CN102519790A - Method for determining support pressure on excavation face of slurry shield tunnel - Google Patents

Abstract

The invention relates to a method for determining the reasonable range of support pressure for the excavation face of mud-water shield tunnel construction, which adopts the method of combining test test-numerical simulation calculation-theoretical judgment; samples the tunnel construction soil on site and conducts performance tests. Based on the test data and the specific actual conditions of the tunnel, an analysis model of the excavation face of the mud-water shield tunnel construction that meets the site construction conditions is established and calculated. The principal stress of the soil in front of the excavation face, combined with the Mohr-Coulomb failure criterion of the soil, is used to judge the damage of the soil unit in front of the excavation face, and finally determine the reasonable range of support pressure for the excavation face of the mud-water shield tunnel construction. The method can carry out real-time analysis to determine the reasonable range of the support pressure of the excavation face according to different construction conditions and states while the tunnel construction is advancing, and has the characteristics of wide application, high reliability and convenient application.

Description

Method for Determining Supporting Pressure of Slurry Shield Tunnel Excavation Face

technical field

The invention belongs to the field of shield tunnel engineering construction, in particular to a method for determining the excavation face support pressure of a mud-water shield tunnel, which can determine a reasonable range of the mud-water shield tunnel excavation face support pressure.

Background technique

In tunnel engineering, the shield tunneling method has shown great advantages because it is not affected by the interference of external factors such as seasons and weather conditions, and has the characteristics of fast construction speed, fewer construction personnel, and high construction precision. In particular, the mud-water balance shield construction is suitable for various complex geological environments, and has been widely used in the construction of large and medium-sized tunnels in the world, especially in the tunnel construction of urban underground projects.

During the construction of slurry shield, underground construction will inevitably have an impact on the stratum and surrounding buildings or structures. If the impact is too large, it will cause large deformation of the surrounding soil, and even the subsidence of the stratum and the damage of the surrounding buildings may occur, resulting in major safety accidents. In recent years, in the tunnel construction in Shanghai, Guangzhou, Hangzhou, Shenzhen and other places, due to the complex construction conditions, ground collapse accidents have occurred. Therefore, in order to reduce the impact of mud-water shield construction on the surrounding environment and ensure construction safety, it is necessary to formulate a special construction process plan, set reasonable mud-water shield construction parameters, and strengthen the monitoring of the surrounding environment during construction.

The support pressure of the excavation face is the most important process parameter in the mud-water shield construction process, and it is one of the most important control objectives to control the impact of the mud-water shield tunnel construction on the surrounding environment. During the construction of the mud-water shield tunnel, if the set mud-water support pressure is too small, the soil in front of the excavation face will not be supported and pour into the mud-water tank, causing excessive surface settlement and even subsidence; while the set mud-water If the support pressure is too large, the soil in front of the excavation face will be subjected to a large force, which may cause surface uplift, mud ejection, and even soil splitting and damage. Therefore, determining the reasonable range of support pressure on the excavation face is the key issue in formulating the construction technology plan of mud-water shield and ensuring construction safety.

At present, the method of determining the support pressure of the excavation surface of the mud-water shield is mainly to use the empirical formula for simple calculation. This method has a weak theoretical foundation, and it is impossible to accurately determine the support pressure of the excavation surface, and it cannot guarantee construction safety. There are many factors that affect the support pressure of the mud-water shield excavation surface, including: buried depth of the tunnel, soil conditions, groundwater level, distribution of underground structures, mud-water characteristics, diameter of the mud-water shield, etc., and the geological conditions of different tunnels. The conditions and surrounding environment are different, and the construction status of the tunnel under construction will not be exactly the same as that of the completed tunnel project. Therefore, according to different geological conditions, surrounding environment and construction conditions, it is possible to accurately determine the excavation surface support of mud-water shield construction. A method with a reasonable range of pressure is necessary.

Contents of the invention

In order to achieve the purpose of accurately determining the reasonable range of support pressure for the excavation face of mud-water shield tunnel construction under different geological conditions, surrounding environments and construction conditions, the present invention provides an excavation face unit strength method, which is a comprehensive and comprehensive method. This method adopts the combination of experimental test-numerical simulation calculation-theoretical judgment, and finally determines the support pressure range of the excavation face according to the strength of the soil unit in front of the excavation face.

The technical solution adopted by the present invention to solve its technical problems is:

A method to determine the reasonable range of support pressure for the excavation face of mud-water shield tunnel construction, which adopts the method of combining experimental test-numerical simulation calculation-theoretical judgment; sampling and performing performance tests on the soil of the tunnel construction site, based on test data and According to the specific actual conditions of the tunnel, an analysis model of the excavation face of the mud-water shield tunnel construction that meets the site construction conditions is established and calculated. The principal stress of the soil, combined with the Mohr-Coulomb failure criterion of the soil, is used to judge the damage of the soil unit in front of the excavation face, and finally determine the reasonable range of the support pressure of the excavation face in the mud-water shield tunnel construction; the specific implementation steps of this method are as follows :

(1) Conduct on-site tunnel construction soil performance test, the specific steps are as follows:

1) According to the geological conditions of the site, select the corresponding soil sampling plan for each layer of soil; take 3-4 test blocks for each layer of soil; when soil is taken, disturbance to the soil should be avoided;

2) Place the test block in the shear box, and the gap between the shear box and the sample should be filled with expansive cement mortar;

3) Apply vertical pressure to compress the soil of the test block, and the pressure is divided into 3 to 4 levels in equal amounts and gradually increased until the vertical deformation of the soil of the test block is stable;

4) Apply shear force to shear the soil of the test block. The shear force is loaded equally every 1 minute and the corresponding shear force and shear deformation are recorded; when the shear deformation of the test block soil increases sharply or the shear deformation When it reaches 1/10 of the sample size, it is considered that the soil is destroyed;

以及土体的粘聚力值；  5) Draw the relationship curve between shear strength and vertical pressure, and determine the internal friction angle of each soil layer

and cohesion of the soil value;

(2) Carry out the numerical simulation of the mud-water shield tunnel construction, using the finite element method, and the specific steps are as follows:

1) According to the actual geological conditions and surrounding environment of tunnel construction, establish a nonlinear finite element simulation model for tunnel construction;

2) The elastic-plastic constitutive relation is adopted for the soil, and boundary conditions such as free surface, symmetrical surface and normal displacement constraints are set;

(3) Non-linear finite element numerical simulation calculation is carried out by applying the soil weight of the tunnel construction section and the ground overload force to obtain the initial in-situ stress field of the tunnel construction, so as to determine the original lateral earth pressure of the excavation section of the mud-water shield tunnel construction section;

(4) Set the lateral earth pressure of the original stratum in the excavation section of the mud-water shield tunnel as the excavation surface pressure, apply it as the force boundary condition and perform nonlinear finite element numerical simulation calculation; take the displacement of the center point of the excavation surface as the judgment index, Determine whether the center of the excavation surface has reached the balance of force; through numerical experiments, if the displacement of the center point of the excavation surface is positive, it means that the pressure is too high; otherwise, it means that the pressure is too small; the absolute value of the displacement of the center of the excavation surface is the smallest, approximately zero , determine the equilibrium pressure at the center of the excavation face;

(5) Keep the balance pressure at the center of the excavation face unchanged, and use the top and bottom displacements of the excavation face as judgment indicators to judge whether the overall excavation face has reached the force balance; the pressure of the excavation face is distributed in a trapezoid along the depth direction of the excavation section , presented as a slanted line; through numerical experiments, adjust the slope of the pressure slant line, if the top and bottom displacements of the excavation surface are positive, it means that the pressure is too large; otherwise, it means that the pressure is too small; the top and bottom of the excavation surface When the absolute value of the displacement is the smallest and approximately zero, the equilibrium mud-water pressure on the excavation face is determined;

(6) Apply the determined balance mud-water pressure on the excavation face to obtain the stress state of the soil in front of the excavation face, and determine the principal stress of the soil mass in front of the excavation face;

的函数： (7) Combined with the Mohr-Coulomb strength theory, that is, the shear strength of any plane of the soil, that is, the failure surface is the normal stress on the surface

The function:

为土体的粘聚力，

为土体的内摩擦角，其值由步骤（1）试验中测定； In the formula

is the cohesion of the soil,

is the internal friction angle of the soil, and its value is determined in the test in step (1);

During the construction of mud-water shield tunnels, the method of controlling the pressure at the center point of the excavation surface is usually used to control the stability of the excavation surface, so the pressure ratio is defined as:

为开挖面中心点泥水压力设定值；

为开挖面中心点初始泥水压力值；通过调整

值，改变开挖面压力并进行开挖面前方土体单元破坏情况的判断，确定开挖面支护压力的合理范围。 In the formula

Set value for the muddy water pressure at the center point of the excavation face;

is the initial muddy water pressure value at the center point of the excavation face; by adjusting

value, change the pressure of the excavation face and judge the damage of the soil unit in front of the excavation face to determine the reasonable range of the support pressure of the excavation face.

The beneficial effect of the present invention is that, adopting the method of combining experimental test-numerical simulation calculation-theoretical judgment, according to the different geological conditions, surrounding environment and construction conditions of mud-water shield tunnel construction, through numerical simulation calculation, combined with soil Moore-Coulomb damage Accurately determine the reasonable range of support pressure for the excavation face of mud-water shield tunnel construction. This method gets rid of the problem of determining the support pressure of the excavation surface based on empirical formulas in the past, which leads to high construction risks; in addition, this method can also conduct real-time analysis to determine the The reasonable range of support pressure on the excavation face has the characteristics of wide application, high reliability and convenient application.

Description of drawings

Fig. 1 is the operation flowchart of the inventive method.

Fig. 2 is the construction numerical simulation model diagram of mud-water shield tunnel of the present invention.

Fig. 3 is a schematic diagram of the soil unit in front of the excavation face of the present invention.

Fig. 4 is a diagram of the process from instability to splitting failure of the excavation face of the present invention.

Fig. 5 is a diagram of the process from instability to collapse of the excavation face of the present invention.

Figure 6 shows the range diagram of the support pressure for the excavation face of mud-water shield tunnel construction.

Detailed ways

Below in conjunction with accompanying drawing and embodiment the present invention is further described:

As shown in Figure 1, a method for determining the reasonable range of support pressure for the excavation face of mud-water shield tunnel construction uses a combination of experimental testing-numerical simulation calculation-theoretical judgment. On-site tunnel construction soil samples were taken and performance tests were carried out. Based on the test data and the specific actual conditions of the tunnel, an analysis model of the excavation surface of the mud-water shield tunnel construction in line with the on-site construction conditions was established and calculated. By determining the excavation strata of the tunnel construction section The lateral earth pressure, the center equilibrium pressure of the excavation face, and the principal stress of the soil in front of the excavation face are combined with the Mohr-Coulomb failure criterion of soil to judge the damage of the soil unit in front of the excavation face, and finally determine the construction of the mud-water shield tunnel. Reasonable range of support pressure for the excavation face.

以及土体的粘聚力。具体步骤如下： (1) Carry out on-site tunnel construction soil performance test. In situ direct shear test of the soil was sampled to obtain the internal friction angle of the soil

and cohesion of the soil . Specific steps are as follows:

1) According to the geological conditions of the site, select the corresponding soil borrowing scheme for each layer of soil. Take 3-4 test blocks for each layer of soil. When taking soil, it is necessary to avoid disturbing the soil.

2) Place the test block in the shear box, and the gap between the shear box and the sample should be filled with expansive cement mortar.

3) Apply vertical pressure to compress the soil of the test block, and the pressure is divided into 3 to 4 levels in equal amounts and gradually increased until the vertical deformation of the soil of the test block is stable.

4) Apply shear force to shear the soil mass of the test block. The shear force is loaded equally every 1 minute and the corresponding shear force and shear deformation are recorded. When the shear deformation of the test block soil increases sharply or the shear deformation reaches 1/10 of the sample size, the soil is considered to be damaged.

以及土体的粘聚力值。  5) Draw the relationship curve between shear strength and vertical pressure, and determine the internal friction angle of each soil layer

and cohesion of the soil value.

(2) The numerical simulation method of mud-water shield tunnel construction is the finite element method, and its specific steps are as follows:

1) According to the actual geological conditions and surrounding environment of tunnel construction, a nonlinear finite element simulation model of tunnel construction is established. In this example model, the excavation diameter of the tunnel is 11.22m; the buried depth of the tunnel is 9.59m, the axial (Y direction) length of the tunnel is 75 m, the horizontal (X direction) width is 50 m, and the vertical (Z direction) depth is 60 m.

2) The elastic-plastic constitutive relation is adopted for the soil, and boundary conditions such as free surface, symmetrical surface and normal displacement constraints are set, as shown in Fig. 2.

(3) Non-linear finite element numerical simulation calculation is carried out by applying the soil weight and ground overload force in the tunnel construction section to obtain the initial in-situ stress field of the tunnel construction, so as to determine the original lateral soil pressure of the excavation section of the mud-water shield tunnel construction section.

The finite element simulation of the tunnel construction is carried out, and the nonlinear finite element solution equation is established according to the nonlinearity of the soil as

                               

                               

为整体刚度矩阵，它是单元节点位移

的函数，为位移矩阵， 

为土体自重，

为地面超载作用力。 in,

is the overall stiffness matrix, which is the element nodal displacement

The function, is the displacement matrix,

is the weight of the soil,

is the ground overload force.

(4) Set the lateral earth pressure of the original formation in the excavation section of the mud-water shield tunnel as the excavation surface pressure, apply it as the force boundary condition, and perform nonlinear finite element numerical simulation calculation. Taking the displacement of the center point of the excavation face as the judgment index, it is judged whether the center of the excavation face has reached the force balance. Through numerical experiments, if the displacement of the center point of the excavation surface is positive, it means that the pressure is too high; otherwise, it means that the pressure is too small. When the absolute value of the center displacement of the excavation face is the smallest and approximately zero, the equilibrium pressure at the center of the excavation face is determined.

(5) Keep the balance pressure at the center of the excavation face unchanged, and use the top and bottom displacements of the excavation face as judgment indicators to judge whether the overall excavation face has reached a force balance. The pressure on the excavation surface is distributed in trapezoidal shape along the depth direction of the excavation section, presenting as a slanted line. Through numerical experiments, the slope of the pressure slope is adjusted. If the top and bottom displacements of the excavation surface are positive, it means that the pressure is too large; otherwise, it means that the pressure is too small. When the absolute values of the top and bottom displacements of the excavation face are the smallest and approximately zero, the equilibrium mud-water pressure of the excavation face is determined.

(6) Apply the determined balance mud-water pressure on the excavation face to obtain the stress state of the soil in front of the excavation face, and determine the unit principal stress of the soil in front of the excavation face by conversion according to the following formula.

                       

                       

,

为三个主应力，

，

，

，

。其中

为三个应力不变量。如图3所示。 In the formula ,

,

are the three principal stresses,

,

,

,

. in

are three stress invariants. As shown in Figure 3.

是该面上法向应力

的函数： (7) Combined with the Mohr-Coulomb strength theory, that is, the shear strength on any plane (failure plane) of the soil

is the normal stress on the surface

The function:

                           

                           

为土体的粘聚力，

为土体的内摩擦角，其值由步骤（1）试验中测定。 In the formula

is the cohesion of the soil,

is the internal friction angle of the soil, and its value is determined in the test in step (1).

When the principal stress of the soil is known, the Mohr circle of the soil cuts the failure envelope, that is

                       

                    

The soil is in a state of destruction.

During the construction of mud-water shield tunnels, the method of controlling the pressure at the center point of the excavation surface is usually used to control the stability of the excavation surface, so the pressure ratio is defined as:

                                     

                                     

为开挖面中心点泥水压力设定值；

为开挖面中心点初始泥水压力值。进行开挖面前方土体单元破坏情况的判断，确定开挖面支护压力的合理范围。 In the formula

Set value for the muddy water pressure at the center point of the excavation face;

is the initial mud-water pressure value at the center point of the excavation face. Judgment of the damage of the soil unit in front of the excavation face is carried out to determine the reasonable range of the support pressure of the excavation face.

调整开挖面压力进行计算，将压力比

由1以0.01的增量逐步增大，开挖面泥水压力也将逐步增大，相应的开挖面土体将出现变形、失稳，失稳加剧直至劈裂破坏的过程，如图4所示。在不同压力比

下，确定开挖面前方土体单元主应力，结合莫尔-库仑破坏准则对开挖面前方的土体单元进行破坏判定。本实例中，当

=1.00时，开挖面处于初始状态，开挖面中心点泥水压力为初始泥水压力值，如图4(a)所示；增大

值，当

=1.40时，开挖面前方土体单元主应力符合莫尔-库仑破坏准则，开挖面开始失稳，此时的开挖面压力即为开挖面支护压力的上限值，如图4(b)所示；继续增大

值，开挖面失稳的土体单元逐渐增多，破坏逐步发展，当=2.50时的破坏发展状况如图4(c)所示；继续增大

值，当=3.50时，开挖面前方土体单元出现破坏滑移面，呈现劈裂破坏，如图4(d)所示。 By changing

Adjust the excavation face pressure to calculate, the pressure ratio

Gradually increasing from 1 to 0.01 increments, the mud-water pressure on the excavation surface will also gradually increase, and the corresponding excavation surface soil will be deformed and unstable, and the instability will intensify until the process of splitting and failure, as shown in Figure 4 Show. at different pressure ratios

Next, determine the principal stress of the soil unit in front of the excavation face, and combine the Mohr-Coulomb failure criterion to judge the failure of the soil unit in front of the excavation face. In this example, when

=1.00, the excavation face is in the initial state, and the mud-water pressure at the center point of the excavation face is the initial mud-water pressure value, as shown in Figure 4(a); increasing

value when

=1.40, the principal stress of the soil unit in front of the excavation face conforms to the Mohr-Coulomb failure criterion, and the excavation face begins to lose stability. 4(b); continue to increase

value, the unstable soil units of the excavation face gradually increase, and the damage develops gradually. =2.50, the damage development status is shown in Fig. 4(c); continue to increase

value when =3.50, the soil unit in front of the excavation face has a failure slip surface, showing splitting failure, as shown in Figure 4(d).

由1逐步减小，直至相应土体发生坍塌破坏，如图5所示。通过判定可确定开挖面支护压力的下限值。本实例中，当

=1.00时，开挖面处于初始状态，开挖面中心点泥水压力为初始泥水压力值，如图5(a)所示；减小

值，当

=0.78时，开挖面开始失稳，此时的开挖面压力即为开挖面支护压力的下限值，如图5(b)所示；继续减小

值，开挖面失稳的土体单元逐渐增多，破坏逐步发展，当=0.50时的破坏发展状况如图5(c)所示；继续减小

值，当

=0.10时，开挖面前方土体单元出现破坏滑移面，呈现坍塌破坏，如图5(d)所示。 Similarly, the pressure ratio

Decrease gradually from 1 until the corresponding soil collapses and fails, as shown in Figure 5. The lower limit of the support pressure of the excavation face can be determined by judging. In this example, when

=1.00, the excavation face is in the initial state, and the mud-water pressure at the center point of the excavation face is the initial mud-water pressure value, as shown in Figure 5(a);

value when

=0.78, the excavation surface begins to lose stability, and the pressure on the excavation surface at this time is the lower limit of the support pressure on the excavation surface, as shown in Figure 5(b); continue to decrease

value, the unstable soil units of the excavation face gradually increase, and the damage develops gradually. =0.50, the damage development status is shown in Fig. 5(c); continue to decrease

value when

=0.10, the soil unit in front of the excavation face has a failure slip surface, showing collapse failure, as shown in Figure 5(d).

Finally, the reasonable range of support pressure for the excavation face of mud-water shield tunnel construction was determined, as shown in Figure 6.

Claims (1)

1. A method for determining the reasonable range of support pressure for the excavation face of mud-water shield tunnel construction, which is characterized in that it adopts the method of combining experimental testing-numerical simulation calculation-theoretical judgment; sampling the tunnel construction soil on site and performing performance Test, based on the test data and the specific actual conditions of the tunnel, establish an analysis model of the excavation face of the mud-water shield tunnel construction that meets the site construction conditions and perform calculations. By determining the lateral soil pressure of the excavation stratum in the tunnel construction section and the center balance of the excavation face Pressure and principal stress of the soil in front of the excavation face, combined with the Mohr-Coulomb failure criterion of the soil to judge the damage of the soil unit in front of the excavation face, and finally determine the reasonable range of support pressure for the excavation face of the mud-water shield tunnel construction; The concrete implementation steps of this method are as follows: (1) Conduct on-site tunnel construction soil performance test, the specific steps are as follows: 1) According to the geological conditions of the site, select the corresponding soil sampling plan for each layer of soil; take 3-4 test blocks for each layer of soil; when soil is taken, disturbance to the soil should be avoided; 2) Place the test block in the shear box, and the gap between the shear box and the sample should be filled with expansive cement mortar; 3) Apply vertical pressure to compress the soil of the test block, and the pressure is divided into 3 to 4 levels in equal amounts and gradually increased until the vertical deformation of the soil of the test block is stable; 4) Apply shear force to shear the soil of the test block. The shear force is loaded equally every 1 minute and the corresponding shear force and shear deformation are recorded; when the shear deformation of the test block soil increases sharply or the shear deformation When it reaches 1/10 of the sample size, it is considered that the soil is destroyed; 5) Draw the relationship curve between shear strength and vertical pressure, and determine the internal friction angle of each soil layer and cohesion of the soil

value; (2) Carry out the numerical simulation of the mud-water shield tunnel construction, using the finite element method, and the specific steps are as follows: 1) According to the actual geological conditions and surrounding environment of tunnel construction, establish a nonlinear finite element simulation model for tunnel construction; 2) The elastic-plastic constitutive relation is adopted for the soil, and boundary conditions such as free surface, symmetrical surface and normal displacement constraints are set; (3) Non-linear finite element numerical simulation calculation is carried out by applying the soil weight of the tunnel construction section and the ground overload force to obtain the initial in-situ stress field of the tunnel construction, so as to determine the original lateral earth pressure of the excavation section of the mud-water shield tunnel construction section; (4) Set the lateral earth pressure of the original stratum in the excavation section of the mud-water shield tunnel as the excavation surface pressure, apply it as the force boundary condition and perform nonlinear finite element numerical simulation calculation; take the displacement of the center point of the excavation surface as the judgment index, Determine whether the center of the excavation surface has reached the balance of force; through numerical experiments, if the displacement of the center point of the excavation surface is positive, it means that the pressure is too high; otherwise, it means that the pressure is too small; the absolute value of the displacement of the center of the excavation surface is the smallest, approximately zero , determine the equilibrium pressure at the center of the excavation face; (5) Keep the balance pressure at the center of the excavation face unchanged, and use the top and bottom displacements of the excavation face as judgment indicators to judge whether the overall excavation face has reached the force balance; the pressure of the excavation face is distributed in a trapezoid along the depth direction of the excavation section , presented as a slanted line; through numerical experiments, adjust the slope of the pressure slant line, if the top and bottom displacements of the excavation surface are positive, it means that the pressure is too large; otherwise, it means that the pressure is too small; the top and bottom of the excavation surface When the absolute value of the displacement is the smallest and approximately zero, the equilibrium mud-water pressure on the excavation face is determined; (6) Apply the determined balance mud-water pressure on the excavation face to obtain the stress state of the soil in front of the excavation face, and determine the principal stress of the soil mass in front of the excavation face; (7) Combined with the Mohr-Coulomb strength theory, that is, the shear strength of any plane of the soil, that is, the failure surface

is the normal stress on the surface

The function: In the formula

is the cohesion of the soil,

is the internal friction angle of the soil, and its value is determined in the test in step (1); During the construction of mud-water shield tunnels, the method of controlling the pressure at the center point of the excavation surface is usually used to control the stability of the excavation surface, so the pressure ratio is defined as: In the formula

Set value for the muddy water pressure at the center point of the excavation face;

is the initial muddy water pressure value at the center point of the excavation face; by adjusting

value, change the pressure of the excavation face and judge the damage of the soil unit in front of the excavation face to determine the reasonable range of the support pressure of the excavation face.

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