CN104359772A - Method for determining normal stress threshold value of peak friction angles of rock mass structural planes - Google Patents

Abstract

The invention discloses a method for determining a normal stress threshold value of peak friction angles of rock mass structural planes. The method comprises the following steps: 1) calibrating a test direction; 2) selecting structural planes for test and the number of test samples; 3) measuring a roughness coefficient which is shown in the description, of each structural plane; 4) obtaining peak friction angles phi 1i and phi 2i of the structural planes under each level of normal stress by virtue of direct shear test, and performing direct shear test on each structural plane test sample under different normal stress conditions; 5) determining a relative error value delta of each engineering rock mass structural plane; 6) determining a normal stress threshold value sigmai of the peak friction angle of each structural plane; 7) determining a final normal stress threshold value which is shown in the description, of the peak friction angles of the group of structural planes: when a range of the normal stress threshold values sigmai of the peak friction angles of m structural planes in the group is smaller than an average value of 15 percent, adopting the average value which is shown in the description, of the normal stress threshold values sigmai of the peak friction angles of the m structural planes as the normal stress threshold value of the peak friction angles of the structural planes in the group. The method is clear in principle, convenient to operate and low in cost, and has the good using effect, and engineering application is facilitated.

Description

The normal stress threshold value determination method of rock mass discontinuity peak value angle of friction

Technical field

The invention belongs to field of engineering technology, relate to the normal stress threshold value determination method of rock mass discontinuity peak value angle of friction, be applicable to the normal stress threshold value determination method in the correlation engineering such as water conservancy, traffic, mining, geology, nuclear waste disposal, oil with the rock mass discontinuity peak value angle of friction of stress effect.

Background technology

Before the present invention makes, still there is no the normal stress threshold value determination method of rock mass discontinuity angle of friction at present.Rock mass discontinuity peak value angle of friction is the important parameter of engineering rock structural face Stability Assessment.Joint straight shear test under different normal stress condition shows, structural plane peak value angle of friction presents nonlinear attenuation with the increase of normal stress, as shown in Figure 1.

Shown by the test findings of Fig. 1, when normal stress is less, peak value angle of friction is larger; When normal stress is larger, peak value angle of friction diminishes; When normal stress increases to certain value, peak value angle of friction tends towards stability value substantially, the minimum normal stress that at this moment can meet the requirement of Practical Project rock mass discontinuity peak value angle of friction relative error is called normal stress threshold value, and peak value angle of friction is called the stress effect of rock mass discontinuity angle of friction with the effect that normal stress changes.Because the normal stress of engineering rock mass is usually comparatively large, therefore, need in actual rock mass engineering project to adopt the structural plane peak value angle of friction tended towards stability.But the normal stress loading range adopted due to direct shear test under normal test conditions is limited, particularly for large-scale structure face, because the Normal stress applied is excessive, the conventional loading equipemtn in laboratory is difficult to meet the requirement of loading normal stress, therefore the normal stress threshold value of engineering rock structural face peak value angle of friction ultimate value requirement can not be obtained, and multistage high normal stress direct shear test expense is large, the cycle is long, is difficult to engineering demands.Therefore, how to determine that structural plane peak value angle of friction normal stress threshold value is key issue urgently to be resolved hurrily in engineering quickly and easily.

Summary of the invention

In order to solve in prior art the deficiency of the normal stress threshold value cannot determining rock mass discontinuity peak value angle of friction, the invention provides a kind of definite principle, easy to operate, cost is low, result of use is good, be convenient to the normal stress threshold value determination method of the rock mass discontinuity peak value angle of friction carrying out engineer applied.

In order to solve the problems of the technologies described above proposed technical scheme:

A normal stress threshold value determination method for rock mass discontinuity peak value angle of friction, described defining method comprises the following steps:

1) rating test direction: rating test direction on selected engineering rock structural face;

2) Selection experiment structural plane and sample quantities: according to the scale of engineering rock structural face, selectes one group not with the structural plane size of size effect change, and carries out sampling processing to the structural plane of selected size; This group structural fece sample number to be m, m be not less than 3 natural number;

3) the roughness coefficient JRC of i-th structural plane in this group m structural plane is measured _i.According to certain intervals line on i-th structural plane, and measure the roughness coefficient of every bar scribing position; Then the roughness coefficient of surveys line all on this structural plane is averaged and obtain this structural plane JRC _i;

4) the peak value angle of friction φ of lower i-th structural plane of two-stage low normal stress condition is obtained by direct shear test _1i, φ _2i.I-th structural fece sample in this group is carried out to the direct shear test under the low normal stress condition of two-stage, normal stress is taken as σ respectively _1i=0.25MPa, σ _2i=0.5MPa, can obtain the structural plane peak shear strength τ under the low normal stress condition of two-stage _1iand τ _2i, then according to formula obtain the structural plane peak value angle of friction of this structural plane under the low normal stress condition of two-stage ${\mathrm{\φ}}_{1i}=\arctan \left(\frac{{\mathrm{\τ}}_{1i}}{{\mathrm{\σ}}_{1i}}\right),{\mathrm{\φ}2}_i=\arctan \left(\frac{{\mathrm{\τ}}_{2i}}{{\mathrm{\σ}}_{2i}}\right);$

5) the relative error magnitudes δ of engineering rock structural face peak value angle of friction is determined;

6) the normal stress threshold value σ of i-th structural plane peak value angle of friction is determined _i; By the rate of change formula of normal stress obtain the normal stress threshold value σ of i-th structural plane peak value angle of friction _i>=2.3JRC _i/ (g _2iδ), wherein: $g_{\mathrm{ni}}=\frac{{\mathrm{\φ}}_{\mathrm{ni}}-{\mathrm{\φ}}_{\mathrm{ni}-1}}{{\mathrm{\σ}}_{\mathrm{ni}}-{\mathrm{\σ}}_{\mathrm{ni}-1}},g_{2i}=\frac{{\mathrm{\φ}}_{2i}-{\mathrm{\φ}}_{1i}}{{\mathrm{\σ}}_{2i}-{\mathrm{\σ}}_{1i}},$ N in subscript is n-th grade of normal stress, and i is i-th structural plane in this group m structural plane, and 2 is second level normal stress; g _nibe the rate of change of the structural plane peak value angle of friction of i-th structural plane under n-th grade of normal stress, g _2iit is the rate of change of the structural plane peak value angle of friction of i-th structural plane under the 2nd grade of normal stress;

7) determine that the method for average of this group structural plane peak value angle of friction is to stress threshold as this group m structural plane peak value angle of friction normal stress threshold value σ _iextreme difference when being less than mean value 15%, described extreme difference is the difference of maximal value and minimum value, gets the normal stress threshold value σ of m structural plane peak value angle of friction _imean value as the normal stress threshold value of this group structural plane peak value angle of friction.

Further, described step 7) in, as the normal stress threshold value extreme difference σ of m structural plane peak value angle of friction _iwhen being greater than mean value 15%, the structural fece sample progressively increasing same size carries out direct shear test, until the method for average wherein having the extreme difference of m sample to be less than a selected m sample to stress threshold 15% time, the mean value getting selected m sample peak value angle of friction normal stress threshold value as the final method of this group structural plane peak value angle of friction to stress threshold.

The present invention compared with prior art, the beneficial effect had is mainly reflected in: rock mass discontinuity peak value angle of friction normal stress threshold value determination method has definite principle, simple to operate, cost is low, result of use is good, there are larger implementary value and economic results in society.

Accompanying drawing explanation

Fig. 1 is the stress effect threshold figure of structural plane peak value angle of friction.

Embodiment

The present invention will be further described below.

With reference to Fig. 1, a kind of normal stress threshold value determination method of rock mass discontinuity peak value angle of friction, comprises the following steps:

1) rating test direction: rating test direction on selected engineering rock structural face;

2) Selection experiment structural plane and sample quantities: according to the scale of engineering rock structural face, select one group not with the structural plane size (usual scope is between 300mm × 300mm-1000mm × 1000mm) of size effect change, and sampling processing is carried out to the structural plane of selected size; This group structural fece sample number to be m, m be not less than 3 natural number;

3) the roughness coefficient JRC of the i-th structural plane of m structural plane in this group is measured _i.According to certain intervals line on i-th structural plane, and measure the roughness coefficient of every bar scribing position; Then the roughness coefficient of surveys line all on this structural plane is averaged and obtain this structural plane JRC _i;

4) the peak value angle of friction φ of lower i-th structural plane of two-stage low normal stress condition is obtained by direct shear test _1i, φ _2i.I-th structural fece sample in this group is carried out to the direct shear test under the low normal stress condition of two-stage, normal stress is respectively σ _1i=0.25MPa, σ _2i=0.5MPa, can obtain the structural plane peak shear strength τ under the low normal stress condition of two-stage _1iand τ _2i, then according to formula obtain the structural plane peak value angle of friction of this structural plane under the low normal stress condition of two-stage ${\mathrm{\φ}}_{1i}=\arctan \left(\frac{{\mathrm{\τ}}_{1i}}{{\mathrm{\σ}}_{1i}}\right),{\mathrm{\φ}2}_i=\arctan \left(\frac{{\mathrm{\τ}}_{2i}}{{\mathrm{\σ}}_{2i}}\right);$

5) the relative error magnitudes δ of engineering rock structural face peak value angle of friction is determined;

6) the normal stress threshold value σ of i-th structural plane peak value angle of friction is determined _i, by the rate of change formula of normal stress obtain the normal stress threshold value σ of i-th structural plane peak value angle of friction _i>=2.3JRC _i/ (g _2iδ), wherein: $g_{\mathrm{ni}}=\frac{{\mathrm{\φ}}_{\mathrm{ni}}-{\mathrm{\φ}}_{\mathrm{ni}-1}}{{\mathrm{\σ}}_{\mathrm{ni}}-{\mathrm{\σ}}_{\mathrm{ni}-1}},g_{2i}=\frac{{\mathrm{\φ}}_{2i}-{\mathrm{\φ}}_{1i}}{{\mathrm{\σ}}_{2i}-{\mathrm{\σ}}_{1i}},$

7) determine that the method for average of this group structural plane peak value angle of friction is to stress threshold as this group m structural plane peak value angle of friction normal stress threshold value σ _iextreme difference when being less than 15% of mean value, described extreme difference is the difference of maximal value and minimum value, gets the normal stress threshold value σ of m structural plane peak value angle of friction _imean value as the normal stress threshold value of this group structural plane peak value angle of friction.

Further, described step 7) in, as the normal stress threshold value extreme difference σ of m structural plane peak value angle of friction _iwhen being greater than mean value 15%, the structural fece sample progressively increasing same size carries out direct shear test, until the method for average wherein having the extreme difference of m sample to be less than a selected m sample to stress threshold 15% time, the mean value getting selected m structural fece sample peak value angle of friction normal stress threshold value as the final method of this group structural plane peak value angle of friction to stress threshold.

In order to obtain executing a normal stress threshold value for slope project structural plane peak value angle of friction, adopt the normal stress threshold value determination method of rock mass discontinuity angle of friction.The relative error meeting engineering rock mass angle of friction is 10%.

The normal stress threshold value determination method of the rock mass discontinuity angle of friction of the present embodiment, its determining step is as follows:

1) rating test direction.Rating test direction on selected engineering rock structural face;

2) Selection experiment structural plane and sample quantities.According to the scale of engineering rock structural face, selected one group is not of a size of 600mm with the structural plane of size effect change, and carries out sampling processing to the structural plane of selected size; This group structural fece sample quantity is 3.

3) the roughness coefficient JRC of i-th structural plane is measured _i.I-th structural plane is spaced apart to the line of 100mm, and measures the roughness coefficient of every bar scribing position; Then the roughness coefficient of all surveys line of this structural plane is averaged JRC _i.Wherein, i=1,2,3.As shown in table 1.

The roughness coefficient of each structural plane of table 1 is averaged JRC _i

4) the peak value angle of friction φ of lower i-th structural plane of the low normal stress of two-stage is obtained by direct shear test _1i, φ _2i.Carry out direct shear test to i-th structural plane, normal stress is taken as σ respectively _1i=0.25MPa, σ _2i=0.5MPa, can obtain the structural plane peak shear strength τ under the low normal stress condition of two-stage _1iand τ _2i, then according to formula obtain the peak value angle of friction φ of this structural plane under the low normal stress condition of two-stage _1i, φ _2i.Wherein, i=1,2,3.As shown in table 2.

Structural plane	1st structural plane	2nd structural plane	3rd structural plane
				φ 1i	51.16°	50.78°	49.68°
φ 2i	46.25°	45.77°	45.20°

The peak value angle of friction φ of each structural plane of table 2 _1i, φ _2i

5) the relative error magnitudes δ of engineering rock structural face peak value angle of friction is determined.Be δ=10% according to engine request.

6) the normal stress threshold value σ of i-th structural plane peak value angle of friction is determined _i.By the rate of change formula of structural plane peak value angle of friction obtain the normal stress threshold value σ of i-th structural fece sample peak value angle of friction _i>=2.3JRC _i/ (g _2iδ), wherein: $g_{\mathrm{ni}}=\frac{{\mathrm{\φ}}_{\mathrm{ni}}-{\mathrm{\φ}}_{\mathrm{ni}-1}}{{\mathrm{\σ}}_{\mathrm{ni}}-{\mathrm{\σ}}_{\mathrm{ni}-1}},g_{2i}=\frac{{\mathrm{\φ}}_{2i}-{\mathrm{\φ}}_{1i}}{{\mathrm{\σ}}_{2i}-{\mathrm{\σ}}_{1i}}.$ As shown in table 3.

Structural plane	1st structural plane	2nd structural plane	3rd structural plane
				g 2i	19.65	18.85	17.93
σ i(MPa)	11.01	10.63	10.40

The g of each structural plane of table 3 _2iwith normal stress threshold value σ _i

7) determine that the final method of this group structural plane peak value angle of friction is to stress threshold the normal stress threshold value σ of this group 3 structural fece sample peak value angle of frictions _iextreme difference be 5.7% of mean value, be less than 15% of mean value, thus the mean value 10.68MPa getting the normal stress threshold value of all 3 structural plane peak value angle of frictions as final method to stress threshold.

Claims (2)

1. a normal stress threshold value determination method for rock mass discontinuity peak value angle of friction, is characterized in that: described defining method comprises the following steps:

1) rating test direction: rating test direction on selected engineering rock structural face;

2) Selection experiment structural plane and sample quantities: according to the scale of engineering rock structural face, selectes one group not with the structural plane size of size effect change, and carries out sampling processing to the structural plane of selected size; This group structural fece sample number to be m, m be not less than 3 natural number;

3) the roughness coefficient JRC of i-th structural plane in this group m structural plane is measured _i, according to certain intervals line on i-th structural plane, and measure the roughness coefficient of every bar scribing position; Then the roughness coefficient of surveys line all on this structural plane is averaged and obtain this structural plane JRC _i;

4) the peak value angle of friction φ of lower i-th structural plane of two-stage low normal stress condition is obtained by direct shear test _1i, φ _2i, i-th structural fece sample in this group is carried out to the direct shear test under the low normal stress condition of two-stage, normal stress is taken as σ respectively _1i=0.25MPa, σ _2i=0.5MPa, can obtain the structural plane peak shear strength τ under the low normal stress condition of two-stage _1iand τ _2i, then according to formula obtain the structural plane peak value angle of friction of this structural plane under the low normal stress condition of two-stage ${\mathrm{\φ}}_{1i}=\arctan \left(\frac{{\mathrm{\τ}}_{1i}}{{\mathrm{\σ}}_{1i}}\right),$ ${\mathrm{\φ}}_{2i}=\arctan \left(\frac{{\mathrm{\τ}}_{2i}}{{\mathrm{\σ}}_{2i}}\right),$

5) the relative error magnitudes δ of engineering rock structural face peak value angle of friction is determined;

6) the normal stress threshold value σ of i-th structural plane peak value angle of friction is determined _i; By the rate of change formula of normal stress obtain the normal stress threshold value σ of i-th structural plane peak value angle of friction _i>=2.3JRC _i/ (g _2iδ), wherein: n in subscript is n-th grade of normal stress, and i is i-th structural plane in this group m structural plane, and 2 is second level normal stress; _gnibe the rate of change of the structural plane peak value angle of friction of i-th structural plane under n-th grade of normal stress, _g2iit is the rate of change of the structural plane peak value angle of friction of i-th structural plane under the 2nd grade of normal stress;

7) determine that the method for average of this group structural plane peak value angle of friction is to stress threshold as this group m structural plane peak value angle of friction normal stress threshold value σ _iextreme difference when being less than mean value 15%, described extreme difference is the difference of maximal value and minimum value, gets the normal stress threshold value σ of m structural plane peak value angle of friction _imean value as the normal stress threshold value of this group structural plane peak value angle of friction.

2. the normal stress threshold value determination method of rock mass discontinuity peak value angle of friction as claimed in claim 1, is characterized in that: described step 7) in, as the normal stress threshold value extreme difference σ of m structural plane peak value angle of friction _iwhen being greater than mean value 15%, the structural fece sample progressively increasing same size carries out direct shear test, until the method for average wherein having the extreme difference of m sample to be less than a selected m sample to stress threshold 15% time, the mean value getting selected m structural fece sample peak value angle of friction normal stress threshold value as the final method of this group structural plane peak value angle of friction to stress threshold.