Piles subjected to torsional cyclic load: Numerical analysis

© 2019 Nimbalkar, Punetha, Basack and Mirzababaei. Pile foundations supporting large structures (such as high-rise buildings, oil drilling platforms, bridges etc). are often subjected to eccentric lateral load (in addition to the vertical loads) due to the action of wind, waves, high speed traffic, and ship impacts etc. The eccentric lateral load, which is usually cyclic (repetitive) in nature, induces torsion in the pile foundation. This paper presents a numerical model based on boundary element approach to study the performance of a single pile subjected to the torsional cyclic load. The model is initially validated by comparing it with the experimental data available from the literature. Thereafter, the model has been utilized to conduct a parametric study to understand the influence of the torsional cyclic loading parameters on the axial pile capacity. The results indicated that the model is able to capture the degradation in the axial pile capacity due to the torsional cyclic loading with a reasonable accuracy. Moreover, the parametric study showed that the frequency, amplitude and number of cycles play a significant role in the torsional cyclic response of the pile. The present study is essential for the development of design guidelines for pile foundations subjected to torsional cyclic load

Computation of point of application of seismic passive resistance by pseudo-dynamic method

Computation of seismic passive resistance and its point of application is an important aspect of seismic design of retaining wall. Several researchers in the past had obtained seismic passive earth pressures by using the conventional pseudo-static method. In this pseudo-static method, peak ground acceleration is assumed as constant and seismic passive pressure thus obtained shows the linear variation along the height of the retaining wall. There is hardly any scope to find out the point of application of seismic passive resistance by pseudo-static approach but to assume it to act at one-third height from the base of the wall. Rectifying these errors, in recently developed pseudo-dynamic method of analysis, all these factors are considered to compute seismic passive earth pressures. In this paper, an attempt has been made to compute the point of application of seismic passive resistance using limit equilibrium method of analysis with pseudo-dynamic approach. Effects of variation of parameters like wall friction angle, time period of earthquake ground motion, seismic shear and primary wave velocities of backfill soil, soil amplification and seismic peak horizontal and vertical ground accelerations on the seismic passive earth pressure are studied.© IACMA

Pseudo-dynamic approach of seismic active earth pressure behind retaining wall

Knowledge of seismic active earth pressure behind rigid retaining wall is very important in the design of retaining wall in earthquake prone region. Commonly used Mononobe-Okabe method considers pseudo-static approach, which gives the linear distribution of seismic earth pressure in an approximate way. In this paper, the pseudo-dynamic method is used to compute the distribution of seismic active earth pressure on a rigid retaining wall supporting cohesionless backfill in more realistic manner by considering time and phase difference within the backfill. Planar rupture surface is considered in the analysis. Effects of a wide range of parameters like wall friction angle, soil friction angle, shear wave velocity, primary wave velocity and horizontal and vertical seismic accelerations on seismic active earth pressure have been studied. Results are provided in tabular and graphical non-dimensional form with a comparison to pseudo-static method to highlight the realistic non-linearity of seismic active earth pressures distribution

Effects of Tunneling-Induced Ground Movements on Stability of Piled Raft Foundation: Three-Dimensional Finite-Element Approach

© 2020 American Society of Civil Engineers. Across the globe, rapid urbanization demands the construction of tunnels within the vicinity of high-rise buildings supported on piled raft foundations. As a consequence, ground movements caused by such tunneling works could interfere with the serviceability of the foundations. Hence, the prediction of tunnel-induced ground deformation is of utmost importance. In the current study, a three-dimensional numerical analysis was carried out to study the response of an existing piled raft foundation with a 2 × 2 pile arrangement subjected to ground movements induced by a 6 m-diameter tunnel. The results obtained from the numerical simulations were further compared with a field study. The field measured lateral pile deflections were found to be in fair agreement with those computed using the present method. The numerical analysis was then extended to understand the influence of various factors, such as tunnel diameter, tunnel longitudinal axis, pile diameter, pile position from tunnel, and soil stiffness on the response of pile raft in the vicinity of an adjacent tunnel. The results obtained from the parametric study was finally summarized in simple semi-empirical equations to estimate the maximum lateral deflection and bending moment for both short and long piles

External stability of reinforced soil walls under seismic conditions

Determination of the external stability of reinforced soil walls under earthquake condition is an important topic of research for geotechnical engineers. In the present paper, a pseudo-dynamic method, which considers the effect of phase difference in both the shear and primary waves travelling through the backfill due to seismic excitation, is considered to obtain the minimum length of the geosynthetic reinforcement to resist direct sliding and overturning failure of the reinforced soil wall. A two-part wedge mechanism is used for determining the external stability of the reinforced soil wall against direct sliding. Reinforced soil walls with cohesionless backfill soil are considered in the present analysis. Results are presented in both graphical and tabular form to show the required length of the geosynthetic reinforcement to maintain the external stability of the reinforced soil wall under seismic conditions. The effects of variation of parameters such as soil friction angle, horizontal and vertical seismic accelerations on the external stability of the reinforced soil wall have been studied. With increase of seismic accelerations in both the horizontal and vertical directions, the external stability of the reinforced soil wall decreases significantly and a greater length of geosynthetic reinforcement is needed to maintain the external stability of the wall. For most practical cases, the minimum length required to resist direct sliding failure is found to govern the design rather than overturning failure under seismic conditions. Comparisons of the present results with available pseudo-static results found in the literature are shown, and the improvements using the proposed pseudo-dynamic approach are highlighted

Seismic stability of reinforced soil-wall by pseudo-dynamic method

Determination of internal stability of reinforced soil walls under earthquake conditions is an important part of seismic design. The horizontal method of slices is used for determining internal stability or tieback analysis of the reinforced soil wall. A pseudo-dynamic method is adopted in the present analysis, which considers the effect of phase difference in both the shear and primary waves traveling through the backfill due to seismic excitation. Reinforced soil walls with cohesionless backfill material have been considered in the analysis. Results are presented in graphical and tabular form to show the required tensile force and length of geosynthetic reinforcement to maintain the stability of the reinforced soil wall under seismic conditions. Effects of variation of parameters such as soil friction angle, and horizontal and vertical seismic accelerations on the stability of the reinforced soil wall have been studied. With increase of seismic accelerations both in horizontal and vertical directions, stability of the reinforced soil wall decreases significantly and thus needs greater strength and length of geosynthetic reinforcement to maintain stability of the wall. The seismic vertical acceleration in an upward direction gives higher values of required geosynthetic tensile strength, and the seismic vertical acceleration in the downward direction yields higher values of length of geosynthetic reinforcement. Comparisons of present results with available pseudo-static results are shown and the limitations of the pseudo-static results are highlighted

Piles subjected to torsional cyclic load: Numerical analysis

Pile foundations supporting large structures (such as high-rise buildings, oil drilling platforms, bridges etc). are often subjected to eccentric lateral load (in addition to the vertical loads) due to the action of wind, waves, high speed traffic, and ship impacts etc. The eccentric lateral load, which is usually cyclic (repetitive) in nature, induces torsion in the pile foundation. This paper presents a numerical model based on boundary element approach to study the performance of a single pile subjected to the torsional cyclic load. The model is initially validated by comparing it with the experimental data available from the literature. Thereafter, the model has been utilized to conduct a parametric study to understand the influence of the torsional cyclic loading parameters on the axial pile capacity. The results indicated that the model is able to capture the degradation in the axial pile capacity due to the torsional cyclic loading with a reasonable accuracy. Moreover, the parametric study showed that the frequency, amplitude and number of cycles play a significant role in the torsional cyclic response of the pile. The present study is essential for the development of design guidelines for pile foundations subjected to torsional cyclic load

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Not AvailableThe present investigation was conducted for two years (2018-19 and 2019-20) to study the effect of rootstocks (Dogridge, 110R, 140Ru, Salt Creek and own roots of Red Globe) on growth parameters of Red Globe grapevines. The vigour and growth parameters such as pruning weight was found maximum on vines grafted on Dogridge rootstocks while minimum days to sprout and cane maturity was recorded in own rooted Red Globe vines. Number of canes/vine, shoot length, shoot diameter, leaf area and stock: scion ratio varied significantly among the rootstocks and were found maximum in vines grafted on Dogridge rootstock followed by Salt Creek and 110R rootstocks. The present study revealed that Red Globe grapevines grafted on Dogridge followed by Salt Creek rootstock proved better for growth parameters but in terms of growth period Red Globe own rooted vines was early to sprout and took minimum days for cane maturity over the vines grafted on rootstocks.Not Availabl