CN111811937A - Method for pre-judging failure mode of geosynthetic material in sandy soil - Google Patents
Method for pre-judging failure mode of geosynthetic material in sandy soil Download PDFInfo
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- CN111811937A CN111811937A CN202010653273.1A CN202010653273A CN111811937A CN 111811937 A CN111811937 A CN 111811937A CN 202010653273 A CN202010653273 A CN 202010653273A CN 111811937 A CN111811937 A CN 111811937A
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N3/08—Investigating strength properties of solid materials by application of mechanical stress by applying steady tensile or compressive forces
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- G—PHYSICS
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
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Abstract
The invention relates to a method for pre-judging failure modes of geosynthetics in sandy soil, which is characterized in that normal pressure borne by a rib is collected before a drawing experiment, the collected normal pressure is input into a pre-judging model to obtain the critical effective length of the rib failure mode, and the obtained critical effective length of the rib failure mode is compared with the effective length of the rib obtained by pre-detection to obtain the failure mode of the rib.
Description
Technical Field
The invention relates to the technical field of civil engineering, in particular to a method for pre-judging failure modes of geosynthetics in sandy soil.
Background
The statements herein merely provide background information related to the present disclosure and may not necessarily constitute prior art.
The geosynthetic material has two failure modes, namely pulling out and pulling out under the interaction of the reinforced soil, the reinforced soil interface parameters are usually evaluated through a reinforced soil direct shear test, and the mechanical parameters and the failure modes of the geosynthetic material in a confining pressure soil environment are evaluated through a pulling test. The inventor finds that the current domestic regulations stipulate that the drawing test is only carried out within a small deformation range, and the failure mode of the geosynthetic material is not involved. Foreign codes allow testing of geosynthetic failure modes in pull tests, but no literature has been found to suggest a predictive theory or methodology for geosynthetic failure modes in pull tests. The current drawing test needs to carry out a complete test process on the research of the failure mode of the geosynthetic material, and is not beneficial to the early warning of the failure of the reinforced soil structure.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide a method for pre-judging the failure mode of the geosynthetic material in sandy soil, which can judge the mode of the geosynthetic material to fail finally before the drawing test is started, and is beneficial to researching the problems of failure early warning of a reinforced soil structure and the like.
In order to achieve the purpose, the invention adopts the following technical scheme:
in a first aspect, an embodiment of the present invention provides a method for predicting a failure mode of a geosynthetic material in sandy soil, where a normal pressure applied to a reinforcement is collected before a drawing experiment, the collected normal pressure is input into a prediction model to obtain a critical effective length of a reinforcement failure mode, and the obtained critical effective length of the reinforcement failure mode is compared with an effective length of a reinforcement obtained in advance, so as to obtain the failure mode of the reinforcement.
With reference to the first aspect, an embodiment of the present invention provides a possible implementation manner of the first aspect, where if a critical effective length of an obtained failure mode of a rib is smaller than an effective length of a rib obtained by pre-detection, the failure mode of the rib is a snap failure; and if the obtained critical effective length of the failure mode of the rib is larger than the effective length of the rib detected in advance, the failure mode of the rib is extraction failure.
In a second aspect, an embodiment of the present invention provides a method for predicting failure modes of geosynthetics in sandy soil, where effective lengths of reinforcements are collected before a drawing experiment, the collected effective lengths are input into a prediction model to obtain critical normal pressures of the reinforcement failure modes, and the obtained critical normal pressures of the reinforcement failure modes are compared with detected normal pressures applied to current reinforcements to obtain failure modes of the reinforcements.
With reference to the second aspect, an embodiment of the present invention provides a possible implementation manner of the second aspect, where if the obtained critical normal pressure of the rib failure mode is smaller than the detected normal pressure applied to the current rib, the rib failure mode is a snap failure; and if the obtained critical normal pressure of the rib failure mode is greater than the detected normal pressure borne by the current rib, the failure mode of the rib is extraction failure.
The invention has the beneficial effects that:
according to the method, the mode of failure of the reinforcement can be judged in advance by acquiring the effective length and normal pressure of the reinforcement before the drawing experiment, the method is simple, and the method is beneficial to researching the project front-edge problems such as reinforcement structure failure early warning and the like.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate embodiments of the application and, together with the description, serve to explain the application and are not intended to limit the application.
FIG. 1 is a schematic flow chart of example 1 of the present invention;
FIG. 2 is a drawing of a drawing end of a bar in example 1 of the present invention;
FIG. 3 is a graph showing the relationship between displacement distribution and interfacial shear stress distribution in the interface characteristics of the strain-hardened soil reinforcement in example 1 of the present invention;
FIG. 4 is a schematic diagram of a boundary between two critical states of failure modes in either embodiment 1 or embodiment 2 of the present invention;
Detailed Description
It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments according to the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.
As introduced in the background art, the existing failure mode of the reinforcement in the sandy soil cannot be predicted before the drawing experiment starts, and is not beneficial to the forward research of projects such as reinforcement structure failure early warning and the like.
In example 1 of a typical embodiment of the present application, as shown in fig. 1, a method for pre-embedding a failure mode of a rib in sandy soil includes acquiring a normal pressure applied to the rib before a drawing experiment is started, inputting the acquired normal pressure into a pre-judgment model to obtain a critical effective length of the failure mode of the rib, and comparing the obtained critical effective length of the failure mode of the rib with an effective length of the rib obtained by pre-detection to obtain the failure mode of the rib.
The method for obtaining the prediction model comprises the following steps:
as shown in fig. 2, from the mechanical balance of the bar in the pulled state, a mechanical balance model of the bar under the tensile force can be obtained:
in the formula F0Is the drawing force (N) borne by the front end of the bar material; sigma0Is the tensile stress (Pa) borne by the front end of the rib material; w is the tendon width (m); a is the cross-sectional area (m) of the rib2) For a rectangular cross-section, A-wt, t is the rib thickness(m); x is the distance (m) between the rib and the drawing end, and the maximum value is the effective length l of the rib; τ is the reinforcement interface shear stress (Pa), τ (x) represents a function of the reinforcement interface shear stress along the length of the reinforcement, the function being the integral of the function along the length of the reinforcement
I.e. the earth-reinforced interface force per unit width.
When the rib material is broken or pulled out, the ultimate balance state is reached. In the critical state of pulling-off and pulling-out, the bar material reaches the breaking strength, and the interaction of the bar and the soil reaches the maximum value. The two are in mechanical balance, and a mechanical balance model of the bar material in a critical state when the bar material is pulled off or pulled out is obtained according to the formula (1):
in the formula sigmafIs the breaking strength (Pa) of the tendon; lcrIs the effective length (m) of the reinforcement material in the critical failure mode
In a sandy soil environment, the characteristics of the reinforced soil interface are strain hardening characteristics, namely, the shear stress of the reinforced soil interface is gradually increased along with the increase of the relative displacement u of the reinforced soil, and the shear failure strength tau of the reinforced soil interface is achievedfThe strength is then maintained as shown in fig. 3. Therefore, when the shear failure strength tau of the reinforced soil interface is increasedfWhen distributed along the whole length of the bar material, the acting force of the bar soil interface
Reach a maximum value, i.e.:
the reinforced soil interface parameter is determined through a reinforced soil direct shear test, and in the embodiment, the reinforced soil interface parameter is the apparent cohesive force c of the reinforced soil interfacesgAngle of friction with reinforced soil interface
The above-mentionedThe relative density of the sandy soil where the rib material of the rib soil direct shear test is located is the same as that of the sandy soil where the rib material of the failure model to be predicted is located.
Obtaining a relation model of the reinforced soil interface parameters, the normal pressure and the shear failure strength of the reinforced soil interface according to the Mokolun criterion:
in the formula csgThe apparent cohesive force (Pa) of the reinforced soil boundary surface;
is the angle of friction (degree) of the rib soil interface; sigmavIs the normal pressure (Pa).
The pre-judging model can be obtained by simultaneous formulas (2), (3) and (4):
effective length l in formula (5)crAnd normal pressure σvIs a variable, σf、t、csgAnd
are all constant parameters that can be measured.
Collecting normal pressure sigma borne by the bar before drawing experimentvThe critical effective length l of the failure mode of the rib material is obtained according to the formula (5)crIf the effective length l of the rib material obtained by pre-detection is larger than lcrAnd the failure mode of the rib material is the breaking failure. If the effective length l of the rib material is less than lcrAnd the failure mode of the rib material is pull-out failure.
In another exemplary embodiment of the present application, example 2, the prediction model and the method of obtaining the prediction model are the same as those in example 1, and will not be described in detail.
Inputting the collected effective length of the rib into a pre-judgment model before the drawing experiment to obtain the critical normal pressure of the rib failure mode, and comparing the obtained critical normal pressure of the rib failure mode with the detected normal pressure borne by the current rib to obtain the failure mode of the rib.
If the obtained critical normal pressure of the rib failure mode is smaller than the detected normal pressure borne by the current rib, the failure mode of the rib is pull-out failure, and if the obtained critical normal pressure of the rib failure mode is larger than the detected normal pressure borne by the current rib, the failure mode of the rib is pull-out failure.
In an engineering example of embodiment 1 and embodiment 2 of the present application:
the prior geotextile belt with the width of 45mm and the thickness of 1.8 mm. The tensile breaking strength of the alloy is 14.0MPa by a tensile test. The sand is dry sand without cohesive force, and the internal friction angle is 29.5 degrees. The key particle size parameters are: d10＝0.23mm，d30＝0.53mm，d50＝0.95mm，d601.27 mm. The uniformity coefficient Cu and the curvature coefficient Cc of the sandy soil are respectively 5.52 and 0.96, and the maximum and minimum dry densities are respectively 1.920g/cm3And 1.395g/cm3. The direct shear test of the reinforced soil is developed in the sandy soil, and the apparent cohesive force c of the reinforced soil interface surface under the relative density of 90 percent is measuredsgAngle of friction with interface
17.5kPa and 61.8, respectively.
From the above parameters, it can be determined that each parameter in equation (5) is: sigmaf＝14.0MPa；t＝1.8mm；csg＝17.5kPa；
And (4) carrying out drawing tests on the geotechnical belts with different lengths under different normal phase pressures. The soil used for the test was sandy soil having a relative density of 90%. The effective length of the geobelt is 20-60cm, and for the geobelt with the same effective length, a drawing test under high normal pressure is carried out to ensure that a test piece is pulled out; and then, sequentially decreasing the normal pressure from high to low by 5kPa until the geotechnical belt with the same length is finally pulled out. The drawing test conditions were developed in the order shown in table 1.
TABLE 1 drawing test conditions
The final failure mode of each set of drawing tests is compared with the results of the formula calculation, as shown in fig. 4. The dotted line is the formula calculation result, the solid point represents the drawing test condition that the failure mode is pulling out, and the hollow point represents the drawing test condition that the failure mode is pulling out. As can be seen in fig. 4, the results of the formula calculation are slightly less than the test results, but the critical state of the failure mode is better represented. The method can be used for drawing tests and failure mode prejudgment of reinforced soil structures.
Although the embodiments of the present invention have been described with reference to the accompanying drawings, it is not intended to limit the scope of the present invention, and it should be understood by those skilled in the art that various modifications and variations can be made without inventive efforts by those skilled in the art based on the technical solution of the present invention.
Claims (10)
1. A method for pre-judging failure modes of geosynthetics in sandy soil is characterized in that normal pressure borne by a rib is collected before a drawing experiment, the collected normal pressure is input into a pre-judging model to obtain critical effective length of the rib failure mode, and the obtained critical effective length of the rib failure mode is compared with the effective length of the rib obtained through pre-detection to obtain the failure mode of the rib.
2. The method for predicting failure mode of geosynthetic material in sandy soil as claimed in claim 1, wherein if the obtained critical effective length of failure mode of the tendon is less than the predetermined detected effective length of the tendon, the failure mode of the tendon is pull-out failure, and if the obtained critical effective length of failure mode of the tendon is greater than the predetermined detected effective length of the tendon, the failure mode of the tendon is pull-out failure.
3. A method for pre-judging failure modes of geosynthetics in sandy soil is characterized in that effective lengths of reinforcements are collected before a drawing experiment is carried out, the collected effective lengths are input into a pre-judging model to obtain critical normal pressure of the reinforcement failure modes, and the obtained critical normal pressure of the reinforcement failure modes is compared with the detected normal pressure borne by the current reinforcements to obtain the failure modes of the reinforcements.
4. The method for predicting failure mode of geosynthetic material in sandy soil as claimed in claim 3, wherein if the obtained critical normal pressure of the failure mode of the tendon is less than the detected normal pressure to which the current tendon is subjected, the failure mode of the tendon is pull-out failure, and if the obtained critical normal pressure of the failure mode of the tendon is greater than the detected normal pressure to which the current tendon is subjected, the failure mode of the tendon is pull-out failure.
5. The method for predicting failure modes of geosynthetics in sandy soil as claimed in claim 1 or 3, wherein a mechanical balance model of the tendon in a critical state when pulled out is obtained according to the mechanical balance model when the tendon is pulled out, and the pre-determination model is obtained by bringing the tendon interface parameters and normal pressure into the mechanical balance model in the critical state.
6. The method of predicting geosynthetic failure mode in sandy soil of claim 5 wherein said reinforcement soil interface parameters are reinforcement soil interface apparent cohesion and reinforcement soil interface friction angle.
7. The method for pre-judging failure modes of geosynthetics in sandy soil as claimed in claim 5, wherein said pre-judging model is obtained by substituting a model of relationship between the parameters of the soil interface, normal pressure and shear failure strength of the soil interface into a mechanical equilibrium model under a critical state.
8. The method for predicting failure modes of geosynthetics in sandy soil as recited in claim 7 wherein the model of the relationship between the parameters of the soil interface, normal pressure and the strength of the soil interface is derived using the Moore coulomb criterion.
9. The method of predicting geosynthetic failure mode in sandy soil of claim 5 wherein said geosynthetic interface parameter is determined by a direct shear test of geosynthetic soil.
10. The method for predicting failure modes of geosynthetics in sandy soil as defined in claim 9 wherein the relative densities of the sandy soil in which the reinforcing material of the reinforced-soil direct shear test is located and the sandy soil in which the reinforcing material of the failure model to be predicted is located are the same.
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