Solution-mined salt caverns for the disposal of hazardous chemical wastes

The need for storage caverns (oil, gas) and depositories (radioactive waste, toxic chemical waste) is rising world-wide. Rock salt (halite) formations are particularly suitable for the construction of cavities for such purposes. Rock salt is practically impermeable to gases and liquids. The solution mining method provides the means for the creation of large storage capacities at economic costs and, due to its favourable geomechanical properties, halite remains stable over long periods of time without support. Moreover, it can be shown that underground depositories in salt are safer from an environmental point of view compared with conventional depositories in shallow ground. Howover, safety analysis has to be carried out in each case based on specific site-investigated data. The geotechnical behavior of rock salt is well-known, with sufficient details for dimensioning purposes. For liquid-filled cavities, long-term sealing from the biosphere is of particular cementation has to be proved and it must be shown that the natural pressure rise in the closed cavity due to long-term convergence does not exceed the frac pressure. It is shown that the risk of hydraulic fracturing can be calculated with the aid of finite element computations. Hydraulic fracturing depends on the height and depth of the cavity as well as on the pressure increase rate.     

Engineering geological and safety technological aspects for the final disposal of in situ-consolidated radioactive waste in hard rock and salt formations

In connection with its research and development work the Gesellschaft für Strahlen- und Umweltforschung mbH München (GSF) has successfully developed and tested methods for the final disposal of low and medium radioactive waste in 200 litre containers at the Asse salt mine. The low radioactive waste (LLW) was disposed of in chambers using various methods. The medium radioactive waste (MLW) was transported in single radiation shielding containers of almost 9 t weight into the former rocksalt mine. Subsequently the 200 l containers were lowered into the storage chamber. Analysis of past experience indicated that the storage methods as developed could be improved upon. Under the direction of the Reprocessing Project (PWA: Projekt Wiederaufarbeitung) in Kalrsruhe an R & D programme was started for the containerless final disposal of low and medium radioactive waste with subsequent consolidation in situ into a quasi-monolithic block. The process consists of the following steps: The low and medium radioactive waste produced in a reprocessing plant is processed into a 5 mm cement granulate. The hardened cement granulate is mixed in an aboveground installation with a cement slurry. The mixed product is dosed with additives and channelled under gravity down a vertical conduit of only 60 mm diameter into 75 000 cm³ caverns. Several other parties are involved in the project, which has been underway since 1976 in three main phases.

Phase I Proof of technical feasibility in principle

Phase II Preparation of a detailed technical concept

Phase III Large scale testing with 1 000 m³ inactive simulated product and transport of this product down approx. 1 000 m production pipe into the 10 000 m³ prototype cavern at Asse.

The caverns are constructed either conventionally, i.e. drilling and blasting or part-face heading machies or by solution mining in rock salt structures. This paper deals in particular with the drilling engineering, problems and solutions, and the storage area construction and sealing techniques.     

Acoustic emission in host-rock material for radioactive waste disposal: comparison between clay and rock salt

The use of clay masses for radioactive waste disposal requires a comprehensive analysis of fracture processes in clay. Acoustic emission (AE) was used to obtain a better insight into damage evolution during uniaxial loading of Boom Clay specimens. A comparison of AE in clay and rock salt shows a much lower AE activity in clay. This, together with the higher attenuation, would inhibit the use of the AE technique for large-scale in-situ monitoring in clay masses. Cyclic uniaxial tests showed that, similarly to rock salt, clay exhibits a very well-pronounced Kaiser effect in AE with Felicity ratios around unity. The Kaiser effect takes place at different loading stages (before and at the flow limit) and, during reloading, it coincides with the deformation curve inflection. Further research is required to study the applicability of the Felicity ratio as a measure of the intensity of healing processes in clay. Electronic Publication     

Evaluation of dissolution for radioactive waste repositories in salt deposits

Several evaporite basins containing bedded salt and dome salt deposits in the USA and Europe are currently being investigated as potential repositories for radioactive waste. While salt has good geomechanical properties for the long-term isolation of radioactive wastes, all such deposits have undergone various degrees of dissolution by circulating unsaturated groundwater. The extent and rate of such dissolution poses a challenge to the geologists evaluating an area for a repository. Detailed investigations at the Waste Isolation Pilot Plant (WIPP), a proposed repository for transuranic (TRU) radioactive wastes located in the Delaware Basin in Southeastern New Mexico, U.S.A., have outlined a broad dissolution front for the Salado formation. An approximate rate of advance of the dissolution front at 1 km per 100,000 years horizontally and 10 meters per 100,000 years vertically, has been calculated. Similar calculations have been performed for other basins with different degrees of uncertainty due to the limitations in surface mapping and core or well-log correlations. Unless such calculations can be performed satisfactorily, questions will remain about the future integrity of a repository located in such an area.     

Geohydromechanical processes in the Excavation Damaged Zone in crystalline rock, rock salt, and indurated and plastic clays—in the context of radioactive waste disposal

The creation of an excavation disturbed zone (EdZ) or excavation damaged zone (EDZ) is expected around all man-made openings in geologic formations. Macro- and micro-fracturing, and in general a redistribution of in situ stresses and rearrangement of rock structures, will occur in this zone, resulting in drastic changes of permeability to flow, mainly through the fractures and cracks induced by excavation. The EDZ may have significant implications for the operation and long-term performance of an underground nuclear waste repository. Various issues of concern need to be evaluated, such as processes creating fractures in the EDZ, the degree of permeability increase, and the potential for sealing or healing (with permeability reduction) in the zone. In recent years, efforts along these lines have been made for a potential repository in four rock types—crystalline rock, salt, indurated clay, and plastic clay—and these efforts have involved field, laboratory, and theoretical studies. The present work involves a synthesis of the ideas and issues that emerged from presentations and discussions on EDZ in these four rock types at a CLUSTER Conference and Workshop held in Luxembourg in November 2003. First, definitions of excavation disturbed and EDZs, that may be applicable to all four rock types, are proposed. Then, an approach is suggested for the synthesis and intercomparison of geohydromechanical processes in the EDZ for crystalline rock, salt, indurated clay, and plastic clay. Comparison tables of relevant processes, associated factors, and modelling and testing techniques are developed. A discussion of the general state-of-the-art and outstanding issues is also presented. A substantial bibliography of relevant papers on the subject is supplied at the end of the paper.     

Thermal and mechanical behaviour of refrigerated caverns in hard rock

One key issue in the design of unlined caverns for low temperature products is understanding the disturbance of the rock fracture network. Increasing aperture and extension of fractures inevitably affect the rock mass stability, the heat loss from stored products, and the risk of ice growth in cases when water invades the cavern. Consequently, it is essential that the designer of a refrigerated cavern has appropriate knowledge of the coupled thermal and mechanical behaviour of the fractured rock mass. Chalmers University of Technology in Gothenburg, Sweden has for several years, carried out research in the field of mechanical and physical phenomena of rock masses subjected to low temperatures. The main investigation was performed in a pilot scale cavern in hard rock, constructed as a vertical cylinder with a diameter of 7 m and a height of 15 m. The facility was equipped with comprehensive instrumentation, including approximately 200 temperature gauges and 140 deformation gauges. In the test, the temperature in the cavern was reduced in a stepwise manner to −40 °C, with comprehensive monitoring of relevant parameters such as relative humidity, air and rock temperature, rock strain, rock fracture aperture, cavern convergence and rock mass deformation. Prior to the field test, major efforts were made to predict the field results by analytical and numerical methods. The essential results of the theoretical analyses and the actual measurements of thermal and mechanical behaviour of the cavern are given in this paper.     

The generation and disposal of solid wastes in Australia

In Australia there has been an increasing consumption of such materials as plastics, paper and metals which ultimately form solid wastes. It is expected that within the next 30 years the per capitasolid waste production, now 1#lb75 lbs/person/day, will double. This has led to a number of factors causing environmental problems. Attention is focussed on pollution, resource depletion and possible alternative resource usage, some of the problems which occur directly as a result of the consumption of a natural resource. In addition the problems caused by the production of waste containers, paper and such are discussed. These include garbage disposal and litter control in an urban society. Recycling of glass and paper products is now widely practised in Australia and plans have been made to recycle metal containers. In addition, some of the social issues pertinent to these topics are briefly outlined.     

Design and construction aspects of unlined oil storage caverns in rock

An underground oil storage facility comprising six storage caverns is under construction in southern Korea. Each of the horseshoe-shaped caverns is 18 m wide, 30 m high, and 400–600 m long. The artificial water curtain system used consisted of water curtain tunnels and horizontal boreholes drilled from these tunnels, and pre-grouting measures have been introduced to keep the bedrock saturated all the time in order prevent oil from migrating through rock mass. The results of site investigation show that the bedrock at the site was very competent and impermeable and, hence, a suitable medium for the storage of oil. This conclusion was confirmed later by the results of design analysis, the revised instrumentation program, and hydraulic tests performed during construction. In general, design concepts for the excavation and support and water curtain system have been verified to be reasonably good in terms of the technical soundness and economy. The results of the revised instrumentation program indicate that the three-dimensional excavation behaviour is complex and should be studied in more detail.     

Fuzzy approach for preliminary design of weak rock slopes in lignite mines

Rock slope failure modes are either driven by structurally controlled mechanisms (planar, wedge, or toppling failure) or lean upon the highly jointed or weak rock mass (circular failure). Developing practical tools for preliminary slope design is a popular topic among geotechnical society. This study proposes a practical methodology to predict a safe overall slope angle for weak rock slopes of lignite mines. Rock mass rating (RMR) and slope mass rating (SMR) classification systems can be remarkably misleading for weak rocks. Fuzzy modification was proven to improve rock and slope quality predictions. In addition, structurally controlled failures can be estimated more precisely. Later, a popular slope performance chart of Bieniawski that is based on RMR was modified by the fuzzy approach, and the computer models of a weak rock mass failure in a Turkish lignite mine are presented. The modified methodology was proven to be better suited to the weak rock conditions.     

下金煤矿半煤岩巷道支护设计与应用研究

对下金煤矿的情况和支护历史做了简单分析,重点论述了锚网喷支护技术在回风下山巷道中的应用,并与其他用U型钢支护的巷道在经济上和实际支护效果上做了简要对比,表明了锚网喷支护技术在煤矿巷道支护方面的优越性。     

A new framework for evaluation of rock fragmentation in open pit mines

The main purpose of blasting in open pit mines is to produce the feed for crushing stage with the optimum dimensions from in situ rocks. The size distribution of muck pile indicates the efficiency of blasting pattern to reach the required optimum sizes. Nevertheless, there is no mature model to predict fragmentation distribution to date that can be used in various open pit mines. Therefore, a new framework to evaluate and predict fragmentation distribution is presented based on the image analysis approach. For this purpose, the data collected from Jajarm bauxite mine in Iran were used as the sources in this study. The image analysis process was performed by Split-Desktop software to find out fragmentation distribution, uniformity index and average size of the fragmented rocks. Then, two different approaches including the multivariate regression method and the decision-making trial and evaluation laboratory (DEMATEL) technique were incorporated to develop new models of the uniformity index and the average size to improve the Rosin-Rammler function. The performances of the proposed models were evaluated in four blasting operation sites. The results obtained indicate that the regression model possesses a better performance in prediction of the uniformity index and the average size and subsequently the fragmentation distribution in comparison with DEMATEL and conventional Rosin-Rammler models.     

An interval fuzzy comprehensive assessment method for rock burst in underground caverns and its engineering application

Bulletin of Engineering Geology and the Environment - Rock burst is a dynamic process involving the sudden release of elastic energy accumulated in overstressed rocks and coal masses during...     

Construction and utilization of rock caverns in Singapore Part B: Development costs and utilization

This part examines the potential uses of underground caverns such as shelter and recreational centre, water collection storage and treatment, sewage treatment, oil and gas storage, cold and dry storage, power station, underground pumped hydroelectric storage, military installation, and industrial waste repository in Singapore. It also presents the cost aspects of cavern-development. The costs of a crude oil storage and a warehouse scheme are closely examined and comparisons are made with above-ground development costs. The benefits of using underground caverns in Singapore are discussed.     

Engineering geological characteristics,failure modes and protective measures of Longyou rock caverns of 2000 years old

The Longyou rock caverns are a group of large ancient underground caverns. They were caved manually in pelitic siltstone in the Quxian Formation of Upper Cretaceous. They have the following five characteristics: more than 2000 years old, man-caved, large spanned, near ground surface and medium to hard surrounding rock. They were unearthed by local farmers who were pumping water out of five small pools on a rough-flat ground in 1992. This discovery called the attention of many specialists from China, Japan, Poland, Singapore and USA. One of the most interesting and challenging questions is why the five caverns have been able to keep their integrity for more than 2000 years. To address this question, this paper presents the engineering geological conditions of the caverns and their adjacent areas. They include the following five conditions: (a) geological setting, (b) hydrogeological conditions, (c) seepage in integrity caverns, (d) fractures in integrity caverns and (e) failed caverns. Based on these investigation results, the paper further examines the potential failures of the integrity caverns and their protective measures.     

A regional-scale engineering geological study for selecting suitable rock masses for constructing unlined oil storage caverns in Southern Zagros,Iran

Bulletin of Engineering Geology and the Environment - The southern section of the Zagros zone in southwestern Iran, a well-known sedimentary basin, was investigated to address two key questions:...     

Design,construction and mechanical behavior of relics of complete large Longyou rock caverns carved in argillaceous siltstone ground

This paper presents a comprehensive summary of data, analyses and findings from the investigations over the past twelve years about the relics of large Longyou rock caverns carved about 2 000 years ago at shallow depths in argillaceous siltstone. The paper presents the typical features associated with the rock caverns. They include structures, large spans, portals, extreme shallow-buried depths, imprints, drainages, inclined ceiling, inclined sidewalls, slender rock pillars, rock staircases, site and strata...     

Prediction of rock burst in underground caverns based on rough set and extensible comprehensive evaluation

Bulletin of Engineering Geology and the Environment - In high terrestrial stress regions, rock burst is a major geological disaster influencing underground engineering construction significantly....     

Construction and utilization of rock caverns in Singapore Part A: The Bukit Timah granite bedrock resource

The Bukit Timah granite underlaying central and northern Singapore has been studied for the feasibility of hosting large unsupported rock caverns. Detailed geological investigation, comprising mapping, seismic refraction and electrical resistivity surveys, deep vertical and inclined drilling, conventional and geophysical borehole logging and in-situ hydraulic testing (at a selected location), as well as laboratory testing, have been performed. The results indicate that the granite is of extremely good quality and suitable for the construction of large unsupported caverns. Therefore, the Bukit Timah granite should be considered as a valuable resource for cavern and underground space development in Singapore.     

Implications of safety requirements for the treatment of THMC processes in geological disposal systems for radioactive waste

The mission of nuclear safety authorities in national radioactive waste disposal programmes is to ensure that people and the environment are protected against the hazards of ionising radiations emitted by the waste.It implies the establishment of safety requirements and the oversight of the activities of the waste management organisation in charge of implementing the programme.In Belgium,the safety requirements for geological disposal rest on the following principles:defence-in-depth,demonstrability and the radiation protection principles elaborated by the International Commission on Radiological Protection(ICRP).Applying these principles requires notably an appropriate identification and characterisation of the processes upon which the safety functions fulfilled by the disposal system rely and of the processes that may affect the system performance.Therefore,research and development(RD)on safety-relevant thermo-hydro-mechanical-chemical(THMC)issues is important to build confidence in the safety assessment.This paper points out the key THMC processes that might influence radionuclide transport in a disposal system and its surrounding environment,considering the dynamic nature of these processes.Their nature and significance are expected to change according to prevailing internal and external conditions,which evolve from the repository construction phase to the whole heatingecooling cycle of decaying waste after closure.As these processes have a potential impact on safety,it is essential to identify and to understand them properly when developing a disposal concept to ensure compliance with relevant safety requirements.In particular,the investigation of THMC processes is needed to manage uncertainties.This includes the identification and characterisation of uncertainties as well as for the understanding of their safety-relevance.RD may also be necessary to reduce uncertainties of which the magnitude does not allow demonstrating the safety of the disposal system.