Disclosure of Invention
In order to overcome the problems in the prior art, the invention provides a method for measuring the lateral expansion coefficient of expansive soil by considering the lateral deformation characteristic of a flexible supporting structure, and the lateral expansion coefficient can be obtained by adopting a simple experiment, and the specific technical scheme is as follows:
Taking soil on the engineering site, and measuring the maximum dry density and the optimal water content of the expansive soil;
according to the maximum dry density and the optimal water content, preparing a standard triaxial test piece and a cuboid test piece, wherein the initial water content of the cuboid test pieceIs the optimal water content;
Carrying out an unsaturated soil triaxial test on a standard triaxial test piece to establish an elastic modulusRelational and poisson ratioRelation formula:,;
Wherein: The water content is the water content of the water-based paint,、、、Fitting parameters;
carrying out a humidifying two-dimensional expansion test on a cuboid test piece, and establishing lateral expansion forceRelational and vertical expansion strainRelation formula:
,;
Wherein: For lateral strain, determining multiple lateral strains according to geogrid type and elastic stage elongation thereof;Determining a plurality of overburden pressures according to the depth of the atmospheric influence of the engineering site for overburden pressure;Is the increment of the water content,In order to achieve the final water content,Is the initial water content;、、、、、、、 Fitting parameters;
establishing theoretical horizontal strain of cuboid test pieceRelation and theoretical vertical strainRelation formula:
,;
In the formula,As a component of the horizontal stress,As a component of the stress in the vertical direction,In order to achieve a coefficient of expansion in the horizontal direction,The coefficients of expansion in the vertical direction;
Corresponding to,Corresponding to,Corresponding to,Corresponding to,Corresponding toCombining lateral expansion forcesRelational, vertical expansion strainRelational and theoretical horizontal strainRelational and theoretical vertical strainThe relation type obtains the lateral expansion coefficient of the expansive soilThe calculation formula is as follows:
。
further, the determination of the maximum dry density and the optimal water content of the filling soil comprises wet heavy compaction test determination and dry heavy compaction test determination. The maximum dry density and the optimal water content of the expansive soil are subjected to standard measurement by adopting the measurement method.
Further, the compactness of the rectangular solid test piece is [93%, 100%) to meet the compactness of the expressway under embankment specified by the highway subgrade design specification (JTGD-2015) must reach 93% or more.
Further, the manufacturing method of the cuboid test piece comprises a layering static pressure method. The layering static pressure method can avoid that the prepared test piece is not influenced by lateral pressure caused by the overlying load.
Further, the geogrid type comprises a glass fiber grid, and the elongation rate of the glass fiber grid at the elastic stage is [0.5 percent, 1.5 percent ] so as to ensure that the geogrid flexible supporting structure made of glass fiber is in elastic deformation instead of plastic deformation so as to ensure the deformability in the horizontal direction.
Further, the geogrid type comprises a steel-plastic grid, and the elongation rate of the steel-plastic grid at the elastic stage is [0.8 percent, 2 percent) so as to ensure that the geogrid flexible supporting structure made of the steel-plastic material is in elastic deformation instead of plastic deformation so as to ensure the deformability in the horizontal direction.
Further, the geogrid type comprises an HDPE (high-density polyethylene) grid, and the elongation rate of the HDPE grid at the elastic stage is 1 percent and 3 percent so as to ensure that the geogrid flexible supporting structure made of HDPE is elastically deformed instead of plastically deformed so as to ensure the deformability in the horizontal direction.
Further, the geogrid type comprises a polyester grid, and the elastic stage elongation rate of the polyester grid is 2 percent and 4 percent so as to ensure that the geogrid flexible supporting structure made of the polyester is elastically deformed instead of plastically deformed so as to ensure the deformability in the horizontal direction.
Compared with the prior art, the invention has the following beneficial effects:
according to the method for measuring the lateral expansion coefficient of the expansive soil, the anisotropic characteristic of the expansive soil in the flexible supporting structure is considered according to the stress and deformation characteristics of the flexible supporting structure, the defect that the lateral expansion coefficient of the expansive soil allowed to deform in the horizontal direction cannot be obtained in the traditional loaded expansion test is overcome, and the method is suitable for calculating the lateral expansion coefficients of the expansive soil at different depths inside the geogrid reinforced flexible supporting structure. The obtained lateral expansion coefficient can be used for humidifying the expansive soil, performing lateral deformation, performing stress analysis, calculating a humidity stress field and a displacement field and calculating the reinforcement distance of the flexible supporting structure, and has the advantages of high precision, simplicity in operation and easiness in popularization.
Detailed Description
In order to more clearly and fully describe the technical aspects of the present invention, the present invention will be further described in detail by the following specific examples, and unless otherwise defined, 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 invention belongs.
The invention provides a method for measuring the lateral expansion coefficient of expansive soil, which comprises the following steps:
S1, taking soil on an engineering site according to the regulations of the highway geotechnical test procedure (JTG 3430-2020), carrying out a wet heavy compaction test or a dry heavy compaction test specified by the geotechnical test method Standard (GB/T50123) on an expansive soil sample retrieved on site to obtain the maximum dry density and the optimal water content of expansive soil filled by a flexible supporting structure, and setting the dry density of a cuboid test piece according to the requirement that the compactness of an expressway under embankment specified by the highway subgrade design specification (JTGD-2015) must reach 93% or moreAnd (3) adopting a layered static pressure method (see Long Mingxu. A reinforced expansive soil slope stability analysis method taking the influence of lateral expansion into consideration and application_ Long Mingxu [ D ]. Changsha university, 2021) to manufacture a plurality of groups of cuboid test pieces, manufacturing a plurality of groups of standard triaxial parallel test pieces according to geotechnical test method standard (GB/T50123-2019), and placing the test pieces in a humidity preservation box for humidity preservation. Initial moisture content of rectangular test pieceThe test pieces have the optimal water content, the sizes of 54.77mm long, 54.77mm wide and 20mm high, and multiple groups of standard triaxial parallel test pieces have different water contents;
S2, performing triaxial test on the triaxial test piece in S1 according to the rule of highway geotechnical test procedure (JTG 3430-2020) to establish elastic modulusAnd water contentRelationship between the Poisson's ratio and the water contentThe relation between:
,
;
Wherein, the、、、Fitting parameters;
S3, consulting data or adopting a dynamic sounding test to determine local atmospheric influence depth, and determining a plurality of overlying pressures according to the engineering site atmospheric influence depth and combining the dead weights of soil bodies at different depths in the flexible supporting structure;
S4, selecting different types of geogrids according to deformation characteristics of roadbed, and determining a plurality of lateral strains according to the types of the geogrids and the elongation of the geogrids in the elastic stage. The elongation at elastic stage refers to the recoverable elongation deformation of the geogrid in the stretching process from the beginning of stress to the moment when the geogrid reaches the proportion limit or yield point, specific numerical values are determined by a standard wide strip tensile test, and the specific requirements of relevant design specifications are met simultaneously by referring to a product technical data table provided by each manufacturer, and the lateral strain is determined according to the specific requirements of engineering on deformation control and the actual elongation at elastic stage of the geogrid of the specific type, model and manufacturerLateral strainThe flexible support structure is in the range of the elongation at the elastic stage of various different geogrids, so that the flexible support structure is in elastic deformation rather than plastic deformation to ensure the deformability in the horizontal direction. The geogrid comprises a glass fiber grid, a steel-plastic grid, an HDPE (HIGHDENSITY POLYETHYLENE, high-density polyethylene) grid and a polyester grid, wherein the elastic stage elongation of the glass fiber grid is [0.5%, 1.5%), [0.8%, 2%), [ 1%, 3%), [ 2%,4% >;
s5, performing a plurality of humidifying two-dimensional expansion tests on a cuboid test piece by adopting a two-dimensional expansion instrument shown in FIG. 1, wherein the humidifying two-dimensional expansion tests comprise the following operation steps:
S51, placing a cuboid test piece on a test piece box above a base 1 of a two-dimensional dilatometer, smearing thin layers of vaseline on the two sides and the bottom of the test piece box, placing cut filter paper at the bottom of the test piece box, wherein the size is slightly smaller than the plane size of the test piece;
s52, the overlying pressure determined according to S3Applying a load, i.e. a determined overlying pressure, to the upper part of the test piece at one timeWhen the displacement reading of the vertical dial indicator 12 per hour is not more than 0.01mm, the deformation of the test piece is considered to be stable, and the reading of the pressure sensor 11 is recorded;
s53, lateral strain determined by S4Determining lateral displacement, rotating the lateral displacement screw rod 10 until the reading of the lateral dial indicator 13 on the displacement marker post 8 reaches the determined lateral displacement, setting the reading of the vertical dial indicator 12 to zero, then injecting pure water into the water tank 3, always keeping the water surface to exceed the top surface of the test piece by 5mm, immersing the pure water in the water tank 3 into the cuboid test piece through the water inlet hole 2 and the permeable stone 5, recording the reading of the vertical dial indicator 12 every two hours after immersing, and recording the reading of the vertical dial indicator 12 and the reading of the pressure sensor 11 when the reading of the displacement per hour is not more than 0.01mm, wherein the reading difference of the pressure sensor 11 in the step S52 and the step S53 is the lateral expansion forceThe difference between the initial and final readings of the vertical dial gauge 12 is the vertical expansion strain;
S54, discharging water, relieving load, taking out the test piece, wiping the annular wall and other floating water, weighing and drying the cuboid test piece to obtain the final water content of the cuboid test pieceAnd calculate the water content increment:;
S56, repeating S51 to S54, and respectively performing a plurality of overlaying pressures on the rest of the cuboid test piecesAnd a plurality of lateral strainsIs a two-dimensional expansion test of humidification;
S6, carrying out data analysis on the test result obtained in the step S5, and establishing lateral expansion forceAnd lateral strainAnd an overburden pressureIncrement of water contentEstablishing a vertical expansion strainAnd an overburden pressureLateral expansion forceIs defined by the relation:
,
;
S7, because the expansion deformation test adopts a cuboid test piece, the stress strain of the test piece can be solved by a rectangular coordinate system, and the soil body is assumed to be an elastic material, and the expansion coefficient of the expansion soil sample in the horizontal direction and the vertical direction is considered to be anisotropic, the physical equation of plane strain can be used for representing the horizontal strain component and the vertical strain component caused by moisture absorption, namely the theoretical horizontal strain of the cuboid test pieceRelation and theoretical vertical strainRelation formula:
,
;
In the formula,As a component of the horizontal stress,As a component of the stress in the vertical direction,In order to achieve a coefficient of expansion in the horizontal direction,Coefficient of vertical expansion, lateral strain due to a two-dimensional expansion test of humidificationAnd theoretical horizontal strainCorrespondingly, the vertical expansion strain of the humidifying two-dimensional expansion testAnd theoretical vertical strainCorrespondingly, the lateral expansion force of the humidifying two-dimensional expansion testAnd a horizontal stress componentCorrespondingly, the upper coating pressure of the humidifying two-dimensional expansion testAnd a vertical stress componentCorrespondingly, the coefficient of expansion in the horizontal directionI.e. coefficient of lateral expansion. Combined with lateral expansion forcesRelational, vertical expansion strainRelational and theoretical horizontal strainRelational and theoretical vertical strainThe relation type obtains the lateral expansion coefficient of the expansive soilThe calculation formula is as follows:
。
In practical application, lateral strainDetermined by the elongation of the geogrid, the overburden pressureIs determined according to the soil taking depth,、Obtained by triaxial test of unsaturated soil, strain in vertical directionLateral expansion forceAnd water content incrementFrom the two-dimensional expansion test of humidification, the lateral expansion coefficient of the flexible supporting structure in specific engineering is determined by the lateral expansion coefficientAnd (5) calculating a calculation formula.
Examples
A geogrid reinforced expansive soil flexible supporting structure of an expansive soil side slope of a highway is taken as an example, as shown in figure 2, the geogrid reinforced expansive soil flexible supporting structure of the expansive soil side slope is characterized in that the bottom layer of the supporting structure is a permeable foundation layer, a seepage ditch is excavated below the permeable foundation layer, a permeable layer is arranged between the supporting structure and an excavation surface and is integrated with the permeable foundation layer, geogrid 001 reinforced rib materials are paved layer by layer in the whole supporting structure, the rib materials of each geogrid 001 exceed the width of the supporting structure, are reversely wrapped on the upper layer and are connected with the rib materials of the upper layer, and each layer of rib materials is backfilled and compacted by the excavated expansive soil 002. The slope ratio of the expansive soil side slope is 1:1.5, the local atmospheric influence depth is 2.5m, the geogrid is made of HDPE material, the filling water content is controlled according to the optimal water content of 20.5 percent obtained by a wet heavy compaction test, the compactness is 93 percent, and the dry density is 1.65x103kg/m3. Preparing 30 cuboid test pieces with initial water content of 20.5% and dimensions of 54.77mm long by 54.77mm wide by 20mm high from site taken expansive soil filler by static pressure method, and water content30 Standard triaxial test pieces with dimensions phi 50mm by 100mm are 18%, 20.5%, 22%, 24%, 26%.
Carrying out an unsaturated soil triaxial test on a standard triaxial test piece, and fitting to obtain an elastic modulusPoisson's ratioAnd water contentThe relation between them is:
;
;
Since the local atmospheric depth of influence was 2.5m, 4 overburden pressures were determinedThe elongation at the elastic stage of the HDPE grids produced by a certain manufacturer is 2.8%, and the 5 lateral strains are determined to be 0%, 0.5%, 1.0%, 1.5% and 2.0%. The test results of the humidifying two-dimensional expansion test on the cuboid test piece are shown in table 1.
Lateral expansion force is plotted against the data in Table 1Strain with vertical expansionFitting the relation to obtain:
;
;
increasing the water contentLateral strainCoating pressureModulus of elasticity after fittingPoisson's ratioLateral expansion forceLateral expansion coefficient of substituted expansive soilThe calculation formula is as follows: the lateral expansion coefficients of the HDPE geogrid at different depths in the range of the atmospheric influence depth are obtained, and specific data are shown in Table 2.
TABLE 1 two-dimensional expansion test results
TABLE 2 calculation of lateral expansion coefficients at different depths of flexible support structure
The reinforcement length of the geogrid in the flexible support is determined by dividing the local atmospheric influence depth by the slope rate and multiplying the local atmospheric influence depth by a safety coefficient, wherein the reinforcement length is usually 3.5-4.5m, and the reinforcement distance is usually 0.5m. The method does not consider the stress condition of the geogrid and the expansion characteristics of the expansion soil in different areas, namely the strong expansion soil, the medium expansion soil or the weak expansion soil, the length and the interval of the reinforcement are the same, the design value in the strong expansion soil area is excessively dangerous, the expansion soil cutting slump and other consequences are caused, and the design value in the weak expansion soil area is more conservative, so that the material waste is caused. The method for measuring the lateral expansion coefficient of the expansive soil can calculate the lateral expansion coefficient of the expansive soil of the engineering field, the design of the supporting structure is carried out according to the lateral expansion coefficient, and the supporting structure is correspondingly adjusted along with the increase of the lateral expansion coefficient, such as the adjustment of the tensile strength of the grid, the adjustment of the spacing of a reinforcement layer, the anchoring length, the thickness of a buffer layer or the density of a drain pipe, and the like, so that the constructed flexible supporting structure can maintain the stability of a side slope, avoid slumping and reduce the later maintenance cost.
The embodiments of the present invention have been described above with reference to the accompanying drawings, which are illustrative only and not limiting, and many forms can be made by those of ordinary skill in the art without departing from the spirit of the invention and the scope of the claims, which are all within the scope of the invention.