Foundation pit excavation analogue simulation method and system

Abstract

The invention provides a foundation pit excavation analogue simulation method and system, belongs to the technical field of foundation pit construction analogue simulation, and aims to solve the problem that in the prior art, the research on applying risk evaluation to deep foundation pit construction is less. Comprising the steps that 1, geometric information of a foundation pit design scheme is converted and established into a grid model based on a model establishment rule, the established grid model is subjected to three-dimensional boundary grouping, and soil layers are divided according to a geological exploration report; 2, performing initial stress calculation on the grid model established in the step 1 and a stress calculation rule to obtain an initial stress state of the grid model; 3, based on the grid model and step-by-step excavation of the foundation pit, simulation is conducted on foundation pit excavation according to the principle that excavation is conducted after supporting; the simulation of foundation pit excavation comprises the steps of simulating a foundation pit soil body based on a Mohr-Coulomb model, simulating a foundation pit support structure based on an elastic constitutive model, simulating a foundation pit excavation face based on an empty model, and simulating a foundation pit support structure.

Description

Technical Field

[0001] The invention belongs to the technical field of foundation pit construction simulation, and in particular relates to a foundation pit excavation simulation method and system. Background Art

[0003] The present invention proposes a foundation pit excavation simulation method and system, which can simulate the numerical value of a deep foundation pit and conduct risk assessment for subsequent collection of subway construction accidents. Summary of the invention

[0004] In view of this, the present invention provides a foundation pit excavation simulation method and system.

[0005] The technical solution adopted by the present invention is as follows:

[0006] A foundation pit excavation simulation method, comprising:

[0007] Step 1: Based on the model building rules, the geometric information of the foundation pit design scheme is converted into a grid model, the established grid model is grouped into three-dimensional boundaries, and the soil layers are divided according to the geological survey report;

[0008] In step 1, the model building rules include:

[0009] If the excavation pit geometry is regular, it can be converted into a plane problem for strain analysis and modeled directly using command streams;

[0010] If the excavation pit has an irregular geometry and there are surrounding building structures, use Rhino modeling and griddle to divide the grid;

[0011] If there is a certain symmetry in the geometric shape of the excavation pit, and the stratum fluctuation of the entire excavation pit is very small, half or one-quarter of the simulation model and the boundary conditions are determined according to the situation of the symmetry surface. If the entire model is required, a complete model can be obtained directly through mirroring.

[0012] The size of the model is determined by the size of the foundation pit and the surrounding environment. In order to minimize the influence of time and space effects, the model boundary is generally defined in the following way: the top of the model is a free end, the bottom of the model constrains the vertical displacement, and the vertical truncation boundary of the model only constrains the normal horizontal displacement.

[0013] Step 2: Perform initial stress calculation on the mesh model established in step 1 based on the stress calculation rule to obtain the initial stress state of the mesh model;

[0014] In step 2, the stress calculation rule includes:

[0015] If the foundation pit project is located in an environment with many large buildings and large vehicles around it, the loads generated by the surrounding buildings and the disturbances caused by large vehicles should be taken into consideration when calculating stress;

[0016] If there are tunnels or underground pipelines near the foundation pit, the stress calculation should take into account the influence of soil unloading and the bearing limit of the tunnel or underground pipeline;

[0017] If there are large buildings or large vehicles coming in and out frequently around, add corresponding dynamic loads during stress calculation to determine the initial stress state of the foundation pit at this time.

[0018] Step 3: Simulate the excavation of the foundation pit based on the grid model of step 2 and the principle of excavation in stages and support before excavation;

[0019] The simulation of foundation pit excavation includes: simulating the foundation pit soil based on the Mohr-Coulomb model, simulating the foundation pit retaining structure based on the elastic constitutive model, simulating the foundation pit excavation surface based on the empty model, and simulating the foundation pit supporting structure.

[0020] In step 3, the empty model removes the excavation surface unit body, but it does not mean deletion. The empty model defaults to a unit strength of 0, which will not affect the calculation results.

[0021] In step 3, the simulation of the foundation pit soil based on Mohr-Coulomb method specifically includes the following steps:

[0022] Step A1: Obtain the yield criterion of the soil, as shown below:

[0023]

[0024] in, is the expansion angle produced by shear, C is the cohesion, is the friction angle, σ1, σ2 and σ3 represent the three principal stresses;

[0025] The tensile yield function of the soil is obtained as shown below:

[0026] f t =σ3-σ t (2)

[0027] In the formula, σ t is the tensile strength;

[0028] The tensile strength of the material cannot exceed f s =t and σ1 = σ3, the maximum tensile strength is as follows:

[0029]

[0030] Step A2: Introduce the potential function to define the shear plastic flow and tensile plastic flow after the soil reaches yield, as shown in the following formula:

[0031]

[0032] Step A3: According to formula (1) and formula (2), let f s = t and f t =t, establish the (σ1, σ3) plane rectangular coordinate system, divide the plastic flow area into two areas, define area 1 as the shear failure area and area 2 as the tensile failure area. If the stress point is in area 1, it is shear failure, and if it is in area 2, it is tensile failure.

[0033] In step 3, the elastic constitutive model follows Hooke's linear reversible law, as shown in the following formula:

[0034] NΔδ ij =2GΔ∈ ij +α2Δ∈ kk δ ij (5)

[0035] Among them, δ ij is the Kronecker increment symbol, and α2 is a constant that replaces the bulk modulus K and shear modulus G of the material parameters, as shown in the following formula:

[0036]

[0037] Combining equations (5) and (6) above, we can derive a new stress value, as shown below:

[0038]

[0039] The bulk modulus K and shear modulus G are related to Young's modulus E and Poisson's ratio V as shown in formulas (8) and (9) or (10) and (11):

[0040]

[0041]

[0042]

[0043]

[0044] In step 3, the simulation of the foundation pit support structure specifically includes the simulation of bored piles, the simulation of underground continuous walls and the simulation of steel supports.

[0045] The simulation of bored piles specifically includes:

[0046] Step B1: According to the principle of equivalent stiffness, the underground continuous wall thickness (D+t) is derived from the pile diameter D and pile spacing t of the bored pile, as shown in the following formula:

[0047] ((D+t)h 3 ) / 12=(πD^4) / 64 (12)

[0048] Step B2: Based on formula (12), the converted thickness h of the underground continuous wall is obtained as shown in the following formula:

[0049]

[0050] The simulation of the steel support specifically includes: using a beam unit model to simulate, defining the strength and moment of inertia of the beam according to the strength of the steel pipe and the soil contact area, and assigning Poisson's ratio μ, elastic modulus E, cross-sectional area A and moment of inertia I of the cross section to the beam structure unit during simulation;

[0051] The calculation formula of the moment of inertia I and the cross-sectional area A of the reinforced concrete support section is shown in formula (14):

[0052] I=bh 3 / 12 (14)

[0053] The calculation formula of the moment of inertia I1 and the cross-sectional area A of the steel support section is shown in formulas (15) and (16):

[0054] I1=πD1 4 / 64 (15)

[0055] A=πD1 2 / 4. (16)

[0056] A foundation pit excavation simulation system, comprising:

[0057] Model building module: Based on the model building rules, the geometric information of the foundation pit design scheme is converted into a grid model, the established grid model is grouped into three-dimensional boundaries, and the soil layers are divided according to the geological survey report;

[0058] Initial stress calculation module: performs initial stress calculation on the mesh model and stress calculation rules established in step 1 to obtain the initial stress state of the mesh model;

[0059] Simulation module: simulates the excavation of the foundation pit based on the grid model in step 2 and the principle of step-by-step excavation of the foundation pit and supporting before excavation;

[0060] The simulation of foundation pit excavation includes: simulating the foundation pit soil based on the Mohr-Coulomb model, simulating the foundation pit retaining structure based on the elastic constitutive model, simulating the foundation pit excavation surface based on the empty model, and simulating the foundation pit supporting structure.

[0061] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0062] 1. In the present invention, a numerical simulation model of deep foundation pit excavation support is established to study the horizontal deformation of the retaining structure of the deep foundation pit, the settlement of the surrounding soil, and the uplift of the pit bottom. This can effectively predict the deformation of the foundation pit under different working conditions before engineering construction, predict the occurrence of collapse accidents, and facilitate rapid identification of causes and accident points after accidents occur, thereby avoiding major safety accidents and reducing economic losses and casualties.

[0063] 2. In the present invention, compared with field experiments, the method is repeatable, low-cost, high-efficiency and highly applicable. Different subway deep foundation pits or other types of building deep foundation pits can use this method by simply adjusting parameters. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] The present invention will now be described by way of example with reference to the accompanying drawings, in which:

[0065] Figure 1 is a failure criterion diagram of Example 1 of the present invention;

[0066] Figure 2 is a flow law diagram of Example 1 of the present invention;

[0067] Figure 3 This is a model grid division diagram of Example 3 of the present invention;

[0068] Figure 4 This is a model boundary definition diagram of Example 3 of the present invention;

[0069] Figure 5 Schematic diagram of the initial maximum unbalanced force of Example 3 of the present invention;

[0070] Figure 6 This is a schematic diagram of the initial ZZ direction stress of Example 3 of the present invention;

[0071] Figure 7 Schematic diagram of displacement of the enclosure structure in the Y direction in working condition 1 of embodiment 3 of the present invention;

[0072] Figure 8 Schematic diagram of displacement of the enclosure structure in the Y direction in working condition 2 of embodiment 3 of the present invention;

[0073] Fig. 9 Schematic diagram of displacement of three enclosure structures in the Y direction in working condition 3 of embodiment 3 of the present invention;

[0074] Fig.10 Schematic diagram of the Y-direction displacement of the underground continuous wall in working condition 4 of embodiment 3 of the present invention;

[0075] Fig.11 Schematic diagram of deformation of underground continuous wall in various working conditions of Example 3 of the present invention;

[0076] Fig.12 This is a schematic diagram of the surrounding surface settlement of Example 3 of the present invention;

[0077] Fig.13 This is a schematic diagram of soil uplift in a pit according to Embodiment 3 of the present invention;

[0078] Fig.14 This is a schematic diagram of the process structure of Example 1 of the present invention. DETAILED DESCRIPTION

[0079] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0080] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. 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.

[0081] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features of the embodiments may be combined with each other.

[0082] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0083] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may include that the first and second features are in direct contact, or may include that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, a first feature being "above", "above" and "above" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply indicates that the first feature is higher in level than the second feature. A first feature being "below", "below" and "below" a second feature includes that the first feature is directly below and obliquely below the second feature, or simply indicates that the first feature is lower in level than the second feature.

[0084] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features of the embodiments may be combined with each other.

[0085] Example 1

[0086] like Fig.14 As shown, an embodiment of the present invention discloses a foundation pit excavation simulation method, comprising:

[0087] Step 1: Based on the model building rules, the geometric information of the foundation pit design scheme is converted into a grid model, the established grid model is grouped into three-dimensional boundaries, and the soil layers are divided according to the geological survey report;

[0088] In step 1, the model building rules include:

[0089] If the excavation pit geometry is regular, it can be converted into a plane problem for strain analysis and modeled directly using command streams;

[0090] If the excavation pit has an irregular geometry and there are surrounding building structures, use Rhino modeling and griddle to divide the grid;

[0091] If there is a certain symmetry in the geometric shape of the excavation pit, and the stratum fluctuation of the entire excavation pit is very small, half or one-quarter of the simulation model and the boundary conditions are determined according to the situation of the symmetry surface. If the entire model is required, a complete model can be obtained directly through mirroring.

[0092] The size of the model is determined by the size of the foundation pit and the surrounding environment. In order to minimize the influence of time and space effects, the model boundary is generally defined in the following way: the top of the model is a free end, the bottom of the model constrains the vertical displacement, and the vertical truncation boundary of the model only constrains the normal horizontal displacement.

[0093] Step 2: Perform initial stress calculation on the mesh model established in step 1 based on the stress calculation rule to obtain the initial stress state of the mesh model; (Before simulating the excavation of the deep foundation pit, the initial stress of the model is balanced. The balance is the ground stress field formed by the model only under the action of gravity. For the division of the foundation pit elastic-plastic area, it is necessary to perform initial stress calculation on the foundation pit. On the basis of the initial stress calculation, the foundation pit is excavated. First, the displacement generated by the model under the initial ground stress is restored to zero, and then the foundation pit is excavated step by step to facilitate the observation of the rebound of the foundation pit.)

[0094] In step 2, the stress calculation rule includes:

[0095] If the foundation pit project is located in an environment with many large buildings and large vehicles around it, the loads generated by the surrounding buildings and the disturbances caused by large vehicles should be taken into consideration when calculating stress;

[0096] If there are tunnels or underground pipelines near the foundation pit, the stress calculation should take into account the influence of soil unloading and the bearing limit of the tunnel or underground pipeline;

[0097] If there are large buildings or large vehicles coming in and out frequently around, add corresponding dynamic loads during stress calculation to determine the initial stress state of the foundation pit at this time.

[0098] Step 3: Simulate the excavation of the foundation pit based on the grid model of step 2 and the principle of excavation in stages and support before excavation;

[0099] The simulation of foundation pit excavation includes: simulating the foundation pit soil based on the Mohr-Coulomb model, simulating the foundation pit retaining structure based on the elastic constitutive model, simulating the foundation pit excavation surface based on the empty model, and simulating the foundation pit supporting structure.

[0100] In step 3, the empty model removes the excavation surface unit body, but it does not mean deletion. The empty model defaults to a unit strength of 0, which will not affect the calculation results.

[0101] In step 3, the simulation of the foundation pit soil based on Mohr-Coulomb method specifically includes the following steps:

[0102] Step A1: Obtain the yield criterion of the soil, as shown below:

[0103]

[0104] in, is the expansion angle produced by shear, C is the cohesion, is the friction angle, σ1, σ2 and σ3 represent the three principal stresses;

[0105] The tensile yield function of the soil is obtained as shown below:

[0106] f t =σ3-σ t (2)

[0107] In the formula, σ t is the tensile strength;

[0108] The tensile strength of the material cannot exceed f s =t and σ1 = σ3, the maximum tensile strength is as follows:

[0109]

[0110] The Mohr-coulomb failure criterion is as follows: Figure 1 shown.

[0111] Step A2: Introduce the potential function to define the shear plastic flow and tensile plastic flow after the soil reaches yield, as shown in the following formula:

[0112]

[0113] Step A3: According to formula (1) and formula (2), let f s = t and f t = t, establish the (σ1, σ3) plane rectangular coordinate system, divide the plastic flow area into two areas, which are defined as area 1 as the shear failure area and area 2 as the tensile failure area, such as Figure 2 As shown, if the stress point is in area 1, it is shear failure, and if it is in area 2, it is tensile failure.

[0114] In step 3, the elastic constitutive model follows Hooke's linear reversible law, as shown in the following formula:

[0115] NΔδ ij =2GΔ∈ ij +α2Δ∈ kk δ ij (5)

[0116] Among them, δ ij is the Kronecker increment symbol, and α2 is a constant that replaces the bulk modulus K and shear modulus G of the material parameters, as shown in the following formula:

[0117]

[0118] Combining equations (5) and (6) above, we can derive a new stress value, as shown below:

[0119]

[0120] The bulk modulus K and shear modulus G are related to Young's modulus E and Poisson's ratio V as shown in formulas (8) and (9) or (10) and (11):

[0121]

[0122]

[0123]

[0124]

[0125] In step 3, the simulation of the foundation pit support structure specifically includes the simulation of bored piles, the simulation of underground continuous walls and the simulation of steel supports.

[0126] The simulation of bored piles specifically includes:

[0127] Step B1: According to the design documents of this foundation pit, the retaining structure is bored cast-in-place piles. However, bored cast-in-place piles are not used in the numerical simulation because it is found in the study that the stress mode of the underground continuous wall is very similar to that of the bored cast-in-place piles. Therefore, according to the principle of equivalent stiffness, the thickness of the underground continuous wall (D+t) is derived based on the pile diameter D and pile spacing t of the bored cast-in-place piles, as shown in the following formula:

[0128] ((D+t)h 3 ) / 12=(πD^4) / 64 (12)

[0129] Step B2: Based on formula (12), the converted thickness h of the underground continuous wall is obtained as shown in the following formula:

[0130]

[0131] The simulation of the steel support specifically includes: using a beam unit model to simulate, defining the strength and moment of inertia of the beam according to the strength of the steel pipe and the soil contact area, and assigning Poisson's ratio μ, elastic modulus E, cross-sectional area A and moment of inertia I of the cross section to the beam structure unit during simulation;

[0132] The calculation formula of the moment of inertia I and the cross-sectional area A of the reinforced concrete support section is shown in formula (14):

[0133] I=bh 3 / 12 (14)

[0134] The calculation formula of the moment of inertia I1 and the cross-sectional area A of the steel support section is shown in formulas (15) and (16):

[0135] I1=πD1 4 / 64 (15)

[0136] A=πD1 2 / 4. (16)

[0137] In step 3, the simulation of the underground continuous wall specifically includes: the simulation of the underground continuous wall using solid units is achieved through the contact between the side of the wall and the wall ground, which is not suitable for models with irregular shapes and large volumes. Because the model volume is large, the contact surface will increase, the parameter setting is easy to miss and difficult to determine, and the model calculation equilibrium convergence is difficult, which reduces the accuracy of the calculation results. After the model is balanced, it is difficult to extract the deformation data of the wall. If you want to know the stress of the wall, you need to get it through conversion, and you can't get it directly. Therefore, the underground continuous wall is realized by lining units, which can solve the problems of difficult acquisition of solid unit data, difficult to determine parameters and easy to miss. It is realized by connecting nodes in the normal and tangential directions, and the calculation results are accurate. The lining unit also has the characteristics of the shell unit, and can withstand the tension and normal pressure generated by the friction between the grid.

[0138] Example 2

[0139] This embodiment provides a foundation pit excavation simulation system, including:

[0140] Model building module: Based on the model building rules, the geometric information of the foundation pit design scheme is converted into a grid model, the established grid model is grouped into three-dimensional boundaries, and the soil layers are divided according to the geological survey report;

[0141] Initial stress calculation module: performs initial stress calculation on the mesh model and stress calculation rules established in step 1 to obtain the initial stress state of the mesh model;

[0142] Simulation module: simulates the excavation of the foundation pit based on the grid model in step 2 and the principle of step-by-step excavation of the foundation pit and supporting before excavation;

[0143] The simulation of foundation pit excavation includes: simulating the foundation pit soil based on the Mohr-Coulomb model, simulating the foundation pit retaining structure based on the elastic constitutive model, simulating the foundation pit excavation surface based on the empty model, and simulating the foundation pit supporting structure.

[0144] Example 3

[0145] This embodiment is a specific implementation of embodiment 1, taking a three-element station project as an example:

[0146] 1. Determine the model size

[0147] The main body of the Sanyuan Station is 482.827m long, 23.1m wide, and 11.86m deep. Taking into account computer performance and to reduce calculation duplication, the excavation length of the foundation pit is 150m, and the width and excavation depth remain unchanged. The actual model size is 320m in length, 210m in width, and 70m in depth. To avoid excessive calculation time, this model encrypts the grid near the foundation pit excavation, and sparsely divides the grid farther away from the foundation pit, which ensures the calculation accuracy of the soil near the foundation pit excavation and shortens the model calculation time. In the division of foundation pit soil layers, the horizontal undulations of the surface are ignored, the soil layers are divided horizontally, and the soil is regarded as an isotropic medium. Figure 3 shown.

[0148] 2. Model Boundary Definition

[0149] The model boundary is divided into virtual boundary and physical boundary. The virtual boundary limits the front, back, left, right and bottom of the model, restricts the horizontal displacement of the model in the X and Y directions, but removes the restriction in the Z direction; the physical boundary is the top of the model, the bottom of the foundation pit, and the boundary between soil layers, such as Figure 4 shown.

[0150] 3. Simulate excavation steps

[0151] Foundation pit excavation is the process of unloading soil load, and should follow the principle of "excavation in steps, support first and then excavation". Combined with the engineering case, before excavation, the construction of the retaining structure is completed within the excavation range to ensure that the surrounding soil is less affected by the soil unloading during the excavation process, and to reduce the deformation of the surrounding soil; the support structure uses A609 steel pipes, and the steel pipes have three layers of support with a spacing of 5m. When excavating one layer, one layer of support is made until the last layer is excavated. The numerical simulation of this model is divided into four steps of excavation, and the specific steps are shown in Table 1.

[0152] Table 1 Model excavation steps

[0153]

[0154] 4. Model related parameters

[0155] The calculation model parameters were selected. The soil layer was simplified into 5 layers according to the longitudinal section. The soil parameters were obtained according to the engineering cases, geological survey reports and related papers. The constitutive model of the soil adopted the Mohr-Coulomb model, as shown in Table 2. The main retaining structure adopted Φ1200@2200mm reinforced concrete bored piles. The thickness of the underground continuous wall was calculated to be 895mm according to Formula 3.15. For the convenience of modeling, the thickness of the underground continuous wall was set to 900mm, and the embedding depth of the soil was 12.5m. The elastic model was adopted for the constitutive model of the continuous wall. The internal support of the steel pipe was not made into a solid unit, but was simulated by beam unit with a spacing of 5m, as shown in Table 3.

[0156] Table 2 ± Layer Parameters

[0157]

[0158] Table 3 Support structure parameters

[0159]

[0160] 5. Numerical analysis of simulation results

[0161] 5.1 Initial balance and maximum unbalanced force

[0162] Before the model is simulated for excavation balance calculation, the maximum unbalanced force of the model is first analyzed and the maximum unbalanced force of the model is recorded. At this time, the model is only affected by gravity and no soil treatment is performed. The gravity acceleration of the soil is taken as 9.8m / s 2The soil is consolidated and stable under the action of gravity, which is mainly reflected in whether the internal and external forces of the nodes are balanced. The maximum unbalanced force can be selected as a basis for judging whether the model has reached equilibrium. If the maximum unbalanced force converges to zero, the model is in absolute equilibrium; or converges to a stable constant, the model is in relative equilibrium, and the forces on each node on the model are balanced. When the model calculates to 500 steps, the maximum unbalanced force begins to converge. When the calculation is close to 900 steps, the model stops calculating and reaches equilibrium. Figure 5 As shown. At this time, the model corresponds to the stress cloud diagram in the ZZ direction, as shown Figure 6 As shown in the figure, it can be seen that the vertical stress gradient distribution of the soil layer is obvious. The closer to the surface, the smaller the gravity effect on the soil layer, the smaller the stress value, but the stress fluctuates. The closer to the bottom of the model, the greater the gravity effect on the soil layer, the greater the stress value, and the stress distribution is very stable. The stress cloud map distribution in the ZZ direction also reflects the vertical stress distribution of the soil body only affected by the gravity field before the foundation pit excavation.

[0163] 5.2 Analysis of deformation of enclosure structure

[0164] The retaining structure will unload as the deep foundation pit is excavated, and the original soil pressure balance will be broken, and the soil outside the pit will move into the pit. However, due to the existence of the retaining structure, the soil outside the pit is blocked from moving inward, and the retaining structure itself will be squeezed by the soil outside the pit, resulting in horizontal displacement. The horizontal displacement of this model mainly occurs in the Y direction and close to the corner of the pit, such as Figures 7-10 As shown in the figure, the displacement of the retaining structure in the Y direction under various working conditions shows that the retaining structure moves into the pit, and the maximum deformation occurs at the corner of the pit near the deep foundation pit excavation. However, as the excavation depth of the soil in the pit increases, the deformation of the retaining structure increases, and the maximum displacement moves downward.

[0165] from Fig.11 It can be seen that in working condition 1, the maximum horizontal displacement of the enclosure structure in the Y direction is 5.43mm. The maximum displacement occurs at the top of the enclosure, which roughly shows a linear law. From the depth of 12m to the bottom of the enclosure structure, the displacement change rate gradually approaches zero, and the displacement change tends to be stable. The deformation of the enclosure structure is similar to 2.4a. Figure 1 As a result, the damage of the retaining structure is similar to that of a cantilever.

[0166] In working condition 2, the maximum horizontal displacement of the retaining structure in the Y direction is 6.95mm, and the maximum displacement occurs at the top of the retaining structure. The displacement change is very small from 0 to 4m, and the displacement change rate increases from 4 to 12m. After 12m, the law presented is similar to working condition 1. However, as the excavation depth of the foundation pit increases, the retaining structure is more affected by the movement of the soil outside the pit into the pit, the displacement and deformation of the retaining structure increases, and the displacement and deformation at the bottom of the retaining structure are 2.09mm.

[0167] The maximum horizontal displacement of the retaining structure in the Y direction of working conditions 1 and 2 both appear at the top of the retaining structure, but both show a linear pattern. The maximum horizontal displacement of the retaining structure in the Y direction increases from working conditions 1 to working conditions 2, with an increment of 1.52 mm. The main reason is that the excavation depth increases, the unloading in the pit increases, and the supporting effect of the supporting structure decreases with the increase of excavation depth. This is because the influence of soil unloading on the horizontal deformation of the retaining structure is greater than that of the supporting structure. At the position of the supporting structure, the displacement deformation increment of the retaining structure decreases.

[0168] In working condition 3, the maximum horizontal displacement of the enclosure structure in the Y direction is 11.4 mm, which is at a depth of 6 m. The displacement deformation of the enclosure structure shows a parabolic law of increasing first and then decreasing from top to bottom. The maximum deformation moves downward, and the minimum displacement appears at the bottom of the enclosure, with a size of 3.89 mm. However, the displacement change rate of the enclosure structure approaches zero and appears after 12 m of the enclosure structure, which is similar to the 2.4b parabola.

[0169] In working condition 4, the maximum horizontal displacement of the retaining structure in the Y direction is 18.7mm, which is 12m in the middle of the retaining structure. The displacement deformation of the retaining structure shows the characteristics of increasing first and then decreasing from the top to the bottom. The displacement change rate from 0 to 12m gradually decreases, which is similar to the 2.4b parabola. At the top and bottom, the displacement deformation increases with the increase of excavation depth. Because the influence of unloading gradually increases with the increase of excavation depth, the distance from the supporting structure to the bottom of the pit increases, and the effect decreases. At 20m near the retaining structure, the displacement change rate gradually approaches zero, and the minimum displacement is 5.9mm. Therefore, working condition 4 is larger than the previous three working conditions in terms of both value and increment.

[0170] When excavated to the bottom of the pit, the maximum horizontal displacement deformation of the retaining structure in the Y direction increased from 5.43mm to 18.7mm, and the deformation was less than 30mm, which is within the design requirements of the first-level deep foundation pit retaining structure and within the requirements of the "Technical Specifications for Building Code Engineering Testing" (GB50497-2009).

[0171] 5.3 Analysis of soil deformation outside the pit

[0172] The excavation of this foundation pit is carried out in the middle of the model, and the settlement of the soil outside the pit is monitored from the edge of the deep foundation pit to the edge of the model. The unloading of the deep foundation pit causes the redistribution of the surrounding soil pressure, and the surrounding soil produces vertical and horizontal displacements. Excessive deformation of the surrounding soil will have an impact on surrounding buildings, underground pipelines, etc. Fig.12 As shown in the figure, the surface settlement diagram around the deep foundation pit excavation.

[0173] from Fig.12It can be seen that the maximum settlement occurs at a position about 8m away from the foundation pit. From the pit edge to the maximum settlement position, it gradually increases. From the maximum position to the edge of the model, the settlement gradually decreases, showing a "funnel-shaped" law as a whole. With the increase of excavation depth, the settlement increases, and the rate of change increases. From the maximum settlement position to 40m away from the pit edge, the settlement decreases, and the rate of change also decreases. 40m away from the pit edge, the settlement begins to stabilize. It can be concluded that the excavation depth of the foundation pit has a large influence on the surrounding soil, which is about 4 times the excavation depth of the foundation pit. The excavation depth of the foundation pit has a great influence on the settlement of the soil, which is in the range of 3 to 4 times the excavation depth. The maximum settlement of working condition 1 is 5.67mm, the maximum settlement of working condition 2 is 7.68mm, the maximum settlement of working condition 3 is 10.56mm, and the maximum settlement of working condition 4 is 13.69mm.

[0174] Analysis of settlement causes: When deep foundation pits are excavated and unloaded, the soil pressure around them changes, and the soil outside the pit deforms, causing the soil to settle. The deeper the excavation, the more obvious the surrounding settlement, and the wider the impact range.

[0175] From working condition one to working condition four, the settlement at the pit edge gradually increases with the increase of excavation depth. This is because as the excavation depth in the foundation pit increases, the soil at the pit edge moves toward the inside of the pit. However, due to the existence of the retaining structure, there is a certain inhibitory effect on the settlement of the soil outside the pit. However, with the increase of excavation depth, the inhibitory effect of the retaining structure gradually decreases, resulting in a gradual increase in the maximum settlement. As the soil outside the pit moves farther and farther away from the pit edge, the inhibitory effect of the retaining structure becomes smaller and smaller, and the soil within a certain range outside the pit will also settle. Since the soil has a certain self-stability, the farther the soil is from the pit edge, the smaller the settlement, and finally it tends to be stable, and the rate of change of soil settlement also gradually decreases.

[0176] When excavated to the bottom of the pit, the maximum deformation of the soil outside the pit increased from 5.67mm to 13.69mm, and the deformation was less than 30mm, which is within the design requirements of the first-level deep foundation pit retaining structure and within the requirements of the "Technical Specifications for Building Code Engineering Testing" (GB50497-2009).

[0177] 4.4 Analysis of pit bottom uplift

[0178] When the foundation pit is excavated, the vertical load of the soil in the pit is reduced, the soil pressure in the pit is released, the balance of soil pressure inside and outside the pit is broken, and the soil outside the pit moves into the pit, causing the soil inside the pit to bulge. Fig.13 As shown, the soil in the pit is bulging.

[0179] As can be seen from the figure, the pit bottom uplift deformation curves from working conditions 1 to 4 show a deformation law of "large in the middle and small at both ends". The uplift increases as the pit edge is away from the middle of the pit bottom. As the excavation depth of the foundation pit increases, the vertical soil stress release increases, and the pit bottom uplift increases. The maximum uplifts from working conditions 1 to 4 are 7.9mm, 10.4mm, 13.9mm, and 16.4mm, respectively. It can be seen from the figure that the rate of change of the uplift increases, and the minimum uplift is similar, occurring near the pit wall, which are 3.2mm, 3.3mm, 3.4mm, and 3.3mm, respectively.

[0180] Causes of pit bottom bulge: When unloading during deep foundation pit excavation, the original stress state of the soil at the bottom of the pit is destroyed, and the stress of the soil below the excavation surface is released, causing the pit bottom to bulge. However, as the foundation pit is excavated deeper and deeper, the height difference between the soil inside and outside the pit becomes larger and larger, and the shear stress generated at the bottom of the pit increases. The shear stress component in the horizontal direction squeezes the soil, causing the soil to lift and bulge; the shear stress component in the vertical direction will also produce bulge displacement; the maximum bulge of the soil at the bottom of the pit is near the center of the bottom of the pit, and the overall characteristic is "large in the middle and small at both ends".

[0181] In summary, at the center of the short side of the foundation pit, the maximum uplift of the pit bottom is 16.4mm, which meets the first-level foundation pit settlement, and the deformation is less than 25mm to 35mm, which is within the requirements of the Technical Specifications for Construction Engineering Testing (GB50497-2009).

[0182] The circuits, electronic components and modules involved are all prior art and can be fully implemented by those skilled in the art. Needless to say, the content protected by the present invention does not involve improvements to software and methods.

[0183] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0184] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A foundation pit excavation simulation method, characterized in that: include: Step 1: Based on the model building rules, the geometric information of the foundation pit design scheme is converted and established into a grid model, the established grid model is grouped into three-dimensional boundaries, and the soil layers are divided according to the geological survey report; Step 2: Perform initial stress calculation on the mesh model established in step 1 based on the stress calculation rule to obtain the initial stress state of the mesh model; Step 3: Simulate the excavation of the foundation pit based on the principle of step-by-step excavation of the foundation pit, support first and then excavation, and the grid model of step 2; The simulation of foundation pit excavation includes: simulating the foundation pit soil based on the Mohr-Coulomb model, simulating the foundation pit retaining structure based on the elastic constitutive model, simulating the foundation pit excavation surface based on the empty model, and simulating the foundation pit supporting structure.

2. A foundation pit excavation simulation method according to claim 1, characterized in that: In step 1, the model building rules include: If the excavation pit geometry is regular, convert it into a plane problem for strain analysis and use command flow modeling; If the excavation pit has an irregular geometry and there are surrounding building structures, use Rhino modeling and griddle to divide the grid; If the geometric shape of the excavation pit is symmetrical, and the stratum of the entire excavation pit has little undulation, simulate half or one-quarter of the pit. The boundary conditions are determined according to the situation of the symmetry surface. If the entire model is required, the complete model can be obtained by mirroring.

3. A foundation pit excavation simulation method according to claim 1, characterized in that: In step 2, the stress calculation rule includes: If the foundation pit project is located in an environment with many large buildings and large vehicles around it, the loads generated by the surrounding buildings and the disturbances caused by large vehicles should be taken into consideration when calculating stress; If there are tunnels or underground pipelines near the foundation pit, the stress calculation should take into account the influence of soil unloading and the bearing limit of the tunnel or underground pipeline; If there are large buildings or large vehicles coming in and out frequently around, add corresponding dynamic loads during stress calculation to determine the initial stress state of the foundation pit at this time.

4. A foundation pit excavation simulation method according to claim 1, characterized in that: In step 3, the simulation of the foundation pit soil based on Mohr-Coulomb method specifically includes the following steps: Step A1: Obtain the yield criterion of the soil, as shown below: in, C is the cohesion of soil, is the internal friction angle, σ1 and σ3 represent the two principal stresses; The tensile yield function of the soil is obtained as shown below: f t =σ3-σ t (2) In the formula, σ t is the tensile strength; Step A2: Introduce the potential function to define the shear plastic flow and tensile plastic flow after the soil reaches yield, as shown in the following formula: Among them, δ s represents the potential function; Step A3: According to formula (1), formula (2) and formula (3), let f s =0 and f t =0, establish the (σ1, σ3) plane rectangular coordinate system, divide the plastic flow area into two areas, define area 1 as the shear failure area and area 2 as the tensile failure area. If the stress point is in area 1, it is shear failure, and if it is in area 2, it is tensile failure.

5. A foundation pit excavation simulation method according to claim 4, characterized in that: In formula (2) of step A1, the tensile strength of the material cannot exceed f s =0 and σ1=σ3, the maximum tensile strength As shown below: Here, c represents cohesion.

6. A foundation pit excavation simulation method according to claim 1, characterized in that: In step 3, the elastic constitutive model follows Hooke's linear reversible law, as shown in the following formula: NΔd ij =2GΔ∈ ij +α2Δ∈ kk d ij (5) Where N represents stress, δ ij is the Kronecker increment symbol, and α2 is a constant that replaces the bulk modulus K and shear modulus G of the material parameters, as shown in the following formula: Combining equations (5) and (6) above, we can derive a new stress value, as shown below: in, Indicates stress; The bulk modulus K and shear modulus G are related to Young's modulus E and Poisson's ratio V as shown in formulas (8) and (9) or (10) and (11):

7. The foundation pit excavation simulation method according to claim 1, characterized in that: In step 3, the simulation of the foundation pit support structure specifically includes the simulation of bored piles, the simulation of underground continuous walls and the simulation of steel supports.

8. A foundation pit excavation simulation method according to claim 7, characterized in that: The simulation of bored piles specifically includes: Step B1: According to the principle of equivalent stiffness, the underground continuous wall thickness (D+t) is derived from the pile diameter D and pile spacing t of the bored pile, as shown in the following formula: ((D+t)h 3 ) / 12=(πD^4) / 64 (12) Step B2: Based on formula (12), the converted thickness h of the underground continuous wall is obtained as shown in the following formula:

9. The foundation pit excavation simulation method according to claim 7, characterized in that: The simulation of the steel support specifically includes: using a beam unit model to simulate, defining the strength and moment of inertia of the beam according to the strength of the steel pipe and the soil contact area, and assigning Poisson's ratio μ, elastic modulus E, cross-sectional area A and moment of inertia I of the cross section to the beam structure unit during simulation; The calculation formula of the moment of inertia I and the cross-sectional area A of the reinforced concrete support section is shown in formula (14): I=bh 3 / 12 (14) Where b is the cross-sectional width; The calculation formula of the moment of inertia I1 and the cross-sectional area A of the steel support section is shown in formulas (15) and (16): I1=πD1 4 / 64 (15) A=πD1 2 / 4。 (16) 10. A foundation pit excavation simulation system, used to implement a foundation pit excavation simulation method according to claims 1-9, characterized in that: include: Model building module: Based on the model building rules, the geometric information of the foundation pit design scheme is converted into a grid model, the established grid model is grouped into three-dimensional boundaries, and the soil layers are divided according to the geological survey report; Initial stress calculation module: performs initial stress calculation on the mesh model and stress calculation rules established in step 1 to obtain the initial stress state of the mesh model; Simulation module: simulates the excavation of the foundation pit based on the grid model in step 2 and the principle of step-by-step excavation of the foundation pit and supporting before excavation; The simulation of foundation pit excavation includes: simulating the foundation pit soil based on the Mohr-Coulomb model, simulating the foundation pit retaining structure based on the elastic constitutive model, simulating the foundation pit excavation surface based on the empty model, and simulating the foundation pit supporting structure.

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