In the present paper an appreciation table is suggested in which the stability of karst caverns is classified into four ranks. By the use of orthotropic finite element analysis stresses and displacements around a karst cavern are obtained. In examining the stability of a whole cavern, Mohr-Coulomb strength theory is applied to check the stability of rock and weak structural faces. In respect to analyzing the stability of part of a cavern, the theory of "block equilibrium" is adopted. The stability of caverns are measured in-situ with the pressure cells. Actual examples are illustrated.
In diesem Artikel wird eine Tablle aufgestellt, in der die stabilitat des Karstes in vier Klassen unterteilt wird mit der ortho-anisotropischen Finite-Element Methode werden die Spannungen und Verschiebungen zweiter Ordnung des umschließenden Gesterinskörpers berechet. Durch Untersuchungen der Festigkeit des Gesteins und der schwachen Strukturflachen mit der Mohr-Coulomb Theorie wird die Gesamtstabilitat des höhenumschließenden Gesteinskorpers bewertet, und die teilweise Stabilitat wird dann mit der "block-equilibrium Theorie untersucht. Die Stabilitat des Gesteinskörpers wird durch Messung mit der "Druckbuechsen" verfolgt.
Les presents papiers vous montront le tableau de degre evaluant la stabilite en quatre degres. On calcule et analyse des elements limitatifs et orthoanisotropiques afin d''obtenir le deplacement et la contrainte secondire d''une caverne. Pour evaluer la stablite en ensemble de la caverne, on emploie la theorie de l''intensite Mohr-Coulomb à examiner l''intensite des roojes et de la surface de structire faible, et d''apres la theorie "equilibre bloc", evaluer la stabilite des parties localisees de cette caverne. Prendre sur place la "boite à presser" pour examiner la stabili te de la caverne en question.
Karst caverns are formed by dissolution and erosion along the slits of soluble rock by filtering ground water. In the process of dissolution and erosion the unstable blocks of caverns will collapse, thus their cross-sectional areas will further increase.
There are many karst caverns scattered over all districts in Chongqing, China. For energy savings and cultivated land conservation these karst caverns may be utilized for underground storage of petroleum or gas, for treatment of waste material or for other purposes. As a matter of fact several karst caverns have been converted into parks as well as underground factories, etc. Hence, it is becoming very important to use these resources more efficiently and rationally.
How to determine whether the surrounding rock of karst cavern is stable is a question to be solved before making the decision to use it. As the process by which karst caverns are formed is quite different from that of man-made ones, the way to evaluate the stability of the former is slightly different. It depends essentially on the qualitative engineering geologic appraisal combined with rockmass mechanics quantative evaluation. This paper is intended to make a discussion on the following subjects: the engineering geologic stability index of a karst cavern, stresses in surrounding rock, global or local stability of surrounding rock, as well as long time monitoring the stability in-situ. Illustrated actual examples are cited.
(Table in full paper)
The main factors influencing stability of karst cavern are the nature of rock formation, geological structure, hydrogeological condition, state of cavern roof, unstable rocks, etc. These factors have a close tie with the stability of the surrounding rock.
In accordane with the preceding five main factors affecting stability, we have made a complete analysis of many actual karst caverns in Chongqing and proposed a stability index as the criteria to determine the stability of karst caverns for various uses, see table 2.1. The stability is classified into four ranks: in stable, basically stable, less stable and unstable.
Indices of karst cave and unstable rock" classification are shown in table 2.2; indices of degree of fissuration in table 2.3; indices of rock thickness classification in table 2.4.
In the classification of rock inclination, it is called an "inclined state" when the angle of slope of the rock is above 15°, and a "flat state" when below 15°.