B. K. Maheshwari

Seismic Behavior of Soil-Pile-Structure Interaction in Liquefiable Soils: Parametric Study

Nonlinearity of the soil medium plays a very important role on the seismic behavior of soil-pile-structure interaction. The problem of soil-pile-structure interaction is further complicated when the piles are embedded in liquefiable soil medium. A finite-element code was developed in MATLAB to model three-dimensional soil-pile-structure systems. Frequency dependent Kelvin elements (spring and dashpots) were used to model the radiation boundary conditions. A work-hardening plastic cap model was used for constitutive modeling of the soil medium. The pore pressure generation for liquefaction was incorporated by a two-parameter volume change model reported in the literature. In this paper, a 2×2 pile group in liquefiable soil is considered and a parametric study is conducted to investigate its seismic behavior. The effects of loading intensity and stiffness of the soil on the seismic behaviour of the soil-pile system are investigated, considering nonlinearity and liquefaction of the soil medium for a wide ran...

Effects of Separation on the Behavior of Soil-Pile Interaction in Liquefiable Soils

Separation and sliding between soil and pile have a significant effect on the complex behavior of pile groups under dynamic condition. In addition to separation between soil and pile, the behavior of soil medium surrounding the piles is nonlinear during strong excitations. Therefore, soil is modeled using a nonlinear work-hardening plastic cap model. Because of shaking, there is an increase in pore water pressure. To simulate it, the pore-pressure generation capability is added in modeling the behavior of the soil medium. A full three-dimensional finite-element soil-pile model has been developed with approximate radiation condition at infinity simulated by frequency dependent Kelvin elements. The model and the process of computation have been verified with the established literature. The effects of separation on the dynamic stiffness and seismic response of single pile and pile groups have been examined considering work-hardening soil-plasticity without and with pore-pressure generation capability for a wide range of frequencies of excitation. Real-time earthquake motions are also applied and the effects of separation on the responses of pile groups are investigated. Significant effects of separation of the soil medium on the response of the soil-pile system have been observed and approximately quantified.

Run-up and Inundation Pattern Developed During the Indian Ocean Tsunami of December 26, 2004 Along the Coast of Tamilnadu (India)

The tsunami run-up, inundation and damage pattern observed along the coast of Tamilnadu (India) during the deadliest Indian Ocean tsunami of December 26, 2004 is documented in this paper. The tsunami caused severe damage and claimed many victims in the coastal areas of eleven countries, bordering the Indian Ocean. Along the coast of Indian mainland, the damage was caused by the tsunami only. Largest tsunami run-up and inundation was observed along the coast of Nagapattinam district and was about 10–12 m and 3.0 km, respectively. The measured inundation data were strongly scattered in direct relationship to the morphology of the seashore and the tsunami run-up. Lowest tsunami run-up and inundation was measured along the coast of Thanjavur, Puddukkotai and Ramnathpuram districts of Tamilnadu in the Palk Strait. The presence of shadow of Sri Lanka, the interferences of direct/receded waves with the reflected waves from Sri Lanka and Maldive Islands and variation in the width of continental shelf were the main cause of large variation in tsunami run-up along the coast of Tamilnadu.

Modeling Using Coupled FEM-SBFEM for Three-Dimensional Seismic SSI in Time Domain

AbstractFor soil-structure interaction (SSI) problems, accurate modeling of the unbounded domain is an important issue. This paper deals with the three-dimensional seismic SSI analysis based on the substructure method by coupling the FEM and the scaled boundary FEM (SBFEM) approaches. The entire analysis is performed in the time domain making the proposed approach capable of dealing with nonlinearity of soil. To verify the developed program, the results from the present analysis are compared with those available in the literature. This verification has been performed for both externally applied dynamic load and seismic load. The effect of boundary conditions on the SSI response is evaluated. The numerical study performed indicates that the SBFEM can act as a computationally efficient boundary when compared with the conventional viscous dashpots. Next, application of the FEM-SBFEM for SSI problems is demonstrated. A dam-foundation interaction analysis is carried out, and the effect of the inhomogeneity of ...

Dynamic properties of Solani sand at large strains: a parametric study

Abstract During earthquakes, the behavior of soil is much dependent on its dynamic characteristics. Dynamic properties of sands are important features which govern its seismic behavior. Himalayan region is seismically active area and Roorkee (India) city falls under its subduction zone. The city has experienced earthquakes in the past and faces the danger of severe seismic threat in future also. Major area of Roorkee is covered by soil from the bed of Solani river i.e. Solani sand.In this paper, the strength characteristics of Solani sand has been investigated by a series of cyclic triaxial tests, which has not been reported in the literature. Strain controlled undrained cyclic triaxial tests were performed to evaluate dynamic properties viz. shear modulus and damping ratio of the Solani sand. The paper presents, effects of three parameters i.e. relative density, confining pressure and frequency of cyclic loading on dynamic properties of Solani sand in the large shear strain range (0.037% to 0.75%). The effect of relative density and confining pressure on shear modulus is significant.

Effect of soil nonlinearity and liquefaction on dynamic stiffness of pile groups

Abstract Determination of the behavior of pile groups under dynamic condition is a complex problem. The complexity becomes more intricate when the soil medium surrounding the piles behaves nonlinearly due to higher cyclic loading under dynamic condition. Further if the soil is saturated then the behavior of pile groups is also affected due to liquefaction. In this paper, nonlinear dynamic analyses of pile groups have been performed with and without generation of pore water pressure.A three-dimensional finite element soil-pile model has been developed with proper radiation boundary conditions. Frequency dependent Kelvin elements have been used for simulating radiation conditions at infinity. The numerical model and the process of computation have been verified with the established literature. For soil nonlinearity, work-hardening plastic cap model has been considered for further investigation. The pore pressure generation for liquefaction has been incorporated by two-parameter volume change model reported in literature.The effects of nonlinearity and liquefaction of soil medium on dynamic stiffness of single pile and pile groups have been investigated. Effects of frequency of excitation have been examined. It has been observed that the work-hardening soil plasticity and generation of pore water pressure has a significant influence on dynamic behavior of pile groups.

Improvement in liquefaction resistance of pond ash using stone-sand columns

Abstract Aim of this paper is to demonstrate improvement in liquefaction resistance of the pond ash (fly ash) due to its strengthening with stone-sand columns. Tests were carried out on a vibration table (shake table) to evaluate the liquefaction resistance of the pond ash without and with stone-sand columns. In the present study, the liquefaction resistance is evaluated in-terms of pore pressure ratio (ru). The effects of spacing of stone-sand columns on liquefaction resistance of the pond ash have been studied. Tests results indicate that the addition of stone-sand columns increases the liquefaction resistance of the pond ash significantly. Further, increasing the number of stone-sand columns, the liquefaction resistance of the pond ash increases considerably. This also decreases significantly the time for building-up of maximum pore pressure; duration for which maximum pore pressures stays and total time for dissipation of pore water pressure which indicates decrease in drainage path. The proposed technique of improvement is simple and has very much practical significance.

Effects of cyclic loads on dynamic properties of soils in the Ganga basin

Abstract Seismic behaviour of soils is primarily governed by dynamic properties under cyclic loads. In this paper, this has been investigated for NW Himalayan region. The study focuses primarily on two sites: Dhanauri and Roshnabad, both located in the Ganga foreland basin. The Dhanauri site comprises distinct layers of clay, silt, and sand, and the Roshnabad site comprises predominantly gravelly soil. The soil samples were collected from two sites from different depths using SPT. The MASW tests have been also conducted on these sites. The strength characteristics of soil samples collected from Dhanauri and Roshnabad were investigated by a series of cyclic triaxial tests. Strain controlled undrained cyclic triaxial tests were performed to evaluate dynamic properties of the soil. The effect of shear strain on shear modulus reduction and damping has been investigated. It was observed that the variation in shear modulus ratio with shear strain is large for the samples collected at higher depth. Moreover, at high shear strains, the difference in shear modulus ratios decreases with depth.

Relationship between shear velocity and SPT resistance for sandy soils in the Ganga basin

Abstract The correlation between shear wave velocity Vs and standard penetration test resistance N is investigated in Northwest Himalaya. The study focuses primarily on two sites: Dhanauri and Roshnabad in the Ganga foreland basin. The Dhanauri site comprises a mixture of clay, silt and sand, and the Roshnabad site comprises predominantly gravelly soil. A new empirical formula is suggested to correlate shear wave velocity and standard penetration resistance, based on a dataset collected as part of an earthquake risk evaluation study in the Northwest Himalayan region, India. The formula is based on geotechnical exploration (standard penetration test) and seismic experiments (multichannel analysis of surface wave). The relationship derived was compared with existing correlations in the literature.

Effects of soil nonlinearity and liquefaction on seismic response of pile groups

Abstract The seismic behavior of pile groups is very complicated if piles are passing through liquefiable soil. In this paper, the effects of soil nonlinearity and liquefaction on seismic response of pile groups are investigated. A three-dimensional finite element soil-pile model was developed with Kelvin elements for simulating radiation conditions at infinity. The effect of soil nonlinearity was investigated considering work-hardening plastic cap model for the soil. The liquefaction of the soil medium was simulated using two parameter volume change model.Seismic responses of a single pile and pile groups were examined considering soil nonlinearity and liquefaction. The study was performed for range of frequency of excitation. Finally analysis is carried out for real time earthquake motion. A significant effect of soil nonlinearity and liquefaction of the soil medium on the seismic response of pile groups was observed and it was also noticed that this effect is very much dependent on peak ground acceleration and frequency characteristics of the input motion.