ABHIJIT SAHA, Ph.D., P.E. - Academia.edu (original) (raw)

Papers by ABHIJIT SAHA, Ph.D., P.E.

INDIAN GEOTECHNICAL CONFERENCE 2022, GEOLEAP (GEOTECHNICS - LEARNING, EVALUATION, ANALYSIS & PRACTICE), 2022

The popularity of nature-inspired meta-heuristics in solving complex optimization problems is on ... more The popularity of nature-inspired meta-heuristics in solving complex optimization problems is on a steady rise within a rapidly evolving world. Swarm intelligence (SI) optimization inspired by the behavior of social organisms in flocks of bird, schools of fish, colonies of ants and bees perform the search through agents whose trajectories are primarily adjusted stochastically and sporadically deterministically, in accordance with golden rules drawn from Mother Nature. Each entity within the swarm is influenced by its own 'best' and group 'best' position, while moving randomly to converge to optimal through competition and cooperation. The sparrow search algorithm (SSA), developed by Xuea and Shen (2020) and slightly improvised (LSSA) by Ouyang, Zhu and Wangis (2021) is a very recent SI approach which adopts the sparrow producer-scrounger model metaphorically for designing optimum searching strategies, inspired by the group wisdom, foraging and anti-predation behavior of sparrows. LSSA is experimented on some hard benchmark test functions to test its effectiveness and thereafter, applied in searching the critical failure surface in slope-stability problem. The objective function is the factor of safety against failure. The stability analysis is performed integrating the present tool with Bishop's simplified method (1955). Results show LSSA is a strong contender to methods like geneticalgorithm, simulated-annealing, big-bang big-crunch and artificial bee colony algorithms. The study illustrates the flexibility, efficiency and robustness of the methodology in function optimization.

2nd International Conference on Sustainable Water Management organized by Water Resources Department, Govt. of Maharashtra during November 6-8, 2019 at Pune, Maharashtra, India , 2019

Many reservoirs have been built in India since independence under several multipurpose river vall... more Many reservoirs have been built in India since independence under several multipurpose river valley projects. As a natural process over the time domain, the upstream sediments are gradually being carried over by the stream network flowing towards these reservoirs from its adjoining catchments, which in turn are being gradually filled up by the same. The less is sediment inflow into the reservoirs, the more will be their useful life and storage capacity. Reservoir survey has revealed that most of the reservoirs in the eastern fringe of Chotanagpur plateau have significantly been losing their capacity. There are in total 41 large, medium and small dams in West Bengal. In the present investigation, out of the total, five dams have been examined in regard to the sedimentation aspect at large, critically probing into the rate of sedimentation and the nature of sediment, along-with the morphogenetic changes of the concerned catchments. The reservoirs Kangsabati-Kumari, Massanjore, Beko, Barabhum and Extension of Bandhu have been considered in the present study. Modern instruments, methods and software have been used in computation of Area-Elevation-Capacity Curves. Soil sample analysis has been done on the samples collected from the reservoirs. Present data have been compared with the design pre-dam reservoir capacity and subsequent earlier post reservoir data. Land use land cover (LULC) pattern of the catchments has been analysed on RS-GIS platform. It generally transpires that small dams are susceptible to considerable sediment deposition within a span of 20-30 years where as the large ones within a period of 50-60 years. It emerged that less vegetated catchment of the reservoir contributes more sediment to the reservoir. To combat this problem, traditional solutions like catchment area treatments, afforestation of upper catchments may prove to be beneficial.

Two analytical closed-form elastic-rigid-plastic solution methods to predict the rigid foundation... more Two analytical closed-form elastic-rigid-plastic solution methods to predict the rigid foundation behaviour on stone-column reinforced soil are compared, both of which takes into account the stone material yield within the host soil according to stress-dilatancy theory. These are the mechanistic methods developed by the author (2004, 2005) [that presently incorporates the dilatancy angle as per Schanz and Vermeer (1996)] and that developed by Pulko and Majes (2006), that takes into account the column yield as per Rowe dilatancy theory. Since optimal design of stone column necessitates optimum stress concentration on column, which is generally composed of dense gravel with/or without sand, the vertical stress on granular column is often close to its peak strength and the material dilates. To arrive at closed-form analytic solution to this complex soil-stone column interaction problem, some common assumptions like axi-symmetric soil-stone column 'unit-cell', elastic host soil and rigid-plastic Mohr-Coulomb stone column material are combined with equilibrium and kinematic conditions. The results reflect the beneficial effect of dilatancy within the optimal range or techno-economic domain of area-ratio. The settlement predictions are compared with other analytical methods available in literature as well as with measured settlement reduction of stone-column reinforced ground at different subsoil conditions around the globe reported in literature.

The stone columns improve the performance of foundations on soft and loose soil due to the abilit... more The stone columns improve the performance of foundations on soft and loose soil due to the ability of composite ground to sustain increased structural loads under reduced settlements. The interaction between the two basic elements: the ambient subsoil and installed column, present a complexity of behaviour, both in terms of applied stresses and resulting strains. Moreover, as the same is provided in-group in a regular array beneath foundations, the performance of an individual column is likely to be influenced by the presence of neighbouring columns. The present paper addresses this very issue. Analysis of reported field hydro-test data of large diameter oil storage tanks in soft ground in reference to some existing theories led to the development of the stone-column 'group efficiency factor'. In order that such factor is of general use, it was felt necessary to examine the applicability of the factor to different sizes of groups under varied subsoil conditions. With this in view, some model test results reported in literature of single and group of columns have been analysed and in the process an explicit relationship regarding the stone-column 'group-effect' could be established.

Calcutta-the birthplace, shelter and centre for livelihood of millions-of the glamorous rich to t... more Calcutta-the birthplace, shelter and centre for livelihood of millions-of the glamorous rich to the dismal poor, speaks the story of a diversified tradition of sect, religion and culture. This has attracted towards her, the prince and the pauper alike in the diverse social, political and economic arena of the region that effected in the construction of magnificent apartments, prototype interwoven "match box" multistoried, endless gloomy, poverty stricken hutment, each overlooking the other; standing in harmony and all set out for a tint of the blue and a handful of the fast depleting green. Fast pace urbanization of city fringes has left a little place for her drainage system to develop or improvise over the age old network implemented over a century back. On the doorsteps of 21 st century, this is high time to realize that health of the Calcutta Metropolis depends to a large extent on the long term management and protection of her environment through sound policy and planning, linked to appropriate regulatory and enforcement capacity, development of effective monitoring measures and incorporation of the environment criteria into the land-use planning process. The successful accomplishment of the said 'set' requires a thorough knowledge of historical background of the area to appreciate technically the geo-hydro-morphological changes in the rivers which has influenced to a great extent, down the ages, the land-use pattern and dominance of human interference. Sound sanitary conditions being a prime factor deciding the health and prosperity of a metropolis and her inhabitants, need for an efficient drainage system for quick and effective disposal of sewage and storm discharge had been, and remained, in the forefront of the problems requiring attention of the policy makers. The drainage arteries, specialty the outfalls being the 'life-line' of the city, an effort has been made in the present paper to identify the areas requiring attention for its survival. The study has been made in the light of fluvial hydrologic changes in the river systems down the ages to which the city of Calcutta has its drainage outfall in the broad perspective of its geographic location within the largest delta of the world.

Two multi-storied occupied apartment buildings and a clinic of 'Red-Cross Society' in Chandernago... more Two multi-storied occupied apartment buildings and a clinic of 'Red-Cross Society' in Chandernagore-a former French colony, located very close to the banks of tidal river 'Hooghly' (the southernmost part of River Ganges-the major hydrodynamic system that formed the world's largest delta) are standing precariously, following some recurrent slides of high riverbank during the last year's monsoons. The area where the ground caved in, is on the end of the famous Strand Bank Road (in Hooghly district of West Bengal in India); which is supposed to be the best decorated bank of the river 'Ganges' along its entire length of 2500 km. The opposite river bank is an official sand mining site. The river over considerable stretch at both upstream and downstream apparently seemed stable when analyzed over an extensive temporal domain from old Survey of India toposheets, recent satellite imagery, digital elevation model, field hydrographical survey synthesized in Geographical Information System (GIS) platform. A closer look into the geotechnical aspects supported by subsurface exploration, post failure on-site exposures and stability analysis revealed certain startling facts when considered in association with the hydro-meteorological factors and fluvial dynamics. An in-depth study of the factors responsible for the localized erosion is presented based on site observations and evidences, analyzed in association with real time hydrological and meteorological data.

“Geotechnique Today- Prediction, Modelling & Construction”: Proceedings of Indian Geotechnical Society, Kolkata Chapter, Kolkata, India, Feb 28, 2014

The popularity of nature-inspired meta-heuristics in solving complex multidimensional and combina... more The popularity of nature-inspired meta-heuristics in solving complex multidimensional and combinatorial optimization problems is on the rise. The biologically inspired computation and their solution frameworks abstracted from the natural world are largely due to its flexibility of hybridization and customization to different problem environments. Swarm intelligence is a research field that models the collective intelligence in swarms of insects or animals. Artificial Bee Colony (ABC) algorithm is one of the most recently introduced (Karaboga, 2005) swarm-based algorithms that simulates the intelligent foraging behaviour of a honeybee swarm. A slight modified version of ABC algorithm proposed by the author is initially tested on some hard benchmark test functions and then applied in searching the critical failure surface in soil slopes where the independent design variables are the abscissa (CX), ordinate (CY) of slip circle centre, and depth factor (Nd) of the slip surface. The objective function is the factor of safety (FOS) against failure. The stability analysis is carried out integrating the present tool with Bishop's simplified method (1955) and results compared with examples from literature to highlight the robustness of the present methodology. Results produced by ABC and some other nature-inspired meta-heuristics like Genetic Algorithm (GA), Genetic Algorithm-Simulated Annealing (GA-SA) hybrid, Big Bang-Big Crunch (BB-BC) method have been compared (Saha 2003, 2008, 2011, 2013) to demonstrate its versatility.

Proceedings of the 18th International Conference on Soil Mechanics and Geotechnical Engineering, Paris, 2013, Sep 2013

The paper addresses the topic of single objective optimisation of a three dimensional real-world ... more The paper addresses the topic of single objective optimisation of a three dimensional real-world problem and introduces a hybrid technique of an iterative random population search within a geometrically shrinking hypercube and a sort of simplified Design of Experiments (DOE). A ‘population’ of design variables are generated and augmented with the multivariable objective function, and the design variables pertaining to the local optima are perturbed by a factor (k) sequentially in both positive and negative directions to create 2(2N-1) offspring in the neighbourhood of local optima to hopefully produce some better progeny. The ‘fittest’ perturbed offspring decides a new contracted search interval for the consecutive generation according to a geometric decay rule commensurate with the generation number. A ‘simple hill-climbing’ strategy in Artificial Intelligence context is followed subsequently and the loop is continued to produce fresh generations of refined offspring till the outcome converges to the global optimum. The method is applied in searching the critical slip-surface of a vulnerable soil-slope and it was revealed that the optimum found by this method is superior to that found by traditional and non-traditional (genetic algorithms) optimization techniques while using much less computational resources.

Proceedings of Indian Geotechnical Conference, Roorkee, December 22-24, 2013, Geotechnical Advances and Novel Geomechanical Applications, ISBN: 978-81-925548-1-5, Paper No.-82, Dec 2013

Nature is the principal source of inspiration of non-traditional optimization methods like the ge... more Nature is the principal source of inspiration of non-traditional optimization methods like the genetic algorithm (GA) or the simulated annealing (SA) methods. All evolutionary algorithms are heuristic population-based search procedures incorporating randomness as the key element of selection. The present novel optimization method is based on the theory of evolution of the universe: the “Big-Bang and Big-Crunch” (BB-BC) theory. In the initial phase of ‘Big-Bang’, the kinetic energy dissipation produces disorder or chaos where randomness is the principal feature; whereas, in the ‘Big-Crunch’ phase, randomly distributed particles are drawn into an ordered state to produce a convergent solution. The method is applied in evaluating stability of soil slopes where the objective function is the factor of safety against failure. The stability analysis is carried out integrating the present mathematical tool with the Bishop's simplified method of stability analysis and results compared with examples from literature to highlight the robustness of the present methodology.

Proceedings of Indian Geotechnical Society, Kolkata Chapter, Kolkata, India, Sep 2011

Nature-inspired algorithms are among the most powerful algorithms for optimization. The Big Bang ... more Nature-inspired algorithms are among the most powerful algorithms for optimization. The Big Bang – Big Crunch algorithm is a novel nature-inspired heuristic population-based evolutionary algorithm based on the theory of evolution of the universe: the “Big-Bang and Big-Crunch” (BB-BC) theory. In the initial phase of ‘Big-Bang’, the kinetic energy dissipation produces disorder or chaos where randomness is the principal feature; whereas, in the ‘Big-Crunch’ phase, randomly distributed particles are drawn into an ordered state to produce a convergent solution. The method is applied in evaluating stability of soil slopes where the objective function is the factor of safety against failure. The stability analysis is carried out integrating the present artificial intelligence (AI) tool with the Bishop's (1955) simplified method of slope-stability analysis and results compared with examples from literature to highlight the robustness of the present methodology.

Proceedings of Indian Geotechnical Conference, IGC-2010, (Vol.-II), GeoTrendz, Mumbai, India, Dec 2010

Ground improvement by installation of stone columns has emerged as a powerful and effective means... more Ground improvement by installation of stone columns has emerged as a powerful and effective means of ground improvement technique. The field application of the technology has developed faster than the design methodology because the mechanism of interaction between the two basic elements- the installed column and the native soil is complex, both in terms of induced stresses and resulting strains. The output behaviour of the ‘unit-cell’ comprising of the column and soil is influenced by the interdependence of the external stress level, the material properties of host soil and backfilled column and its dimensions, the construction procedure and its installation array. An effort has been made in the present paper to predict the upper and lower bounds in application of this technology for optimal cost effectiveness in terms of the area ratio of unit-cell and height-diameter ratio of column for a given set of material properties. For validation of the model, the results are compared with some field tests reported in literature, and the salient interesting findings are discussed

Proceedings of the National Seminar on Emerging Trends in Ground Improvement, Kolkata, , 2009, May 2009

Despite the widespread use of stone columns, present design methods are largely based on empirica... more Despite the widespread use of stone columns, present design methods are largely based on empirical data and / or simplified concepts of the action of columns. Nevertheless, this method has emerged as a powerful and effective means of ground improvement technique. The field application of the technology has developed much faster than the design methodology because the mechanism of interaction of load sharing between the two basic elements- the installed column and the native soil is complex, both in terms of induced stresses and resulting strains. As such, the soil-stone column interaction in field situations calls for a rational understanding, since the output behavior is influenced by the interdependence of the external stress level, the material properties of host soil and backfilled column, the column dimensions, construction procedure and its installation array. The present investigation analyzes some full-scale load test results in available literature (Prakash et al, 2005) on rammed stone columns installed in a wide range of alluvials ranging from loose to medium dense sands / silty sands and clayey silt / silty clays with and without fill over them. The back analysis is in the light of theoretical concepts and mechanistic models developed by the author (Saha, 2007). The extensive load tests and penetration tests prior to and after construction of columns and the extent of improvement achieved have been critically examined in the light of theoretical concepts encompassing the relevant design parameters, and some interesting findings are reported.

Proceedings of 13th Asian Regional Conference in Soil Mechanics & Geotechnical Engineering, Kolkata, India, 2007, Dec 2007

An in depth study of the load-settlement behavior of stone column treated ground has been made en... more An in depth study of the load-settlement behavior of stone column treated ground has been made encompassing all the relevant parameters governing design and performance including material properties of the in-situ soil and backfilled stone column, the external vertical stress level and geometry of column installation under different sets of assumptions and boundary conditions. The predictions based on the proposed method are compared with existing theories and ultimate column capacities reported in literature. The stress concentration on column and settlement reduction of composite ground developed by the proposed model has been presented, and results compared with other approaches available in literature. Finally, back analysis of published full scale load test results on ultimate column capacities available in literature has been done by the proposed model, and significant findings presented.

Proceedings of 14th Asian Regional Conference on Soil Mechanics & Geotechnical Engineering (14th ARC)-2011, Hong Kong, China., May 2011

Analysis of consolidation of fine grained soils by drain-wells by Barron (1947) is a classical ex... more Analysis of consolidation of fine grained soils by drain-wells by Barron (1947) is a classical example of the underlying mathematics governing the radial flow through the installed well, usually consisting of sand as a backfill material. Till today, the most frequently and extensively used method to account for accelerating radial consolidation is due to his pioneering work. However, Barron equation accounts for the factors affecting the water dissipation through the drain-well, without navigating into the strength factor that the sand ‘well’ or ‘column’ incorporates to the virgin ground due to its inherent higher rigidity. The present analytical study ventures into this very issue of radial drainage vis-à-vis load-settlement behavior of the reinforced ground. The consolidation and simultaneous strength increase of the composite system has been investigated in predicting the performance of soil-stone column cylindrical ‘unit’ loaded by a rigid raft (equal vertical strain) at upper boundary.

Proceedings of Indian Geotechnical Conference-2006 at IIT, Chennai. , Dec 2006

An effort has been made in the present investigation to explain the complex mechanism of soil-sto... more An effort has been made in the present investigation to explain the complex mechanism of soil-stone column interaction in the light of arching action of soils, which is–"one of the most universal phenomena encountered in soils both in the field and in the laboratory" as noted by Terzaghi (1943). Regardless of the plastic-versus-elastic state, simple force equilibrium at the column-soil boundary has been analyzed to explain the improvement in terms of the stress orientation angle- the natural free-standing, self-supported "thrust ring action" that follow the equation of a catenary-the shape taken by a chain held at the ends. The vertical, horizontal and shear stresses have been quantified in terms of the material properties of the in-situ soil and the installed column. The capacity of the stone column has been obtained using arching theory and findings are compared with some available results in published literature.

Proceedings of Indian Geotechnical Conference, Warangal, India, Dec 2004

The study presents a mechanistic model backed by a detailed analysis of dilating granular column ... more The study presents a mechanistic model backed by a detailed analysis of dilating granular column in soil-stone column interaction in ground improvement technology. For an optimal design of stone column, an optimum stress concentration on the column is required and the column material used being generally dense gravel with/ or without sand, the vertical stress on the stone column is often close to its peak strength and the granular material dilates. The effect of this dilatancy is investigated by incorporating a dilatancy factor in the proposed model. The results reflect the beneficial effect of dilatancy within the optimal range or economically feasible domain of area ratio. The settlement predictions are compared with Van Impe & Madhav’s (1992) model of dilating stone-column along-with measured settlement reduction of stone-column reinforced ground at different subsoil conditions reported in literature. The significance of inclusion of such refinement in the ‘unit-cell’ model to explain the reported settlement reduction of treated ground is highlighted.

Proceedings of 14th Asian Regional Conference on Soil Mechanics & Geotechnical Engineering (14th ARC)-2011, Hong Kong, China., May 2011

Genetic Algorithms (GA)-a new generation nontraditional search and optimization procedure is used... more Genetic Algorithms (GA)-a new generation nontraditional search and optimization procedure is used in the present investigation for locating the critical surface in slope stability. The method mimics the principles of Darwin’s natural selection and survival of the fittest rule which starts with a randomly generated population of ‘artificial chromosomes’ where every character present is an ‘artificial gene’. The radius and coordinate of sliding circle are taken as searching tri-variables in the analysis. Further, to improvise upon the search procedure, the genetic algorithm is combined with ‘Boltzmann’ selection. It is an approach similar to simulated annealing (SA) - the stochastic evolution of thermodynamic state of slow cooling of molten metals to achieve a crystalline absolute minimum energy state, where a perpetual decreasing sequence of temperature controls the reproduction rate. In essence, the present global search procedure-a hybrid GA-SA search combines the advantages of efficiency of neighbor-search of the simulated annealing and the robustness of genetic algorithm. Diverse aspects are presented to demonstrate the efficiency and robustness of the method. The spectrum of application area of hybrid GA-SA is widespread as it is a direct search method where no specific search direction is used and multivariable functions, both continuous and discontinuous can be handled.

International Conference on Civil Engineering in the New Millennium: Opportunities and Challenges (CENeM-2007), Bengal Engineering and Science University, Shibpur, Howrah, WB, India , Jan 2007

The present paper deals with genetic algorithms (GA) to find out the minimum Factor of Safety (FO... more The present paper deals with genetic algorithms (GA) to find out the minimum Factor of Safety (FOS) of a virgin slope vis-à-vis stone column reinforced slope and highlights some potent points that emerged during the search process. GA-a new generation and nontraditional search and optimization procedure is fast becoming popular for its increased versatility in handling complex engineering problems, since it does not require problem specific knowledge for carrying out the search. It is a tool guided by stochastic principles instead of gradients and hence one has the liberty to start with a wide range of values (or a ‘population’ of points) for the decision variables to process the value convergence of the objective function to near optimal solution at a very rapid rate. The output is found to be independent of the value of the initial vector. The slope stability analysis is carried out on the computer using GA as a function optimizer in slope analysis. The present paper is a sequel to author’s previous study (2001, 2003a, 2003b) wherein the raw data of a virgin slope example cited by Spencer (1967) is used as input, and the output was obtained by integrating GA with Bishop's simplified method of slices (1960) for virgin slope and Author’s (2001) method for stone-column reinforced slope. The search process, besides unfolding increase in FOS of stone-column reinforced slope over virgin slope against failure on a cylindrical slip surface, unleashed some other powerful features that are described in the paper.

Proceedings of Indian Geotechnical Conference, (IGC-2003)- ‘Geotechnical Engineering for Infrastructural Development’, Roorkee, Dec 2003

A mathematical model of a unit cell had been analyzed (Saha Abhijit, 2001) to predict the increas... more A mathematical model of a unit cell had been analyzed (Saha Abhijit, 2001) to predict the increased resistance of the potential sliding mass of the ‘pinned’ slope due to higher shear strength and free-draining characteristics of the ‘granular-pin’. The present investigation addresses the issue of determination of factor of safety by the introduction of genetic algorithms (GA), a relatively new search procedure, which does not require problem specific knowledge for carrying out the search since it is a tool guided by stochastic principles instead of gradients. Hence, one has the liberty to start with a very wide range of values (a ‘population’ of points) for the decision variables and process the value convergence of the objective function to near optimal solution at a rapid rate which is found to be independent of the initial vector. Increase in factor of safety of stone-column reinforced earth slope over a virgin slope against failure on a cylindrical slip surface has been searched using genetic algorithms as a function optimizer in the slope analysis.

Proceedings of 17th International Conference on Soil Mechanics & Geotechnical Engineering, Alexandria, Egypt, 2009, Oct 2009

A mathematical model of a unit cell of a ‘granular-pinned’ slope had been analyzed (Saha 2001) to... more A mathematical model of a unit cell of a ‘granular-pinned’ slope had been analyzed (Saha 2001) to predict the increased resistance of potential sliding mass of the ‘pinned’ slope due to higher shear strength and free-draining characteristics of the ‘granular-pin’ or column. The present investigation illustrates the effectiveness of a new generation optimization procedure, the genetic algorithms (GA), to find out the minimum Factor of Safety of virgin slope vis-à-vis reinforced slope. GA does not require problem specific knowledge for carrying out the search since it is a tool guided by stochastic principles instead of gradients. The objective function to be optimized in the two cases has been taken as the factor of safety expression of Bishop's simplified method (1960) for virgin slope
and Saha’s (2001) expression for reinforced slope. A specific stretch of vulnerable ‘Bhagirathi-Hooghly’ river bank (-the southern part of River Ganges- the major hydrodynamic system that formed the world's largest delta) has been chosen for the analysis. The study compares the results of prediction of failure susceptibility of river bank by directed grid-search in literature (Parua, 1992) with the present random search analysis. It emerged from the study that marked improvement in stability of such slopes could be achieved by granular-pinning that results in changing the potential virgin failure surface. Both gradual drawdown (GD) and instantaneous drawdown (ID) analysis exhibited marked improvement; though improvement in ID case, that is likely to govern in tidal deltaic zones, is about thrice than that obtained in GD case.