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The deformational behaviour of salt rocks in situ: Hypotheses vs. measurements
Summary Published controversies regarding the in situ behaviour of salt rocks have been going on for many years. At the Fourth International Symposium on Salt, Houston 1973, an attempt was made to narrow the gap between theoreticians and practitioners in a specially arranged discussion session on applied rock mechanics. The results, recently reported in the Proceedings, were inconclusive, but alarming and led to the conclusion that we should proceed with caution with new “unprecedented” design methods; obviously, the gap between two schools of thought, the theoretical or stress envelope concept and the direct measurement school, is wider than ever, partly due to misleading publications which are corrected in this paper. The reasons why theoretical calculations based on laboratory experiments must not be applied to in situ conditions in conventional salt mines and in solution-mined caverns, are outlined with reference to published in situ measurement data:In situ deformations of salt rocks are not affected by strain-hardening that makes most laboratory testing procedures useless for practical application. In situ, the long-term opening convergence rates are constant under constant conditions.The first creep into new excavations in salt deposits is stress-relief creep; the creep rates decrease rapidly for few days until the original stresses in large zones around the openings are sufficiently adjusted to the very low creep limits of salt rocks.Reloading of stress-relieved zones depends on overburden subsidence which can be prevented by appropriate design to keep the long-term constant creep rates small. In cases where overburden subsidence occurs, the tension zones of subsidence troughs require particular attention. The overlapping of tension zones which approached each other from opposite directions has resulted in heavy rockbursts over potash mines. To avoid such potentially dangerous configurations, careful planning of the mining sequence is required in conventional mining as well as in solution mining of multiple cavern systems. Surface subsidence measurements carried out over many decades cannot be reconciled with hypothetical stable stress arches postulated again in some recent publications; in this regard,1nature has taught some serious lessons which made stress arches disappear from the German literature since 1958. More recently, expensive lessons were learned in North American potash mining and solution mining, particularly in Canada. It is strongly suggested that those who apparently mistake laboratory experiments for actual mining operations, learn the lessons taught by nature and exercise restraint in publications prior to doing the necessary homework.
The deformational behaviour of salt rocks in situ: Hypotheses vs. measurements
Summary Published controversies regarding the in situ behaviour of salt rocks have been going on for many years. At the Fourth International Symposium on Salt, Houston 1973, an attempt was made to narrow the gap between theoreticians and practitioners in a specially arranged discussion session on applied rock mechanics. The results, recently reported in the Proceedings, were inconclusive, but alarming and led to the conclusion that we should proceed with caution with new “unprecedented” design methods; obviously, the gap between two schools of thought, the theoretical or stress envelope concept and the direct measurement school, is wider than ever, partly due to misleading publications which are corrected in this paper. The reasons why theoretical calculations based on laboratory experiments must not be applied to in situ conditions in conventional salt mines and in solution-mined caverns, are outlined with reference to published in situ measurement data:In situ deformations of salt rocks are not affected by strain-hardening that makes most laboratory testing procedures useless for practical application. In situ, the long-term opening convergence rates are constant under constant conditions.The first creep into new excavations in salt deposits is stress-relief creep; the creep rates decrease rapidly for few days until the original stresses in large zones around the openings are sufficiently adjusted to the very low creep limits of salt rocks.Reloading of stress-relieved zones depends on overburden subsidence which can be prevented by appropriate design to keep the long-term constant creep rates small. In cases where overburden subsidence occurs, the tension zones of subsidence troughs require particular attention. The overlapping of tension zones which approached each other from opposite directions has resulted in heavy rockbursts over potash mines. To avoid such potentially dangerous configurations, careful planning of the mining sequence is required in conventional mining as well as in solution mining of multiple cavern systems. Surface subsidence measurements carried out over many decades cannot be reconciled with hypothetical stable stress arches postulated again in some recent publications; in this regard,1nature has taught some serious lessons which made stress arches disappear from the German literature since 1958. More recently, expensive lessons were learned in North American potash mining and solution mining, particularly in Canada. It is strongly suggested that those who apparently mistake laboratory experiments for actual mining operations, learn the lessons taught by nature and exercise restraint in publications prior to doing the necessary homework.
The deformational behaviour of salt rocks in situ: Hypotheses vs. measurements
Baar, C. A. (author)
1975
Article (Journal)
English
The deformational behaviour of salt rocks in situ: Hypotheses vs. measurements
| Online Contents | 1975
| British Library Online Contents | 2000
| Engineering Index Backfile | 1958