Simulation method for construction process of composite open caisson anchorage foundation under action of soil resistance

Abstract

The invention discloses an analogue simulation method for a construction process of a composite open caisson anchorage foundation under the action of soil resistance, which comprises the following steps of: A, modeling by adopting a stratigraphic structure method model, basically and truly restoring a construction site by the whole model, and mainly comprising a soil body model, a rock, an open caisson, an in-cavity soil body and an anchorage foundation, and the sizes of all structures are set according to actual engineering. According to the method, dynamic calculation and analysis are carried out on the whole process of anchorage construction, the displacement characteristics of the anchorage foundation can be obtained under different working conditions of the anchorage foundation, the internal force response of the anchorage foundation is further analyzed, and the anti-sliding performance of the anchorage foundation under the action of soil resistance is obtained through calculation on the basis of finite element analysis. And the stress bearing capacity of the foundation is checked, and finally, the follow-up bridge forming state and the deformation of the anchorage foundation 20 years after construction are predicted.

Description

Technical Field

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

[0002] The design method of ordinary anchor foundation is no longer suitable for large bridge foundations, especially the foundation of super-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 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 caisson-related research results at home and abroad, the methods for analyzing the force and stability of caissons during the sinking construction stage usually include theoretical calculation, on-site monitoring, indoor experiments and numerical analysis. For theoretical calculation methods, in the early stage of large-scale caisson applications in China, the focus was mainly 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 provisions in the current foundation design specifications involve the forces borne by the caisson structure during the sinking stage. As the main research method at present, the on-site monitoring method can easily 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 field monitoring data, a calculation method and empirical formula for side wall friction resistance were proposed, and the formula recommended by the specification 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 appeared in China. Regarding numerical analysis research methods, most of them are limited to the analysis and research of the implantation stage before caisson sinking, the construction process after sinking into place, and the stress 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 the suspension bridge with the main span of 1000 to 1500m as the object, and stipulates that the allowable value of the horizontal displacement of the anchor bowl of the long and long span suspension bridge 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 used while considering that the displacement of the anchor bowl would not cause excessive deflection of the stiffening beam. A similar study was conducted on the Great Belt Bridge in Denmark, and the horizontal displacement was expected to be 0.1m one year after its 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 the anchor during the construction and operation stages are not clear, mainly because the rock and soil layers around the anchor foundation are not sufficiently considered. Therefore, by combining actual projects, the stress and deformation analysis of the caisson as a gravity foundation of the retaining structure from construction to operation is carried out. Based on the in-depth study of the existing design methods for the gravity anchor foundation of suspension bridges in my country, after considering the disturbance and creep of the rock and soil layers and other advanced behaviors, a design system and theoretical method considering the interaction between the rock and soil and the anchor foundation is established, providing technical support for the revision of relevant specifications for basic 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, and then the force and deformation mechanism of the anchor during the construction process are deeply discussed. A design theoretical 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 simulation method for the construction process of a composite caisson anchor foundation under soil resistance, the simulation method comprising the following steps: A. The stratum structure model was used for modeling. The entire model basically restored the construction site. The model mainly includes soil model, rock, caisson, soil in the cavity and anchor foundation, and the dimensions of all structures are set according to the actual project; B. In the model, the soft soil creep SSC constitutive model is used for the muddy soil, the Hoek-Brown constitutive model is used for the rock, and the small strain soil hardening model is used for the rest of the soil. Based on the final model and in combination with the existing specifications, the influence of soil resistance on the overall stability of the composite caisson anchor foundation is considered. Finally, based on the above parameters, the subsequent construction and operation of the composite caisson anchor foundation after beam erection can be predicted and analyzed; C. The length, width and height of the caisson foundation are 50m×70m×50m, embedded in the gravel layer, and the soil model size is 3 to 5 times of it, and the length, width and height of the model size is 300m×300m×83m; 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 normally fixed, that is, the soil is horizontally constrained and vertically free.

[0008] As a preferred solution, the silty soil in the construction site area adopts the PLAXIS built-in SSC soft soil creep constitutive model, including: PLAXIS is a software for analyzing deformation and stability of large geotechnical engineering projects. By selecting a suitable soil constitutive model to simulate the silty soil in the site area, the time-dependent creep effect of soft soil is further considered. The parameter values ​​of the SSC constitutive model are calibrated. The SSC model is based on the soft soil model and takes into account the time-dependent creep effect of soft soil, that is, the secondary consolidation effect after the main 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: In the formula, —Secondary compression creep index; The volume creep strain is considered in the SSC model and its expression is: Where: — stress measurement; —generalized preconsolidation pressure; — volume creep strain; — elasticity matrix; —Corrected compression index; — Correction of inflation indicators; —Corrected creep coefficient.

[0009] As a preferred solution, the rock adopts the Hoek-Brown constitutive model built into PLAXIS, including: PLAXIS is a software used to analyze deformation and stability of large geotechnical engineering projects. It simulates the rock in the construction site area by selecting a suitable rock constitutive model; The Hawke-Brown failure criterion uses the maximum principal stress and minimum principal stress The relationship between is used to describe the critical stress state of jointed rock mass; Where: — Complete rock parameters reduction of , — auxiliary material parameters of rock blocks; In the formula , Determined by the following formula: Where: GSI- Geospatial strength index; D－ Disturbance factor; From this it can be considered and All rely on the geological intensity 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:

[0010] 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 value and deformation modulus: Where: — deformation modulus of intact rock mass; MR — modulus ratio; — rock mass deformation modulus; As a preferred solution, the parameters 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 , 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 factor λ The relationship is: ,

[0011] Taking the middle value of 20, we can get the main parameters of the SSC constitutive model for soft soil in the anchor foundation area: compression coefficient λ =0.0475, coefficient of rebound κ =0.0076, creep coefficient μ =0.0024; Combining rock compression test and splitting test, the parameters of Hoek-Brown constitutive model of conglomerate with different weathering degrees are obtained; Moderately weathered conglomerate: compression modulus E rm =1026MPa, compression strength Σ ci =24.67MPa, tensile strength Σ ti =1.52MPa, geological strength index GSI =55; Slightly weathered conglomerate: compression modulus E rm =1710MPa, compression strength Σ ci =31.25MPa, tensile strength Σ ti =3.22MPa, geological strength index GSI =70.

[0012] As a preferred solution, the contribution value of soil resistance to the anti-sliding of anchor foundation is 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 Calculate as follows: Where: —Anti-sliding stability coefficient of bridge and culvert pier foundation; — total vertical force; —The sum of the horizontal anti-sliding stabilizing forces; — total sliding horizontal force; —The coefficient of friction between the bottom surface of the foundation and the foundation soil, determined through experiments; Through 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 are 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 is obtained. In the initial stage: k c =6.028; Intermediate stage k c =3.397; Completion stage k c =2.962.

[0013] As a preferred solution, the contribution value of soil resistance to the anti-overturning of anchor foundation is 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 the superstructure is considered, and the anti-overturning stability coefficient is Calculate as follows: Where: ─ Anti-overturning safety factor; - The distance from the centroid of the cross section to the calculated overturning axis on the extension line from the centroid of the cross 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 of 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 its partial factors and combination factors; e i ─Vertical force P iThe 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 verified section (m); Through 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 are 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 is obtained. In the initial stage: k =9.726; intermediate stage k =4.904; Completion stage k =4.115.

[0014] As a preferred solution, the stress bearing capacity of the substrate is verified as follows: 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: Where: — Resistance coefficient, which is 1.25 during the construction phase and 1 for other conditions; [ f a ]—allowable value of foundation bearing capacity; The bearing layer of the caisson foundation is a gravel layer, and the allowable value is [ f a ] is 3346kPa, and the resistance coefficient in the construction stage is 1.25. Under different working conditions of the upper structure construction beam erection, all stresses are compressive, and the maximum base stress is lower than 4182.5kP, meeting the bearing capacity requirements.

[0015] As a preferred solution, the prediction and analysis of the subsequent working conditions of beam erection are as follows: After the erection of the bridge beam section was completed, the deformation and force of the caisson and its upper anchor foundation were predicted through three-dimensional finite element simulation based on the verification of the above-mentioned 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 one year after construction. After one year, the deformation basically tended to be stable.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The present invention dynamically calculates and analyzes the entire process of anchor construction. Under different working conditions of the anchor foundation, the displacement characteristics of the anchor foundation can be obtained, and the internal force response of the anchor foundation is further analyzed. 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 subsequent bridge completion state and the deformation of the anchor foundation twenty years after construction are predicted. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The geological drilling plan layout diagram of the present invention; Figure 2 This is a structural diagram of the caisson solution of the present invention; Figure 3 This is a diagram of the anchor model of the present invention; Figure 4 This is a grid division diagram of the anchor model of the present invention; Figure 5 is a relationship diagram between volume strain and average stress of the SSC model of the present invention; Figure 6 For the present invention - Yield surface of SSC model on the plane; Figure 7 is the yield surface of the SSC model in the principal stress space of the present invention; Figure 8 The calculation diagram of the anchor foundation of the present invention; Fig. 9 The figure is a comparison diagram of the finite element calculation and the measured results of the vertical displacement of the front and rear end points of the anchor foundation of the present invention; Fig.10 The figure is a comparative analysis diagram of the finite element calculation and measured results of the horizontal displacement of the anchor point of the anchor foundation of the present invention; Fig.11 The diagram is a diagram showing the variation of the maximum and minimum normal stresses of the anchor foundation base under different working conditions of the present invention; Fig.12 The diagram is a variation law diagram of the maximum tangential stress of the anchor foundation base under different working conditions of the present invention; Fig.13 The diagram is a variation law diagram of the maximum soil resistance of the anchor foundation caisson under different working conditions of the present invention; Fig.14 It is the cloud diagram of the base stress and the soil resistance of the caisson foundation of the present invention; Fig.15 This is a deformation grid diagram of the anchor after the steel beam of the present invention is installed; Fig.16 It is a relationship diagram of horizontal displacement change of anchor cable points on the upper foundation of anchorage under the condition of constant load + live load in the operation stage of the present invention; Fig.17It is a relationship diagram of horizontal displacement change of anchor cable points on the upper foundation of anchorage under the main force + additional force condition in the operation stage of the present invention; Fig.18 It is a relationship diagram of vertical displacement change of the front end point of the upper foundation of the anchor under the condition of constant load + live load in the operation stage of the present invention; Fig.19 It is a vertical displacement variation relationship diagram of the front end point of the upper foundation of the anchor under the main force + additional force condition in the operation stage of the present invention; Fig. 20 It is a relationship diagram of vertical displacement change of the rear end point of the upper foundation of the anchor under the condition of constant load + live load in the operation stage of the present invention; Fig.21 This is a relationship diagram of the vertical displacement changes of the rear end point of the upper foundation of the anchor under the main force + additional force conditions in the operation stage of the present invention. DETAILED DESCRIPTION

[0018] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. 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 creative work are within the scope of protection of the present invention.

[0019] 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: A. The stratum structure model was used for modeling. The entire model basically restored the construction site. The model mainly includes soil model, rock, caisson, soil in the cavity and anchor foundation, and the dimensions of all structures are set according to the actual project; B. In the model, the soft soil creep SSC constitutive model is used for the muddy soil, the Hoek-Brown constitutive model is used for the rock, and the small strain soil hardening model is used for the rest of the soil. Based on the final model and in combination with the existing specifications, the influence of soil resistance on the overall stability of the composite caisson anchor foundation is considered. Finally, based on the above parameters, the subsequent construction and operation of the composite caisson anchor foundation after beam erection can be predicted and analyzed; C. The length, width and height of the caisson foundation are 50m×70m×50m, embedded in the gravel layer, and the soil model size is 3 to 5 times of it, and the length, width and height of the model size is 300m×300m×83m; 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 normally fixed, that is, the soil is horizontally constrained and vertically free.

[0020] 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 for analyzing deformation and stability of large geotechnical engineering projects. By selecting a suitable soil constitutive model to simulate the silty soil in the site area, the time-dependent creep effect of soft soil is further considered. The parameter values ​​of the SSC constitutive model are calibrated. The SSC model is based on the soft soil model and takes into account the time-dependent creep effect of soft soil, that is, the secondary consolidation effect after the main 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: In the formula, —Secondary compression creep index; The volume creep strain is considered in the SSC model and its expression is: Where: — stress measurement; —generalized preconsolidation pressure; — volume creep strain; — elasticity matrix; —Corrected compression index; — Correction of inflation indicators; —corrected creep coefficient; The rock uses the Hoek-Brown constitutive model built into PLAXIS, including: PLAXIS is a software used to analyze deformation and stability of large geotechnical engineering projects. It simulates the rock in the construction site area by selecting a suitable rock constitutive model; The Hawke-Brown failure criterion uses the maximum principal stress and minimum principal stress The relationship between is used to describe the critical stress state of jointed rock mass; Where: — Complete rock parameters reduction of , — auxiliary material parameters of rock blocks; In the formula , Determined by the following formula: Where: GSI-Geospatial Index; D－ Disturbance factor; From this it can be considered and All rely on the geological intensity 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:

[0021] 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 value and deformation modulus: Where: — deformation modulus of intact rock mass; MR — modulus ratio; — rock mass deformation modulus; 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 , 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 factor λ The relationship is: ,

[0022] Taking the middle value of 20, we can get the main parameters of the SSC constitutive model for soft soil in the anchor foundation area: compression coefficient λ =0.0475, coefficient of rebound κ =0.0076, creep coefficient μ =0.0024; Combining rock compression test and splitting test, the parameters of Hoek-Brown constitutive model of conglomerate with different weathering degrees are obtained; Moderately weathered conglomerate: compression modulus E rm =1026MPa, compression strength Σ ci =24.67MPa, tensile strength Σ ti =1.52MPa, geological strength index GSI =55; Slightly weathered conglomerate: compression modulus E rm =1710MPa, compression strength Σ ci =31.25MPa, tensile strength Σ ti =3.22MPa, geological strength index GSI =70.

[0023] 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 Calculate as follows: Where: —Anti-sliding stability coefficient of bridge and culvert pier foundation; — total vertical force; —The sum of the horizontal anti-sliding stabilizing forces; — total sliding horizontal force; —The coefficient of friction between the bottom surface of the foundation and the foundation soil, determined through experiments; Through 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 are 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 is obtained. In the initial stage: k c=6.028; Intermediate stage k c =3.397; Completion stage k c =2.962.

[0024] 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 the superstructure is considered, and the anti-overturning stability coefficient is Calculate as follows: Where: ─ Anti-overturning safety factor; - The distance from the centroid of the cross section to the calculated overturning axis on the extension line from the centroid of the cross 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 of 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 its 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 verified section (m); Through 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 are 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 is obtained. In the initial stage: k =9.726; intermediate stage k =4.904; Completion stage k =4.115.

[0025] The bearing capacity of the base stress is verified as follows: 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: Where: — Resistance coefficient, which is 1.25 during the construction phase and 1 for other conditions; [ f a ]—allowable value of foundation bearing capacity; The bearing layer of the caisson foundation is a gravel layer, and the allowable value is [ f a ] is 3346kPa, and the resistance coefficient in the construction stage is 1.25. Under different working conditions of the upper structure construction beam erection, all stresses are compressive, and the maximum base stress is lower than 4182.5kP, meeting the bearing capacity requirements.

[0026] The prediction and analysis of subsequent working conditions after beam erection are as follows: After the erection of the bridge beam section was completed, the deformation and force of the caisson and its upper anchor foundation were predicted through three-dimensional finite element simulation based on the verification of the above-mentioned 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 one year after construction. After one year, the deformation basically tended to be stable.

[0027] See also Figures 1 to 4 First, the anchor 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, strongly weathered bedrock is well developed, and the medium weathered bedrock is 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 value of bearing capacity is [ f a ]=3346kPa. The first section is a steel shell concrete caisson, 8m high, and the rest are reinforced concrete caissons. The original plan size of the anchor foundation caisson is 74×56m (longitudinal×transverse), with 24 wells, and the well size is 11.65×10.3m (longitudinal×transverse); the outer wall thickness of the caisson is 2.2m, and the inner wall thickness is 1.6m; the rear 5 rows of wells are filled with sand, and the front row of wells are filled with water. The thickness of the bottom concrete is 12m, and the thickness of the front half of the caisson top cover is 6m, and the thickness of the rear half is 10m. The plan size of the optimized plan is 70×50m (longitudinal×transverse).

[0028] A numerical calculation model was established in PLAXIS to analyze the stress and deformation of the anchor foundation under different construction stages of the bridge superstructure. The Hoek-Brown constitutive model was used for rock, the soft soil creep SSC constitutive model was used for silt soil, and the small strain soil hardening model was used for the rest of the soil. The lower foundation is a rectangular caisson with a length, width and height of 50m×70m×50m, embedded in a round gravel layer. The soil model size is 3 to 5 times that of the rectangular caisson, and the model size is 300m×300m×83m in length, width and height. The model is meshed, and the mesh of the caisson, the soil in the cavity, and the anchor foundation is optimized. The model mesh is divided by a 10-node unit of a space tetrahedron. The calculation model has a total of 133,490 soil units and 196,007 nodes. 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 surroundings of the model are normally fixed, that is, the soil is horizontally constrained and vertically free.

[0029] See also Figures 5 to 7 In order to select the most suitable soil constitutive model for actual engineering, PLAXIS is a large-scale finite element calculation program specially used for analyzing deformation and stability of 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 soil and rock in the construction site area can be selected.

[0030] (1) SSC constitutive model The soft soil model is suitable for simulating normally consolidated clay, clay silt and peat, which 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 the mean effective stress are assumed to be The relationship is as follows: Figure 5 As shown: Isotropic unloading and reloading follow a different straight line path: The yield function of the soft soil model is defined as follows: in Stress state ( , ), the preconsolidation stress is a function of the plastic strain: ,

[0031] Yield function of SS model f exist , The plane is an ellipse, such as Figure 6 As shown, a completely plastic Mohr-Coulomb yield function is tested to simulate the failure state. The model failure line is fixed, but the cap increases in the main 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 the principal stress space is shown in Figure .

[0032] Modified Compression Index in SS Model Modified Inflation Index It can be obtained from the one-dimensional compression test: Where: — compression index; —Resilience index; Modified Compression Index in Soft Soil Models and compression modulus The relationship between them is as follows: Unloading / Reloading Modulus Modified Inflation Index The relationship is as follows:

[0033] The soft soil creep SSC model was proposed by Neher & Vermeer. It takes into account the time-dependent 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: Where: —Secondary compression creep index; The volume creep strain is considered in the SSC model and its expression is:

[0034] (2) Hoek-Brown constitutive model 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 through on-site sampling and the relevant research results of existing literature on the rock mass of the anchoring site. 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: Where: — Complete rock parameters reduction of 、 — auxiliary material parameters of rock blocks; In the formula 、 Determined by the following formula: Where: GSI- Geospatial strength index; D－ Disturbance factor; 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.

[0035] Table 1 SSC constitutive model parameters

[0036] Table 2 Hoek-Brown constitutive model parameters

[0037] Table 3 HSS constitutive model parameters

[0038] 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.

[0039] Table 4 Tension of single main cable of Xianxin Road bridge superstructure at different construction stages

[0040] See also Figures 9 and 10 Based on the above measured analysis of the anchor foundation: under the action of the main cable tension, the anchor foundation overturns at a certain angle: the horizontal displacement of the anchor point points to the south, and the vertical displacement is manifested as the front end point sinking and the rear end point uplifting. Therefore, the front end point and the rear end point are selected to perform finite element calculation and measurement comparison analysis of the vertical displacement of the anchor foundation, and the anchor point is selected to perform finite element calculation and measurement comparison analysis of the horizontal displacement of the anchor foundation.

[0041] according to Fig. 9The finite element calculation results of the vertical displacement of the front and rear end points of the anchor are compared with the field measurements. The overall trend is consistent with the actual measurement. The vertical displacement of the anchor foundation is characterized by settlement at the front end point (B8) and uplift at the rear end point (B4), and the deviation between the measured value and the calculated value is not large: the measured value of the maximum settlement of the anchor foundation is 11.50mm, corresponding to the condition where the upper structure 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 where the upper structure is installed to the 79th beam section. The finite element calculation result of the uplift of point B4 under this condition is 9.31mm.

[0042] according to Fig.10 The comparison between the finite element calculation results of the horizontal displacement of the anchor point of the anchor foundation and the actual measurement on site shows that with the increase of the main cable tension, the horizontal displacement of the anchor point should increase to a certain extent. Overall, the finite element calculation results of the horizontal displacement of the anchor point are in good agreement with the actual measurement on site, among which the maximum horizontal displacement measured value is 25.80mm, and the finite element calculation value is 31.26mm, which are relatively close.

[0043] See also Figures 11 to 13 The curves showing the changing 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.

[0044] Fig.11 Since the center of gravity of the anchor caisson and the internal foundation is located at the rear end, in the above-mentioned working condition of the upper structure installation beam section (upper structure installation beam section 0 to 19 beam sections), the maximum base stress is located at the rear end, and with the increase of the main cable tension, the rear end vertical displacement is upward, and the maximum base stress decreases to a certain extent, from -1290kPa to -1158kPa; when the upper structure is installed with the 19th beam section, the maximum base stress is located at the front end, and with the continuous increase of the main cable tension, the anchor foundation overturns at a certain angle beyond the front end, and the maximum base normal stress increases continuously, from -1158kPa to -1300kPa; while the minimum normal stress decreases continuously, from -537.6kPa to -478.1kPa. The maximum and minimum normal stresses are both compressive stresses, and no tensile damage occurs.

[0045] Fig.12 As the tension of the main cable 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 tension of the main cable.

[0046] Fig.13As 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.

[0047] See also Fig.14 and Fig.15 On the basis of existing specifications, considering the contribution of soil resistance to the anti-sliding and anti-overturning of anchor foundations, the anti-sliding stability coefficient and anti-overturning stability coefficient of anchor foundations are calculated according to the three-dimensional finite element calculation results of the stratum structure method of the above-mentioned anchor foundations, and the specific conclusions under various typical working conditions are listed in Tables 5 and 6: Table 5 Calculation structure statistics of the anti-sliding stability coefficient of anchorage under various typical working conditions

[0048] Table 6 Calculation structure statistics of the anti-overturning stability coefficient of anchorage under various typical working conditions

[0049] With the increase of main cable tension, the anti-sliding stability coefficient of the anchor foundation decreases significantly, but it meets the requirements of the specification when it is above 2.0; 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.

[0050] The bearing layer of the caisson is a gravel layer, and the allowable value is [ f a ] is 3346 kPa, and the resistance coefficient in the construction stage is 1.25. Under different working conditions of bridge superstructure construction and beam erection, the calculation results of the maximum and minimum anchor base stress are summarized as shown in Table 7, where all stresses are in compression, and the maximum base stress is less than 4182.5 kP, which meets the bearing capacity requirements.

[0051] Table 7 Anchor base stress bearing capacity verification table

[0052] See also Figures 16 to 21, the horizontal displacement and vertical displacement of the anchor point and the rear end point of the anchor upper foundation along the bridge are extracted, and the displacement change relationship with different working conditions is shown in the figure. If under the condition of constant load + live load, 20 years after construction and operation, the maximum horizontal displacement of the anchor point of the anchor foundation is -11.632mm, the maximum settlement of the front end point is -3.686mm, and the maximum uplift of the rear end point is 4.465mm; if under the condition of main force + additional force, 20 years after construction and operation, the maximum horizontal displacement of the anchor point of the anchor foundation is -13.303mm, the maximum settlement of the front end point is -4.234mm, and the maximum uplift of the rear end point is 5.091mm; in the post-construction stage, the largest stage of displacement change of the anchor foundation is mainly concentrated in one year after construction, and one year later, the deformation basically tends to be stable.

[0053] Under different calculation conditions, the maximum displacements of the anchor foundation and the lower caisson foundation 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. If the load is constant and live, 20 years after construction, the maximum horizontal displacement of the anchor upper foundation along the bridge is -11.650mm, the maximum horizontal displacement across the bridge is -0.052mm, and the maximum vertical displacement is 4.474mm, showing uplift; the maximum horizontal displacement of the caisson foundation along the bridge is -6.860mm, the maximum horizontal displacement across the bridge is 0.072mm, and the maximum vertical displacement is 4.341mm, showing uplift. The displacements of the anchor upper foundation and the caisson foundation at this stage are both incremental displacements, that is, the displacement of the anchor foundation after construction during operation. If the main force + additional force condition is used, 20 years after construction, the maximum horizontal displacement of the anchor upper foundation along the bridge is -13.320mm, the maximum horizontal displacement across the bridge is -0.058mm, and the maximum vertical displacement is 5.101mm, showing uplift; the maximum horizontal displacement of the caisson foundation along the bridge is -7.849mm, the maximum horizontal displacement across the bridge is 0.081mm, and the maximum vertical displacement is 4.950mm, showing uplift. The displacements of the anchor upper foundation and the caisson foundation at this stage are both incremental displacements, that is, the displacement of the anchor foundation after construction during operation.

[0054] Table 8 Maximum displacement of anchor foundation under various working conditions

[0055] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution 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 solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A simulation method for the construction process of a composite caisson anchor foundation under soil resistance, characterized in that: The simulation method includes the following steps: A. The stratum structure model was used for modeling. The entire model basically restored the construction site. The model mainly includes soil model, rock, caisson, soil in the cavity and anchor foundation, and the dimensions of all structures are set according to the actual project; B. In the model, the soft soil creep SSC constitutive model is used for the muddy soil, the Hoek-Brown constitutive model is used for the rock, and the small strain soil hardening model is used for the rest of the soil. Based on the final model and in combination with the existing specifications, the influence of soil resistance on the overall stability of the composite caisson anchor foundation is considered. Finally, based on the above parameters, the subsequent construction and operation of the composite caisson anchor foundation after beam erection can be predicted and analyzed; C. The length, width and height of the caisson foundation are 50m×70m×50m, embedded in the gravel layer, and the soil model size is 3 to 5 times of it, and the length, width and height of the model size is 300m×300m×83m; 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 normally fixed, that is, the soil is horizontally constrained and vertically free.

2. The method for simulating the construction process of a composite caisson anchor foundation under soil resistance according to claim 1 is characterized in that: The silty soil in the construction site area adopts the SSC soft soil creep constitutive model built into PLAXIS, including: PLAXIS is a software for analyzing deformation and stability of large geotechnical engineering projects. By selecting a suitable soil constitutive model to simulate the silty soil in the site area, the time-dependent creep effect of soft soil is further considered. The parameter values ​​of the SSC constitutive model are calibrated. The SSC model is based on the soft soil model and takes into account the time-dependent creep effect of soft soil, that is, the secondary consolidation effect after the main 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: In the formula, —Secondary compression creep index; The volume creep strain is considered in the SSC model and its expression is: Where: — stress measurement; —generalized preconsolidation pressure; — volume creep strain; — elasticity matrix; —Corrected compression index; — Correction of inflation indicators; —Corrected creep coefficient.

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 rock adopts the Hoek-Brown constitutive model built into PLAXIS, including: PLAXIS is a software used to analyze deformation and stability of large geotechnical engineering projects. It simulates the rock in the construction site area by selecting a suitable rock constitutive model; The Hawke-Brown failure criterion uses the maximum principal stress and minimum principal stress The relationship between is used to describe the critical stress state of jointed rock mass; Where: — Complete rock parameters reduction of , — auxiliary material parameters of rock blocks; In the formula , Determined by the following formula: Where: GSI- Geospatial strength index; D－ Disturbance factor; From this it can be considered and All rely on the geological intensity 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 value and deformation modulus: Where: — deformation modulus of intact rock mass; MR — modulus ratio; —Deformation modulus of rock mass.

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

5. The method for simulating the construction process of a composite caisson anchor foundation under soil resistance according to claim 1, characterized in that: The contribution of soil resistance to the anti-sliding of anchor foundation is 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 Calculate as follows: Where: —Anti-sliding stability coefficient of bridge and culvert pier foundation; — total vertical force; —The sum of the horizontal anti-sliding stabilizing forces; — total sliding horizontal force; —The coefficient of friction between the bottom surface of the foundation and the foundation soil, determined through experiments; Through 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 are 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 is obtained. In the initial stage: k c =6.028; Intermediate stage k c =3.397; Completion stage k c =2.

962.

6. The method for simulating the construction process of a composite caisson anchor foundation under soil resistance according to claim 1, characterized in that: The contribution of soil resistance to the anti-overturning of anchor foundation is 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 the superstructure is considered, and the anti-overturning stability coefficient is Calculate as follows: Where: ─ Anti-overturning safety factor; - The distance from the centroid of the cross section to the calculated overturning axis on the extension line from the centroid of the cross 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 of 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 its 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 verified section (m); Through 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 are 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 is obtained. In the initial stage: k =9.726; intermediate stage k =4.904; Completion stage k =4.

115.

7. The method for simulating the construction process of a composite caisson anchor foundation under soil resistance according to claim 1, characterized in that: The base stress bearing capacity verification is as follows: 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: Where: — Resistance coefficient, which is 1.25 during the construction phase and 1 for other conditions; [ f a ]—allowable value of foundation bearing capacity; The bearing layer of the caisson foundation is a gravel layer, and the allowable value is [ f a ] is 3346kPa, and the resistance coefficient in the construction stage is 1.

25. Under different working conditions of the upper structure construction beam erection, all stresses are compressive, and the maximum base stress is lower than 4182.5kP, meeting the bearing capacity requirements.

8. 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 of the beam erection are as follows: After the erection of the bridge beam section was completed, the deformation and force of the caisson and its upper anchor foundation were predicted through three-dimensional finite element simulation based on the verification of the above-mentioned 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 one year after construction. After one year, the deformation basically tended to be stable.

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