KR20150091635A

KR20150091635A - Testing Method of Brittle Failure Potential of Rock Specimen

Info

Publication number: KR20150091635A
Application number: KR1020140012089A
Authority: KR
Inventors: 송기일
Original assignee: 인하대학교 산학협력단
Priority date: 2014-02-03
Filing date: 2014-02-03
Publication date: 2015-08-12

Abstract

The present invention relates to a method for evaluating the possibility of the brittle fracture of rock and, more specifically, to a method for evaluating the possibility of the brittle fracture of rock including a step of acquiring a fracture curve by performing a normal uniaxial compression test of a rock specimen; a step of acquiring a rock specimen similar with the rock specimen tested in the step of acquiring the fracture curve and placing the similar rock specimen on a brittle potential testing device; a step of installing a lateral strain meter on the center of the rock specimen; a step of acquiring an uniaxial stress-strain curve by applying a vertical load to the brittle potential testing device; a step of reducing the load using a servo control to make a speed of lateral strain constant; a step of acquiring a fracture curve acquired by a brittle fracture test and a linear curve by reducing the load by stages; and a step of calculating an area of a region formed by the fracture curve acquired by the brittle fracture test and the fracture curve.

Description

{Test Method of Brittle Failure Potential of Rock Specimen}

The present invention relates to a method for evaluating the brittle fracture possibility of a rock mass, and more particularly, to a method for quantitatively evaluating the possibility of rock fracture by evaluating the brittleness of a rock through a brittle potential test.

Recently, the utilization of underground space is expected to increase in order to solve environmental, energy and security problems in Korea. Underground spaces are being developed for various purposes, such as railway facilities in urban areas, nuclear waste storage facilities, storage caves, underground roads, and the demand for them is increasing.

In particular, the construction of a storage cabin in the environment with poor resources such as Korea is a national task, and the construction of a safe storage facility for nuclear power generation waste used for power generation is a crucial task for the next generation . In addition, more than 70% of the whole country is made up of mountainous terrain, so it is essential to construct a tunnel for balanced development of next-generation high-speed railway and land.

The ground remains equilibrium until disturbed by artificial excavation. The stresses are redistributed as a result of the excavation, resulting in a new equilibrium of stress, but tunnel excavation always causes initial equilibrium disturbances. In tunnel construction, disturbance and redistribution of these stresses are repeated. However, the rocks experience more excessive stresses due to the loss of ground that was supported during the redistribution of stresses. These excessive stresses are concentrated on the tunnel excavation surface.

The fracture modes of rock mass due to the ground stress can be classified into soft fracture and brittle fracture. Ductile fracture causes gradual destruction of rock mass, but brittle fracture means sudden destruction of rock mass. The change in the stress on the wall of the tunnel is the same as the work on the rock, and the strain energy is accumulated in the rock by work. At this time, the greater the strength of the rock mass, the greater the amount of strain energy accumulated. The rock mass is ruptured by the sudden release of the strain energy accumulated in the rock mass.

These rock mass ruptures occur mainly at the side and at the top of the tunnel and are often reported to occur at the bottom. Obert and Duvall (1967) defined the rupture of a rock as an explosion of a sudden rock mass, which was attributed to stresses that exceeded the strength of the rock mass. Several researchers have studied rock break mechanism during mine development, and this has often been the case in deep mines and has been treated as one of the major disasters.

However, there are few studies on rock fracture phenomenon in civil engineering field, and there are few studies related to rock fracture due to limited information. In recent years, as the depth of construction of underground space including traffic tunnel has been increased, the rupture of rock in the tunnel is frequently reported. Therefore, it is necessary to study the rupture of rock in terms of disaster in construction as well as stability of tunnel .

In addition, stress relief is applied to the rocks subjected to excessive stress due to excavation of high-degree tunnels, and exposed rock masses are subjected to stress reallocation due to arching effects to continuously accumulate strain energy, The brittle fracture, which is suddenly destroyed, occurs. However, there is no method to simulate this by laboratory experiments.

In this paper, we propose a method to characterize rock breakage caused by hyperbaric pressure, which should be considered as an essential factor in the construction of underground space.

SUMMARY OF THE INVENTION The present invention provides a method for evaluating the probability of brittle fracture of a rock mass in which the probability of rock fracture can be quantitatively evaluated by evaluating the brittleness of the rock.

According to an embodiment of the present invention, there is provided a method of analyzing fracture characteristics of a rock, comprising the steps of: performing a general uniaxial compression test on a rock sample to obtain a fracture curve; Acquiring and locating a rock sample similar to the rock sample tested in the method of obtaining the breaking curve in a brittle potential tester; Installing a transverse strain meter at the center of the rock sample; Obtaining a uniaxial stress-strain curve by applying a vertical direction load to the brittle po- tential tester; Reducing the load through the servo control so that the lateral strain rate is constant; Obtaining a brittle potential breaking curve and a linear curve by gradually reducing the load; And calculating the width of the region formed by the destruction curve and the brittle potential breaking curve.

According to an aspect of the present invention, the step of decreasing the load through the servo control such that the velocity of the lateral strain is constant may be performed when the stress-strain curve of the rock sample obtained in the method of obtaining the fracture curve is out of the linear, It is possible to reduce the load through the servo control so that the velocity of the directional strain is constant.

According to another aspect of the present invention, the brittle point potential tester may be equipped with a controller capable of receiving the lateral strain as a signal and adjusting the load in the vertical direction.

According to another aspect, the area formed by the breaking curve and the brittle potential breaking curve can be calculated by an area integral method.

According to another aspect of the present invention, in the step of calculating the width of the region formed by the fracture curve and the fracture curve obtained from the brittle-strength potential test, the width of the region can represent the brittleness of the rock sample.

According to the embodiments of the present invention, it is possible to evaluate the brittleness of the rock mass and quantitatively evaluate the possibility of rock fracture.

In addition, it is possible to prevent the occurrence of disasters during construction as well as stability problems of tunnels caused by lack of research and information on rock breakage phenomena.

1 is a basic stress-strain curve of a rock according to an embodiment of the present invention.
2 is a schematic diagram of a brittle-strength potential tester and method of a rock mass according to an embodiment of the present invention.
3 is a flow chart of a method for evaluating brittle fracture of a rock in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

The present embodiments relate to a method for quantitatively evaluating the possibility of fracture of a rock by evaluating the brittleness of the rock through a brittle potential test.

Uniaxial compression tester is a tester that can measure uniaxial compressive strength of rock. Rock failure can be classified into gradual failure mode due to ductile failure and sudden failure mode due to brittle failure, and general unconfined tester can only acquire ductile failure mode. This is a gradual failure that occurs because the stiffness of the test apparatus is much greater than the test material.

1 is a basic stress-strain curve of a rock according to an embodiment of the present invention.

Fig. 1 shows the failure mode of the fracture curve 100 due to the stress-strain. The destructive curve 100 can be obtained by performing a uniaxial compression test on a brittle rock.

However, this can not quantify how likely the brittle fracture is from this curve, with the rock already fractured after its ultimate strength. In the case of the rock samples deviating from the linear stress-strain curves, the plastic deformation after the fracture is reduced, the load in the vertical direction is reduced so that the lateral strain of the rock samples is destroyed at a constant speed, A curve 110 can be obtained.

The width of the region 120 formed by the fracture curve 110 and the fracture curve 100 obtained from the brittle potential test is the brittle potential energy of the rock. That is, by evaluating the brittleness of the rock mass from the area of the area 120, it is possible to quantitatively evaluate the possibility of rock fracture.

2 is a schematic diagram of a brittle-strength potential tester and method of a rock mass according to an embodiment of the present invention.

As shown in FIG. 2, the brittle potential tester has a load sensor 200 on its upper portion and a base plate 210 on its lower portion. And a lateral strain meter (220) is installed at a central portion of the rock sample to obtain a stress-strain curve in a uniaxial direction by applying a load in the vertical direction. An axial strain meter 230 may be installed between the load sensor 200 and the base plate 210 to confirm the axial stress.

The brittleness potential obtained from the brittle potential test by reducing the load through the servo control so that the stress-strain curve of the rock specimen deviates from the linearity, that is, from the maximum value (Peak) of the stress- The breaking curve 110 and the linear curve 130 can be obtained.

Accordingly, the brittleness of the rock sample can be determined by the area of the region 120 formed by the fracture curve 100 and the fracture curve 110 obtained from the brittle-phase potential test.

3 is a flow chart of a method for evaluating brittle fracture of a rock in accordance with an embodiment of the present invention.

In Fig. 3, a tester and a test method capable of evaluating the brittleness of a rock by using the method of obtaining the fracture curve 100 in Fig. 1 are presented.

First, in step S300, a general uniaxial compression test is performed on a rock sample to obtain the destruction curve 100. [

In step S310, a rock sample which is closest to the rock sample tested in step S300 is obtained and placed in a brittle po- tential tester equipped with a controller capable of receiving a lateral strain as a signal and capable of adjusting the load in the vertical direction .

Then, in step S320, the lateral strain meter is installed at the center of the rock sample.

In step S330, a vertical direction load is applied to obtain a uniaxial stress-strain curve. At this time, the load can be applied to the displacement control method or the load control method.

In step S340, it is determined whether the stress-strain curve of the rock sample obtained in step S300 is deviated from the linear shape or when the lateral strain is generated, that is, from the maximum value Peak of the stress- The load is reduced through the servo control so that the speed is constant.

Then, in step S350, the destruction curve obtained from the brittle potential test is obtained by gradually reducing the load.

Finally, in step S360, an area integral of the fracture curve and the fracture curve obtained from the brittle potential test is calculated by area integration method. At this time, in the step of calculating the width of the area formed by the fracture curve and the fracture curve obtained from the brittle-potential test, the width of the area indicates the brittleness of the rock sample and means the possibility of fracture of the rock.

100: Breaking curve 110: Breaking curve obtained from brittle potential test
120: area 130: linear curve
200: load sensor 210: base plate
220: transverse strain meter 230: axial strain meter

Claims

In a method for analyzing fracture characteristics of a rock,
Performing a general uniaxial compression test on a rock sample to obtain a fracture curve;
Acquiring and locating a rock sample similar to the rock sample tested in the method of obtaining the breaking curve in a brittle potential tester;
Installing a transverse strain meter at the center of the rock sample;
Obtaining a uniaxial stress-strain curve by applying a vertical direction load to the brittle po- tential tester;
Reducing the load through the servo control so that the lateral strain rate is constant;
Obtaining a fracture curve and a linear curve obtained from the brittle potential test by gradually reducing the load; And
And calculating an area width of the fracture curve and a fracture curve obtained from the brittle point potential test.

The method according to claim 1,
The step of reducing the load through the servo control such that the velocity of the transverse strain is constant may be characterized in that when the stress-strain curve of the rock sample obtained in the method of obtaining the fracture curve deviates from the linearity, Wherein the load is reduced through servo control so as to constantly determine the brittle fracture possibility of the rock.

The method according to claim 1,
Wherein said brittle potential tester is equipped with a controller capable of receiving the lateral strain as a signal and adjusting the load in the vertical direction.

The method according to claim 1,
Wherein the area formed by the fracture curve and the fracture curve obtained from the brittle-potential test is calculated by an area integration method.

The method according to claim 1,
Wherein the area of the area represents the brittleness of the rock sample in the step of calculating the area of the area formed by the fracture curve and the fracture curve obtained from the brittle point potential test.