Hemanta Hazarika

Wall displacement modes dependent active earth pressure analyses using smeared shear band method with two bands

Abstract A new numerical method, based on a smeared shear band technique, has been proposed for the analysis of earth pressure that incorporates two shear bands for a localized element. The method, which is valid for plane strain condition, is applied to explain the generation of the active earth pressure against a rigid retaining wall for different modes of the displacement that the wall is likely to undergo. It exposes the deficiency of the conventional methods of analysis based on continuity of stress throughout the entire deformation process of the backfill. The proposed methodology can adequately capture the progressive deformation characteristics of the backfill. The wall displacement modes are seen to govern the progressive failure pattern. As a result, depending on the modes of displacement, the active state distribution of the earth pressure and the related parameters at the active state differ in magnitudes.

Investigation of tire chips-sand mixtures as preventive measure against liquefaction

This paper presents results of a series of element testing and model testing in which tire derived geosynthetics such as tire chips are utilized as liquefaction preventive backfill material. Undrained cyclic shear tests were conducted on tire chips and sand mixed tire chips for various percentages of mixtures, and the liquefaction potentials of the mixtures were evaluated. The best mixing percentage of tire chips was found to be close to 50% by the total volume of sand. Also, a model shaking table test on a caisson type quay wall was conducted on liquefaction prevention measures for backfill sand reinforced with tire chips. The test results have demonstrated that, despite the fact that the tire chips reinforced composite backfill has a very low relative density, there was no liquefaction in the backfill. Also, the earth pressure on the wall and its residual displacement could be substantially reduced, implying a good performance of the soil-structure system during earthquake loading.

Effects of reinforcement on the performance of breakwater foundation subjected to earthquake loadings

This paper deals with reinforcing technique for foundation of breakwater which provides resiliency to breakwater against earthquakes. Gabions and sheet piles were used in foundation of breakwater as reinforcing measures against earthquake loadings. Shaking table tests were performed to evaluate the effectiveness of the technique under different earthquake loadings, and comparisons were made between conventional and the reinforced foundation. Numerical analyses were also performed to elucidate the mechanism of the reinforcement–soil–breakwater system during earthquakes. The results of this study reveal the advantages of the technique in reducing settlement and horizontal displacement of the breakwater during different earthquake loadings.

Countermeasures for breakwater foundation subjected to foreshocks and main shock of earthquake loading

ABSTRACT Coastal protective structures, such as composite breakwaters, are generally vulnerable to earthquake. It was observed that breakwaters damage mainly due to failure of their foundations. However, the seismically induced failure process of breakwater foundation has not been well understood. This study describes failure mechanism of breakwater foundation as well as a newly developed reinforcing model for breakwater foundation that can render resiliency to breakwater against earthquake-related disasters. Steel sheet piles and gabions were used as reinforcing materials for foundation. The experimental program consisted of a series of shaking table tests for conventional and reinforced foundation of breakwater. Numerical analyses were conducted using finite difference method, and it was observed that the numerical models were capable to elucidate the seismic behavior of soil–reinforcement–breakwater system. This paper presents an overview of the results of experimental and numerical studies of the seismic response of breakwater foundation. Overall, the results of these studies show the effectiveness of the reinforced foundation in mitigating the earthquake-induced damage to the breakwater. Moreover, numerical simulation was used for parametric study to determine the effect of different embedment depths of sheet piles on the performance of breakwater foundation subjected to seismic loading.

Effect of Backfill Reinforcement on Retaining Wall Under Dynamic Loading

This paper presents numerical analysis of a reinforced soil retaining wall under static and dynamic loading. Finite difference programme, FLAC, was used to analyze behaviour of the reinforced soil retaining wall. In the analysis, behavior of soil–wall interaction, soil-reinforcement interaction has been considered. Analyses were conducted using different backfill conditions and loading conditions. The lateral displacement and earth pressure were analysed in order to evaluate the effect of reinforcement on the retaining wall. Comparisons were made between unreinforced (conventional) and reinforced soil retaining wall. The results show that length of the reinforcing layer affects earth pressures as well as lateral displacement significantly. Incremental dynamic earth pressure was affected by length of reinforcing layer.

Resilient and Sustainable Geotechnical Solution: Lessons Learned from the 2011 Great East Japan Disaster

This paper first describes the field tests conducted on a tire retaining wall that miraculously survived in the 2011 Great East Japan disaster. The paper then proposes a new concept of using waste tires behind the seawall in order to protect such coastal structures from the damage due to impact force of tsunami. A physical model for tsunami impact force simulation was developed and described to evaluate the reduction effect of tsunami impact force by the tire structures. Finally, from aesthetic point of view, cultivation of suitable plants inside the tires was proposed. Field tests on planting trees that can grow in saline soil conditions were performed to see whether tire structures can preserve the greenery of the area. The results of this research, thus, can go a long way toward providing a sustainable solution for infrastructure development in the future.

Sustainable Solution for Seawall Protection against Tsunami-Induced Damage

AbstractTo protect coastal structures from the damage caused by the impact force of a tsunami, a new concept of using waste tires behind such structures is introduced in this paper. A physical model for tsunami impact force simulation was developed to evaluate the reduction effect of tsunami impact force by the tire structures. Model tests also were performed to evaluate the stiffness of tire structures. From an esthetic point of view, cultivation of suitable plants inside the tires is also proposed. Field tests on planting trees that can grow in saline soil conditions were performed to see whether such a structure can preserve the greenery of the area. Results show that the tsunami impact force could be reduced considerably by placing filled tires (with a suitable material) behind seawalls, and this technique can protect the structures from the tsunami impact force and the resulting scouring. The greening effect could be maintained by the appropriate selection of the shrubs and trees planted inside the t...

Estimation of lateral force acting on piles to stabilize landslides

The lateral force on stabilizing piles due to the movement of the landslide has been studied by many researchers. One of the most widely used methods was proposed by Ito and Matsui in 1975 based on the plastic deformation theory. This paper aims to extend the approach of Ito and Matsui by considering the soil arching effects along the height of the sliding layer between two neighboring piles. The analysis is carried out in two stages. First stage involves the plastic deformation of soil adjacent to piles. In this stage, considering the arching effects along the height of the sliding layer, a typical cross section of the soil is employed to analyze the soil stress in the rear of piles. In the second stage, the plastic deformation theory proposed by Ito and Matsui is adopted to analyze the squeezing effects between two neighboring piles. Moreover, the parametric analysis is performed to investigate the susceptibility of the governing factors, which include the geometric and mechanical parameters. The results show that both the geometric and mechanical parameters impart the significant influence on the lateral force. Finally, both the numerical simulation results and the field experiment data from the literatures are introduced to validate the proposed approach. The comparison charts illustrate that the predictions by the proposed approach are consistent with the experimental results.

Behavior of Breakwater Foundation Reinforced with Steel Sheet Piles Under Seismic Loading

Waterfront structures such as breakwater, coastal dike, sea wall, etc., suffer serious damage from the earthquake and tsunami. The breakwaters are designed to protect coastline and seaport from the devastation effect of wave and current of tsunami by absorbing their wave energy and reducing overtopping. The port of Kamaishi (Iwate Prefecture, Japan) suffered heavy causalities due to the Great East Japan Earthquake in March 2011 mainly due to the damage of breakwater mound/foundation which was caused due to collapse of the breakwater. On the other hand, mitigation of compound disaster due to predicted future earthquakes such as Tokai earthquake, Nankai Earthquake, and Tonankai-Nankai Earthquake is a matter of great concern. The stability and safe performance of breakwater is very important for the protection of structures and population living near to coastline. It is, therefore, necessary to develop a new earthquake and tsunami resistant reinforcement technique for breakwater foundations which will make the breakwater resilient against the earthquake and tsunami forces. This paper deals with the development of an effective reinforcement technology for breakwater foundation which provides resiliency to the mound against earthquake. The technique involves use of steel sheet piles and gabion type mound (gravel wrapped up in steel wired mesh), which is effective in preventing breakwater subsidence and horizontal displacement. As a part of the study, a series of shaking table test in 1 g of gravitational field were performed and through the tests, the reinforcement effect by the steel sheet pile and gabion under earthquake loading and its influence on breakwater performance was made clear.

Numerical Study on the Seismic Response of Waterfront Retaining Wall Reinforced with Cushion

This paper describes the findings on the effectiveness of waterfront retaining structure reinforced with cushion made of tire chips, which has been analyzed using commercial software, PLAXIS 2D. The numerical model was subjected to the real earthquake recorded during the 1995 Hyogo-ken Nanbu earthquake. The results of the numerical analysis were presented in term of the deformation of the mesh, the displacement of the quay wall horizontally and vertically, and the settlement of the soil behind the quay wall. In general, the utilization of tire chip as a cushion behind a waterfront retaining wall was able to improve the behavior of the wall against an earthquake loading.