part, a positioning and reinforcing part and a monitoring and feedback part, the test piece main body part is composed of a stress test piece and a high-strength concrete outer layer, and the prestress applying part applies prestress through prestressed steel bars arranged in three directions by a post-tensioning method and is fixed; the positioning reinforcement part realizes prestressed reinforcement positioning and concrete protection, and the monitoring feedback part acquires strain data. According to the invention, the problems of unstable stress, low scene reduction degree and too high cost in the existing crustal stress simulation technology are solved, and the three-dimensional crustal stress environment of the deep ground can be accurately simulated.

Description

Technical Field

[0001] This invention belongs to the field of deep-earth environment mechanics testing technology, specifically, it relates to a device and method for simulating triaxial geostress environment with prestressed steel bars. Background Technology

[0002] Triaxial in-situ stress in deep earth is a core characteristic of the mechanical environment of deep rock masses. It typically refers to the three-dimensional spatial stress state of varying magnitudes and directions experienced by rock masses in strata buried at depths exceeding one kilometer. With the deepening of energy extraction, deep-buried tunnels, and underground storage projects, deep rock masses often find themselves in complex environments characterized by high in-situ stress, high geothermal temperature, high permeability, and intense mining disturbance. High in-situ stress is particularly critical, not only because its magnitude is significantly higher than in shallower areas, but also because its distribution exhibits strong heterogeneity and anisotropy, exerting a controlling influence on surrounding rock stability, rock burst generation, fracture propagation, and support design. Therefore, simulating the deep triaxial in-situ stress environment realistically, stably, and independently in a laboratory setting has become a crucial foundation for conducting research on the mechanical properties of deep rock masses, evaluating engineering safety, and optimizing engineering design.

[0003] Currently, indoor simulation of deep-earth triaxial stress environments typically employs methods such as hydraulic loading, mechanical pressurization, conventional triaxial testing, or large-scale physical model testing systems. While hydraulic loading can apply confining pressure, the system is complex, requires high sealing, and struggles to achieve independent and precise triaxial control. Mechanical pressurization easily leads to stress concentration, failing to accurately reflect the three-dimensional stress state within the rock mass. Conventional triaxial testing equipment, limited by its axisymmetric loading mode, cannot simulate the true triaxial stress state commonly found in real strata. Large-scale physical model testing systems, while capable of reproducing geological conditions well, suffer from inherent limitations such as high cost, long cycle time, poor operational flexibility, and difficulty in adapting to test specimens of different sizes. Therefore, there is a pressing need for a device and method that can accurately simulate deep-earth triaxial stress environments. Summary of the Invention

[0004] To overcome the shortcomings of existing technologies, this invention provides an apparatus and method for simulating triaxial geostress environment with prestressed steel bars.

[0005] This method utilizes post-tensioned prestressing technology, employing high-strength concrete as the transfer medium to uniformly apply prestress to the target stress specimen, thereby constructing an efficient and controllable deep-earth triaxial geostress environment. This method addresses the problems of stress instability and low scene reproduction in existing geostress simulation technologies, enabling precise application and independent control of triaxial geostress.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] 1. A device and method for simulating a triaxial stress environment in prestressed steel reinforcement, comprising: a main body of the specimen, a prestressing application section, a positioning and reinforcement section, and a monitoring and feedback section; wherein: the main body of the specimen includes, from the inside out, a stressed specimen and a high-strength concrete outer layer. The high-strength concrete outer layer bears the prestress of the steel reinforcement, uniformly transferring the stress to the stressed specimen. The prestressing application section consists of steel reinforcement, tensioning equipment, anchors, and corrugated pipes. The prestressed steel reinforcement is independently arranged along the specimen in three directions: up / down, left / right, and front / back, achieving independent control of the triaxial stress. The tensioning equipment is used to apply the pre-set prestress using the post-tensioning method, and the anchors are installed at both ends of the steel reinforcement to fix the prestress and prevent stress attenuation. The positioning and reinforcement section consists of a perforated template and a grid of additional steel reinforcement. The template has perforations according to the number and arrangement of the prestressed steel reinforcement for fixing the prestressed steel reinforcement; the grid of additional steel reinforcement is laid inside the template to prevent local crushing of the concrete during tensioning and to provide secondary fixation of the prestressed steel reinforcement. The monitoring and feedback section consists of resistance strain gauges and a data acquisition instrument. Resistance strain gauges are attached to the surface of the stressed specimen; a data acquisition instrument is used to collect strain data of the stressed specimen, calculate prestress values, and realize data acquisition and analysis.

[0008] Compared with the prior art, the present invention has the following advantages:

[0009] 1. By using prestressed steel bars and applying stress through post-tensioning, the magnitude of the principal stresses in the length, width, and height directions can be independently controlled, thereby accurately simulating the three-dimensional geostress environment in deep earth.

[0010] 2. After the prestressed steel bars are fixed, their stress state remains stable over a long period of time, ensuring the long-term stability of the simulated triaxial geostress field and the reliability of the test results.

[0011] 3. The device has a relatively flexible structure and can prepare simulated specimens of different sizes according to experimental requirements.

[0012] 4. The system structure has lower construction and operation costs than large hydraulic true triaxial systems, and the stress magnitude, direction and path can be flexibly adjusted. Attached image description:

[0013] Figure 1 This is a schematic diagram of a prestressed steel reinforcement device for simulating a triaxial geostress environment.

[0014] Figure 2 This is a detailed schematic diagram of the tensioning end and the fixed end node of the prestressed steel bar.

[0015] Figure 3 This is a schematic diagram of the perforation template.

[0016] Figure 4 This is a schematic diagram of the grid with added reinforcing bars.

[0017] Figure 5This is a schematic diagram of the overall specimen cross-section and the arrangement of resistance strain gauges. Detailed implementation method:

[0018] As shown in the figure, this invention discloses a device for simulating a triaxial geostress environment with prestressed steel bars: including an overall specimen part, a prestressing application part, a positioning and reinforcement part, and a monitoring and feedback part; wherein: the prestressing application is applied to the overall specimen to realize the application of different geostresses in the three directions of the overall specimen; the positioning and reinforcement system realizes the casting and molding of the main body system of the specimen; the monitoring and feedback is carried out in real time by arranging resistance strain gauges on the surface of the stressed specimen.

[0019] The specimen consists of a load-bearing specimen and high-strength concrete. The high-strength concrete bears the prestress of the reinforcing steel and uniformly transfers the stress to the internal load-bearing specimen.

[0020] The prestressing application section includes prestressed steel bars, corrugated pipes, fixed-end extrusion anchors, anchor plates, bearing plates, spiral stirrups, tensioning-end wedge anchors, and a hydraulic tensioning machine. Specifically: corrugated pipes and steel bars are embedded through template ducts; prestressing is applied using a hydraulic tensioning machine; tensioning-end wedge anchors are used to fix the tension of the steel strands; anchor plates bear concentrated forces and achieve stress diffusion; spiral stirrups under the anchors provide circumferential restraint to counteract splitting tensile stress; fixed-end extrusion anchors are pre-embedded in the non-tensioning end of the concrete to provide reliable reaction force for the tensioning operation.

[0021] Positioning and reinforcement components include perforated formwork and reinforced grid reinforcement. Specifically, the formwork is precisely perforated according to the designed number and spacing of the reinforcement bars to ensure that each corrugated pipe is positioned and fixed in the preset direction before concrete pouring. The reinforced grid reinforcement is placed inside the formwork, coordinated with the corrugated pipes and reinforcement bars, to enhance the local compressive strength of the high-strength concrete and prevent crushing.

[0022] The monitoring and feedback section includes resistance strain gauges and a data acquisition instrument. The resistance strain gauges are attached to the surface of the stressed specimen; the data acquisition instrument is used to collect strain data from the stressed specimen, calculate prestress values, and achieve real-time monitoring and analysis of prestress data.

[0023] The following is a method for simulating a triaxial geostress environment with prestressed steel bars:

[0024] (1) Based on the target triaxial stress values, calculate the number of prestressed steel bars required in each direction, their spacing, and the tension force per bar. Design the perforation template accordingly, ensuring that the perforation positions on each side of the template are consistent with the design scheme. Prepare components such as additional reinforcing bars for the grid, anchor plates, spiral stirrups under the anchor, fixed-end extrusion anchors, and tension-end wedge anchors.

[0025] (2) Install the fixed template and install the grid reinforcement inside the template to form a preliminary spatial skeleton. Pre-embed the extrusion anchor, anchor plate and spiral hoop at the fixed end to ensure that the anchor plate is perpendicular to the axis of the duct. Pre-embed the tension end bearing plate and spiral hoop at the tensioning end.

[0026] (3) Use templates for end positioning, pre-embed corrugated pipes, seal the corrugated pipe joints tightly, ensure the duct is straight, and insert the prestressed tendons into the duct before concrete pouring.

[0027] (4) Place the stress specimen in the center of the template frame at the designed position and fix it. Attach resistance strain gauges to the selected positions on the surface of the stress specimen, lead out wires and connect them to the data acquisition instrument to complete the debugging of the monitoring section.

[0028] (5) Pour high-strength concrete in layers inside the formwork, vibrate to ensure compaction, and ensure that the prestressed steel bars and internal test specimens do not shift. After pouring, perform standard curing until the concrete reaches the design strength.

[0029] (6) Remove the lateral formwork. Install the wedge anchors and hydraulic tensioning machine at the tensioning end. Perform post-tensioning on the prestressed tendons in each direction according to the design tension value.

[0030] (7) After the three-dimensional prestressed steel bars are tensioned and anchored, grout is injected from the grouting hole at the tensioning end. After the vent hole flows out thick grout without air bubbles, the vent hole is sealed and pressure is maintained.

[0031] (8) After the grouting and curing are completed, the system is in a stable triaxial stress state. The strain recorder collects and monitors the data throughout the test.

Claims

1. A device for simulating a triaxial geostress environment with prestressed steel bars, comprising: The specimen consists of four main parts: the main body, the prestressing application section, the positioning and reinforcement section, and the monitoring and feedback section. The main body, from the inside out, comprises the stressed specimen and a high-strength concrete outer layer. The prestressing application section consists of prestressed steel bars, corrugated pipes, tensioning equipment, and anchors. The prestressed steel bars are evenly distributed along the specimen in three directions: vertical, horizontal, and front-back (with corrugated pipes). The tensioning equipment uses post-tensioning to apply prestress, and anchors are installed at both ends of the prestressed steel bars to fix the prestress. The positioning and reinforcement section includes perforated templates and a grid of additional reinforcing bars. The templates have perforations based on the number and spacing of the reinforcing bars; the grid of additional reinforcing bars is laid inside the templates and arranged in conjunction with the prestressed steel bars. The monitoring and feedback section consists of resistance strain gauges and a data acquisition instrument. The method for simulating a triaxial geostress environment using prestressed steel bars described above is as follows: (1) Based on the target triaxial stress value, calculate the number of prestressed steel bars required in each direction, their spacing, and the tension force per bar. Design the perforation template accordingly, ensuring that the perforation positions on each side of the template are consistent with the positions of the steel bars. Prepare components such as steel reinforcement grid, anchor plates, spiral stirrups under the anchor, fixed end extrusion anchors, and tension end wedge anchors. (2) Install the fixed template and install additional reinforcing bars in the grid on the inside of the template. Pre-embed extrusion anchors, anchor plates and spiral hoops at the fixed end to ensure that the anchor plates are perpendicular to the axis of the duct. Pre-embed tension end bearing plates and spiral hoops at the tensioning end. (3) Use templates for end positioning, pre-embed corrugated pipes, seal the corrugated pipe joints tightly, ensure the duct is straight, and insert the prestressed tendons into the duct before concrete pouring. (4) Place the stress specimen in the center of the template frame at the designed position and fix it. Attach resistance strain gauges to the selected positions on the surface of the stress specimen, lead out wires and connect them to the data acquisition instrument to complete the debugging of the monitoring section. (5) High-strength concrete is poured in layers inside the formwork and vibrated to ensure that the prestressing tendons and internal specimens do not shift. After pouring, standard curing is carried out until the concrete reaches the design strength. (6) Remove the lateral formwork. Install the wedge anchors and hydraulic tensioning machine at the tensioning end. Perform post-tensioning on the prestressed tendons in each direction according to the design tension value. (7) After the three-dimensional prestressed steel bars are tensioned and anchored, grout is injected from the grouting hole at the tensioning end. After the vent hole flows out thick grout without air bubbles, the vent hole is sealed and pressure is maintained. (8) After the grouting and curing are completed, the system is in a stable triaxial stress state. The strain recorder collects and monitors the data throughout the test.

2. The apparatus and method for simulating a triaxial geostress environment with prestressed steel bars according to claim 1, characterized in that: The anchorages in the prestressing system include a fixed-end compression anchor, a tensioning-end wedge anchor, an anchor plate, and a spiral hoop under the anchor. The compression anchor is embedded in the fixed end of the concrete to provide reaction force for tensioning. The wedge anchor is used to tension and lock the reinforcing bars. The anchor plate receives and diffuses the concentrated force. The spiral hoop provides circumferential restraint to prevent high-strength concrete from splitting.

3. The apparatus and method for simulating a triaxial geostress environment with prestressed steel bars according to claim 1, characterized in that: The template is designed with openings according to requirements to ensure that each steel bar is fixed in the preset direction and position; the additional steel bars in the grid are arranged in coordination with the steel bars.

4. The apparatus and method for simulating a triaxial geostress environment with prestressed steel bars according to claim 1, characterized in that: Post-tensioning prestressing requires embedding the reinforcing bars in corrugated pipes to form a temporary protective function; the prestressed reinforcing bars are arranged independently in the three directions of up and down, left and right, and front and back of the specimen to achieve triaxial stress control.

5. The apparatus and method for simulating a triaxial geostress environment with prestressed steel bars according to claim 1, characterized in that: High-strength concrete bears the prestress of prestressed steel bars, and transmits the stress evenly to the stressed specimen.

6. The apparatus and method for simulating a triaxial geostress environment with prestressed steel bars according to claim 1, characterized in that: The monitoring and feedback section includes resistance strain gauges and a data acquisition instrument to collect stress and strain data during the test.

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