CN103953349A - Test method for tunnel model with duct piece connectors with rigidity in controllable changes - Google Patents

Abstract

A tunnel model test method with controllable variation of segment joint stiffness, the method is: A, model making: pre-embed electromagnet (2) at the joint end of model tunnel segment (1); B, instrument layout and initialization: Strain gauges (3) or displacement gauges are arranged on the side of the joint end of the model tunnel segment (1); the initial current is passed to the electromagnet (2), so that the magnetic force of the electromagnet simulates the initial stiffness of the joint; C, loading Test: Calculate the corresponding electromagnet current calculation value according to the load and measured displacement value of each stage, change the current value of the electromagnet when the next stage is loaded into the current calculation value, and simulate the segments of each stage The stiffness of the joint. When this method is tested, the stiffness of the segment joint will change with the change of the load, which is more in line with the mechanical behavior of the tunnel segment joint in the actual project. Provide accurate and reliable test basis.

Description

A Tunnel Model Test Method with Controllable Variation of Segment Joint Stiffness

technical field

The invention relates to a tunnel model test method with controllable variation of segment joint stiffness.

Background technique

In tunnel engineering, the actual engineering and structural prototypes are generally large and complex, and their mechanical properties and stress mechanism cannot be obtained through direct research on the structure. Instead, model tests must be used, that is, with the help of models, tests are carried out according to the similarity principle and similarity criterion, so as to obtain various data and performance of the structure, and provide test basis for the design and construction of the tunnel. Shield tunnels are spliced by segments, and there are joints between the segments. There are many ways to connect the segment joints, such as bolted joints, joints without connectors, plug-in joints, and pin-insert joints. Due to its structural characteristics, the role of segment joints in the entire structure is very important. Whether it is from the macroscopic calculation model or the microscopic structure of segment joints, the structural shape, deformation and stress state of segment joints have important Typical non-linear features. The changes in mechanical properties such as stiffness at the segment joints will have an important impact on the contact relationship at the joints and the load on the overall structure, especially when the load reaches the critical state of structural instability, it will affect the overall stress state and deformation of the tunnel structure. have a very large impact. Therefore, in the test, the change of the mechanical properties of the segment joint should be considered to truly reflect the actual working conditions.

At present, there are two methods for simulating the stiffness of segment joints in tunnel model tests:

The first type of method is to use screws + thin plastic sheets (PE sheets) to simulate the joints of models made of synthetic materials such as polyethylene pipes (PE pipes) after calculating the similarity ratio. The material used in this method differs greatly from the mechanical properties of concrete. The method of fixing with screws + PE sheets is not the actual joint connection method. The screw holes also weaken the rigidity of the overall structure and cause stress concentration. Although the arrangement of the joints can be Adjustment, but its stress mechanism is different from the actual one, and cannot truly reflect the mechanical properties of the joint.

The second type of method is to use the model made of gypsum and other cementitious materials to cut grooves and weaken the section in the tension area of the tunnel lining structure, and determine the required opening depth of each joint corresponding to the specific load condition through calculation. Cut grooves of corresponding depth. However, since the depth of the cutting groove cannot be changed with the load and other factors in the test, it cannot truly reflect the change of the mechanical properties of the segment joint during tunnel excavation and operation.

However, the stiffness of segment joints in actual engineering changes with changes in the external environment such as loads. Therefore, the simulation of joint stiffness in the above method can only be aimed at a specific stress state of segment joints. The mechanical properties such as stiffness cannot be changed with other factors such as load during the test, which is inconsistent with the mechanical behavior of the tunnel joint in the actual project, resulting in large errors and low reliability in the test results of these model test methods, which cannot be used for the design of tunnel projects. , Construction and maintenance provide accurate and reliable test basis. At the same time, due to the fixed stiffness of segment joints, the existing joint simulation methods cannot study the influence of segment joint stiffness on the overall deformation and stress state of the tunnel structure.

Contents of the invention

The purpose of the present invention is to provide a tunnel model test method in which the rigidity of segment joints can be controlled and changed. In the tunnel model test process, the stiffness of segment joints will change accordingly with the change of load, which is more in line with the tunnel pipe in actual engineering. The mechanical behavior of the sheet joint, so that the test data are more accurate and reliable, and can provide accurate and reliable test basis for the design, construction and maintenance of tunnel engineering.

The technical solution adopted by the present invention to solve the technical problem is a tunnel model test method with controllable variation of segment joint rigidity, and its method is:

A. Make a model to make a separate model tunnel segment, and pre-embed an electromagnet at the joint end of the model tunnel segment, and use a mold to assemble the model tunnel segment into a model tunnel;

B. Instrument layout and initialization Arrange strain gauges or displacement gauges on the side of the joint end of the model tunnel segment; pass the set initial current to the electromagnet, so that the magnetic force of the electromagnet simulates the initial stiffness of the joint between the segments;

C. Loading test

Load the model tunnel step by step; after each stage of loading, calculate the internal force of the segment joint end of the model tunnel according to the loaded load and the strain value or displacement measured by the strain gauge or displacement measurement, and obtain the corresponding stiffness of the segment joint at this stage The current value of the electromagnet at this stage; then pass the current value of this stage to the electromagnet through the power supply to simulate the stiffness of the model tunnel segment joint at this stage, and then carry out the next stage of loading until the set value is loaded Series or shield tunnel model destruction.

Compared with prior art, the beneficial effect of the present invention is:

1. Change the rigidity of the tunnel structure joints in the existing test from being fixed to changing with the change of the load, that is, calculate the corresponding electromagnet current calculation value according to the load and the measured displacement value of each stage, and pass the electromagnet The current value in is changed to the current calculation value, and the stiffness of the segment joint at this stage is simulated. In this way, the nonlinear change of the stiffness of the tunnel lining structure joint in the actual project can be simulated more accurately and realistically, which is more in line with the mechanical behavior of the tunnel joint in the actual project, so that the test data is more accurate and reliable, and can be used for the design and construction of the tunnel project. Provide accurate and reliable test basis for maintenance and maintenance.

2. The method of the present invention can quantitatively control the stiffness of the joint through equivalent calculation results, so that the mechanical behavior and failure form of the segment joint under different external conditions can be obtained through experiments, and the stiffness of the corresponding segment can also be obtained through experiments. Under the joint stiffness condition, the mechanical behavior and failure form of the entire tunnel structure under other external conditions are convenient for studying the influence of the tunnel structure joint stiffness on the deformation and stress state of the overall structure.

The electromagnets pre-embedded at the joint end of the above-mentioned model tunnel segment are multi-layered, and there are multiple electromagnets in each layer.

Using multiple multi-layer electromagnets to control the stiffness of the segment joints can better simulate the different stress conditions of each part of the segment joints in the actual tunnel, so as to better reflect the real working conditions of the segment joints in the test.

The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

Description of drawings

Fig. 1 is a schematic structural diagram of a simulated segment joint according to an embodiment of the present invention.

Figure 2 is a schematic diagram of the stress state of the actual segment joint.

Fig. 3 is a schematic diagram of a stressed state of a simulated segment joint according to an embodiment of the present invention.

Fig. 4 is a mechanical characteristic curve of the simulated segment joint of the embodiment of the present invention.

Detailed ways

Example

Fig. 1 shows, a kind of specific embodiment of the present invention is, a kind of tunnel model test method of segment joint rigidity controllable variation, and its practice is:

A. Make a model Make a separate model tunnel segment 1, and pre-embed an electromagnet 2 at the joint end of the model tunnel segment 1, and use a mold to align the model tunnel segment 1 into a model tunnel;

B. Instrument layout and initialization Arrange strain gauges 3 or displacement gauges on the side of the joint end of the model tunnel segment 1; pass a set initial current to the electromagnet 2, so that the magnetic force of the electromagnet simulates the initial stiffness of the joint between the segments;

C. Loading test

Load the model tunnel step by step; after each stage of loading, calculate the internal force at the joint end of the model tunnel segment 1 according to the loaded load and the strain value or displacement measured by the strain gauge 3 or the displacement measurement, and obtain the corresponding segment joint at this stage The current value of the current stage of the electromagnet 2 of the stiffness; then the current value of the current value of the stage is passed to the electromagnet 2 through the power supply to simulate the stiffness of the joint of the model tunnel segment 1 at this stage, and then the next stage of loading is carried out. Until the set number of stages is loaded or the shield tunnel model is destroyed.

The electromagnet 2 embedded in the joint end of the model tunnel segment 1 of this example is multi-layer, and there are multiple electromagnets 2 in each layer.

The calculation method of the corresponding current value of simulating segment joint stiffness in the present invention is as follows:

According to the actual stress state of the segment joint, as shown in Figure 2, the bending stiffness of the segment joint is defined as:

$K_{\mathrm{\θ}}=\frac{m}{\mathrm{\θ}}$ ①

① In the formula, θ is the opening angle of the joint, which is measured by the test equipment; M is the force couple acting on the joint.

Due to the complex force at the joint, multiple rows of electromagnets were used to simulate in the test, and its force state is shown in Figure 3, then:

M＝∑F _i h _i ②

② In the formula, h _i is the distance from each row of electromagnets to the resultant force point in the pressure zone; F _i is the suction force of each row of electromagnets, which is controlled by current, and its calculation formula is calculated and determined according to the following empirical formula:

$f=\frac{{\left(\mathrm{NI}\right)}^2{\mathrm{\μ}}_{0}S}{2K_f^2{\mathrm{\δ}}^2}$ ③

③In the formula, N is the number of coil turns of the electromagnet, I is the electric current of the electromagnet, and μ ₀ is the air permeability coefficient, which is taken as 1.25× ^10-8 H/cm during calculation; S is the total surface area of the magnetic pole; K _f is The flux leakage coefficient varies according to the electromagnet used, and is generally approximately 3.5-4, which can be determined by the suction test of the electromagnet; δ is the length of the air gap, which is determined by the parameters of the electromagnet.

The required electromagnet attraction force F _i is determined according to the mechanical characteristic curve F=f(M _i , N _i ) of the existing segment joint and scaled according to the similarity principle, as shown in Fig. 4 .

It can be seen from the above that the relationship between the equivalent stiffness of the joint and the current of the electromagnet can be obtained by combining the formulas ①, ②, and ③. According to this principle and the internal force and deformation measured in real time in the test, the electromagnet can be obtained. The current that needs to be supplied.

Claims (2)

1. A tunnel model test method with controllable variation of segment joint stiffness, the method is: A. Make a model Making separated model tunnel segments (1), pre-embedding electromagnets (2) at joint ends of the model tunnel segments (1), and aligning the model tunnel segments (1) with molds to form a model tunnel; B. Instrument layout and initialization Strain gauges (3) or displacement gauges are arranged on the side of the joint end of the model tunnel segment (1); a set initial current is passed to the electromagnet (2), so that the magnetic force of the electromagnet simulates the initial stiffness of the joint between segments; C. Loading test Load the model tunnel step by step; after each stage of loading, calculate the internal force of the joint end of the model tunnel segment (1) according to the loaded load and the strain value or displacement measured by the strain gauge (3) or displacement measurement, and obtain the corresponding The current value of the electromagnet (2) of the stiffness of the segment joint; then pass the current value of the current value to the electromagnet (2) through the power supply to simulate the model tunnel segment (1) joint at this stage. Stiffness, and then proceed to the next level of loading until the set number of levels is loaded or the shield tunnel model is destroyed. 2. the tunnel model test method of a kind of segment joint stiffness controllable variation according to claim 1, is characterized in that: the electromagnet (2) embedded in the joint end of described model tunnel segment (1) is There are multiple layers, and there are multiple electromagnets (2) in each layer.