Method for predicting jacking force in whole construction process of vertical jacking method

Abstract

The present invention provides a method for predicting a jacking force in the whole construction process of a vertical jacking method. Two jacking force calculation models are provided on the basis of a spherical hole expansion theory and a shear failure principle, i.e., a spherical hole expansion-sliding friction model and a shear failure-sliding friction model, and the corresponding calculation formulas are deduced. When an overlying soil layer is high, and the jacking force calculated by using the spherical hole expansion-sliding friction model is small, a spherical hole expansion problem is regarded at a pipe cover of a vertical pipe; when the overlying soil layer is low, and the jacking force calculated by using the shear failure-sliding friction model is small, the form of the soil body failure at the pipe cover of the vertical pipe is shear failure. According to the present invention, the influence of the dynamic change in the thickness of the overlying soil on the head-on resistance is considered, a more objective and comprehensive theoretical basis is achieved, and the jacking force in the whole construction process of the vertical jacking method can be estimated more accurately.

Description

A method for predicting lifting force during the entire vertical lifting construction process Technical Field

[0001] The invention belongs to the technical field of underground tunnel engineering and relates to a method for predicting jacking force during the entire construction process of a vertical jacking method. Background Art

[0002] With the rapid growth of my country's economy, the number of drainage projects for large-scale thermal power plants and nuclear power plants in coastal areas has also increased. In addition, the construction of underground projects such as urban pipeline corridors often encounters many construction problems such as ventilation and maintenance shafts. In this context, the vertical jacking method is widely used due to its advantages such as short construction period, small impact on the environment and high efficiency.

[0003] Determining the lifting force, particularly the maximum lifting force, is crucial in vertical jacking construction. This not only impacts the feasibility of the lift and the stability of the horizontal tunnel, but also involves the design of the lifting pipe segments, the reinforcement of the tunnel bottom, and the need for drag reduction measures such as upper soil excavation. Excessive lifting force can cause deformation and cracking of the jacking riser and instability of the horizontal tunnel. Excessively low lifting force can render the lift impossible. Therefore, systematic research on the lifting force of vertical jacking is necessary. However, limited research exists on the calculation of lifting force and its dynamic behavior.

[0004] The research on vertical jacking method at home and abroad mostly focuses on its construction technology and water-stopping measures. The calculation of jacking force is mainly based on experience and is not theoretical. There are two main ways to calculate jacking force. One is proposed by Wang Shousheng et al., which assumes that the top of the shear failure line is 1.2D~1.5D (D is the outer diameter of the riser). The jacking force is composed of five parts: water weight, soil weight inside the failure line, self-weight of the jacking pipe, shear force between the pipe and soil, and friction during the jacking process; the other is the Shanghai Pipe Jacking Engineering Construction Specifications. [2] The recommended empirical algorithm provides a formula for calculating the maximum lifting force, assuming that the lifting force is greatest when the first pipe section is lifted. The groundbreaking force is considered the largest component affecting the lifting force, and empirical values ​​are given for sand and clay, respectively. The shortcomings of the above method are:

[0005] 1) In actual engineering cases, the maximum lifting force does not occur at the initial jacking, but generally occurs during the jacking process;

[0006] 2) It is not specified whether the value used in Wang Shousheng's algorithm is 1.2 or 1.5;

[0007] 3) Most of the values ​​are based on experience and are slightly lacking in theoretical basis.

[0008] In the vertical jacking method, the vertical pipe is continuously lifted upward, and the soil's resistance to it is constantly changing, so the lifting force is dynamic. Therefore, based on the construction characteristics, it is necessary to consider the changes in the thickness of the overburden. Therefore, a new method for predicting the lifting force during the entire vertical jacking construction process is proposed.

[0009] Summary of the Invention

[0010] The purpose of the present invention is to address the shortcomings of the existing technology and provide a method for predicting the lifting force of the entire vertical jacking construction process, which can more accurately and dynamically estimate the lifting force required during construction. To this end, the present invention adopts the following technical solutions

[0011] A method for predicting the lifting force during the entire vertical lifting construction process, characterized by comprising the following steps:

[0012] Step 1: Determine the components of the lifting force in vertical jacking construction.

[0013] The lifting force F of the vertical lifting method is matched according to three parts, namely, the head-on resistance F y , Friction force between pipe and soil F f Weight of pipe G p ; The head-on resistance F y is the sum of the forces acting on the riser cover; that is, F = F yb +F f +G p ;

[0014] Step 2: Select the force model during the riser lifting process and calculate the head-on resistance F y ,

[0015] According to the thickness of the overburden, the force of the head-on resistance is divided into two force models, namely the spherical hole expansion-sliding friction model and the shear failure-sliding friction model. When the overburden is high, there is F yb <F ys When the riser cover is considered as a spherical hole expansion problem, When the overlying soil layer is low, there is F ys <F yb When the soil failure mode at the riser cover is shear failure, then F y =F ys =G s +G w +F cf , where G s is the weight of soil within the shear failure line (kN), G s =γ′πh[R d 2 +R m 2 +R d Rm ] / 3, G w is the weight of water within the riser range (kN), F cf is the resistance caused by soil cohesion within the shear breaking line (kN), F yb is the head-on resistance under the spherical hole expansion-sliding friction model (kN), F ys is the head-on resistance under the shear failure-sliding friction model (kN), P u is the ultimate expansion pressure (kPa), R d is the riser radius (m), γ' is the effective weight of the soil (kN·m -3 ), h is the height of the riser cover from the mud surface (m), R m is the distance between the shear failure line and the mud surface line and the center of the riser (m), γ w is the weight of water (kN·m -3 ), H is the height of the upper side of the horizontal tunnel from the mud surface line (m), and c is the cohesion (kPa).

[0016] Step 3: According to the calculated F=F y +F f +G p , calculate the lifting force.

[0017] Furthermore, the friction force F between pipe and soil f The value of is calculated according to the following formula: f =μKπDL 2 [γ′h+γ w h w +γ w (H+h) / 2]. μ is the friction coefficient between pipe and soil, K is the lateral earth pressure coefficient, and D is the outer diameter of the riser (m).

[0018] Furthermore, the pipe weight G p The value of G is calculated according to the following formula: p =nG′, n is the number of pipe sections that have been lifted, and G′ is the average deadweight of the pipe sections (kN).

[0019] The present invention takes into account the influence of the dynamic change of the overburden thickness on the head-on resistance, has a more objective and comprehensive theoretical basis, and can more accurately estimate the jacking force of the entire construction process of the vertical jacking method. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is the force diagram of the riser during vertical jacking construction.

[0021] Figure 2 is a schematic diagram of the force on the spherical hole expansion-sliding friction riser.

[0022] Figure 3 is a schematic diagram of the shear failure line-sliding friction riser force.

[0023] Figure 4 is a schematic diagram of the basic problem of spherical hole expansion.

[0024] Figure 5 is a flowchart for solving the lifting force.

[0025] Figure 6 is a comparison of the first set of riser jacking force results.

[0026] Figure 7 is a comparison of the second set of riser lifting force results. DETAILED DESCRIPTION

[0027] The following describes in detail a method for calculating the lifting force of the entire vertical jacking construction process provided by the present invention in combination with the logical reasoning process in the research.

[0028] Step 1: Determine the components of the lifting force in vertical jacking construction

[0029] During the construction of vertical jacking method, it is necessary to overcome the resistance of the upper layers in order to successfully push out the riser. Similar to the force analysis in the horizontal pipe jacking construction project, the lifting force of the vertical jacking method is matched with three parts (see Figure 1). The riser is mainly subjected to: ① head resistance F y ② Friction force between pipe and soil F f ; ③ Tube deadweight G p The head-on resistance is the sum of the forces acting on the riser cover, and is also the focus of this invention.

[0030] Step 2: Establish the force model during the riser jacking process

[0031] Based on construction characteristics, the force mechanism of head-on resistance is related to the height of the overburden. When the overburden is high, the vertical lifting process can be considered a spherical hole expansion problem; when the overburden is shallow, the soil failure form is shear failure. Based on this, two lifting force calculation models are proposed. When the overburden is above the threshold, the vertical lifting process can be considered a spherical hole expansion problem, using the spherical hole expansion-sliding friction model (see Figure 2); when the overburden is below the threshold, the soil failure form is shear failure, using the shear failure-sliding friction model (see Figure 3). The following assumptions are made for these two models:

[0032] (1) The spherical hole expansion-sliding friction model assumes that the initial radius is 0 and the final hole expansion radius is the riser radius; the shear failure-sliding friction model assumes that the angle between the failure line and the vertical direction is (2) When the jacking force calculated by the spherical hole expansion-sliding friction model is less than the jacking force calculated by the shear failure-sliding friction model, spherical hole expansion yielding occurs during vertical jacking, otherwise only shear failure occurs; (3) During the initial jacking, the initial value of the head-on resistance is the water and soil pressure within the riser range. During the jacking process from the initial jacking to the maximum head-on resistance, the head-on resistance changes linearly with the jacking distance, and the position of the maximum head-on resistance occurs at the compression amount of the overlying soil layer; (4) The contact between the riser and the soil is "full contact", that is, the contact between the pipe and the soil is sufficient.

[0033] Step 3: Establish calculation formulas for each component of lifting force

[0034] (1) Heading resistance F of spherical hole expansion-sliding friction model yb

[0035] The basic problem of spherical hole expansion is shown in Figure 4. The equilibrium equation, geometric equation, and physical equation are as follows:

[0036] dσ r / dr+2(σ r -σ θ )r=0 (1)

[0037]

[0038]

[0039] Where: σ r , σ θ are radial and tangential stresses, respectively, u r is the radial displacement, ν is the Poisson's ratio, and E is the elastic modulus;

[0040] According to the boundary conditions:

[0041]

[0042] Where: R p is the plastic zone radius, R u is the final hole expansion radius, which is D / 2 here, σ p is the critical pore expansion pressure, P0 is the initial pore pressure, P u is the ultimate hole expansion pressure;

[0043] The stress and displacement solutions of the elastic zone soil can be solved:

[0044]

[0045] Where: G is the shear modulus.

[0046] The soil yield obeys the Mohr-Coulomb strength yield criterion, then:

[0047]

[0048] Where: c is the cohesion, is the internal friction angle;

[0049] Combined with the boundary conditions, we have:

[0050]

[0051] At the elastic-plastic stress boundary, the soil will satisfy both the elastic zone boundary conditions and the plastic zone boundary conditions. The stress expression at the elastic-plastic boundary can be obtained as follows:

[0052]

[0053] When r=R u When , combining equations (7) and (8), we have:

[0054]

[0055] Where: λ = R p / R u .

[0056] Circumferential strain ε at the elastic-plastic boundary θp , radial displacement u rp It can be expressed as:

[0057]

[0058]

[0059] For plastic deformation, Carter [3] It is deduced that the radial displacement of the plastic zone can be expressed as:

[0060]

[0061] T=1-A+B (13)

[0062]

[0063]

[0064]

[0065]

[0066]

[0067]

[0068]

[0069]

[0070] Where: ψ is the dilatancy angle, α, β, A, B, T, Z, S, M, and N are all dimensionless intermediate parameters.

[0071] In order to solve the plastic zone radius, the plastic zone volume strain Δ is introduced:

[0072]

[0073] Combining equations (2) and (12), we have:

[0074]

[0075] It is the ratio of the volume change of the plastic zone to the total volume of the plastic zone. Before and after hole expansion, according to the law of volume conservation:

[0076] R u 3 -R0 3 =R p 3 -(R p -u rp ) 3 +Δ(R p 3 -R u 3 ) (twenty four)

[0077] Expand Ignore rp High-order terms, and substituting formula (11) into:

[0078]

[0079] At this point, the radius of the plastic zone can be solved. The specific solution process is as follows:

[0080] 1) According to the soil parameters measured by experiment, determine the various parameters c, The values ​​of ψ, ν, E, and G;

[0081] 2) Determine the dimensionless intermediate parameters α, β, A, B, T, and S based on soil parameters;

[0082] 3) Solve the transcendental equations (22) and (25) using Matlab software to find λ and then solve R p .

[0083] Then the head-on resistance F of the spherical hole expansion-sliding friction model is yb The possible values ​​are:

[0084]

[0085] Where R d is the riser radius.

[0086] (2) Shear failure-sliding friction model head-on resistance F ys

[0087] According to Figure 3, F ys It can be calculated by the following formula:

[0088] F ys =G s +G w +F cf (27)

[0089] G s =γ′πh[R d 2 +R m 2 +R d R m ] / 3 (28)

[0090]

[0091]

[0092]

[0093] Where γ' is the effective weight, γ w The weight of water.

[0094] (3) Friction force F between pipe and soil f

[0095] The friction between the pipe and soil is related to the lifting distance, and can generally be calculated using the following formula:

[0096]

[0097] Where: μ is the friction coefficient between pipe and soil, K is the lateral earth pressure coefficient, which can be taken as

[0098] (4) Tube deadweight G p

[0099] The deadweight of the riser is related to the jacking pipe section and can be calculated as follows:

[0100] G p =nG′ (33)

[0101] Where: n is the number of pipe segments that have been lifted, and G' is the average pipe segment weight.

[0102] Step 4: Selection of lifting force

[0103] At this point, a reasonable calculation system for predicting jacking force has been established. The jacking force can be calculated by simply knowing the position of the riser, soil parameters, and riser dimensions. The specific solution flow chart is shown in Figure 5.

[0104] When F yb <F ys When:

[0105] F=F yb +F f +G p (34)

[0106] When F ys <F yb When:

[0107] F=F ys +F f +G p (35)

[0108] The technical effects of the technical solution of the present invention are further illustrated below with reference to specific embodiments.

[0109] A case study of a drainage project in a certain city was used to calculate the lifting force during the entire vertical jacking construction process. This drainage project involves the tailwater discharge pipeline from a sewage treatment plant to the sea. The section constructed using the vertical jacking method is located between Well No. 2 and the B3 outfall. This section has a total length of 1,420 meters. The horizontal tunnel has an outer diameter of 2 meters and a wall thickness of 22 mm. Within 400 meters of the outfall, 29 risers were jacked. Each riser has a diameter of 0.5 meters and a wall thickness of 20 mm. Each riser has a jacking height of 12.5 meters and consists of a 0.5-meter-long first pipe section and 20 0.6-meter-long standard pipe sections. In this project, the height from sea level to the mud surface line is 14.41 meters, and the mud surface line is 11.5 meters from the upper side of the horizontal tunnel.

[0110] The risers can be divided into two groups based on the soil penetration conditions: the first group penetrates a single soil layer, and the second group penetrates multiple soil layers. The three risers with the most representative jacking forces in the first group and two risers in the second group, totaling five risers, were selected as typical risers for jacking force calculation and analysis. The first group of risers involved risers No. 3, No. 4, and No. 5, while the second group involved risers No. 11 and No. 12. The first group of risers required traversing an 11.5-meter coarse gravel and sand layer and a 1-meter clear water layer. The second group of risers penetrated a 0.5-meter clay layer, an 11-meter clay layer, and a 1-meter clear water layer.

[0111] According to the engineering geological report, the weight of coarse sand is 19.8 kN·m -3 , cohesion is 0, internal friction angle is 41.9°, compression modulus is 46MPa, and clay density is 19.6kN·m -3 , cohesion is 47.4kPa, internal friction angle is 13.2°, and compression modulus is 12MPa.

[0112] Using equations (13)-(21), calculate the plastic zone radius R p , substituted into formula (26) and compared with formula (27) to obtain the head-on resistance. Using formulas (32) and (33), the friction resistance between the pipe and the soil and the pipe's own weight are calculated. According to formulas (34) and (35), the calculated value of the vertical jacking method riser lifting force can be obtained during the vertical jacking method construction process. In order to better evaluate the correctness of the theoretical calculation method, the two groups of vertical pipe measured values ​​are compared with the theoretical calculation results of this paper and the results of the current mainstream calculation method. The comparison chart of the first group of vertical pipe lifting force results is shown in Figure 6, and the comparison chart of the second group of vertical pipe lifting results is shown in Figure 7. In addition, for the maximum lifting force, which is of most concern in the project, the calculation results of different algorithms are shown in Table 1.

[0113] Table 1. Comparison of maximum lifting force of different algorithms

[0114]

[0115] The documents cited in the preceding text of the present invention are as follows:

[0116] References [1] Wang Shousheng, Ge Chunhui. Discussion on calculation method of vertical pipe jacking [J]. Special Structures, 2009, 26(5): 18-21.

[0117] Reference [2] DG / TJ 08-2049-2016 Pipe Jacking Engineering Construction Specifications [S]. Tongji University Press, 2017.

[0118] Literature[3]Carter JP,Booker JR,Yeung S K.Cavity expansion in cohesive frictional soils[J].Geotechnique,1986,36(3):349-358.

[0119] Reference [4] Dong Shengxian, Luo Shuqing. Application of vertical jacking method in power plant drainage tunnel engineering [J]. Electric Power Survey and Design, 2012(6):47-51.

[0120] Reference [5] Liu Guirong. Research on construction technology of water intake structure of large nuclear and thermal power plants [D]. Shanghai Jiaotong University, 2014.

[0121] From Figure 6, we can see that before the lifting distance is 2.3m, F yb <F ys , calculated using formula (34), for a lifting distance of 2.9m and above, F ys <F yb , calculated using formula (35). The maximum lifting forces of the first group of risers were 1920 kN, 2040 kN, and 1760 kN, respectively, with an average value of 1906.7 kN. The theoretical value calculated by the present invention was 1981.5 kN, which was 3.9% larger than the theoretical value. The terminal lifting forces were 760 kN, 510 kN, and 510 kN, respectively, with an average value of 593.3 kN. The theoretical value calculated by the present invention was 681.7 kN, which was 14.9% larger than the theoretical value.

[0122] As can be seen from Figure 7: before the lifting distance is 2.3m, F yb <F ys , calculated using formula (34), for a lifting distance of 2.9m and above, F ys <F yb , calculated using formula (35). The maximum lifting force of the second set of risers was 2160 kN. The theoretical value calculated by the present invention was 1987.5 kN, which was 8% larger than the measured value. The terminal lifting forces were 510 kN and 640 kN, respectively, with an average value of 575 kN. The theoretical value calculated by the present invention was 688.2 kN, which was 19.7% larger than the theoretical value.

[0123] As can be seen from Figures 6 and 7, in actual engineering, the jacking force is not the largest when the first pipe section is jacked up, but presents a two-stage change of first increasing and then decreasing. For the positions where the maximum jacking force occurs, the first group occurs at 2.9m, 2.3m, and 2.9m, respectively, with an average value of 2.7m (0.235H), and the second group occurs at 2.9m (0.252H). The values ​​calculated by the theoretical method of the present invention are all 2.3m (0.2H).

[0124] In addition, for the maximum lifting force that is of most concern in the project, it can be seen from Table 1 that the calculation result of the calculation method of the present invention is closest to the actual value, indicating that the calculation formula derived by the present invention is in good agreement with the project.

[0125] This engineering example shows that the present invention, based on the basic solution of the spherical hole expansion method and the shear failure theory, takes into account the influence of the dynamic change of the overburden thickness on the head-on resistance, and can provide a theoretical reference for the calculation method of the jacking force in the entire construction process of the vertical jacking method.

Claims

1. A method for predicting the lifting force during the whole process of vertical lifting construction, characterized in that The following steps are involved: Step 1: Determine the components of the lifting force in vertical lifting construction. The lifting force F of the vertical lifting method is matched according to three parts, namely, the head-on resistance F y , Friction between pipe and soil F f Weight of pipe G p ; The head-on resistance F y is the sum of the forces on the riser cover; that is, F = F y +F f +G p ; Step 2: Select the force model during the riser lifting process and calculate the head-on resistance F y , According to the thickness of the overlying soil layer, the force of the head-on resistance is divided into two force models, namely the spherical hole expansion-sliding friction model and the shear failure-sliding friction model. When the overlying soil layer is high, there is F yb <F ys When the riser cover is considered as a spherical hole expansion problem, When the overlying soil layer is low, there is F ys <F yb When the soil at the riser cover is damaged by shear failure, then F y =F ys =G s +G w +F cf , where G s is the soil weight within the shear failure line (kN), and G s =γ′πh[R d 2 +R m 2 +R d R m ] / 3, G w is the water weight within the riser range (kN), F cf is the resistance caused by soil cohesion within the shear breaking line (kN), F yb is the head-on resistance under the spherical hole expansion-sliding friction model (kN), F ys is the head-on resistance under the shear failure-sliding friction model (kN), P u is the limit expansion pressure (kPa), R d is the riser radius (m), γ' is the effective weight of the soil (kN·m -3 ), h is the height of the riser cover from the mud surface (m), R m is the distance between the shear failure line and the mud surface line and the center of the riser (m), γ w is the weight of water (kN·m -3 ), H is the height of the upper side of the horizontal tunnel from the mud surface line (m), and c is the cohesion (kPa); Step 3: According to the calculated F=F y +F f +G p , calculate the lifting force.

2. A method for predicting the lifting force of the entire vertical lifting construction process as claimed in claim 1, characterized in that Friction between pipe and soil F f The value of is calculated according to the following formula: f =μKπDL 2 [γ′h+γ w h w +γ w (H+h / 2]; μ is the friction coefficient between pipe and soil, K is the lateral soil pressure coefficient, and D is the outer diameter of the riser (m).

3. A method for predicting the lifting force of the entire vertical lifting construction process as claimed in claim 1, characterized in that Tube weight G p The value of is calculated according to the following formula: p =nG′, n is the number of pipe sections that have been lifted, and G' is the average deadweight of the pipe sections (kN).

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