DISASTER ANALYSIS AND COUNTERMEASURES OF LAND SUBSIDENCE CAUSED BY COAL CUTTING IN CHINA

In recent years, many coal-producing countries have paid great atte ntion to the land subsidence caused by coal cutting. In China, because of the de nse population in coalfield areas, the land subsidence hazard is more serious. A fter a brief analysis on the mechanism of land subsidence, this paper gives a co mprehensive and systematical account on all kinds of hazards caused by the land subsidence in China. The study shows that land subsidence has endangered land, b uildings, traffic and communication lines, dykes and dams. It also causes damage to ecological and social environment. In order to lessen the hazard of land sub sidence, preventive measures should be taken to reduce the collapse amount, such as extraction with stowing, banded mining system, succession and coordination m ining system, or high-pressure mudflow between rock strata. Measures of reinfor cing or moving certain buildings should also be taken to reduce the destructive degree. In order to harness the subsidence land and bring them under control for farming, measures should be taken such as filling with spoil or fine breeze, ex cavating the deeper and covering the shallower land.

Reliability analysis of the velocity matching of coal cutting and caving in fully mechanized top-coal caving face

The matching relationship between coal cutting and caving in fully mechanized top-coal caving face is analyzed in detail from the angle of reliability. The coupling equation of reliability is established correspondingly, and the mathematical equation of the coefficient of velocity matching of coal cutting and caving is obtained, which meets a certain reliability demand for making the working procedure of coal caving not influence coal cutting of coal-cutter. The results show that the relationship between the coefficient of the velocity matching and the reliability of coal cutting and caving system is linear on the whole when R <0.9. It is pointed out that different numerical value should be selected for different coal face according to different demand for reliability.

IMPACT COAL CUTTING AND TESTING

The paper analyses the stress characteristics in longwall face and its interaction with impact coal cutting, and puts forward the operation method for impact coal cotting. Similar material to the coal in particular mine was used to simulate the coal mass. Impact coal breaking test was performed on the test rig. The traveling pattern of the impact stress wave in coal and the dynamic response of impact parameters on coal property is analyzed.

New risk assessment methodology for coal mine excavated slopes

This paper presents a new risk assessment methodology for coal mine excavated slopes. This new empirical-statistical slope.stability assessment m. ethodology （SSAM! is intended for use by geotechnical engineers at both the design review and operational stages of a mine＇s life to categonse the risk of an excavated coal mine slope. A likelihood of failure is determined using a new slope stability classification system for excavated coal mine slopes developed using a database of 119 intact and failed case studies sourced from open cut coal mines in Australia. Consequence of failure is based on slope height and stand-off distance at the toe of the excavated slope. Results are presented in a new risk matrix, with slope risk being divided into low, medium and high categories. The SSAM is put forward as a new risk assess- ment methodology to assess the potential for, and consequence of, excavated coal mine slope failure. Unlike existing classification systems, assumptions about the likely failure mode or mechanism are not required. Instead, the SSAM applies an approach which compares the conditions present within the exca- vated slope face, with the known past performance of slopes with similar geotechnical and geometrical conditions, to estimate the slope＇s propensity for failure. The SSAM is novel in that it considers the depo- sitional history of strata in an excavated slope and how this sequence affects slope stability. It is further novel in that it does not require explicit measurements of intact rock, rock mass and/or defect strength to rapidly calculate a slope＇s likelihood of failure and overall risk. Ratings can be determined entirely from visual observations of the excavated slope face. The new SSAM is designed to be used in conjunction with existing slope stability assessment tools.