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Influence of Geometry on the Broken Zone of Underground Cavity

Author: SunYouWei
Tutor: BaoJingShan
School: China Seismological Bureau, Institute of Engineering Mechanics
Course: Geotechnical Engineering
Keywords: Underground cavity Broken zone Factor of geometry Numerical simulation
CLC: TU457
Type: Master's thesis
Year: 2006
Downloads: 429
Quote: 12
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Abstract

The development and exploitations of underground space is one of theimportant trends of Geotechnical Engineering. Underground cavities aresome kinds of useful structures which are built in rock or soil. Thecavities break the balance of the natural stress. They make the stress tocome to a new balance. One of the important ways that analyze thestability of underground cavities is how to make out the stress ofsurrounding rocks. There are many factors which can influence the stressof surrounding rocks. Broken zone is a very important factor.When we build an underground cavity, the stress of the surroundingrock will change. If it changes enough that the rock can not sustain, thesurrounding rocks will change its elastic state into plastic. We call therange of rocks plastic broken zone, or broken zone for general. The zonehas some main characteristics: the number of crannies increase;thecohesion, friction angle and modulus become much smaller. The researchabout the range and the distribution features of broken zone makessignificant sense. It can help to make sure the stress of surrounding rockand finish the design of liners. The distribution of broken zone isinfluenced by many factors. This thesis studies the important factor ofgeometry, which mainly involves the following aspects:1. After referring to a large amount of literature materials, itsummarizes the history and the present state of the research on thetheory of broken zone, expounds in details about the presenttheories all over the world, and also points out their using range andlimitation. It gives a general introduction about the numericalmethod analyzing.2. A brief summary of the basic theory of underground cavity brokenzone, the influence of surrounding rock made by underground cavity,methods of calculating, which mainly consists of the introductionabout basis theory of broken zone, the redistribution of stress ofsurrounding rocks caused by digging, range of the stress whichbecomes a new balance and methods about calculating.3. A brief summary of the history, factors and steps of solvingproblems about FLAC. It also gives an introduction aboutsuperiorities of FLAC in numerical analysis of underground cavityand some useful commands.4. The conclusion after having the numerical analysis of theinfluencing factor of geometry:1) The influence of section’s area: with the increase of the section’s area,the broken zone will concentrate on the two sides;the range of brokenzone becomes larger and expands faster. The range of broken zone onthe top of cavity becomes larger.2) The influence of section’s height: with the increase of the section’sheight, the broken zone on the two sides becomes larger, the zone onthe corner deepens;the range of broken zone expands faster and has awider influence towards the direction of height.3) The influence of section’s span: with the increase of the section’s span,the range of the broken zone in the area of the top and two sidesbecomes larger;especially, the zone in the top area expands obviously;the broken zone become larger and more damageable.4) The influence of complex shape: some kinds of shape can make thecavity damageable, some can’t. If you choose a right shape, you willdesign an underground cavity with smaller broken zone.5. On the basis of the above research about the influencing factors, thisthesis gives a method of stress research: when you want to study thestress of complex-shape cavities, you can consider the stressdistribution of some simple shapes. There are several differences incertain parts. You can check it by numerical analysis.6. On the basis of the research about the influencing factors, this thesisgives some useful suggestions about tunnel liners:1) An underground cavity being built, the liners should be quickly builtat the initial stage, which makes the range of broken zone smaller.2) The liners should be made on the sides, on the top or at the corners.3) If you use shield-driven tunneling technique, the tunnel liners shouldbe built as early as you can, which can avoid the break of undergroundcavities.

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