Pipe curtain pre-reinforcement protection method for pipe jacking construction under ancient city wall foundation

Abstract

The application discloses a pipe curtain pre-reinforcement protection method for pipe jacking construction underpassing an ancient city wall foundation, belongs to the technical field of underground engineering construction and cultural relic protection, and comprises the following steps: obtaining physical and mechanical parameters of the ancient city wall foundation soil layer; performing area weighting equivalence on the ancient city wall masonry structure and the foundation soil layer by using a stratum equivalence method to obtain equivalent stratum parameters; calculating various settlements during pipe jacking construction based on a Mindlin displacement solution and a modified Peck formula and superimposing the various settlements to obtain total settlement, and determining pipe jacking construction control parameters according to the total settlement; performing a circular small pipe curtain outside a pipe jacking excavation contour according to the control parameters, injecting cement mortar into the steel pipe, and injecting cement-water glass double-liquid slurry between the steel pipes to form a hard shell protective cover; and performing pipe jacking construction under the protection of the hard shell protective cover; the hard shell protective cover is formed by the circular small pipe curtain, the disturbance of pipe jacking construction on the upper ancient city wall is effectively controlled, and the method has the advantages of small construction disturbance and quantifiable evaluation of reinforcement effect.

Description

Technical Field

[0001] This invention relates to the fields of underground engineering construction and cultural relic protection technology, and in particular to a method for pre-reinforcement and protection of pipe jacking construction under the foundation of an ancient city wall. Background Technology

[0002] Pipe jacking is widely used in urban underground pipeline construction due to its minimal impact on surface traffic and the surrounding environment. However, when pipe jacking passes under immovable cultural relics such as ancient city walls, the soil disturbance induced by construction may lead to uneven settlement of the cultural relic's foundation or even structural instability, making the conflict between cultural relic protection and engineering construction particularly prominent.

[0003] Ancient city walls typically have a composite structure consisting of an outer brick and stone masonry wall and an inner rammed earth core wall. The stiffness difference between the two can be tens to hundreds of times, making them extremely sensitive to external disturbances. When pipe jacking is used to tunnel under such structures, differential settlement between the masonry and rammed earth can cause the contact surface to become void or peel off, leading to irreversible damage.

[0004] Currently, foundation pre-reinforcement measures for pipe jacking under important buildings mainly include horizontal grouting reinforcement, pipe roof, and pipe jacking. Among these, the pipe jacking method, which involves pre-inserting steel pipes outside the excavation outline and grouting to form a support structure, has been applied in some projects. However, existing pipe jacking methods mostly use rectangular or arched large-diameter pipe jacks, and the superimposed effect of ground disturbance during the construction of multiple pipes during the pipe jacking process is significant. At the same time, the influence mechanism of different pipe jacking forms, pipe diameters, wall thicknesses, and spacing on the reinforcement effect is still unclear. In engineering, pipe jacking parameters are usually selected based on experience, lacking quantitative design basis. In addition, the construction of the pre-reinforcement measures themselves may also disturb the ground. For example, when constructing pile foundations on both sides of a city wall, the drilling and concrete pouring may cause stress redistribution in the ground, which may increase the risk of deformation.

[0005] In summary, existing technologies lack a pipe jacking pre-reinforcement scheme that minimizes construction disturbance and allows for quantifiable evaluation of reinforcement effects, as well as a quantitative calculation method for improving the foundation stiffness after pipe jacking reinforcement. Summary of the Invention

[0006] The purpose of this invention is to provide a method for pre-reinforcement and protection of pipe jacking construction under the foundation of an ancient city wall, so as to solve the problems mentioned in the background art.

[0007] To achieve the above objectives, this invention provides a method for pre-reinforcement and protection of pipe jacking construction under the foundation of an ancient city wall, comprising the following steps: Step 1: Conduct geological surveys in the pipe jacking construction area to obtain the physical and mechanical parameters of the soil layer of the ancient city wall foundation. Step 2: Based on the physical and mechanical parameters, the area-weighted equivalent of the ancient city wall masonry structure, the core wall rammed earth structure and the foundation soil is performed using the stratum equivalence method to obtain the homogenized equivalent stratum parameters, including the equivalent elastic modulus, the equivalent compression modulus and the equivalent Poisson's ratio. Step 3: Based on the Mindlin displacement solution and the modified Peck formula, calculate the settlement of the city wall foundation caused by the additional thrust of the tunneling machine at the front during the pipe jacking construction, the settlement caused by the friction between the tunneling machine and the surrounding soil, the settlement caused by the friction between the subsequent pipeline and the surrounding soil, and the settlement caused by construction factors. The above four settlements are superimposed to obtain the total settlement during the pipe jacking construction under the ancient city wall, and the control parameters of the pipe jacking construction are determined based on the total settlement. Step 4: Based on the control parameters determined in Step 3, a circular small pipe curtain is pre-constructed outside the pipe jacking excavation outline. The circular small pipe curtain is composed of multiple steel pipes arranged along the outer periphery of the pipe jacking excavation outline. Grouting is injected inside the steel pipes and between the steel pipes to form a hard shell protective cover. Step 5: Under the protection of the hard shell protective cover, the pipe jacking construction is carried out, so that the pipe jacking passes through the foundation of the ancient city wall inside the protective cover formed by the circular small pipe curtain.

[0008] Preferably, in step two, the equivalent elastic modulus and equivalent compression modulus are calculated as the weighted average of the elastic modulus and compression modulus of the ancient city wall masonry and the foundation soil layer, respectively, with their respective heights as the weight; the equivalent Poisson's ratio is calculated as the weighted average of the Poisson's ratio of the ancient city wall masonry and the foundation soil layer, with their respective heights as the weight, and the calculation formula is as follows: ; ; ; in, For the equivalent elastic modulus, The elastic modulus of the ancient city wall masonry. The elastic modulus of the foundation soil layer. This refers to the vertical height of the ancient city wall. This refers to the vertical height of the foundation soil layer; For equivalent compressive modulus, The compression modulus of the ancient city wall masonry. The compression modulus of the foundation soil layer; For the equivalent Poisson ratio, The Poisson's ratio for the masonry of the ancient city wall The Poisson's ratio is the ratio of the soil layer in the foundation.

[0009] Preferably, in step three, the construction factors include grouting filling rate, grouting pressure ratio, eccentric over-excavation rate, and tunneling machine pitch slope; the modified Peck formula uses a stiffness correction method to correct the stiffness contribution of the ancient city wall structure, and the stiffness correction method introduces a stiffness correction coefficient. Settlement trough width parameters for natural ground The corrected parameters are the width of the settling trough. The calculation formula is as follows: ; ; in, The shear stiffness of the cross section of the ancient city wall structure.

[0010] Preferably, in step three, the control parameters for pipe jacking construction include eccentric over-excavation rate, pipe jacking pitch slope, grouting filling rate, grouting pressure ratio, frontal additional thrust, friction between the tunneling machine and the surrounding soil, and friction between the subsequent pipeline and the surrounding soil.

[0011] Preferably, the eccentric over-excavation rate is ≤0.2%, the pipe jacking slope is ≤0.1%, the grouting filling rate is ≥1.0, and the grouting pressure ratio is ≥1.04.

[0012] Preferably, in step four, the diameter of the steel pipes used for the circular small-diameter pipe curtain is... Steel pipe wall thickness Spacing between steel pipes Based on the equivalent elastic modulus of the foundation after pipe jacking reinforcement The value of is determined, and the equivalent elastic modulus of the foundation after pipe jacking reinforcement is determined. Calculate using the following formula: ; in, The equivalent elastic modulus of the tube curtain complex. For the area covered by the tube curtain, The draining elastic modulus of the natural foundation soil. This refers to the total area affected by the pipe jacking construction. This represents the cross-sectional area of ​​the pipe jacking excavation.

[0013] Preferably, the equivalent elastic modulus of the tube curtain composite The calculation formula is as follows: ; in, The cross-sectional area of ​​the steel pipe used for the pipe curtain is... The elastic modulus of steel, This represents the cross-sectional area of ​​the cement mortar inside the steel pipe. This refers to the elastic modulus of cement mortar after it has cured. This refers to the cross-sectional area of ​​the grout-cured soil between the steel pipes. This refers to the elastic modulus of the grouting and solidification soil.

[0014] Preferably, the coverage area of ​​the tube curtain , cross-sectional area of ​​pipe jacking excavation Total area affected by pipe jacking construction The calculation formula is as follows: ; ; ; in, The length of the area affected by the pipe jacking reinforcement. The outer radius of the jacking pipe, The depth of the pipe jacking arch is determined by the following: This refers to the total length of the area affected by the pipe jacking construction.

[0015] Preferably, the cross-sectional area of ​​the steel pipe Cross-sectional area of ​​cement mortar inside the steel pipe The cross-sectional area of ​​the grouting and solidification soil between the steel pipe and the steel pipe The calculation formula is as follows: ; ; ; in, The quantity of steel pipes used in the pipe curtain installation; Quantity of steel pipes for pipe curtain Calculate using the following formula: ; in, The gap between the pipes inside the pipe curtain. This refers to the spacing between the steel pipes.

[0016] Therefore, the present invention employs the above-mentioned method for pre-reinforcement and protection of pipe jacking construction under the foundation of ancient city walls, which has the following beneficial effects: (1) This invention realizes the quantitative characterization of the pre-reinforcement effect of pipe curtain; existing pipe curtain engineering design usually relies on experience to select pipe curtain parameters. This invention provides a quantitative basis for the optimization design of pipe curtain parameters by establishing the equivalent elastic modulus of the circular small pipe curtain composite and the calculation method of the equivalent elastic modulus of the foundation after pipe curtain reinforcement.

[0017] (2) The present invention effectively reduces the differential settlement between the masonry and the rammed earth core of the ancient city wall. In view of the composite structure characteristics of the ancient city wall masonry and rammed earth with stiffness differences of up to hundreds of times, the present invention significantly improves the overall stiffness of the foundation by pre-reinforcing with circular small pipe curtains, so that the settlement difference between the masonry and rammed earth is reduced from several millimeters when unreinforced to less than 1mm, thus avoiding the separation or peeling between the masonry and rammed earth.

[0018] (3) The present invention causes little disturbance during construction and forms a “hard shell protective cover” to ensure safe tunneling of the pipe jacking. Compared with pile foundation reinforcement and arched large pipe curtain reinforcement, the circular small pipe curtain method adopted in the present invention causes the least disturbance to the stratum and forms a closed protective structure outside the pipe jacking excavation outline, so that the pipe jacking can be excavated inside it, effectively isolating the impact of construction on the upper cultural relics.

[0019] (4) This invention provides the preferred range of control parameters for pipe jacking construction; Based on the settlement prediction model inversion, this invention determines the range of key control parameters for pipe jacking construction, including eccentric over-excavation rate, pipe jacking pitch slope, grouting filling rate and grouting pressure ratio, etc., providing a reference construction control standard for similar underpass projects.

[0020] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0021] Figure 1 This is a flowchart of a pipe jacking construction method for pre-reinforcement and protection of pipe jacking under the foundation of an ancient city wall, according to the present invention. Figure 2 This is a schematic diagram of the equivalent treatment of the city wall foundation in an embodiment of the present invention; Figure 3 This is a schematic cross-sectional view of Scheme 1 - pile foundation reinforcement in an embodiment of the present invention; Figure 4 This is a schematic cross-sectional view of Scheme 2 - circular small tube curtain reinforcement in an embodiment of the present invention; Figure 5 This is a schematic cross-sectional view of Scheme 3 - arched large pipe curtain reinforcement in the embodiment of the present invention; Figure 6 This is a schematic cross-sectional view of Scheme 4 - combined reinforcement of pile foundation and arched pipe curtain in the embodiment of the present invention; Figure 7 This is a schematic diagram of the design parameters for the combined reinforcement of pile foundation and arched pipe curtain in Scheme 4 of this invention. Figure 8 This is a graph showing the impact of pipe jacking construction on the heave and settlement of the city wall masonry and core wall rammed earth when no pre-reinforcement measures are taken in this embodiment of the invention. Figure 9 This is a graph showing the impact of pipe jacking construction after pile foundation pre-reinforcement in an embodiment of the present invention on the heave and settlement of the city wall masonry and core wall rammed earth. Figure 10 This is a graph showing the impact of the pre-reinforced circular small-tube curtain construction of Scheme 2 on the heave and settlement of the city wall masonry and the rammed earth of the core wall in an embodiment of the present invention. Figure 11 This is a curve showing the impact of the pre-reinforced arched pipe curtain construction (Scheme 3) on the heave and settlement of the city wall masonry and the rammed earth core wall in an embodiment of the present invention. Figure 12This is a graph showing the impact of the combined reinforcement of the pile foundation and the arched pipe curtain in Scheme 4 of this invention on the heave and settlement of the masonry and rammed earth core of the city wall. Detailed Implementation

[0022] The following detailed description of embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely illustrates selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0023] Example like Figure 1 As shown, this invention provides a method for pre-reinforcement and protection of pipe jacking construction under the foundation of an ancient city wall, comprising the following steps: Step 1: Conduct geological surveys in the pipe jacking construction area to obtain the physical and mechanical parameters of the soil layer of the ancient city wall foundation.

[0024] The following is an example of a pipe jacking project under a section of an ancient city wall. This section of the wall is approximately 12m high, 12-14m wide at the top, and 15-18m wide at the bottom. The wall structure is a composite structure consisting of an outer brick and stone masonry wall enclosing an inner rammed earth core wall.

[0025] Before pipe jacking construction, a detailed geological survey of the site is required. According to the survey report, the geological structure within 20m below the surface consists of artificial fill layers (Q4) from top to bottom. ml Quaternary Holocene alluvial-diluvial loess layer (Q3) eol Late Pleistocene aeolian loess layer (Q3) eol Late Pleistocene residual paleosol layer (Q3) el ) and the Middle Pleistocene aeolian loess and alluvial silty clay layers (Q2) al+p The groundwater at the site is of the phreatic type, with a stable water level depth ranging from 5.20 to 10.80 meters during the exploration period. The site is a non-self-weight collapsible loess site, with a collapsibility level of I.

[0026] In the section where the pipe jacking passes through, the mechanical parameters of the masonry wall are obtained, including: axial compressive strength, tensile strength, shear strength, and modulus of elasticity; the physical and mechanical parameters of each layer of foundation soil are obtained, including: natural water content, natural unit weight, liquid limit, plastic limit, plasticity index, liquidity index IL, compression modulus, cohesion, internal friction angle, modulus of elasticity, and thickness of each soil layer.

[0027] The mechanical parameters of the city wall masonry in different regions are shown in Table 1.

[0028] Table 1 Mechanical parameters of city wall masonry in different regions

[0029] The physical and mechanical properties of the foundation strata of the city wall are shown in Table 2.

[0030] Table 2 Physical and mechanical properties of the foundation strata of the city wall

[0031] In addition, a current status survey of existing defects in the city wall should be conducted. Technologies such as ground-penetrating radar, 3D laser scanning, infrared thermal imaging, and rebound hammers should be comprehensively utilized to detect defects in the city wall, obtaining the location, morphology, and degree of development of defects such as cracks, spalling, mortar loss, efflorescence, bulging, and settlement on the surface and inside the wall. For the masonry of the city wall, rebound values ​​should be obtained through rebound tests, and the axial compressive strength, tensile strength, shear strength, and modulus of elasticity of the masonry should be calculated according to standard methods.

[0032] Step 2: Based on the physical and mechanical parameters, the area-weighted equivalent of the ancient city wall masonry structure, the core wall rammed earth structure, and the foundation soil is used with the stratum equivalence method to obtain the homogenized equivalent stratum parameters, including the equivalent elastic modulus, the equivalent compression modulus, and the equivalent Poisson's ratio.

[0033] Specifically, since the ancient city wall is a structure protruding from the natural ground surface, its stiffness differs significantly from that of the foundation soil (the elastic modulus of the city wall masonry is approximately 2.4 GPa, while the compression modulus of the foundation soil is only 5-7 MPa). Directly using natural stratum parameters to calculate the settlement of the city wall caused by pipe jacking construction will result in a large error. Therefore, this embodiment proposes the stratum equivalence method, which considers the city wall masonry structure and the rammed earth core structure as part of the "stratum," and performs area-weighted equivalence calculations on their physical and mechanical parameters with the foundation soil parameters.

[0034] The equivalent elastic modulus and equivalent compression modulus are calculated as the weighted average of the elastic modulus and compression modulus of the ancient city wall masonry and the foundation soil layer, respectively, with their respective heights as the weight; the equivalent Poisson's ratio is calculated as the weighted average of the Poisson's ratio of the ancient city wall masonry and the foundation soil layer, with their respective heights as the weight. The calculation formulas are as follows: ; ; ; in, For the equivalent elastic modulus, The elastic modulus of the ancient city wall masonry. The elastic modulus of the foundation soil layer. This refers to the vertical height of the ancient city wall. This refers to the vertical height of the foundation soil layer; For equivalent compressive modulus, The compression modulus of the ancient city wall masonry. The compression modulus of the foundation soil layer; For the equivalent Poisson ratio, The Poisson's ratio for the masonry of the ancient city wall The Poisson's ratio is the ratio of the soil layer in the foundation.

[0035] For this embodiment, the elastic modulus of the city wall masonry... =2.39 GPa, Poisson's ratio =0.212; Equivalent elastic modulus of foundation soil ≈15.57~21.33MPa, equivalent Poisson's ratio ≈0.3; height of the city wall =12m, foundation soil layer height The thickness of the natural strata above the jacking pipe axis is taken. The equivalent elastic modulus is obtained through the above formula. Equivalent compression modulus and equivalent Poisson ratio .

[0036] Drainage elastic modulus of natural foundation soil According to the compression modulus in soil mechanics The conversion relationship with the elastic modulus is determined, that is ~=3 In this embodiment, the compression modulus of each soil layer is shown in Table 2. The corresponding drainage elastic modulus is 5.06~7.11 MPa. It is approximately 15~21 MPa (0.015~0.021 GPa).

[0037] Figure 2 This is a schematic diagram of the equivalent treatment of the city wall foundation, showing the treatment method of treating the city wall masonry and the foundation soil layer as equivalent to a homogenized stratum.

[0038] Step 3: Based on the Mindlin displacement solution and the modified Peck formula, calculate the settlement of the city wall foundation caused by the additional thrust of the tunnel boring machine at the front during the pipe jacking construction, the settlement caused by the friction between the tunnel boring machine and the surrounding soil, the settlement caused by the friction between the subsequent pipeline and the surrounding soil, and the settlement caused by construction factors. The above four settlements are superimposed to obtain the total settlement during the pipe jacking construction under the ancient city wall, and the control parameters of the pipe jacking construction are determined based on the total settlement.

[0039] Before construction, the key mechanical parameters for pipe jacking must be determined using standardized methods. The total jacking force F required for pipe jacking is estimated using the following formula: ; ; ; in, The total jacking force is (kN). The frictional resistance (kN) between the outer wall of the pipeline and the soil layer. The frontal resistance of the pipe jacking machine (kN); The outer diameter of the pipe (m). The length of the pipe jacking is (m). This represents the average frictional resistance (kPa) between the outer wall of the pipe and the soil. The diameter of the pipe jacking machine is in meters (m). Mesh extrusion resistance (kN / m) 2 According to the "Technical Specification for Pipe Jacking Construction of Urban Integrated Utility Tunnels" (DB 61 / T 5104-2024), the unit friction force f should be taken as 2~7 kPa, and the mesh extrusion resistance R 1 100~500kN / m 2 .

[0040] Grouting pressure Estimate using the following formula: ; in, The grouting pressure is (kPa). The grouting coefficient is taken as 0.8~1.2. The unit weight of soil (kN / m) 3 ), The burial depth of the pipeline axis is (m). Calculations show that the grouting pressure can be selected from 239.89~359.83 kPa when passing under rammed earth areas, and from 238.95~358.43 kPa when passing under masonry areas.

[0041] The above specifications can be used to calculate the additional thrust at the front of the pipe jacking. Take 20 kPa as the frictional force per unit area between the tunneling machine and the surrounding soil. Take 10 kPa (corresponding to 20 kPa for the unit friction force of the tunneling machine, deducting the friction-reducing effect of the thixotropic mud), the unit area friction force between the subsequent pipeline and the surrounding soil. A value of 5 kPa (corresponding to the median of the recommended values ​​of 2-7 kPa) is used as the basic input parameter for subsequent settlement prediction.

[0042] Specifically, in 1936, Mindlin proposed a mathematical solution in elasticity for solving the stress and displacement at any point within a semi-infinite body when subjected to a concentrated force. This embodiment, based on this displacement solution, approximates the additional thrust on the front of the tunnel boring machine as a uniformly distributed circular load, and the frictional force between the tunnel boring machine, the subsequent pipeline, and the surrounding soil as a uniformly distributed frictional force, calculating the settlement of the city wall foundation caused by each factor.

[0043] The calculation formulas for settlement caused by frontal thrust, settlement caused by tunneling machine friction, and settlement caused by subsequent pipeline friction are as follows: ; ; ; in, Settlement caused by the additional thrust applied to the front of the tunneling machine To apply additional thrust (kPa) to the front of the tunneling machine, take 20 kPa. The horizontal distance (m) from the excavation face is taken as the positive direction of the jacking. The equivalent shear modulus of the soil. It represents the vertical distance from the ground, with downward as the positive direction. This is the distance from the pipe jacking axis to the ground. and For polar coordinate integration variables, The diameter of the tunneling machine (m); This settlement is caused by the friction between the tunneling machine and the surrounding soil. This refers to the frictional force per unit area between the tunneling machine and the surrounding soil. The outer radius of the tunneling machine. The length of the tunneling machine; This settlement is caused by the friction between the pipeline and the surrounding soil. This refers to the frictional force per unit area between the pipeline and the surrounding soil. For the outer radius of the subsequent pipeline, For the subsequent pipeline length, , , , , , All of these are intermediate variables.

[0044] ; ; ; ; ; .

[0045] Construction factors include grouting filling rate, grouting pressure ratio, eccentric over-excavation rate, and tunneling machine pitch angle, as well as settlement caused by these construction factors. Calculations are based on Peck's formula. In 1969, Peck first proposed the concept of ground loss, arguing that the surface settlement curve caused by tunnel excavation exhibits a Gaussian normal distribution, hence the Peck formula. To consider the constraint and adjustment effect of superstructure stiffness on ground displacement, this embodiment employs the stiffness correction method (BGI method, i.e., Building-Ground Interaction method). This method quantifies the constraint and adjustment effect of structural stiffness on ground displacement by comparing the morphological differences between the settlement curves of the natural ground and the building, and introduces a stiffness correction coefficient. Settlement trough width parameters for natural ground The Peck formula parameters are corrected by adding correction factors for foundation depth and the angle between the tunnel and the building.

[0046] Corrected settling trough width parameters The calculation formula is: ; Stiffness correction factor The calculation formula is: ; in, The shear stiffness of the cross section of the ancient city wall structure.

[0047] For the masonry structure of the city wall, M = E × A, where E is the elastic modulus of the masonry and A is the cross-sectional area of ​​the city wall structure (taken as the product of the width affected by pipe jacking construction and the height of the city wall). For the rammed earth core structure of the city wall, M = Erammed × Arammed, where Erammed is the elastic modulus of the rammed earth and Arammed is the cross-sectional area of ​​the rammed earth core.

[0048] Settlement caused by construction factors The calculation formula is: ; in, Settlement caused by factors related to pipe jacking construction; This represents the maximum surface subsidence. The burial depth of the centerline of the pipe jacking tunnel; The settlement trench width parameter was adjusted to take into account the structural stiffness of the ancient city wall; It is the standard normal distribution function; and These are the coordinate values ​​in the coordinate systems established in the pipe jacking direction and the horizontal direction, respectively. and These are the starting and ending points of the affected section during pipe jacking construction.

[0049] Maximum surface subsidence The calculation formula is as follows: ; in, Formation loss rate, This represents the cross-sectional area of ​​the pipe jacking excavation. This is the settling trough width coefficient; Formation loss rate Total settlement at the arch of the pipe jacking Sure: ; ; in, The outer radius of the tunneling machine; The settlement of the arch caused by the grouting filling rate; This refers to the crown settlement caused by the grouting pressure ratio; The settlement of the crown is caused by the eccentric over-excavation rate; This refers to the settlement of the arch crown caused by the pitching slope of the tunneling machine.

[0050] Crown settlement caused by grouting filling rate Crown settlement caused by grouting pressure ratio Crown settlement caused by eccentric over-excavation rate Crown settlement caused by the pitch slope of the tunnel boring machine The calculation formula is as follows: ; ; ; ; in, For grouting filling rate, The physical gap at the shield tail (i.e., the difference between the outer diameter of the pipe jacking machine and the pipe jacking pipe). This refers to the physical gap between the pipe wall and the soil. The outer radius of the tunneling machine. The Poisson's ratio for undrained soil is 0.5 in this example. For the undrained shear strength of the soil, The undrained elastic modulus of the soil. The grouting pressure ratio, This refers to the vertical earth pressure at the tunnel axis. For eccentric over-excavation rate, The length of the tunneling machine; This represents the pitch angle of the tunneling machine (positive for pitching up and negative for pitching down).

[0051] The four settlement parameters calculated in step three are... , w3 and By superimposing the data, we obtain the predicted total settlement value during the pipe jacking construction under the ancient city wall: ; in, This represents the final predicted settlement value.

[0052] The total settlement of the city wall foundation under different combinations of construction parameters was calculated using the formula for predicting total settlement. This was then combined with the allowable settlement control standards for the ancient city wall (maximum settlement). ≤-15mm, maximum bulge (≤+5mm), the control parameters for pipe jacking construction are determined through inversion. The calculated control parameters for pipe jacking construction include: eccentric over-excavation rate. ≤0.2%, pipe jacking slope ≤0.1%, grouting filling rate ≥1.0, grouting pressure ratio ≥1.04, frontal additional thrust =20kPa, frictional force between the tunneling machine and the surrounding soil =10kPa, frictional force between the subsequent pipeline and the surrounding soil =5kPa.

[0053] Step 4: Based on the control parameters determined in Step 3, a circular small pipe curtain is pre-constructed outside the jacking excavation outline. The circular small pipe curtain is composed of multiple steel pipes arranged along the outer periphery of the jacking excavation outline. Grouting is injected inside the steel pipes and between the steel pipes to form a hard shell protective cover.

[0054] The construction of the circular small-diameter pipe curtain is carried out before pipe jacking. First, at the designed location, multiple steel pipes are jacked into the stratum along the outer perimeter of the pipe jacking excavation outline using horizontal directional drilling or pipe ramming. The steel pipes are arranged around the arched area of ​​the pipe jacking excavation outline (for circular small-diameter pipe curtains, around the entire circumference of the pipe jacking), with a certain spacing between each steel pipe. After the steel pipes are jacked in, cement mortar is injected into the inside of the steel pipes to form a solid steel-concrete composite. At the gaps between the steel pipes, cement-water glass double-liquid grout is injected through grouting holes. After the grout diffuses, it forms solidified soil with the surrounding soil, connecting all the steel pipes into a whole, forming a closed "hard shell protective cover". Figure 4 This is a cross-sectional schematic diagram of Scheme 2 - Circular Small Pipe Curtain Reinforcement in an embodiment of the present invention. The steel pipes are arranged along the entire circumference of the jacking pipe excavation outline to form a fully enclosed circular protective structure.

[0055] Before constructing the pipe jacking, the geometric parameters of the pipe jacking need to be determined based on the control parameters established in step three and the expected reinforcement effect; the diameter of the steel pipes in the small circular pipe jacking... Steel pipe wall thickness Spacing between steel pipes Based on the equivalent elastic modulus of the foundation after pipe jacking reinforcement The value of is determined, and the equivalent elastic modulus of the foundation after pipe jacking reinforcement is determined. Calculate using the following formula: ; in, The equivalent elastic modulus of the tube curtain complex. The area covered by the pipe jacking (i.e., the area occupied by the entire pipe jacking within the influence range of the pipe jacking). The drained elastic modulus of the natural foundation soil (taken as 3 times the compression modulus of the natural foundation soil). This refers to the total area affected by the pipe jacking construction. This represents the cross-sectional area of ​​the pipe jacking excavation.

[0056] Equivalent elastic modulus of tube curtain complex Calculated based on the area-weighted average of the elastic moduli of each component material: ; in, The cross-sectional area of ​​the steel pipe used for the pipe curtain is... The elastic modulus of steel (for Q235B steel, =200GPa), This represents the cross-sectional area of ​​the cement mortar inside the steel pipe. The elastic modulus of cement mortar after curing is taken as 20 GPa. This refers to the cross-sectional area of ​​the grout-cured soil between the steel pipes. The elastic modulus of the grouting and solidified soil is 0.2 GPa.

[0057] Tube curtain coverage area , cross-sectional area of ​​pipe jacking excavation Total area affected by pipe jacking construction The calculation formula is as follows: ; ; ; in, The influence length of the pipe jacking reinforcement range (determined by the pipe jacking layout range). The outer radius of the jacking pipe, The buried depth of the pipe jacking arch (i.e., the distance from the top of the pipe jacking to the ground). This refers to the total length of the area affected by the pipe jacking construction.

[0058] steel pipe cross-sectional area Calculated based on the area of ​​the annulus: ; Cement mortar cross-sectional area inside steel pipe Calculated based on the area of ​​the circle corresponding to the inner diameter of the steel pipe: ; Cross-sectional area of ​​grouting and solidification between steel pipes The remaining portion after deducting the area of ​​steel pipes and jacking pipes from the total area of ​​the pipe jacking: ; in, The quantity of steel pipes used in the pipe curtain installation; Quantity of steel pipes for pipe curtain Determined by dividing the perimeter of the tube jack by the arc length occupied by a single steel pipe: ; in, This refers to the gap between the inner edge of the steel pipe and the outer wall of the jacking pipe (i.e., the reserved gap between the inner edge of the steel pipe and the outer wall of the jacking pipe). This refers to the spacing between steel pipes (i.e., the net distance between the outer walls of adjacent steel pipes).

[0059] In this embodiment, the outer radius of the jacking pipe... =1.5m (corresponding to a pipe jacking diameter of 3000mm), burial depth of the pipe jacking arch =4.5m. To determine the optimal pipe jacking parameters, this embodiment performed calculations and comparisons for various pipe jacking design conditions. The calculation results of the equivalent elastic modulus E of the foundation after pipe jacking reinforcement with different combinations of pipe diameter and wall thickness are shown in Table 3.

[0060] Table 3 Equivalent Modulus of Foundation After Scheme 2 - Circular Small Tube Curtain Reinforcement

[0061] As shown in Table 3, the equivalent elastic modulus of the foundation increases with the increase of the steel pipe diameter and wall thickness. Considering the reinforcement effect, construction difficulty, and economy, the optimal parameters for a small circular pipe jacking are: steel pipe diameter... =402mm, steel pipe wall thickness =16mm, steel pipe spacing =153mm, gap between pipe culverts inside the pipe curtain =0.2m, slurry diffusion radius outside the pipe curtain =0.5m. Using the above parameters, the original foundation elastic modulus is approximately 0.015~0.021 GPa (compression modulus). Approximately 5~7 MPa, drainage elastic modulus ≈3 Equivalent elastic modulus of foundation after pipe jacking reinforcement The value is 1.08 GPa.

[0062] In step four, in order to verify the superiority of the circular small pipe curtain scheme selected in this embodiment, the reinforcement effects of scheme 1 (pile foundation), scheme 3 (arched large pipe curtain) and scheme 4 (combined reinforcement of pile foundation and arched pipe curtain) were calculated and compared.

[0063] Figure 3 This is a cross-sectional schematic diagram of Scheme 1 – pile foundation reinforcement in this embodiment. Scheme 1 employs double-row bored pile reinforcement measures on both sides of the inner and outer city walls. The reinforcement mechanism is as follows: constructing pile foundations on the ground outside the city walls effectively enhances the composite stiffness of the foundation, providing horizontal constraint on the foundation at the bottom of the city walls, thus reducing the possibility of uneven settlement and overall slippage failure of the city wall foundation. The reinforcement effect of Scheme 1 is calculated using the pile-soil area replacement ratio. The outer pile arrangement is considered as a square double-row pile layout, with short piles on the upper part of the jacking pipe and long piles on both sides. The compression modulus of the reinforced composite foundation is... ,in The equivalent compression modulus of the composite foundation after pile foundation reinforcement. The soil-pile area replacement ratio. The pile-soil stress ratio is given. The calculation results of the equivalent elastic modulus of the foundation after pile reinforcement are shown in Table 4.

[0064] Table 4 Equivalent Modulus of Foundation After Drilled Piles Reinforcement (Scheme 1)

[0065] Figure 5 This is a schematic cross-sectional view of Scheme 3 – the arched large-diameter pipe jacking reinforcement – ​​in this embodiment. Scheme 3 replaces the circular pipe jacking in Scheme 2 with a larger-diameter arched (semi-circular) large-diameter pipe jacking pre-reinforcement measure. Its reinforcement mechanism is similar to Scheme 2, except that the size of the pipe jacking is increased and the material of the lower semi-circular pipe jacking is reduced. The calculation method for the equivalent modulus of the arched pipe jacking is similar to that of the circular pipe jacking, only the pipe jacking arrangement range is changed from a full circle to an arched region. The calculation results of the equivalent elastic modulus of the foundation after Scheme 3 reinforcement are shown in Table 5.

[0066] Table 5 Equivalent Modulus of Foundation After Scheme 3 - Arched Tube Curtain Reinforcement

[0067] Figure 6This is a cross-sectional schematic diagram of Scheme 4 – the combined reinforcement of pile foundation and arched pipe curtain – in this embodiment. Scheme 4 combines Schemes 1 and 3, reducing the size of the semi-circular pipe curtain and rigidly connecting the pipe curtain to the pile foundations on both sides of the city wall, forming an "H"-shaped protective system at the bottom of the city wall. The design dimensions of the pile foundations on both sides of the city wall are: pile diameter 1.0m, pile spacing 1.5m, top pile length 2.5m, pile length on both sides of the pipe curtain 8.75m, and pile distance 3.75m from the outer wall of the city wall. The steel pipes of the arched pipe curtain are arranged along the arched area of ​​the pipe curtain excavation outline, forming a semi-enclosed arched protective structure.

[0068] The difference between Scheme 4 and Scheme 2 is that: (1) the range of the pipe curtain arrangement is changed from the full circumference to an arched area, and the pipe curtain coverage area is... Calculated based on the area of ​​the arched region (2) On the basis of pipe curtain reinforcement, bored piles were added on both sides of the city wall, and the equivalent compression modulus of the pile foundation reinforcement zone was increased. Calculated based on the pile-soil area replacement ratio. The cross-sectional area of ​​the steel pipe in the pipe jacking section of Scheme 4. Cross-sectional area of ​​cement mortar inside the steel pipe , cross-sectional area of ​​grouting and solidification between steel pipes and the number of steel pipes for pipe draping The calculation method is the same as above, except that the cross-sectional area of ​​the steel pipe, the cross-sectional area of ​​the cement mortar inside the steel pipe, the cross-sectional area of ​​the grouting and solidified soil between the steel pipes, and the number of steel pipes in the pipe drape calculation formula are all included. Replace with That's sufficient. The area of ​​the pile foundation reinforcement zone in Option 4... Calculated based on the layout range of the pile foundation.

[0069] Equivalent elastic modulus of foundation after pipe jacking reinforcement in Scheme 4 Calculate using the following formula: ; in, The area covered by the arched tube curtain. The equivalent compression modulus of the composite foundation after pile reinforcement is calculated using the following formula: ; in, For the pile diameter, The equivalent circle diameter of the treated foundation area shared by a single pile ( =1.13S, where S is the pile spacing). The pile-soil stress ratio is taken as 2 to 4 for cohesive soil, and n=2 in this embodiment. The compression modulus of the natural foundation soil; This refers to the area of ​​the pile foundation reinforcement zone; This refers to the total area affected by the pipe jacking construction. This represents the cross-sectional area of ​​the pipe jacking excavation.

[0070] Figure 7 This is a schematic diagram of the design parameters for the combined reinforcement of pile foundation and arched pipe curtain in Scheme 4 of this embodiment.

[0071] When using Scheme 4, the equivalent elastic modulus of the foundation after pipe jacking reinforcement under different combinations of pipe diameter and wall thickness is... The calculation results are shown in Table 6.

[0072] Scheme 4 - Equivalent Modulus of Foundation After Pile Foundation + Arched Small Pipe Curtain Reinforcement

[0073] Table 7 shows a comparison of the reinforcement effects of each scheme.

[0074] Table 7 Comparison of city wall heave and deformation before and after different pre-reinforcement measures were adopted.

[0075] As shown in Table 7, after adopting the preferred circular small-tube jacking pre-reinforcement scheme (Scheme 2) in step four of this embodiment, the maximum settlement of the city wall masonry is only -0.13 mm, and the maximum heave is 0.06 mm; the maximum settlement of the rammed earth core wall is only -0.86 mm, and the maximum heave is 0.95 mm. The settlement difference between the city wall masonry and the rammed earth core wall is reduced from 5.11 mm (the difference between -7.93 mm and -2.82 mm) before reinforcement to 0.73 mm (the difference between -0.86 mm and -0.13 mm), effectively avoiding the separation or delamination between the masonry and the rammed earth. Compared with Scheme 1 (pile foundation), Scheme 3 (arched large-tube jacking), and Scheme 4 (pile foundation + arched tube jacking), Scheme 2 has the most significant reinforcement effect.

[0076] Figure 8 The curves showing the impact of pipe jacking construction on the heave and settlement of the city wall masonry and core wall rammed earth without pre-reinforcement measures are presented. Figures 9-12 The curves showing the impact of pre-reinforcement schemes 1-4 on the heave and settlement of the masonry and rammed earth core of the city wall after pipe jacking construction are presented respectively. Figure 10 It can be seen that after adopting the circular small tube curtain pre-reinforcement scheme of this embodiment, the heave and deformation of the city wall masonry and rammed earth are controlled within 1mm, which is significantly better than the unreinforced scheme and other comparative schemes, verifying the technical superiority of this embodiment.

[0077] Step 5: Under the protection of the hard shell protective cover, the pipe jacking construction is carried out, so that the pipe jacking passes through the foundation of the ancient city wall inside the protective cover formed by the circular small pipe curtain.

[0078] After the circular small-diameter pipe curtain is completed and the grouting material reaches the designed strength, a "hard shell protective cover" with a certain rigidity is formed. Under the protection of this protective cover, the pipe jacking machine advances from the starting shaft to the receiving shaft. When the pipe jacking passes through the foundation section of the city wall, it advances entirely inside the pipe curtain protective structure. The pipe curtain structure bears the load of the overlying soil and the city wall, effectively isolating the surrounding soil from the disturbance of the pipe jacking excavation and controlling the settlement of the city wall foundation caused by the pipe jacking construction within the allowable range.

[0079] Therefore, the present invention adopts the above-mentioned pipe jacking construction method for pre-reinforcement and protection of ancient city wall foundations. It achieves accurate prediction of settlement of the city wall composite structure through the stratum equivalence method. The pre-reinforcement of the circular small pipe jacking forms a "hard shell protective cover" to effectively control the disturbance of the upper cultural relics caused by the pipe jacking construction. It has the advantages of small construction disturbance, quantitative evaluation of reinforcement effect, and applicability to the protection of various ancient city wall composite structures.

[0080] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for pre-reinforcement and protection of pipe jacking construction under the foundation of an ancient city wall, characterized in that, Includes the following steps: Step 1: Conduct geological surveys in the pipe jacking construction area to obtain the physical and mechanical parameters of the soil layer of the ancient city wall foundation. Step 2: Based on the physical and mechanical parameters, the area-weighted equivalent of the ancient city wall masonry structure, the core wall rammed earth structure and the foundation soil is performed using the stratum equivalence method to obtain the homogenized equivalent stratum parameters, including the equivalent elastic modulus, the equivalent compression modulus and the equivalent Poisson's ratio. Step 3: Based on the Mindlin displacement solution and the modified Peck formula, calculate the settlement of the city wall foundation caused by the additional thrust of the tunneling machine at the front during the pipe jacking construction, the settlement caused by the friction between the tunneling machine and the surrounding soil, the settlement caused by the friction between the subsequent pipeline and the surrounding soil, and the settlement caused by construction factors. The above four settlements are superimposed to obtain the total settlement during the pipe jacking construction under the ancient city wall, and the control parameters of the pipe jacking construction are determined based on the total settlement. Step 4: Based on the control parameters determined in Step 3, a circular small pipe curtain is pre-constructed outside the pipe jacking excavation outline. The circular small pipe curtain is composed of multiple steel pipes arranged along the outer periphery of the pipe jacking excavation outline. Grouting is injected inside the steel pipes and between the steel pipes to form a hard shell protective cover. Step 5: Under the protection of the hard shell protective cover, the pipe jacking construction is carried out, so that the pipe jacking passes through the foundation of the ancient city wall inside the protective cover formed by the circular small pipe curtain.

2. The method for pre-reinforcement and protection of pipe jacking construction under the foundation of an ancient city wall as described in claim 1, characterized in that, In step two, the equivalent elastic modulus and equivalent compression modulus are calculated as the weighted average of the elastic modulus and compression modulus of the ancient city wall masonry and the foundation soil layer, respectively, with their respective heights as the weight; the equivalent Poisson's ratio is calculated as the weighted average of the Poisson's ratio of the ancient city wall masonry and the foundation soil layer, with their respective heights as the weight. The calculation formulas are as follows: ； ； ； in, For the equivalent elastic modulus, The elastic modulus of the ancient city wall masonry. The elastic modulus of the foundation soil layer. This refers to the vertical height of the ancient city wall. This refers to the vertical height of the foundation soil layer; For equivalent compressive modulus, The compression modulus of the ancient city wall masonry. The compression modulus of the foundation soil layer; For the equivalent Poisson ratio, The Poisson's ratio for the masonry of the ancient city wall The Poisson's ratio is the ratio of the soil layer in the foundation.

3. The method for pre-reinforcement and protection of pipe jacking construction under the foundation of an ancient city wall as described in claim 1, characterized in that: In step three, construction factors include grouting filling rate, grouting pressure ratio, eccentric over-excavation rate, and tunneling machine pitch angle. The modified Peck formula uses a stiffness correction method to adjust the stiffness contribution of the ancient city wall structure, introducing a stiffness correction coefficient. Settlement trough width parameters for natural ground The corrected parameters are the width of the settling trough. The calculation formula is as follows: ； ； in, The shear stiffness of the cross section of the ancient city wall structure.

4. The method for pre-reinforcement and protection of pipe jacking construction under the foundation of an ancient city wall as described in claim 1, characterized in that: In step three, the control parameters for pipe jacking construction include eccentric over-excavation rate, pipe jacking pitch slope, grouting filling rate, grouting pressure ratio, frontal additional thrust, friction between the tunneling machine and the surrounding soil, and friction between the subsequent pipeline and the surrounding soil.

5. A method for pre-reinforcement and protection of pipe jacking construction under the foundation of an ancient city wall as described in claim 4, characterized in that: The eccentric over-excavation rate is ≤0.2%, the pipe jacking slope is ≤0.1%, the grouting filling rate is ≥1.0, and the grouting pressure ratio is ≥1.

04.

6. A method for pre-reinforcement and protection of pipe jacking construction under the foundation of an ancient city wall as described in claim 1, characterized in that, In step four, the diameter of the steel pipes in the circular small-diameter pipe curtain... Steel pipe wall thickness Spacing between steel pipes Based on the equivalent elastic modulus of the foundation after pipe jacking reinforcement The value of is determined, and the equivalent elastic modulus of the foundation after pipe jacking reinforcement is determined. Calculate using the following formula: ； in, The equivalent elastic modulus of the tube curtain complex. For the area covered by the tube curtain, The draining elastic modulus of the natural foundation soil. This refers to the total area affected by the pipe jacking construction. This represents the cross-sectional area of ​​the pipe jacking excavation.

7. A method for pre-reinforcement and protection of pipe jacking construction under the foundation of an ancient city wall as described in claim 6, characterized in that, Equivalent elastic modulus of tube curtain complex The calculation formula is as follows: ； in, The cross-sectional area of ​​the steel pipe used for the pipe curtain is... The elastic modulus of steel, This represents the cross-sectional area of ​​the cement mortar inside the steel pipe. This refers to the elastic modulus of cement mortar after it has cured. This refers to the cross-sectional area of ​​the grout-cured soil between the steel pipes. This refers to the elastic modulus of the grouting and solidification soil.

8. A method for pre-reinforcement and protection of pipe jacking construction under the foundation of an ancient city wall as described in claim 7, characterized in that, Tube curtain coverage area , cross-sectional area of ​​pipe jacking excavation Total area affected by pipe jacking construction The calculation formula is as follows: ； ； ； in, The length of the area affected by the pipe jacking reinforcement. The outer radius of the jacking pipe, The depth of the pipe jacking arch is determined by the following: This refers to the total length of the area affected by the pipe jacking construction.

9. A method for pre-reinforcement and protection of pipe jacking construction under the foundation of an ancient city wall as described in claim 8, characterized in that, steel pipe cross-sectional area Cross-sectional area of ​​cement mortar inside the steel pipe The cross-sectional area of ​​the grouting and solidification soil between the steel pipe and the steel pipe The calculation formula is as follows: ； ； ； in, The quantity of steel pipes used in the pipe curtain installation; Quantity of steel pipes for pipe curtain Calculate using the following formula: ； in, The gap between the pipes inside the pipe curtain. This refers to the spacing between the steel pipes.

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