Shear wave velocity (Vs) information of near surface strata is one of the critical parameters in soil dynamics and engineering geology. Milliolithic limestone deposits, commonly found in India, are present either as outcrops or at shallow depths with very less overburden. Rippability assessment were earlier based on qualitative assessments, equipment trial runs and laboratory estimates of seismic velocities, which had to be relied upon, as there were no tools available for direct determination of shear wave velocity in field. Seismic profiling using multichannel analysis of surface waves (MASW) provides good and reliable information not only to assess rippability characteristics, but also to know the near surface variation of the overlying strata. MASW method consists of data acquisition, data processing and shear wave velocity profiles. This paper provides a methodology of MASW tests conducted for rippability assessment of limestone. The study area consists of milliolithic horizontal bedded limestone formation resting over the trap (Basalt) rocks of Eocene age. Compressional wave velocity (V p), one of the valuable by-product obtained from the seismic data set, is used to determine the rippability of limestone. Variation of seismic wave velocity of strata with depth & its rippability, is then determined from the seismic profiles.
Overburden or rock mass removal from surface in any opencast mine is dependent on rock properties, environmental constraints and the production need of the processing plant. Drilling and blasting has been found to be an easy and cheap solution for overburden loosening. With stringent environmental enforcements, mining in urban areas & mines approaching habitats or settlements, search for other alternatives has become a necessity. Ripping is one such alternative. In surface mines, selection of equipments becomes a vital decision, as any wrong selection of equipment or technique, leads to large irrecoverable expenditure.
Correct, meticulous and reliable rippability assessment studies in consideration with excavation characteristics of rock need to be conducted to arrive at crucial decision of equipment selection. Specification of machinery or equipment like, rippers, dozers, tractors and other equipment is needed to be matched, with the rippability of rocks, to arrive at a final match for ripping the rock strata.
Seismic profiling methods provide vital information related to geotechnical parameters like shear and bulk moduli from S-wave (Vs) and P-wave (V p) velocities of near-surface materials. Multichannel analysis of surface waves (MASW) is one such non-destructive testing (NDT) seismic method that can be used for geotechnical characterization of near-surface materials, to infer Vs variation with depth. A Vs profile is obtained from measurement of surface Rayleigh waves. Unlike other seismic methods, this method has advantages in several respects. First, the field survey is easiest, as compared to borehole methods, because of the strong nature of surface-wave energy that can be generated by using a simple impact source (a sledge hammer). Second, the data can be processed for determination of optimum parameters and the method is simple. Third, the surface waves respond most effectively to various types of near-surface anomalies that are common targets of geotechnical investigations.
