Block caving is a most cost effective underground mining method and it is expected as a major mining method in the near future by replacing large-scale/massive open pits where a risk of slope failure and waste/ore ratio is higher as pit depth is deeper. The Northparkes Mines is well known as a pioneer of block caving mining in Australia and has ever produced copper-gold ore by using block caving from 1995. The E48 mine is the fourth block caving project in the mines and its development was started in 2006 following the block cave production in the E26 mine. The ore body can be categorised as a porphyry copper-gold deposit and the geometry is almost shaped pipe. The extraction level is located about 600m below the surface and its footprint is sized only 310m x 193m in plan, which means the E48 has very 'tall' mining zone comparing to other block caving projects in the world. The cavability has been assessed by intensive geotechnical studies based on the past experiences in the E26 mine. The extraction level is designed to maximise not only mining recovery but also productivity, taking into account stability of all the drives. Post-undercut method was selected to initiate caving and designed carefully not to damage the extraction level excessively by stress concentration and blasting. In order to improve safety, work environment, productivity and mining cost, all underground electric loaders are unmanned and to be operated remotely from the surface office by only a couple of operators.
Force-displacement curves such as penetration resistance-penetration curve in rock drilling have very important role for accurately estimating the performance of excavation machinery. The simplest model to represent the bit-rock interaction is a linear spring of which the spring constant is used to be determined experimentally and so difficult to find the relation with the rock physical properties. In this study, a variable compliance type constitutive equation proposed on the basis of experimental data was used instead of the conventional linear spring. Simulation to estimate penetration-time and penetration resistance-time curves were carried out for four excavation machines; rock drill, large rock hammer, roadheader and tunnel boring machine. In all cases, penetration resistance increases linearly at first and soon reaches the peak value that depends on parameters in the constitutive equation. Finally the resistance decreases very rapidly. The calculated results are considered to be reasonable and consistent with the measured data in qualitative means. It can be said that the proposed method could be applied to more realistic and sophisticated simulations combined with FEM or other appropriate calculation methods.
Rocks exhibit anisotropy due to their microscopic structure. Anisotropy of mechanical properties, especially the deformability, is an important parameter for geotechnical designs and overcoring stress measurement. Theoretical and experimental studies have been done to evaluate the anisotropy of rocks using elastic wave tests and loading tests. For soft rocks, the pressure dependency of anisotropy is considered not to be negligible. This paper deals with the method of evaluating the anisotropy and its pressure dependency of soft rocks. The method is based on loading tests instead of elastic wave tests, because anisotropy at the strain level of loading tests is suitable for the engineering purposes. Orthogonal anisotropy is considered here. The directions of anisotropic axes are treated unknown. A thorough evaluation of the anisotropy at low stress level has been found possible by uniaxial loading tests of specimens from 6 directions (X,Y,Z,XY,YZ,ZX). Four rosette gauges with 3 elements have been attached at the sides of each specimen. The direction of the main anisotropic plane analytically determined from the uniaxial tests coincided well with the bedding plane observed on the rock. Then hydrostatic pressure test has been adopted to measure the pressure dependency of the principal normal stiffness C11, C22 and C33. The curves of these 3 stiffnesses and 3 parameters of anisotropic direction have been obtained against the pressure from 0 to 20 MPa. Thus an experimental and analytical procedure of determining orthogonal anisotropy and its pressure dependency has been proved. The rock used in this study is Opalinus clay. Some findings about this rock are that hypothesis of transverse isotropy may not be accurate enough even for a rock with clear lamina, and that C11/C33 can be so large as more than 3 even at high confining pressure of about 20 MPa.
The migration phenomena of CO2 in the porous rock sample were visualized by X-ray CT. Then the storage ability of the rock sample was analyzed as the replacement ratio determined from the X-ray CT image data. This is the fundamental study related to the CO2 geological sequestration and the understanding CO2 migration process during and after the storage is one of the most important factors. In this study, CO2 migration visualization system was newly developed and the CO2 injection test into the water saturated porous rock samples was conducted. The nominal density change due to the replacement by CO2 was visualized by X-ray CT. Here, the method to evaluate the amount of CO2 replacement in the rock sample from the X-ray CT data was introduced, and the value of Berea sandstone was estimated. From the observation of replacement process in the rock sample, anisotropy of the migration process and storage ability was clarified.
Seasonal variation of heavy metal accumulation in soils was investigated from March 2002 to December 2003 in a constructed wetland in Kaminokuni, Hokkaido, Japan. Precipitation of iron (oxyhydro)oxides in the wetland is the principal reaction and also governs the immobilization of trace heavy metals. Immobilized forms of heavy metals were related with microbial metabolism and reactions of anaerobic microorganisms, which are active in wetland plant root zones in summer seasons. Mn(III,IV) -reducing and Fe(III)-reducing microorganisms enhanced the reductive dissolution of manganese and iron (oxyhydro)oxides, which resulted in the release of Mn(II) and Fe(II) and other bound heavy metals. Heterotrophic microorganisms such as sulfate-reducers decomposed organic matters to lower molecular weight acids and bicarbonates leading to increase in alkalinity, formation of zinc carbonates and complexation with Cu(II). Populations of sulfate-reducing bacteria in the wetland soil varied seasonally with 1~2 orders of magnitude and, depending on the depth, increased especially around root zones of wetland vegetations.
Heavy metal contents in representative emergent vegetations, Phragmites australia and Typha latifolia, were investigated from March 2002 to December 2003 in a constructed wetland in Kaminokuni, Hokkaido, Japan. Typha latifolia was more effective to Mn2+ sorption than Phragmites australis. Manganese was accumulated in leaves in Typha latifolia, upto 14 mg/g-dry weight. Accumulation of Mn in leaves of Typha latifolia was likely the result of activated demand of Mn in photosynthesis during summer and autumn. In contrast, Fe, Zn and Cu distributions were markedly localized and mostly concentrated in root sections of both plants in all seasons. They increase in Fe, Zn and Cu contents in roots of vegetations may be a protection mechanism against excess uptake of unnecessary heavy metals in aerial parts of the plants.