Simulation method for construction process of composite caisson anchor foundation under soil resistance

Abstract

The present invention discloses a simulation method for the construction process of a composite caisson anchor foundation under the action of soil resistance, and the simulation method includes the following steps: A. A stratum structure method model is used for modeling, and the entire model basically and realistically restores the construction site, wherein the model mainly includes a soil model, rock, caisson, soil in the cavity and anchor foundation, and the dimensions of all structures are set according to the actual project. The present invention performs dynamic calculation and analysis on the entire process of anchor construction, and can obtain the displacement characteristics of the anchor foundation under different working conditions of the anchor foundation, and further analyze the internal force response of the anchor foundation. On the basis of finite element analysis, the anti-slip and anti-overturning coefficients of the anchor foundation under the action of soil resistance are calculated, and the stress bearing capacity of the base is verified. Finally, the deformation of the anchor foundation in the subsequent bridge completion state and 20 years after construction is predicted.

Description

Technical Field

[0001] The invention relates to the technical field of anchor construction, in particular to a simulation method for a composite caisson anchor foundation construction process under soil resistance. Background Art

[0002] The design method of ordinary anchor foundation is no longer suitable for large bridge foundations, especially the foundation of ultra-long span suspension bridges. The larger the span of the suspension bridge, the nonlinear growth of the force acting on the anchor foundation, resulting in an increase in the plane size and depth of the anchor foundation. The foundation needs to enter the underlying pebble layer and rock layer. At this time, the proportion of the lateral force provided by the rock and soil layer is also increasing. The current anchor design method does not consider the resistance of the surrounding rock and soil layers, but still uses a gravity foundation, which only provides vertical and horizontal support from the base, which is not suitable for the actual stress state of the anchor foundation.

[0003] Among the existing research results related to caissons at home and abroad, the methods for analyzing the force and stability of caissons during the sinking construction stage usually include theoretical calculation, field monitoring, indoor testing and numerical analysis. As for the theoretical calculation method, in the early stage of large-scale caisson application in China, the focus was on the theoretical calculation method of the well wall earth pressure based on the measured earth pressure. In recent years, only a small number of scholars have indirectly analyzed the changing trend of the side wall friction resistance from the perspective of the blade foot reaction force. Only a few clauses in the current foundation design specifications involve the force exerted on the caisson structure during the sinking stage. As the main research method at present, the field monitoring method can more conveniently obtain the measured data such as the caisson side wall and blade foot earth pressure. Through further analysis of the monitoring data, the distribution law of the caisson side wall earth pressure along the depth and the side friction of each caisson section can be summarized. Resistance, friction coefficient between caisson and soil layer, etc. Based on the field monitoring data, a calculation method and empirical formula for side wall friction resistance were proposed, and the formula recommended by the code was preliminarily revised. Regarding indoor experimental methods, most foreign scholars have studied the structural response of caissons when subjected to vertical and horizontal loads; there are also relevant studies on model tests of bridge anchorage bearing capacity based on caissons. Only in recent years have relevant indoor tests on caisson sinking force research appeared in China. Regarding numerical analysis research methods, most of them are limited to the analysis and research of the landing stage before caisson sinking, the construction process after sinking into place, and the force and settlement deformation of caisson structure and surrounding soil during the bridge operation stage. There are few numerical simulation studies on the caisson sinking construction process. The existing relevant studies abroad are mostly based on suction caissons for analysis.

[0004] In existing research, the thickness of the caisson wall is closely related to the sinking depth, soil friction and construction method. The specification requires the caisson wall thickness to be between 0.8 and 1.5m. The north anchor of Jiangyin Bridge and the anchor of Taizhou Yangtze River Bridge in China both use large caisson foundations. Among them, the inner wall of the north anchor caisson of Jiangyin Bridge is 100cm thick and the outer wall is 200cm thick; the inner wall of the anchor foundation of Taizhou Yangtze River Bridge is 220cm thick and the outer wall is 240cm thick. The Japan Honshi Bridge Corporation takes suspension bridges with main spans of 1000 to 1500m as the object and stipulates that the allowable value of horizontal displacement of the anchor bowl of long and large span suspension bridges is 0 .00017 times the main span. In addition, this fourth standard requires that the tower base stress caused by horizontal displacement or vertical displacement shall not exceed 5% of its allowable stress. When designing the Jiangyin Yangtze River Bridge, the influence of horizontal displacement and vertical settlement on the structural stress was studied, and the displacement limit of the north bank anchor bowl (the foundation is a caisson foundation) was determined to be 0.1m for horizontal displacement and 0.2m for settlement. This value was adopted while considering that the displacement of the anchor bowl would not cause excessive deflection of the stiffening beam. Similar research was also conducted on the Great Belt Bridge in Denmark, and the horizontal displacement was expected to be 0.1m one year after opening. The actual observed value was only 0.03m.

[0005] In summary, both the specifications and engineering practice show that the stress and deformation of anchors during construction and operation are not clear, mainly because the rock and soil layers around the anchor foundation are not sufficiently considered. Therefore, by combining actual projects, a stress and deformation analysis of the gravity foundation of the caisson as a retaining structure from construction to operation is carried out. Based on an in-depth study of the existing design methods for gravity anchor foundations of suspension bridges in my country, and considering the disturbance and creep of the rock and soil layers, a design system and theoretical method considering the interaction between rock and soil and anchor foundations are established, providing technical support for the revision of relevant specifications for foundation engineering. Summary of the Invention

[0006] The purpose of the present invention is to provide a simulation method for the construction process of a composite caisson anchor foundation under the action of soil resistance. By adopting finite element dynamic simulation technology, the displacement characteristics of the anchor foundation under different working conditions are comprehensively analyzed. Subsequently, the force and deformation mechanism of the anchor during the construction process are deeply explored, and a design theory method considering the soil resistance of the anchor foundation is proposed to solve the problem of insufficient consideration of soil resistance.

[0007] To achieve the above object, the present invention provides the following technical solution: a method for simulating the construction process of a composite caisson anchor foundation under soil resistance, the simulation method comprising the following steps:

[0008] A. The stratum structure model was used for modeling. The entire model essentially reproduces the construction site. The model mainly includes the soil model, rock, caisson, cavity soil and anchor foundation. The dimensions of all structures are set according to the actual project.

[0009] B. The model uses the soft soil creep SSC constitutive model for silty soil, the Hoek-Brown constitutive model for rock, and the small strain soil hardening model for the remaining soils. Based on the final model and in conjunction with existing specifications, the impact of soil resistance on the overall stability of the composite caisson anchor foundation is considered. Ultimately, based on these parameters, a predictive analysis can be conducted on the subsequent construction and operation of the composite caisson anchor foundation after beam erection.

[0010] C. The caisson foundation dimensions are 50m x 70m x 50m in length, width and height, embedded in a gravel layer. The soil model dimensions are 3 to 5 times the length, width and height of the caisson foundation, and 300m x 300m x 83m in length, width and height.

[0011] D. The boundary conditions of the model are: the bottom of the model is completely fixed, that is, the horizontal and vertical displacements of the soil are constrained; the four sides of the model are fixed in the normal direction, that is, the soil is constrained horizontally and free vertically.

[0012] As a preferred solution, the silty soil in the construction site area adopts the PLAXIS built-in SSC soft soil creep constitutive model, which includes:

[0013] PLAXIS is a software used to analyze deformation and stability of large-scale geotechnical engineering projects. By selecting an appropriate soil constitutive model to simulate the silty soil in the site area, the time-dependent creep effect of soft soil is further considered.

[0014] The parameters of the SSC constitutive model are calibrated. The SSC model is based on the soft soil model and takes into account the time-related creep effect of soft soil, that is, the secondary consolidation effect after the primary consolidation settlement of the soil. Compared with the SS model, the SSC model adds a modified creep coefficient , which can be obtained from the long-term volumetric strain and time logarithmic curve:

[0015] Where, —Secondary compression creep index;

[0016] The volume creep strain is considered in the SSC model and its expression is:

[0017] Where: — stress measurement;

[0018] —generalized pre-consolidation pressure;

[0019] — volume creep strain;

[0020] — elasticity matrix;

[0021] —Modified compression index;

[0022] —corrected inflation indicators;

[0023] —Corrected creep coefficient.

[0024] As a preferred solution, the rock adopts the Hoek-Brown constitutive model built into PLAXIS, including:

[0025] PLAXIS is a software used to analyze deformation and stability of large-scale geotechnical engineering projects. It simulates the rock in the construction site area by selecting an appropriate rock constitutive model.

[0026] The Hawke-Brown failure criterion uses the maximum principal stress and minimum principal stress The critical stress state of jointed rock mass is described by the relationship of

[0027] Where: — Complete rock parameters reduction;

[0028] 、 — auxiliary material parameters of rock blocks;

[0029] In the formula 、 Determined by the following formula:

[0030] Where: GSI- geological intensity index;

[0031] D－ disturbance factor;

[0032] From this it can be considered and All depend on the geological strength index GSI and disturbance factor D Therefore, the parameter does not appear in the Hawke-Brown empirical criterion. 、 ;

[0033] is the uniaxial compressive strength of intact rock, according to The uniaxial compressive strength of a specific rock can be obtained for:

[0034] for GSIRock mass >25:

[0035] for GSI Rock mass ≤25:

[0036]

[0037] The determination of deformation modulus is based on field load test and is an important parameter. However, due to certain conditions of field load test, this method has certain limitations. Therefore, under the premise of test data and quality evaluation, in order to quickly and conveniently estimate the deformation modulus of rock mass, it is necessary to establish RMR index, GSI Relationship between the value and the deformation modulus:

[0038] Where:

[0039] —deformation modulus of intact rock mass;

[0040] MR —modulus ratio;

[0041] — rock mass deformation modulus;

[0042] As a preferred solution, the parameters of the SSC constitutive model and the Hoek-Brown constitutive model are as follows:

[0043] The SSC model is a soft soil creep model that comes with PLAXIS. The main calculation parameters include the compression coefficient λ , coefficient of rebound κ and creep coefficient μ; The compression index and rebound index of the soft soil in the construction site area can be measured experimentally. The compression coefficient of the soft soil in the construction site area can be obtained through the conversion relationship of the following formula: λ , rebound coefficient κ Creep coefficient μ and compression coefficient λ The relationship is:

[0044] ,

[0045] Taking the middle value of 20, we can get the main parameters of the SSC constitutive model for the soft soil in the anchor foundation area: compression coefficient λ =0.0475, rebound coefficient κ =0.0076, creep coefficient μ =0.0024;

[0046] Combining rock compression test and splitting test, the parameters of the Hoek-Brown constitutive model of conglomerate with different weathering degrees are obtained;

[0047] Moderately weathered conglomerate: compression modulus E rm =1026MPa, compressive strength Σ ci =24.67MPa, tensile strength Σ ti =1.52MPa, geological strength index GSI =55;

[0048] Slightly weathered conglomerate: compression modulus E rm =1710MPa, compressive strength Σ ci =31.25MPa, tensile strength Σ ti =3.22MPa, geological strength index GSI =70.

[0049] As a preferred solution, the contribution of soil resistance to the anti-sliding of the anchor foundation is as follows:

[0050] On the basis of existing specifications, the contribution of soil resistance to the anti-sliding of anchor foundation at different construction stages of the superstructure is considered, and the anti-sliding stability coefficient is calculated. Calculate as follows:

[0051] Where:

[0052] —Anti-sliding stability coefficient of bridge and culvert pier foundation;

[0053] — total vertical force;

[0054] —The total amount of anti-sliding stabilizing horizontal forces;

[0055] — total sliding horizontal force;

[0056] —The coefficient of friction between the foundation bottom surface and the foundation soil is determined through experiments;

[0057] Based on the three-dimensional finite element calculation results, the typical working conditions of the initial stage, intermediate stage, and completion stage of the bridge superstructure beam segment erection were analyzed. Combined with the above formula, the anti-sliding stability coefficient of the anchor foundation under each typical working condition considering the effect of soil resistance was obtained. In the initial stage: k c =6.028; intermediate stagek c =3.397; completion stage k c =2.962.

[0058] As a preferred solution, the contribution of soil resistance to the anti-overturning of the anchor foundation is as follows:

[0059] On the basis of existing specifications, the contribution of soil resistance to the anti-overturning of anchor foundation at different construction stages of superstructure is considered, and the anti-overturning stability coefficient is calculated. Calculate as follows:

[0060] Where:

[0061] ─ Anti-overturning safety factor;

[0062] - The distance from the centroid of the section to the calculated overturning axis on the extension line from the centroid of the section to the point of action of the resultant force (m);

[0063] ─The combined force of all external forces R The eccentricity of the point of action of the verification section to the centroidal axis of the base;

[0064] P i - Vertical force (kN) caused by standard value combination of actions or standard value combination of accidental actions (except earthquake) without considering their partial factors and combination factors;

[0065] e i ─Vertical force P i The moment arm of the center of gravity of the verified section (m);

[0066] H i - horizontal force (kN) caused by standard value combination of actions or standard value combination of accidental actions (except earthquake) without considering their partial factors and combination factors;

[0067] h i ─The force arm of the horizontal force on the verification section (m);

[0068] Based on the three-dimensional finite element calculation results, the typical working conditions of the initial stage, intermediate stage, and completion stage of the bridge superstructure beam segment erection were analyzed. Combined with the above formula, the anti-overturning stability coefficient of the anchor foundation under each typical working condition considering the effect of soil resistance was obtained. In the initial stage: k =9.726; intermediate stage k=4.904; completion stage k =4.115.

[0069] As a preferred solution, the stress bearing capacity of the substrate is verified as follows:

[0070] According to existing specifications, the front and rear end bases of the anchorage should not have tensile stress during the construction and operation stages, and the maximum stress value is Should meet the following requirements:

[0071] Where:

[0072] — Resistance coefficient, which is 1.25 during the construction phase and 1 for other working conditions;

[0073] [ f a ]—allowable value of foundation bearing capacity;

[0074] The bearing layer of the caisson foundation is a gravel layer, and the allowable value is [ f a ] is 3346 kPa, and the resistance coefficient during the construction phase is 1.25. Under different working conditions of superstructure construction and beam erection, all stresses are compressive, and the maximum base stress is less than 4182.5 kPa, meeting the bearing capacity requirements.

[0075] As a preferred solution, the prediction and analysis of the subsequent working conditions after beam erection is as follows:

[0076] After the erection of the bridge beam section was completed, the deformation and stress of the caisson and its upper anchor foundation were predicted through three-dimensional finite element simulation based on the verification of the aforementioned calculation parameters for subsequent construction and operation conditions: in the post-construction stage, the stage with the largest change in anchor displacement was mainly concentrated in the first year after construction. After one year, the deformation basically tended to be stable.

[0077] Compared with the prior art, the present invention has the following beneficial effects:

[0078] The present invention dynamically calculates and analyzes the entire process of anchorage construction. Under different working conditions of the anchorage foundation, the displacement characteristics of the anchorage foundation can be obtained, and the internal force response of the anchorage foundation is further analyzed. On the basis of finite element analysis, the anti-slip and anti-overturning coefficients of the anchorage foundation under the action of soil resistance are calculated, and the stress bearing capacity of the base is verified. Finally, the subsequent bridge completion status and the deformation of the anchorage foundation 20 years after construction are predicted. BRIEF DESCRIPTION OF THE DRAWINGS

[0079] Figure 1 The geological drilling plan layout diagram of the present invention;

[0080] Figure 2This is a structural diagram of the caisson solution of the present invention;

[0081] Figure 3 This is a diagram of the anchor model of the present invention;

[0082] Figure 4 This is a grid division diagram of the anchor model of the present invention;

[0083] Figure 5 is a relationship diagram between volume strain and average stress of the SSC model of the present invention;

[0084] Figure 6 For the present invention - Yield surface of the SSC model on a plane;

[0085] Figure 7 is the yield surface of the SSC model in the principal stress space of the present invention;

[0086] Figure 8 The calculation diagram of the anchor foundation of the present invention;

[0087] Figure 9 A comparison diagram of the finite element calculation and measured results of the vertical displacement of the front and rear end points of the anchor foundation of the present invention;

[0088] Figure 10 This is a comparative analysis diagram of the finite element calculation and measured results of the horizontal displacement of the anchor cable points of the anchor foundation of the present invention;

[0089] Figure 11 The diagram is a diagram showing the variation of the maximum and minimum normal stresses of the anchor foundation under different working conditions of the present invention;

[0090] Figure 12 This is a diagram showing the variation of the maximum tangential stress of the anchor foundation base under different working conditions of the present invention;

[0091] Figure 13 This is a diagram showing the variation of the maximum soil resistance of the anchor foundation caisson under different working conditions of the present invention;

[0092] Figure 14 This is a cloud diagram of base stress and caisson foundation soil resistance of the present invention;

[0093] Figure 15 This is the anchor deformation grid diagram after the steel beam of the present invention is installed;

[0094] Figure 16 This is a graph showing the relationship between the horizontal displacement of the anchor cable points on the upper foundation of the anchorage under the conditions of constant load + live load during the operation phase of the present invention;

[0095] Figure 17 This is a graph showing the relationship between the horizontal displacement of the anchor cable point on the upper foundation of the anchorage under the main force + additional force conditions during the operation phase of the present invention;

[0096] Figure 18 This is a graph showing the vertical displacement variation of the front end point of the anchor upper foundation under the conditions of dead load + live load during the operation phase of the present invention;

[0097] Figure 19 This is a relationship diagram of the vertical displacement change of the front end point of the upper foundation of the anchor under the main force + additional force working condition during the operation stage of the present invention;

[0098] Figure 20 This is a graph showing the vertical displacement variation of the rear end point of the upper foundation of the anchor under the conditions of dead load + live load during the operation phase of the present invention;

[0099] Figure 21 This is a diagram showing the vertical displacement change relationship of the rear end point of the upper foundation of the anchor under the main force + additional force working condition during the operation phase of the present invention. DETAILED DESCRIPTION

[0100] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0101] The present invention provides a simulation method for the construction process of a composite caisson anchor foundation under soil resistance, and the simulation method comprises the following steps:

[0102] A. The stratum structure model was used for modeling. The entire model essentially reproduces the construction site. The model mainly includes the soil model, rock, caisson, cavity soil and anchor foundation. The dimensions of all structures are set according to the actual project.

[0103] B. The model uses the soft soil creep SSC constitutive model for silty soil, the Hoek-Brown constitutive model for rock, and the small strain soil hardening model for the remaining soils. Based on the final model and in conjunction with existing specifications, the impact of soil resistance on the overall stability of the composite caisson anchor foundation is considered. Ultimately, based on these parameters, a predictive analysis can be conducted on the subsequent construction and operation of the composite caisson anchor foundation after beam erection.

[0104] C. The caisson foundation dimensions are 50m x 70m x 50m in length, width and height, embedded in a gravel layer. The soil model dimensions are 3 to 5 times the length, width and height of the caisson foundation, and 300m x 300m x 83m in length, width and height.

[0105] D. The boundary conditions of the model are: the bottom of the model is completely fixed, that is, the horizontal and vertical displacements of the soil are constrained; the four sides of the model are fixed in the normal direction, that is, the soil is constrained horizontally and free vertically.

[0106] The silty soil in the construction site area uses the PLAXIS built-in SSC soft soil creep constitutive model, which includes:

[0107] PLAXIS is a software used to analyze deformation and stability of large-scale geotechnical engineering projects. By selecting an appropriate soil constitutive model to simulate the silty soil in the site area, the time-dependent creep effect of soft soil is further considered.

[0108] The parameters of the SSC constitutive model are calibrated. The SSC model is based on the soft soil model and takes into account the time-related creep effect of soft soil, that is, the secondary consolidation effect after the primary consolidation settlement of the soil. Compared with the SS model, the SSC model adds a modified creep coefficient , which can be obtained from the long-term volumetric strain and time logarithmic curve:

[0109] Where, —Secondary compression creep index;

[0110] The volume creep strain is considered in the SSC model and its expression is:

[0111] Where: — stress measurement;

[0112] —generalized pre-consolidation pressure;

[0113] — volume creep strain;

[0114] — elasticity matrix;

[0115] —Modified compression index;

[0116] —corrected inflation indicators;

[0117] —corrected creep coefficient;

[0118] The rock model uses the built-in Hoek-Brown constitutive model of PLAXIS, which includes:

[0119] PLAXIS is a software used to analyze deformation and stability of large-scale geotechnical engineering projects. It simulates the rock in the construction site area by selecting an appropriate rock constitutive model.

[0120] The Hawke-Brown failure criterion uses the maximum principal stress and minimum principal stress The critical stress state of jointed rock mass is described by the relationship of

[0121] Where: — Complete rock parameters reduction;

[0122] 、 — auxiliary material parameters of rock blocks;

[0123] In the formula 、 Determined by the following formula:

[0124] Where: GSI- geological intensity index;

[0125] D－ disturbance factor;

[0126] From this it can be considered and All depend on the geological strength index GSI and disturbance factor D Therefore, the parameter does not appear in the Hawke-Brown empirical criterion. 、 ;

[0127] is the uniaxial compressive strength of intact rock, according to The uniaxial compressive strength of a specific rock can be obtained for:

[0128] for GSI Rock mass >25:

[0129] for GSI Rock mass ≤25:

[0130]

[0131] The determination of deformation modulus is based on field load test and is an important parameter. However, due to certain conditions of field load test, this method has certain limitations. Therefore, under the premise of test data and quality evaluation, in order to quickly and conveniently estimate the deformation modulus of rock mass, it is necessary to establish RMR index, GSI Relationship between the value and the deformation modulus:

[0132] Where:

[0133] —deformation modulus of intact rock mass;

[0134] MR —modulus ratio;

[0135] — rock mass deformation modulus;

[0136] The parameter values ​​of the SSC constitutive model and the Hoek-Brown constitutive model are as follows:

[0137] The SSC model is a soft soil creep model that comes with PLAXIS. The main calculation parameters include the compression coefficient λ , rebound coefficient κ and creep coefficient μ; The compression index and rebound index of the soft soil in the construction site area can be measured experimentally. The compression coefficient of the soft soil in the construction site area can be obtained through the conversion relationship of the following formula: λ , rebound coefficient κ Creep coefficient μ and compression coefficient λ The relationship is:

[0138] ,

[0139] Taking the middle value of 20, we can get the main parameters of the SSC constitutive model for the soft soil in the anchor foundation area: compression coefficient λ =0.0475, rebound coefficient κ =0.0076, creep coefficient μ =0.0024;

[0140] Combining rock compression test and splitting test, the parameters of the Hoek-Brown constitutive model of conglomerate with different weathering degrees are obtained;

[0141] Moderately weathered conglomerate: compression modulus E rm =1026MPa, compressive strength Σ ci =24.67MPa, tensile strength Σ ti =1.52MPa, geological strength index GSI =55;

[0142] Slightly weathered conglomerate: compression modulus E rm =1710MPa, compressive strength Σ ci =31.25MPa, tensile strength Σ ti =3.22MPa, geological strength index GSI=70.

[0143] Consider the contribution of soil resistance to the anti-sliding of anchor foundation as follows:

[0144] On the basis of existing specifications, the contribution of soil resistance to the anti-sliding of anchor foundation at different construction stages of the superstructure is considered, and the anti-sliding stability coefficient is calculated. Calculate as follows:

[0145] Where:

[0146] —Anti-sliding stability coefficient of bridge and culvert pier foundation;

[0147] — total vertical force;

[0148] —The total amount of anti-sliding stabilizing horizontal forces;

[0149] — total sliding horizontal force;

[0150] —The coefficient of friction between the foundation bottom surface and the foundation soil is determined through experiments;

[0151] Based on the three-dimensional finite element calculation results, the typical working conditions of the initial stage, intermediate stage, and completion stage of the bridge superstructure beam segment erection were analyzed. Combined with the above formula, the anti-sliding stability coefficient of the anchor foundation under each typical working condition considering the effect of soil resistance was obtained. In the initial stage: k c =6.028; intermediate stage k c =3.397; completion stage k c =2.962.

[0152] Consider the contribution of soil resistance to the anti-overturning of anchor foundation as follows:

[0153] On the basis of existing specifications, the contribution of soil resistance to the anti-overturning of anchor foundation at different construction stages of superstructure is considered, and the anti-overturning stability coefficient is calculated. Calculate as follows:

[0154] Where:

[0155] ─ Anti-overturning safety factor;

[0156] - The distance from the centroid of the section to the calculated overturning axis on the extension line from the centroid of the section to the point of action of the resultant force (m);

[0157] ─The combined force of all external forces R The eccentricity of the point of action on the verification section to the centroidal axis of the base;

[0158] P i - Vertical force (kN) caused by standard value combination of actions or accidental actions (except earthquake) without considering their partial factors and combination factors;

[0159] e i ─Vertical force P i The moment arm of the center of gravity of the verified section (m);

[0160] H i - horizontal force (kN) caused by standard value combination of actions or standard value combination of accidental actions (except earthquake) without considering their partial factors and combination factors;

[0161] h i ─The force arm of the horizontal force on the verification section (m);

[0162] Based on the three-dimensional finite element calculation results, the typical working conditions of the initial stage, intermediate stage, and completion stage of the bridge superstructure beam segment erection were analyzed. Combined with the above formula, the anti-overturning stability coefficient of the anchor foundation under each typical working condition considering the effect of soil resistance was obtained. In the initial stage: k =9.726; intermediate stage k =4.904; completion stage k =4.115.

[0163] The stress bearing capacity of the base is verified as follows:

[0164] According to existing specifications, the front and rear end bases of the anchorage should not have tensile stress during the construction and operation stages, and the maximum stress value is Should meet the following requirements:

[0165] Where:

[0166] — Resistance coefficient, which is 1.25 during the construction phase and 1 for other working conditions;

[0167] [ f a ]—allowable value of foundation bearing capacity;

[0168] The bearing layer of the caisson foundation is a gravel layer, and the allowable value is [ f a] is 3346 kPa, and the resistance coefficient during the construction phase is 1.25. Under different working conditions of superstructure construction and beam erection, all stresses are compressive, and the maximum base stress is less than 4182.5 kPa, meeting the bearing capacity requirements.

[0169] The prediction and analysis of subsequent working conditions after beam erection are as follows:

[0170] After the erection of the bridge beam section was completed, the deformation and stress of the caisson and its upper anchor foundation were predicted through three-dimensional finite element simulation based on the verification of the aforementioned calculation parameters for subsequent construction and operation conditions: in the post-construction stage, the stage with the largest change in anchor displacement was mainly concentrated in the first year after construction. After one year, the deformation basically tended to be stable.

[0171] See also Figures 1 to 4 First, the anchorage is located in the alluvial plain area on the north bank, with a surface elevation of about 4.4m. From the surface downward, it is ①1 miscellaneous fill, ②-1b3 silty clay, ②-2b4 silty clay with silt, ②-2d3-4 silt sand, ②-3d2-3 silty fine sand, ②-3d2 silty fine sand, ②-4d1 silty fine sand, ②-4d (z) 1 medium sand, ②-4e1-2 rounded gravel. The bedrock is muddy siltstone and silt sand, with strongly weathered bedrock and moderately weathered bedrock being extremely soft rock. The base of the caisson is placed on rounded gravel soil. The total height of the caisson foundation is 49.5m, the bearing layer is rounded gravel soil, and the allowable bearing capacity value is [ f a =3346kPa. The first section is a steel-shell concrete caisson, 8m high, while the remaining sections are reinforced concrete. The original plan for the anchor foundation caisson had plan dimensions of 74 x 56m (longitudinal x transverse), with 24 wells measuring 11.65 x 10.3m (longitudinal x transverse). The outer wall thickness of the caisson was 2.2m, and the inner wall thickness was 1.6m. The rear five rows of wells were filled with sand, while the front row was filled with water. The bottom concrete seal was 12m thick, and the front half of the caisson cover was 6m thick, while the rear half was 10m thick. The optimized plan had plan dimensions of 70 x 50m (longitudinal x transverse).

[0172] A numerical model was constructed in PLAXIS to analyze the stress and deformation of the anchor foundation during different construction stages of the bridge superstructure. The Hoek-Brown constitutive model was used for rock, the soft soil creep (SSC) constitutive model for silt soil, and the small strain soil hardening model for the remaining soils. The substructure consists of a rectangular caisson with dimensions of 50m × 70m × 50m, embedded in a gravel layer. The soil model dimensions are 3 to 5 times larger, measuring 300m × 300m × 83m. The model was meshed, and the meshes of the caisson, the soil within the cavity, and the anchor foundation were optimized. The model mesh was constructed using 10-node tetrahedrons, resulting in a total of 133,490 soil elements and 196,007 nodes. The model boundary conditions were: the bottom of the model was completely fixed, meaning that the soil was constrained in both horizontal and vertical displacements; and the surrounding areas were fixed in the normal direction, meaning that the soil was horizontally constrained but vertically free.

[0173] See also Figures 5 to 7 To select the most suitable soil constitutive model for actual engineering applications, PLAXIS is a large-scale finite element calculation program specifically designed for analyzing deformation and stability in geotechnical engineering. It has multiple built-in constitutive models that can simulate the stress-strain relationship of different soils and rocks. By comparing the characteristics of these constitutive models, the most suitable model for simulating the soil and rock in the construction site area was selected.

[0174] (1) SSC constitutive model

[0175] The soft soil model is suitable for simulating normally consolidated clay, clay silt and peat. These soils are collectively called soft soils and have high compressibility. Unlike the HS model, the SS model uses a modified compression index. and Modified Inflation Index In the soft soil model, the volume strain and mean effective stress are assumed to be The relationship is as follows: Figure 5 As shown:

[0176] Isotropic unloading and reloading follow a different straight line path:

[0177] The yield function of the soft soil model is defined as follows:

[0178] in Stress state ( , ), the preconsolidation stress is a function of the plastic strain:

[0179] ,

[0180] Yield function of SS model f exist 、 The plane is an ellipse, such as Figure 6 As shown, a fully plastic Mohr-Coulomb yield function is tested to simulate the failure state. The model failure line is fixed, but the cap increases during primary compression. The yield surface of the SS model is defined by six yield functions: three compressive yield functions and three Mohr-Coulomb yield functions. Figure 7 The total yield contour resulting from these six yield functions in principal stress space is shown in FIG.

[0181] Modified Compression Index in SS Model Modified Inflation Index It can be obtained from the one-dimensional compression test:

[0182] Where: — compression index;

[0183] —Resilience index;

[0184] Modified Compression Index in Soft Soil Models and compression modulus The relationship between them is as follows:

[0185] Unloading / reloading modulus Modified Inflation Index The relationship is as follows:

[0186]

[0187] The soft soil creep SSC model was proposed by Neher & Vermeer. It takes into account the time-related creep effect of soft soil on the basis of the soft soil model, that is, the secondary consolidation effect after the primary consolidation settlement of the soil. Compared with the SS model, the SSC model adds a modified creep coefficient. , which can be obtained from the long-term volumetric strain and time logarithmic curve:

[0188] Where: —Secondary compression creep index;

[0189] The volume creep strain is considered in the SSC model and its expression is:

[0190]

[0191] (2) Hoek-Brown constitutive model

[0192] For the constitutive model of rock, the Hoek-Brown constitutive model is widely used in engineering to describe the mechanical behavior of rock mass. The parameters of the Hoek-Brown constitutive model are calibrated by field sampling and the relevant research results of the anchoring site rock mass in the existing literature. The Hoek-Brown failure criterion adopts the maximum principal stress and minimum principal stress The critical stress state of jointed rock mass is described by the relationship:

[0193] Where: — Complete rock parameters reduction;

[0194] 、 — auxiliary material parameters of rock blocks;

[0195] In the formula 、 Determined by the following formula:

[0196] Where: GSI- geological intensity index;

[0197] D－ disturbance factor;

[0198] Therefore, considering the calculation efficiency, the SSC constitutive model is used for the silty soil in the anchor foundation site area, the Hoek-Brown constitutive model is used for the rock, and the HSS constitutive model is used for the remaining soils. The specific calculation parameters are listed in Table 1-3.

[0199] Table 1 SSC constitutive model parameters

[0200]

[0201] Table 2 Hoek-Brown constitutive model parameters

[0202]

[0203] Table 3 HSS constitutive model parameters

[0204]

[0205] See also Figure 8 The calculation conditions include the simulation of the entire process of anchor foundation construction and bridge superstructure construction. The construction process of the bridge superstructure is simulated according to the size of the anchor cable force. The main cable tension under the installation of different beam sections is shown in Table 4.

[0206] Table 4 Tension of a single main cable at different construction stages of the Xianxin Road bridge superstructure

[0207]

[0208] See also Figures 9 and 10 Based on the aforementioned measured analysis of the anchor foundation, under the action of the main cable tension, the anchor foundation overturned at a certain angle: the horizontal displacement of the anchor cable points pointed to the south, and the vertical displacement manifested as the front end point sinking and the rear end point rising. Therefore, the front and rear end points were selected for finite element calculations and comparative analysis of the vertical displacement of the anchor foundation, and the anchor cable points were selected for finite element calculations and comparative analysis of the horizontal displacement of the anchor foundation.

[0209] according to Figure 9 The comparison between the finite element calculation results of the vertical displacement of the front and rear end points of the anchor and the actual measurement shows that the overall trend is consistent with the on-site measurement. The vertical displacement of the anchor foundation is manifested as settlement at the front end point (B8) and uplift at the rear end point (B4), and the deviation between the measured and calculated values ​​is not large: the measured value of the maximum settlement of the anchor foundation is 11.50mm, corresponding to the condition when the superstructure is installed to the 79th beam section. The finite element calculation result of the settlement of point B8 under this condition is 11.36mm; the measured value of the maximum uplift of the anchor foundation is 5.4mm, corresponding to the condition when the superstructure is installed to the 79th beam section. The finite element calculation result of the uplift of point B4 under this condition is 9.31mm.

[0210] according to Figure 10 Comparison of the finite element calculation results of the horizontal displacement of the anchor cable points with field measurements shows that as the main cable tension increases, the horizontal displacement of the anchor cable points should increase. Overall, the finite element calculation results of the horizontal displacement of the anchor cable points agree well with the field measurements. The maximum horizontal displacement measured is 25.80mm, and the finite element calculation value is 31.26mm, which is quite close.

[0211] See also Figures 11 to 13 The curves showing the change rules of the normal stress and tangential stress at the bottom of the anchor foundation and the soil resistance of the caisson foundation at different stages of superstructure construction are shown respectively.

[0212] Figure 11Because the center of gravity of the anchor caisson and internal foundation is located at the rear end, the maximum base stress is located at the rear end during the aforementioned working condition of superstructure beam installation (superstructure beam installation segments 0 to 19). As the main cable tension increases, the rear end vertically displaces upward, and the maximum base stress decreases slightly, from -1290 kPa to -1158 kPa. After the 19th beam segment is installed, the maximum base stress is located at the front end. As the main cable tension continues to increase, the anchor foundation overturns at a certain angle beyond the front end, and the maximum base normal stress increases continuously, from -1158 kPa to -1300 kPa. The minimum normal stress decreases continuously, from -537.6 kPa to -478.1 kPa. Both the maximum and minimum normal stresses are compressive, and no tensile failure occurs.

[0213] Figure 12 As the main cable tension continues to increase, the maximum tangential stress of the base continues to increase, that is, the horizontal resistance provided by the base continues to increase, from 30.01kPa to 43.49kPa, to resist the increasing main cable tension.

[0214] Figure 13 As the main cable tension on the middle anchor foundation continued to increase, the horizontal displacement increased significantly, and the soil resistance on the caisson foundation also continued to increase to resist the main cable tension. The maximum soil resistance on the caisson foundation increased from -922.6kPa to -1155kPa.

[0215] See also Figure 14 and Figure 15 On the basis of existing specifications, the contribution of soil resistance to the anti-sliding and anti-overturning of anchor foundations was considered. According to the three-dimensional finite element calculation results of the stratum structure method of the anchor foundation mentioned above, the anti-sliding stability coefficient and anti-overturning stability coefficient of the anchor foundation were calculated. The specific conclusions under various typical working conditions are listed in Tables 5 and 6:

[0216] Table 5 Calculation structure statistics of anti-sliding stability coefficient of anchorage under various typical working conditions

[0217]

[0218] Table 6 Calculation structure statistics of anchorage's anti-overturning stability coefficient under various typical working conditions

[0219]

[0220] With the increase of main cable tension, the anti-sliding stability coefficient of the anchor foundation decreases significantly, but it is above 2.0, meeting the requirements of the specification; according to the anti-overturning calculation results of the anchor foundation with and without considering the soil resistance, when the soil resistance is considered, the anti-overturning stability coefficient of the anchor foundation increases to a certain extent, but the increase is small, and the contribution of soil resistance to the anti-overturning stability coefficient is smaller than that to the anti-sliding stability coefficient.

[0221] The bearing layer of the caisson is a gravel layer, and the allowable value is [ f a ] is 3346 kPa, and the resistance coefficient during the construction phase is 1.25. Table 7 summarizes the maximum and minimum anchor base stress calculations under different conditions of bridge superstructure construction and beam erection, showing that all stresses are compressive, and the maximum base stress is less than 4182.5 kPa, meeting the bearing capacity requirements.

[0222] Table 7 Anchor base stress bearing capacity verification table

[0223]

[0224] See also Figures 16 to 21 The horizontal and vertical displacements of the anchor cable points and rear endpoints of the anchorage upper foundation along the bridge were extracted, and the relationship between the displacement changes under different working conditions is shown in the figure. Under the conditions of dead load + live load, 20 years after construction and operation, the maximum horizontal displacement of the anchor cable points of the anchorage foundation is -11.632mm, the maximum settlement of the front end is -3.686mm, and the maximum uplift of the rear end is 4.465mm. Under the conditions of main force + additional force, 20 years after construction and operation, the maximum horizontal displacement of the anchor cable points of the anchorage foundation is -13.303mm, the maximum settlement of the front end is -4.234mm, and the maximum uplift of the rear end is 5.091mm. In the post-construction stage, the maximum displacement change of the anchorage foundation is mainly concentrated in the first year after construction. After one year, the deformation basically tends to be stable.

[0225] The maximum displacements of the anchor foundation and lower caisson foundation under different calculation conditions are shown in Table 8 below. After the construction of the bridge was completed, the maximum horizontal displacement of the anchor foundation along the bridge was -49.480mm, the maximum horizontal displacement across the bridge was -0.151mm, and the maximum vertical displacement was -18.930mm, which manifested as settlement. The maximum horizontal displacement of the caisson foundation along the bridge was -28.600mm, the maximum horizontal displacement across the bridge was 0.257mm, and the maximum vertical displacement was -19.340mm, which manifested as settlement. Under the conditions of dead load and live load, 20 years after construction, the anchorage upper foundation experienced a maximum horizontal displacement along the bridge of -11.650mm, a maximum horizontal displacement across the bridge of -0.052mm, and a maximum vertical displacement of 4.474mm, indicating uplift. The caisson foundation experienced a maximum horizontal displacement along the bridge of -6.860mm, a maximum horizontal displacement across the bridge of 0.072mm, and a maximum vertical displacement of 4.341mm, indicating uplift. The displacements of the anchorage upper foundation and the caisson foundation during this period were both incremental, representing the post-construction displacements of the anchorage foundation during operation. Under the main force + additional force condition, 20 years after construction, the maximum horizontal displacement of the anchor upper foundation along the bridge was -13.320mm, the maximum horizontal displacement across the bridge was -0.058mm, and the maximum vertical displacement was 5.101mm, indicating uplift. The maximum horizontal displacement of the caisson foundation along the bridge was -7.849mm, the maximum horizontal displacement across the bridge was 0.081mm, and the maximum vertical displacement was 4.950mm, indicating uplift. The displacements of the anchor upper foundation and the caisson foundation during this period were incremental displacements, i.e., the post-construction displacements of the anchor foundation during operation.

[0226] Table 8 Maximum displacement of anchor foundation under various working conditions

[0227]

[0228] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for simulating the construction process of a composite caisson anchor foundation under soil resistance, characterized by: The simulation method includes the following steps: A. The stratum structure model was used for modeling. The entire model essentially reproduces the construction site. The model mainly includes the soil model, rock, caisson, cavity soil and anchor foundation. The dimensions of all structures are set according to the actual project. B. The model uses the soft soil creep SSC constitutive model for silty soil, the Hoek-Brown constitutive model for rock, and the small strain soil hardening model for the remaining soils. Based on the final model and in conjunction with existing specifications, the impact of soil resistance on the overall stability of the composite caisson anchor foundation is considered. Ultimately, based on these parameters, a predictive analysis can be conducted on the subsequent construction and operation of the composite caisson anchor foundation after beam erection. C. The caisson foundation dimensions are 50m x 70m x 50m in length, width and height, embedded in a gravel layer. The soil model dimensions are 3 to 5 times the length, width and height of the caisson foundation, and 300m x 300m x 83m in length, width and height. D. The boundary conditions of the model are: the bottom of the model is completely fixed, that is, the soil is constrained in both horizontal and vertical displacements; the four sides of the model are fixed in the normal direction, that is, the soil is constrained horizontally and free vertically; The silty soil in the construction site area uses the PLAXIS built-in SSC soft soil creep constitutive model, which includes: PLAXIS is a software used to analyze deformation and stability of large-scale geotechnical engineering projects. By selecting an appropriate soil constitutive model to simulate the silty soil in the site area, the time-dependent creep effect of soft soil is further considered. The parameters of the SSC constitutive model are calibrated. The SSC model is based on the soft soil model and takes into account the time-related creep effect of soft soil, that is, the secondary consolidation effect after the primary consolidation settlement of the soil. Compared with the SS model, the SSC model adds a modified creep coefficient , which can be obtained from the long-term volumetric strain and time logarithmic curve: ； Where, —Secondary compression creep index; The volume creep strain is considered in the SSC model and its expression is: ； Where: — stress measurement; —generalized pre-consolidation pressure; — volume creep strain; — elasticity matrix; —Modified compression index; —corrected inflation indicators; —corrected creep coefficient; The rock is modeled using the Hoek-Brown constitutive model built into PLAXIS, which includes: PLAXIS is a software used to analyze deformation and stability of large-scale geotechnical engineering projects. It simulates the rock in the construction site area by selecting an appropriate rock constitutive model. The Hawke-Brown failure criterion uses the maximum principal stress and minimum principal stress The critical stress state of jointed rock mass is described by the relationship of ； Where: — Complete rock parameters reduction; 、 — auxiliary material parameters of rock blocks; In the formula 、 Determined by the following formula: ； ； ； Where: GSI- geological intensity index; D－ disturbance factor; From this it can be considered and All depend on the geological strength index GSI and disturbance factor D Therefore, the parameter does not appear in the Hawke-Brown empirical criterion. 、 ; is the uniaxial compressive strength of intact rock, according to The uniaxial compressive strength of a specific rock can be obtained for: ； for GSI Rock mass >25: ； ； for GSI Rock mass ≤25: ； ； The determination of deformation modulus is based on field load test and is an important parameter. However, due to certain conditions of field load test, this method has certain limitations. Therefore, under the premise of test data and quality evaluation, in order to quickly and conveniently estimate the deformation modulus of rock mass, it is necessary to establish RMR index, GSI Relationship between the value and the deformation modulus: ； ； Where: —deformation modulus of intact rock mass; MR —modulus ratio; — rock mass deformation modulus; Consider the contribution of soil resistance to the anti-sliding of anchor foundation as follows: On the basis of existing specifications, the contribution of soil resistance to the anti-sliding of anchor foundation at different construction stages of the superstructure is considered, and the anti-sliding stability coefficient is calculated. Calculate as follows: ； Where: —Anti-sliding stability coefficient of bridge and culvert pier foundation; — total vertical force; —The total amount of anti-sliding stabilizing horizontal forces; — total sliding horizontal force; —The coefficient of friction between the foundation bottom surface and the foundation soil is determined through experiments; Based on the three-dimensional finite element calculation results, the typical working conditions of the initial stage, intermediate stage, and completion stage of the bridge superstructure beam segment erection were analyzed. Combined with the above formula, the anti-sliding stability coefficient of the anchor foundation under each typical working condition considering the effect of soil resistance was obtained. In the initial stage: k c =6.028; intermediate stage k c =3.397; completion stage k c =2.962; Consider the contribution of soil resistance to the anti-overturning of anchor foundation as follows: On the basis of existing specifications, the contribution of soil resistance to the anti-overturning of anchor foundation at different construction stages of superstructure is considered, and the anti-overturning stability coefficient is calculated. Calculate as follows: ； ； Where: ─ Anti-overturning safety factor; - The distance from the centroid of the section to the calculated overturning axis on the extension line from the centroid of the section to the point of action of the resultant force (m); ─The combined force of all external forces R The eccentricity of the point of action on the verification section to the centroidal axis of the base; P i - Vertical force (kN) caused by standard value combination of actions or standard value combination of accidental actions (except earthquake) without considering their partial factors and combination factors; e i ─Vertical force P i The moment arm of the center of gravity of the verified section (m); H i - horizontal force (kN) caused by standard value combination of actions or standard value combination of accidental actions (except earthquake) without considering their partial factors and combination factors; h i ─The force arm of the horizontal force on the verification section (m); Based on the three-dimensional finite element calculation results, the typical working conditions of the initial stage, intermediate stage, and completion stage of the bridge superstructure beam segment erection were analyzed. Combined with the above formula, the anti-overturning stability coefficient of the anchor foundation under each typical working condition considering the effect of soil resistance was obtained. In the initial stage: k =9.726; intermediate stage k =4.904; completion stage k =4.

115.

2. The method for simulating the construction process of a composite caisson anchor foundation under soil resistance according to claim 1 is characterized by: The parameter values ​​of the SSC constitutive model and the Hoek-Brown constitutive model are as follows: The SSC model is a soft soil creep model that comes with PLAXIS. The main calculation parameters include the compression coefficient λ , coefficient of rebound κ and creep coefficient μ; The compression index and rebound index of the soft soil in the construction site area can be measured experimentally. The compression coefficient of the soft soil in the construction site area can be obtained through the conversion relationship of the following formula: λ , coefficient of rebound κ ; Creep coefficient μ and compression coefficient λ The relationship is: ， ； Taking the middle value of 20, we can get the main parameters of the SSC constitutive model for the soft soil in the anchor foundation area: compression coefficient λ =0.0475, rebound coefficient κ =0.0076, creep coefficient μ =0.0024; Combining rock compression test and splitting test, the parameters of the Hoek-Brown constitutive model of conglomerate with different weathering degrees are obtained; Moderately weathered conglomerate: compression modulus E rm =1026MPa, compressive strength Σ ci =24.67MPa, tensile strength Σ ti =1.52MPa, geological strength index GSI =55; Slightly weathered conglomerate: compression modulus E rm =1710MPa, compressive strength Σ ci =31.25MPa, tensile strength Σ ti =3.22MPa, geological strength index GSI =70.

3. The method for simulating the construction process of a composite caisson anchor foundation under soil resistance according to claim 1, characterized in that: The prediction and analysis of the subsequent working conditions after beam erection are as follows: After the erection of the bridge beam section was completed, the deformation and stress of the caisson and its upper anchor foundation were predicted through three-dimensional finite element simulation based on the verification of the aforementioned calculation parameters for subsequent construction and operation conditions: in the post-construction stage, the stage with the largest change in anchor displacement was mainly concentrated in the first year after construction. After one year, the deformation basically tended to be stable.

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