CN106525978A - Method for calculating structural disturbance degree of soft soil by utilizing changes of shear modulus - Google Patents

Abstract

The invention discloses a method for calculating a structural disturbance degree of soft soil by utilizing changes of shear modulus. The method comprises the following steps: before sampling, carrying out field in-situ shear wave velocity testing to obtain an in-situ shear wave velocity; taking soil samples with different depths and marking; testing the obtained soil samples with different depths by utilizing a bending element shear wave velocity testing device respectively after stress of the soil samples is released and the soil samples are remolded so as to obtain a shear wave velocity under a stress-free state after sampling disturbance and a shear wave velocity after a soil body is remolded; calculating average effective stress and overlying effective stress of the soil body before sampling; and calculating to obtain the structural disturbance degree of the soil body, caused by sampling of each depth. The method disclosed by the invention is simple in testing step and accurate in testing result; and two influence factors including soil body structural disturbance (unrecoverable disturbance) and stress state changes (recoverable disturbance) in a sampling process are separated so that the structural disturbance degree of the soil body, caused by the sampling process, can be calculated in field and indoors respectively.

Description

A kind of method of utilization modulus of shearing change calculations Structure of Soft Clay disturbance degree

Technical field

The present invention relates to soil disturbance computational methods, and in particular to a kind of utilization modulus of shearing change calculations structure of soft clay The method of property disturbance degree.

Background technology

At present soil body physico-mechanical properties is evaluated and mainly pass through test in situ and laboratory test two parts.It is indoor Test have the advantages that it is economical, flexible and easily controllable, but in existing sampling process, although have passed through Enter, still inevitably cause disturbance to the soil body.In order to reduce impact of the sampling disturbance to laboratory test results, accurately test Soil body physical mechanical property index, in addition to improving sampling equipment and improving technical level and reduce disturbance as far as possible, should also set up and take Quantitative Evaluation System of the sample to the structural disturbance degree of soil sample.Drill hole sampling causes soil sample disturbance to can be divided mainly into Stress Release and soil The structural disturbance two parts of body, the disturbance that the former causes can recover, and the latter is irrecoverable.Existing sampling disturbance computational methods master The longer and if undesirable chance for easily missing again sub-sampling of result is taken based on indoor consolidation test, test.Also have logical The method that shear wave velocity is metrics evaluation sampling disturbance is crossed, this method can be sampled Disturbance evaluation at the scene, with lossless Detection and time-consuming short advantage.But it may be noted that shear wave velocity concentrated expression stress level and structural, not and structural perturbation Direct correlation, fails to distinguish Stress Release and Soil Body disturbance.Can be made by all kinds of experimental rigs in laboratory test Soil sample sets back stress state level to eliminate impact of the Stress Release factor to laboratory test results, and during bury sampling The structural disturbance for causing then causes soil body grain structure to damage, and cannot recover when testing indoors.In sum, survey in ground The field of examining lacks a set of quantitative calculation method for causing Soil Body disturbance to sampling process and measuring technology.

The content of the invention

The purpose of the present invention be for existing method calculate sampling process caused by Soil Body disturbance degree deficiency it A kind of place, there is provided method of utilization modulus of shearing change calculations Structure of Soft Clay disturbance degree, so as to realize using stress normalizing Small-strain shear modulus index after change calculates Soil Body disturbance degree caused by sampling process.Soil small strain modulus of shearing It is a physical quantity of comprehensive characterization Soil Body and stress level state, with Non-Destructive Testing and indoor and scene association in situ With the outstanding advantage of test.The principal element for affecting small-strain shear modulus is effective stress and Soil Microstructure (particle Contact number, directionality and contact form), the stress level state and Soil Body when corresponding sample is disturbed respectively, the soil body Stress level is higher, and Soil Body is stronger, then small-strain shear modulus are bigger.Small-strain shear modulus have clear and definite physics Meaning, scene original position value and laboratory test value are easy to determine, and the soil disturbance caused to sampling process is more sensitive, and whole survey Examination process is minimum to the disturbance for testing soil sample.

The technical solution used in the present invention is comprised the following steps：

1) live in situ shear wave test is carried out in plan sampling utilization of area cross hole method before sampling, obtain the place different In situ shear wave V before the sampling disturbance of depth_s0；

2) in sampling place according to the soil sample for drafting deep drilling and taking different depth, soil sample depth is marked on sampler barrel Degree；

3) soil sample to taken different depth, is carried out with flexure element shear wave speed test device after its Stress Release respectively Test, as institute test specimens are the soil samples that stress state is zero after sampling, therefore unstress state is cut after obtaining sampling disturbance Cut velocity of wave V_s1；

4) soil sample to taken different depth, is reinvented so that Soil Body is preferably minimized, then uses flexure element respectively Shear wave speed test device is tested, and obtains the shear wave velocity V after the soil body is reinvented_s2, i.e. soil structures degree disturbance degree SD= 100% shear wave velocity V_s2；

5) calculate the soil body mean effective stress σ ' before sampling_m0With soil body overlying effective stress σ before sampling '_v0；

6) it is calculated Soil Body disturbance degree SD caused by each depth sampling.

The flexure element shear wave speed test device specifically can be using the patent of invention of Application No. 201610096076.8 Technical scheme in application.

Stress Release of the present invention and reinvent step sampling disturbance can both be narrow sense drill hole sampling disturbance, or Sampling disturbance comprising broad sense such as drill hole sampling disturbance, shipping storage disturbance and preparation of soil sample disturbances, above-mentioned disturbance can be used The inventive method calculates Soil Body disturbance degree.

The step 5) in sampling before soil body mean effective stress σ '_m0Calculated using below equation：

Wherein, effective unit weights of the γ ' for upper earthing, z are that the soil body samples front depth, K₀For soil body lateral pressure coefficient.

Ordinary circumstance is for weak soil, K₀Take 0.5 for soil body lateral pressure coefficient, formula can abbreviation be

For the mean effective stress σ ' of the soil body after Stress Release_m1With reinvent after the soil body mean effective stress σ '_m2, as the now soil body is in unstress state, thus both mean effective stress can value be 1kpa, i.e. σ '_m1= σ'_m2=1kPa.

The step 5) in sampling before soil body overlying effective stress σ_v'₀Calculated using below equation：

σ′_v0=γ ' z

Wherein, effective unit weights of the γ ' for upper earthing, z are depth before soil body sampling.

If wherein for OCR ON SECONDARY CONSOLIDATION OCR before sampling₀, for normally consolidated soil, overconsolidation ratio OCR₀=1.For Overconsolidation ratio OCR of the soil body after Stress Release₁With reinvent after the soil body overconsolidation ratio OCR₁And OCR₂Below equation is adopted Calculate：

Wherein, σ '_v0For overlying effective stress before soil body sampling, effective unit weights of the γ ' for upper earthing, before z is soil body sampling Depth.

Modulus only after stress normalization, can individually characterize Soil Body, and conventional computational methods are by stress water Gentle Soil Body overall merit and stress state changes (can recover disturbance) and soil structures in failing to separate sampling process Property disturbance (irrecoverable disturbance) two factors of influence, the inventive method be using stress normalization after small-strain shear modulus Index calculates Soil Body disturbance degree caused by sampling process, and concrete principle is as follows：

The computing formula of Soil Body disturbance degree SD of the present invention is that going out first with the small-strain shear modulus derivation of equation should Characterized Soil Body after power level normalization is strong and weak and parameter A of degree of injury is evaluating the soil body caused by sampling process Structural disturbance degree.

Firstly, for bury, small-strain shear modulus have below equation：

G_max=AF (e) (σ '_m)ⁿ(OCR)^k

Wherein, G_maxIt is small-strain shear modulus；A is the parameter for reacting Soil Body, and its size can be used to characterize the soil body Structural strong and weak and degree of injury；σ'_mIt is mean effective stress；N is fitting constant；K is the index of overconsolidation ratio OCR, with Plastic flow of soil correlation of indices；F (e) is void ratio function, is regarded as steady state value generally for bury.

The characterized Soil Body gone out after stress level normalization followed by the small-strain shear modulus derivation of equation is strong Parameter A of weak and degree of injury is derived according to above-mentioned formula conversion evaluating Soil Body disturbance degree caused by sampling process Soil Body parameter A can be obtained：

Wherein, G_maxIt is small-strain shear modulus；A is the parameter for reacting Soil Body, and its size can be used to characterize the soil body Structural strong and weak and degree of injury；σ'_mIt is mean effective stress；N is fitting constant；K is the index of overconsolidation ratio OCR, with Plastic flow of soil correlation of indices；F (e) is void ratio function, is regarded as steady state value generally for bury.

Then, the formula G according to derived from the communication theory of elastomer medium wave_max=ρ V_s ², ρ represents soil body density, V_sRepresent Shear wave velocity, soil small strain modulus of shearing can be derived by by its shear wave velocity and soil body density, and measurement undisturbed soil, sampling are disturbed Break ground, reinvent soilborne plant disease and can derive small-strain shear modulus, evaluated by the change amplitude of Soil Body parameter A Sample disturbance degree.Derive as follows：

Wherein, A₀、σ'_m0、OCR₀、V_s0It is Soil Body parameter, mean effective stress respectively before sampling disturbance, super solid Knot ratio, shear wave velocity；A₁、σ'_m1、OCR₁、V_s1It is Soil Body parameter, mean effective stress respectively after sampling disturbance, super Consolidation ratio, shear wave velocity；A₂、σ'_m2、OCR₂、V_s2It is Soil Body parameter, mean effective stress after respectively reinventing, super solid Knot ratio, shear wave velocity.

According to above-mentioned inference, OCR₀=1, OCR₁=OCR₂=σ '_v0, σ '_m1=σ '_m2=1kPa, described each depth sampling Caused Soil Body disturbance degree SD can be reduced to below equation calculating：

Wherein, n is fitting constant；K is the index of overconsolidation ratio OCR；σ'_m0It is the soil body mean effective stress before sampling； σ'_v0Soil body overlying effective stress before sampling.

The caused Soil Body disturbance degree SD of each depth sampling that the present invention is obtained can be used for qualitative evaluation drilling and take The degree that sample is disturbed to Soil Body, the laboratory test carried out for after provide reference.

Being directed to the different parameters of weak soil soil sample selection of different nature in being embodied as makes Soil Body disturbance degree meter It is more accurate to calculate.

The invention has the beneficial effects as follows：

This method calculates clear and definite, and testing procedure is simple, and test result is accurate, not to testing soil sample in whole test process Cause to disturb the advantage of i.e. Non-Destructive Testing.By separation, in sampling process, Soil Body disturbs (irrecoverable disturbance) and answers Power state change (can recover disturbance) the two factors of influence, can respectively at the scene with indoor calculating and pass judgment on sampling process and cause Soil Body level of disruption.

Especially the present invention is using by the normalization of parameter stress rather than directly using the side of small-strain shear modulus Method, has not only acted as accurate quantitative analysis and has calculated the strong and weak effect of Soil Body before and after sampling, also acted positive certainty evaluation and take The effect that sample process is disturbed to Soil Body.The laboratory test follow-up to soil sample has important directive significance.

The inventive method is applicable not only to once evaluate the scene of Soil Body disturbance degree after sampling, and it is right to be also applied for The indoor secondary evaluation of the structural disturbance degree of soil sample before laboratory test.

Description of the drawings

Fig. 1 unstress state soil sample test signal and is reinvented after sampling disturbance at embodiment of the present invention depth selection 4m Soil sample test signal.

Fig. 2 is embodiment of the present invention in situ shear wave, unstress state soil sample and reinvent rear soil sample and cut after sampling disturbance Cut velocity of wave figure.

Fig. 3 is embodiment of the present invention Soil Body disturbance degree SD result of calculation figures.

Specific embodiment

Below in conjunction with the accompanying drawings and embodiment is described in further detail to the present invention.

The present embodiment is reconnoitred for certain subway foundation pit job site, passes through the Laboratory Evaluation soil body at the scene after drill hole sampling Physical mechanical property index, thus it is higher to drill hole sampling quality requirement, and sampling process needs sufficiently small to Soil Body disturbance degree. Sampling process is calculated to Soil Body level of disruption using the inventive method.

The specific implementation step of the inventive method is as follows：

(1) live in situ shear wave test is carried out in plan sampling utilization of area cross hole method before sampling, obtain the place not With in situ shear wave V before the sampling disturbance of depth_s0(Fig. 2), now it should be noted that shear wave velocity measurement depth should be greater than plan takes The depth capacity of sample；

Depth is obtained for 4m, 7m, 10m, 13m, 16m, 19m, 22m, in situ shear wave value V of the soil body at 25m_s1Respectively 67.7m/s, 91.7m/s, 104.1m/s, 109.0m/s, 126.2m/s, 151.0m/s, 154.9m/s, 167.5m/s.

(2) soil sample is marked in sampling place on sampler barrel according to the soil sample for drafting deep drilling and taking different depth Depth；

(3) soil sample to taken different depth, is entered with flexure element shear wave speed test device after its Stress Release respectively Row test, due to institute's test specimens be sampling after stress state be zero soil sample, so secondary test result be sampling disturbance after without should The shear wave velocity V of power state_s1(Fig. 2)；

Each depth soil sample is tested using portable piezoelectric ceramic bending element shear wave speed test device.By what is taken out The part soil body is prepared as the cylindrical sample that length is L, and the draw ratio of sample should be greater than 3, inserts excitation respectively at sample two ends curved Qu Yuan and reception flexure element, record the insertion depth l of flexure element piezoelectric ceramics.By curved by receiving after excitation flexure element excitation signal Bent unit receives signal, records shearing wave propagation time t in the sample, you can obtain sample shear wave velocity(Fig. 1)；

Obtain sampling front depth for 4m, 7m, 10m, 13m, 16m, 19m, 22m, the shearing wave at 25m after soil sample sampling disturbance Fast value V_s1Respectively 37.2m/s, 46.6m/s, 50.6m/s, 50.1m/s, 55.1m/s, 66.0m/s, 65.8m/s, 71.4m/s.

(4) soil sample to taken different depth, is reinvented so that its Soil Body is preferably minimized value, respectively with bending First shear wave speed test device is tested, and this time test result is reinvented for the soil body and soil structures degree disturbance degree SD=100% Shear wave velocity V_s2(Fig. 2)；

It is 4m, 7m, 10m, 13m, 16m, 19m, 22m to obtain depth, and at 25m, the soil body reinvents shear wave velocity value V_s2Respectively 24.1m/s, 29.7m/s, 24.3m/s, 25.5m/s, 20.4m/s, 29.0m/s, 38.1m/s, 39.7m/s.

(5) calculate the soil body mean effective stress before samplingWherein γ ' is effective for upper earthing Severe；Z is depth before soil body sampling；K₀For soil body lateral pressure coefficient.Formula can abbreviation be

(6) soil body overlying effective stress σ before sampling is calculated using below equation_v'₀：

σ′_v0=γ ' z

Effective unit weights of the wherein γ ' for upper earthing；Z is depth before soil body sampling；

(7) Soil Body disturbance degree SD caused by each depth sampling is quantitatively calculated, simplification of a formula is as follows：

For bury used by the present embodiment, fitting constant n values are 0.57, and overconsolidation ratio coefficient k is 0.24.

The present embodiment Soil Body disturbance degree SD result of calculations are shown in Table 1.

Soil Body disturbance degree SD result of calculations in 1 the present embodiment of table

Fig. 1 is visible, and at the present embodiment depth selection 4m, after sampling disturbance, unstress state soil sample and remoulded sample test are believed Actuation duration and shearing wave first passage time clear and definite in number, can accurately calculate the shear wave velocity of correspondence soil sample.Soil Body Disturbance degree SD finally draw as shown in figure 3, visible in table 1 and Fig. 3 by the depth in the soil body according to which, with conventional soil disturbance with The increase of depth and increase and compare, with the increase of depth selection, Soil Body disturbance degree SD has and subtracts the present embodiment soil sample Little trend, shows that the inventive method changes the two factors of influence by separating Soil Body disturbance and stress state, will After impact normalization of the stress state to modulus of shearing, sampling process is evaluated to the soil body by calculating Soil Body disturbance degree SD The degree of structural perturbation, the laboratory test follow-up to soil sample are significant.

Claims (4)

1. a kind of method of utilization modulus of shearing change calculations Structure of Soft Clay disturbance degree, it is characterised in that step is as follows：

1) live in situ shear wave test is carried out in plan sampling utilization of area cross hole method before sampling, obtain the place different depth In situ shear wave V before the sampling disturbance at place_s0；

2) in sampling place according to the soil sample for drafting deep drilling and taking different depth, soil sample depth is marked on sampler barrel；

3) soil sample to taken different depth, is surveyed with flexure element shear wave speed test device after its Stress Release respectively Examination, obtains the shear wave velocity V of unstress state after sampling disturbance_s1；

4) soil sample to taken different depth, is reinvented so that Soil Body is preferably minimized, then is sheared with flexure element respectively Wave velocity testing device is tested, and obtains the shear wave velocity V after the soil body is reinvented_s2；

5) calculate the soil body mean effective stress σ ' before sampling_m0There are effect, power σ ' with the soil body overlying before sampling_v0；

6) it is calculated Soil Body disturbance degree SD caused by each depth sampling.

2. the method for a kind of utilization modulus of shearing change calculations Structure of Soft Clay disturbance degree according to claim 1, which is special Levy and be：The step 5) in sampling before soil body mean effective stress σ '_m0Calculated using below equation：

${\mathrm{\σ}}_{m0}^{\′}=\frac{{\mathrm{\γ}}^{\′}z(1+2K_0)}{3}$

Wherein, effective unit weights of the γ ' for upper earthing, z are that the soil body samples front depth, K₀For soil body lateral pressure coefficient.

3. the method for a kind of utilization modulus of shearing change calculations Structure of Soft Clay disturbance degree according to claim 1, which is special Levy and be：The step 5) in sampling before soil body overlying effective stress σ '_v0Calculated using below equation：

σ′_v0=γ ' z

Wherein, effective unit weights of the γ ' for upper earthing, z are depth before soil body sampling.

4. the method for a kind of utilization modulus of shearing change calculations Structure of Soft Clay disturbance degree according to claim 1, which is special Levy and be：Caused by described each depth sampling, Soil Body disturbance degree SD is calculated using below equation：

$SD=\frac{\frac{V_{S0}^2}{{\left({\mathrm{\σ}}_{m0}^{\′}\right)}^n}-\frac{V_{S1}^2}{{\left({\mathrm{\σ}}_{v0}^{\′}\right)}^k}}{\frac{V_{S0}^2}{{\left({\mathrm{\σ}}_{m0}^{\′}\right)}^n}-\frac{V_{S2}^2}{{\left({\mathrm{\σ}}_{v0}^{\′}\right)}^k}}\×100\%$

Wherein, n is fitting constant, and k is the index of overconsolidation ratio OCR, σ '_m0Be sampling before soil body mean effective stress, σ '_v0It is Soil body overlying effective stress before sampling.