Method for controlling micro-settlement of the ground surface under the large-section tunnel and buildings

Abstract

The present invention relates to the field of tunnel and underground engineering technology, and discloses a method for controlling the surface micro-settlement of the underpass surface and structures of a large-section tunnel. The method includes: calculating the surface settlement caused by tunnel excavation, the surface settlement caused by the superposition of a group of pipes, and the surface settlement caused by the over-consolidation of the soil. The sum of the three is the total surface settlement of the underpass surface and structures of the large-section tunnel; controlling the surface settlement by adjusting the values ​​of the pipe curtain stiffness and the support stiffness; controlling the surface settlement by adjusting the number of pipe curtains; controlling the surface settlement by adjusting the value of the grouting pressure, and arranging a lubricating slurry pipeline system in the pipe and a nozzle system evenly arranged around the pipe wall; formulating corresponding groundwater control measures for different strata according to the surface settlement caused by the over-consolidation of the soil. The present application provides an effective method and means for controlling the surface micro-settlement of the underpass surface and structures of a large-section tunnel, which helps to ensure the safe operation of tunnel construction, airplanes and high-speed railways, and the stability of structures.

Description

Technical Field

[0001] The invention relates to the technical field of tunnels and underground engineering, and in particular to a method for controlling surface micro-settlement of a large-section tunnel underpass and buildings. Background Art

[0002] With the rapid development of urban underground space in my country, the expansion and reconstruction of existing underground space, the elimination of hidden dangers, the expansion of functions, and the improvement of quality are important ways to coordinate urban spatial layout, intensively utilize resources, and enhance urban sustainable development. There will be more and more large-section tunnels buried shallowly under sensitive urban areas such as airport runways, railway stations, and important buildings, and the construction risks are extremely high.

[0003] The micro-settlement control standards in sensitive environments are generally at the millimeter level, which makes control extremely difficult, especially for large-section tunnels, which have many excavation steps, frequent deformation iterations, and a lack of theoretical support for deformation control. Summary of the invention

[0004] In view of this, the purpose of the present invention is to overcome the deficiencies in the prior art and provide a method for controlling surface micro-settlement of a large-section tunnel underpass and buildings.

[0005] The present invention provides the following technical solutions:

[0006] In a first aspect, the present disclosure provides a method for controlling surface micro-settlement of a large-section tunnel underpass and buildings, the method comprising:

[0007] S1: Calculate the cross-sectional surface settlement and the longitudinal section surface settlement caused by tunnel excavation, calculate the sum of the cross-sectional surface settlement and the longitudinal section surface settlement, and obtain the surface settlement caused by tunnel excavation;

[0008] S2: Calculate the ground settlement caused by the jacking of a single pipe of the pipe curtain and the correction coefficient of the ground settlement caused by the jacking of a group of pipes, calculate the sum of the correction coefficients of the ground settlement caused by the jacking of a group of pipes, and multiply it by the ground settlement caused by the jacking of the single pipe to obtain the ground settlement caused by the superposition of the group of pipes;

[0009] S3: calculating the overconsolidation settlement of the first layer of micro-element soil when the water level drops, integrating the overconsolidation settlement of the first layer of micro-element soil to obtain the overconsolidation settlement of the first layer of soil;

[0010] S4: Calculate the overconsolidation settlement of the i-th soil layer and the n-th soil layer according to S3, and sum the overconsolidation settlement of each soil layer to obtain the surface settlement caused by overconsolidation of the soil;

[0011] S5: Add the surface settlement caused by the tunnel excavation, the surface settlement caused by the superposition of the group pipes and the surface settlement caused by the overconsolidation of the soil to obtain the total surface settlement of the underpass surface and buildings of the large-section tunnel;

[0012] S6: Determine the load pipe curtain stiffness ratio according to the initially given tunnel excavation longitudinal section ground settlement control value, obtain a first relationship curve between the pipe curtain stiffness and the longitudinal section ground settlement by calculating in S1 according to the actual project, obtain the pipe curtain stiffness to be adjusted by dividing the given load value by the load pipe curtain stiffness ratio, and adjust the pipe curtain stiffness to be adjusted to a first preset range according to the first relationship curve, and obtain the longitudinal section ground settlement corresponding to the adjusted pipe curtain stiffness;

[0013] S7: Determine the load-support stiffness ratio according to the initially given tunnel excavation cross-section surface settlement control value, obtain a second relationship curve between support stiffness and cross-section surface settlement by calculating in S1 according to the actual project, obtain the support stiffness to be adjusted by dividing the given load value by the load-support stiffness ratio, and adjust the support stiffness to be adjusted to within a second preset range according to the second relationship curve to obtain the cross-section surface settlement corresponding to the adjusted support stiffness;

[0014] S8: According to the width of the settlement trough generated by the single-tube jacking, determine the distance where the pipe curtain jacking does not affect the maximum settlement as half of the width of the settlement trough, determine the number of pipe curtains according to half of the width of the settlement trough, and take the maximum surface settlement generated by the single-tube jacking and the sum of the settlement influence values ​​generated by the jacking of each pipe within the half width of the settlement trough on the left and right as the maximum surface settlement generated by the pipe curtain jacking;

[0015] S9: a third relationship curve between the grouting pressure and the surface settlement caused by the single-tube jacking is calculated by S2, a target grouting pressure corresponding to when the surface settlement caused by the single-tube jacking is 0 is determined according to the third relationship curve, the actual grouting pressure is adjusted according to the target grouting pressure, and a lubricating slurry pipeline system is arranged inside the pipe and a nozzle system is evenly arranged around the pipe wall to form a drag-reducing slurry sleeve outside the super-long pipe curtain steel pipe;

[0016] S10: Based on the surface settlement caused by over-consolidation of soil due to groundwater drop in different strata, formulate corresponding groundwater control measures for different strata.

[0017] Optionally, the calculating of the cross-sectional surface settlement and the longitudinal surface settlement caused by tunnel excavation includes:

[0018] S11: Acquire first basic data, wherein the first basic data at least includes soil bulk density, tunnel burial depth, initial support stiffness, tunnel cross-sectional width, tunnel height, lateral pressure coefficient, pipe curtain stiffness, and soil elastic resistance coefficient;

[0019] S12: establishing a differential equation for the bending of the tunnel lateral support structure according to the first basic data, solving the differential equation to obtain a settlement formula for the tunnel cross section, and substituting initial conditions into the settlement formula for the tunnel cross section to obtain the surface settlement of the cross section;

[0020] S13: Calculate the settlement of the face soil according to the Winkel hypothesis, calculate the maximum deflection of the pipe curtain from the tunnel face to the primary support closed section using the structural mechanics method, add the settlement of the face soil to the maximum deflection to obtain the surface settlement of the longitudinal section.

[0021] Optionally, the expression formula for the cross-sectional surface settlement is:

[0022] ,

[0023] The expression formula of the longitudinal section surface settlement is:

[0024] ,

[0025] In the formula, is the soil bulk density, is the tunnel burial depth, is the initial support stiffness, is the cross-sectional width of the tunnel, is the lateral pressure coefficient, is the tunnel height, is the tube curtain stiffness, It is half of the distance from the tunnel face to the closed ring of initial support. is the elastic resistance coefficient of the soil, is the surface settlement of the cross section, is the surface settlement of the longitudinal section.

[0026] Optionally, the calculating of the ground surface settlement caused by the jacking of a single pipe of the pipe curtain includes:

[0027] S21: Acquire second basic data, where the second basic data at least includes maximum settlement of a single-tube construction vault, tube curtain radius, tube curtain spacing, tube curtain burial depth, cohesion, internal friction angle, grouting pressure, soil pressure, soil shear modulus, excavation area, first parameter, and second parameter;

[0028] S22: using the Peck formula to obtain a surface settlement formula for single-tube jacking construction, wherein the surface settlement formula for single-tube jacking construction includes a stratum loss rate and a distance from the symmetry center of the settlement trough to the inflection point of the curve;

[0029] S23: using the second basic parameter to simplify the formation loss rate and the distance from the symmetric center of the settlement tank to the curve inflection point, to obtain the simplified formation loss rate and the simplified distance from the symmetric center of the settlement tank to the curve inflection point, and substitute the simplified formation loss rate and the simplified distance from the symmetric center of the settlement tank to the curve inflection point into the single-tube construction jacking surface settlement formula to obtain the surface settlement caused by the single-tube jacking;

[0030] The expression formula for the surface settlement caused by the single-tube jacking is:

[0031] ,

[0032] In the formula, is the grouting pressure, is the earth pressure, is the first parameter, is the second parameter, is the excavation area, is the distance from the symmetry center of the sedimentation tank to the inflection point of the curve, is the soil shear modulus, It is the surface settlement caused by the single-pipe jacking.

[0033] Optionally, the calculating the sum of the surface settlement correction coefficients of the group-pipe jacking and multiplying it by the surface settlement caused by the single-pipe jacking to obtain the surface settlement caused by the superposition of the group-pipes includes:

[0034] The expression formula of the surface settlement correction coefficient of the group pipe jacking is:

[0035] ,

[0036] The expression formula for the surface settlement caused by the superposition of the group pipes is:

[0037] ,

[0038] In the formula, is the tube-curtain spacing, is the surface settlement correction coefficient for the pipe group jacking, is the width coefficient of the sedimentation tank, is the sedimentation tank width threshold, is the maximum surface settlement correction factor, is the earth pressure, It is the surface settlement caused by the superposition of the group pipes.

[0039] Optionally, the calculating the overconsolidation settlement of the first layer of micro-element soil mass when the water level is lowered, integrating the overconsolidation settlement of the first layer of micro-element soil mass to obtain the overconsolidation settlement of the first layer of soil mass, comprises:

[0040] The expression formula of overconsolidation settlement of the first microelement soil is:

[0041] ,

[0042] The expression formula of the overconsolidation settlement of the first layer of soil is:

[0043] ,

[0044] In the formula, is the weight of water, is the Poisson's ratio of the first soil layer, is the thickness of the soil layer unit, is the initial water level, is the thickness of the first soil layer, is the elastic modulus of the first soil layer, where As a constant term, is the overconsolidation settlement of the first microelement soil layer, is the overconsolidation settlement of the first soil layer.

[0045] Optionally, respectively calculating the overconsolidation settlement of the i-th soil layer and the n-th soil layer includes:

[0046] The expression formula of the overconsolidation settlement of the i-th layer of soil is:

[0047] ,

[0048] The expression formula of the overconsolidation settlement of the nth layer of soil is:

[0049] ,

[0050] In the formula, is the height of water level drop, , are the Poisson's ratios of the i-th soil layer and the n-th soil layer, respectively. , , are respectively the i-th soil layer, the layer of soil, the thickness of the nth layer of soil, , are the elastic moduli of the i-th soil layer and the n-th soil layer, respectively. , As a constant term, , They are respectively layer of soil, overconsolidation settlement of the nth layer of soil.

[0051] Optionally, the summing of the overconsolidation settlements of each layer of soil to obtain the surface settlement caused by overconsolidation of the soil includes:

[0052] The expression formula for the surface settlement caused by the overconsolidation of the soil is:

[0053] ,

[0054] In the formula, is the surface settlement caused by overconsolidation of the soil, where: Divide the soil into layers. When the groundwater level is at the surface and drops through only one layer of soil, ,at this time , when the groundwater level is below the surface and drops only through a layer of soil, ,at this time , when the groundwater level is below the surface and descends through multiple layers of soil, ,at this time .

[0055] Optionally, according to the surface settlement caused by over-consolidation of soil due to groundwater drop in different strata, corresponding groundwater control measures are formulated for different strata, including:

[0056] S101: For pebble and gravel formations, no groundwater control measures are required;

[0057] S102: For medium sand, coarse sand and gravel sand formations, grouting is used as a groundwater control measure;

[0058] S103: For silt sand, fine sand and silt soil formations, adopt freezing groundwater control measures.

[0059] Beneficial effects of this application:

[0060] The method for controlling micro-settlement of the ground surface of large-section tunnel underpasses and buildings provided in the embodiments of the present application provides an effective method and means for controlling micro-settlement of the ground surface of large-section tunnel underpasses and buildings, which helps to ensure tunnel construction and the safe operation of airplanes and high-speed railways and the stability of buildings.

[0061] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and understandable, preferred embodiments are given below and described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work. In each of the drawings, similar components are numbered similarly.

[0063] Figure 1 A flow chart of a method for controlling micro-settlement of a large-section tunnel underpass and a building surface provided in an embodiment of the present application is shown;

[0064] Figure 2 A schematic diagram of mechanical calculation of a tunnel cross section provided in an embodiment of the present application is shown;

[0065] Figure 3 A schematic diagram of calculating the influence range of overburden load on an aerial soil body provided in an embodiment of the present application is shown;

[0066] Figure 4 A schematic diagram of a mechanical calculation model of a single-tube pipe curtain for a micro-shield construction provided in an embodiment of the present application is shown;

[0067] Figure 5 A schematic diagram of a group-pipe superposition effect model provided in an embodiment of the present application is shown;

[0068] Figure 6 A simplified diagram of overconsolidation settlement calculation provided by an embodiment of the present application is shown;

[0069] Figure 7 A first relationship curve between a load pipe curtain stiffness ratio and a longitudinal section ground settlement provided in an embodiment of the present application is shown;

[0070] Figure 8 A curve showing the relationship between the stiffness of a pipe roof and the longitudinal surface settlement provided in an embodiment of the present application is shown;

[0071] Fig. 9 A second relationship curve between a load-support stiffness ratio and a cross-sectional surface settlement provided in an embodiment of the present application is shown;

[0072] Fig.10 A curve showing the relationship between support stiffness and cross-section surface settlement provided in an embodiment of the present application is shown;

[0073] Fig.11 A relationship curve between the stacking coefficients of the tube curtain partition holes provided in an embodiment of the present application is shown;

[0074] Fig.12A third relationship curve between a grouting pressure and ground settlement caused by single-pipe jacking provided in an embodiment of the present application is shown;

[0075] Fig.13 A schematic diagram of a pipe outer wall pressure maintaining and drag reducing system provided in an embodiment of the present application is shown;

[0076] Fig.14 A schematic diagram of overconsolidation settlement calculation for a highly permeable stratum provided in an embodiment of the present application is shown;

[0077] Fig.15 A schematic diagram of a soil layer provided in an embodiment of the present application is shown;

[0078] Fig.16 A schematic diagram of consolidation settlement calculation for a medium sand stratum, a coarse sand stratum, and a gravel sand stratum provided in an embodiment of the present application is shown;

[0079] Fig.17 A schematic diagram of controlling water level by a grouting method provided in an embodiment of the present application is shown;

[0080] Fig.18 A schematic diagram of overconsolidation settlement calculation for a silt sand formation, a fine sand formation, and a silt soil formation provided in an embodiment of the present application is shown;

[0081] Fig.19 A schematic diagram of controlling groundwater level by a freezing method provided in an embodiment of the present application is shown. DETAILED DESCRIPTION

[0082] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0083] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0084] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein in the specification of the template are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0085] Example 1

[0086] First of all, it should be noted that when a large-section tunnel passes under sensitive environmental areas such as airport runways, railway stations, and important buildings, in order to control surface micro-subsidence, it is generally necessary to use pipe curtains for advance support before tunnel excavation, and adopt a multi-step excavation method. The surface subsidence caused by the partial excavation of a large-section tunnel under the protection of pipe curtains consists of three parts: tunnel excavation surface subsidence , Surface settlement during pipe curtain construction and soil consolidation and surface settlement .

[0087] like Figure 1 , which is a flow chart of a method for controlling micro-settlement of a large-section tunnel underpass and a surface of a building structure in an embodiment of the present application. The method for controlling micro-settlement of a large-section tunnel underpass and a surface of a building structure provided in an embodiment of the present application comprises the following steps:

[0088] Step S1, calculating the cross-sectional surface settlement and the longitudinal section surface settlement caused by tunnel excavation, calculating the sum of the cross-sectional surface settlement and the longitudinal section surface settlement, and obtaining the surface settlement caused by tunnel excavation.

[0089] In this embodiment, it is assumed that the overburden load on the tunnel is the soil deadweight stress and is evenly distributed, the tunnel side pressure is evenly distributed, and the surface settlement is equal to the tunnel crown settlement.

[0090] like Figure 2 The figure shows a schematic diagram of mechanical calculation of cross-sectional surface settlement caused by tunnel excavation. First, the first basic data is obtained, including at least soil bulk density, tunnel burial depth, initial support stiffness, tunnel cross-sectional width, tunnel height, lateral pressure coefficient, pipe curtain stiffness, and soil elastic resistance coefficient.

[0091] According to the above first basic data, the differential equation of the bending of the tunnel lateral support structure is established:

[0092] ,

[0093] Integrate the differential equation twice and solve it to get the settlement formula of the tunnel cross section:

[0094] ,

[0095] Substituting the boundary conditions of 0 deflection at both ends into equation (1-2), we obtain:

[0096] ,

[0097] The maximum deflection Substituting the conditions into formula (1-2), we get:

[0098] ,

[0099] It is understandable that the tunnel excavation creates an open face and is not closed into a ring with initial support. This part of the load is borne by the soil in front of the tunnel face and the closed ring initial support, and each bears half. The calculation diagram is as follows: Figure 3 The influence range of the load above the pipe curtain transferred to the primary support is about 5m, and the load added to the primary support per unit width is ,therefore, , substituting into formula (1-4), we get the cross-sectional surface settlement:

[0100] ,

[0101] In the formula, is the soil bulk density, unit is kN / m 3 ; is the tunnel burial depth, in m; is the initial support stiffness, unit kN / m 2 ; is the tunnel cross-sectional width, in m; is the lateral pressure coefficient, is the tunnel height, in m; It is half of the distance from the tunnel face to the closed ring of initial support, in m; Cross-sectional surface subsidence.

[0102] It should be noted that if the tunnel has temporary support, the temporary support can be simplified to increase the stiffness of the initial support of the tunnel, and its equivalent stiffness can be calculated:

[0103] ,

[0104] In the formula, is the number of vertical temporary supports, To provide temporary support stiffness, use the compression rod stabilization method. , is the stiffness of the vertical temporary support.

[0105] Furthermore, the mechanical calculation of the tunnel longitudinal section pipe curtain is briefly described in Figure 3 The tunnel excavation creates an open face and is not closed into a ring with initial support. This part of the load is borne by the soil in front of the face and the closed ring initial support, and each bears half. The load above the pipe curtain is transferred to the soil in front of the face. The influence range is about 5m. The load added to the unit width of the soil is .

[0106] According to Winkel's hypothesis, the settlement of the soil at the tunnel face is calculated:

[0107] ,

[0108] The pipe curtain from the tunnel face to the primary support is assumed to be a beam with fixed ends at both ends. The maximum deflection is calculated using the structural mechanics method:

[0109] ,

[0110] Therefore, by adding equations (1-7) and (1-8), we can obtain the longitudinal surface settlement:

[0111] ,

[0112] In the formula, is the tube curtain stiffness, unit kN / m 3 ; is the elastic resistance coefficient of soil (assuming elastic support) in kN / m; It is the surface settlement in the longitudinal section.

[0113] In summary, the surface settlement caused by tunnel excavation is the sum of the longitudinal section surface settlement and the cross-section surface settlement. The formula is as follows:

[0114] ,

[0115] Simplifying the formula (1-10) using the function, we get:

[0116] ,

[0117] In the formula, Surface settlement caused by tunnel excavation.

[0118] The above method accurately calculates the surface settlement of the tunnel cross section and longitudinal section, and uses the sum as the surface settlement caused by tunnel excavation, providing a basis for designing the corresponding pipe curtain stiffness and support system for subsequent settlement control.

[0119] Step S2, calculating the surface settlement caused by the jacking of a single pipe of the pipe curtain and the surface settlement correction coefficient of the jacking of a group of pipes, calculating the sum of the surface settlement correction coefficients of the jacking of the group of pipes, and multiplying it by the surface settlement caused by the jacking of the single pipe to obtain the surface settlement caused by the superposition of the group of pipes.

[0120] It can be understood that the surface settlement caused by pipe curtain construction is mainly composed of the surface settlement caused by single pipe jacking and the surface settlement caused by the superposition of pipe groups. Among them, the surface settlement caused by single pipe jacking is greatly affected by the grouting pressure, while the surface settlement caused by the superposition of pipe groups is greatly affected by the pipe spacing.

[0121] First, the second basic data is obtained, including at least the maximum settlement of the arch under single-tube construction, the radius of the pipe curtain, the spacing between the pipe curtains, the buried depth of the pipe curtains, the cohesion, the internal friction angle, the grouting pressure, the soil pressure, the soil shear modulus, the excavation area, the first parameter and the second parameter.

[0122] Specifically, in 1969, R.B.Peck studied the surface settlement and believed that the instantaneous ground settlement caused by tunnel excavation occurred without drainage. The volume of the settlement trough should be equal to the volume of the stratum loss, which can be described by Gaussian distribution. The schematic diagram of the mechanical calculation model of the single pipe of the micro-shield construction pipe curtain is as follows: Figure 4 As shown. Using the Peck formula, the surface settlement formula caused by single-pipe jacking is obtained:

[0123] ,

[0124] In the formula, is the formation loss rate, is the distance between tubes and curtains, is the distance from the symmetry center of the sedimentation tank to the inflection point of the curve, is the excavation area, , is the tube curtain radius.

[0125] in:

[0126] ,

[0127] In the formula, It is the maximum settlement of the vault in single-tube construction.

[0128] because Much smaller than , therefore, formula (2-2) is simplified to:

[0129] ,

[0130] Known:

[0131] ,

[0132] In the formula, The buried depth of the pipe curtain is is the internal friction angle.

[0133] Vault settlement The Levy-Mises constitutive relation and the Hoek-Brown yield criterion can be used to theoretically solve the problem under ideal elastic-plastic conditions:

[0134] ,

[0135] In the formula, is the grouting pressure, is the earth pressure, , due to the shallow burial depth, , is the soil shear modulus, is the first parameter, is the second parameter, and Determined by the compression cone fitting condition under three-dimensional stress state:

[0136] ,

[0137] In the formula, For cohesion.

[0138] Substitute equation (2-5) into equation (2-3) and then into equation (2-1) to simplify. The maximum surface settlement value S max Surface settlement for single-tube construction:

[0139] ,

[0140] Furthermore, the surface settlement caused by the construction of double-hole shield tunnels at different relative positions was studied. It was considered that the second tunnel was excavated in disturbed soil. The superposition diagram of the group of tubes is shown in the figure below. Figure 5 shown.

[0141] Understandably, the surface subsidence caused by the superposition of multiple pipes is:

[0142] ,

[0143] In the formula, is the correction coefficient of surface settlement of group pipe jacking, and the solution formula is:

[0144] ,

[0145] In the formula, is the maximum surface settlement correction coefficient, expressed as follows:

[0146] ,

[0147] When the horizontal distance between the center lines of the two tunnels Greater than When the maximum ground settlement caused by the construction of the second tunnel is not affected by the construction of the first tunnel, Take it as 0, Take 2.5 or 3. The influence of ground disturbance on the root canal curtain steel pipe, Root steel pipe ( )The surface settlement correction function of jacking construction is:

[0148] ,

[0149] Therefore, the surface settlement caused by the superposition of multiple pipes is:

[0150] ,

[0151] In the formula, Surface settlement due to pipe curtain construction.

[0152] When calculating the surface settlement of pipe-roof construction, the above method takes into account the surface settlement of single-pipe construction and the superimposed surface settlement of group pipes, thereby more accurately predicting the impact of pipe-roof construction on surface settlement.

[0153] Step S3, calculating the overconsolidation settlement of the first layer of micro-element soil when the water level is lowered, integrating the overconsolidation settlement of the first layer of micro-element soil to obtain the overconsolidation settlement of the first layer of soil.

[0154] Step S4, according to S3, respectively calculate the over-consolidation settlement of the i-th soil layer and the n-th soil layer, and sum the over-consolidation settlement of each soil layer to obtain the surface settlement caused by the over-consolidation of the soil.

[0155] Understandably, the change of groundwater level during tunnel construction usually causes the change of effective stress in the soil, which in turn leads to overconsolidation settlement of the soil layer. The calculation diagram of overconsolidation settlement is as follows: Figure 6 shown.

[0156] Specifically, we first calculate the overconsolidation settlement of a single layer of soil: , calculate the overconsolidation settlement of the first microelement soil layer:

[0157] ,

[0158] In the formula, is the overconsolidation settlement of the first micro-element soil layer, in mm; is the change of effective stress of the first layer of soil before and after precipitation, unit: MPa; is the compression modulus of the first layer of soil, in kN / m 2 ; is the thickness of the soil layer unit, in m.

[0159] in, , They can be calculated as follows:

[0160] ,

[0161] In the formula, is the weight of water, is the Poisson's ratio of the first soil layer, is the initial water level, is the elastic modulus of the first soil layer, is the initial water level.

[0162] Substituting equations (3-2) and (3-3) into equation (3-1), we can obtain the overconsolidation settlement of the first microelement soil layer:

[0163] ,

[0164] Integrate equation (3-4) to calculate the overconsolidation settlement of the first layer of soil:

[0165] ,

[0166] In the formula, is the thickness of the first soil layer, As a constant term, is the overconsolidation settlement of the first micro-element soil layer, It is the overconsolidation settlement of the first soil layer.

[0167] According to the above method, the overconsolidation settlement of the i-th layer of soil is calculated in the same way:

[0168] (3-6),

[0169] According to the above method, the overconsolidation settlement of the i-th layer of soil is calculated in the same way:

[0170] ,

[0171] In the formula, is the height of water level drop, Divide the soil into layers, , are the Poisson’s ratios of the i-th and n-th soil layers, respectively. , , are the i-th soil layer, the The thickness of the nth layer of soil, , are the elastic moduli of the i-th and n-th soil layers, respectively. , As a constant term, , Respectively Overconsolidation settlement of the nth layer of soil and the nth layer of soil.

[0172] Finally, the over-consolidation settlement of each layer of soil is summed to obtain the surface settlement caused by over-consolidation of soil:

[0173] ,

[0174] In the formula, It is the surface settlement caused by over-consolidation of soil. When the groundwater level is at the surface and drops through only one layer of soil, ,at this time , only the first term in the formula is calculated; when the groundwater level is below the surface and drops only through a layer of soil, ,at this time , only the first term in the formula is calculated; when the groundwater level is below the surface and descends through multiple layers of soil, At this time , calculate the three terms in the formula.

[0175] The above method calculates the overconsolidation settlement of each layer of soil and sums the settlement of each layer of soil to obtain the overconsolidation surface settlement of the soil, thereby more accurately predicting the impact of changes in groundwater levels on surface settlement.

[0176] Step S5, adding the surface settlement caused by the tunnel excavation, the surface settlement caused by the superposition of the group pipes and the surface settlement caused by the over-consolidation of the soil to obtain the total surface settlement of the underpass surface and buildings of the large-section tunnel.

[0177] Finally, the total settlement of the ground underpass and buildings of the large-section tunnel is obtained:

[0178] ,

[0179] The above method adds the surface settlement caused by tunnel excavation, the surface settlement caused by the superposition of multiple pipes, and the surface settlement caused by soil overconsolidation to obtain the total surface settlement of the underpass surface and structures of the large-section tunnel. This step provides a basis for evaluating the impact of tunnel construction on the surface and structures.

[0180] Step S6, determine the load pipe curtain stiffness ratio according to the preliminary given tunnel excavation longitudinal section surface settlement control value, obtain the first relationship curve between the pipe curtain stiffness and the longitudinal section surface settlement by calculating S1 according to the actual project, obtain the pipe curtain stiffness to be adjusted by dividing the given load value by the load pipe curtain stiffness ratio, and adjust the pipe curtain stiffness to be adjusted to a first preset range according to the first relationship curve to obtain the longitudinal section surface settlement corresponding to the adjusted pipe curtain stiffness.

[0181] Understandably, according to step S1, the main factors affecting the ground settlement above the pipe curtain are load and tube curtain stiffness In order to better analyze the surface settlement law, the load pipe curtain stiffness ratio is proposed. The concept of load pipe curtain stiffness ratio is established based on the preliminary given tunnel excavation longitudinal section ground settlement control value. and surface subsidence The first relationship curve of Figure 7 According to the excavation settlement control standard, the load-roof stiffness ratio is obtained. The buried depth of the pipe-roof for a specific project is known, that is, the load above the pipe-roof is known, and the pipe curtain stiffness to be adjusted is determined by dividing the known load value by the load-to-tube curtain stiffness ratio.

[0182] According to the known load Draw the relationship curve between the longitudinal section ground settlement and the pipe curtain stiffness, such as Figure 8 As shown. It can be seen that when the pipe curtain stiffness is on the AB line, the increase in the pipe curtain stiffness will significantly reduce the surface settlement; when the pipe curtain stiffness is on the CD line, the increase in the pipe curtain stiffness has no obvious control on the surface settlement; and the BC section is the transition section from the sharp decline section to the gentle section of the curve. The pipe curtain stiffness is within the first preset range. The pipe curtain stiffness set in this section can effectively control the surface settlement of the tunnel longitudinal section and is relatively economical and reasonable. Therefore, the design of the pipe curtain stiffness should be selected within this range, and the pipe curtain stiffness to be adjusted is adjusted to the first preset range, and then the longitudinal section surface settlement corresponding to the adjusted pipe curtain stiffness is obtained.

[0183] The above method determines the value of pipe curtain stiffness by analyzing the relationship between tunnel excavation surface settlement and pipe curtain stiffness to control tunnel excavation surface settlement. This step helps to optimize pipe curtain design and improve the effect and economy of surface settlement control.

[0184] Step S7, determine the load-support stiffness ratio according to the preliminary given tunnel excavation cross-section surface settlement control value, obtain the second relationship curve between the support stiffness and the cross-section surface settlement according to the actual project calculated by S1, obtain the support stiffness to be adjusted by dividing the given load value by the load-support stiffness ratio, and adjust the support stiffness to be adjusted to a second preset range according to the second relationship curve to obtain the cross-section surface settlement corresponding to the adjusted support stiffness.

[0185] Understandably, according to step S1, the main factors affecting the surface settlement above the support are load and support stiffness In order to better analyze the law of surface settlement, the load-support stiffness ratio is proposed. Based on the concept of tunnel excavation cross-section surface settlement control value, the load-support stiffness ratio is determined and the load-support stiffness ratio is established. and surface subsidence The second relationship curve is as follows: Fig. 9 According to the excavation settlement control standard, the load-support stiffness ratio is obtained. The buried depth of the support for a specific project is known, that is, the load above the support is known, and the support stiffness to be adjusted is determined by dividing the known load value by the load-support stiffness ratio.

[0186] According to the known load Draw the relationship curve between cross-section surface settlement and support stiffness, such as Fig.10 As shown. It can be seen that when the support stiffness is on the AB line, the increase in support stiffness will significantly reduce the surface settlement; when the support stiffness is on the CD line, the increase in support stiffness has no obvious control on the surface settlement; and the BC section is the transition section from the sharp decline section to the gentle section of the curve. The support stiffness is within the second preset range. The support stiffness set in this section can effectively control the surface settlement of the tunnel cross section and is relatively economical and reasonable. Therefore, the support stiffness design should be selected within this range, and the support stiffness to be adjusted should be adjusted to the second preset range, so as to obtain the cross-section surface settlement corresponding to the adjusted support stiffness.

[0187] It should be noted that the support system mainly has the following two forms:

[0188] (1) Initial support + temporary support. By implementing initial support + temporary support and adopting the method of partial tunnel excavation, the disturbance to the surrounding soil is reduced. Temporary support is equivalent to effectively increasing the stiffness of the initial support, thereby further suppressing surface settlement.

[0189] (2) Support structure integration. The construction process of this scheme includes first constructing an advanced support structure, and then excavating the tunnel after the concrete in the steel pipe curtain hardens and forms a support system together with the steel pipe curtain and the initial support. At this time, the stiffness of the tunnel support structure has been greatly improved. As the tunnel face advances, the vertical displacement and settlement of the tunnel vault will be significantly reduced.

[0190] The above method analyzes the relationship between tunnel excavation surface settlement and support stiffness, and determines the value of support stiffness to control tunnel excavation surface settlement. This step helps to optimize support design and improve the effect and economy of surface settlement control.

[0191] Step S8, according to the width of the settlement trough caused by the single-tube jacking, determine the distance at which the pipe curtain jacking does not affect the maximum settlement is half of the width of the settlement trough, determine the number of pipe curtains according to half of the width of the settlement trough, and take the maximum surface settlement caused by the single-tube jacking and the sum of the settlement influence values ​​caused by the jacking of each pipe within the half width of the settlement trough on its left and right sides as the maximum surface settlement caused by the pipe curtain jacking.

[0192] Understandably, when a single pipe is constructed sequentially, the construction period is delayed significantly, and when a group of pipes is constructed, the soil is disturbed significantly and the surface settlement value is relatively large. Considering the requirements of saving construction period and controlling surface settlement, when constructing the pipe curtain, in order to reduce the superposition effect of the group of pipes, it is necessary to construct the pipes at the same time, and determine the distance at which the pipe curtain does not affect the maximum settlement as half the width of the settlement trough. The number of pipe curtains is determined based on half the width of the settlement trough. Under the superposition effect of the group of pipes, the settlement caused by the first pipe needs to be multiplied by the superposition coefficient of the group of pipes, such as Fig.11 As shown, when the tube spacing is greater than the preset tube curtain spacing threshold When the settlement troughs between pipe curtains are no longer superimposed, since the construction of the first pipe curtain has reached the maximum surface settlement value, the surface settlement caused by the single-pipe jacking during the construction of adjacent pipe curtains is calculated by adjusting the construction sequence. The maximum surface settlement caused by the single-pipe jacking and the sum of the settlement influence values ​​caused by the jacking of each pipe within half the width of the settlement trough on its left and right sides is taken as the maximum surface settlement caused by the pipe curtain jacking.

[0193] The above method can optimize the number and layout of pipe curtains, accurately predict the maximum surface settlement, optimize the pipe curtain construction plan, reduce surface settlement, and at the same time improve construction safety and efficiency and save construction time.

[0194] Step S9, obtain the third relationship curve between the grouting pressure and the surface settlement caused by the single-pipe jacking by calculation in S2, determine the target grouting pressure corresponding to the surface settlement caused by the single-pipe jacking being 0 according to the third relationship curve, adjust the actual grouting pressure according to the target grouting pressure, and lay out the lubricating slurry pipeline system in the pipe and the nozzle system evenly laid out around the pipe wall to form a drag-reducing slurry sleeve outside the super-long pipe curtain steel pipe.

[0195] Understandably, controlling the surface settlement caused by the pipe curtain requires reasonably adjusting the grouting pressure to ensure that the grouting pressure reaches the saturated grouting pressure to minimize the surface settlement value and avoid surface settlement caused by too low grouting pressure or surface uplift caused by too high grouting pressure.

[0196] The third relationship curve between grouting pressure and ground settlement caused by single-pipe jacking is obtained by calculation from S2, as shown in Fig.12 As shown. According to the third relationship curve, the surface settlement caused by single-pipe jacking is determined to be 0 ( Fig.12 The target grouting pressure is the horizontal dotted line in the figure, and the actual grouting pressure is adjusted according to the target grouting pressure.

[0197] It should be noted that the jacking of the pipe curtain must have the functions of maintaining pressure at the tunnel gate, lubricating and maintaining pressure around the pipe, and synchronous grouting. For this purpose, this application specially developed a pressure maintaining device for entering and exiting the tunnel gate and a lubricating and maintaining pressure system around the pipe, such as Fig.13As shown in the figure. During the process of cutting soil with a micro shield machine, the diameter of the cutterhead is larger than the diameter of the steel pipe, and there is a certain gap between the two. The total settlement of this gap is the main factor leading to the settlement of the jacking construction. Therefore, the slurry needs to be injected evenly at a constant pressure during the jacking process to control the collapse and sinking of the hole wall, and at the same time play a role in lubrication and drag reduction.

[0198] In order to achieve pressure maintenance and drag reduction around the pipe, the present application arranges a lubricating slurry pipeline system inside the pipe and a nozzle system evenly arranged around the pipe wall to form a drag-reducing slurry sleeve outside the super-long pipe curtain steel pipe.

[0199] For example, a longitudinal grouting main pipeline with a diameter of 40 mm can be set in the steel pipe of the pipe curtain, and a three-way valve is set every 3 meters along the pipeline to connect with the annular branch pipeline. In order to prevent the slurry in the lubrication cavity from losing pressure instantly due to cracks and gaps in the soil within a few hundred meters, a compartment partition ring is set every 30 meters along the longitudinal direction of the steel pipe.

[0200] It should be noted that the above data used in the embodiments of the present application are only used as a selection method. The specific data and values ​​can be determined according to actual conditions. The embodiments of the present application do not limit this and are all within the protection scope of the present application.

[0201] The above method determines the value of the target grouting pressure by analyzing the relationship between surface settlement and grouting pressure to control the surface settlement of pipe curtain construction. This step helps to optimize the grouting process and improve the effect of surface settlement control. In addition, a lubricating slurry pipeline system is laid inside the pipe and a nozzle system is evenly laid around the pipe wall to form a drag-reducing slurry sleeve outside the super-long pipe curtain steel pipe, which can effectively achieve pressure maintenance and drag reduction around the pipe.

[0202] Step S10, formulating corresponding groundwater control measures for different strata according to the surface settlement caused by over-consolidation of soil due to groundwater drop in different strata.

[0203] Understandably, the change of groundwater level during tunnel construction usually causes the change of effective stress of soil, which in turn leads to over-consolidation settlement of soil. The change range of over-consolidation settlement of different soil layers (including pebble layer, gravel layer and other highly permeable layer, medium sand layer, coarse sand layer, gravel sand layer, silt sand layer, fine sand layer and silt soil layer) with the decrease of water level is different from the corresponding water control measures. In view of this, the groundwater level maintenance technology during tunnel construction has been developed, as follows:

[0204] (1) For highly permeable formations such as pebble formations and gravel formations:

[0205] The over-consolidation settlement caused by the groundwater level in this type of stratum is small, and there is no need to control the groundwater level. Calculate and draw the settlement change curve of non-self-water-retaining strata as the groundwater level decreases, such as Fig.14As shown in Figure 2, as the groundwater level drops, the overconsolidation settlement of the soil increases continuously, and its rate of change is slow. When the groundwater level drops to about 10m, the overconsolidation settlement is only 2.96mm, as shown in Figure 2. Fig.15 As shown, no groundwater control measures such as grouting or freezing are required.

[0206] (2) For medium sand formation, coarse sand formation and gravel sand formation:

[0207] For medium sand, coarse sand and gravel sand formations, grouting is used to control the groundwater level. The settlement curve of this type of formation as the groundwater level decreases is calculated and plotted as follows: Fig.16 As shown in the figure, with the decline of groundwater level, the over-consolidation settlement of soil increases continuously, and its rate of change also increases continuously and is significantly higher than that of highly permeable strata. When the groundwater level drops to about 4m, the over-consolidation settlement reaches 2.8mm, and the subsequent decline of groundwater level will significantly affect the increase of settlement. Therefore, the water level reduction height for this type of stratum is controlled within 4m. This type of soil has good effects of grouting alone, freezing alone, or grouting first and then freezing. The best method should be selected to control the groundwater level according to the actual engineering soil conditions. The grouting method is used in this calculation condition to control the groundwater level. Fig.17 shown.

[0208] (3) For silt sand, fine sand and silt soil strata:

[0209] For silt sand, fine sand and silt soil, freezing method is used to control the groundwater level. The settlement curve of this type of stratum as the groundwater level decreases is calculated and plotted as follows: Fig.18 As shown in the figure, as the groundwater level drops, the over-consolidation settlement of the soil increases continuously, and the rate of change is segmented with 9m and 18m as the dividing line. Analysis shows that when the groundwater level drops to about 3m, the over-consolidation settlement reaches 3mm, and the subsequent drop in the groundwater level will significantly affect the settlement. Therefore, the water level drop height for this type of stratum is controlled within 3m. The grouting effect of this type of soil is poor, and the freezing method is better, such as Fig.19 shown.

[0210] The above method formulates different groundwater control measures for different strata according to the surface settlement of soil consolidation. This step helps to reduce the impact of groundwater level changes on surface settlement and protect the safety of the surface and buildings. At the same time, appropriate water control measures are selected according to the characteristics of different soil layers, which improves the pertinence and effectiveness of the measures.

[0211] The method for controlling micro-settlement of the ground surface of large-section tunnel underpasses and buildings provided in the embodiments of the present application provides an effective method and means for controlling micro-settlement of the ground surface of large-section tunnel underpasses and buildings, which helps to ensure tunnel construction and the safe operation of airplanes and high-speed railways and the stability of buildings.

[0212] In the embodiments provided in the present application, it should be understood that the disclosed method can also be implemented in other ways. The device embodiments described above are merely schematic, for example, the flowcharts and structure diagrams in the accompanying drawings show the architecture, functions and operations that may be implemented according to the methods of the embodiments of the present invention. In this regard, each box in the flowchart or block diagram can represent a module, a program segment or a part of a code, and the module, a program segment or a part of a code contains one or more executable instructions for implementing the specified logical functions. It should also be noted that in an alternative implementation, the functions marked in the box can also occur in a different order from the order marked in the accompanying drawings. For example, two consecutive boxes can actually be executed substantially in parallel, and they can sometimes be executed in the opposite order, depending on the functions involved. It should also be noted that each box in the structure diagram and / or the flow diagram, and the combination of the boxes in the structure diagram and / or the flow diagram, can be implemented with a dedicated hardware-based system that performs a specified function or action, or can be implemented with a combination of dedicated hardware and computer instructions.

[0213] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for controlling micro-settlement of the surface of a large-section tunnel underpass and buildings, characterized in that: The method comprises: S1: Calculate the cross-sectional surface settlement and the longitudinal section surface settlement caused by tunnel excavation, calculate the sum of the cross-sectional surface settlement and the longitudinal section surface settlement, and obtain the surface settlement caused by tunnel excavation; S2: Calculate the ground settlement caused by the jacking of a single pipe of the pipe curtain and the correction coefficient of the ground settlement caused by the jacking of a group of pipes, calculate the sum of the correction coefficients of the ground settlement caused by the jacking of a group of pipes, and multiply it by the ground settlement caused by the jacking of the single pipe to obtain the ground settlement caused by the superposition of the group of pipes; S3: calculating the overconsolidation settlement of the first layer of micro-element soil when the water level drops, integrating the overconsolidation settlement of the first layer of micro-element soil to obtain the overconsolidation settlement of the first layer of soil; S4: Calculate the overconsolidation settlement of the i-th soil layer and the n-th soil layer according to S3, and sum the overconsolidation settlement of each soil layer to obtain the surface settlement caused by overconsolidation of the soil; S5: Add the surface settlement caused by the tunnel excavation, the surface settlement caused by the superposition of the group pipes and the surface settlement caused by the overconsolidation of the soil to obtain the total surface settlement of the underpass surface and buildings of the large-section tunnel; S6: Determine the load pipe curtain stiffness ratio according to the initially given tunnel excavation longitudinal section ground settlement control value, obtain a first relationship curve between the pipe curtain stiffness and the longitudinal section ground settlement by calculating in S1 according to the actual project, obtain the pipe curtain stiffness to be adjusted by dividing the given load value by the load pipe curtain stiffness ratio, and adjust the pipe curtain stiffness to be adjusted to a first preset range according to the first relationship curve, and obtain the longitudinal section ground settlement corresponding to the adjusted pipe curtain stiffness; S7: Determine the load-support stiffness ratio according to the initially given tunnel excavation cross-section surface settlement control value, obtain a second relationship curve between support stiffness and cross-section surface settlement by calculating in S1 according to the actual project, obtain the support stiffness to be adjusted by dividing the given load value by the load-support stiffness ratio, and adjust the support stiffness to be adjusted to within a second preset range according to the second relationship curve to obtain the cross-section surface settlement corresponding to the adjusted support stiffness; S8: According to the width of the settlement trough generated by the single-tube jacking, determine the distance where the pipe curtain jacking does not affect the maximum settlement as half of the width of the settlement trough, determine the number of pipe curtains according to half of the width of the settlement trough, and take the maximum surface settlement generated by the single-tube jacking and the sum of the settlement influence values ​​generated by the jacking of each pipe within the half width of the settlement trough on the left and right as the maximum surface settlement generated by the pipe curtain jacking; S9: a third relationship curve between the grouting pressure and the surface settlement caused by the single-tube jacking is calculated by S2, a target grouting pressure corresponding to when the surface settlement caused by the single-tube jacking is 0 is determined according to the third relationship curve, the actual grouting pressure is adjusted according to the target grouting pressure, and a lubricating slurry pipeline system is arranged inside the pipe and a nozzle system is evenly arranged around the pipe wall to form a drag-reducing slurry sleeve outside the super-long pipe curtain steel pipe; S10: Based on the surface settlement caused by over-consolidation of soil due to groundwater drop in different strata, formulate corresponding groundwater control measures for different strata.

2. The method for controlling surface micro-settlement of a large-section tunnel underpass and buildings according to claim 1 is characterized in that: The calculation of the cross-section surface settlement and the longitudinal section surface settlement caused by tunnel excavation includes: S11: Acquire first basic data, wherein the first basic data at least includes soil bulk density, tunnel burial depth, initial support stiffness, tunnel cross-sectional width, tunnel height, lateral pressure coefficient, pipe curtain stiffness, and soil elastic resistance coefficient; S12: establishing a differential equation for the bending of the tunnel lateral support structure according to the first basic data, solving the differential equation to obtain a settlement formula for the tunnel cross section, and substituting initial conditions into the settlement formula for the tunnel cross section to obtain the surface settlement of the cross section; S13: Calculate the settlement of the face soil according to the Winkel hypothesis, calculate the maximum deflection of the pipe curtain from the tunnel face to the primary support closed section using the structural mechanics method, add the settlement of the face soil to the maximum deflection to obtain the surface settlement of the longitudinal section.

3. The method for controlling surface micro-settlement of a large-section tunnel underpass and buildings according to claim 1 is characterized in that: The calculation of the ground settlement caused by the jacking of a single pipe of the pipe curtain includes: S21: Acquire second basic data, where the second basic data at least includes maximum settlement of a single-tube construction vault, tube curtain radius, tube curtain spacing, tube curtain burial depth, cohesion, internal friction angle, grouting pressure, soil pressure, soil shear modulus, excavation area, first parameter, and second parameter; S22: using the Peck formula to obtain a surface settlement formula for single-tube jacking construction, wherein the surface settlement formula for single-tube jacking construction includes a stratum loss rate and a distance from the symmetry center of the settlement trough to the inflection point of the curve; S23: using the second basic data, simplifying the formation loss rate and the distance from the symmetric center of the settlement tank to the curve inflection point, obtaining the simplified formation loss rate and the simplified distance from the symmetric center of the settlement tank to the curve inflection point, substituting the simplified formation loss rate and the simplified distance from the symmetric center of the settlement tank to the curve inflection point into the single-tube construction jacking surface settlement formula, and obtaining the surface settlement caused by the single-tube jacking; The formulas of the first parameter and the second parameter are: In the formula, is the cohesive force, is the internal friction angle.

4. The method for controlling surface micro-settlement of a large-section tunnel underpass and buildings according to claim 1 is characterized in that: The step of calculating the overconsolidation settlement of the first layer of micro-element soil mass when the water level is lowered and integrating the overconsolidation settlement of the first layer of micro-element soil mass to obtain the overconsolidation settlement of the first layer of soil mass comprises: The expression formula of overconsolidation settlement of the first layer of micro-element soil is: The expression formula of overconsolidation settlement of the first layer of soil is: In the formula, is the weight of water, is the Poisson's ratio of the first soil layer, is the thickness of the soil layer unit, is the initial water level, is the thickness of the first soil layer, is the elastic modulus of the first soil layer, where As a constant term, is the overconsolidation settlement of the first microelement soil layer, is the overconsolidation settlement of the first soil layer.

5. The method for controlling surface micro-settlement of a large-section tunnel underpass and buildings according to claim 4 is characterized in that: The respectively calculating the overconsolidation settlement of the i-th soil layer and the n-th soil layer comprises: The expression formula of the overconsolidation settlement of the i-th layer of soil is: The expression formula of the overconsolidation settlement of the nth layer of soil is: In the formula, is the height of water level drop, , are the Poisson's ratios of the i-th soil layer and the n-th soil layer, respectively. , , are respectively the i-th soil layer, the layer of soil, the thickness of the nth layer of soil, , are the elastic moduli of the i-th soil layer and the n-th soil layer, respectively. , As a constant term, , They are respectively layer of soil, overconsolidation settlement of the nth layer of soil.

6. The method for controlling surface micro-settlement of a large-section tunnel underpass and buildings according to claim 5 is characterized in that: The over-consolidation settlement of each layer of soil is summed to obtain the surface settlement caused by over-consolidation of the soil, including: The expression formula for the surface settlement caused by the overconsolidation of the soil is: In the formula, is the surface settlement caused by overconsolidation of the soil, where: Divide the soil into layers. When the groundwater level is at the surface and drops through only one layer of soil, ,at this time , when the groundwater level is below the surface and drops only through a layer of soil, ,at this time , when the groundwater level is below the surface and descends through multiple layers of soil, ,at this time .

7. The method for controlling surface micro-settlement of a large-section tunnel underpass and buildings according to claim 1 is characterized in that: According to the surface settlement caused by the over-consolidation of soil due to the groundwater drop in different strata, corresponding groundwater control measures are formulated for different strata, including: S101: For pebble and gravel formations, no groundwater control measures are required; S102: For medium sand, coarse sand and gravel sand formations, grouting is used as a groundwater control measure; S103: For silt sand, fine sand and silt soil formations, adopt freezing groundwater control measures.

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