Proceedings of the Indian Geotechnical Conference 2022 Volume 2

The present study analyzes response of a circular footing on two-layered clays. Several solutions are available for the ultimate bearing capacity of foundations on two-layered soil but none considers the compressibility of the layers. Strong and stiff layer of thickness, H, overlies a soft and weak clay with E1 > E2 and cu1 = 2.5cu2, where 1 and 2 correspond to top and bottom layers, respectively. Finite element axisymmetric analysis is carried out to evaluate the bearing pressure, q, versus settlement responses for ranges of stiffness ratio (RE  = E1/E2) and different thicknesses of top layer. Variations of bearing pressure factors (Ncf = q/cu1) for circular footings of diameter, D, are obtained at different settlement ratios (SR), for a wide range of RE. Results are validated with the Merifield and Nguyen (Geomech Geoengin 1:151–162, 2006) for considered cases of layered clays with different H/D. Variation of Ncf with stiffness ratio, RE, for different SR and H/D ratios are presented and analyzed.

The behavior of a piled raft foundation (PRF) depends on complex raft–soil–pile interactions. In the present paper, the effects of pile number, pile spacing, pile length, and pile diameter on the settlement-dependent variation of raft–soil–pile interactions and load-sharing behavior of large PRFs in clay soil have been evaluated. Three-dimensional numerical analyses were performed on different foundation types such as piled raft, unpiled raft, pile group, and single pile. Results show that the piles-to-piles (P-P) interaction effect approaches unity at a particular settlement value, and the value is larger for a higher pile number, pile length, and pile diameter. With the same number of piles, at higher settlement levels, the raft-to-piles (R-P) interaction effect is slightly larger at wider pile spacing. An insignificant effect in the settlement-dependent variation of the R-P interaction effect is observed for variation in pile number, pile length, and pile diameter. The piles-to-raft (P-R) interaction effect firstly decreases within initial settlement range and then increases as PRF settlement increases. The proportion of load carried by piles in PRF initially increases and then decreases with PRF settlement. The settlement at which the pile load proportion reaches a peak is larger for a higher pile number, pile length, and pile diameter.

Pile foundations are widely used in weaker soil site to support superstructures. Study on bearing capacity of pile foundations is still gaining much attention to the geotechnical researchers. Besides laboratory and field tests, numerical method such as finite element method is used increasingly to deal with analysis of pile foundation problem. In this paper, a general-purpose finite element-based software “ABAQUS” has been used to explore the load-bearing capacity of piled-rafts. Soil profile has been used in this study which is cohesionless soil with varying relative densities. While we draw the load-settlement curve form “ABAQUS” viewport, the result shows nonlinear variation. To determine load capacity in pile-raft system, interaction factor has been considered as available in literature. In accordance with the proposed pile-raft model, the load-sharing ratio decreases as settlement increases which depends on the load capacity ratio. The value of load-sharing ratio is increase with load capacity ratios. The proposed load-sharing model has been verified using established formulas.

Normally consolidated soils have strength increasing with depth and with a desiccated layer near the top due to diurnal variations of temperature and weathering effects. Desiccated depth usually has high stiffness and strength which reduce to those values that correspond to the normally consolidated lower depth whose undrained shear strength increases linearly with depth. In this study, desiccated normally consolidated (DNC) ground was considered as a two-layer soil with non-homogeneities of these layers accounted for with decreasing and increasing rates of strength and stiffness with depth in top desiccated and the lower NC soil, respectively. A circular footing resting on desiccated zone overlying compressible NC deposit was analyzed considering the compressibility of the soils in the form of rigidity index. Bearing pressure–settlement responses of DNC are obtained by numerical analysis. Parametric study was carried out to study the effect of desiccation on undrained bearing pressure of footing on DNC. Bearing pressure of footings resting on DNC ground, increases with increase in rigidity index and non-homogeneity of NC soil. Thickness and non-homogeneity of desiccated zone significantly affect the ultimate bearing capacity of footing resting on DNC ground.

Pile termination decision at site is replete with dealing with uncertainties and challenges in identifying grade of rock in the case of rock socketed piles. This paper deals with application of pile termination criteria for some stretch in Chennai metro project. Methods of determining the criteria to decide on pile termination using rock classification, geological identification and pile termination ratio have been explored. A site friendly method for applying the pile termination at field has been executed and recommended as a guideline in this paper.

Open caissons are classified as deep foundations. Caissons are sunk into the ground by removal of soil within the caisson shaft. A cutting edge with a tapered inner face is provided at the bottom of the caisson to allow the bearing failure of the soil. The bearing failure of soil results in the formation of influence zone which is termed as failure zone. In this study, the 1g caisson model tests on sand are carried out with different configurations of cutting edge, i.e., varying radii ratio and different cutting angles and different sinking depths to evaluate the radial and vertical extents of failure zone. In the tests, the half-cut caisson models are penetrated in the sand and series of photos are captured. Using the captured photos, image analysis is performed to obtain the experimental failure zone. Based on the literature, the predictive equations to determine the extents of failure zone are assessed by comparing the extents of failure zone obtained from the experiments and the equations. The predictive equations help in quick estimation of the extent of failure zone based on the configuration of the open caisson adopted at the construction site.

The present study involves the development of a small-scale physical model for analyzing the settlement profiles under shallow strip footing resting on geosynthetic-reinforced sands. Air-dried sand with an average particle size (D50) of 0.48 mm was used as the model soil. The selection of model reinforcement was made by adopting scaling laws linking the tensile strength characteristics of model geosynthetic to that of commercial prototypes. A series of experiments were performed by pluviating sand at a relative density of 90%, and by varying the number and spacing between the subsequent reinforcing layers. The tests were performed under displacement-controlled conditions, and instrumented using a load cell and linearly variable displacement transducer (LVDT). The front side of the container was made of a perspex sheet to aid in the particle image velocimetry (PIV) technique. The results were interpreted by plotting the load–displacement curve and the displacement vectors obtained through PIV analysis. The reinforcement inclusion was observed as effective in controlling the heaving of the foundation and overall soil settlement. From the displacement vectors, the load dispersion angle was observed to be in the range of 20° to 30°, and was found to increase with higher reinforcement layers.

This paper focus on understanding the behaviour of dynamic Group Efficiency Ratio (GER) for different pile groups (3-pile, 2 × 2, 2 × 3 and 3 × 3) under harmonic vibration. The coupled vibration tests are conducted on the pile foundation in the field for varying eccentric moments (0.868, 1.269, 1.631, 1.944 Nm) to obtain the dynamic responses for all the pile groups considered. The pile groups are constructed in field with hollow steel piles of outer diameter 0.114 m and length 3 m. By utilizing continuum approach, theoretical studies are conducted for perceiving the frequency-amplitude responses of all the pile groups. The theoretical responses are found to be well-matched in comparison with the experimental responses. From numerical analysis, the stiffness and damping of all the pile groups has been also established and subsequently GER of the stiffness and damping has been computed which is the ratio of stiffness or damping of pile group to the sum of stiffness or damping of individual pile. The results exemplify that GER for stiffness is reduced below unity, which indicates the reduction in pile group stiffness due to dynamic pile-soil-pile interaction as the number of piles in group increases.

Traditional circular piles are frequently used as a foundation for offshore as well as onshore structures because of easy installation process. Though, in some critical cases, these traditional piles are not reliable for developing significant axial capacity during installation of pile. To overcome this problem, an innovative modification, i.e., spin fin pile foundation over a circular pile is developed. Spin fin piles are circular piles equipped with steel plate known as fins which is attached at the upper or bottom section of piles. In this paper a numerical solution for triangular shape and trapezoidal shape spin fin pile under axially loading is presented. To developed model along with an elastic–plastic soil model, an elastic fin and pile material, and interface elements a MIDAS GTS-NX software is used. The behavior of triangular shape and trapezoidal shape spin fin pile for different inclinations of fin and pile group for loose and medium dense sand are investigated. The load distribution within the spin fin pile and the settlement of pile are shown. Analysis shows that, the vertical resistance is more in trapezoidal shape fin pile as compare to triangular shape spin fin pile.

Under-reamed piles are generally a choice of foundation for structures subjected to the uplift load, especially for the transmission line towers, patrolling towers, chimneys, tall and slender structures, etc. In the study, the undrained uplift capacity of single under-reamed pile embedded in layered clay is evaluated using finite element (FE) method-based software Plaxis 2D. The geometry of the under-reamed pile is chosen as per the standard codal provision. In the analysis, the soil is assigned with Mohr–Coulomb model and pile is assigned with Linear Elastic model. The thickness of layered clays, i.e., soft clay overlain hard clay and hard clay overlain soft clay is varied with cohesion ratio = 2. The FE results are compared with the solutions available in the literature. The uplift capacity ratio defined as ultimate uplift capacity of under-reamed pile in single clay to that in layered clay having different clay layer thickness ratios (h/H = 0 to 1) is evaluated. The present study results are represented as design charts so as to be used in the design practice.

Helical pile is a type of deep foundation consisting of a steel shaft with round steel plates welded to it. Their applications have significantly increased since the late 1990s with the development of high torque generating machines. They are used in solar power plants, boardwalks, retrofitting works, transmission towers, transmission towers, and even residential buildings. Significant advancement has been made over the years using various laboratory tests, field tests, and software simulations to improve the design and strength of helical piles. However, research is still in progress for upgrading their design and predicting their load-carrying capacities. Codes have also been developed by a few countries for their design such as AC358 (the USA), BS 8004:2015 (the UK), CFEM 2006 (Canada), AS-2159:2009 (Australia). Field practices have also been carried out based on design manuals formulated by companies manufacturing helical piles. Currently, no Indian Standard code is available for their application in Indian conditions. In this paper, the most critical design and calculation methods framed by various researchers and the codal provisions have been discussed and compared. An overview of the essential design parameters influencing the helical pile capacity and a design recommendation have been provided which will be helpful in the design practices of helical piles.

This article presents a comparative assessment of the behaviors of connected piled raft (CPR) and disconnected piled raft (DPR) systems on the basis of an experimental study. Large-scale physical model tests are performed on 2 × 2 CPR and 2 × 2 DPR foundations embedded in sandy soil under static vertical load to understand the fundamental difference in the load transfer process involved in these two geometrically different foundation systems. Test results indicate that the inclusion of granular cushion platform under the raft in case of DPR plays the pivotal role in altering its load transfer mechanism from that of the conventional CPR system. The CPR shows higher load bearing capacity as well as higher settlement efficiency as compared to DPR. However, the DPR, upon loading, exhibits completely opposite pile-raft load-sharing phenomenon than conventional CPR system as the raft is observed to take majority of the externally applied load initially and then the pile load share is found to increase gradually with settlement. In CPR, the connected piles reduce the raft stiffness, whereas, in DPR, the piles enhance the raft stiffness and act as soil reinforcements.

The growth of urban infrastructure has forced the introduction of tall buildings under any subsoil condition. Many a times, pile foundation becomes an absolute choice causing increased cost of construction. In such situations, pile raft foundation can be a convenient alternative, wherein the raft also contributes toward a part of the load transfer, and hence number of piles required can be reduced. This results in reducing the total foundation cost leading toward sustainable solution. Many tall towers across the globe have been built on pile raft foundations, and they are performing successfully. The present paper focuses on assessing the load transfer mechanism of pile raft foundation. For this purpose, PLAXIS-3D software is used. Pile raft foundation system is idealized as a continuum. The soil is modeled using Mohr–Coulomb criteria, and structural components of the foundation system are modeled as rigid, elastic, and concrete structures. The objective of the present paper is to identify the mechanism of load transfer and hence to arrive at the total load carrying capacity of the system. Here, an attempt is made to explain how the load is transferred to the soil from pile raft foundation system, and an attempt is also made to identify the conditions under which pile raft foundation becomes more appropriate.

Wind energy is one of the most promising renewable energy sources. Offshore wind turbines (OWTs) are now used in many countries. Most OWT farms use driven monopiles as their foundation. The purpose of this study was to investigate the behavior of monopile under torsional load. Quasi-static analysis using finite element analysis is performed in PLAXIS3D. The performed study is used to evaluate the deformation and frictional mobilization of the surrounding soil. The rotor axis of an OWT rotor is usually not aligned with the wind since the wind is continuously changing its direction. The yaw mechanism, which rotates the nacelle around the tower axis, can help to increase energy capture. Any failure in the power control units, torsional loading is added to the monopile foundation. It initiates a twist (ɵ) at the pile head, reduces its axial capacity, and increases the settlement of the foundation. This study includes the torsional effect caused by the failure of the yaw and bearing system, and thus, the corresponding strength mobilization of soil is being done. The experimental investigation was done by varying the relative density of the sandy soil. Parametric studies are also done by changing the embedded length of the monopile and varying the soil stratum. Through the numerical studies, the effect of cyclic loads on the rate of accumulated displacements, shear stress variation with respect to the depth, and changes in soil–pile stiffness were discussed.

Load sharing ratio between pile and raft is an important parameter in designing the piled raft foundation. Load sharing ratio between pile and raft in piled raft foundation depends on many factors such as raft, pile and soil properties, spacing between piles, raft–pile area ratio, stiffness ratio of the pile, raft, and soil. In the present study, limited number of experimental study and extensive numerical analysis has been carried out to understand the behavior of piled raft foundation. Based on the experimental studies, the load sharing mechanism of pile and raft in a piled raft has been presented. Load sharing between pile and raft has been evaluated through experimental investigations on the model piled raft and three-dimensional finite element-based numerical analysis. The nonlinear variation of load sharing between pile and raft with foundation settlement has been discussed by determining the pile–pile and pile–raft interactions. The influence of soil stiffness, soil–raft stiffness, pile group area and length to pile diameter ratio on load sharing of pile and raft in piled raft foundation has been presented. The parameters of numerical analysis have been considered similar to the experimental studies for the purpose of comparison of results. The study will be useful in developing the load sharing model for estimating the nonlinear load sharing between pile and raft in a piled raft foundation. The paper describes the modeling procedure, material properties, parameters adopted in the analysis, and the results.

In the piled-raft (PR) foundation design, evaluating the load shared between the raft and piles is important as both contribute to the load-carrying capacity. For the present study, three-dimensional numerical modeling has been carried out to investigate the load-sharing ratio of a large piled-raft foundation in dense sand with respect to settlement by varying parameters like spacing and length of pile and thickness of raft. Initially, the individual load–settlement responses of the raft and piles in PR are determined for all PR configurations and then compared with the individual responses of the unpiled raft and group piles. Results show that the load-carrying capacity of raft and piles in PR is found to be greater than unpiled raft and group piles, respectively, for smaller pile spacing. The load-sharing ratio increases with increase of pile spacing at all settlement levels. With increasing settlement, the load-sharing ratio decreases for smaller pile spacing, whereas, for larger pile spacing, it increases initially and then decreases. As pile length increases, the proportion of load carried by piles increases at all settlement levels for smaller pile spacing; but for larger pile spacing, the variation of the proportion of load carried by piles is not significant at smaller settlement levels. For all raft thicknesses at higher pile spacing, the proportion of load carried by piles increases initially at initial settlement and then becomes almost constant toward higher settlement.

Reinforced earth forms one of the ground improvement techniques using in-situ soil reinforcement for purposes of improving the strength and stiffness of soil, for instance, the use of Geosynthetics to increase the bearing capacity and decrease the settlement of foundations. In the past, various researches have been conducted to study the behavior of reinforced soil under various types of footings and loading conditions. However, the behavior of reinforced ring foundation is still a relatively unexplored area. But its use in geotechnical engineering is an economically viable alternative to circular foundation. Furthermore, it is used in a variety of special structures such as cooling towers, silos and oil storages, transmission towers etc. In the present study, numerical analyses of reinforced ring foundation subjected to eccentric-inclined loading have been performed using PLAXIS 3D. It has been observed that with the eccentric-inclined loading, the design of ring foundation may be permitted up to the ratio of internal to external radii of 0.1875 without compromising the bearing capacity of circular foundation with equal external diameter. The effect of soil reinforcement has been found to be the maximum when the depth of the first layer of reinforcement is kept within the range of (0.2B–0.4B), where B is the outer diameter of the ring foundation.

Caissons and piles are commonly used foundation types for deep water bridges. Caisson is appropriate for long-span bridges, deep alluvial deposits, liquefiable soils, and significant vessel collisions, although they can occasionally become problematic because of difficulties in sinking and insufficient earthquake resilience. Because of its extensive length, decreased rigidity, limited vessel crash protection, and challenging construction requirements, pile foundations are not appropriate for deep sea. A composite caisson-pile foundation (CCPF), also known as a caisson and pile combination, can be used as a solution to the aforementioned issue. It is an innovative hybrid foundation that takes into account the benefits of both foundation kinds. The CCPF reduces construction costs and time while providing creative answers to difficult site conditions in deep water. This foundation structure is commonly used for river and sea crossing bridges. However, due to a lack of significant research on its geotechnical and structural properties, CCPF has not been extensively used. Reduced-scale model tests on instrumented CCPF in sand under static vertical loads were carried out based. The load-settlement responses of the foundation under static monotonic vertical loading are presented and discussed in this study.

Bridges are prime components of transportation network. Subsoil conditions, water table depth, and seismicity have crucial impact on the foundation part of a bridge abutment which may mainly consist of pile or open foundation. Hence, it is necessary to study the effect of soil–structure interaction of bridge foundation under seismic force. To study the nonlinear behavior of bridge abutment and its foundation, different sets of soil models with various seismic forces have been developed by using FEM-based software for a typical bridge abutment foundation. To gain an insight into the seismic response of abutment foundation, its geometrical profile has been further modeled for both pile and open foundations. Different surrounding subsoil conditions (soft soil, weathered rock, etc.) provide variation in safe bearing capacity, ground settlement, stability factor, etc. The results of the present study show that the factor of safety of the bridge abutment gradually increases by 4–12% and ground settlement decreases by 6–16% when ground condition changes from medium to stiff clay followed by weathered rock. Ground settlement increases by 30–135% when seismic zone changes from Zone-III to Zone-IV with higher PGA, even for same soil condition.

Estimation of the ultimate bearing capacity of the pile is considered to be the main challenge in geotechnical engineering from a technical and economical viewpoint. To avoid pile failure under design axial superstructure load, end bearing and skin friction capacity of the pile should be carefully estimated. Calculation of skin friction capacity of the pile for soft soils is crucial when compared to other soils. As soft soils are considered to possess less shear strength, they undergo large deformation leading to variation in skin friction capacities. This paper focuses on the estimation of skin friction capacity of pile for a cohesive soil stratum, considering the variation in adhesion factor along the depth of the strata, using PLAXIS software. As observed by many authors, the adhesion factor for soil pile is dependent on different parameters. Therefore, by the numerical modeling, the adhesion factor values calculated based on different empirical equations are validated.

This study presents a numerical investigation on development of vertical axial force–shear force (V–H) capacity envelopes of strip footing placed on the surface of cohesionless soil having different ϕ overlying on the soft rock with constant GSI, mi, and D values. Force-based swipe analyses are conducted using OptumG2 following lower bound solution for finite-element limit analysis. The results are presented in terms of variation in bearing capacity ratio (Bcr) with soil-rock thickness ratios (Ts/B) and V–H capacity envelope varying with ϕ and Ts/B. It is found that the normalized capacity envelope for strip footing placed at top of pure cohesionless soil is almost similar for any value of ϕ. Further, for a particular Ts/B, the shape of normalized V–H capacity envelope increases with the increase in higher ϕ values. The normalized capacity envelope was found unaffected by Ts/B value beyond 4.0, for a soil with any value of ϕ.

A skirted foundation is a new solution that has been developed to improve the shallow foundation’s bearing capacity and settlement. A skirt foundation comprises plates or skirts that wrap one or more sides of the soil mass beneath the footing to keep the loaded soil contained. Confinement works with the overlain foundation to practically transfer the superstructure load to the ground at the skirt tip, resulting in increased bearing capacity and reduced structure settlement. The current research adopted numerical analysis to examine the axially loaded shallow foundation resting on sand with and without a skirt. The behaviour of a skirted foundation has been studied in terms of skirt depth, vertical and inclined skirts, variations in skirt inclination, and one-sided, both-sided skirts. The effects of foundation size on bearing capacity and settlement of skirted foundations are also investigated. The findings show that when the skirt depth increases, the bearing capacity increases and settlement reduces. Further, it is found that the inclined skirt is quite promising as compared to the vertical skirt for inclination up to 12 degrees away from the foundation (positive skirt). However, the inclination of the skirt towards the foundation (negative skirt) has an adverse effect on the bearing capacity and settlement.

Dynamic tests subjected to vertical vibration were conducted on a small-scale block footing of aspect ratio (L/B = 1.0) and depth of 0.5 m resting on the ground surface. The tests were conducted under a static load of (WS) 6.6 kN to determine the dynamic amplitude responses for different excitation intensities. The theory of nonlinear vibrations was used to back-calculate the dynamic nonlinear responses from the experimental response curves. The nonlinear responses indicate the disparity in the undamped natural frequencies with vertical translational amplitudes. It was observed that the approach well anticipates the nonlinear characteristics of the frequency–amplitude responses of the soil-foundation machine oscillator system.

Large diameter piles are generally used to provide the foundation system for the elevated tanks. The behavior of the laterally loaded pile is influenced by the pile head conditions, position of load application, pile length, and the soil resistance below ground. Understanding the load deflection behavior of the pile is an essential requirement for the consistent and reliable design of the tank. In this paper, performance of 1 m diameter pile installed in layered soils and tested 2 m above ground level is discussed. The pile is modeled by Finite Difference and Finite Element approaches to understand behavior of pile. This paper illustrates theoretical and actual behavior of laterally loaded long piles tested above ground level.

An 85 m high bungy-jumping tower set to be the highest in India is under construction in Rishikesh. Located on right bank of River Hule at Shivpuri between the North Almoda Thrust and the Saknindhar Thrust, rocks in the area are sheared and disturbed. The paper presents the geotechnical conditions at site and the foundation system for the tower. Appropriate slope stabilization measures were implemented for long-term stability.

Shallow footings are extensively used when hard strata exist near ground level. Design of foundations must satisfy ultimate bearing capacity and allowable settlements (Meyerhof in The ultimate bearing capacity of foundations on slopes, pp 384–386, 1957). The bearing capacity of foundations depends on density, deformation, and shear characteristics of soil. Footing on sloping ground becomes important due to limit of land availability, right of way, cost-effectiveness, and many more. In hilly regions, construction of footings on slopes becomes essential which require appropriate designs with a suitable factor of safety. It is found that research is limited on rigid footing resting on sloping ground. Researchers majorly focused on shallow footing resting on sloping ground either of cohesive or cohesionless. In this context, it is necessary to address the behavior of shallow footing resting on steep (>30°) sloping ground consisting c-ϕ soil. Hence, the present experimental study on a lab scale model is an attempt to understand the behavior of circular shallow footing of size 0.11 m in diameter (B) resting on the top of a 45° sloping ground having c-ϕ soil, i.e., clayey sand having c = 14 kN/m2 and ϕ = 28° with De/B ratio of 1. Load-settlement behavior of footing is observed and presented.

Construction over Plastic soil can cause adverse effects on the performance of the earth structures, due to the low load carrying capacities of such soils. Many civil engineering structures like Buildings, Major and Minor bridges, Under passes, and Flyovers collapse and undergo crack formation in areas where Plastic soil with poor load carrying capacity is present. Geosynthetic reinforcements have successfully been used in recent times as a low cost method for reinforcing such soils to improve their stability and bearing capacity. However, to recover significant benefit from the geosynthetics, the materials need to be placed at optimum locations within the foundation. Hence, in this paper, small scale laboratory footing tests have been performed to study the effect of depth of the first layer of reinforcement (u), number of reinforcement layers (N), width of reinforcement (b), and the vertical spacing between reinforcements (h). The results obtained demonstrated that the placement and the loading condition of the geosynthetics greatly influences the bearing capacity of the foundation. The results obtained from the experimental analysis were used for the computation of a regression model in R Studio, for the determining the load carrying capacity of reinforced soil foundation. The model presented obtained a confidence level of more than 95%, when parameters significant for the computation of load carrying capacity of square footing were included, thus showing great convergence with the experimental results.

In view of the marine steel tubular pile foundation design verification for Duroob Island, offshore of the Abu Dhabi mainland, a program of pile load tests using the static load test (SLT) and high-strain dynamic pile testing (HSDPT)/Pile Driving Analyzer (PDA) tests was initiated in the Gravelly, weak Calcarenite, and Mudstone formations. Despite the fact that the SLT is more expensive and time-consuming than the PDA test, most designers use the PDA test as a frequent alternate method for predicting pile capacity. This paper presents the ultimate capacity evaluation of 20.60 mm thick offshore steel tubular pile P03, 31.05 m long, and 1118 mm outer diameter, interpreted from both methods. The SLT result shows a deflection of around 4.30 mm and that of 4.00 mm from PDA at a load of 1650 kN. The ultimate capacity predicated using the Chin and Van der method exhibits good agreement with the PDA result. The findings revealed a higher limit of ultimate pile capacity of 6458 kN, which is reached by pile settlement rather than soil failure. The ultimate capacity calculated from pile driving using CAPWAP shows a value of 6460 kN, indicating that both methods are accurate enough to estimate the pile capacity and can be adopted in similar offshore conditions.

The future of the offshore wind market is looking forward to floating foundations as they are more promising in deep waters. Seismicity is a concern along the offshores of the Western United States and East Asia, which has fueled scientific interest in seismic design. This study focuses on the performance-based seismic design of spar floating wind turbines. Spar is a ballast stabilized structure anchored to seabed using catenary mooring lines. A three-dimensional model of the platform-mooring-anchor system is developed in ABAQUS CAE, where the soil is modeled using non-linear Winkler’s spring. The hydrostatic stiffness is represented using springs. Hybrid beam elements (high axial stiffness compared to bending stiffness) are used to model the mooring line. The effect of high-intensity earthquake shaking, peak ground acceleration, predominant frequency, and the impact of combined seismic-wave loading are evaluated in detail. Wave loads are observed to govern the design of spar wind turbines. In all the cases considered, seismic responses are found to be minimal. This preliminary study noted that spar floating wind turbines are less susceptible to earthquake dynamics due to the catenary shape, low mass of cable, and the long natural vibration period. This study will help to evaluate the feasibility of spar floating wind turbines in seismically vulnerable areas.

A parametric study has been covered for the performance of monopile founded offshore wind turbine (OWT) in clay. The change in deflection of monopile head is considered for this study to verify the behavior of monopile founded OWT. Diameter of the pile, the load applied on the wind turbine and the height of the tower are varying to verify the response of the monopile. The change in displacement due to different soil properties also considered in this study. A numerical model is considered in this study where the monopile is modeled based on American Petroleum Institute (API)-based static p–y and t–z curves. The base of the monopile is considered to be fixed for this study to fulfill the ‘zero-toe-kick’ criteria.

Globally, the hydrocarbon industry has enough experience to carry out the offshore metocean, geophysical and geotechnical surveys, and therefore that knowledge has been extended to offshore wind farms as well with suitable modifications owing to their different construction, design, extent, and other characteristics as compared to hydrocarbon drilling arrangement. However, historically, the Environmental Baseline Survey (EBS) has not been given as much importance as other surveys since it doesn’t directly affect the revenues, instead, is sometimes seen as an additional expense. Further, there is a lack of long-term studies of the EBS techniques adopted for offshore wind farms since this renewable source of energy has been exploited at a large scale only over the past few decades. A well-designed EBS helps to strive for: protection of existing ecological environment and development with minimum harm to marine habitat. This paper describes the methodology to conduct the EBS for benthos, littoral habitats, birds, basking sharks, marine mammals, cultural heritage, coastal processes, fisheries, and physical–chemical characteristics of water. Further, the paper also discusses the best practices to conduct EBS worldwide and the applicability of such practices in Indian context. Some important factors to be considered while planning out the EBS are also highlighted.

Offshore pipelines are often considered one of the most reliable fluidized fuel transportation systems. However, the transporting fuel with enhanced temperature induces thermal stress in the pipeline, which further threatens to buckle and rupture the offshore pipelines. In the current study, the buckling resistance behaviour of an offshore pipeline is studied using a finite element package (PLAXIS 2D). Furthermore, a comparison of uplift resistances for the homogeneous and normally consolidated (NC) soil beds is performed to understand the effect of soil homogeneity. The numerical model is validated with the past studies, and a good match is obtained. Moreover, different soil and installation parameters are varied to perform a parametric study and investigate the pipeline uplift resistance behaviour. Two different buckling resistance (Pu) behaviours of the pipeline are obtained in pre-peak and post-peak conditions for both homogeneous and NC soil bed conditions. The magnitudes of Pu for homogeneous and NC soil conditions are compared, and the changes in Pu are reported and justified. The variation of the Pu with different parameters (soil unit weight and embedment depth ratio) is also described using the failure mechanism of the soil around the pipeline.

The load from the jack-up rig is transferred into the ground through a spudcan foundation. This spudcan foundation is mostly used in offshore drilling operations. The jack-up rig is usually triangular or rectangular whereas the spudcan is a conical-shaped axisymmetric footing. The effects, of such a footing in a non-homogenous soil, are still sparsely explored in the literature. Therefore, for a conical footing on a non-homogenous soil (with linearly increasing cohesion), the Bearing Capacity Factor (Nc) is presented in the present study using finite element limit analysis. The dimensionless parameters such as internal friction angle (ϕ), cohesion gradient ratio (m), and cone apex angle (β) are considered in this study. It has been observed that the Bearing Capacity Factor increases with the increase in the value of cohesion gradient ratio (m) and internal friction angle (ϕ) whereas decreases with the increase of cone apex angle (β).