Method for controlling the axis of an oversize section rectangular pipe

Abstract

The application discloses a method for controlling the axis of an ultra-large-section rectangular pipe jacking, and belongs to the technical field of pipe jacking construction, and specifically comprises the following steps: S1, according to a field geological survey report, determining a section with a too large water head height difference between two sides of a tunnel, and performing reconnaissance and line marking; S2, according to survey data of strata on the two sides and investigation and analysis of underground structures, obtaining the permeability coefficients of the two sides of the section, and analyzing the seepage state, and constructing a pressure relief shaft on the side with a high pressure water head or the side with blocked seepage; S3, selecting a section as a test section to perform a pumping test, and determining the construction position, specification size and spacing quantity of the pressure relief shafts of each section through theoretical calculation; S4, constructing the pressure relief shafts of each section according to actual construction; and S5, monitoring the pressure on the two sides of the section during pipe jacking, and stopping the pipe jacking when the water head difference exceeds a limited value, and then balancing again by blocking the pressure relief shafts or increasing the number of the pressure relief shafts. The pipe jacking and subsequent construction can be successfully and high-quality completed.

Description

Technical Field

[0001] This invention relates to a method for controlling the axis of ultra-large cross-section rectangular pipe jacking, belonging to the field of pipe jacking construction technology. Background Technology

[0002] Due to rapid economic development and gradual urbanization in recent years, surface construction has become saturated, leading to a surge in underground construction projects such as pipeline upgrades and underground space renovations. Pipe jacking, a type of trenchless underground pipeline construction, is gaining increasing attention due to its advanced technology, smaller footprint, minimal environmental impact, and economic efficiency. It is widely used for trenchless construction of urban underground water supply and drainage pipelines, natural gas and oil pipelines, communication cables, pedestrian underpasses, subway stations, and other underground pipelines and structures.

[0003] Pipe jacking is typically buried deep underground. During excavation, issues may arise such as inconsistent geological formations on both sides of the tunnel, differences in groundwater levels, confined water, or the presence of prefabricated tunnels or basements on one side. Under normal drag-reducing grouting conditions, the seepage fields on both sides of the tunnel become inconsistent due to the influence of these impermeable structures, resulting in significant differences in pressure heads. This causes the grout to flow from the higher head to the lower head, resulting in transverse seepage of the grout across the tunnel cross-section. According to Darcy's law, the amount of seepage Q is directly proportional to the cross-sectional area A of the soil sample and the hydraulic gradient i, i.e.:

[0004] Q=kAi (1)

[0005] In the formula, Q is the amount of seepage water, m 3 / d;

[0006] k is the soil permeability coefficient, in m / d;

[0007] A is the cross-sectional area of ​​the seepage flow, in meters. 2 ;

[0008] i represents the hydraulic gradient, which is dimensionless. Δh is the head loss of the water after seepage flows through a soil layer of length L.

[0009] When seepage occurs, it exerts forces such as pushing and friction on each soil particle; these forces are called seepage force j. Seepage force is a volume force, and its relationship with hydraulic gradient is as follows:

[0010] j = γ w i (2)

[0011] In the formula, j is the seepage force, kN / m 3 ;

[0012] γ w The soil's unit weight is kN / m. 3.

[0013] As can be seen from equation (2), the greater the hydraulic gradient i, the greater the seepage force j.

[0014] like Figure 4 This is a schematic diagram of the pipe jacking construction plan, in which there is a water-proof structure on the right side of the jacking direction.

[0015] At the impermeable structure, the seepage rate Q = 0, meaning the hydraulic gradient i = 0 in the structure and the soil layer on the right, and the seepage occurs in the direction away from the impermeable structure. However, there is no impermeable structure obstructing the left side of the tunnel jacking, so the seepage path is unobstructed. Therefore, water from the right seeps into the soil on the left, causing the jacking pipe to experience a seepage force to the left. When the seepage force exceeds the frictional force between the jacking tunnel and the soil layer, the jacking machine will move to the left, causing the jacking pipe axis to shift.

[0016] During pipe jacking, the formation of the mud jacket reduces the friction between the tunnel and the soil, making the tunnel more susceptible to the aforementioned lateral seepage forces and exacerbating the deviation of the tunnel axis. Existing technology uses pipe jacking machine correction jacks for correction, but if the axis deviation is too large, or for short-distance pipe jacking, it is impossible to correct the deviation by increasing the correction angle. This will cause the pipe jacking operation to fail to exit the tunnel according to the design axis, resulting in serious quality problems. Summary of the Invention

[0017] The technical problem to be solved by this invention is to provide a method for controlling the axis of ultra-large cross-section rectangular pipe jacking. This method reduces the pressure head on the high water head side during the tunneling process by constructing a pressure relief shaft before tunneling, thereby reducing seepage between the two sides of the tunnel and preventing the ultra-large cross-section pipe jacking tunnel from deviating from the design axis due to seepage force. This solves the problem that excessive deviation in water head on both sides of the pipe jacking tunnel causes seepage between the tunnels, leading to deviation from the predetermined axis, or even making it impossible to exit the tunnel according to the axis due to excessive deviation. This ensures high-quality and smooth completion of pipe jacking and subsequent construction.

[0018] To solve the above problems, the following technical solutions are provided:

[0019] A method for controlling the axis of ultra-large cross-section rectangular pipe jacking is designed, and the specific steps include:

[0020] S1. Based on the on-site geological survey report, identify the sections with excessively large differences in water head on both sides of the tunnel, and conduct reconnaissance and marking.

[0021] S2. Based on the exploration data of the strata on both sides and the investigation and analysis of underground structures, the permeability coefficients on both sides of the above section are obtained, and the seepage state is analyzed. Pressure relief shafts are constructed on the side with high pressure head or on the side where seepage is obstructed (waterproof structures and the sidewall of the jacking tunnel).

[0022] S3. Select a section as a test section for pumping test, and determine the construction location, specifications, dimensions, and number of pressure relief shafts in each section through theoretical calculation;

[0023] S4. Construct pressure relief shafts in each section according to the actual construction situation;

[0024] S5. During pipe jacking, monitor the pressure on both sides of the above-mentioned section. If the head difference exceeds the limit, stop the tunneling and then rebalance by sealing the pressure relief shaft or increasing the number of shafts.

[0025] Furthermore, in S1, the section with excessive water head deviation is the section where the strata and water conditions on both sides of the tunnel are inconsistent or affected by existing structures.

[0026] Furthermore, in S2, the specific steps for the seepage state analysis include, when the soil and water conditions on both sides of the section are consistent:

[0027] During pipe jacking, the cutterhead over-excavates the surrounding soil, creating voids between the tunnel and the soil. These voids require continuous grouting to fill. To prevent settlement, a constant pressure must be maintained. However, on the side where the shaft is constructed, existing structures act as water barriers, preventing the pressure head from decreasing through seepage under the same grouting conditions on both sides. Therefore, before the shaft is constructed, this location can be considered under constant pressure. After the shaft is constructed, the seepage state can be calculated as a complete confined well flow. In 1863, Dupuit proposed a formula for calculating complete well flow, which assumes:

[0028] 1) The wells are located in a homogeneous and isotropic horizontal aquifer with a horizontal natural water surface (pressure surface);

[0029] 2) On the circumference at a certain distance d from the well axis, a long water head is maintained and the drawdown value is zero, that is, there is a constant water head supply around the circumference;

[0030] 3) The movement of water in an aquifer obeys Darcy's law.

[0031] Based on Dupuit's assumptions and formula derivation, taking the lower edge of the tunnel as the reference plane, and considering only seepage on both sides of the tunnel, the aquifer thickness is simplified to the tunnel height h. The seepage flow rate of a single shaft is calculated as follows:

[0032]

[0033] In the formula, Q1 is the seepage flow rate of the vertical shaft, in meters. 3 / d;

[0034] K is the equivalent permeability coefficient, which is the weighted average value based on the soil layer thickness within the tunnel height range, in m / d;

[0035] H0 is the water head at both sides of the tunnel edge, i.e., the water head of the grouting pressure of the drag-reducing mud on the sidewall, in meters;

[0036] H w1 The head of the vertical shaft after depressurization is measured in meters (m).

[0037] d represents the distance between vertical shafts, in meters (m).

[0038] r w The well diameter is in meters (m).

[0039] h is the tunnel height, in meters;

[0040] The side with normal seepage flow can be approximated as laminar seepage for calculation. Based on Darcy's law, the lower edge of the tunnel is set as the reference plane. The seepage flow on the side corresponding to the seepage area of ​​the shaft is calculated as follows:

[0041]

[0042] In the formula, L is the distance from the center of the shaft to one side of the pipe jacking machine (closest to the shaft), in meters;

[0043] Q2 is the seepage flow rate of the vertical shaft, in meters. 3 / d;

[0044] H w2 The water head on the other side of the tunnel corresponding to the shaft location is in meters (m).

[0045] Based on the seepage state on the side without structures, the Laplace equation is established as follows:

[0046]

[0047] Since the normal seepage is unaffected in this calculation example, only the horizontal seepage is considered. Therefore, the above formula can be simplified to

[0048]

[0049] Its general solution is:

[0050] H = C1x + C2 (6)

[0051] Where C1 and C2 are two undetermined integration constants. Substituting the boundary conditions, i.e., the water head of the measuring pipe at the edge of the construction tunnel is H0, i.e., when x = 0, H = H0, substituting into (4), we obtain C2 = H0, and substituting into (6)

[0052] H = C1x + H0 (7)

[0053] The result of the transformation is:

[0054]

[0055] Where i is the hydraulic gradient, which is a constant and can be determined through pumping tests, therefore:

[0056] H = -ix + H0 (8)

[0057] Based on the above formula, we can obtain:

[0058] H w2 =-iL+H0 (9)

[0059] To balance the water head on both sides of the tunnel, the flow rate at corresponding locations on both sides must be consistent, i.e., Q1 = Q2.

[0060]

[0061] Substituting (9) into (10), we get:

[0062]

[0063] Among them, H0, H1, and i can be obtained from local hydrological conditions, geological survey reports, pumping tests, and the depth of drainage channels, and are constants, so they can be set as follows: Obviously, B is a constant, so (11) can be simplified to

[0064]

[0065] Furthermore, in step S3, after a pumping test, the hydraulic gradient i on the side with normal seepage is determined. The permeability coefficients K1 and K2 on both sides of the construction tunnel are obtained from the geological survey report. Based on the analysis of the actual construction conditions on site, the depth of the drainage channel or the pumping depth is determined, and the head H of the pressure relief well is determined. w1 The constant B is calculated based on the above parameters, and the mathematical relationship between the shaft diameter and spacing is determined according to formula (12).

[0066] Furthermore, in S4, the pressure relief shaft can be drilled by a geological drilling rig or a rotary drilling rig, and the shaft can be backfilled with pebbles and the water can be dewatered by a water pump or a drainage channel. Alternatively, bagged sand wells or plastic drainage boards can be used.

[0067] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0068] Before pipe jacking, a pressure relief shaft is constructed to reduce the pressure head on the high water head side during the tunneling process, thereby reducing seepage between the two sides of the tunnel. This prevents the seepage force caused by seepage in ultra-large cross-section pipe jacking tunnels from deviating from the design axis. It solves the problem that excessive deviation in water head on both sides of the pipe jacking tunnel can cause seepage between the tunnels, leading to deviation from the predetermined axis, or even making it impossible to exit the tunnel along the axis due to excessive deviation. This ensures the smooth and high-quality completion of pipe jacking and subsequent construction. Attached Figure Description

[0069] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0070] Figure 1 This is a diagram showing the load distribution of the surrounding soil and mud ring on the pipe jacking tunnel during the construction phase of the present invention.

[0071] Figure 2 The diagram shows the plan view and AA cross-sectional view of the structure for controlling the axis of the ultra-large cross-section rectangular jacking pipe of the present invention.

[0072] Figure 3 This is a schematic diagram of the pipe jacking construction plan and a detailed structural diagram of the pressure relief shaft of the present invention;

[0073] Figure 4 This is a schematic diagram of pipe jacking construction in the existing technology; Detailed Implementation

[0074] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0075] like Figure 1 - Figure 3 As shown in the figure, this embodiment provides a method for controlling the axis of an ultra-large cross-section rectangular pipe jacking project, the specific steps of which include:

[0076] S1. Based on the on-site geological survey report, identify the sections with excessively large differences in water head on both sides of the tunnel, and conduct reconnaissance and marking.

[0077] S2. Based on the exploration data of the strata on both sides and the investigation and analysis of underground structures, the permeability coefficients on both sides of the above section are obtained, and the seepage state is analyzed. Pressure relief shafts are constructed on the side with high pressure head or on the side where seepage is obstructed (waterproof structures and the sidewall of the jacking tunnel).

[0078] S3. Select a section as a test section for pumping test, and determine the construction location, specifications, dimensions, and number of pressure relief shafts in each section through theoretical calculation;

[0079] S4. Construct pressure relief shafts in each section according to the actual construction situation;

[0080] S5. During pipe jacking, monitor the pressure on both sides of the above-mentioned section. If the head difference exceeds the limit, stop the tunneling and then rebalance by sealing the pressure relief shaft or increasing the number of shafts.

[0081] Furthermore, in S1, sections with excessively large deviations in water head are those where the strata and water conditions on both sides of the tunnel are inconsistent or affected by existing structures.

[0082] Furthermore, in S2, the specific steps for seepage state analysis include, when the soil and water conditions on both sides of the section are consistent:

[0083] During pipe jacking, the cutterhead over-excavates the surrounding soil, creating voids between the tunnel and the soil. These voids require continuous grouting to fill. To prevent settlement, a constant pressure must be maintained. However, on the side where the shaft is constructed, existing structures act as water barriers, preventing the pressure head from decreasing through seepage under the same grouting conditions on both sides. Therefore, before the shaft is constructed, this location can be considered under constant pressure. After the shaft is constructed, the seepage state can be calculated as a complete confined well flow. In 1863, Dupuit proposed a formula for calculating complete well flow, which assumes:

[0084] 1) The wells are located in a homogeneous and isotropic horizontal aquifer with a horizontal natural water surface (pressure surface);

[0085] 2) On the circumference at a certain distance d from the well axis, a long water head is maintained and the drawdown value is zero, that is, there is a constant water head supply around the circumference;

[0086] 3) The movement of water in an aquifer obeys Darcy's law.

[0087] Based on Dupuit's assumptions and formula derivation, taking the lower edge of the tunnel as the reference plane, and considering only seepage on both sides of the tunnel, the aquifer thickness is simplified to the tunnel height h. The seepage flow rate of a single shaft is calculated as follows:

[0088]

[0089] In the formula, Q1 is the seepage flow rate of the vertical shaft, in meters. 3 / d;

[0090] K is the equivalent permeability coefficient, which is the weighted average value based on the soil layer thickness within the tunnel height range, in m / d;

[0091] H0 is the water head at both sides of the tunnel edge, i.e., the water head of the grouting pressure of the drag-reducing mud on the sidewall, in meters;

[0092] H w1 The head of the vertical shaft after depressurization is measured in meters (m).

[0093] d represents the distance between vertical shafts, in meters (m).

[0094] r w The well diameter is in meters (m).

[0095] h is the tunnel height, in meters;

[0096] The side with normal seepage flow can be approximated as laminar seepage for calculation. Based on Darcy's law, the lower edge of the tunnel is set as the reference plane. The seepage flow on the side corresponding to the seepage area of ​​the shaft is calculated as follows:

[0097]

[0098] In the formula, L is the distance from the center of the shaft to one side of the pipe jacking machine (closest to the shaft), in meters;

[0099] Q2 is the seepage flow rate of the vertical shaft, in meters. 3 / d;

[0100] H w2 The water head on the other side of the tunnel corresponding to the shaft location is in meters (m).

[0101] Based on the seepage state on the side without structures, the Laplace equation is established as follows:

[0102]

[0103] Since the normal seepage is unaffected in this calculation example, only the horizontal seepage is considered. Therefore, the above formula can be simplified to

[0104]

[0105] Its general solution is:

[0106] H = C1x + C2 (6)

[0107] Where C1 and C2 are two undetermined integration constants. Substituting the boundary conditions, i.e., the water head of the measuring pipe at the edge of the construction tunnel is H0, i.e., when x = 0, H = H0, substituting into (4), we obtain C2 = H0, and substituting into (6)

[0108] H = C1x + H0 (7)

[0109] The result of the transformation is:

[0110]

[0111] Where i is the hydraulic gradient, which is a constant and can be determined through pumping tests, therefore:

[0112] H = -ix + H0 (8)

[0113] Based on the above formula, we can obtain:

[0114] H w2 =-iL+H0 (9)

[0115] To balance the water head on both sides of the tunnel, the flow rate at corresponding locations on both sides must be consistent, i.e., Q1 = Q2.

[0116]

[0117] Substituting (7) into (8), we get:

[0118]

[0119] Among them, H0, H1, and i can be obtained from local hydrological conditions, geological survey reports, pumping tests, and the depth of drainage channels, and are constants, so they can be set as follows: Obviously, B is a constant, so (11) can be simplified to

[0120]

[0121] When the soil and water conditions on both sides of a section are inconsistent (i.e., the K values ​​are inconsistent), the seepage coefficients on the left and right sides can be set as K1 and K2, respectively, and the following can be obtained: If we assume Since K1 and K2 are also constants, B is a constant, and the result remains unchanged. A specific calculation example is as follows:

[0122] The following calculation example assumes that there are existing structures on one side of the construction tunnel:

[0123] Based on Dupuit's assumptions and formula derivation, taking the lower edge of the tunnel as the reference plane, and considering only seepage on both sides of the tunnel, the aquifer thickness is simplified to the tunnel height h. The seepage flow rate of a single shaft is calculated as follows:

[0124]

[0125] In the formula, Q1 is the seepage flow rate of the vertical shaft, in meters. 3 / d;

[0126] K1 is the equivalent permeability coefficient, which is the weighted average value based on the soil layer thickness within the tunnel height range on the side with the impermeable structure, in m / d;

[0127] H0 is the water head at both sides of the tunnel edge, i.e., the water head of the grouting pressure of the drag-reducing mud on the sidewall, in meters;

[0128] H w1 The head of the vertical shaft after depressurization is measured in meters (m).

[0129] d represents the distance between vertical shafts, in meters (m).

[0130] r w The well diameter is in meters (m).

[0131] h is the tunnel height, in meters;

[0132] The side with normal seepage flow can be approximated as laminar seepage for calculation. Based on Darcy's law, the lower edge of the tunnel is set as the reference plane. The seepage flow on the side corresponding to the seepage area of ​​the shaft is calculated as follows:

[0133]

[0134] In the formula, L is the distance from the center of the shaft to one side of the pipe jacking machine (closest to the shaft), in meters;

[0135] Q2 is the seepage flow rate of the vertical shaft, in meters. 3 / d;

[0136] H w2 The water head on the other side of the tunnel corresponding to the shaft location is in meters (m).

[0137] K2 is the equivalent permeability coefficient, which is the weighted average value based on the soil layer thickness within the tunnel height range on the side with normal seepage, in m / d;

[0138] Based on the seepage state on the side without structures, the Laplace equation is established as follows:

[0139]

[0140] Since the normal seepage is unaffected in this calculation example, only the horizontal seepage is considered. Therefore, the above formula can be simplified to

[0141]

[0142] Its general solution is:

[0143] H = C1x + C2 (6)

[0144] Where C1 and C2 are two undetermined integration constants. Substituting the boundary conditions, i.e., the water head of the measuring pipe at the edge of the construction tunnel is H0, i.e., when x = 0, H = H0, substituting into (4), we obtain C2 = H0, and substituting into (6)

[0145] H = C1x + H0 (7)

[0146] The result of the transformation is:

[0147] Where i is the hydraulic gradient, which is a constant and can be determined through pumping tests, therefore:

[0148] H = -ix + H0 (8)

[0149] Based on the above formula, we can obtain:

[0150] H w2 =-iL+H0 (9)

[0151] To balance the water head on both sides of the tunnel, the flow rate at corresponding locations on both sides must be consistent, i.e., Q1 = Q2.

[0152]

[0153] Substituting (9) into (10), we get:

[0154]

[0155] Among them, H0, Hw1, i, K1, and K2 can be obtained from local hydrological conditions, geological survey reports, pumping tests, and the depth of drainage channels, and are constants, so they can be set as follows: Obviously, B is a constant, so (11) can be simplified to

[0156]

[0157] In S3, after pumping tests, the hydraulic gradient i on the side with normal seepage was determined. The permeability coefficients K1 and K2 on both sides of the tunnel were found through the geological survey report. Based on the analysis of the actual construction conditions on site, the depth of the drainage channel or the pumping depth was determined, and the head H of the pressure relief well was determined. w1 The constant B is calculated based on the above parameters, and the mathematical relationship between the shaft diameter and spacing is determined according to formula (12). In this embodiment, a certain physical project is used as an example. Project overview: The project consists of two parallel pipe jacking sections being excavated one after the other, with a spacing of 1.5m and a pipe jacking cover of 9.75m. The tunnel cross-section size is 11.1m*8.1m. The first pipe jacking tunnel forms a water-blocking structure when the second pipe jacking is excavated, causing seepage to be blocked on one side. The excavation range of the pipe jacking channel is basically located in the silty clay layer, and the water and soil conditions on both sides are the same.

[0158] According to the geological survey report, K1 = K2 = 0.05, and the normal water head depth is 4m. Taking the lower edge of the pipe section as the baseline, the normal water head is 13.85m. Based on section 9.5.2-4 of the "Technical Specification for Rectangular Pipe Jacking Engineering" (DBJ / T15-229-2021), which states that "the grouting pressure should be controlled at 0.02MPa to 0.04MPa higher than the groundwater pressure, and grouting should be replenished promptly when the pressure drops," this project uses 0.02MPa as the control, meaning the grouting head H0 = 15.85m. Based on the actual site conditions, a drainage pipe will be buried at the location of the pressure relief shaft at a depth of 3.85m, meaning the pressure relief well head H0 is... w1 =14m According to equation (11), we can obtain

[0159]

[0160] Pumping tests were conducted in this section, and the value of i was measured to be 0.631. Substituting this value into the above formula, we obtained B = 8.004.

[0161] Substituting into equation (12), that is

[0162]

[0163] Based on the actual site conditions and existing mechanical equipment, a pressure relief shaft with a diameter of 800mm was used for pressure relief, i.e., the shaft diameter r w =0.4. Based on the above formula, the following equation can be obtained.

[0164]

[0165] According to the analytical method of transcendental equations, d∈(8,9), so d is taken as 8m;

[0166] Therefore, on-site, a pressure relief shaft was constructed every 8 meters between the pipe jacking tunnel and the preceding tunnel. The shaft diameter was 800mm. According to the geological survey report, the friction coefficient f at the contact surface between the pipe section and the soil in this section was 6, and the unit weight γ... w The value is 18.1, according to equation (17). When the water pressure difference between the two sides of the jacking pipe exceeds 36.796 kPa during tunneling, tunneling must be stopped, and measures such as sealing the pressure relief shaft or increasing the number of shafts should be taken to rebalance the pressure.

[0167] In S4, pressure relief shafts can be drilled using geological drilling rigs or rotary drilling rigs, with the shafts backfilled with pebbles and water pumps or drainage channels used for dewatering. Alternatively, bagged sand wells or plastic drainage boards can be used.

[0168] In S5, according to the "Technical Specification for Pipe Jacking in Water Supply and Drainage Engineering" (CECS246:2008) and the "Technical Specification for Rectangular Pipe Jacking Engineering" (DBJ / T15-229-2021), the axial side friction of the rectangular pipe is calculated as follows:

[0169] F f =2f(B1+H1)L d (13)

[0170] In the formula, F f The total frictional resistance of the rectangular jacking pipe is given in kN.

[0171] f is the coefficient of friction between the tunnel section and the soil during tunneling, in kN / m. 2 ;

[0172] B1 is the outer width of the rectangular pipe section, in meters;

[0173] H1 is the outer height of the rectangular pipe section, in meters;

[0174] L d The jacking distance of the rectangular pipe section is in meters (m).

[0175] Because pipe jacking is an over-excavation construction, there is an over-excavation gap on its side after excavation. Therefore, the lateral offset frictional resistance in the over-excavation gap can be calculated according to formula (13). Since the lateral frictional resistance only acts on the upper and lower sides of the pipe section, H1 = 0, that is...

[0176] F f1 =2fB1L d (14)

[0177] In the formula F f1 The lateral offset frictional resistance of the rectangular jacking pipe is given in kN.

[0178] During the tunneling process, to avoid settlement, grouting is continuously injected to fill the over-excavated voids. Therefore, the side edge of the jacking pipe can be regarded as a constant pressure state, that is, the hydraulic gradient i of the upper and lower sides of the jacking pipe remains unchanged. According to equation (3), it is easy to obtain that the seepage force on the upper and lower sides of the pipe section remains unchanged and is constant. Therefore, the effect of the seepage force on the upper and lower sides is integrated, that is...

[0179] E j =2∫jdxdy=2jB1L d (15)

[0180] In the formula E j The surface permeability of the tunneling pipe section is expressed in kN.

[0181] According to mechanical equilibrium, when Ej > F f1 At that time, its penetrating force will disturb the tunneling pipe section; that is, the critical condition for pipe section disturbance is...

[0182] 2jB1L d >2fB1L d

[0183] Simplifying, we get: j>f

[0184] According to equation (2) and Transformed into

[0185] Simplify to get

[0186]

[0187] Among them, f, B1, γ w Both and are constants, so let's assume . The critical condition for pipe section disturbance

[0188] Δh>D (16)

[0189] And, P w =ρgh

[0190] In the formula, P w Groundwater pressure, Pa;

[0191] ρ is the density of water, kg / m³ 3 ;

[0192] g is the acceleration due to gravity, m / s² 2 ;

[0193] h is the depth from the pressure measurement point to the grouting water level, in meters;

[0194] Substituting into (16), we obtain ΔP. w >10 4 D (17)

[0195] In the description of this invention, it should be understood that the terms "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. In the description of this invention, unless otherwise specified and limited, it should be noted that the terms "installed," "connected," and "linked" should be interpreted broadly. For example, they can refer to mechanical or electrical connections, or internal connections between two elements; they can be direct connections or indirect connections through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms according to the specific circumstances.

[0196] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for controlling the axis of an ultra-large cross-section rectangular pipe jacking project, characterized in that, The specific steps include: S1. Based on the on-site geological survey report, identify the sections with excessively large differences in water head on both sides of the tunnel, and conduct reconnaissance and marking. S2. Based on the exploration data of the strata on both sides and the investigation and analysis of underground structures, the permeability coefficients on both sides of the above section are obtained, and the seepage state is analyzed. Pressure relief shafts are constructed on the side with high pressure head or the side where seepage is obstructed. S3. Select a section as a test section for pumping test, and determine the construction location, specifications, dimensions, and number of pressure relief shafts in each section through theoretical calculation; S4. Construct pressure relief shafts in each section according to the actual construction situation; S5. During pipe jacking, monitor the pressure on both sides of the above-mentioned section. If the head difference exceeds the limit, stop the tunneling and then rebalance by sealing the pressure relief shaft or increasing the number of shafts. In S2, the specific steps for seepage state analysis include, when the soil and water conditions on both sides of the section are consistent: During the pipe jacking process, the cutterhead over-excavates the surrounding soil, creating gaps between the tunnel and the soil. This requires continuous grouting to fill the gaps. To prevent settlement, a constant pressure must be maintained. However, on the side where the shaft is constructed, the existing structure acts as a water barrier, preventing the pressure head at that location from being reduced by seepage under the same grouting conditions on both sides. Therefore, this location can be considered as a constant pressure condition before the shaft is constructed. After the shaft is constructed, its seepage state can be calculated as a complete pressurized well flow. Based on Dupuit's assumptions and formula derivation, taking the lower edge of the tunnel as the reference plane, and considering only seepage on both sides of the tunnel, the aquifer thickness is simplified to the tunnel height. h The seepage flow rate of a single vertical shaft is calculated as follows: （3） In the formula, Q 1 represents the seepage flow rate of the vertical shaft, in meters. 3 / d; K The equivalent permeability coefficient is the weighted average value based on the soil layer thickness within the tunnel height range, expressed in m / d. H 0 represents the water head at both sides of the tunnel edge, i.e., the water head of the grouting pressure for drag reduction mud on the sidewall, in meters; H w1 The head of the vertical shaft after depressurization is measured in meters (m). d The distance between the vertical shafts is in meters (m). r w The well diameter is in meters (m). h The tunnel height is in meters (m). The side with normal seepage flow can be approximated as laminar seepage for calculation. Based on Darcy's law, the lower edge of the tunnel is set as the reference plane. The seepage flow on the side corresponding to the seepage area of ​​the shaft is calculated as follows: （4） In the formula, L The distance from the center of the shaft to one side of the pipe jacking machine is in meters (m). Q 2 represents the seepage flow rate of the vertical shaft, in meters. 3 / d; H w2 The water head on the other side of the tunnel corresponding to the shaft location is in meters (m). Based on the seepage state on the side without structures, the Laplace equation is established as follows: （5） Since the normal seepage is unaffected in this calculation example, only the horizontal seepage is considered. =0, therefore the above expression can be simplified to Its general solution is: （6） in, C 1. C 2 represents two undetermined constants; substituting the boundary conditions, i.e., the water head in the side pipe at the edge of the construction tunnel is... H 0, that is x When =0, H = H 0, substituting into formula (4), we obtain C 2= H 0, substitute into (6) （7） The result of the transformation is: in, i Let be the hydraulic gradient, which is a constant and can be determined through pumping tests. Therefore: （8） Based on the above formula, we can obtain: （9） To balance the water head on both sides of the tunnel, the flow rate at corresponding locations on both sides must be consistent, that is... Q 1= Q 2. Yes （10） Substituting (9) into (10), we get: （11） in, H 0、 H 1. i Based on local hydrological conditions, geological survey reports, pumping tests, and the depth of the drainage channel, and given that this depth is a constant, we assume... Obviously, B is a constant, so (11) can be simplified to （12）。 2. The method for controlling the axis of an ultra-large cross-section rectangular pipe jacking project according to claim 1, characterized in that, In S1, the section with excessive water head deviation is the section where the strata and water conditions on both sides of the tunnel are inconsistent or affected by existing structures.

3. The method for controlling the axis of an ultra-large cross-section rectangular pipe jacking project according to claim 1, characterized in that, In step S3, the hydraulic gradient on the side with normal seepage is determined through a pumping test. i The geological survey report determined the permeability coefficients on both sides of the tunnel under construction. K 1. K 2. Determine the depth of the drainage channel or the pumping depth based on the actual construction conditions on site, and determine the head of the pressure relief well. H w1 According to the above Calculated constants B Then, the mathematical relationship between the diameter and spacing of the shaft is determined according to formula (12).

4. The method for controlling the axis of an ultra-large cross-section rectangular pipe jacking project according to claim 1, characterized in that, In S4, the pressure relief shaft is drilled by a geological drilling rig or a rotary drilling rig, and the shaft is backfilled with pebbles and water is pumped or drained to reduce water level. Alternatively, bagged sand or plastic drainage boards can be used.

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