Pile foundation p-y curve determination method combining indoor test and in-situ test

Abstract

The invention discloses a method for determining a pile foundation p-y curve in combination with an indoor test and an in-situ test. The method comprises the following steps that S1, a geological profile map is drawn according to a geological drilling histogram, and then a typical stratum is determined; s2, strength parameters of the typical stratum are determined by combining an indoor test and an in-situ test; and S3, determining p-y curves of different types of rock-soil bodies according to the strength parameters. According to the method, the strength parameter of the rock-soil body is determined according to the empirical relationship between the on-site in-situ test result (standard penetration test (N1) 60 or static penetration test qc) of a typical stratum and the internal friction angle phi and undrained shear strength Su obtained indoors, so that the influence of sampling disturbance and sample size effect on the strength parameter of the rock-soil body can be eliminated; furthermore, the p-y curves of different types of rock-soil bodies are more accurately calculated, so that the internal force and deformation calculation of the pile foundation is more accurate, and the safety of bridge engineering is further ensured.

Description

Technical Field

[0001] The invention relates to the technical field of pile foundation design calculation methods, and in particular to a pile foundation py curve determination method combining indoor tests and in-situ tests. Background Art

[0002] Among the existing bridge projects, some bridge projects across rivers, seas and lakes are inevitably built near active fault zones or even directly cross faults, facing severe near-fault seismic problems. In actual projects, pile foundations are widely used as bridge engineering foundations due to their good seismic performance and settlement control. During earthquakes, the tilting and collapse of the superstructure due to large deformation of bridge pile foundations is one of the main forms of bridge engineering damage. At the same time, the large deformation of bridge pile foundations under seismic loads will seriously affect the normal operation of the bridge. Therefore, it is of great scientific significance and practical need to study the calculation method of internal forces and deformations of bridge pile foundations under large deformation during earthquake loads.

[0003] At present, the m method that does not consider the nonlinearity of the soil is often used in the analysis and calculation of the internal forces and deformations of bridge pile foundations in China. This method can obtain relatively accurate calculation results when the soil is in the small deformation stage. However, the pile foundation will produce large deformations under the action of seismic loads. At this time, the py curve method that considers the nonlinearity of the soil can more accurately calculate the internal forces and deformations of the bridge pile foundation. The py curve is significantly affected by the type and strength parameters of the soil around the pile. Since the strength parameters of the rock and soil are related to the stress conditions and it is difficult to obtain the original soil, the strength parameters of the rock and soil obtained by conventional indoor unit tests and the actual results have large errors. For example, the sampling of sandy soil is easily disturbed, and it is difficult for soil samples to reproduce the boundary conditions of the original ground stress, and there is a large uncertainty in the test results. Summary of the invention

[0004] In view of the above problems, the present invention aims to provide a method for determining the py curve of a pile foundation by combining indoor tests and in-situ tests.

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

[0006] A method for determining a pile foundation py curve combining indoor tests and in-situ tests comprises the following steps:

[0007] S1: Draw a geological profile based on the geological drill hole column chart to determine the typical strata;

[0008] S2: Determine the strength parameters of typical formations by combining laboratory tests and in-situ tests;

[0009] S3: Determine the py curves of different types of rock and soil bodies according to the strength parameters.

[0010] Preferably, in step S2, the strength parameters include undrained shear strength of clay and internal friction angle of sand;

[0011] The undrained shear strength of the clay is calculated by the following formula:

[0012] S u =(q c -σ v0 ) / N kt (1)

[0013] Where: S u is the undrained shear strength of clay; q c is the cone tip resistance value in the static penetration test; σ v0 is the vertical stress; N kt is the empirical coefficient;

[0014] The sand internal friction angle is calculated by the following formula:

[0015]

[0016] or

[0017]

[0018] (N 1 ) 60 =(P a / σ v0 ) c ·N 60 (4)

[0019] Where: is the internal friction angle of sand; a, b, c, m, n are all empirical parameters; is the fitting parameter; (N 1 ) 60 is the standard penetration test result after correction considering the overburden stress; P a is the atmospheric pressure; N 60 is the corrected standard penetration number.

[0020] Preferably, when the sand contains powder particles, the internal friction angle of the sand is reduced by 3° based on the calculated value; when the sand contains gravel particles, the internal friction angle of the sand is increased by 2° based on the calculated value.

[0021] Preferably, in step S3, the different types of rock and soil bodies include clay, sand and weathered rock.

[0022] Preferably, for clay, its static py curve is obtained by the following formula:

[0023] p=0.5·(y / y c )1 / 3 ·p u (5)

[0024] y c =2.5·ε 50 ·D (6)

[0025]

[0026] z R =6·D / [(γ·D) / S u +J] (8)

[0027] Where: p is the soil resistance per unit length; y is the displacement per unit length; y c is the reference displacement; P u is the ultimate soil resistance per unit length; ε 50 is the strain value corresponding to 0.5 times the maximum deviator stress in the undrained compression test of the original soil sample, %; D is the pile diameter; S u is the undrained shear strength of clay; γ is the gravity; z is the depth below the ground; J is the empirical coefficient; z R is the depth of the turning point of the ultimate soil resistance per unit length;

[0028] When the depth below the ground is less than or equal to the depth of the turning point of the ultimate soil resistance per unit length, the dynamic py curve is obtained by the following formula:

[0029]

[0030] When the depth below the ground is greater than the depth of the turning point of the ultimate soil resistance per unit length, the dynamic py curve is obtained by the following formula:

[0031]

[0032] Preferably, when the undrained shear strength of the clay is less than or equal to 25 kPa, ε 50 The value is 0.02, and the value of J is 0.5;

[0033] When the undrained shear strength of the clay is in the range of 25-50 kPa, ε 50 The value is 0.01, and the value of J is 0.25;

[0034] When the undrained shear strength of the clay is in the range of 50-100 kPa, ε 50 The value is 0.007 and the value of J is 0.25.

[0035] Preferably, for sandy soil, its py curve is obtained by the following formula:

[0036]

[0037] Where: A is a coefficient related to the load type; K is the growth rate of the initial modulus of foundation reaction force with depth; P us is the ultimate bearing capacity of shallow sand; P ud is the ultimate bearing capacity of deep sand; C 1 , C 2 , C 3 All of them are parameters related to the internal friction angle of sand.

[0038] Preferably, when the load type is a static load, the coefficient A associated with the load type is selected as a larger value between A=3-0.8z / D and A=0.9; when the load type is a cyclic load, the coefficient A associated with the load type is selected as A=0.9.

[0039] Preferably, the growth rate K of the initial modulus of the foundation reaction force with depth is obtained through Table 1:

[0040] Table 1

[0041]

[0042]

[0043] When the internal friction angle of sand is not in Table 1, the corresponding growth rate K of the initial modulus of foundation reaction force with depth is obtained by interpolating the data in Table 1;

[0044] The parameter C related to the internal friction angle of sand 1 , C 2 , C 3 Use Table 2 to obtain the value:

[0045] Table 2

[0046]

[0047]

[0048]

[0049] When the internal friction angle of sand is not in Table 2, the corresponding parameter C related to the internal friction angle of sand is 1 , C 2 , C 3 Obtained by interpolating the data in Table 2.

[0050] Preferably, for weathered rock, its py curve is obtained by the following formula:

[0051]

[0052] K ir =kir E ir (14)

[0053]

[0054] y rm =k rm D (18)

[0055]

[0056] Where: p is the soil resistance per unit length; K ir is the slope of the linear part; y is the displacement per unit length; y A is the y value corresponding to the end point of the linear part; p ur is the ultimate resistance of rock; rm is the intermediate parameter; k ir is a dimensionless constant; E ir is the initial modulus of rock; z is the depth below the ground; D is the pile diameter; α r is the intensity attenuation coefficient; q ur is the compressive strength of rock; RQD is the rock quality index; k rm is the strain factor.

[0057] The beneficial effects of the present invention are:

[0058] The present invention is based on the results of on-site in-situ tests of typical formations (standard penetration test (N 1 ) 60 Or static penetration test c ) and the internal friction angle φ and undrained shear strength S obtained indoors u The empirical relationship between them is used to determine the strength parameters of rock and soil, and the results are more accurate, so that the py curves of clay, sand and weathered rock can be obtained more accurately, providing technical support for ensuring the safety of bridge projects. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0060] Figure 1 It is a schematic flow chart of a method for determining a pile foundation py curve combining indoor tests and in-situ tests according to the present invention;

[0061] Figure 2 It is a schematic diagram of the py curve results of different types of rock and soil bodies in a specific embodiment. DETAILED DESCRIPTION

[0062] The present invention is further described below in conjunction with the accompanying drawings and embodiments. It should be noted that, in the absence of conflict, the embodiments in this application and the technical features in the embodiments can be combined with each other. It should be noted that, unless otherwise specified, all technical and scientific terms used in this application have the same meanings as those generally understood by those of ordinary skill in the art to which this application belongs. The words "including" or "comprising" and the like used in the disclosure of the present invention mean that the elements or objects appearing before the word cover the elements or objects listed after the word and their equivalents, without excluding other elements or objects.

[0063] like Figure 1 As shown, the present invention provides a method for determining a pile foundation py curve combining indoor tests and in-situ tests, comprising the following steps:

[0064] S1: Draw a geological profile based on the geological drill hole column chart to determine the typical strata.

[0065] In a specific embodiment, firstly, the stratigraphic information is obtained according to the target area borehole histogram, including stable water level, borehole coordinates, hole mouth elevation, borehole depth, soil layer number, soil layer name, layer bottom thickness and elevation, soil layer description, sample number and other information; then, the geological profile is drawn according to different borehole histograms to further determine the main stratigraphic distribution law and typical stratigraphic layers. It should be noted that determining typical stratigraphic layers is a prior art, and the specific steps are not repeated here.

[0066] S2: Determine the strength parameters of typical strata by combining indoor tests and in-situ tests, wherein the strength parameters include undrained shear strength of clay and internal friction angle of sand.

[0067] In a specific embodiment, the undrained shear strength of the clay is calculated by the following formula:

[0068] S u =(q c -σ v0 ) / N kt (1)

[0069] Where: S u is the undrained shear strength of clay; q c is the cone tip resistance value in the static penetration test; σ v0 is the vertical stress; N kt It is an empirical coefficient (the value varies in different site conditions and is obtained through indoor tests).

[0070] In the above embodiment, for clay, the present invention uses indoor triaxial test to obtain its undrained shear strength S u, the cone tip resistance q for static penetration test c and the undrained shear strength S of clay obtained from indoor tests u Perform regression analysis and establish q c and S u The empirical relationship between them is used to obtain the empirical formula for the undrained shear strength of clay based on field tests as shown in formula (1), so that the undrained shear strength of clay can be determined by using this empirical formula when there is a lack of indoor test results in actual projects.

[0071] In a specific embodiment, the sand internal friction angle is calculated by the following formula:

[0072]

[0073] or

[0074]

[0075] (N 1 ) 60 =(P a / σ v0 ) c ·N 60 (4)

[0076] Where: is the internal friction angle of sand; a, b, c, m, n are all empirical parameters; is the fitting parameter; (N 1 ) 60 is the standard penetration test result after correction considering the overburden stress; P a is the atmospheric pressure; N 60 is the corrected standard penetration number.

[0077] In the above embodiment, for sand, the present invention uses indoor tests to obtain its internal friction angle Cone tip resistance q for static penetration test c The internal friction angle of sand obtained from indoor tests Perform regression analysis and establish the q c and By comparing the standard penetration test results with the indoor test results, the standard penetration test (N) shown in formula (3) is established. 1 ) 60 Friction angle with soil When there is a lack of indoor test results in actual projects, the empirical formula shown in the above formula (2) or formula (3) can be used to determine the internal friction angle of sand. At the same time, the results of standard penetration test or static penetration test can be used to evaluate the liquefaction tendency of sand.

[0078] In a specific embodiment, when the sand contains powder particles, the internal friction angle of the sand is reduced by 3° based on the calculated value; when the sand contains gravel particles, the internal friction angle of the sand is increased by 2° based on the calculated value.

[0079] In the above embodiment, by taking into account the influence of relative density and other particle components (silt particles, gravel particles) to correct the value of the sand internal friction angle, the result of the sand internal friction angle can be made more accurate, thereby obtaining a more accurate py curve.

[0080] In a specific embodiment, for the indoor test data and field in-situ data of different boreholes in the same soil layer, their comprehensive values ​​are taken to evaluate the shear strength parameters of the rock and soil mass. This can avoid the amplification of the spatial differences of the rock and soil mass by traditional statistical analysis, making the results more accurate.

[0081] S3: Determine py curves of different types of rock and soil bodies according to the strength parameters, where the different types of rock and soil bodies include clay, sand and weathered rock.

[0082] In a specific embodiment, for clay, its static py curve is obtained by the following formula:

[0083] p=0.5·(y / y c ) 1 / 3 ·p u (5)

[0084] y c =2.5·ε 50 ·D (6)

[0085]

[0086] z R =6·D / [(γ·D) / S u +J] (8)

[0087] Where: p is the soil resistance per unit length; y is the displacement per unit length; y c is the reference displacement; P u is the ultimate soil resistance per unit length; ε 50 is the strain value corresponding to 0.5 times the maximum deviator stress in the undrained compression test of the original soil sample, %; D is the pile diameter; S u is the undrained shear strength of clay; γ is the gravity; z is the depth below the ground; J is the empirical coefficient; z R is the depth of the turning point of the ultimate soil resistance per unit length;

[0088] When the depth below the ground is less than or equal to the depth of the turning point of the ultimate soil resistance per unit length, the dynamic py curve is obtained by the following formula:

[0089]

[0090] When the depth below the ground is greater than the depth of the turning point of the ultimate soil resistance per unit length, the dynamic py curve is obtained by the following formula:

[0091]

[0092] In the above embodiment, when using the present invention, firstly, the undrained shear strength S of clay obtained by formula (1) is u Substitute into formula (8) to calculate P u The turning depth z R , and then determine the P of saturated clay according to formula (7): u Finally, the static py curve of clay can be obtained according to formula (5)-(6), and the dynamic py curve of clay can be obtained by formula (9) or (10).

[0093] In a specific embodiment, when the undrained shear strength of the clay is less than or equal to 25 kPa, ε 50 The value is 0.02, and the value of J is 0.5; when the undrained shear strength of the clay is in the range of 25-50 kPa, ε 50 The value is 0.01, and the value of J is 0.25; when the undrained shear strength of the clay is in the range of 50-100 kPa, ε 50 The value is 0.007 and the value of J is 0.25.

[0094] In a specific embodiment, the gravity is taken as the underwater effective gravity γ'=γ sat -γ w , where γ sat is the saturation weight, γ w The weight of water.

[0095] In a specific embodiment, for sandy soil, its py curve is obtained by the following formula:

[0096]

[0097] Where: A is a coefficient related to the load type; K is the growth rate of the initial modulus of foundation reaction force with depth; P us is the ultimate bearing capacity of shallow sand; P ud is the ultimate bearing capacity of deep sand; C 1 , C 2 , C 3 All of them are parameters related to the internal friction angle of sand.

[0098] In the above embodiment, when using the present invention, firstly, the internal friction angle of sand is obtained according to formula (2) or formula (3)-(4): Secondly, combined with the growth rate K of the initial modulus of foundation reaction force with depth in Table 1 and Table 2, the parameter C related to the internal friction angle of sand is determined. 1 , C 2 , C 3 ; Then, according to formula (12), the ultimate bearing capacity P of shallow sand is determined us and the ultimate bearing capacity of deep sand P ud , take P us and P ud The smaller value between u ; Finally, the py curve of sand is obtained according to formula (11).

[0099] In a specific embodiment, when the load type is a static load, the coefficient A associated with the load type selects a larger value between A=3-0.8z / D and A=0.9; when the load type is a cyclic load, the coefficient A associated with the load type selects A=0.9.

[0100] In a specific embodiment, the growth rate K of the initial modulus of the foundation reaction force with depth is taken from Table 1:

[0101] Table 1

[0102]

[0103]

[0104] When the internal friction angle of sand is not in Table 1, the corresponding growth rate K of the initial modulus of foundation reaction force with depth is obtained by interpolating the data in Table 1;

[0105] The parameter C related to the internal friction angle of sand 1 , C 2 , C 3 Use Table 2 to obtain the value:

[0106] Table 2

[0107]

[0108]

[0109] When the internal friction angle of sand is not in Table 2, the corresponding parameter C related to the internal friction angle of sand is 1 , C 2 , C 3 Obtained by interpolating the data in Table 2.

[0110] It should be noted that in the above embodiment, interpolation value acquisition is a prior art, and the specific value acquisition method will not be repeated here.

[0111] In a specific embodiment, for weathered rock, its py curve is obtained by the following formula:

[0112]

[0113] K ir =k ir E ir (14)

[0114]

[0115] y rm =k rm D (18)

[0116]

[0117] Where: p is the soil resistance per unit length; K ir is the slope of the linear part; y is the displacement per unit length; y A is the y value corresponding to the end point of the linear part; p ur is the ultimate resistance of rock; rm is the intermediate parameter; k ir is a dimensionless constant; E ir is the initial modulus of rock; z is the depth below the ground; D is the pile diameter; α r is the intensity attenuation coefficient; q ur is the compressive strength of rock; RQD is the rock quality index; k rm is the strain factor.

[0118] In the above embodiment, when the present invention is used, the rock quality index RQD is first obtained based on the on-site drilling core, and the rock compressive strength q is obtained based on the indoor test. ur Then, the rock strength attenuation coefficient α is determined based on the rock quality index RQD combined with formula (17): r ; Then according to formula (16), the ultimate resistance of rock p is obtained ur ; The initial modulus of the rock is calculated according to equations (14)-(15), and finally the py curve of the weathered rock is determined according to equations (13) and (18)-(19).

[0119] In a specific embodiment, taking a certain target area as an example, the py curve of the pile foundation is determined by combining the indoor test and the in-situ test described in the present invention. The result is as follows: Figure 2 shown.

[0120] In summary, the present invention can more accurately determine the py curve by combining indoor tests and in-situ tests. Compared with the prior art, the present invention has significant progress.

[0121] The above description is only a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as a preferred embodiment as above, it is not intended to limit the present invention. Any technician familiar with the profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the scope of the technical solution of the present invention.

Claims

1. A method for determining the py curve of a pile foundation by combining indoor tests and in-situ tests, characterized in that: The following steps are involved: S1: Draw a geological profile based on the geological drill hole column chart to determine the typical strata; S2: Determine the strength parameters of typical formations by combining laboratory tests and in-situ tests; S3: Determine the py curves of different types of rock and soil bodies according to the strength parameters.

2. The method for determining the pile foundation py curve combining indoor test and in-situ test according to claim 1 is characterized in that: In step S2, the strength parameters include undrained shear strength of clay and internal friction angle of sand; The undrained shear strength of the clay is calculated by the following formula: S u =(q c -s v0 ) / N kt (1) Where: S u is the undrained shear strength of clay; q c is the cone tip resistance value in the static penetration test; σ v0 is the vertical stress; N kt is the empirical coefficient; The sand internal friction angle is calculated by the following formula: or (N1) 60 =(P a / s v0 ) c ·N 60 (4) Where: is the internal friction angle of sand; a, b, c, m, n are all empirical parameters; is the fitting parameter; (N1) 60 is the standard penetration test result after correction considering the overburden stress; P a is the atmospheric pressure; N 60 is the corrected standard penetration number.

3. The method for determining the pile foundation py curve combining indoor test and in-situ test according to claim 2 is characterized in that: When the sand contains silt particles, the internal friction angle of the sand is reduced by 3° based on the calculated value; when the sand contains gravel particles, the internal friction angle of the sand is increased by 2° based on the calculated value.

4. The method for determining the pile foundation py curve by combining indoor test and in-situ test according to any one of claims 1 to 3, characterized in that: In step S3, the different types of rock and soil bodies include clay, sand and weathered rock.

5. The method for determining the pile foundation py curve combining indoor test and in-situ test according to claim 4 is characterized in that: For clay, the static py curve is obtained by the following formula: p=0.5·(y / y c ) 1 / 3 ·p u (5) y c =2.5·ε 50 ·D (6) z R =6·D / [(γ·D) / S u +J] (8) Where: p is the soil resistance per unit length; y is the displacement per unit length; y c is the reference displacement; P u is the ultimate soil resistance per unit length; ε 50 is the strain value corresponding to 0.5 times the maximum deviator stress in the undrained compression test of the original soil sample, %; D is the pile diameter; S u is the undrained shear strength of clay; γ is the gravity; z is the depth below the ground; J is the empirical coefficient; z R is the depth of the turning point of the ultimate soil resistance per unit length; When the depth below the ground is less than or equal to the depth of the turning point of the ultimate soil resistance per unit length, the dynamic py curve is obtained by the following formula: When the depth below the ground is greater than the depth of the turning point of the ultimate soil resistance per unit length, the dynamic py curve is obtained by the following formula:

6. The method for determining the pile foundation py curve combining indoor test and in-situ test according to claim 5, characterized in that: When the undrained shear strength of the clay is less than or equal to 25 kPa, ε 50 The value is 0.02, and the value of J is 0.5; When the undrained shear strength of the clay is in the range of 25-50 kPa, ε 50 The value is 0.01, and the value of J is 0.25; When the undrained shear strength of the clay is in the range of 50-100 kPa, ε 50 The value is 0.007 and the value of J is 0.

25.

7. The method for determining the pile foundation py curve combining indoor test and in-situ test according to claim 4, characterized in that: For sandy soil, the py curve is obtained by the following formula: Where: p is the soil resistance per unit length; A is a coefficient related to the load type; P u is the ultimate soil resistance per unit length; K is the growth rate of the initial modulus of foundation reaction force with depth; z is the depth below the ground; y is the displacement per unit length; P us is the ultimate bearing capacity of shallow sand; P ud is the ultimate bearing capacity of deep sand; C1, C2, C3 are parameters related to the internal friction angle of sand; D is the pile diameter; γ is the weight.

8. The method for determining the pile foundation py curve combining indoor test and in-situ test according to claim 7, characterized in that: When the load type is a static load, the coefficient A associated with the load type selects a larger value between A=3-0.8z / D and A=0.9; when the load type is a cyclic load, the coefficient A associated with the load type selects A=0.

9.

9. The method for determining the pile foundation py curve combining indoor test and in-situ test according to claim 7, characterized in that: The growth rate K of the initial modulus of the foundation reaction force with depth is obtained through Table 1: Table 1 When the internal friction angle of sand is not in Table 1, the corresponding growth rate K of the initial modulus of foundation reaction force with depth is obtained by interpolating the data in Table 1; The parameters C1, C2, and C3 related to the internal friction angle of sand are taken from Table 2: Table 2 When the internal friction angle of sand is not in Table 2, the corresponding parameters C1, C2, and C3 related to the internal friction angle of sand are obtained by interpolating the data in Table 2.

10. The method for determining the pile foundation py curve combining indoor test and in-situ test according to claim 4, characterized in that: For weathered rock, its py curve is obtained by the following formula: K ir =k ir E ir (14) y rm =k rm D (18) Where: p is the soil resistance per unit length; K ir is the slope of the linear part; y is the displacement per unit length; y A is the y value corresponding to the end point of the linear part; p ur is the ultimate resistance of rock; rm is the intermediate parameter; k ir is a dimensionless constant; E ir is the initial modulus of rock; z is the depth below the ground; D is the pile diameter; α r is the intensity attenuation coefficient; q ur is the compressive strength of rock; RQD is the rock quality index; k rm is the strain factor.

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