A Case History of Tehri Tunnels

Tehri Dam Project, a multipurpose river valley project, is being constructed in Garhwal, Himalaya. The project consists of a 260 m high earth and rock fill dam with a clay core, four diversion tunnels each of 11 m finish diameter, four head race tunnels each of 8.5 m finish diameter and two underground powerhouses cavities each measuring 180 m long, 49.5 m high and 21.5 m wide. The project is located near the district headquarters of Tehri in the state of Uttar Pradesh. The rock masses in the project area are fragile, tectonically active and geologically disturbed. The terrain is rugged and inaccessible and therefore precludes thorough geotechnical investigations for the design of the cavern. The diversion and the head race tunnels were therefore used to conduct geotechnical investigations with the purpose of collecting geotechnical data for the design of two caverns. Goodman Jack tests were used to estimate the modulus of deformation of the rock masses. Load cells and tape extensometers were used to monitor the support pressure and the tunnel closures. The modulus of deformation varied from 0.18 to 0.32 kg/cm.sq. X 105. Tunnel closures were about 0.3% of the tunnel size. The support pressure stabilized within three months of excavation and the measured support pressures varied between 0.16 and 1.14 kg/cm.sq. This geotechnical data indicate that the rock masses behaviour was elastic in nature and the cavern could be designed without much difficulties

Cavern Wall Support Requirements in a Hydro-Electric Project

Construction of a 23m wide, 57m high, and 210m long underground power house cavern is in progress as a part of the multi-purpose Sardar Sarovar Project in India. The rock mass around the cavern is basalt which is intruded by a number of dolerite dykes. In view of the high side walls of the cavern, and the presence of a 1 to 2m thick shear zone running across the cavern width, a comprehensive approach was worked out for estimation of the wall support requirements. The approach included estimation of the roof support requirements using the four available approaches, and comparison of these requirements with the roof support system actually provided, and established as safe and adequate by the instrumentation data of six years. A favourable comparison established the reliability of the approaches used, and the most reliable of these approaches, i.e., the Barton\u27s approach was then used with confidence for estimation of the wall support requirements

Case History of Maneri-Uttarkashi Power Tunnel

A 8.56 km long circular tunnel of 4.75 m diameter has been constructed under Maneri hydel project on the river Bhagirathi. The tunnel passes alternatively through quartzitic and metabasic rock formations of the young Himalayan terrain. Tunnel excavation was started from four faces, one at the upstream end at maneri, two from an intermediate adit at Heena, and one at the downstream end near Uttarkashi where a 80 MW surface powerhouse is located. In excavating the tunnel from different faces, the problems of tunnel face collapse with heavy ingress of water, cavity formations and large tunnel closures leading to buckling of steel ribs on account of squeezing ground conditions were encountered. In the paper the approach of these problems has been dealt in detail. The predicted values of support pressure obtained from Terzaghi, Barton et al and CMRS approaches have been compared with the observed values of support pressure. The CMRS approach shows promise for better results in both squeezing and the elastic ground conditions

Experiences of the Support Designs in the Two Large Underground Openings in India

Support requirements for two caverns arc worked out by empirical and the numerical approaches. The adequacy of the shotcrete-rock bolt support system is monitored by measuring the deformations of caverns walls and roof. The measurements are compared with the results obtained from the numerical approach. Brief geology, the supports, and the results of performance monitoring are presented in the paper

Squeezing Problems in Indian Tunnels

Case histories of three Indian tunnels indicate that squeezing conditions are created due to plastic flow of rock masses under the influence of high cover pressures. These examples emphasize that a tunnel experiencing squeezing conditions must be allowed to deform to optimize support costs and avoid delays. Allowance for desirable tunnel deformations must, therefore, be made while planning the size of excavation. Field data has shown that a flexible support system of compressible backfill and steel ribs may be used as an alternative to shotcrete support which is unpractical in Indian tunnels excavated largely by conventional methods. Instrumentation indicates that large broken zones are associated with late stabilization and that the coefficient of volumetric expansion of failed rock masses is significantly lower than believed so far. Comparison of measured rock pressures with those estimated from available methods shows that the elasto-plastic theory may provide reliable predictions provided that the strength parameters of rock masses are known precisely

A source of polarized electrons based on photoemission of GaAsP.

The source described is based on photoemission of electrons from 100-GaAs0.62P0.38 activated to negative electron affinity. It is built to inject a beam of polarized electrons into the 350 MeV linear accelerator in Mainz. It is capable of delivering a mean current of 28 μA spin-polarized longitudinally to a degree of 0.44. The lifetime of the cathode under operational conditions is better than 200 h. The source was successfully run in a parity experiment, in which the analysing power of quasielastic scattering from beryllium for longitudinally polarized electrons was measured

Disentangling the formation history of galaxies via population-orbit superposition: method validation

We present population-orbit superposition models for external galaxies based on Schwarzschild's orbit-superposition method, by tagging the orbits with age and metallicity. The models fit the density distributions, as well as kinematic, age and metallicity maps from Integral Field Unit (IFU) spectroscopy observations. We validate the method and demonstrate its power by applying it to mock data, similar to those obtained by the Multi-Unit Spectroscopic Explorer (MUSE) IFU on the Very Large Telescope (VLT). These mock data are created from Auriga galaxy simulations, viewed at three different inclination angles ($\vartheta=40^o, 60^o, 80^o$). Constrained by MUSE-like mock data, our model can recover the galaxy's stellar orbit distribution projected in orbital circularity $\lambda_z$ vs. radius $r$, the intrinsic stellar population distribution in age $t$ vs. metallicity $Z$, and the correlation between orbits' circularity $\lambda_z$ and stellar age $t$. A physically motivated age-metallicity relation improves recovering the intrinsic stellar population distributions. We decompose galaxies into cold, warm and hot + counter-rotating components based on their orbit circularity distribution, and find that the surface density, mean velocity, velocity dispersion, age and metallicity maps of each component from our models well reproduce those from simulation, especially for projections close to edge-on. These galaxies exhibit strong global age vs. $\sigma_z$ relation, which is well recovered by our model. The method has the power to reveal the detailed build-up of stellar structures in galaxies, and offers a complement to local resolved, and high-redshift studies of galaxy evolution.Comment: 20 pages, submitted to MNRA

Navigation-guided osteotomies improve margin delineation in tumors involving the sinonasal area: A preclinical study

Objectives: To demonstrate and quantify, in a preclinical setting, the benefit of three-dimensional (3D) navigation guidance for margin delineation during ablative open surgery for advanced sinonasal cancer. Materials and methods: Seven tumor models were created. 3D images were acquired with cone beam computed tomography, and 3D tumor segmentations were contoured. Eight surgeons with variable experience were recruited for the simulation of osteotomies. Three simulations were performed: 1) Unguided, 2) Guided using real-time tool tracking with 3D tumor segmentation (tumor-guided), and 3) Guided by 3D visualization of both the tumor and 1-cm margin segmentations (margin-guided). Analysis of cutting planes was performed and distance from the tumor surface was classified as follows: “intratumoral” when 0 mm or negative, “close” when greater than 0 mm and less than or equal to 5 mm, “adequate” when greater than 5 mm and less than or equal to 15 mm, and “excessive” over 15 mm. The three techniques (unguided, tumor-guided, margin-guided) were statistically compared. Results: The use of 3D navigation for margin delineation significantly improved control of margins: unguided cuts had 18.1% intratumoral cuts compared to 0% intratumoral cuts with 3D navigation (p < 0.0001). Conclusion: This preclinical study has demonstrated the significant benefit of navigation-guided osteotomies for sinonasal tumors. Translation into the clinical setting – with rigorous assessment of oncological outcomes – would be the proposed next step

Improved limits on the weak, neutral, hadronic axial vector coupling constants from quasielastic scattering of polarized electrons.

In scattering polarized electrons (P1 = 44% by 9Be at an energy of 300 MeV at angles 115°⩽ϑ⩽145° a parity violating asymmetry of Acorr = (−3.5 ± 0.7 ± 0.2) × 10−6 was measured. After correction for finite electron polarization and background we deduce an experimental asymmetry of Acx = (−9.4 ± 1.8 ± 0.5) × 10−6. The quoted errors indicate the statistical and the systematic uncertainties, respectively. The asymmetry, which is dominated by the quasielastic cross section, is interpreted in terms of model-independent electron-nucleon coupling constants of the weak neutral current. The error limits in the sector of axial vector coupling constants have been improved by a factor of 3 over previous results. A model-dependent analysis for the Weinberg angle yields the result sin2θw = 0.221 ± 0.014 ± 0.004