Showing papers by "T. G. Sitharam published in 2016"

Response of laterally loaded pile in soft clay on sloping ground

Abstract: This paper presents the results of static lateral-load test carried out on a single aluminium model pile embedded in soft clay (consistency index, Ic = 0.42) on a sloping ground. A series of laboratory model tests had been carried out on the instrumented aluminium pile with outer diameter of 25.46 mm on a sloping ground of varying slopes (1V:1H, 1V:1.5H, 1V:2H, 1V:3H and 1V:5H) and with varying embedment length-to-diameter ratio (L/D) of 20, 25 and 30. To quantify the effect of slopes, the tests were also carried out on a horizontal ground surface. From the experimental results, the lateral load-carrying capacity of the pile, load–deflection response of the pile at pile head, effect of slopes and embedment length on pile capacity and bending-moment profile along the pile shaft were studied. The experimental results have been compared with those obtained from finite element analysis PLAXIS 3D and found to be in good agreement.

Behaviour of geocell reinforced soft clay bed subjected to incremental cyclic loading

Abstract: The paper deals with the results of the laboratory cyclic plate load tests performed on the reinforced soft clay beds. The performances of the clay bed reinforced with geocells and geocells with additional basal geogrid cases are compared with the performance of the unreinforced clay beds. From the cyclic plate load test results, the coefficient of elastic uniform compression (C-u) was calculated for the different cases. The Cu value was found to increase in the presence of geocell reinforcement. The maximum increase in the Cu value was observed in the case of the clay bed reinforced with the combination of geocell and geogrid. In addition, 3 times increase in the strain modulus, 10 times increase in the bearing capacity, 8 times increase in the stiffness and 90% reduction in the settlement was observed in the presence of the geocell and geogrid. Based on the laboratory test results, a hypothetical case of a prototype foundation subjected to cyclic load was analyzed. The results revealed that the natural frequency of the foundation-soil system increases by 4 times and the amplitude of the vibration reduces by 92% in the presence of the geocells and the geogrids.

Effect of frequency of cyclic loading on liquefaction and dynamic properties of saturated sand

Abstract: The effect of frequency of cyclic loading on liquefaction and post-liquefaction resistance of original Ahmedabad sand has been presented in this technical paper. Saturated and consolidated specimens prepared to a particular relative density were subjected to varied frequencies at a constant cyclic stress ratio under undrained conditions. Specimens were cyclically loaded till liquefaction. It was observed that the rate of generation of excess pore water pressure increases with increase in frequency of cyclic loading as a result the cyclic liquefaction resistance decreases with increase in the loading frequency. From the study on dynamic properties, it is found that the shear modulus decreases and damping ratio increases with increase in frequency. The frequency of cyclic loading has no influence on the shear modulus at a particular shear strain. It is also seen that the shear modulus decreases and damping ratio increases with increase in shear strain.

Effect of aging on the leachate characteristics from municipal solid waste landfill

Abstract: Leachate emanating from solid waste deposited in landfill possess dissolved or an entrained environmentally harmful substances. They consist of soluble organic and inorganic compounds as well as suspended particles. These leachates also have a distinguishing characteristic in that they are highly variable and contain significantly elevated concentrations of undesirable material derived from the waste. Depending on whether leachate flow increases (during rainy season) and decreases (during dry/summer season) can change the composition. The concentration of waste change dramatically changes over the life of the landfill due to chemical degradation and biological decay of organic matter present. Consequently, the physical characteristics also vary considerably depending on the age of the waste. This paper brings out the effect of aging on the leachate characteristics from a municipal solid waste located at the Terra Firma Biotechnologies Ltd situated at Gundlahalli village in Doddaballapur taluk, near Bangalore. For the sake of comparison the leachates from two different parts of the site one from the location where old waste was dumped and another from the location where the waste was dumped relatively recently during the same period. Thus the two leachate samples from the same site representing different stages degradation of waste were collected to represent leachate from old waste and another from relatively fresh waste. The samples were analyzed for various physicochemical parameters to estimate its pollution potential. The results showed that most of the parameters examined in the leachate samples such as colour, conductivity, hardness, BOD, COD, TOC were found higher in the fresh leachate than aged leachate. In addition, low BOD/COD ratio of <0.1 in aged leachate and BOD/COD ratio of 0.33 in fresh leachate are observed. This shows that the major portion is organic matter which is not quickly biodegradable in the leachate from Terra Firma Biotechnology. The compost site is non-engineered solid waste landfill, which has neither bottom liner system nor any leachate collection and treatment system. Hence, leachate may percolate through subsoil causing pollution to ground water and surface water resources. Further the properties of soil below can change due to changing composition of the pore fluid.

Site specific design response spectrum proposed for the capital city of Agartala, Tripura

Abstract: The design response spectrum is smooth in shape compared to other response spectra. The objective of design spectra is to estimate the possible earthquake lateral loads which may experience on a particular structure during its design life. In this study, an attempt has been made to develop, design response spectra for the Agartala city, Tripura which is one of the North Eastern states in India considered at the highest level of seismic activity in the country having a zone factor 0.36g as per Indian seismic code (BIS 1893-2002). Based on the present data set collected from 1731-2011, the region is characterized and the seismicity parameters estimated separately for each source zone by Gutenberg and Richter (G-R) relationship. The two ground motion models were used for the hazard prediction. However, hazard curve, and uniform hazard response spectra (UHRS) (2% and 10% probability level for 50 years) has been developed for the Agartala at seismic bedrock level condition. Further, the NEHRP (National...

Long-wavelength propagation of waves in jointed rocks - study using resonant column experiments and model material

Abstract: The wave propagation in jointed rock mass depends on many factors, in particular the wave frequency, existing stress conditions and the induced strain levels. When the wavelength of the propagating wave is much longer than the spacing of the joints, it is referred to as long-wavelength condition. This is a dominant condition in seismological studies due to the presence of closely spaced joints in rocks. A comprehensive study on long-wavelength propagation of shear and compression waves in very weak rocks has been carried out with the help of a resonant column apparatus using a model material (plaster of Paris) at various strain levels. The working principle and suitability of the apparatus for testing stiff samples are discussed. The velocity reductions of shear and compression waves across joints are obtained. The influence of frictional and filled joints in attenuating stress waves under various strain levels is analysed. Wave velocities are found to be reduced with increasing strain levels and ...

Seismic Zonations at Micro and Macro-Level for Regions in the Peninsular India

Abstract: Due to the lack of proper preparedness in the country against natural disasters, even an earthquake of moderate magnitude can cause extensive damage. This necessitates seismic zonation. Seismic zonation is a process in which a large region is demarcated into small zones based on the levels of earthquake hazards. Seismic zonation is generally carried out at micro-level, meso-level and macro-level. Presently, there are only a few guidelines available regarding the use of a particular level of zonation for a given study area. The present study checks the suitability of various levels of seismic zonation for different regions and reviews the feasibility of various methodologies for site characterization and site effect estimation. Further the seismic zonation was carried out both at the micro (for the Kalpakkam) and macro-level (for Karnataka state) using the appropriate methodologies. Based on this, recommendations have been made regarding the suitability of various methodologies as well as the grid size to be adopted for different level of zonation based on actual studies.

Performance Evaluation of Premium Services in Bangalore Metropolitan Transport Corporation (BMTC)

Abstract: In this paper we are measuring the performance of Bangalore Metropolitan Transport Corporation (BMTC) specifically aiming at premium bus services of BMTC operating in Bangalore city. The performance measurement of premium bus services is done using two different approaches. Ratios were computed considering different operational and financial indicators and these ratios are benchmarked by considering the best performing units as the target to compare the bus depots performance. Further we studied the performance of bus depots using data envelopment analysis (DEA). Our analysis indicated that most of the depots are efficient where as depot 13 have significant opportunities for improvements. (C) 2016 The Authors. Published by Elsevier B.V.

Effect of Earthquake on a Single Pile Located in Sloping Ground

Abstract: Piles are often constructed on natural slope such as sea bed slope in off-shore structures. When piles are constructed on sloping ground, the behaviour of piles under earthquake loading is different from the piles on horizontal ground surface. The dynamic response of a pile subjected to external excitation is a complex phenomenon resulting from the interactions between the pile and the surrounding soil. In the present study, a finite element analysis of a single field pile located on sloping ground was carried out. A single pile of length 30m with embedment length to diameter ratios (L/D) 20, 25 and 30 was located on a crest of soft clay of slopes 1V:1H and 1V:5H, and subjected to dynamic earthquake loading (California Earthquake,1990). From the study, the behaviour of acceleration with time, lateral displacement and bending moment behavior along the pile shaft was studied.

Municipal Solid Waste Landfills Construction and Management-A Few Concerns

Abstract: In Bangalore city, one of the major problems is municipal solid management (MSW) due to ever increasing waste quantity along with its changing waste characteristics. Municipal solid waste includes non-hazardous waste generated in house, institutions, commercial and business establishments in an urban area. As city grow and produce more municipal solid waste and their waste collection systems become more efficient, due the environmental impact from dump site becomes increasingly intolerable. A report on waste management prepared for the Government of India (1998) by a sub-committee of the Supreme Court describes this as a serious situation. The municipal bodies in Bangalore have been unable to manage the rapid changes that have led to both increased waste quantities and changes in the waste composition this leading to an over-loading of the service. MSW rules do not permit to dump mixed waste in direct land filling and hence, the waste needs to be segregated in order to collect and reuse all recyclable and the organic matter needs to be stabilized. The generated and collected MSW needs to be processed/ treated with only non-biodegradable MSW and the rejects of the processing facility being dumped in landfill. Leachate emanating from solid waste deposited in landfill possess dissolved or an entrained environmentally harmful substances. Generally, environmental impacts and economic damages of poor leachate management practices on groundwater and receiving surface waters are not clearly understood. With this context, this study, the concept of leachate pollution index, a tool for quantifying the leachate pollution potential and water quality index for surrounding water bodies of Mavallipura landfill site in Bangalore has been applied. It has been found that the leachate generated from the Mavallipura landfill site has high contamination potential to the surrounding water bodies. The results revealed that quality of ground water resources in Mavallipura landfill is deteriorating largely, as a result of the poor practice of solid waste management. Hence, an effective remedial plan needs to be prepared for the sustainable water quality maintenance of the area.

Transformations of Obliquely Striking Waves at a Rock Joint: Numerical Simulations

Abstract: Knowledge of wave propagation across rock joints is necessary for understanding distinctions between wave attenuation and lithology. Whenever a propagating seismic wave strikes a rock joint at an angle not normal to the joint, wave transformation occurs. The rock joints existing in the field are not oriented in the condition for normal incidence of the wave; hence, wave transformations are very common. In this paper, transformations of P and Sv waves have been modeled numerically with the help of a distinct element method. Validation of the numerical model has been carried out by comparing the wave velocities obtained from bender/extender elements. The dependence of the transformation of obliquely striking waves on the frequency of incident waves and stiffness of the joint has been studied. The velocities of propagating waves and the ratios of stress amplitudes of propagating waves with respect to the incident wave have been obtained and compared for all the possible angles of incidence. The wave ...

Influence of sand and low plasticity clay mixtures on the liquefaction and postliquefaction behavior

Abstract: Liquefaction resistance changes with the presence of certain amount of fines in sand but literature related to laboratory and field investigations and the ground behaviour under earthquakes have clearly highlighted the conflicting evidence of the presence of fines on the liquefaction behaviour of sand-fines mixtures particularly low plasticity clay fines. Some studies have indicated decrease in liquefaction resistance with increase in plasticity and vice-versa. The postcyclic undrained shear behaviour of sand and low plasticity are controlled by excess pore pressure ratio and the behaviour is independent of density and confining pressure. In this paper, a series of undrained stress controlled cyclic triaxial shear tests and monotonic undrained shear loading were conducted on reconstituted sample of sand-fines mixtures to evaluate the liquefaction and postliquefaction behavior. Sand was procured from Cauvery river bed, Karnataka, India and locally available low plasticity clay fines were used to prepare sand-fines mixtures. The results indicate that Cyclic Resistance Ratio (CRR) increases with relative density and the post cyclic monotonic strength show increased stress at Ru = 0.

Investigation of the Geotechnical Properties of Municipal Solid Waste

Abstract: Geotechnical characterization plays a major role in the rehabilitation of waste dumps. Because the rising cost of land has made it necessary to utilize the waste dumps and development of methods for construction and assessment based on the geotechnical properties of wastes. Geotechnical properties of waste play a vital role in the reclamation of the landfill. For this, it is necessary to evaluate geotechnical properties by appropriate methods as most of the geotechnical testing may not be directly applicable. Also, there is a potential threat to groundwater and surface water bodies from leachates generated from the waste for a prolonged period. This book describes a detailed field and laboratory study performed to evaluate the geotechnical properties of the municipal solid wastes in the Mavallipura landfill in Bangalore and characteristics of leachate generated by the same. Also, the shear modulus reduction and damping ratio curves for Mavallipura landfill has been developed using laboratory measured values and validated with semi-empirical methods.

Numerical Simulation of Resonant Column Tests on Jointed Rocks Using DEM

Abstract: A resonant column apparatus can provide the wave velocities of geomaterials under torsional and flexural vibrations for a range of strain levels, within the elastic limit. The testing specimen is vibrated in its fundamental mode and the frequency that produces maximum strains in the sample is picked up as the resonant frequency. The wave velocities are obtained from the resonant frequencies and elastic moduli of the material can be calculated from the wave velocities. The paper presents the numerical simulation of the resonant column tests on jointed rocks by employing a distinct element method (DEM). The resonant frequency has been evaluated by monitoring the displacements at the edges of the sample during vibrations. Resonant frequencies of the testing jointed samples under long wavelength condition have been obtained under various strain levels and have been compared against that obtained from laboratory experiments. When the wavelength of propagating wave is much longer than the joint spacing, it is known as a long wavelength condition. The long wavelength propagation of waves is a general condition in earthquake engineering. The transmission of vibrations across joints has also been shown for the samples with multiple parallel joints.

Post-liquefaction Data Collection and Analyses for Earthquakes in New Zealand

Abstract: Post-liquefaction data collection is a long, time consuming and laborious process. After Darfield earthquake on 4 September 2010 in New Zealand, national and international post-liquefaction reconnaissance survey teams were formed within weeks. However, huge information was available within days in social electronic media such as blogs, Facebook, etc. These information were collected and used in initial reconnaissance planning and early reports. These new methods of data collection are discussed in this paper. Then, site investigation processes such as lateral spreading, SWS (Swedish Sounding), CPT (Cone Penetration Test), etc., are discussed briefly. The post-liquefied CPT data reveal that soils are still liquefiable even after initial liquefaction during Darfield earthquake. This explains why some sites were re-liquefied during aftershocks. This paper also discusses about post-liquefaction data collection and analysis for identifying re-liquefiable sites.