Device for simulating three-dimensional crustal stress environment by prestressed reinforcement in consideration of temperature and pressure load

Abstract

The invention belongs to the technical field of deep ground environment mechanical testing, and discloses a device for simulating a three-dimensional ground stress environment by a prestressed reinforcement considering a temperature-pressure load, and the principle of the device is that a temperature effect is converted into additional stress, and the additional stress is superposed with original ground stress, so that the simulation of the stress on the structure effect under the temperature change is realized. 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 after temperature change 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 for simulating triaxial geostress environment using prestressed steel bars that consider temperature and pressure loads. Background Technology

[0002] Traditional geostress analysis systems focus on the superposition of self-weight stress and tectonic stress, treating temperature as a secondary disturbance. However, as engineering projects expand into deeper areas, this simplified approach is no longer adequate for practical needs. In deep resource development, the initial geothermal temperature of deep rock masses is high. As the temperature rises, the structure undergoes thermal expansion. Due to underground confinement (surrounding rock masses, tectonic boundaries), it cannot freely elongate. The constrained expansion deformation is transformed into additional compressive stress. The superposition of this additional compressive stress and the original geostress further increases the total geostress. Differences in the thermal expansion coefficients of different materials can also cause stress concentration at the interface of composite structures. All these scenarios require geostress analysis to incorporate the influence of temperature.

[0003] While existing thermoelasticity mechanics clearly defines the transmission logic of temperature effects—"thermal deformation-constraint-stress"—and can quantify the superposition effect of additional thermal stress and original geostress, traditional geostress simulation devices still have limitations: hydraulic loading methods struggle to achieve precise three-dimensional independent control; mechanical pressurization methods are prone to stress concentration, making it difficult to accurately reflect the three-dimensional stress state within the rock mass; and while large-scale physical model testing systems can better reproduce geological conditions, they suffer from inherent limitations such as high cost, long cycle time, poor operational flexibility, and difficulty in adapting to test specimens of different sizes. To address these issues, a device capable of simulating a three-dimensional geostress environment with varying temperatures is needed to study the mechanical response of stressed objects to temperature effects within a geostress field. Summary of the Invention

[0004] To overcome the shortcomings of existing technologies, this invention provides a device for simulating triaxial geostress environment using prestressed steel bars that considers thermo-pressure loads.

[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. Through calculation, it superimposes the additional stress caused by temperature changes and the in-situ stress to construct a deep-earth triaxial in-situ stress environment considering thermo-baric loads. This method can solve the problem of temperature affecting stress in existing in-situ stress simulation technologies, and achieve precise application and independent control of triaxial in-situ stress.

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

[0007] 1. A device for simulating a triaxial geostress environment of prestressed steel bars considering thermo-pressure loads, 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 bars, uniformly transferring the stress to the stressed specimen. The prestressing application section consists of steel bars, a tensioning device, anchors, and corrugated pipes. The prestressed steel bars are independently arranged along the specimen in three directions: up / down, left / right, and front / back, achieving independent control of triaxial stress. The tensioning device is used to apply the pre-set prestress using the post-tensioning method, and the anchors are installed at both ends of the steel bars to fix the prestress and prevent stress attenuation. The positioning and reinforcement section consists of a perforated template and a grid of additional steel bars. The template has perforations according to the number and arrangement of the prestressed steel bars for fixing them; the grid of additional steel bars is laid inside the template to prevent local crushing of the concrete during tensioning and to provide secondary fixation for the prestressed steel bars. 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. Calculate the additional stress caused by temperature, superimpose it with the ground stress, and apply stress through post-tensioning of prestressed steel bars to accurately simulate the triaxial ground stress environment after the influence of temperature.

[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 that simulates a triaxial geostress environment considering temperature and pressure loads.

[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 5 This 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 triaxial geostress environment of prestressed steel bars considering thermo-pressure loads: including an overall specimen part, a prestressing application part, a positioning and reinforcement part, and a monitoring and feedback part; wherein: the prestressing application acts on the entire 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 for data monitoring.

[0019] The overall 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 formwork 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] A method for simulating a triaxial geostress environment using prestressed steel bars that considers thermo-pressure loads is as follows:

[0024] (1) After the temperature of the specimen rises, the additional stress generated by the temperature change is calculated based on the linear elastic coefficient and elastic model of the structure, and the original ground stress is superimposed to form a new stress field.

[0025] (2) Based on the superimposed stress field, 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.

[0026] (3) 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.

[0027] (4) 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.

[0028] (5) 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.

[0029] (6) 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.

[0030] (7) 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.

[0031] (8) 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.

[0032] (9) After the grouting and curing are completed, the system is in a triaxial geostress state after considering temperature and pressure loads. The strain recorder collects and monitors the data throughout the test.

[0033] Temperature effects can be applied through temperature stress. For bedrock, the formula for calculating uniaxial temperature stress is as follows:

[0034] σ T =α·E·T (1)

[0035] In the formula, α is the coefficient of thermal expansion, E is the elastic modulus, and T is the temperature change.

[0036] Example: The change in gas and liquid pressure within a cavity can be derived thermodynamically from ΔP. T ;

[0037] Initial axial stress σ under external pressure x0 , σ y0 , σz0 Additional axial stress σ due to temperature rise xT , σ yT , σ zT ;

[0038] Initial internal pressure P0; temperature rise ΔP T ;

[0039] Bedrock temperature stress can be simulated using triaxial prestressing.

[0040] Internal and external pressure difference Δσ 差 =P 内 -σ 外 ;

[0041] △σ x =(P0+△P)-(σ x0 +σ xT (2)

[0042] △σ y =(P0+△P)-(σ y0 +σ yT (3)

[0043] △σ z =(P0+△P)-(σ z0 +σ zT (4)

[0044] For the strength design of the cavity wall, the wall plane stress is calculated as follows: Using Huke's theorem to simulate the cavity wall, the element force is divided into normal direction (Z) and radial direction (X,Y), and the element control stress is the combination of in-plane stress.

[0045]

[0046]

[0047] Considering the simultaneous action of triaxial stress, the stresses of each axis are modified and combined.

[0048]

[0049] In the formula, k1, k2, and k3 are the corrected combination coefficients, which are 1, 0.85, and 0.65, respectively; the cavity design strength f is obtained through formulas 5, 6, 7, and 8.

Claims

1. A device for simulating a three-dimensional stress environment of prestressed steel bars considering temperature and pressure loads, comprising: The test piece main body part, the prestress applying part, the positioning and reinforcing part, the monitoring and feedback part; wherein: the test piece main body part includes the stress test piece and the high-strength concrete outer layer from inside to outside in turn. The prestress applying part is composed of the prestressed reinforcement, the bellows, the tensioning equipment and the anchorage device. The prestressed reinforcement is uniformly arranged along the up and down, left and right, front and back three directions (with the bellows); the tensioning equipment adopts the post-tensioning method to apply the prestress, the anchorage device is installed at the two ends of the prestressed reinforcement and is used for fixing the prestress. The positioning and reinforcing part includes the perforated formwork and the square net additional reinforcement. The formwork is perforated according to the number and arrangement interval of the reinforcement; the square net additional reinforcement is laid in the formwork and is arranged cooperatively with the prestressed reinforcement. The monitoring and feedback part is composed of the resistance strain gauge and the data acquisition instrument. The method for simulating the three-directional ground stress environment of the prestressed reinforcement considering the temperature and pressure load is as follows: (1) after the temperature of the test piece is raised, the additional stress generated by the temperature change is calculated according to the linear elastic coefficient and the elastic model of the structure, the original ground stress is superposed, and a new stress field is formed. (2) according to the superposed stress field, the number, arrangement interval and single tensioning force of the prestressed reinforcement in each direction are calculated, the perforated formwork is designed according to the same, and the perforated position of each surface of the formwork is ensured to be consistent with the position of the arranged reinforcement. The reinforcement square net, the anchor pad, the spiral hoop at the anchor, the fixed end extrusion anchor and the clamping anchor of the tensioning end and other components are prepared. (3) the fixed formwork is installed, the square net additional reinforcement is installed on the inner side of the formwork, the fixed end extrusion anchor, the anchor pad and the spiral hoop are pre-buried, the anchor pad is ensured to be perpendicular to the hole axis, and the tensioning end is pre-buried with the pressure bearing plate and the spiral hoop. (4) the end positioning is performed by using the formwork, the bellows is pre-buried, the bellows joint is sealed tightly, the hole is ensured to be straight, and the prestressed reinforcement is inserted into the hole before the concrete is poured. (5) the stress test piece is placed in the central design position of the formwork framework and is fixed. The resistance strain gauge is pasted on the surface of the stress test piece at the selected position, the lead wire is led out and is connected to the data acquisition instrument, and the monitoring part debugging is completed. (6) the high-strength concrete is poured in layers in the formwork, is vibrated and is compacted, the position of the prestressed reinforcement and the internal test piece is ensured not to be displaced. After the pouring is completed, the standard curing is performed until the concrete reaches the design strength. (7) the lateral formwork is removed. The clamping anchor and the hydraulic tensioning machine are installed at the tensioning end. The post-tensioning method is used to tension the prestressed reinforcement in each direction according to the designed tensioning force value. (8) after the three-directional prestressed reinforcement tensioning and anchoring are completed, the grouting is performed from the grouting hole at the tensioning end. After the exhaust hole flows out the thick grout and there is no air bubble, the exhaust hole is blocked and the pressure is maintained. (9) after the grouting curing is completed, the system is in the three-directional ground stress state considering the temperature and pressure load. The data acquisition and monitoring are performed by the strain recorder during the whole test.

2. The device for simulating three-dimensional stress environment of prestressed reinforcement considering temperature, pressure and load according to claim 1, characterized in that: The anchorage device in the prestress applying system includes the fixed end extrusion anchor, the clamping anchor of the tensioning end, the anchor pad and the spiral hoop under the anchor; wherein, the extrusion anchor is pre-buried in the fixed end of the concrete and provides the counterforce for the tensioning; the clamping anchor is used for tensioning and locking the reinforcement; the anchor pad receives and diffuses the concentrated force; the spiral hoop provides the hoop constraint and prevents the high-strength concrete from splitting.

3. The device of claim 1, wherein the device is a device for simulating a three- dimensional stress environment of prestressed reinforcement considering temperature, pressure and load. The formwork is designed to be perforated according to the requirements and ensures that each reinforcement is fixed along the preset direction and position; the square net additional reinforcement is arranged cooperatively with the reinforcement.

4. The device of claim 1, wherein the device is a device for simulating a three- dimensional stress environment of prestressed reinforcement considering temperature, pressure and load. The post-tensioning method prestress is applied by embedding the steel bar into the corrugated pipe to form a temporary protection function. The prestressed steel bars are independently arranged in the up-down, left-right and front-back directions of the test piece to realize three-way stress control.

5. The device of claim 1, wherein the device is a device for simulating a three- dimensional stress environment of prestressed reinforcement considering temperature, pressure and load, characterized in that: The high-strength concrete bears the pre-compression stress of the prestressed steel bars and uniformly transmits the stress to the stressed test piece.

6. The device of claim 1, wherein the device is a device for simulating a three- dimensional stress environment of prestressed reinforcement considering temperature, pressure and load, characterized in that: The monitoring feedback part includes a resistance strain gauge and a data acquisition instrument to realize the collection of stress and strain data during the test process and verify the temperature additional stress.

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