Faculty Publications
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Item Numerical Study on Interference of Surface Strip Footings Resting on Stiff Clay(Springer Science and Business Media Deutschland GmbH, 2020) Hridya, P.; Anaswara, S.; Shivashankar, R.In the present study, the interference effects of two closely spaced strip footings on the surface of stiff clay were investigated. The effect of interference on characteristic behaviour like bearing pressure, settlement and tilt is observed using two-dimensional plane strain analysis. Finite element analysis software PLAXIS 2D is used for this. The behaviour of individual footing on stiff clay is first established. Parametric study is done by varying the width of footing and the spacing between the footings. The results are presented in terms of efficiency factors, which are defined as the ratio of settlement or bearing pressure of interfering footing to that of the isolated footing. The effect of interference is particularly noticeable in terms of settlement. Maximum settlement and tilt occur at a spacing 1.5B irrespective of the footing width. Effect of shear keys placed beneath the footings at different locations beneath the footing and the interference of such footings were also studied. It is found that the presence of shear keys has a significant effect on the interference between the footings, compared to without the shear keys. © 2020, Springer Nature Singapore Pte Ltd.Item Study of Tilt on Adjacent Strip Footings(Springer Science and Business Media Deutschland GmbH, 2021) Anaswara, S.; Shivashankar, R.The primary function of the foundation of a structure is to safely transfer the loads from the superstructure to the soil beneath without occurrence of shear failure and excessive settlements. Due to rapid urbanisation, very often structures and their foundations are built close to each other. Foundation of the newly built and the already existing structures interferes with each other to some extent depending on their relative positions. Due to large stresses at points between the footings (due to overlapping of stresses), there is a non-uniform pressure distribution beneath the footings and beyond in the gap between the footings. There is an increase in stresses from the outer edge of the footing to the inner edge. This causes tilt in the footings. This numerical study looks into the tilt of two adjacent strip footings on the surface of cohesive and cohesionless soils. Numerical analysis using a finite element-based software is being used. The parameters varied in this study are the clear distance between the two adjacent rigid strip footings and width of the footings. One of the footings representing an already existing foundation is loaded with half of the estimated failure load of isolated footing and adjacent footing loaded up to failure. The effect of interference is observed to be particularly significant in terms of the tilt. © 2021, Springer Nature Singapore Pte Ltd.Item A Numerical Study on Interference Effects of Closely Spaced Strip Footings on Cohesionless Soils(Springer Science and Business Media Deutschland GmbH, 2021) Anaswara, S.; Shivashankar, R.Foundations of buildings often need to be placed at close spacings to meet the various structural or functional requirements. In such cases, the combined action of adjacent footings is different from that of a single foundation. The combined effect causes interference of the stress zones. Numerical analysis is carried out on two closely spaced strip footings on sands, by varying the affecting parameters, to study the interference effects. Interference effects are analysed in terms of bearing pressure, settlement and tilt of foundations. In this study, the interference effects of closely spaced strip footings on the surface of cohesionless soils are being investigated. Parametric studies are done for two foundations by varying the clear spacing between the foundations. The results are presented in terms of interference factors. New structures near to the old construction may alter the settlement, pressure and rotational characteristics of the old footing and could lead to its distress. Above all, the load-carrying capacity of the new foundation will be very different from what it would have carried if it were independent—without the interference of the other footing. First footing representing an already existing footing is loaded with half of the estimated failure load of single independent strip footing and second adjacent footing loaded up to failure. The effect of interference of the old foundation is observed to be particularly significant in terms of the settlement and tilt. © 2021, Springer Nature Singapore Pte Ltd.Item Studies on Tilt of Closely Spaced Strip Footings on Unreinforced and Reinforced Sands(Springer Science and Business Media Deutschland GmbH, 2021) Anaswara, S.; Shivashankar, R.Two or more strip footings are quite often built close to each other, due to which there will be overlapping of stresses in zones or at points between the footings. There is a non-uniform pressure distribution in the foundation soil beneath the footings, in the space between the footings and beyond. There is also an increase in confining pressure of the soils between the footings. All these result in the tilt of the footings. This numerical study looks into the tilt of the already existing strip footings due to the construction of an adjacent new strip footing on the surface of cohesionless soils. A parametric study is conducted including the effect of geogrid reinforcement/s beneath the new footing. One of the footings representing an already existing foundation is loaded with half of the estimated failure load of a single-strip footing, and adjacent new strip footing is loaded up to failure. The property boundary line is assumed to be midway between the two footings. Geogrid reinforcement layers beneath the new footing are considered to be extending equally beyond the footing on either side, up to the property line. Both unreinforced and reinforced sands are considered beneath the new footing for analyses. Tilts are observed to increase with the width of footing. At closer spacings, tilt was found to be more in case of loose sand. Results of this study indicate that there is a considerable increase in the tilt of the old footing in the presence of reinforcements beneath the new footing. © 2021, Springer Nature Singapore Pte Ltd.Item Study on Behaviour of Two Adjacent Strip Footings on Granular Bed Overlying Clay with a Void(Springer, 2020) Anaswara, S.; Shivashankar, R.This paper numerically examines the behaviour of two adjacent strip footings on granular bed over weak soil having a void. Voids could be formed in weak soil strata due to various reasons such as due to water leakage from the water supplying lines or sewer lines, poor drainage and erosion of soil, animal burrows, etc. A parametric study is carried out to understand the influence of granular bed thickness, width of footings, spacing between the footings, and the presence of a void beneath the footing in the weak soil, on the behaviour of footings. To understand the failure mechanism, shear strain contours, for different cases, are being studied. It is observed that there is a certain critical spacing between the two adjacent footings at which the footing/s carry the maximum load. This critical spacing depends on the type of loading, whether equal and simultaneous loading or unequal and sequential loading. The presence of voids also affects the performance of footings. Such voids tend to reduce the load carrying capacity of the footing/s and alter failure pattern. © 2020, Springer Science+Business Media, LLC, part of Springer Nature.Item Interference Studies of Adjacent Strip Footings on Unreinforced and Reinforced Sands(Springer, 2020) Anaswara, S.; Lakshmy, G.S.; Shivashankar, R.Interference effects of two and three strip footings placed adjacent to each other on unreinforced and reinforced sands are being studied in this paper. Effects on stresses in foundation soil, bearing capacity, settlements and tilts of footings are being looked into. Parameters varied in this study are (i) the number of footings (In the case of two footings loaded simultaneously, both experimental and numerical studies are conducted. In the case of two footings loaded sequentially and three footings, numerical studies are done.), (ii) loading conditions, (iii) clear spacing between the footings and (iv) number of reinforcement layers in foundation soil. With two footings, two loading conditions are considered. In the first loading condition, both footings are loaded simultaneously up to failure. In the second loading condition, one of the footings representing an already existing foundation is loaded with half of the estimated failure load of single strip footing and adjacent footing loaded up to failure. With two adjacent strip footings on unreinforced and reinforced sands, both loaded simultaneously, some laboratory-scale experimental studies are also conducted to compare with the numerical results. It is observed that there is a certain critical spacing at which the footing/s carry the maximum load. This critical spacing depends on the loading condition. Reinforcements in the foundation soil used are in the form of hexagonal wire meshes. The effect of providing the reinforcements in layers in the foundation soil is seen in the increased bearing capacity, reduced settlements and reduced tilts of the footings under simultaneous loading condition. Tilts are also found to be influenced by the loading condition. © 2020, Springer Science+Business Media, LLC, part of Springer Nature.Item Study on Behaviour of Two Adjacent Strip Footings on Unreinforced/Reinforced Granular Bed Overlying Clay with Voids(Springer Science and Business Media Deutschland GmbH, 2021) Anaswara, S.; Shivashankar, R.This paper numerically studies the behaviour of two adjacent strip footings on unreinforced and reinforced granular bed (RGB) overlying clay having voids. The influence of different parameters such as granular bed thickness, length of reinforcement/s, number of layers of reinforcement, presence of void/s beneath the footing/s in the weak soil, on the behaviour of footings are carried out in this study. It is found that there is a certain optimum spacing between the two adjacent strip footings at which the footing/s carry the maximum load. The voids could be formed in weak soil due to various reasons and the presence of voids may affect the performance of footings. Such voids tend to reduce the load carrying capacity of the footing/s. However, providing a RGB over weak soil can be used as an effective method to maintain the good performance of footings, even when voids could be formed in future. © 2020, Springer Nature Switzerland AG.Item Bearing capacity of interfered adjacent strip footings on granular bed overlying soft clay: An analytical approach(Salehan Institute of Higher Education, 2021) Shivashankar, R.; Anaswara, S.In the present paper, the interference effects on bearing capacity of two and three closely spaced strip footings resting on granular bed overlying clay are being studied. A simple analytical model is proposed to predict the load-carrying capacity and the interference factor of an interfered footing, when adjacent strip footings are optimally placed on the surface of a Granular Bed (GB) overlying clay and both the footings are simultaneously loaded. A punching shear failure mechanism is envisaged in the analytical model. The load-carrying capacity of the footing is taken as the sum of total shearing resistances along the two vertical planes through the edges of the strip footing in the upper granular layer and the load-carrying capacity of the soft clay beneath the GB. Insights gained from finite element simulations are used to develop the new modified punching shear model for interfering footing. Bearing capacity can be easily calculated by using the proposed punching shear model for interfering footing. The analytical model is validated with numerical analyses and previous experimental results and found to be in reasonably good agreement. The influence of different parameters such as granular bed thickness, width of footing, number of footings are carried out in this study. © 2021 by the authors. Licensee C.E.J, Tehran, Iran.