CN109142056B - Soft rock point load strength equivalent area test method considering weathering degree - Google Patents
Soft rock point load strength equivalent area test method considering weathering degree Download PDFInfo
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N3/08—Investigating strength properties of solid materials by application of mechanical stress by applying steady tensile or compressive forces
Abstract
A point load strength equivalent area test method considering the weathering degree of soft rock. The method mainly comprises the following steps: A. sample preparation: taking an upper point and a lower point near the center of the sample as loading points, measuring and recording the average width of the minimum section of the sample and the distance between the loading points, wherein the ratio of the distance between the loading points to the average width is 0.3-1.0; B. point load strength test: after the test, the damage section penetrates through the whole sample and passes through two loading points, so that the test is effective; C. repeating the operation A-B until the number of effective tests is more than or equal to 10; D. calculating the load strength of the sample points: the point load strength I of the sample of the n-th test was obtained from the following formulas n，Is n＝Pn/(ψWnDn) (ii) a E. Calculating load strength of the weathered soft rock point: the point load intensity I of each times nThe maximum value, the sub-maximum value, the minimum value and the sub-minimum value in the point load strength calculation process are removed, and the remaining point load strength I is calculateds nAnd (4) obtaining the average value of the total weight. The point load strength value of the weathered soft rock measured by the method is more reliable and more accurate.
Description
Technical Field
The invention relates to a point load strength equivalent area test method considering the weathering degree of soft rock.
Background
Uniaxial compressive strength is an important index for rock strength classification and rock weathering zonation and must be obtained by conducting uniaxial compressive strength tests in a laboratory. The sample with uniaxial compressive strength usually needs to be drilled on site to obtain a core and then is transported to a laboratory for cutting and polishing; the preparation process of the sample is difficult and complicated. For weak, severely weathered and joint-developed rocks, because the complete core cannot be taken out normally or processed into a standard sample, the strength is difficult to be measured by adopting a standard rock test method.
In order to solve the problem, the International Society of Rock Mechanics (ISRM) sets a point load strength test method, a sample is placed between two loading cones of a point load strength tester, concentrated point load is applied to break the sample, the point load strength of the rock is calculated, and then the point load strength is converted into uniaxial compressive strength. The point load strength tester has small volume, light weight and convenient carrying, and can carry out tests indoors and outdoors or on site because of small required breaking load. The test has lower requirements on the sample, and the rock is slightly trimmed by the hammer, so that the manufacturing cost of the sample is greatly reduced, and the test efficiency is improved. The rock strength testing device provides convenience for rock strength testing which cannot be carried out by standard tests, and is widely applied.
The principle of the point load strength test method is as follows: the compressive stress is only distributed near the sample loading point and on the surface for a certain depth, and is represented as lateral uniform tensile stress in a large range, and finally, the tensile fracture is formed. The mechanical nature of point load strength is the maximum tensile stress that the specimen can withstand per unit area of failure between the two loading cones. For homogeneous regular square block samples, when the thickness D and the average width W of the sample are in the specification limit range, the minimum section passing through the two loading points is damaged under the action of point load, and the area actually bearing tensile stress is equal to the product of the thickness D (the distance between the two loading cones and the distance between the loading points) of the sample and the average width W (the average value of the top width and the bottom width of the minimum section) of the minimum section, so that the point load strength meterIs given by formula IsP/(WD); wherein IsFor point load strength, P is the breaking load (the pressure exerted on the loading cone when the specimen breaks).
For a homogeneous regular square block, the tested stress concentration section is the minimum section passing through two loading points, so the actual damage section of the block is superposed with the minimum section; the point load strength obtained by the point load strength test is accurate and reliable. However, for soft rock, the actual failure section of the soft rock is overlapped with the brittle section near the two loading points, the brittle section is often not overlapped with the minimum section, the actual failure section is usually deviated from the minimum section, namely the actual failure section is often larger than the minimum section, and the measured point load strength IsThe calculated value of (A) is larger; and the greater this deviation of the weathered soft rock, the greater its measured point load strength I, with increasing weatheringsThe basis for rock strength classification and rock weathering zoning is unreliable and inaccurate.
Disclosure of Invention
The invention aims to provide a soft rock point load strength equivalent area test method considering weathering degree, the point load strength value measured by the method is closer to the actual point load strength of the weathered soft rock, the test value is more reliable and accurate, and more reliable and accurate test basis can be provided for rock strength classification and rock weathering zonation.
The technical scheme adopted for realizing the aim of the invention is that the soft rock point load strength equivalent area test method considering the weathering degree comprises the following steps:
A. sample preparation:
selecting a long-strip weathered soft rock body with the thickness direction perpendicular to the bedding as a sample, taking an upper point and a lower point near the center of the sample as loading points, measuring and recording the average width of the minimum section of the sample passing through the two loading points and the distance between the loading points, and accurately measuring to 0.1 mm; the distance between the loading points is more than or equal to 15mm and less than or equal to 100mm, and the ratio of the distance between the loading points and the average width is 0.3-1.0;
B. point load strength test:
carrying out a point load strength test on the sample obtained in the step A, and recording a damage load; after the test, the damage section penetrates through the whole sample and passes through two loading points, so that the test is effective;
C. repeating the operation of the step A and the operation of the step B until the number N of effective tests is more than or equal to 10;
D. calculating the load strength of the sample points:
the point load strength I of the sample of the n-th test was obtained from the following formulas n，
Is n＝Pn/(ψWnDn)
In the formula, subscript N represents the serial number of the effective test, and N is 1,2, 3.., N; pnDestructive load, W, for the n-th test of effectivenessnAverage width of minimum cross section of sample passing two loading points for n-th effective test, DnThe distance between the loading points of the sample of the n-th effective test;
phi is an equivalent area coefficient, and the phi is 1.40 for a slightly weathered soft rock mass phi with a small amount of weathered traces and no loose substances; clear bedding, but obvious joint cracks, a small amount of weathered materials are filled in the cracks, the cracks are difficult to dig by using picks, and a weakly weathered soft rock mass psi which can be drilled by using a core drill is 1.43; the layer is unclear, and a pick can be used for excavating a strongly weathered soft rock mass psi of 1.46;
E. calculating load strength of the weathered soft rock point:
the point load strength I of the sample of each effective test is measureds nThe maximum value, the sub-maximum value, the minimum value and the sub-minimum value in the test sample are removed, and the point load strength I of the remaining test samples in the effective test is calculateds nThe average value of (1) is the point load strength I of the irregular soft rocks。
Compared with the prior art, the invention has the beneficial effects that:
the applicant researches and discovers that when the point load strength test is carried out on the soft rock, the actual failure section of the soft rock does not coincide with the minimum section, and the actual failure sectional area is larger than the minimum sectional area. And as the degree of efflorescence increases, this deviation increases: for soft rock with slight, weak and strong efflorescenceThe desired values for the ratios of the cross-sectional area of destruction to the minimum cross-sectional area were 1.40, 1.43 and 1.46, respectively; or the equivalent area coefficient psi of the irregular soft rock point load strength test is respectively 1.40, 1.43 and 1.46 according to the micro, weak and strong weathering degrees of the rock sample. Further, a point load strength correction expression formula I of a point load strength test considering the weathering degree of the soft rock is constructedsP/(ψ WD). The calculated area psi WD in the expression is closer to the actual failure sectional area, and the measured point load strength IsThe value is more accurate, and more reliable and accurate test basis can be provided for rock strength classification and rock weathering zonation.
The present invention will be further described with reference to the following embodiments.
Detailed Description
Examples
The invention relates to a method for testing the equivalent area of the load strength of a soft rock point by considering the weathering degree, which comprises the following steps:
A. sample preparation:
selecting a long-strip weathered soft rock body with the thickness direction perpendicular to the bedding as a sample, taking an upper point and a lower point near the center of the sample as loading points, measuring and recording the average width of the minimum section of the sample passing through the two loading points and the distance between the loading points, and accurately measuring to 0.1 mm; the distance between the loading points is more than or equal to 15mm and less than or equal to 100mm, and the ratio of the distance between the loading points to the average width is 0.3-1.0;
B. point load strength test:
carrying out a point load strength test on the sample obtained in the step A, and recording a damage load; after the test, the damage section penetrates through the whole sample and passes through two loading points, so that the test is effective;
C. repeating the operation of the step A and the operation of the step B until the number N of effective tests is more than or equal to 10;
D. calculating the load strength of the sample points:
the point load strength I of the sample of the n-th test was obtained from the following formulas n，
Is n＝Pn/(ψWnDn)
In the formula, subscript N represents the serial number of the effective test, and N is 1,2, 3.., N; pnDestructive load, W, for the n-th test of effectivenessnAverage width of minimum cross section of sample passing two loading points for n-th effective test, DnThe distance between the loading points of the sample of the n-th effective test;
phi is an equivalent area coefficient, and the phi is 1.40 for a slightly weathered soft rock mass phi with a small amount of weathered traces and no loose substances; clear bedding, but obvious joint cracks, a small amount of weathered materials are filled in the cracks, the cracks are difficult to dig by using picks, and a weakly weathered soft rock mass psi which can be drilled by using a core drill is 1.43; the layer is unclear, and a pick can be used for excavating a strongly weathered soft rock mass psi of 1.46;
E. calculating load strength of the weathered soft rock point:
the point load strength I of the sample of each effective test is measureds nThe maximum value, the sub-maximum value, the minimum value and the sub-minimum value in the test sample are removed, and the point load strength I of the remaining test samples in the effective test is calculateds nThe average value of (1) is the point load strength I of the irregular soft rocks。
Test verification
The point load strength of the soft phyllite with micro degree, weak degree and strong weathering degree measured by the existing point load strength test method is 3.88MPa, 2.00MPa and 0.85MPa respectively, and the point load strength measured by the method of the invention is 1.29MPa, 0.76MPa and 0.31 MPa; meanwhile, the actual failure sectional area of the tested sample is accurately measured and calculated to obtain the actual failure sectional area value, and the actual weak and strong weathering soft rock point load strength is 1.31MPa, 0.69MPa and 0.30MPa respectively as the load bearing area. Compared with the actual point load strength, the errors of the method of the invention are respectively (1.29-1.31)/1.31 ═ 1.5%, (0.76-0.69)/0.69 ═ 10.1%, (0.31-0.30)/0.30 ═ 3.3%, and the errors of the existing point load strength test methods are respectively (3.88-1.31)/1.31 ═ 196.2%, (2.00-0.69)/0.69 ═ 189.9%, (0.85-0.30)/0.30 ═ 183.3%. Therefore, the error of the method is far lower than that of the existing point load strength test method.
Claims (1)
1. A soft rock point load strength equivalent area test method considering weathering degree comprises the following steps:
A. sample preparation:
selecting a long-strip weathered soft rock body with the thickness direction perpendicular to the bedding as a sample, taking an upper point and a lower point near the center of the sample as loading points, measuring and recording the average width of the minimum section of the sample passing through the two loading points and the distance between the loading points, and accurately measuring to 0.1 mm; the distance between the loading points is more than or equal to 15mm and less than or equal to 100mm, and the ratio of the distance between the loading points and the average width is 0.3-1.0;
B. point load strength test:
carrying out a point load strength test on the sample obtained in the step A, and recording a damage load; after the test, the damage section penetrates through the whole sample and passes through two loading points, so that the test is effective;
C. repeating the operation of the step A and the operation of the step B until the number N of effective tests is more than or equal to 10;
D. calculating the load strength of the sample points:
the point load strength I of the sample of the n-th test was obtained from the following formulas n，
Is n＝Pn/(ψWnDn)
In the formula, subscript N represents the serial number of the effective test, and N is 1,2, 3.., N; pnDestructive load, W, for the n-th test of effectivenessnAverage width of minimum cross section of sample passing two loading points for n-th effective test, DnThe distance between the loading points of the sample of the n-th effective test;
phi is an equivalent area coefficient, and the phi is 1.40 for a slightly weathered soft rock mass phi with a small amount of weathered traces and no loose substances; clear bedding, but obvious joint cracks, a small amount of weathered materials are filled in the cracks, the cracks are difficult to dig by using picks, and a weakly weathered soft rock mass psi which can be drilled by using a core drill is 1.43; the layer is unclear, and a pick can be used for excavating a strongly weathered soft rock mass psi of 1.46;
E. calculating load strength of the weathered soft rock point:
the point load strength I of the sample of each effective test is measureds nThe maximum value, the sub-maximum value, the minimum value and the sub-minimum value in the test sample are removed, and the point load strength I of the remaining test samples in the effective test is calculateds nThe average value of (1) is the point load strength I of the irregular soft rocks。
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| CN203117044U (en) * | 2013-02-27 | 2013-08-07 | 浙江土工仪器制造有限公司 | Mortar masonry point load tester |
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| CN106644728A (en) * | 2017-02-24 | 2017-05-10 | 中国矿业大学(北京) | Point loading test analysis method based on surrounding rock classification of super-large section tunnel |
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| CN203117044U (en) * | 2013-02-27 | 2013-08-07 | 浙江土工仪器制造有限公司 | Mortar masonry point load tester |
| US9432901B1 (en) * | 2015-07-24 | 2016-08-30 | Cisco Technology, Inc. | System and method to facilitate radio access point load prediction in a network environment |
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