In-situ test method for surrounding rock relaxation depth in columnar jointing rock mass cavity project

Abstract

The invention relates to an in-situ test method for the surrounding rock relaxation depth in a columnar jointing rock mass cavity project. The in-situ test method includes the steps of designing and arranging test drilling holes which are formed in the periphery of a cavity excavated in a columnar jointing rock mass and parallel or perpendicular to the axis of a column body of the columnar jointing rock mass, selecting test projects, determining the relaxation depth, and comprehensively conducting the test. The test drilling holes are distributed in key portions of a monitored fracture surface after the cavity is excavated, surrounding rock elastic waves and jointing fissure characteristics of the monitored fracture surface of the excavated cavity are obtained through an in-situ test means which integrates digital drilling with camera shooting and integrates single hole sound waves with across hole sound waves, and the surrounding rock relaxation depth is comprehensively judged according to reduction of the wave velocity of the sound waves in an unloading relaxation area and the corresponding rock mass fracture condition. The technical scheme is simple, the test means is reliable, comprehensive collection and comparison analysis of columnar jointing rock mass unloading relaxation information are ensured, the surrounding rock relaxation depth is accurately confirmed, the in-situ test method can be widely applied to columnar jointing rock mass excavation and supporting projects such as water conservancy and hydropower projects, traffic projects and underground test site projects.

Description

technical field [0001] The invention relates to an in-situ test method for the relaxation depth of the surrounding rock of a columnar joint cavern project, which can be widely used in excavation and support projects of columnar joint rock mass in water conservancy and hydropower, transportation, underground test sites and the like. Background technique [0002] Columnar joints are a kind of regular columnar primary tensile fracture structure commonly found in volcanic lavas. The columns are basically perpendicular to the extension direction of the lava layer, and the internal joint fissures are abnormally developed. This joint includes columns and columns. The joints between them also include the recessive joints randomly developed inside a single column, and the columnar joint rock mass often presents a mosaic structure. The columnar jointed rock mass is prone to relaxation and cracking under the action of excavation and unloading, the self-stabilization time is short and t...

AI Technical Summary

Problems solved by technology

[0005] However, in actual engineering, the sound wave velocity of surrounding rock is not only affected by the relaxation of surrounding rock, but also affected by lithology, heterogeneity and structure.

Due to the special structure and significant anisotropy of columnar joints, the traditional in-situ acoustic wave testing method is obviously insufficient in determining the relaxation depth of this type of surrounding rock.

First of all, the joint fissures in the original rock of the columnar jointed rock mass are extremely developed, and are cut by the naturally formed interlayer and intralayer staggered zones. This natural defect inside the rock mass reduces the velocity of the acoustic wave, and it is difficult to perform the acoustic wave test under such conditions. Distinguish the original joints in the rock mass and the new cracks produced after excavation and unloading, which greatly affects the accurate determination of the relaxation depth of the surrounding rock; secondly, the existing in-situ acoustic testing is through drilling holes drilled in the surrounding rock After the test, the rock mass with mosaic structure produced surface unloading damage on the hole wall after drilling, and local drop rate occurred, which made the hole wall rock mass present an obvious fragmentation shape. This kind of rock mass structure with hole wall fragmentation It can occur not only in the unloading relaxation area, but also only on the surface of the hole wall, making it difficult for the acoustic wave velocity to truly reflect the integrity of the rock mass, so it is impossible to accurately determine the actual relaxation depth of the surrounding rock; Due to the influence of anisotropy characteristics, the acoustic wave velocity parallel to and perpendicular to the column axis has a significant difference. The existing method evaluates the relaxation limit and relaxation depth of the entire rock mass engineering based on a single wave velocity index, which is no longer suitable for rock masses with columnar joint structures. Reasonable judgment of relaxation depth

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