SLOPE STABILITY IN OPENCAST MINES PRESENTATION TITLED ON SLOPE STABILITY IN OPENCAST MINES PREPARED BY: MAMTA JASWAL (090610122047) Government Engineering College Palanpur

OBJECTIVE Slope Failure is usual phenomenon in opencast mines as observed and noticed. The objective is to find out reasons of slope failure in mines and to control the slope failures by taking remedial measures.

Abstract The presentation is addressing the issues which are responsible for slope failure and find out the factors for slope failures leading to severe losses in mines. The study incorporates design of slope taking into consideration a geotechnical property of strata and suggest remedial measures to mitigate slope failures in lignite mines which can be useful to various mines in Gujarat.

Major factors Factors affecting slope failures are: Excessive build up pressure of pore water pressures within the fill. Placing the toe of a fill on unstable ground beyond the edge of the bench. Placement of soil at slopes too steep to remain stable and possibly, Reduction in soil shear strength due to rapid soil weathering caused by excessive seepage.

Other reasons Dynamic loading caused by blasting, earthquake, etc. shear stresses are momentarily increased as a result of vibration in the rock mass. The most serious problem in rock slope failure often is concerned with the location, orientation and properties of structural discontinuities in the rock mass. If the blasting is not done properly, there shall be chances of formation of ledges in the high wall and chances of slope failure becomes high.

Type of slope failures Planar failure Circular failure Wedge failure Toppling failure Failure due to sheared and decomposed rock.

Precautionary measures The geo mechanical information which are most relevant to the slope stability are shear stability are shear strength or cohesive strength, the angle of friction and the density of rock mass. The angle of slope of bench should be either equal or less than the angle of repose of the bench rocks. In competent rocks angle of slope of high wall benches varies between 65°-80°.

Precautionary measures The slope of angle depends upon the plane of weakness, orientation of bedding planes, etc. however the slope wall should not be retained by the artificial means at an angle in excess of it’s natural angle of repose. Bench slope may be stabilized by practicing controlled blasting (pre-splitting, smooth wall blasting, etc).

Supporting of slopes Supporting of the high wall slopes may control the failure of slopes. The following are the main supporting systems for high wall slopes: Toe ditches Fences Nets Bolting Anchoring Shotcreting

SLOPE MONITORING Terrestrial laser scanner ground based LIDAR i.e. light detection and ranging instrument to obtain a 3 dimensional point cloud for a barren slope area. The data of point cloud were scanned twice on two different dates to analyze the deformation of slope.

Thus, overlapping of the two scanned data sets on same local co-ordinate system shall attain relative slope displacement. The differences between two data sets can be predicted using following procedures: Using triangulated irregular network Importing two triangulated irregular network on the same co ordinate system.

STEPS (1) data acquisition (2) data processing (3)data analysis.

It is fully portable sensor. Range up to 1000m. It doesn’t require any prism commonly used in surveys. Thousands of point are monitored rapidly. No need of fixed installation. It can access over steeply dipping slopes, critical zones prone to hazards.

Limitations It cant access any sort of vegetative slope. Laser cant be worked on high absorption surface like coal due to less or zero reflectivity. It does have limit like field of view, range.

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