CN109752262B - Method for determining dynamic shear modulus parameter of covering soil mass based on in-situ relative density - Google Patents
Method for determining dynamic shear modulus parameter of covering soil mass based on in-situ relative density Download PDFInfo
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Abstract
A method for determining dynamic shear modulus parameters of a covering soil body based on in-situ relative density comprises the following specific steps: determining the relative density of each layer of soil body of the covering layer soil body based on the layering and mechanical characteristics of the covering layer soil body and by combining the change relation of the indoor remolded mechanical index along with the relative density and the stress condition; the method comprises the steps of determining a pressure effect relation of a maximum dynamic shear modulus parameter of a remolded soil sample and a change relation of dynamic shear modulus follow-up shear strain based on the relative density of a covering soil body, determining the maximum dynamic shear modulus parameter considering the soil body structure by combining the pressure effect relation of the maximum dynamic shear modulus of the covering soil body, and further determining a dynamic shear modulus follow-up shear strain attenuation curve considering the soil body structure. The method is used for calibrating and controlling the remolded soil sample in the laboratory through the relative density of the in-situ soil layer, so that the consistency of the remolded soil sample and the in-situ covering layer soil mechanical property is ensured; the shear modulus parameter and the attenuation curve determined by the method can improve the accuracy of safety evaluation.
Description
Technical Field
The invention belongs to the field of soil body dynamic shear modulus determination methods, and particularly relates to a method for determining a overburden soil body dynamic shear modulus parameter based on in-situ relative density.
Background
With the development of engineering construction in China, more and more engineering projects are built on soil bodies with deep covering layers, the situation that a field is located in a high-intensity earthquake area exists, and particularly, hydraulic and hydroelectric engineering in the southwest region, the northwest region and other regions is mostly built on foundations with deep covering layers. So, the antidetonation stability of overburden often becomes the key factor that decides whether the engineering has the feasibility, and the overburden soil body in an area can have the soil layer of the different types along with the difference of degree of depth, and the difference of soil layer type, the precision of its on-the-spot sample also has different differences, has more increaseed the difference of accuracy of indoor test system appearance control relative density.
The dynamic response analysis of the seismic load of the overburden soil body is an important means for researching the seismic stability and the seismic deformation of the overburden, and the sample material of the constitutive model adopted in the test is a prerequisite for evaluating the reliability of the result in the research; at present, an equivalent linear visco-elastic model is mainly adopted to evaluate and determine dynamic reaction under earthquake dynamic load, a soil sample used in a model test is a bulk sample taken on site, and a sample is prepared again according to relative density or relative density control, but due to changes of particle size, gradation, structural property and the like, dynamic characteristic parameters determined by the method often have larger difference with engineering mechanical properties obtained by adopting an original sample or a site in-situ test, and particularly, the influence of the in-situ structural property is more obvious on a deep covering soil body; however, if only the field in-situ test is carried out, the test research under multiple stresses and multiple factors cannot be met, so that the connection relation between the in-situ covering soil and the indoor test needs to be considered, an indoor simulation experiment for preparing a soil sample by using the structural control indexes of the covering soil is established, and the method for forming the dynamic shear modulus parameter of the covering soil is further formed.
Disclosure of Invention
The invention provides a method for determining dynamic shear modulus parameters of a covering soil body based on in-situ relative density, which solves the structural difference between a remolded sample and the covering soil body, considers the dynamic shear modulus parameters and attenuation curves of the original covering soil body with structural determination under an indoor simulation experiment for preparing the remolded sample based on control indexes, and has the following specific technical scheme:
a method for determining dynamic shear modulus parameters of a covering soil mass based on in-situ relative density comprises the following steps:
step one, determining the layered distribution condition and the representative gradation of a covering layer soil body along the depth direction of the covering layer according to an in-situ test;
determining mechanical index characteristic values of different soil layers capable of reflecting the in-situ state of the covering layer according to the soil property characteristics of the different soil layers;
according to the determined representative grading of different soil layers, covering layer soil body materials meeting the representative grading are adopted on site, remolded samples with different relative densities are prepared aiming at different soil layers, the in-situ stress condition of the in-situ soil body is simulated for the remolded samples, an indoor simulation test corresponding to the in-situ test is carried out, the mechanical index characteristic value of the remolded samples under the specific stress condition is determined according to the in-situ stress condition, and then a relation curve of the mechanical index characteristic value of the indoor remolded samples along with the change of the relative density and the consolidation stress is determined;
determining the change relation of the remolded sample mechanical index along with the relative density and stress conditions based on an indoor test;
performing a remodeling sample simulation test indoors, measuring simulation test mechanical index values under different relative densities and different stress conditions, and determining the change relation of the simulation test mechanical index characteristic value along with the relative densities and the stress conditions;
determining the relative density of each layer of soil body of the covering layer soil body based on the covering layer mechanical index characteristic value determined by the field in-situ test and in combination with the change relation of the remolded sample corresponding mechanical index characteristic value determined by the indoor test along with the relative density and the stress condition; the field in-situ test comprises a field shear wave velocity test and a standard penetration test;
step five: adopting a remolded sample determined based on the relative density of the covering soil body to carry out an indoor test, and determining the pressure effect relation of the maximum dynamic shear modulus parameter of the remolded sample and the change relation of the dynamic shear modulus following the dynamic shear strain
Taking the relative density of the covering layer soil body determined in the fourth step as an in-situ remolded sample soil sample control index, developing an indoor dynamic characteristic test of the in-situ remolded sample soil sample under different stress conditions, and determining a pressure effect relation of the maximum dynamic shear modulus and a change relation of the dynamic shear modulus following shear strain;
step six, determining the pressure effect relation of the maximum dynamic shear modulus of the covering soil mass based on the shear wave velocity
Determining the pressure effect relation of the shear wave velocity in the covering soil body according to the change of the field shear wave velocity of the covering soil body along with the depth, and further determining the pressure effect relation of the maximum dynamic shear modulus of the covering soil body by combining an elastic wave theory;
step seven, determining the maximum dynamic shear modulus parameter considering the soil structure
Determining a maximum dynamic shear modulus parameter considering the in-situ structure of the soil body according to the pressure effect relationship of the maximum dynamic shear modulus determined by the indoor test in the step five and the pressure effect relationship of the maximum dynamic shear modulus determined by the field wave speed test in the step six;
step eight, determining a dynamic shear modulus and shear strain attenuation curve considering soil structure
And determining an attenuation curve of the soil body dynamic shear modulus along with the shear strain by considering the in-situ structure effect according to the variation relation between the maximum dynamic shear modulus parameter determined in the seventh step and the dynamic shear modulus along with the shear strain determined in the fifth step.
Further, in the first step, the soil bodies at different depths are subjected to particle grading analysis, the covering soil body is divided into a gravel soil layer, a sand soil layer, a silt soil layer and a cohesive soil layer according to the particle grading analysis result, the large-layer distribution condition of the covering soil body is determined, and a particle grading curve of each large layer is obtained; and further distinguishing sub-layers in the large layers according to the grain grading analysis result of the large layers, determining the final soil body layering condition, and drawing a representative grading curve of the deep and thick covering layer.
Further, soil bodies in the same large layer and different depths are further classified, soil bodies at different depth positions are classified and named according to relevant regulations in GB 50021-plus 2009 geotechnical engineering investigation Specification, soil body classification conditions of the soil bodies of all drill holes along the depth direction are analyzed, and sub-layers are created; or according to the relevant regulations in GB50021-2009 geotechnical engineering survey regulations, dividing the main component particles with the content of more than 50 percent in the same large layer into coarse, medium and fine particles according to the particle size range to determine whether the soil bodies of different drill holes and different depths are in the same category; the soil bodies with the thickness not less than 1m, which are named as the same kind and appear in different drill holes, are divided into the same sub-layer, and the soil bodies which appear in individual drill holes and do not appear in other drill holes can not be considered as the sub-layers.
Further, the medium wave velocity test in the third step can be completed by utilizing an indoor shear wave velocity testing device in a pressure chamber of a resonance column, a triaxial apparatus or a torsional shear apparatus; the remolded sample is subjected to relative density grading preparation and grading loading, and the shear wave velocity under different grades of relative density and stress is measured and represented by a graph, a table or a formula.
Further, the maximum dynamic shear modulus G in the fifth stepmaxThe pressure effect relationship of (a) is shown in formula (1):
Gmax＝Cpa.(σ′0/pa)n(1)
in the formula: sigma'0Is the mean effective consolidation stress, σ'0＝(σ′10+σ′30)/2，σ′10Is axial effective stress, σ'30For laterally effective consolidation stress, paIs standard atmospheric pressure, unit and GmaxAnd σ'0Similarly, C, n are modulus index and modulus index, respectively, determined by experimentation.
Further, the pressure effect relation of the maximum dynamic shear modulus of the covering soil body in the sixth step can be obtained through the following steps of 1) shearing wave velocity VsTo atmospheric pressure paAs shown in equation (2)
VS＝a·(σ′0/pa)b(2)
In the formula: a. b is a fitting parameterNumber (σ'0/pa) Average effective principal stress for non-dimensionalization;
2) maximum dynamic shear modulus G according to elastic wave theorymaxAnd the shear wave velocity is as shown in formula (3)
Gmax＝ρ·Vs 2(3)
In the formula: rho is the natural density of the soil layer, VSIs the shear wave velocity;
3) substituting the formula (2) into the formula (3) to obtain the maximum dynamic shear modulus GmaxPressure effect relationship of (4)
Gmax＝ρ·a2·(σ′0/pa)2b(4)
Further, in the seventh step, the modulus coefficient C and the modulus index n are determined through experiments, that is, by comparing the indoor test value and the field test value measured by the formula (1) and the formula (4), the dynamic shear modulus coefficient C and the modulus index n based on the field shear wave velocity test can be obtained.
Further, in step eight, the attenuation curve of the dynamic shear modulus of the soil body along with the shear strain is determined by considering the in-situ structure effect, as shown in the formula (5):
G＝Gmax/(1+γ/γr) (5)
in the formula: g is the dynamic shear modulus under a certain dynamic shear strain, GmaxIs maximum dynamic shear modulus, gamma is dynamic shear strain, gammarIs a reference shear strain;
wherein the reference shear strain gammaγAs shown in equation (6)
γγ＝τmax/Gmax(6)
In the formula: tau ismaxThe maximum shear stress can be obtained by calculation according to the stress condition and the Mohr-Coulomb failure theory;
the above-mentioned taumaxThe method comprises the following steps of:
in the case of in situ overburden earth conditions, taumaxAs shown in equation (7)
In the formula: k0In order to obtain the coefficient of the pressure at the static side,
σ′vvertical effective stress; c'
Static effective stress intensity parameters;
tau in the stress state of the indoor resonance column testmaxAs shown in equation (8)
In the formula: k0Is the lateral pressure coefficient, K0＝σ′30/σ′10。
Further, the maximum dynamic shear modulus GmaxBased on the hyperbolic assumptions of the Hardin-Drnevich model, and determined in combination with the field shear wave velocity test and the indoor wave velocity test.
The invention has the following beneficial effects:
the method for determining the dynamic shear modulus parameter of the covering soil body based on the in-situ relative density can combine the advantages of taking the in-situ structure effect and indoor tests into consideration to control various stress conditions; the method for determining the in-situ relative density of the soil body of the deep covering layer by considering the soil layer types combines an in-situ test capable of better reflecting the in-situ relative density of the covering layer non-cohesive soil body and an indoor test capable of controlling different relative densities and different consolidation stress conditions, obtains the relative density of each layer of the soil body of the in-situ soil layer through the in-situ test and the indoor test, is used for calibrating and controlling the in-laboratory remolded sample, and ensures the consistency of the remolded sample and the original soil mechanical property.
In the process of analyzing the characteristics of the soil body without the adhesive covering layer, the invention combines relevant specifications and experiences to classify and divide the distribution condition of the soil body in detail, accurately masters the distribution condition of the soil body of the covering layer, accurately and reasonably restores the distribution condition of the actual covering layer in an indoor test, enables the remolded sample to be closer to the actual condition on the premise of economy and reasonability, improves the accuracy and precision of the test, combines the pressure effect relationship of the maximum dynamic shear modulus measured by an in-situ test and the pressure effect relationship of the dynamic shear modulus measured by the remolded sample of the laboratory covering layer, determines the parameter for representing the dynamic shear modulus of the soil body of the covering layer, can better reflect the actual condition of the soil body covering layer, provides a basis for the anti-seismic safety evaluation of the deep foundation covering layer, and improves the accuracy and precision of the safety evaluation.
Drawings
FIG. 1 is an upper and lower level of sand layer in situ in the embodiment, and the upper and lower level of sand layer are provided with a coating line and an average line;
FIG. 2 is the upper and lower level of gravel layer and the average line in the embodiment;
FIG. 3 is a graph showing the variation of the measured standard penetration number of a fine sand layer in gravel with depth according to the example;
FIG. 4 is a graph showing a normalized penetration hammering number distribution of a fine sand layer in gravel according to an example;
FIG. 5 is a graph showing the measured shear wave velocity versus depth for a gravel layer of sand eggs in the example;
FIG. 6 is a graph of shear wave velocity versus depth for an example of an embodiment in which the gravel layer is calibrated to 100 kPa;
FIG. 7 is a graph of relative density of the laboratory remolded samples as a function of standard penetration hammer at 100kPa for the examples;
FIG. 8 is a graph of relative density of remodelled samples from the laboratory test in the examples as a function of shear wave velocity at 100 kPa.
FIG. 9 is a graph of the pressure effect of the maximum dynamic shear modulus determined by laboratory tests;
FIG. 10 is a graph of dynamic shear modulus versus dynamic shear strain variation obtained from laboratory tests;
FIG. 11 is a graph of the pressure effect of the in situ shear wave velocity of the overburden body;
FIG. 12 is a pressure effect relationship graph of the maximum dynamic shear modulus determined by the in-situ wave velocity test of the overburden soil;
FIG. 13 shows G obtained by field and laboratory tests on the overburdenmax/pa～σ′0/paA comparison graph of the relation curves;
FIG. 14 is a plot of overburden G/G field testsmax～γ/γγRelation curve and indoor/Gmax～γ/γγThe relationship curves are compared with the graph.
Detailed Description
Taking a large earth-rock dam project as an example, the project is planned to be built on an ultra-deep covering layer with a thickness and is located in a high seismic intensity area, and the method for determining the dynamic shear modulus parameter of the covering layer soil mass based on the in-situ relative density is explained in detail according to the project.
The dam site area has 100-year exceeding probability of 2% base rock horizontal peak acceleration of over 0.5g, and drilling reveals that the material composition and the hierarchical structure of a riverbed covering layer are complex, and a sandy soil layer with larger thickness is buried in the covering layer and is mixed with medium and fine sand layer lenticules. The sand layer has the characteristics of low natural density, low bearing capacity and low compressibility, and may be liquefied under the action of a designed earthquake.
The dynamic shear modulus parameter of the soil body of the deep and thick covering layer is determined by taking the actual deep and thick covering layer deep-buried sandy soil as a research object and combining a field in-situ test and an indoor simulation test, and the specific steps are as follows.
Step one, determining the layered distribution condition of the covering layer soil body along the depth direction of the covering layer and the representative gradation thereof according to a drilling exploration test
The method specifically comprises the following steps:
(1.1) carrying out particle grading analysis on soil layers at different depths according to a drilling exploration test;
according to the geological survey specification of the hydroelectric power engineering (GB 50487-2008), an exploration profile is determined by combining different engineering survey stages or specific survey purposes and the complexity of geological conditions, drill holes are arranged on an exploration profile line, and the depth of the drill holes of the riverbed is determined according to different engineering survey stages.
During borehole exploration, screening the non-cohesive soil obtained by drilling and carrying out particle grading analysis.
According to geological survey specifications of hydroelectric power engineering (GB 50487) 2008), for dam site exploration arrangement, at least 1 survey profile is required, at least 3 drill holes are required on a survey profile line, and at least 1 drill hole is required at a riverbed part; the drilling depth of the riverbed is preferably 50 to 100 percent of the height of the dam.
In the embodiment, the project is in a planning stage and is a controlled project, 13 drill holes are drilled in the riverbed range, soil samples are screened every 1-2m in the drilling process of each drill hole, and the soil body at the corresponding depth is subjected to grain composition analysis.
(1.2) dividing the covering soil into a gravel soil layer, a sand soil layer, a silt soil layer and a cohesive soil layer according to the grain composition analysis result, determining the large-layer distribution condition of the covering soil layer, and obtaining a grain composition curve of each large layer;
for most dam body soil materials, one or more of a gravel soil layer, a sand soil layer, a silt soil layer or a cohesive soil layer is included, and in the embodiment, the three types of soil layers, namely the gravel soil layer, the sand soil layer and the cohesive soil layer, are included.
(1.3) further distinguishing sub-layers in each large layer according to the grain composition analysis result of each large layer;
the determination method of the sublayer is specifically as follows:
(1.3.1) classifying and naming the soil bodies at different depth positions according to relevant regulations in GB50021-2009 geotechnical engineering investigation Specification;
(1.3.2) analyzing the soil body name assignment condition of each drilling soil body along the depth direction, and creating a sublayer;
establishing a sublayer standard, wherein the grain size of main components with the content of more than 50 percent in the grain composition analysis of the soil layer belongs to the same category according to the relevant regulations in GB50021-2009 geotechnical engineering survey Specification; for the soil bodies of the same category which are present in different drill holes and have the thickness of not less than 1m, the soil bodies are preferably divided into sub-layers, and for the soil bodies which are present in individual drill holes and are not present in other drill holes, the sub-layers are not considered.
(1.4) determining the final soil layering condition, and drawing a representative grading curve of the deep and thick covering layer;
in this embodiment, the determined soil layering conditions are shown in table 1, the determined upper and lower level distribution lines and average lines (i.e., representative grading curves) of the in-situ sandy soil layer on site are shown in fig. 1, and the upper and lower level distribution lines and average lines of the gravel soil layer are shown in fig. 2.
TABLE 1 layering of overburden
Step two, carrying out in-situ test on site according to the soil property characteristics of different soil layers to determine the mechanical index characteristic values of different soil layers capable of reflecting the in-situ state of the covering layer
The field in-situ test comprises a wave velocity test, a standard penetration test, a static sounding test, a large-scale penetration test and the like, different field tests are selected according to the characteristics of the covering layer soil body, when the covering layer soil body is sandy soil, the wave velocity test, the static sounding test or the standard penetration test is adopted, and when the covering layer soil body is sandy gravel, the wave velocity test or the large-scale penetration test is adopted.
In this embodiment, the clay layer is in the range of 0-6.0m, and the in-situ relative density can be determined by taking an original sample, which is not in the scope of the present invention.
In this embodiment, 6.0-28.2m is a sand layer comprising two sub-layers of (i) a-1 gravel-containing medium fine sand layer and (ii) a-2 gravel-containing medium coarse sand layer, the distribution depth ranges are 6.0-26.3m and 26.3-28.2 m, respectively, and a standard penetration test is selected to determine the standard penetration hammering number (N) of each sub-layer1)60。
Performing an on-site standard penetration test according to the standard, performing standard penetration tests at different depth positions in the covering sand layer, and determining the corresponding actually-measured standard penetration number under the overlying effective stress of the test; three drill holes are arranged in a sand layer, field standard penetration test tests under different depths and overlying effective stress are carried out, 27 test points are tested, the test depth ranges are 6.0-26.3m and 26.3-28.2 m, the overlying effective stress range is 60 kPa-260 kPa, and the test result is shown in figure 3.
The specific test method is as follows:
drilling a test deep-buried saturated sandy soil layer to a position 15cm above the elevation of the test soil layer by using a conventional drilling tool, removing residual soil in the hole, and performing wall protection as required; before injection, connecting a standard injection test device, screwing a drill rod joint, putting an injector into a hole to the bottom of the hole, avoiding impacting the bottom of the hole, measuring the depth of the drilled hole, and paying attention to keeping the verticality after the injector, the drill rod and the guide rod are connected; and during penetration, a 63.5kg through-center hammer is adopted, an automatic drop hammer method is adopted at a free drop distance of 76cm, the penetrating device is impacted into the soil for 15cm at a speed of 15-30 min, and then the hammering number of each penetrating device for 10cm is recorded, so that the accumulated hammering number of 30cm, namely the standard penetrating hammering N, is obtained.
Considering the influence of the overlying effective stress, correcting the actually measured standard penetration hammering number N to be under the stress condition of 100kPa by using a formula (1), and normalizing to obtain the standard penetration hammering number (N)1)60；
In the formula, N is the actually measured standard penetration hammering number; p is a radical ofaIs at atmospheric pressure; sigma'ν0Is the overlying effective stress during the drilling test.
In this example, the variation curve of the normalized standard penetration hammering number with depth of the gravel-containing medium fine sand layer with the depth of 6m to 26.3m is shown in fig. 4, and the average value of the normalized standard penetration hammering number is 17.1 shots; the average value of the normalized standard penetration hammering number of the coarse sand layer in the gravel with the depth of 26.3m to 28.2m is 18.6 strokes.
In addition, in the actual construction process, because the 2-layer is deposited on the lower part of the 1-layer, the particles are slightly thicker than the 1-layer, the thickness is thinner, and the distribution is discontinuous, when the model is generalized, the 2-layer and the 1-layer can be regarded as one layer for consideration, and the method is also feasible from the aspect of engineering safety.
In this example, a sand gravel layer is present within a range of 28.2 to 42.3m, and a wave velocity test is selected to determine the shear wave velocity characteristic value of the overburden soil
The method is characterized in that a field wave velocity test is carried out on a covering soil body, and the specific test steps are as follows:
a) arranging a measuring hole: drilling 3 vertical and parallel drill holes in a soil body of a test covering layer, wherein one drill hole is an excitation hole, the other two drill holes are receiving holes, and the hole distance is preferably 2-5 m;
b) arranging measuring points in the holes: the vertical distance between the measuring points is 1-2m, the measuring points near the surface are preferably arranged at the depth of 0.4 times of the hole distance, and the seismic source and the detector are arranged at the same elevation of the same stratum; when the test depth is more than 15m, all test holes must be tested for inclination and inclined orientation, and the test point spacing should not be more than 1 m.
c) Test: firstly, the exciter and the receiver are respectively put into the two holes at the same time to reach the preset measured elevation and fixed. Debugging the instrument to normal working state. Driving the hammer exciter to check whether the received signal is normal, and storing if the received signal is normal. The travel time of the shear wave in the earth is calculated from the received signals. Fourthly, preliminarily checking and calculating the shear wave velocity value, checking whether the shear wave velocity value is within a reasonable range, and if all the shear wave velocity value is normal, testing the next measuring point.
d) And according to the test data, calculating the in-situ shear wave velocity of the overburden soil according to a cross-hole method in foundation dynamic characteristic test specification (GBT 50269-1997).
According to the field wave velocity test procedure, the shear wave velocity is normalized to 100kPa standard stress condition by adopting a formula (2), and the value can be the shear wave velocity V of the gravel-containing medium-coarse sand layer of the covering layerS1The characteristic value of (2).
In the formula: vS1Correcting to the shear wave speed under the stress condition of 100 kPa; vSIs the shear wave velocity; paIs at atmospheric pressure; sigma'ν0Overlying the effective stress.
In this embodiment, the variation curve of the measured shear wave velocity with the depthThe line is shown in FIG. 5, corrected to 100kPa and the shear wave velocity VS1The curve with depth is shown in FIG. 6, and the average value is 230.2 m/s.
Thirdly, determining the change relation of the mechanical index of the remolded sample with the relative density and the stress condition based on an indoor test;
and (3) performing a remodeling sample simulation test indoors, namely performing a simulation test corresponding to the field test selected in the step one under different influence factors, different relative densities and consolidation stress conditions, measuring simulation test mechanical index values under different relative densities and different stress conditions, and determining the change relation of the simulation test mechanical index characteristic value with the relative densities and the stress conditions.
In this example, the standard penetration hammering number and shear wave velocity of different remolded samples under different influence factors, different relative densities and consolidation stress conditions were determined based on an indoor remolding sample simulation test.
The method comprises the steps of adopting determined representative gradation of different soil layers, adopting covering layer soil body materials meeting the representative gradation on site, respectively carrying out relative density tests on a sand soil sample and sand gravel materials in a test room, preparing remolded samples with different relative densities on the basis, simulating in-situ stress conditions of the soil body on the site for the remolded samples, carrying out an indoor simulation test corresponding to the in-situ test, accordingly determining the mechanical index characteristic value of the remolded samples under specific stress conditions, and drawing a relation curve of the mechanical index characteristic value of the indoor remolded samples along with the change of the relative density and the consolidation stress.
In this embodiment, in-situ stress conditions of a field soil body are simulated, an indoor standard penetration test and a wave velocity test are respectively performed, a change relation curve of the relative density of a remolded sample along with the standard penetration hammering number under 100kPa is obtained as shown in fig. 7, and a fitting formula (3) is obtained at the same time; the curve of the variation of the relative density of the remolded sample with the shear wave speed under 100kPa is shown in FIG. 8, and a fitting formula (4) is obtained;
Dr＝1.64.07×((N1)60)0.4799(3)
in the formula: (N)1)60The number of the standard penetration hammering is determined; drFor remodeling a sampleRelative density,%;
Dr＝0.4377Vs1-29.762 (4)
in the formula: drRelative density for remodeled samples,%; vs1To correct for shear wave velocity under 100kPa stress conditions.
Step four, determining the relative density of each layer of soil body based on the mechanical index characteristic value of the covering layer determined by the field in-situ test and the change relation curve of the corresponding mechanical index characteristic value of the remolded sample determined by the indoor test along with the relative density and the stress condition
And determining the relative density corresponding to the indoor simulation test value corresponding to the overburden mechanics index characteristic value according to the overburden mechanics index characteristic value determined by the field test as an indoor simulation test value and combining the change relation of the indoor simulation test mechanics index value along with the relative density and the stress condition, wherein the relative density is the field relative density of the overburden non-sticky soil body.
In this embodiment, based on the mechanical index characteristic value (average value of penetration hammer number of 17.1 hits under 100 kPa) of the overburden sand determined by the field test, and in combination with the change relationship of the relative density determined by the indoor test with the standard penetration hammer number of 100kPa, the relative density of the fine sand layer in the gravel is determined to be 0.64 and the relative density of the coarse sand layer in the gravel is determined to be 0.67 by looking up fig. 7 or calculating according to the fitting formula (3).
In this example, the relative density of the gravel layer of sand eggs was determined to be 0.71 by looking up fig. 8 or calculating according to the fitting formula (4) in combination with the shear wave velocity characteristic value of the gravel layer of sand eggs determined by the field test (the shear wave velocity at 100kPa is 230.2m/s) and the relative density determined by the indoor test as a function of the shear wave velocity at 100 kPa.
Step five, determining the pressure effect relation of the maximum dynamic shear modulus parameter of the remolded sample based on the relative density of the covering soil body and the change relation of the dynamic shear modulus following shear strain by adopting an indoor test
Adopting the relative density determined in the fourth step as a remolded sample preparation control index to prepare an indoor remolded sample, carrying out indoor dynamic characteristic tests under different consolidation stress conditions, and determining the pressure effect of the maximum dynamic shear modulusThe relation and the change relation of the dynamic shear modulus with the dynamic shear strain; the test results show that the maximum dynamic shear modulus GmaxAnd mean effective principal stress σ'0The relationship is approximated as a straight line on a log-log coordinate, as shown in fig. 9, and is fitted to a power function form of equation (5):
Gmax＝Cpa.(σ′0/pa)n(5)
in the formula: sigma'0Is the mean effective consolidation stress, σ'0＝(σ′10+σ′30)/2，σ′10Is axial effective stress, σ'30For laterally effective consolidation stress, paIs standard atmospheric pressure, unit and GmaxAnd σ'0Similarly, C, n are modulus index and modulus index, respectively.
FIG. 10 shows the dynamic shear modulus ratio with the change of the dynamic shear strain, consolidation stress with G/G, obtained from the laboratory testmaxThe gamma curve has certain influence, and the attenuation amplitude of the dynamic shear modulus gradually becomes smaller along with the increase of the average effective stress borne by the soil body. Under the same consolidation ratio, the larger the confining pressure is, the slower the speed of the increase and attenuation of the modulus follow-up shear strain is; the greater the consolidation ratio, the slower the rate at which the increase in modulus-following shear strain decays at the same confining pressure.
Step six, determining the pressure effect relation of the maximum dynamic shear modulus of the covering soil mass based on the shear wave velocity
According to the field shear wave velocity test result of the soil body of the covering layer, the shear wave velocity V of coarse sand in gravel contained in the covering layersAccording to mean effective stress sigma'0The pressure effect relationship of the shear wave velocity is expressed by the formula (6). FIG. 11 shows the shear wave velocity VSAnd passing through the atmospheric pressure paDimensionless mean effective principal stress (σ'0/pa) The fitting relationship of (1).
VS＝a·(σ′0/pa)b(6)
In the formula: a. b is a fitting parameter; wherein a is 309.03 and b is 0.1461.
According to the elastic wave theory, the relationship between the maximum dynamic shear modulus and the shear wave velocity is shown in the formula (7)
Gmax＝ρ·Vs 2(7)
In the formula: rho is the natural density of the soil layer, VSIs the shear wave velocity;
substituting formula (6) into formula (7) results in formula (8)
Gmax＝ρ·a2·(σ′0/pa)2b(8)
Step seven, determining the maximum dynamic shear modulus parameter considering the soil structure
Determining a maximum dynamic shear modulus parameter considering the in-situ structure of the soil body according to the pressure effect relationship of the maximum dynamic shear modulus determined by the indoor test determined in the step five and the pressure effect relationship of the maximum dynamic shear modulus determined by the field wave speed test in the step six;
the maximum dynamic shear modulus G is obtained by adopting an indoor resonance column testmaxAnd mean effective principal stress σ'0Satisfies the power function relationship as shown in formula (5). Therefore, comparing the formula (8) with the formula (5), the dynamic shear modulus coefficient C and the index n obtained according to the shear wave velocity test can be obtained (see table 2). G determined by combining the in-situ wave velocity test (as shown in FIG. 12) and the resonant column testmax/pa～σ′0/paThe relation and the comparison relation are shown in figure 13, and the maximum dynamic shear modulus G determined by considering the in-situ structure effect is within the actual stress range of the sand field with the deep covering layermaxThe test value is obviously greater than that of an indoor resonance column test, and the deep overburden layer deep buried sandy soil layer has a more obvious in-situ structure effect.
TABLE 2 values of dynamic shear modulus coefficient C and index n
Step eight, determining a dynamic shear modulus and shear strain attenuation curve considering soil structure
According to the maximum dynamic shear modulus parameter determined in the seventh step and the dynamic shear determined in the fifth stepAnd obtaining the attenuation curve of the modulus of the soil body determined along with the shear strain by considering the in-situ structure effect according to the change relation of the modulus along with the shear strain. Using the Hardin-Drnevich model, the dynamic shear stress tau of the soil was assumeddAnd dynamic shear strain gammadThe vertex trajectory (skeleton curve) is a hyperbola, and the dynamic shear modulus G is shown in formula (9):
G＝Gmax/(1+γ/γr) (9)
in the formula: g is the dynamic shear modulus under a certain dynamic shear strain, GmaxIs maximum dynamic shear modulus, gamma is dynamic shear strain, gammarIs a reference shear strain;
the resonance column test shows that the dynamic shear modulus ratio G/G under different confining pressures and consolidation ratiosmaxThe attenuation curve with shear strain and the growth curve with shear strain gamma can adopt the reference shear strain gammaγAre respectively roughly normalized to a G/Gmax～γ/γγCurve, wherein the shear strain γ is referencedγAs shown in equation (10):
γγ＝τmax/Gmax(10)
in the formula: tau ismaxThe maximum shear stress can be obtained by calculation according to the stress condition and the Mohr-Coulomb failure theory; tau ismaxThe method comprises the following steps of:
in the case of in situ overburden earth conditions, taumaxAs shown in formula (11):
in the formula: k0In order to obtain the coefficient of the pressure at the static side,
σ′vvertical effective stress; c'
Static effective stress intensity parameters;
tau in the stress state of the indoor resonance column testmaxAs shown in equation (12)：
In the formula: k0Is the lateral pressure coefficient, K0＝σ′30/σ′10。
Using reference shear strain gammaγPair G/GmaxG/G obtained after normalization of gamma curvemax～γ/γγA relationship curve, as shown in FIG. 14; as can be seen from FIG. 14, the G/G obtained by combining the hyperbolic assumption of the backbone curve of the Hardin-Drnevich modelmax～γ/γγThe normalized curve is slightly higher than the corresponding curve of the indoor test, which has certain influence on the dynamic deformation characteristic curve by the consolidation time (reflecting the structure) in the prior research, G/Gmax～γ/γγThe curves are slightly shifted to the right with increasing consolidation time.
Therefore, the maximum dynamic shear modulus G determined by considering the in-situ structure effect of the covering soil layer is adoptedmaxG/G obtained by hyperbolic assumption of skeleton curve of Hardin-Drnevich modelmax～γ/γγThe normalization curve is slightly influenced by the particle size, grading and structure, and can be used for representing the attenuation relation of the in-situ covering layer soil dynamic shear modulus G follow-up shear strain gamma more closely; the shear wave velocity is the comprehensive reflection of the property of the soil body under small strain, the relative density of the covering soil layer can be determined by combining an indoor remolding test, and the maximum dynamic shear modulus G is comprehensively determined by a field wave velocity test and an indoor resonance column testmaxDynamic shear modulus coefficient C and index n, and further determining normalized G/Gmax～γ/γγThe curve is obtained, so that the structural property of the original covering soil body is more effectively considered.
It is to be understood that the foregoing examples are illustrative only for the purpose of clearly illustrating the salient features of the present invention, and are not to be construed as limiting the embodiments of the present invention; it will be apparent to those skilled in the art that other variations and modifications may be made in the foregoing disclosure without the use of inventive changes thereto, all falling within the scope of the present invention.
Claims (7)
1. A method for determining dynamic shear modulus parameters of a covering soil body based on in-situ relative density is characterized by comprising the following steps:
step one, determining the layered distribution condition and the representative gradation of a covering layer soil body along the depth direction of the covering layer according to an in-situ test;
performing particle grading analysis on soil bodies at different depths, dividing the covering soil body into a gravel soil layer, a sand soil layer, a silt soil layer and a cohesive soil layer according to the particle grading analysis result, determining the large-layer distribution condition of the covering soil body, and obtaining a particle grading curve of each large layer; according to the grain composition analysis result of each large layer, further distinguishing sub-layers in each large layer, determining the final soil body layering condition, and drawing a representative grading curve of the deep and thick covering layer;
determining mechanical index characteristic values of different soil layers capable of reflecting the in-situ state of the covering layer according to the soil property characteristics of the different soil layers;
according to the determined representative grading of different soil layers, covering layer soil body materials meeting the representative grading are adopted on site, remolded samples with different relative densities are prepared aiming at different soil layers, the in-situ stress condition of the in-situ soil body is simulated for the remolded samples, an indoor simulation test corresponding to the in-situ test is carried out, the mechanical index characteristic value of the remolded samples under the specific stress condition is determined according to the in-situ stress condition, and then a relation curve of the mechanical index characteristic value of the indoor remolded samples along with the change of the relative density and the consolidation stress is determined;
determining the change relation of the remolded sample mechanical index along with the relative density and stress conditions based on an indoor test;
performing a remodeling sample simulation test indoors, measuring simulation test mechanical index values under different relative densities and different stress conditions, and determining the change relation of the simulation test mechanical index characteristic value along with the relative densities and the stress conditions;
an indoor wave velocity test is completed by utilizing an indoor shear wave velocity testing device in a pressure chamber of a resonance column, a triaxial apparatus or a torsional shear apparatus; carrying out relative density grading preparation and grading loading on the remolded sample, measuring the shear wave velocity under different grades of relative density and stress, and expressing by using a graph, a table or a formula;
determining the relative density of each layer of soil body of the covering layer soil body based on the covering layer mechanical index characteristic value determined by the field in-situ test and in combination with the change relation of the remolded sample corresponding mechanical index characteristic value determined by the indoor test along with the relative density and the stress condition; the field in-situ test comprises a field shear wave velocity test and a standard penetration test;
step five: performing an indoor test by adopting a remolded sample determined based on the relative density of the covering soil body, and determining the pressure effect relation of the maximum dynamic shear modulus parameter of the remolded sample and the change relation of the dynamic shear modulus follow-up shear strain;
taking the relative density of the covering layer soil body determined in the fourth step as an in-situ remolded sample soil sample control index, developing an indoor dynamic characteristic test of the in-situ remolded sample soil sample under different stress conditions, and determining a pressure effect relation of the maximum dynamic shear modulus and a change relation of the dynamic shear modulus following shear strain;
determining the pressure effect relation of the maximum dynamic shear modulus of the covering soil body based on the shear wave velocity;
determining the pressure effect relation of the shear wave velocity in the covering soil body according to the change of the field shear wave velocity of the covering soil body along with the depth, and further determining the pressure effect relation of the maximum dynamic shear modulus of the covering soil body by combining an elastic wave theory;
determining a maximum dynamic shear modulus parameter considering soil structure;
determining a maximum dynamic shear modulus parameter considering the in-situ structure of the soil body according to the pressure effect relationship of the maximum dynamic shear modulus determined by the indoor test in the step five and the pressure effect relationship of the maximum dynamic shear modulus determined by the field wave speed test in the step six;
step eight, determining a dynamic shear modulus and shear strain attenuation curve considering soil structure;
and determining an attenuation curve of the soil body dynamic shear modulus along with the shear strain by considering the in-situ structure effect according to the variation relation between the maximum dynamic shear modulus parameter determined in the seventh step and the dynamic shear modulus along with the shear strain determined in the fifth step.
2. The method for determining the dynamic shear modulus of the overburden mass based on the in-situ relative density as recited in claim 1, wherein: further classifying soil bodies in the same large layer and at different depths, classifying and naming the soil bodies at the positions at different depths according to relevant regulations in GB50021-2009 geotechnical engineering investigation Specification, analyzing soil body classification conditions of the soil bodies of all drill holes along the depth direction, and creating sub-layers; or according to related regulations in GB50021-2009 geotechnical engineering survey Specification, dividing main component particles with content of more than 50% in the same large layer into coarse, medium and fine particles according to particle size range to determine whether soil bodies of different drill holes and different depths are in the same category; the soil bodies with the thickness not less than 1m, which are named as the same kind and appear in different drill holes, are divided into the same sub-layer, and the soil bodies which appear in individual drill holes and do not appear in other drill holes are not considered as the sub-layers.
3. The method for determining the dynamic shear modulus of the overburden mass based on the in-situ relative density as recited in claim 1, wherein: maximum dynamic shear modulus G in step fivemaxThe pressure effect relationship of (a) is shown in formula (1):
Gmax＝Cpa.(σ′0/pa)n(1)
in the formula: sigma'0Is the mean effective consolidation stress, σ'0＝(σ′10+σ′30)/2，σ′10Is axial effective stress, σ'30For laterally effective consolidation stress, paIs standard atmospheric pressure, unit and GmaxAnd σ'0Similarly, C, n are modulus index and modulus index, respectively, determined by experimentation.
4. The method for determining the dynamic shear modulus of the overburden mass based on the in-situ relative density as recited in claim 1, wherein: in the sixth step, the pressure effect relation of the maximum dynamic shear modulus of the covering soil body is obtained through the following steps,
1) shear wave velocity VsTo atmospheric pressure paAs shown in equation (2)
VS＝a·(σ′0/pa)b(2)
In the formula: a. b is a fitting parameter, (σ'0/pa) Average effective principal stress for non-dimensionalization;
2) maximum dynamic shear modulus G according to elastic wave theorymaxAnd the shear wave velocity is as shown in formula (3)
Gmax＝ρ·Vs 2(3)
In the formula: rho is the natural density of the soil layer, VSIs the shear wave velocity;
3) substituting the formula (2) into the formula (3) to obtain the maximum dynamic shear modulus GmaxPressure effect relationship of (4)
Gmax＝ρ·a2·(σ′0/pa)2b(4)。
5. The method for determining the dynamic shear modulus of the overburden mass based on the in-situ relative density as recited in claim 3 or 4, wherein: and in the seventh step, the modulus coefficient C and the modulus index n are determined by tests, namely the dynamic shear modulus coefficient C and the modulus index n based on the field shear wave velocity test are obtained by comparing the indoor test value and the field test value measured by the formula (1) and the formula (4).
6. The method for determining the dynamic shear modulus of the overburden mass based on the in-situ relative density as recited in claim 1, wherein: and step eight, determining an attenuation curve of the dynamic shear modulus of the soil body along with the shear strain by considering the in-situ structure effect, wherein the attenuation curve is shown in a formula (5):
G＝Gmax/(1+γ/γr) (5)
in the formula: g is the dynamic shear modulus under a certain dynamic shear strain, GmaxIs maximum dynamic shear modulus, gamma is dynamic shear strain, gammarIs a reference shear strain;
wherein the reference shear strain gammaγAs shown in equation (6)
γγ＝τmax/Gmax(6)
In the formula: tau ismaxThe maximum shear stress is obtained by calculation according to a Mohr-Coulomb failure theory according to the stress condition;
the above-mentioned taumaxThe method comprises the following steps of:
in the case of in situ overburden earth conditions, taumaxAs shown in equation (7)
In the formula: k0In order to obtain the coefficient of the pressure at the static side,
σ′vvertical effective stress; c'
Static effective stress intensity parameters;
tau in the stress state of the indoor resonance column testmaxAs shown in equation (8)
In the formula: k0Is the lateral pressure coefficient, K0＝σ′30/σ′10。
7. The method for determining the dynamic shear modulus of the overburden mass based on the in-situ relative density as recited in claim 6, wherein: the maximum dynamic shear modulus GmaxThe hyperbolic assumption based on the Hardin-Dmevich mode is determined by combining a field shear wave velocity test and an indoor wave velocity test.
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