Determination of GPS Session Duration in Ground Deformation Surveys in Mining Areas

Extraction of underground minerals causes subsidence of the ground surface due to gravitational forces. The subsidence rate depends on the type of extracted ore, as well as its shape, thickness, and depth. Additionally, the embedding and overburden rock properties influence the time needed for the deformations to reach the surface. Using the results of geodetic deformation monitoring, which supply the information on pattern and magnitude of surface deformation, the performance of the mine may be evaluated. The monitoring can supply information on the actual rock mass behaviour during the operation and in many cases during the years after the mining operations have ceased. Geodetic methods of deformation monitoring supply information on the absolute and relative displacements (changes in position in a selected coordinate system) from which displacement and strain fields for the monitored object may be derived. Thus, geodetic measurements provide global information on absolute and relative displacements over large areas, either at discrete points or continuous in the space domain. The geodetic methods are affected by errors caused by atmospheric refraction and delay of electromagnetic signal. Since geodetic measurements allow for redundancy and statistical evaluation of the quality of the data, they generally provide reliable results. Usually, the designed accuracy of deformation measurements should allow for the detection of at least one third of the expected maximum deformations over the desired time span at the 95% probability level. In ground subsidence studies in mining areas, 10 mm accuracy at 95% level in both vertical and horizontal displacements is typically required. In the case of salt mines, the process of ground subsidence in viscous rock is slow; therefore, subsidence monitoring surveys may be performed once a year. In subsidence determination, two techniques are commonly used: leveling and satellite positioning. The satellite positioning technique is used to determine the 3D (horizontal coordinates and height) or 2D position of monitored points (only horizontal coordinates). When comparing the heights determined from satellite and leveling surveys, it has to be noted that the leveling heights are referred with respect to the geoid (orthometric heights), while heights determined from satellite surveys are referred with respect to the ellipsoid (ellipsoidal height). In the case of satellite surveys, the accuracy of horizontal position is typically 2–3 times better than vertical. The analysis of the optimal session duration lead to the conclusion that in order to achieve the sub-cm accuracy of horizontal coordinates at 95% confidence level, the satellite positioning session length using Global Positioning System (GPS) should be at least three hours long. In order to achieve the sub-cm accuracy of height coordinate at 95% confidence level in a single observation session, the GPS session length should be at least twelve hours long

Integrated analysis of rock mass deformation within shaft protective pillar

The paper presents an analysis of the rock mass deformation resulting from mining in the vicinity of the shaft protection pillar. A methodology of deformation prediction is based on a deterministic method using Finite Element Method (FEM). The FEM solution is based on the knowledge of the geomechanical properties of the various geological formations, tectonic faults, types of mining systems, and the complexity of the behaviour of the rock mass. The analysis gave the stress and displacement fields in the rock mass. Results of the analysis will allow for design of an optimal mining system. The analysis is illustrated by an example of the shaft R-VIII Rudna Mine KGHM Polish Copper SA

An analysis on the effect of crosscuts within shaft protective pillars on deformations of the surrounding rock mass deformations

The development of crosscuts within mining shafts’ protective pillars causes a change of state of stress in the surrounding rock mass. It also causes deformations of the rock mass and the surface. It is essential to conduct prediction analysis of the deformations and stresses in order to secure a proper functioning of a shaft located within the protective pillar. It is recommended that the analysis should be based on the integration of the finite element method (FEM) and geodetic monitoring results. FEM makes it possible to determine the rock mass stresses and displacements in the shaft protective pillars and in the surrounding rock mass. It makes is possible to determine the safety and proper functioning of the shaft. The results of the FEM analysis of the impact of crosscuts and mining activities on rock mass deformations inside and on the surface of the protective shaft pillar are presented. The influence of mining extractions was investigated. The mining panels were located around the safety pillar in three regions NW, SE and SW and the crosscut were located within the safety pillar. The presented methodology will allow for the determination of the deformations and strains in case of farther development of crosscuts within the protective shaft pilar and by planned mining activities around the pillar