CN104330291A - Preparation method of rock test piece containing damage fracture system - Google Patents

Abstract

The invention discloses a method for preparing a rock test piece with a damaged fracture system. The method comprises the following steps: making a complete rock block into a standard rock sample with a diameter of 50 mm and a height of 100 mm; carrying out a uniaxial compression test on the standard rock sample to obtain the uniaxial ultimate compressive strength of the standard rock sample; The axial load of the strength preloads the rock standard sample, so that the rock sample will produce a damaged crack system under the action of the load; the force loading rate of the load (not exceeding) 0.2kN/s; keep the axial load after reaching the predetermined value No change, uninstall after 2min. By applying any axial load not greater than the uniaxial compressive strength to the sample, a rock specimen containing a corresponding damaged fracture system can be obtained.

Description

Preparation method of rock specimen with damaged fracture system

technical field

The invention belongs to the technical field of rock material preparation, and in particular relates to a method for preparing a rock test piece with a damaged fracture system.

Background technique

Rocks were formed in a certain period of geological history and have undergone geological transformation for hundreds of millions of years, so there are inevitably many macro and micro cracks and defects, that is, damage. In essence, damage is the process of formation, development and evolution of microscopic defects such as cracks, holes, slippage and dislocation inside the material. The damage and destruction of materials is the process of the expansion and penetration of a large number of internal micro-cracks, which leads to the deterioration of rock macroscopic properties and even failure and destruction. In actual engineering, due to the impact of engineering disturbances such as blasting, loading, excavation and unloading, new damage cracks will inevitably be generated on the original rock foundation, which will adversely affect the mechanical properties of the rock mass. For example, in the construction of highways, railways, and water conservancy projects, the stability of large rocky high slopes under the action of excavation and unloading, the stability of surrounding rocks such as tunnels, underground powerhouses of water conservancy and hydropower projects, and underground energy strategic reserve caverns under the action of blasting excavation Stability, etc., all involve the physical and mechanical properties of rocks subjected to engineering disturbance (damage). At present, in the field of rock mechanics, making specimens that can characterize the initial damage of rock is one of the key technologies in the experimental research of rock mechanics damage characteristics. How to artificially prepare rock specimens with a certain damaged fracture system using fresh rocks indoors has become a difficult problem in the study of rock damage characteristics.

At present, scholars at home and abroad have made a lot of explorations on the production methods of standard rock specimens with initial damage fractures, such as REYES O (1991), SHEN B (1995), ROBET A (1998), Zhu Weishen (1998), WONG R H C (2001), Chen Weizhong (2003) and others used the pre-embedded thin metal sheet method to create penetrating cracks in rock-like materials, and Liu Dongyan (1994) and Li Yinping (2003) used cutting methods to prefabricate cracks in real rocks. The cracks produced by the above method are all through cracks, which is inconsistent with the fact that many cracks are non-penetrating cracks in actual engineering. For this reason, A.V.Dyskin(2003), E Sahouryeh(2002) used low-temperature resin and other transparent materials to conduct systematic experimental research on the expansion of built-in three-dimensional cracks and their interaction, Li Tingchun (2004), Ren Jianxi (2005), Guo Yanshuang (2007) et al. simulated jointed rock mass by artificially prefabricating cracks on the specimen, and studied the crack propagation mechanism through compression tests. Wang Guoyan (2009) used the method of adding an oval polyester film sheet to the cement mortar to form a discontinuous surface in the concrete to simulate a non-penetrating single crack in the rock mass.

The above methods all use artificially prefabricated macro-cracks to form damage cracks inside or on the surface of the rock to simulate the initial damage to the rock caused by engineering disturbances. However, this method has obvious defects and deficiencies. On the one hand, the initial cracks generated by engineering disturbances are mostly microscopic cracks, while the man-made cracks are macroscopic cracks, and there are obvious differences in scale between the two; The geometric characteristics and spatial distribution characteristics of the damaged cracks in the rock are random, while the man-made cracks are pre-set according to a certain test purpose, which is obviously inconsistent with the shape and development form of the actual rock damaged cracks. Therefore, there are obvious defects and deficiencies in these initial damage crack generation methods.

Contents of the invention

The purpose of the present invention is to overcome the deficiencies of the prior art and provide a method for preparing a rock sample with a certain damage fracture system, the effect of which is more in line with the shape and development form of the actual rock damage fracture.

In order to achieve the above purpose, the following technical solutions are adopted:

A method for preparing a rock specimen with a damaged fracture system, comprising the following steps:

1) Make the complete rock block into a standard rock sample with a diameter of 50mm and a height of 100mm;

2) Carry out uniaxial compression test to standard rock sample, obtain the uniaxial ultimate compressive strength of standard rock sample;

3) Preload the rock standard sample with an axial load less than the ultimate compressive strength, so that the rock sample will produce damage cracks under the action of the load;

4) After reaching the predetermined value, keep the axial load unchanged and unload after 2 minutes.

According to the above scheme, the preload of the rock standard sample in step 3) does not exceed 90% of the uniaxial ultimate compressive strength.

According to the above scheme, the loading rate of step 2) uniaxial compression test and step 3) preloading is not greater than 0.2kN/s.

The beneficial effects of the present invention are:

(1) Realized the preparation of rock specimens containing certain fracture systems in the laboratory to simulate the damage caused by engineering disturbances to rocks, which can be used to study the physical, mechanical, hydraulic and other characteristics of rocks subjected to certain damages.

(2) The rock damage fracture system obtained by this method basically conforms to the micro-crack expansion law of the rock under the external load, and is more consistent with the actual rock damage fracture system.

Description of drawings

Figure 1: Uniaxial compression test stress-strain curve of a saturated schist sample with a schistosclerographic dip angle of 45°.

Detailed ways

The following examples further illustrate the technical solutions of the present invention, but are not intended to limit the protection scope of the present invention.

The preparation process of the rock specimen containing damage fracture system of the present invention is as follows:

1) Make the complete rock block into a standard rock sample with a diameter of 50mm and a height of 100mm;

2) Carry out uniaxial compression test to standard rock sample, obtain the uniaxial ultimate compressive strength of standard rock sample;

3) Preload the rock standard sample with an axial load less than the ultimate compressive strength, so that the rock sample will produce damage cracks under the action of the load; the force loading rate of the load is less than 0.2kN/s;

4) After reaching the predetermined value, keep the axial load unchanged and unload after 2 minutes.

Referring to Figure 1, the uniaxial compression test stress-strain curve of a saturated schist sample with a schistosclerographic dip angle of 45°. It can be seen that the rock undergoes four stages of compaction, elastic deformation, yield and failure during the compression process. Among them, OA is the initial compaction stage. In this stage, schist mineral particles undergo overall unequal displacement along the loading direction, and the sample is gradually compacted. The original gaps are filled and compacted by mineral particles. AB is the elastic deformation stage, which is mainly manifested in the mutual extrusion between mineral particles, without the generation of new cracks and the growth and expansion of original defects, and the macroscopic performance is elastic deformation. BC is the formation stage of distributed microcracks. As the load increases, local stress concentration occurs in some parts of the rock sample, and thus new microcracks or initial cracks are formed. The repeated formation and relaxation of stress concentration gradually form some distribution of microcracks. The CD section is the stage where the overall stress gradually increases after the stress is adjusted by the BC section. Point D is the failure point of the sample. When approaching this point, the bifurcation cracks gradually increase, and the main cracks expand steadily and penetrate through.

In order to explore the mechanical properties of rock specimens subjected to different damage degrees, three saturated samples were firstly taken, and the ultimate compressive strength of the samples was obtained through uniaxial tests, which were 36.430MPa, 42.148MPa, and 46.357MPa, respectively, and the average value was 41.645MPa . According to the above-mentioned initial crack formation method, the above-mentioned schist standard specimens were preloaded with axial loads of 20%, 40%, 60%, and 80% of the saturated ultimate compressive strength, respectively, and then tested by triaxial tests. The results of uniaxial ultimate compressive strength of schist samples are as follows:

From the above exploratory test results, it can be known that the uniaxial ultimate compressive strength of the schist sample is 92.4% of the initial state after the axial load pre-compression of 20%, 40%, 60%, and 80% of the saturated ultimate compressive strength. , 88.6%, 79.8%, 67.4%, the effect of axial preloading on rock damage is more obvious. It can be seen that according to the above method, by applying any axial load not greater than the uniaxial saturated compressive strength to the sample, a rock specimen containing a corresponding damaged fracture system can be obtained.

Claims (3)

1., containing the preparation method of damage fissure system rock sample, it is characterized in that comprising the following steps:

1) intact rock is made into the key rock sample of diameter 50mm, height 100mm;

2) uniaxial compression test is carried out to key rock sample, obtain the terminal compression strength of the single axle of key rock sample;

3) with the xial feed being less than ultimate compression strength, precompressed is carried out to rock standard sample, make rock sample under the effect of load, produce damage crack;

4) keep xial feed constant after reaching predetermined value, unload after continuing 2min.

2., as claimed in claim 1 containing the preparation method of damage fissure system rock sample, it is characterized in that step 3) in 90% of terminal compression strength of the single axle is no more than to the prefabricating load of rock standard sample.

3., as claimed in claim 1 containing the preparation method of damage fissure system rock sample, it is characterized in that step 2) uniaxial compression test and step 3) loading speed of prefabricating load is not more than 0.2kN/s.