Displacement based seismic assessment of base restrained retaining walls

The present work deals with assessment of earthquake-induced displacement of the base restrained retaining walls (RW’s). A detailed and rigorous finite element (FE) investigation has been carried out following the shaking table experiments on a scaled-down RW model. The FE simulations were performed by conducting several nonlinear time history analyses on a two-dimensional (2D) plane strain FE model of a prototype RW. The hardening and softening of backfill have been simulated by calibrating the Mohr Coulomb material model against the triaxial test results. Role of different backfill into the seismic performance of base restrained RW has also been investigated. It was observed that the cohesionless backfill has a slight influence on the earthquake induced displacement of base restrained RW’s. Amplification of horizontal acceleration in backfill has been observed with no direct correlation with the applied earthquake excitation. The understanding and findings based on shaking table experiment and FE simulations have been used for development of an analytical model for estimation of earthquake induced displacement of base restrained RW. The validity of proposed analytical model has also been examined against the shaking table experiment and FE simulation results.

     

A sensor array system for profiling moisture in unsaturated rock and soil

As the scope of hydrologic investigations extend deeper into the subsurface profile, and increasingly include fractured rock, there is a growing need for techniques that can accurately monitor saturation changes at a high spatial and temporal resolution in this environment. We have developed a technique, the Electrical Resistance Sensor Array System (ERSAS), to track moisture dynamics in vadose zone regions that include both fractured rock and soil. The performance of ERSAS was compared with the time domain reflectometry (TDR) technique under controlled and field conditions. We found that ERSAS was effective in determining patterns of saturation changes along vertical soil/rock profiles. Because of the small size of individual sensors, it was able to resolve travel times associated with a wetting front and peak saturation better than TDR. In addition, ERSAS is significantly cheaper than the TDR system, and the sensor arrays are relatively easier to install in the subsurface profile. Published in 2011 by John Wiley & Sons, Ltd.     

Influence of size of granulated rubber and tyre chips on the shear strength characteristics of sand–rubber mix

Use of scrap tyres in isolation systems for seismic damping, requires a knowledge of the engineering properties of sand–rubber mixtures (SRM). The primary objective of this study is to assess the influence of granulated rubber and tyre chips size and the gradation of sand on the strength behaviour of SRM by carrying out large-scale direct shear tests. A large direct shear test has been carried out on SRM considering different granulated rubber and tyre chip sizes and compositions. The following properties were investigated to know the effect of granulated rubber on dry sand; peak shear stress, cohesion, friction angle, secant modulus and volumetric strain. From the experiments, it was determined that the major factors influencing the above-mentioned properties were granulated rubber and tyre chip sizes, percentage of rubber in SRM and the normal stress applied. It was observed that the peak strength was significantly increased with increasing granulated rubber size up to rubber size VI (passing 12.5 mm and retained on 9.5 mm), and by adding granulated rubber up to 30%. This study shows that granulated rubber size VI gives maximum shear strength values at 30% rubber content. It was also found that more uniformly graded sand gives an improved value of shear strength with the inclusion of granulated rubber when compared to poorly graded sand.     

Measurement system for systematic hydrological characterization of unsaturated fractured welded tuff in a mined underground tunnel

A field investigation of unsaturated flow through a lithophysal unit of fractured welded tuff containing lithophysal cavities has been initiated. To characterize flow in this spatially heterogeneous medium, a systematic approach has been developed to perform tests in boreholes drilled at regular intervals in an underground tunnel (drift). The purpose of the testing is to quantify the amounts of water seeping into the drift versus the amount of water moving around the drift when released into boreholes at many equidistant locations along the drift. In this paper, we describe the test equipment system that has been built for this purpose. Because the field-scale measurements--of liquid flow in the unsaturated, fractured rocks--require continuous testing for periods of days to weeks, the control of test equipment has been fully automated, allowing operation with no human presence at the field site. Preliminary results from the first set of tests indicate that, while the effects of evaporation on characterization of hydrological properties of the rock can be significant, these effects can be controlled and quantified. These tests give insight into the role of the cavities as potential storage during the initial transient flow prior to the breakthrough of water at the drift crown, as well as the role of connected fractures that provide the subsequent quasi-steady flow. In addition to the stated purpose of realizing the flow partitioning, the results yield values for the effective porosity in the pathways for liquid flow in the regions tested thus far.     

A passive-discrete water sampler for monitoring seepage

This paper presents the design of the passive-discrete water sampler (PDWS) which has been developed to facilitate investigations of flow partitioning in fractured rocks. The PDWS continuously isolates seeping water into discrete samples while monitoring the seepage rate. The PDWS was used in a flow and transport experiment that investigated fracture-matrix interactions. During the experiment, a mix of conservative tracers with significantly different diffusion coefficients (lithium bromide [LiBr] and pentafluorobenzoic acid [PFBA]) was introduced along a fault located in fractured tuffs, and water seeping through the lower end of the fault was collected by the PDWS and analyzed for tracer concentrations. Preliminary results from this investigation show that samples of effluent captured by the PDWS effectively retained temporal changes in the chemical signature, while providing seepage rates.     

Structural and luminescent characterisation of uraniferous fluorapatite and haematite associated with phosphatic rocks of the Bijawar group in Sagar District,Madhya Pradesh (India)

The structural and spectroscopic characteristics of phosphatic ferruginous shale samples from the Bijawar Group rocks from Sagar District of Madhya Pradesh (India) have been probed for identification of uranium species. Fluorapatite (\(\hbox {Ca}_{5}\hbox {(PO}_{4})_{3}\hbox {F}\), FAP) and haematite (\(\upalpha \)-\(\hbox {Fe}_{2}\hbox {O}_{3}\)) were identified as the main phases in the separated mineral concentrates. The photoluminescence (PL) and X-ray absorption near edge spectroscopy (XANES) studies pointed to a strong experimental evidence of both U(IV) and U(VI) oxidation states in the mineral concentrate portion obtained from the same parent host rock. The PL spectrum has confirmed the charge transfer (f–d) transition bands in UV and near-UV regions with emission peaks at ca. 290, 313, 336, 399 and 416 nm, which has been attributed to the substitution of \(\hbox {Ca}^{2+}\) ions by U(IV) in FAP and broad structureless emission due to stabilisation of U(VI) as \(\hbox {UO}_{6}^{6-}\) in haematite. Time-resolved spectroscopy studies have revealed biexponential decay components lasting 2–5 ns for U(IV) species and \(10\,\upmu \hbox {s}\) for U(VI) species. These characterisations revealed the fundamental information about the oxidation state and form of uranium in this region. Remediation measures for the Bijawar region are also suggested.     

Measurement of soil-gas radon in some areas of northern Rajasthan,India

The health hazards of the radioactive gas radon on general public are well known. In order to understand the level and distribution of ²²²Rn concentrations in soil-gas in Sri Ganganagar district of Rajasthan, a ²²²Rn survey was carried out for the first time using RAD7, an electronic radon detector manufactured by Durridge Company (USA), at different locations covering a total area of 10,978 km ², having a population of approximately 20 lakh. The measurement of ²²²Rn concentration in soil-gas was carried out at four different depths (10, 40, 70, and 100 cm). The radon concentration in soil-gas for 10, 40, 70, and 100 cm depths ranged from 0.09–4.25, 0.15–6.30, 0.50–9.18, and 0.72–10.40 kBq m ^?3, respectively. The minimum value of radon concentration is observed in 33 GB village at 10 cm depth and maximum for Mohanpura village at 100 cm depth. As expected, our data show an increase of soil-gas radon concentration levels with depth. The present results are compared with the available radon data from other studies.