A review on the performance of conventional and energy-absorbing rockbolts

This is a review paper on the performances of both conventional and energy-absorbing rockbolts manifested in laboratory tests. Characteristic parameters such as ultimate load, displacement and energy absorption are reported, in addition to load-displacement graphs for every type of rockbolt. Conventional rockbolts refer to mechanical rockbolts, fully-grouted rebars and frictional rockbolts. According to the test results, under static pull loading a mechanical rockbolt usually fails at the plate; a fully-grouted rebar bolt fails in the bolt shank at an ultimate load equal to the strength of the steel after a small amount of displacement; and a frictional rockbolt is subjected to large displacement at a low yield load. Under shear loading, all types of bolts fail in the shank. Energy-absorbing rockbolts are developed aiming to combat instability problems in burst-prone and squeezing rock conditions. They absorb deformation energy either through ploughing/slippage at predefined load levels or through stretching of the steel bolt. An energy-absorbing rockbolt can carry a high load and also accommodate significant rock displacement, and thus its energy-absorbing capacity is high. The test results show that the energy absorption of the energy-absorbing bolts is much larger than that of all conventional bolts. The dynamic load capacity is smaller than the static load capacity for the energy-absorbing bolts displacing based on ploughing/slippage while they are approximately the same for the D-Bolt that displaces based on steel stretching.

Discovery and Characterization of a Thermostable Esterase from an Oil Reservoir Metagenome

With the aim of identifying novel thermostable esterases, comprehensive sequence databases and cloned fosmid libraries of metagenomes derived from an offshore oil reservoir on the Norwegian Continental Shelf were screened for enzyme candidates using both sequence-and function-based screening. From several candidates identified in both approaches, one enzyme discovered by the functional approach was verified as a novel esterase and subjected to a deeper characterization. The enzyme was successfully over-produced in Escherichia coli and was shown to be thermostable up to 90°C, with the highest esterase activity on short-chain ester substrates and with tolerance to solvents and metal ions. The fact that the thermostable enzyme was solely found by functional screening of the oil reservoir metagenomes illustrates the importance of this approach as a complement to purely sequence-based screening, in which the enzyme candidate was not detected. In addition, this example indicates the large potential of deep-sub-surface oil reservoir metagenomes as a source of novel, thermostable enzymes of potential relevance for industrial applications.

Triassic to Cenozoic multi-stage intra-plate deformation focused near the Bogd Fault system,Gobi Altai,Mongolia

The Gobi Altai region of southern Mongolia has been in the Eurasian plate interior since the midMesozoic,yet has experienced episodic phases of deformation since that time.In this paper,we document field evidence to characterize and date the intra-plate tectonic history of the Gobi Altai region from the Triassic to the present.To this end,we provide detailed mapping of the structure and stratigraphy of the eastern flanks of Mt.Ih Bogd that contains the widest variety of rock-time units in the area.We carry out geochronological analysis of basaltic lavas and basement granite in the area.We demonstrate that a crystalline basement with a 502 ± 8 Ma granitoid（U/Pb） underwent two phases of basin formation in the Mesozoic.which we date with new40Ar/39Ar lava ages of 218.5 ± 1.5,123.2 ± 0.7 and 124.8 ± 1.2 Ma,respectively.Both phases are linked to deposition of fluvio-lacustrine sediments and trap-like basaltic volcanics,with cumulative thicknesses of 1000-1500 m.Both basins were likely north-facing half-grabens that developed underN-S extension,but were subsequently overthrusted by Paleozoic and older crystalline basement during a less well constrained,but likely mid-Cretaceous phase of N-S shortening and basin inversion.Our results are consistent with recent seismic imaging of rift basins100 km to the NE of the study area where a similar history was reconstructed.The multiple phases of intra-plate deformation appear to have parallel structural trends,most likely due to reactivated Paleozoic basement structures created during the original terrane amalgamation of the Central Asian Orogenic Belt continental crust.This strong basement heterogeneity may predispose it to reactivation,and make it sensitive to changes in the overall stress field of the Eurasian plate driven by forces at its margins and base.Detailed study of Mongolia’s multi-stage tectonic history may thus provide a key proxy for the long-term dynamics of the Eurasian plate.In addition,the repeated reactivation of the Gobi Altai region during the last 200 My supports the contention that non-cratonized continental interior regions composed of Phanerozoic terrane collages are particularly susceptible to fault reactivation,much more than older cratonized continental crust.

Gas Turbine Operation Offshore： Online Compressor Wash Operational Experience

Online compressor wash for six GE LM2500PE engines at a Statoil North Sea offshore field is analyzed. Three engines are generator drivers whilst three engines are compressor drivers. Two of the compressor drive engines are running at peak load （T5.4-control）, hence production rate is limited by the available power from these engines. All the six engines analyzed run continuously without redundancy, hence gas turbine uptime is critical for the field＇s production and economy. The performance and operational experience with on-line wash at different water-to-air ratios and engine loads, as well as economy potentials related to successful on-line wash are given. This work is based on long-term operation with on-line wash, where operational data are collected and performance analyzed, over a 4-5 year period. All engines are operated with four-month intervals between maintenance stops, where off-line crank-wash is performed as well as other necessary maintenance and repairs. On-line wash is performed daily between the maintenance stops at full load （i.e., normal operating load for the subject engine）. To keep the engine as clean as possible and reduce degradation between maintenance stops, both an effective on-line water wash system as well as effective air intake filter system, are critical factors. The overall target is to maintain high engine performance, and extend the interval between maintenance stops through effective on-line wash. It is of vital importance to understand the gas turbine performance deterioration. The trending of its deviation from the engine baseline facilitates load-independent monitoring of the gas turbine＇s condition. Engine response to water injection at different loads and water-to-air ratios, as well as engine response to compressor deterioration is documented and analyzed. Instrument resolution and repeatability are key factors required in order to obtain reliable performance analysis results. Offshore instrumentation on older installations is often limited to the necessary instruments for machine control/protection, and additional instruments for effective performance monitoring and analysis are often missing or, if installed, have less accuracy. As a result of these analyses, a set of monitoring parameters is proposed for effective diagnosis of compressor degradation. Avenues for further research and development are proposed in order to further increase the understanding of the deterioration mechanisms and the gas turbine performance and response.