Method for calculating stability of geotextile granular pile composite foundation

Abstract

The present application relates to a kind of geotextile granular pile composite foundation stability calculation method, comprising the following steps: S1 obtains the geometric and physical parameters of foundation and pile;S2 is divided into soil strip to circular sliding surface;S3 total sliding torque M t It is calculated;S4 total anti-sliding torque M a It is calculated;K is calculated by total sliding torque M t And total anti-sliding torque M a Stability safety factor, in the calculation of total anti-sliding torque M a , first, the anti-sliding torque provided by foundation soil is calculated by determining the cohesion and internal friction angle of foundation soil, then the flexural bearing capacity is calculated by determining the flexural bearing capacity correction coefficient of pile, finally, the smaller value of allowable tensile strength of reinforcement and anchoring end reinforcement anti-pulling force is judged as anchoring end reinforcement tension, and the anti-sliding torque provided by horizontal reinforced cushion is calculated using the obtained data.Compared with the prior art, the present application reflects the contribution of pile and soil to sliding torque and anti-sliding torque, and includes the influence of geotextile and horizontal reinforced cushion on the stability of composite foundation, and is widely practical.

Description

Technical Field

[0001] This invention relates to the field of composite foundation stability calculation technology, and in particular to a method for calculating the stability of geotextile granular pile composite foundations. Background Technology

[0002] With the rapid development of infrastructure construction in my country, the requirements for foundations in engineering construction have become increasingly stringent, and the quality of the foundation significantly impacts the engineering projects built upon it. Large areas of soft soil exist along my country's coast. Soft soil not only has high water content but also weak bearing capacity, posing a significant challenge to engineering construction. To meet the requirements of flexural bearing capacity and roadbed stability in engineering projects, various foundation treatment technologies have been applied. Composite foundations, as a foundation treatment method, have been widely used in building foundations, roadbeds, and other engineering projects. To meet the requirements of roadbed stability, various pile structures have emerged in engineering, such as geotextile granular piles and concrete piles. In actual foundation stability calculations, it has been found that the failure mode of concrete piles is considered as shear failure; therefore, the calculation of its sliding moment and anti-sliding moment is similar to that of foundation soil. However, concrete is more troublesome to operate due to its poor drainage and inconvenient construction. Geotextile granular piles, with their good drainage performance, high strength, convenient construction, and low cost, have become an important choice for treating soft soil foundations. However, the failure mode of geotextile granular piles in foundations is bending failure, which is not applicable to existing composite foundation stability calculation methods. A search of Chinese patent CN112195703A reveals a calculation method for stability control of a gravel pile combined with geogrid composite foundation. Based on the rigid body limit equilibrium principle, this method calculates the safety factor of the gravel pile combined with geogrid composite foundation by applying an area equivalence method to the reinforced soil between the gravel piles. This patent solves the problem of safety factor calculation, but it can only obtain the stability safety factor for a single sliding surface and cannot calculate the safety factor for multiple circular arc sliding surfaces. It also cannot determine the most dangerous circular arc sliding surface and does not adequately consider the tensile strength of the stirrups. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a method for calculating the stability of geotextile granular pile composite foundations. This method not only considers the contributions of the pile and soil to the sliding moment and the anti-sliding moment, but also includes the role of geotextile and horizontal reinforcement cushion layer, which has reference value for the stability analysis of geotextile granular pile composite foundations.

[0004] The objective of this invention can be achieved through the following technical solutions:

[0005] A method for calculating the stability of geotextile granular pile composite foundations, the method comprising the following steps:

[0006] S1 obtains the geometric and physical parameters of the foundation and piles;

[0007] Based on the shape, arrangement and physical properties of the foundation and piles, parameters such as pile spacing, pile diameter, number of layers of reinforcement in the horizontal reinforced cushion layer, unit weight of the foundation soil and pile weight are obtained.

[0008] S2 divides the most dangerous circular arc sliding surface into soil strips;

[0009] Obtain parameters such as the radius of the circular sliding surface, the length of the circular arc segment of each soil strip on the most dangerous circular sliding surface, and the inclination angle of the bottom sliding surface of each soil strip.

[0010] S3 calculates the total sliding torque M t :

[0011]

[0012] Where n is the total number of soil strips, W i α i Let S be the weight per unit width at the i-th soil strip and the inclination angle of the bottom slip surface, respectively. c R represents the spacing between geotextile granular piles in the vertical sliding direction, and R is the radius of the circular arc sliding surface.

[0013] S4 calculates the total anti-slip moment M a :

[0014] M a =M s +M p +M r

[0015] Among them, M s The anti-sliding moment provided by the foundation soil, M p M represents the flexural bearing capacity of geotextile granular piles. r The anti-slip moment provided by the reinforcing material in the horizontally reinforced pad layer.

[0016] The cohesion and internal friction angle of the foundation soil were determined by rapid shear test, and the anti-sliding moment M provided by the foundation soil was calculated. s :

[0017]

[0018] Among them, c i , L i These are the cohesion, internal friction angle, and arc segment length on the circular sliding surface of the i-th soil strip, respectively.

[0019] By determining the correction factor for the flexural bearing capacity of the geotextile granular piles, the total flexural bearing capacity M of the geotextile granular piles along the failure sliding surface of the composite foundation is calculated. p :

[0020]

[0021] Where m is the total number of piles, T j d j These are the allowable circumferential tensile strength of the geosynthetic sleeve for the j-th pile and the pile diameter, respectively.

[0022] By selecting the allowable tensile strength T of the reinforcement in the horizontally reinforced pad layer ea and the pull-out strength T of the anchorage section reinforcement P The smaller of the two values ​​is taken as the tensile force T of the anchorage end reinforcement. g T P It can be calculated using the following formula:

[0023] T p =2σ v L e f

[0024] Where, σ v L represents the vertical stress exerted on the reinforcing material by the overlying soil. e denoted as the length of the reinforcement in the anchoring section, and f as the friction coefficient between the reinforcement and the soil, determined by the reinforcement-soil pull-out test.

[0025] The tensile force T of the anchorage end reinforcement is obtained. g The value of M is used to calculate the anti-slip moment M provided by the reinforcement in the horizontally reinforced cushion layer. r :

[0026] M r =T g S c Rcosθ

[0027] Where θ is the elevation angle of the tangent at the intersection of the reinforcement material and the sliding arc in the horizontally reinforced cushion layer.

[0028] S5 passes through the total sliding torque M t Total anti-slip moment M a Calculate the stability safety factor K:

[0029]

[0030] Furthermore, the total flexural bearing capacity M of the geotextile granular piles through which the composite foundation failure sliding surface passes is... p The calculation method is obtained by summing the bending bearing capacity of multiple individual piles. The calculation method for the bending bearing capacity of a single pile includes the following steps:

[0031] Step 1: Obtain the radius and sleeve thickness parameters of the geotextile granular pile;

[0032] Step 2: Analyze the distribution of tensile and compressive stresses in the geotextile granular piles. The maximum tensile stress in the bending reinforcement is σ.tmax The corresponding angle is 53°, the height of the tension zone is 0.9R, the corresponding angle is 6°~174°, and the maximum compressive stress of the flexural granular material is σ. cmax Located at a distance of 0.8R from the center section, the height of the compression zone is R;

[0033] Step 3: Calculate the tensile stress σ of the geotextile and granular material at any angle using the method from Step 2. t and compressive stress σ c ;

[0034] The tensile stress σ corresponding to the tangent at the intersection point of the reinforcement and the slip arc in the horizontally reinforced pad layer is θ. t for:

[0035]

[0036] The compressive stress σ of the crushed stone at the height corresponding to the elevation angle θ of the tangent at the intersection of the reinforcement and the slip arc in the horizontally reinforced subbase. c for:

[0037]

[0038] Step 4: Perform differential calculations on the cross-section of the geotextile granular pile;

[0039] A small angle dθ at the elevation angle θ of the tangent at the intersection of the reinforcement and the slip arc in the horizontally reinforced cushion layer corresponds to the geotextile sleeve area dA. t for:

[0040] dA t =Rtdθ

[0041] Where R is the radius of the geotextile granular pile, and t is the thickness of the geotextile sleeve.

[0042] The area dA of the granular material corresponding to a small angle dθ at the elevation angle θ of the tangent at the intersection of the reinforcement and the sliding arc in the horizontally reinforced pad layer. c for:

[0043] dA c =2R 2 cosθdθ

[0044] Step 5: Perform stress analysis on the cross-section of the geotextile granular pile;

[0045] The axial force and moment of the geotextile granular pile are both zero.

[0046]

[0047] Among them, A t A c These are the areas of the tension region and the compression region, respectively; FN M x M y These are the axial force, axial bending moment, and radial bending moment, respectively.

[0048] Step Six: Combining Steps Three to Five, calculate the maximum compressive stress σ. cmax Maximum tensile stress σ of geotextile tmax And the relationship between the geometric parameters of geotextile granular material piles:

[0049]

[0050] Step 7: Calculate the bending moment of the geotextile granular pile:

[0051] M y =∫(x+0.7R)σ c dA c

[0052] Combining the compressive stress σ in step three c and the maximum compressive stress σ in step six cmax Conclusion:

[0053] M y =2.544tσ tmax R 2

[0054] Step 8: Introduce a correction factor to calculate the flexural bearing capacity M of a single pile in the geotextile granular pile system. p单 :

[0055] M p单 =ζTd 2

[0056] Where T and d are the allowable circumferential tensile strength of the geosynthetic sleeve of the pile and the diameter of the pile body, respectively.

[0057] Furthermore, the correction factor for the flexural bearing capacity of the geotextile granular pile is determined based on the material properties of the geotextile and the actual conditions of the engineering site.

[0058] Furthermore, the pile body of the geotextile granular pile is composed of granular material wrapped in geotextile, and the arrangement can be changed according to the actual situation.

[0059] Compared with the prior art, the present invention has the following beneficial effects:

[0060] 1. This invention calculates the total sliding torque M. t Total anti-slip moment M a This leads to the determination of the stability safety factor K, providing a basis for the calculation method of pile stability in composite foundations under bending failure mode.

[0061] 2. The method for calculating the stability of geotextile granular pile composite foundation proposed in this invention divides the circular arc sliding surface into soil strips and calculates the stability safety factor K. This method can not only obtain the stability safety factor of a single circular arc sliding surface, but also calculate the safety factors of multiple circular arc sliding surfaces, and determine the most dangerous circular arc sliding surface accordingly. The method is simple and easy to operate in practical use.

[0062] 3. This invention obtains the geometric and physical parameters of the foundation and piles, divides the circular arc sliding surface into soil strips, and calculates the total sliding moment M. t Total anti-slip moment M a Furthermore, the calculation process can clearly reflect the contribution of the foundation soil, geotextile granular piles, and horizontally reinforced cushion layer to the anti-sliding moment in the composite foundation, which helps designers adjust the design of each part.

[0063] 4. All parameters required in this invention can be obtained through simple field or indoor tests during the design process. The number of parameters is small and easy to obtain, thus avoiding the consumption of a large amount of manpower and material resources.

[0064] 5. The method for calculating the stability of geotextile granular pile composite foundation proposed in this invention can be applied to any form of geotextile and any pile filler, and has wide applicability. Attached Figure Description

[0065] Figure 1 This is a flowchart of the method for calculating the stability of geotextile granular material pile composite foundation according to the present invention.

[0066] Figure 2 This is a flowchart of the method for calculating the flexural bearing capacity of geotextile granular material piles according to the present invention.

[0067] Figure 3 This is a schematic diagram of the calculation model for the flexural bearing capacity of geotextile granular material piles according to the present invention.

[0068] Figure 4 This is a schematic diagram of the calculation model for the anti-slip moment generated by the reinforcing material in the horizontally reinforced cushion layer of the present invention.

[0069] Figure 5 This is a schematic diagram of the geometric model of the geotextile granular pile composite foundation of the present invention.

[0070] Figure 6 This is a schematic diagram of the arc segmentation method and the most dangerous arc sliding surface of the present invention. Detailed Implementation

[0071] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0072] Example

[0073] Figure 1 The flowchart of the geotextile granular material pile composite foundation stability calculation method of the present invention includes the following steps:

[0074] S1 Obtain the geometric and physical parameters of the foundation and piles, and then proceed to step S2;

[0075] Based on the shape, arrangement and physical properties of the foundation and piles, parameters such as pile spacing, pile diameter, number of layers of reinforcement in the horizontal reinforced cushion layer, unit weight of the foundation soil and pile weight are obtained.

[0076] like Figure 5 The diagram shows a saturated soft soil foundation subjected to embankment load. Considering the symmetry of the subgrade, a half-model is selected for analysis. The model contains 5 geotextile granular piles with a spacing of 2.5m and a pile diameter of 0.8m. There is no horizontal reinforcement layer, and the effective unit weight of the foundation soil is 8kN / m³. 3 The effective unit weight of the pile is 9 kN / m 3 The unit weight of the embankment is 21 kN / m. 3 .

[0077] S2 divides the most dangerous circular arc sliding surface into soil strips, and then executes steps S3 and S4;

[0078] Obtain parameters such as the radius of the circular sliding surface, the length of the circular arc segment of each soil strip on the most dangerous circular sliding surface, and the inclination angle of the bottom sliding surface of each soil strip.

[0079] In examples of the present invention, such as Figure 6 As shown, the radius of the circular sliding surface is 10m. The soil between the piles and the block where the piles are located are divided into 2 and 1 soil strips, respectively. The length of the bottom circular arc segment of each soil strip is simplified to the length of the chord corresponding to the circular arc. The inclination angle of the bottom sliding surface can be obtained by the coordinates of two points.

[0080] S3 calculates the total sliding torque M t :

[0081]

[0082] Where n is the total number of soil strips, W i α i Let S be the weight per unit width at the i-th soil strip and the inclination angle of the bottom slip surface, respectively. c The spacing between the geotextile granular piles is perpendicular to the sliding direction, and R is the radius of the circular arc sliding surface;

[0083] In this example, S c Taking a depth of 1m, when calculating the unit width gravity, the soil strip area is simplified to the product of the soil strip width and the height of the soil strip's midpoint. The total sliding moment M is then calculated. t It is 2438 kNm.

[0084] S4 calculates the total anti-slip moment M a :

[0085] M a =M s +M p +M r

[0086] Among them, M s The anti-sliding moment provided by the foundation soil, M p M represents the total flexural bearing capacity of the geotextile granular piles traversed by the sliding surface of the composite foundation failure. r The anti-slip moment provided by the reinforcing materials in the horizontally reinforced pad layer;

[0087] The cohesion and internal friction angle of the foundation soil are determined by a quick shear test. Since the geotextile granular piles fail by bending in the foundation, it is unnecessary to determine the pile's cohesion and internal friction angle. In this invention example, considering stability under effective stress, the cohesion of both the foundation soil and the embankment is taken as 0. The internal friction angle of the foundation soil is 27.7°, and the internal friction angle of the embankment is 38°. The anti-sliding moment M provided by the foundation soil... s for:

[0088]

[0089] Among them, c i , L i Let M be the cohesion, internal friction angle, and arc length on the circular sliding surface of the i-th soil strip, respectively. Based on the unit weight of the soil strip obtained in step S3, and combined with the internal friction angle of the soil on the sliding surface, the anti-sliding moment M provided by the foundation soil is calculated. s It is 2367 kNm.

[0090] like Figure 2 and Figure 3 As shown, the correction factor for the flexural bearing capacity of geotextile granular piles is determined, and the total flexural bearing capacity M of the geotextile granular piles is... p It needs to be determined through bending load tests. In the preliminary design, it can be calculated using the following formula:

[0091]

[0092] Where m is the total number of piles, T j d jThese represent the allowable circumferential tensile strength of the geosynthetic sleeve and the pile diameter, respectively, for the j-th pile. In this embodiment of the invention, the correction factor for the flexural bearing capacity of the geotextile granular pile is taken as 0.35, and the allowable circumferential tensile strength of the geosynthetic sleeve is 340 kN / m. The calculated total flexural bearing capacity provided by the geotextile granular pile through which the sliding surface passes is 228 kN / m.

[0093] Determine the allowable tensile strength T of the reinforcement in the horizontally reinforced pad. ea and the pull-out strength T of the anchorage section reinforcement P The smaller of the two values ​​is taken as the tensile force T of the anchorage end reinforcement. g T P It can be calculated using the following formula:

[0094] T p =2σ v L e f

[0095] Where, σ v L represents the vertical stress exerted on the reinforcing material by the overlying soil. e Let be the length of the anchorage reinforcement, and f be the coefficient of friction between the reinforcement and the soil, determined by a reinforcement-soil pull-out test. In the horizontally reinforced cushion layer of this invention, there is a layer of horizontal reinforcement with an allowable tensile strength of 210 kN / m. The vertical stress on the reinforcement from the overlying soil is 105 kPa. The anchorage length is 5.6 m, and the reinforcement-soil friction coefficient is taken as 0.35. The calculated pull-out force of the anchorage reinforcement is 411.6 kN / m. Therefore, the tensile force T of the reinforcement at the anchorage end is... g Take 210 kN / m.

[0096] The tensile force T of the anchorage end reinforcement is obtained. g The value of M is used to calculate the anti-slip moment M provided by the reinforcement in the horizontally reinforced cushion layer. r :

[0097] M r =T g S c Rcosθ

[0098] Wherein, θ is the elevation angle of the tangent at the intersection of the reinforcement in the horizontally reinforced cushion layer and the sliding arc. In this embodiment of the invention, the elevation angle of the tangent at the intersection of the reinforcement in the horizontally reinforced cushion layer and the sliding arc is 40°, and the anti-slip moment provided by the reinforcement in the horizontally reinforced cushion layer is calculated to be 1609 kNm.

[0099] In summary, the anti-slip torque M is obtained. s Total flexural bearing capacity M p and anti-slip moment M r The total anti-slip moment M can be obtained through calculation. a It is 4204 kN / m.

[0100] S5 passes through the total sliding torque M t Total anti-slip moment M a Calculate the stability safety factor K:

[0101]

[0102] The stability safety factor of this invention example is 1.72.

[0103] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A method for calculating the stability of a geotextile granular pile composite foundation, characterized in that, Includes the following steps: S1 Obtain the geometric and physical parameters of the foundation and piles, then proceed to step S2; S2. Divide the most dangerous circular arc sliding surface into soil strips, and then execute steps S3 and S4. S3 Calculate the total sliding torque : in, The total number of soil strips, 、 The first The weight per unit width and the inclination angle of the bottom sliding surface at each soil strip. The spacing between geotextile granular piles is the distance between the piles in the vertical sliding direction. Let be the radius of the circular arc sliding surface; S4 Calculate the total anti-slip moment : in, The anti-sliding moment provided to the foundation soil This represents the total flexural bearing capacity of the geotextile granular piles along the sliding surface of the composite foundation failure zone. The anti-slip moment provided by the reinforcing materials in the horizontally reinforced pad layer; S5 via total sliding torque Total anti-slip moment Calculate the stability safety factor : in, Total anti-slip moment With total sliding torque The ratio; In S4, by determining the correction factor for the flexural bearing capacity of the geotextile granular piles, the total flexural bearing capacity of the geotextile granular piles along the failure sliding surface of the composite foundation is calculated. : in, m The total number of piles. , The first j The permissible circumferential tensile strength of the geosynthetic sleeve for the pile and the pile diameter; The total flexural bearing capacity of the geotextile granular piles through which the composite foundation failure sliding surface passes. The calculation method is obtained by summing the bending bearing capacity of multiple individual piles. The calculation method for the bending bearing capacity of a single pile includes the following steps: Step 1: Obtain the radius and sleeve thickness parameters of the geotextile granular pile; Step 2: Analyze the distribution of tensile and compressive stresses in the geotextile granular piles. The maximum tensile stress in the bending reinforcement is... The corresponding angle is 53°, and the height of the tension zone is 0.

9. R The corresponding angles are 6° to 174°, and the maximum compressive stress of the flexural granular material is... Located at a distance of 0.8 from the center section. R At this location, the height of the pressure zone is R ; Step 3: Calculate the tensile stress of the geotextile and granular material at any angle using the methods from Step 2. and compressive stress ; The angle of elevation of the tangent at the intersection of the reinforcement material and the slip arc in the horizontally reinforced pad layer Tensile stress corresponding to the reinforcing wire for: The angle of elevation of the tangent at the intersection of the reinforcement material and the slip arc in the horizontally reinforced pad layer Crushed stone compressive stress at corresponding height for: Step 4: Perform differential calculations on the cross-section of the geotextile granular pile; The angle of elevation of the tangent at the intersection of the reinforcement material and the slip arc in the horizontally reinforced pad layer At a tiny angle Corresponding geotextile sleeve area for: in, R Let be the radius of the geotextile granular pile. The thickness of the geotextile sleeve; The angle of elevation of the tangent at the intersection of the reinforcement material and the slip arc in the horizontally reinforced pad layer At a tiny angle Corresponding granular material area for: Step 5: Perform stress analysis on the cross-section of the geotextile granular pile; The axial force and moment of the geotextile granular pile are both zero. in, , These are the areas of the tension zone and the compression zone, respectively. , , These are the axial force, axial bending moment, and radial bending moment, respectively. Step Six: Combining Steps Three through Five, calculate the maximum compressive stress. Maximum tensile stress of geotextile And the relationship between the geometric parameters of geotextile granular material piles: Step 7: Calculate the bending moment of the geotextile granular pile: M y =∫(x+0.7R)σ c dA c Combining the compressive stress in step three and the maximum compressive stress in step six Conclusion: Step 8: Introduce a correction factor to calculate the flexural bearing capacity of a single pile in the geotextile granular pile system. : in, T , d These represent the allowable circumferential tensile strength of the geosynthetic sleeve for the pile and the pile diameter, respectively.

2. The method for calculating the stability of a geotextile granular pile composite foundation according to claim 1, characterized in that, The geometric and physical parameters obtained in step S1 include: pile spacing, pile diameter, number of layers of reinforcement in the horizontal reinforced cushion layer, unit weight of the foundation soil, and pile weight.

3. The method for calculating the stability of a geotextile granular pile composite foundation according to claim 1, characterized in that, The parameters measured in step S2 for dividing the soil strips include: the radius of the circular sliding surface, the length of the circular arc segment of each soil strip on the most dangerous circular sliding surface, and the inclination angle of the bottom sliding surface of each soil strip.

4. The method for calculating the stability of a geotextile granular pile composite foundation according to claim 1, characterized in that, In step S4, the cohesion and internal friction angle of the foundation soil are determined by a quick shear test, and the anti-sliding moment provided by the foundation soil is calculated. : in, , , The first The cohesion, internal friction angle, and length of the arc segment on the circular sliding surface of each soil strip.

5. The method for calculating the stability of a geotextile granular pile composite foundation according to claim 1, characterized in that, In step S4, the allowable tensile strength of the reinforcing bars in the horizontally reinforced pad layer is selected. Pull-out resistance of anchorage reinforcement The smaller of the two values ​​is used as the tensile force of the anchorage end reinforcement. Calculate the anti-slip moment provided by the reinforcement in the horizontally reinforced cushion layer. : in, θ The angle of elevation of the tangent at the intersection of the reinforcing bar and the sliding arc in the horizontally reinforced cushion layer.

6. The method for calculating the stability of a geotextile granular pile composite foundation according to claim 5, characterized in that, Pull-out resistance of the anchorage section reinforcement Calculate using the following formula: in, This refers to the vertical stress exerted on the reinforcing material by the overlying soil. The length of the reinforcement in the anchorage section. The coefficient of friction between the reinforcement and the soil is determined by the reinforcement-soil pull-out test.

7. The method for calculating the stability of a geotextile granular pile composite foundation according to claim 1, characterized in that, The correction factor for the flexural bearing capacity of the geotextile granular pile is determined based on the material properties of the geotextile and the actual conditions of the engineering site.

8. A method for calculating the stability of a geotextile granular pile composite foundation according to any one of claims 1-7, characterized in that, The pile body of the geotextile granular pile is composed of granular material wrapped in geotextile, and the arrangement can be changed according to the actual situation.

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