Effects of joint orientation and rock mass quality on tunnel blasting

It is a well known fact that rock mass properties influence the process of fragmentation considerably. Model blasts and field investigations were carried out to find the effects of rock mass quality and joint orientation on tunnel blasting. Propagation of shock waves are partially restricted by joint planes. It was observed that the blast results (i.e., average fragment size and depth and cross-sectional area of the broken zone) were considerably influenced by joint orientation. Accordingly, it has been concluded that loading equipment with a larger capacity and deeper blast holes are required in formations with joint planes perpendicular to the tunnel axis. The number of blast holes, however, should be greater when joints are parallel to the tunnel axis. Furthermore, the powder factor (kg/m³) has been found to be directly related to rock mass quality (Q). Optimisation of pull, powder factor and overbreak is required in the case of weak formations with joints perpendicular to the tunnel axis. The use of contour blasting technique seems to be essential in poor and fair rock masses to minimise the overbreak, reduce the support cost and improve the stability of the opening.     

Sea-floor classification using multibeam echo-sounding angular backscatter data: a real-time approach employing hybrid neural network architecture

The presently studied numerical model, e.g., composite roughness, is successful for the purpose of seafloor classification employing processed multibeam angular backscatter data from manganese-nodule-bearing locations of the Central Indian Ocean Basin. Hybrid artificial neural network (ANN) architecture, comprised of the self-organizing feature map and learning vector quantization (LVQ), has been implemented as an alternative technique for sea-floor roughness classification, giving comparative results with the aforesaid numerical model for processed multibeam angular backscatter data. However, the composite-roughness model approach is protracted due to the inherent need for processed data including system-gain corrections. In order to establish that tedious processing of raw backscatter values is unessential for efficient classification, hybrid ANN architecture has been attempted here due to its nonparametric approach. In this technical communication, successful employment of LVQ algorithm for unprocessed (raw) multibeam backscatter data indicates true real-time classification application.     

1420 Ma diabasic intrusives from the Mesoproterozoic Singhora Group,Chhattisgarh Supergroup,India: Implications towards non-plume intrusive activity

Besides offering significant clues towards tracking the geochemical evolution of the mantle and architectural reconstruction of different ‘supercontinent’, geochronological and geochemical appraisal of igneous inputs are also important to bracket the depositional time frame of any lithopackage, particularly, the unfossiliferous sedimentary successions. The present study deals with diabasic intrusive within Mesoproterozoic Saraipalli Formation, which is an argillaceous constituent present at the basal part of nearly 400 m thick four-tiered unmetamorphosed but deformed sedimentary succession of Singhora Group, Chhattisgarh Supergroup, central India. The SE–NW trending intrusive comprises mainly of plagioclase and augite together with minor orthopyroxene, biotite and opaque minerals. Though some plagioclase laths are partially sericitized, the ophitic-to-subophitic texture of the rock is well preserved. Major and trace element geochemical data indicate that this intrusive is basalt-to-basaltic andesite in character and of subalkaline basalt affinity. Multi-element plot shows overall LILE-enrichment and enrichment of Pb and slight depletion of Nb and P, coupled with moderate La/Nb and Th/Nb ratios. Zr, Y and Nb ternary diagrams plot in the fields of within plate basalt. Selected HFSE ratios indicate a non-plume source with crustal assimilation/sediment mixing. Sm–Nd and Rb–Sr isotope data show that the intrusive has Sr_initial and Nd_initial of 0.709377–0.706672 and 0.510919–0.510815, respectively. Positive ε ^t Nd [t = 1420 Ma] values (+0.3 to + 2.3) indicate depleted isotopic nature of their protolith. The calculated T _DM age is 1.7–1.9 Ga. The mineral-whole rock isochron data (Sm–Nd systematics) of the intrusive implies an emplacement age of ca. 1420 Ma. Considering synchronous terrain boundary shear zone development in Bastar craton on the southeastern part of the Singhora basin, mafic magmatism in Eastern Ghats and large-scale basic intrusion in Sausar mobile belt, a major tectono-thermal event around 1400 Ma is surmised that affected eastern Indian craton. Moreover, geochronology of a bedded porcellanite unit (ca. 1500 Ma) at the base and a discordant basic intrusive (ca. 1420 Ma) allowed a unique opportunity to qualitatively offer an upper bound of time bracket for the deposition of Saraipalli Formation, i.e., ∼80 Ma.     

A class of solutions for anisotropic stars admitting conformal motion

We provide a new class of interior solutions for anisotropic stars admitting conformal motion. The Einstein’s field equations in this construction are solved for specific choices of the density/mass functions. We analyze the behavior of the model parameters like radial and transverse pressures, density and surface tension.     

Geochemical evolution of groundwater in southern Bengal Basin: The example of Rajarhat and adjoining areas,West Bengal,India

Detailed geochemical analysis of groundwater beneath 1223 km² area in southern Bengal Basin along with statistical analysis on the chemical data was attempted, to develop a better understanding of the geochemical processes that control the groundwater evolution in the deltaic aquifer of the region. Groundwater is categorized into three types: ‘excellent’, ‘good’ and ‘poor’ and seven hydrochemical facies are assigned to three broad types: ‘fresh’, ‘mixed’ and ‘brackish’ waters. The ‘fresh’ water type dominated with sodium indicates active flushing of the aquifer, whereas chloride-rich ‘brackish’ groundwater represents freshening of modified connate water. The ‘mixed’ type groundwater has possibly evolved due to hydraulic mixing of ‘fresh’ and ‘brackish’ waters. Enrichment of major ions in groundwater is due to weathering of feldspathic and ferro-magnesian minerals by percolating water. The groundwater of Rajarhat New Town (RNT) and adjacent areas in the north and southeast is contaminated with arsenic. Current-pumping may induce more arsenic to flow into the aquifers of RNT and Kolkata cities. Future large-scale pumping of groundwater beneath RNT can modify the hydrological system, which may transport arsenic and low quality water from adjacent aquifers to presently unpolluted aquifer.     

Estimation of mean grain size of seafloor sediments using neural network

The feasibility of an artificial neural network based approach is investigated to estimate the values of mean grain size of seafloor sediments using four dominant echo features, extracted from acoustic backscatter data. The acoustic backscatter data were collected using a dual-frequency (33 and 210 kHz) single-beam, normal-incidence echo sounder at twenty locations in the central part of the western continental shelf of India. Statistically significant correlations are observed between the estimated average values of mean grain size of sediments and the ground-truth data at both the frequencies. The results indicate that once a multi-layer perceptron model is trained with back-propagation algorithm, the values of mean grain size can reasonably be estimated in an experimental area. The study also revealed that the consistency among the estimated values of mean grain size at different acoustic frequencies is considerably improved with the neural network based method as compared to that with a model-based approach.