Site Specific Seismic Analysis of a Deep Stiff Soil Site

Site specific analysis was carried out for a deep stiff soil site located near Ahmedabad, India. The site predominantly consists of sandy clay and silty sand layer in the top 30m with Vs varying from 430 to 750m/s. It is followed by a high plastic stiff clay layer cemented with sand and gravel with unusually high Vs above 1000m/s. The study region surrounded by 13 major faults has experienced several major earthquakes including the disastrous Bhuj earthquake (Mw=7.7). The seismic hazard level at the site was estimated by deterministic approach and the East Cambay fault with Mw of 6.2 is found to be the controlling source capable of causing a surface PGA of 0.46g. 1D ground response analysis carried out using SHAKE 2000 and DEEPSOIL reveals an amplification of the ground with a surface PGA of 0.52g and 0.43g respectively. The design response spectrum obtained by RRS analysis was compared with several contemporary seismic design codes. It is found that the seismic provisions tend to under estimate the spectral acceleration by about 30% at mid period range. The maximum spectral acceleration compares well with those observed at similar deep stiff soil sites at Los Angeles reported by Chang et al (1997)

Dynamic Response of Vertical and Batter Piles

The lateral forced vibration test was carried out on driven cast in-situ concrete vertical piles of 500 mm diameter in a petrochemical complex site in Paradip, India. The site predominantly consists of silty sand for the top 3 m with shear wave velocity of 200 m/s and it is followed by clayey sand with shear velocity increases from 415 m/s to 460 m/s over pile termination depth of about 17 m . The piles were subjected to a sinusoidal lateral force with magnitude of 0.3 kN to 9.5 kN in the frequency range of 5 to 30 Hz. A 3D finite element analysis was carried out on vertical piles using ABAQUS and its results are validated with the field test results. Finite element analysis was extended to batter piles (10˚and 20˚) subjected to lateral dynamic load and it was found that the peak displacement amplitude of batter piles is 15 to 25% less than the same that of vertical piles indicating better performance of batter piles under lateral dynamic loading

Measurement of Vibration in Berthing Structure During Underwater Rock Blasting

Blasting, in particular underwater rock blasting is the most challenging and least understood source of vibration, which may cause considerable damage to the safety of the adjacent buildings and structures and including berthing structures. Though the blast-induced vibration is best controlled by specification of blasting procedures, it is very essential to measure and monitor the blast-induced vibration of the adjacent structures to access its safety. This paper discusses the measurement and monitoring of underwater blast induced vibration on the berthing structure (berth No.8) at Tuticorin in southern part of India. The vibration is recorded using three acceleration transducers mounted on the deck slab of berthing structure and monitored using a data efficiency system consisting of HBM make multi channel carrier frequency amplifier system with digital storage oscilloscope. It is observed that the peak vertical acceleration is much higher than the longitudinal and lateral peak acceleration, because of vibration of deck slab along with frequency of ground excitation. The peak particle velocity (PPV) is obtained from the time history of acceleration by simple integration. From the spectral analysis, the predominant frequency is found as 26 Hz. For this frequency the allowable PPV value is established from various standards as 25mm/sec. The measured PPV values fro all blasts (31 nos) are well below the limit of allowable PPV value, except in few blasts, which shows the berth is safe against underwater blast induced vibration. Pre and post crack survey also proves that there is no considerable damage to the berthing structure

Undrained Response and Liquefaction Behaviour of Non-Plastic Silty Sands Under Cyclic Loading

The undrained response and liquefaction behaviour of fine sand and silty sands consisting of 30% and 50% non-plastic fines were investigated in the present study. The effect of consolidation stress level, cyclic stress amplitude and amount of non-plastic fines on soil liquefaction have been studied through a systematically planned stress controlled cyclic triaxial tests. To examine the effect of consolidation pressure on liquefaction behaviour, the sand-silt specimens were prepared at 40% relative density and consolidated at pressures of 50, 100 and 200 kPa. To investigate the effect of fines content on liquefaction resistance of sands at constant postconsolidation void ratio, the sand-silt specimens were prepared at different relative densities of 20, 40 and 70%. The cyclic loading with CSR in the range of 0.075 to 0.275 was applied at a frequency of 1Hz in different tests. Test results show the influence of the addition of non-plastic fines to the sand on the reduction of liquefaction resistance. Soil specimens had exhibited higher resistance to liquefaction at low consolidation pressures and lower resistance at high consolidation pressures

Stranding of a whale shark, Rhincodon typus (Smith) at Pamban, Gulf of Mannar

The stranding of whale sharks in shallow waters along the Indian coast is not uncommon. Whale shark is listed as an endangered species as per the IUCN Red List (2000)

Effective Stress v/s Total Stress Ground Response Analyses for a Typical Site in Chennai (India)

This paper presents the results of ground response analyses carried out for a typical sandy site in Chennai city by equivalent linear and nonlinear total and effective stress approaches. The soil profile at the site consists of 26m thick sandy layer with SPT blow count increases from 16 to above 50 with depth. The shear wave velocity profile measured using field Multichannel Analysis of Surface Wave (MASW) test is found to increase from 170 m/s to 400 m/s at 26m depth. The equivalent linear ground response analysis was carried out using SHAKE2000. The nonlinear total and effective stress analyses were performed using D-MOD2000. In the nonlinear total stress analysis, the Modified Kondner and Zelasko (MKZ) constitutive model was used. In the case of nonlinear effective stress analysis, modulus degradation and stress degradation models of Matasovic and Vucetic (1993) were used to incorporate the pore pressure parameters. The analyses were carried out for a time history of bedrock acceleration with PGA of 0.16g obtained from the seismic hazard analysis. The results of the analyses are presented in terms of ground acceleration, shear stress and shear strain. The results of the equivalent linear, nonlinear total and effective stress analyses show similar ground response characteristics except marginal variation in the period corresponding to the peak spectral acceleration due to low intensity of input motion

Evaluation of Rock Characteristics for a Power Plant Site in India

Extensive geotechnical and geophysical investigations were carried out for a power plant site situated on the east coast of southern India. It is proposed to construct the foundation on rock at a depth of 18.0 m below the ground level. The geological and geotechnical characterization of the rock have been presented in this paper. Extensive boreholes were drilled up to 40.0 m to 60.0 m depth and a few boreholes up to 120.0 m depth from the ground level. Seismic crosshole tests were conducted at soil/rock strata upto 65.0 m depth for the determination of S-wave and P-wave velocity at different depths. Dilatometer tests were conducted in weathered and hard rock at 5.0 m interval up to a depth of 65.0 m. Field permeability tests were carried out in deep boreholes by single packer method. Various laboratory tests including UCC, Brazilian, and Point load tests were carried out on rock core samples. Modules obtained from UCC tests are compared with the in-situ modulus obtained from Dilatometer tests. Bearing capacity and settlement analysis are carried out for the proposed raft of about 113 m x 105 m size to be supported on rock. The allowing bearing pressure is estimated based on Rock Mass Rating, RQD and strength of rock cores. The settlement analysis is carried out using modulus obtained from Dilatometer tests and from the laboratory unconfined compression tests on rock core samples. The modulus of subgrade reaction and spring constants in vertical, horizontal and rocking modes of vibration are also evaluated for the static and seismic analysis of the raft

Fishing methods in coral reef areas of the Gulf of Mannar

Fishing methods being practised in the reef areas of the Gulf of Mannar for finfishes are trawling, gillnetting, fishing by hooks and lines and traps. Out of these, the most important device is trawling by which the most diverse and the highest quantity of finfishes are being landed from coral reef areas in this region

Rare species of Spanner crab Ranina ranina (Crustacea: Brachyura: Raninidae) from Gulf of Mannar, India

A rare species of the Spanner crab Ranina ranina (Linnaeus, 1758) is reported from Gulf of Mannar, in India. The description of the morphological features of the species is give

Bioluminescent flashes drive nighttime schooling behavior and synchronized swimming dynamics in flashlight fish

Schooling fishes, like flocking birds and swarming insects, display remarkable behavioral coordination. While over 25% of fish species exhibit schooling behavior, nighttime schooling has rarely been observed or reported. This is due to vision being the primary modality for schooling, which is corroborated by the fact that most fish schools disperse at critically low light levels. Here we report on a large aggregation of the bioluminescent flashlight fish Anomalops katoptron that exhibited nighttime schooling behavior during multiple moon phases, including the new moon. Data were recorded with a suite of low-light imaging devices, including a high-speed, high-resolution scientific complementary metal-oxide-semiconductor (sCMOS) camera. Image analysis revealed nighttime schooling using synchronized bioluminescent flashing displays, and demonstrated that school motion synchrony exhibits correlation with relative swim speed. A computer model of flashlight fish schooling behavior shows that only a small percentage of individuals need to exhibit bioluminescence in order for school cohesion to be maintained. Flashlight fish schooling is unique among fishes, in that bioluminescence enables schooling in conditions of no ambient light. In addition, some members can still partake in the school while not actively exhibiting their bioluminescence. Image analysis of our field data and model demonstrate that if a small percentage of fish become motivated to change direction, the rest of the school follows. The use of bioluminescence by flashlight fish to enable schooling in shallow water adds an additional ecological application to bioluminescence and suggests that schooling behavior in mesopelagic bioluminescent fishes may be also mediated by luminescent displays