Jaak J.K. Daemen

Fractal characteristics of rock discontinuities

Abstract The discontinuities in a rock mass usually control its overall behavior. Rock mass deformability, stability of underground excavations, and flow of fluid depend significantly on the intensity, the degree of interconnection, and the characteristics of the fracture network present. We apply the theory of fractal geometry to describe the rock fracture network. Three parameters characterize the discontinuities visible in the exposed face of the investigated rock mass. The first parameter measures the complexity of the network formed by the individual traces of the discontinuities. The intensity and the interconnectivity of the discontinuities are characterized by the fracture density and the block density respectively. We use data from four faces of a copper mine in Arizona. All three parameters show fractal characteristics over the range investigated with coefficients of determination better than 0.99. The fractal structure of these parameters suggests that the rock fracturing process may be a scale-independent phenomenon.

Analysis of major risks associated with hydrocarbon storage caverns in bedded salt rock

Abstract Salt rock is internationally accepted as an ideal medium for energy storage. As an energy storage structure, the safety of hydrocarbon storage caverns in salt rock is related to the national economy and to social public security. Risk analysis is an important method of engineering safety evaluation. In this paper the major risks associated with hydrocarbon storage caverns in bedded salt rock are defined. The major risks are classified under the headings of ‘oil and gas leakage’, ‘ground subsidence’, and ‘cavern failure’, and are discussed under these topical titles. The factors leading to the major risks associated with storage caverns are identified by reviewing descriptions of major accidents of salt storage caverns around the world. Fault tree models for the three major risks are established and analyzed. Basic paths of the risk and their occurrence probability ranking are derived. The risk factors which contribute greatly to the risk are identified by calculating the importance degree of all the basic events. Finally, a comprehensive evaluation methodology for major risk loss is generated based on the analytic hierarchy process. This provides a theoretical foundation for the evaluation and prevention of major risks in the construction and operation of storage caverns in bedded salt rock.

Influence of degree of saturation on the borehole sealing performance of an expansive cement grout

The strength measures of expansive cement grout borehole plugs cast in welded tuff cylinders is investigated as a function of the degree of saturation of the plugged rock cylinder and of borehole size. Details on experimental procedure regarding rock cylinder and cement grout preparation, sample curing conditions, experimental apparatus, sample loading, mechanical characterization of the rock, and cement grout, along with procedures for the determination of the sample saturation assuming uniform saturation, and strength measures are presented. The extrapolated axial strengths to a plug radius of 100 mm show that the more saturated samples show higher strengths as compared to the dry samples. The strength measures decrease with increasing plug radius, obeying a power law.

An empirical strength criterion for heterogeneous tuff

Abstract An empirical failure criterion is formulated by expressing the second invariant of stress deviation at failure as a function of the first invariant of stress, key parameter, and volume. Strength data from Apache Leap tuff specimens are analyzed as a demonstration example. The density variable included as a key parameter for this tuff minimizes the effect of heterogeneity caused by nonuniform distribution of pores, mineralogy, inclusions, welding and grain bonding. The criterion incorporates all principal stresses and the scale effect, and hence allows predicting the strength toward in-situ conditions. The proposed derivation improves the correlations between test results and failure envelope for the heterogeneous tuff. The criterion formulated from the uniaxial and triaxial test data adequately predicts the strengths for biaxial compression tests.

Performance assessment of cement grout borehole plugs in basalt

Abstract Flow tests have been conducted on expansive cement grout plugs with diameters of 160 mm and 200 mm, and length-to-diameter ratios of one, in boreholes in basalt blocks and in steel pipes. Two types of flow tests have been performed: pseudo-constant head tests and transient pulse tests. Hydration temperatures of cement grout plugs have been monitored in steel pipes with inside diameters ranging from 110 mm to 200 mm. During flow tests, basalt blocks have fractured, presumably due to water injection pressure, cement grout expansion, packer pressure and temperature differences. Falling head tests performed on some block fractures indicate a complex interaction between a cement grout borehole plug and the rock, as determined from the hydraulic conductivities of fractures intersecting plugged boreholes.

Electrochemical Corrosion Behavior of Low-Carbon I-Beam Steels in a Simulated Yucca Mountain Repository Environment

Abstract The electrochemical corrosion behavior of low-carbon steel (CS) was examined in a simulated Yucca Mountain (YM) groundwater by varying the electrolyte concentration and temperature under a...

Sealing of boreholes using natural, compatible materials: Granular salt

Granular salt can be used to construct high performance permanent seals in boreholes which penetrate rock salt formations. These seals are described as seal systems comprised of the host rock, the seal material, and the seal rock interface. The performance of these seal systems is defined by the complex interactions between these seal system components through time. The interactions are largely driven by the creep of the host formation applying boundary stress on the seal forcing host rock permeability with time. The immediate permeability of these seals is dependent on the emplaced density. Laboratory test results suggest that careful emplacement techniques could results in immediate seal system permeability on the order of 10{sup {minus}16} m{sup 2} to 10{sup {minus}18} m{sup 2} (10{sup {minus}4} darcy to 10{sup {minus}6}). The visco-plastic behavior of the host rock coupled with the granular salts ability to ``heal`` or consolidate make granular salt an ideal sealing material for boreholes whose permanent sealing is required.