Design method for retaining structure of a partially - loaded foundation pit considering non - limit earth pressure distribution mode

Abstract

The present invention relates to a design method for the retaining structure of a biased foundation pit considering the non-limit earth pressure distribution mode, including determining the profile parameters and soil parameters of the biased foundation pit; determining the displacement modes of the retaining structures on both sides of the biased foundation pit and the overall force analysis diagram of the retaining structure model of the biased foundation pit; determining the displacement values of the internal supports during preliminary design; calculating the axial forces of each level of internal supports; determining the depth to be determined when the earth pressure on the retaining structures on both sides changes from the limit state to the non-limit state and the embedded depths of the retaining structures on both sides; determining the materials and reinforcement of the retaining structures on both sides. The beneficial effects of the present invention are as follows: The present invention can carry out deformation control-based design for the retaining structure of a biased foundation pit, and the calculation formula is simple and feasible. It can effectively save the project cost and reduce the construction volume on the premise of ensuring safety, stability and the requirements of foundation pit deformation control, and has good popularization and application value.

Description

Technical Field

[0001] The present invention relates to the field of underground engineering, and more specifically, it relates to a design method for the retaining structure of a biased foundation pit considering the non-limit earth pressure distribution pattern. Background Art

[0002] The situation of a foundation pit being subjected to a biased load is becoming increasingly common, including the existence of a dam on one side of the foundation pit, different surcharges on both sides of the foundation pit, different buildings on both sides of the foundation pit, etc. However, the conventional calculation method can only be applied to the design of the retaining structure when the pit-side loads on both sides of the foundation pit are symmetric.

[0003] Currently, for a biased foundation pit, the current "Technical Specification for Building Foundation Pit Support" stipulates that the design calculation is carried out according to the most unfavorable action effect side, and this treatment method will cause an increase in investment and construction volume. The biased load on the foundation pit will cause the displacements of the retaining structures on both sides of the foundation pit to be different, and then the earth pressure distributions on the two retaining structures will be different, the internal force distributions will be asymmetric, and the required embedment depths of the two retaining structures will also be different. Summary of the Invention

[0004] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a design method for the retaining structure of a biased foundation pit considering the non-limit earth pressure distribution pattern.

[0005] In a first aspect, there is provided a design method for the retaining structure of a biased foundation pit considering the non-limit earth pressure distribution pattern, including:

[0006] S1. Determine the profile parameters and soil parameters of the biased foundation pit;

[0007] S2. Determine the displacement modes of the retaining structures on both sides of the biased foundation pit and the overall force analysis diagram of the retaining structure model of the biased foundation pit; the two retaining structures include the retaining structure on the large-load side and the retaining structure on the small-load side; the two retaining structures are connected by multiple levels of internal supports;

[0008] S3. Determine the displacement value of the internal support during preliminary design through the load values of the two-sided bias and the allowable displacement control value of the foundation pit;

[0009] S4. According to the displacement value at the support determined in S3, calculate the axial forces of each level of internal support through the stress-strain relationship;

[0010] S5. According to the displacement modes of the retaining structures on both sides of the biased foundation pit, assume that the distribution pattern of the earth pressure on the two retaining structures is: above a certain depth X below the bottom of the pit i is the limit earth pressure distribution, and below this depth is the non-limit earth pressure distribution, which linearly decays to the static earth pressure at the bottom of the pit;

[0011] S6. Calculate the earth pressures on the retaining structures on the large-load side and the small-load side respectively according to the distribution patterns proposed in S5, and determine the depth X to be determined at which the earth pressures on the retaining structures on both sides change from the ultimate state to the non-ultimate state. i And the embedded depths D of the retaining structures on both sides. i ;

[0012] S7. Calculate the moment and shear force distributions of the retaining structures on both sides respectively, and determine the materials and steel reinforcements of the retaining structures on both sides according to the maximum moment and the maximum shear force respectively.

[0013] S8. Conduct overall stability check, anti-overturning check, and anti-heave stability check.

[0014] Preferably, in S1, the eccentrically loaded foundation pit is a foundation pit with a relatively large load on one side of the pit edge and a relatively small load on the other side; the profile parameters of the eccentrically loaded foundation pit include the excavation depth H of the foundation pit, the layout depth h of each level of internal support m , the calculation length B, the compression stiffness EA, the horizontal spacing S, the value q of the pit edge load on the large-load side d and the value q of the pit edge load on the small-load side x ; the soil parameters include the soil layer thickness d, the unit weight γ, the friction angle δ between the wall and the soil, the internal friction angle and the cohesion c within the range of three times the excavation depth.

[0015] Preferably, in S3, the displacement magnitude Δs at one end of the internal support close to the retaining structure on the large-load side dm takes the allowable displacement value [Δ] of the foundation pit retaining structure max ; the displacement magnitude Δs at one end of the internal support close to the retaining structure on the small-load side xm is calculated according to the eccentric loading ratio on both sides of each level of internal support, and the calculation formula is:

[0016]

[0017] where m represents the m-th level of internal support; K a represents the active earth pressure coefficient; is the equivalent unit weight of the soil layer, which is obtained by the layer-wise summation method for multi-layer soil layers.

[0018] Preferably, in S4, the calculation formula for the axial force of each level of internal support is:

[0019]

[0020] Preferably, in S5, the displacement modes of the retaining structures on both sides of the biased foundation pit are as follows: the displacement at the bottom of the retaining structure on the side with larger load is approximately zero, and the part above the bottom shows displacement towards the inside of the pit, with the maximum displacement determined by the allowable displacement value of the foundation pit; the displacement at the bottom of the retaining structure on the side with smaller load is approximately zero, and the part above the bottom shows displacement towards the inside of the pit, and at the same time, affected by the pushing-back displacement of the side with larger load, the displacement is smaller than that of the side with larger load.

[0021] Preferably, in S6, the horizontal force balance equation and the moment balance equation are expressed as:

[0022]

[0023] Among them, i = 1 represents the side with larger load, and i = 2 represents the side with smaller load; S ai represents the resultant value of the active earth pressure in the active zone above the bottom of the pit, that is, S bi represents the resultant value of the active earth pressure in the active zone of the area where the resultant earth pressure below the bottom of the pit decreases to above zero, that is, a i then represents the height of this area, that is, σ i represents the resultant earth pressure at the bottom of the retaining pile (wall) calculated according to the ultimate earth pressure distribution mode, that is,

[0024] σ 2i represents the resultant earth pressure at the bottom of the retaining pile (wall) calculated according to the non - ultimate earth pressure distribution mode, that is,

[0025] Preferably, the retaining structure on the side with larger load is the retaining pile or retaining wall on the side with larger load; the retaining structure on the side with smaller load is the retaining pile or retaining wall on the side with smaller load.

[0026] In the second aspect, a design device for the retaining structure of a biased foundation pit considering the non - ultimate earth pressure distribution mode is provided, which is used to execute the design method for the retaining structure of a biased foundation pit considering the non - ultimate earth pressure distribution mode in any one of the first aspects, including:

[0027] The first determination module is used to determine the section parameters and soil parameters of the biased foundation pit;

[0028] The second determination module is used to determine the displacement modes of the retaining structures on both sides of the biased foundation pit and the overall force analysis diagram of the retaining structure model of the biased foundation pit; the retaining structures on both sides include the retaining structure on the side with larger load and the retaining structure on the side with smaller load; the retaining structures on both sides are connected by multiple - level internal supports;

[0029] The third determination module is used to determine the displacement value of the internal support during preliminary design based on the load values of the lateral biases and the allowable displacement control value of the foundation pit;

[0030] The first calculation module is used to calculate the axial force of each level of internal support based on the stress-strain relationship according to the displacement value at the support determined by the third determination module;

[0031] The assumption module is used to assume that the distribution pattern of the earth pressure on the retaining structures on both sides of the eccentrically loaded foundation pit is as follows: at a certain depth X i above which is the ultimate earth pressure distribution, and below this depth is the non-ultimate earth pressure distribution, which linearly decays to the static earth pressure at the bottom of the pit;

[0032] The second calculation module is used to calculate the earth pressure on the retaining structure on the large-load side and the retaining structure on the small-load side respectively based on the distribution pattern proposed by the assumption module, and determine the depth X to be determined at which the earth pressure on the retaining structures on both sides changes from the ultimate state to the non-ultimate state i and the embedment depth D of the retaining structures on both sides i ;

[0033] The third calculation module calculates the moment and shear force distributions of the retaining structures on both sides respectively, and determines the materials and reinforcement of the retaining structures on both sides according to the maximum moment and the maximum shear force respectively;

[0034] The checking module is used to perform overall stability checking, anti-overturning checking, and anti-heave stability checking.

[0035] In a third aspect, a computer storage medium is provided, in which a computer program is stored; when the computer program runs on a computer, the computer is made to execute the design method for the retaining structure of an eccentrically loaded foundation pit considering the non-ultimate earth pressure distribution pattern according to any one of the first aspects.

[0036] In a fourth aspect, a computer program product is provided, which makes a computer execute the design method for the retaining structure of an eccentrically loaded foundation pit considering the non-ultimate earth pressure distribution pattern according to any one of the first aspects when the computer program product runs on the computer.

[0037] The beneficial effects of the present invention are as follows: The present invention overcomes the situation of the foundation pit under eccentric load that is not considered in the conventional foundation pit design method, and can perform a design based on deformation control for the retaining structure of the eccentrically loaded foundation pit. The calculation formula is simple and feasible, and it can effectively save the project cost and reduce the construction volume on the premise of ensuring safety, stability and the requirements of foundation pit deformation control, and has good popularization and application value. Description of the Drawings

[0038] Figure 1It is a sectional model diagram of a biased-pressure foundation pit retaining structure with a bias voltage;

[0039] Figure 2 It is a schematic diagram of the overall force analysis of a biased-pressure foundation pit considering the non-limit earth pressure distribution mode;

[0040] Explanation of the reference numerals: 1 - Ground surface on the side with larger load, 2 - Retaining structure on the side with larger load, 3 - Displacement mode of the retaining structure on the side with larger load, 4 - Ground surface on the side with smaller load, 5 - Retaining structure on the side with smaller load, 6 - Displacement mode of the retaining structure on the side with smaller load, 7 - Internal support, 8 - Bottom of the pit. Specific implementation mode

[0041] The present invention will be further described below in conjunction with embodiments. The description of the following embodiments is only used to help understand the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several modifications can still be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

[0042] Embodiment 1:

[0043] A design method for the retaining structure of a biased-pressure foundation pit considering the non-limit earth pressure distribution mode includes:

[0044] S1. Determine the sectional parameters and soil parameters of the biased-pressure foundation pit.

[0045] In S1, the biased-pressure foundation pit is a foundation pit with larger load on one side of the pit edge and smaller load on the other side; the sectional parameters of the biased-pressure foundation pit include the excavation depth H of the foundation pit, the layout depth h m of each level of internal support, the calculation length B, the compression stiffness EA, the horizontal spacing S, the value q d of the pit edge load on the side with larger load, and the value q x of the pit edge load on the side with smaller load; the soil parameters include the soil layer thickness d, the unit weight γ, the friction angle δ between the wall and the soil, the internal friction angle and the cohesion c within the range of three times the excavation depth.

[0046] For example, the sectional parameters of a certain biased-pressure foundation pit are as follows:

[0047] Refer to Figure 1 , the ground elevation of the foundation pit is 0, and the bottom elevation of the excavation area is -10.0 m, that is, the excavation depth H = 10.0 m. A first-level internal support is set at an elevation of -1 m, that is, h1 = 1 m, the support length B = 30 m, the support stiffness EA is 1.854×10 6 kN, the support horizontal spacing S = 15 m; the value q d of the pit edge load on the side with larger load of the biased-pressure foundation pit is 50 kN / m 2 and the value q x= 10 kNm 2 。

[0048] The soil parameters within three times the excavation depth are shown in Table 1:

[0049] Table 1 Soil layer parameters

[0050]

[0051] In order to calculate cohesive soil using the Coulomb earth pressure theory, for cohesive soil in actual projects, according to the principle of equal shear strength, it can be equivalent to cohesionless soil through the equivalent internal friction angle and the equivalent formula is Normalize the multi-layer soil by the layer-wise summation method to obtain the equivalent internal friction angle equivalent external friction angle equivalent effective unit weight

[0052] Then, according to the Coulomb earth pressure theory, the active and passive earth pressure coefficients can be calculated as K a = 0.44, K p = 2.59, and K0 = 0.65 can be calculated by the Jaky's coefficient of earth pressure at rest formula.

[0053] S2. Determine the displacement modes of the retaining structures on both sides of the eccentrically loaded foundation pit and the overall force analysis diagram of the retaining structure model of the eccentrically loaded foundation pit; the retaining structures on both sides include the retaining structure on the side with larger load and the retaining structure on the side with smaller load; the retaining structures on both sides are connected by multiple levels of internal supports.

[0054] In S2, the displacement modes of the retaining structures on both sides of the eccentrically loaded foundation pit are as follows: the displacement at the bottom of the retaining structure on the side with larger load is approximately zero, and the part above the bottom shows displacement towards the inside of the pit, and the maximum displacement is determined by the allowable displacement value of the foundation pit; the displacement at the bottom of the retaining structure on the side with smaller load is approximately zero, and the part above the bottom shows displacement towards the inside of the pit, and at the same time, it is affected by the pushing-back displacement of the side with larger load, and the displacement is smaller than that of the side with larger load. The schematic diagram of the displacement mode can be seen in Figure 1 。

[0055] S3. Determine the displacement value of the internal support during preliminary design based on the load values of the eccentric loads on both sides and the allowable displacement control value of the foundation pit.

[0056] In S3, the displacement magnitude Δs at one end of the internal support close to the retaining structure on the side with larger load dm takes the allowable displacement value [Δ] of the retaining structure of the foundation pit max ; the displacement magnitude Δs at one end of the internal support close to the retaining structure on the side with smaller load xm is calculated according to the ratio of the eccentric loads on both sides of each level of internal support, and the calculation formula is:

[0057]

[0058] Among them, m represents the m-th level of internal support; K a represents the coefficient of active earth pressure; is the equivalent unit weight of the soil layer, which is obtained by the layer-wise summation method for multi-layer soil layers.

[0059] Exemplarily, taking the allowable displacement value [Δ] max = 5.0 cm, Δs can be obtained dm = [Δ] max = 5.0 cm, the displacement magnitude Δs of the support on the side with smaller load xm According to the above formula, it can be calculated that Δs x1 = 2.1 cm.

[0060] S4. According to the displacement value at the support determined in S3, calculate the axial force of each level of internal support through the stress-strain relationship.

[0061] In S4, the calculation formula for the axial force of each level of internal support is:

[0062]

[0063] Exemplarily,

[0064] S5. According to the displacement modes of the retaining structures on both sides of the eccentrically loaded foundation pit, assume that the distribution modes of the earth pressure on the retaining structures on both sides are as follows: at a certain depth X i below the bottom of the pit, it is the ultimate earth pressure distribution, and below this depth, it is the non-ultimate earth pressure distribution, and it linearly decays to the static earth pressure at the bottom of the pit.

[0065] S6. As Figure 2 shown, based on the distribution mode proposed in S5, calculate the earth pressure on the retaining structure on the side with larger load and the retaining structure on the side with smaller load respectively, and determine the depth X i at which the earth pressure on the retaining structures on both sides changes from the ultimate state to the non-ultimate state, as well as the embedded depth D i of the retaining structures on both sides.

[0066] In S6, the horizontal force balance equation and the moment balance equation are expressed as:

[0067]

[0068] Among them, i = 1 represents the side with larger load, and i = 2 represents the side with smaller load; S ai represents the resultant value of the active earth pressure in the active zone above the bottom of the pit, that is, S bi represents the resultant value of the active earth pressure in the active zone where the resultant earth pressure below the bottom of the pit decreases to zero or above, that is, a irepresents the height of this area, that is σ i represents the resultant soil pressure at the bottom of the retaining pile (wall) when calculated according to the ultimate soil pressure distribution mode, that is

[0069] σ 2i represents the resultant soil pressure at the bottom of the retaining pile (wall) when calculated according to the non - ultimate soil pressure distribution mode, that is

[0070] Exemplarily, S a1 = 525.8 kN / m, S a2 = 437.8 kN / m, S b1 = 136.1 kN / m, S b2 = 94.3 kN / m, a1 = 2.6 m, a2 = 2.2 m, σ 21 = 155.4 kN / m 2 σ 22 = 129.4 kN / m 2 . Substitute the above formulas into the horizontal force balance equation and the moment balance equation, and solve this system of equations to obtain X1 = 6.7 m, D1 = 14.1 m, X2 = 5.6 m, D2 = 8.2 m.

[0071] S7. Calculate the moment and shear force distributions of the retaining structures on both sides respectively, and determine the materials and reinforcement of the retaining structures on both sides according to the maximum moment and the maximum shear force respectively.

[0072] S8. Conduct overall stability check, anti - overturning check, and anti - heave stability check.

[0073] In summary, compared with the method of directly conducting unilateral design according to the most unfavorable effect side in the prior art, the design method of the retaining structure for a biased - pressure foundation pit provided by the present invention overcomes the situation of the foundation pit under biased - pressure load that is not considered in the conventional foundation pit design method, and can consider the displacement of the retaining structure, control the design from the perspective of deformation, and greatly improves the existing calculation method. In the provided embodiment, about 5.9 m of the retaining structure length per linear meter is saved, saving a large amount of project cost.

Claims

1. Design method for retaining structure of a biased foundation pit considering non-limit earth pressure distribution pattern, characterized in that, Including: S1. Determine the section parameters and soil parameters of the eccentrically loaded foundation pit; the eccentrically loaded foundation pit is a foundation pit with a large load on one side of the pit edge and a small load on the other side; the section parameters of the eccentrically loaded foundation pit include the excavation depth H of the foundation pit and the layout depth h of each level of internal support m , the calculation length B, the compression stiffness EA, the horizontal spacing S, and the value q of the pit edge load on the side with the large load d and the value q of the pit edge load on the side with the small load x ; the soil parameters include the soil layer thickness d, the unit weight γ, the friction angle δ between the wall and the soil, the internal friction angle and the cohesion c within the range of three times the excavation depth S2. Determine the displacement patterns of the retaining structures on both sides of the biased-pressure foundation pit and the overall force analysis diagram of the biased-pressure foundation pit retaining structure model; the retaining structures on both sides include the retaining structure on the side with larger load and the retaining structure on the side with smaller load; the retaining structures on both sides are connected by multiple levels of internal supports; the displacement patterns of the retaining structures on both sides of the biased-pressure foundation pit are as follows: the displacement at the bottom of the retaining structure on the side with larger load is approximately zero, and the part above the bottom shows displacement towards the inside of the pit, and the maximum displacement is determined by the allowable displacement value of the foundation pit; the displacement at the bottom of the retaining structure on the side with smaller load is approximately zero, and the part above the bottom shows displacement towards the inside of the pit, and at the same time, it is affected by the pushing-back displacement of the side with larger load, and the displacement is smaller than that of the side with larger load. S3. Determine the displacement value of the internal support during preliminary design based on the load values of the biases on both sides and the allowable displacement control value of the foundation pit. The displacement Δs of the inner support near one end of the retaining structure on the side with large load dm Take the allowable displacement value [Δ] of the foundation pit retaining structure max ; The displacement Δs of the inner support near one end of the retaining structure on the side with small load xm Calculate according to the ratio of the eccentric pressures on both sides of each level of inner support, and the calculation formula is: Among them, m represents the m-th level of internal support; K a represents the coefficient of active earth pressure; is the equivalent unit weight of the soil layer, which is obtained by the method of summation of layers for multi-layer soil layers; S4. According to the displacement value at the support determined in S3, calculate the axial forces of each level of internal support through the stress-strain relationship; the calculation formula for the axial forces of each level of internal support is: S5. According to the displacement mode of the retaining structures on both sides of the biased foundation pit, assume that the distribution mode of the earth pressure on the retaining structures on both sides is as follows: at a certain depth X below the bottom of the pit i above is the distribution of the ultimate earth pressure, and below this depth is the distribution of the non-ultimate earth pressure, which linearly decays to the static earth pressure at the bottom of the pit; S6. Calculate the earth pressures on the retaining structures on the large-load side and the small-load side respectively according to the distribution patterns proposed in S5, and determine the depth X to be determined at which the earth pressures on the retaining structures on both sides change from the ultimate state to the non-ultimate state. i And the embedment depth D of the retaining structures on both sides. i ; S7. Calculate the moment and shear force distributions of the retaining structures on both sides respectively, and determine the materials and reinforcement of the retaining structures on both sides according to the maximum moment and maximum shear force respectively. S8. Conduct overall stability check, anti-overturning check, and anti-heave stability check.

2. The design method of the retaining structure for a biased foundation pit considering the non-limit earth pressure distribution pattern according to claim 1, wherein In S6, the horizontal force balance equation and the moment balance equation are expressed as: Among them, i = 1 represents the side with a larger load, and i = 2 represents the side with a smaller load; S ai represents the resultant value of the active earth pressure of the part above the bottom of the pit, that is S bi represents the resultant value of the active earth pressure of the area where the resultant earth pressure below the bottom of the pit decreases to above zero, that is Among them, K p is the coefficient of passive earth pressure; a i represents the height of this area, that is σ i represents the resultant earth pressure at the bottom of the retaining pile (wall) calculated according to the ultimate earth pressure distribution mode, that is σ 2i represents the resultant earth pressure at the bottom of the retaining pile (wall) calculated according to the non - ultimate earth pressure distribution mode, that is Among them, K0 is the coefficient of the at - rest earth pressure.

3. The design method of the retaining structure for a biased foundation pit considering the non-limit earth pressure distribution mode according to claim 2, characterized in that, The retaining structure on the side with larger load is the retaining pile or retaining wall on the side with larger load; the retaining structure on the side with smaller load is the retaining pile or retaining wall on the side with smaller load.

4. A design device for retaining structures of a biased foundation pit considering a non-limit earth pressure distribution pattern, characterized in that, A design method for a biased-pressure foundation pit retaining structure considering the non-limit earth pressure distribution pattern, which is used to execute any one of claims 1 to 3, includes: A first determination module for determining the profile parameters and soil parameters of the biased-pressure foundation pit. A second determination module for determining the displacement patterns of the retaining structures on both sides of the biased-pressure foundation pit and the overall force analysis diagram of the biased-pressure foundation pit retaining structure model; the retaining structures on both sides include the retaining structure on the side with larger load and the retaining structure on the side with smaller load; the retaining structures on both sides are connected by multiple levels of internal supports. A third determination module for determining the displacement value of the internal support during preliminary design based on the load values of the biases on both sides and the allowable displacement control value of the foundation pit. A first calculation module for calculating the axial forces of each level of internal support through the stress-strain relationship according to the displacement value at the support determined by the third determination module. Assumption module, which is used to assume that according to the displacement mode of the retaining structures on both sides of the biased foundation pit, the distribution mode of the earth pressure on the retaining structures on both sides is as follows: at a certain depth X below the bottom of the pit i The above is the distribution of the ultimate earth pressure, and below this depth is the distribution of the non-ultimate earth pressure, which linearly decays to the static earth pressure at the bottom of the pit; A second calculation module, configured to calculate the earth pressures on the retaining structures on the large-load side and the small-load side respectively based on the distribution patterns proposed by the assumption module, and determine the depth X to be determined at which the earth pressures on the retaining structures on both sides change from the ultimate state to the non-ultimate state i and the embedment depth D of the retaining structures on both sides i ; A third calculation module for calculating the moment and shear force distributions of the retaining structures on both sides respectively, and determining the materials and reinforcement of the retaining structures on both sides according to the maximum moment and maximum shear force respectively. A check module for conducting overall stability check, anti-overturning check, and anti-heave stability check.

5. A computer storage medium, characterized in that, The computer storage medium stores a computer program; when the computer program runs on a computer, it causes the computer to execute the design method for a biased-pressure foundation pit retaining structure considering the non-limit earth pressure distribution pattern as described in any one of claims 1 to 3.

6. A computer program product, characterized in that, When the computer program product runs on a computer, it causes the computer to execute the design method for a biased-pressure foundation pit retaining structure considering the non-limit earth pressure distribution pattern as described in any one of claims 1 to 3.

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