Reliability Analysis of Rock Supports in Underground Mine Drifts: A Case Study

Support failures in mine drifts represent potential hazards threatening underground mine safety and productivity. The aim of this study is to determine the reliability index associated with the rock supporting elements used in Ridder-Sokolny mine, an underground mine located in East Kazakhstan. Numerical simulations of the drift support and the first order reliability method (FORM) were employed to carry out the analysis. Several support cases were considered including; shotcrete, bolting, concrete, and combined bolting and concrete as well as unsupported drift case. For each support case, the factors of safety (FS), the reliability index (β) and the probability of failure (PF) were determined in accordance with the corresponding rock mass quality and excavation geometry. The results indicated the average FSs varied little for the different support cases (except for shotcrete); while β and PF vary more significantly between 0.62–3.25 and 0.05–27 (×103 %) factor depending on the rock conditions and support installed. The probability of failure of the rock support increases with a decrease in the rock mass quality. Similar trends were observed with an increase of the width/height ratio of the excavations for the same rock domain. These results illustrated that a single FS value obtained from a deterministic method may not always provide a sufficient indication of safety. This is in agreement with the field observations (many of the supports failed). Hence, on the basis of the reliability index of the supports, the requirement in terms of coefficient of variability of the rock mass quality to meet the target performance level was proposed. It is concluded that the results of this study could help improving the drift support design in Ridder-Sokolny mine.

Geochemistry Evaluation and Oil to Source Rock Correlation of Lhokseumawe Area, North Sumatra Basin

The purpose of this study was to evaluate the hydrocarbon source potential of the Middle Miocene Lower Baong Formation of the Lhokseumawe area and further attempt to establish a correlation of this possible source with the oil produced in the area by the mean of biomarkers analysis. Source rock characterization was realized by integrating several geochemical measurements including TOC, HI and Ro from the DY-1 and TM-1 wells. This has allowed us to define the organic content, maturity and kerogen type of the Lower Baong. Meanwhile, multiple produced oil samples from the area of interest were used to characterize their geochemical signature, based on a combination of isoprenoid, triterpane and sterane biomarkers, in an effort to determine maturity of those oils and the depositional environment of their source. This provides the basis of our attempt to correlate genetically oil and source rock in the Lhokseumawe area. The geochemical characterization of the Lower Baong suggest the formation to be an effective active source rock in the Lhokseumawe area with remaining average TOC of c1.5%, Kerogen Type II-III and maturity levels optimal for oil expulsion. Biomarker analysis of oils suggest an origin from a source facies deposited in open marine environment. Maturity level analysis using pentacyclic triterpane supports the source to be at peak maturity level. The correlation of oil with source rock supports largely that the Lower Baong oils are sourced by Lower Baong source facies of marine origin. However it worth noting that one oil family differs from this genetic correlation, opening speculation around other source facies to be active in the Lower Baong or an additional source interval to be active in the Lhokseumawe area. This could be interesting topic to be discuss in future.

In situ nuclear-glass corrosion under geological repository conditions

Silicate glasses are durable materials but laboratory experiments reveal that elements that derive from their environment may induce high corrosion rates and reduce their capacity to confine high-level radioactive waste. This study investigates nuclear-glass corrosion in geological media using an in situ diffusion experiment and multi-component diffusion modelling. The model highlights that the pH imposed by the Callovo–Oxfordian (COx) claystone host rock supports secondary-phase precipitation and increases glass corrosion compared with pure water. Elements from the COx rock (mainly Mg and Fe) form secondary phases with Si provided by the glass, which delay the establishment of a passivating interface. The presence of elements (Mg and Fe) that sustain glass alteration does not prevent a significant decrease in the glass-alteration rate, mainly due to the limited species transport that drives system reactivity. These improvements in the understanding of glass corrosion in its environment provide further insights for predictive modelling over larger timescales and space.

Ormen Lange Gas Field: Immediate Settlement of Offshore Rock Supports

Located approximately 120 km offshore, Ormen Lange, with an estimated 400×109 m3 of natural gas, is the second-largest gas discovery on the Norwegian shelf. The water depth is up to 850 m, making Ormen Lange the first deepwater project on the Norwegian continental shelf. The development of Ormen Lange is under shared operatorship between Norsk Hydro and Shell. Ormen Lange’s untreated well stream will be transported to shore in two 120 km long, 30 in. diameter pipelines to a processing plant at Nyhamna, Norway. From there, gas will be exported via a 42 in., 1200 km subsea pipeline (Langeled) to Easington at the east coast of the UK. The pipelines have to pass over the Storegga slide edge, which rises 200–300 m toward the continental shelf in very steep slopes, which are also encountered in the nearshore Björnsundet area. The uneven and steep seabed conditions require the use of approximately 2.8×106 tons of rock to support and stabilize the pipelines. The sea bottom conditions on the Norwegian continental shelf are characterized by many outcrops as well as very soft clay deposits. The immediate settlement of the rock supports during installation forms a significant amount of the total required rock volume. In this paper a procedure is presented on how to assess these immediate settlements recognizing four contributing components all being discussed separately. The calculation results are compared with a back analysis, performed during the execution of the Ormen Lange rockworks, proving the suitability of the calculation method.

Ormen Lange Gas Field, Immediate Settlement of Offshore Rock Supports

Located approximately 120 km offshore, Ormen Lange, with an estimated 400 billion m3 of natural gas, is the second-largest gas discovery on the Norwegian shelf. The water depth is up to 850 meters, making Ormen Lange the first deepwater project on the Norwegian Continental Shelf. The development of Ormen Lange is under shared operatorship between Norsk Hydro and Shell. Ormen Lange’s untreated well stream will be transported to shore in two 120 km long, 30-inch diameter pipelines to a processing plant at Nyhamna, Norway. From there, gas will be exported via a 42” 1200 km sub sea pipeline (Langeled) to Easington at the east coast of the UK. The pipelines have to pass over the Storegga slide edge which rises 200–300 meters toward the continental shelf in very steep slopes, which are also encountered in the nearshore Bjo¨rnsundet area. The uneven and steep seabed conditions require the use of approximately 2.8 million tons of rock to support and stabilize the pipelines. The sea bottom conditions on the Norwegian continental shelf are characterized by many outcrops as well as very soft clay deposits. The immediate settlement of the rock supports during installation form a significant amount of the total required rock volume. In this paper a procedure is presented on how to assess these immediate settlements recognizing four contributing components all being discussed separately. The calculation results are compared to a back-analysis, performed during the execution of the Ormen Lange rockworks, proving the suitability of the calculation method.

The Korean Final Repository for Low- and Intermediate-Level Radioactive Waste

The underground waste repository site is located at Gyeongju and is selected for the disposal of all the Low- and Intermediate-Level Radioactive Waste (LILW). Its operation is scheduled in the beginning of 2009. The repository, with a disposal capacity of 800,000 drums, will be constructed in granite bedrock near the seashore at the Gyeongju site. The repository will be constructed in phases to reach its final capacity of 800,000 drums. In the first phase of construction, the repository will have a capacity to dispose of 100,000 drums. The first phase of the repository design consists of an access shaft, a construction tunnel, an operating tunnel, an unloading tunnel, and six (6) silos. The silos are located at 80 to 130 meters below Mean Sea Level (MSL), in bedrock. Each silo is 24.8m in diameter and 52.4m in height. The silo will be reinforced with shotcrete, rockbolts and concrete lining for rock supports, and the lining will also act as an engineered barrier to limit radioactive nuclide release after closure. After serving its intended function the repository will be backfilled and sealed. The primary objective of backfilling and sealing is to prevent ground-water flow into the silos through the tunnel system and to prevent inadvertent intrusion into the repository after closure.

Nouvelles observations sur les roches vertes de l'anticlinal de Laniscat-Merleac (Cotes-du-Nord)

Observations on the dolerites of the northern flank of the E-W-trending Laniscat-Merleac anticline in NW France suggest that the rocks were emplaced as coulees. A well-marked granular differentiation in the rock supports this hypothesis; the coarse-grained rocks are in contact with Devonian rocks at the bottom of the coulee and the fine-grained rocks are in contact with Dinantian rocks at the top. Chemical analysis shows that there is a diminishing of Na <sub>2</sub> O and an augmentation of the percentage of CaO ranging from the boundary of the coarse-grained rock to that of the fine-grained. Overlying the green rocks are green schists of comparable chemical composition attributed to former tuffs which were subject to regional epimetamorphism. Finally, a coarse-grained, green rock sample has been traced to the spilite family.