Dynamic Response of Laterally Loaded Pile Groups in Clay

Experimental investigation of vertical and batter pile groups subjected to dynamic loads

Abstract: In the present work, the dynamic responses of cast in-situ reinforced concrete vertical and batter pile groups constructed in the silty sand have been investigated. An experimental study was carried out on four pile groups: a group of three vertical piles and a group of three batter piles arranged in triangular pattern, and a group of four vertical piles and a group of four batter piles arranged in square pattern. All batter piles were inclined at 20° to the vertical. Each pile group had a rigid pile cap supporting the oscillator-motor assembly for generating the dynamic loads. The pile groups were tested by varying the exciting force level in different loading direction, and their responses were compared in terms of resonant frequency and peak displacement. The peak displacement of the batter pile group shows a significant reduction (about 25% and 50% in vertical and lateral directions, respectively) compared to their respective vertical pile groups.

Dynamic experimental studies on lateral behaviour of batter piles in soft clay

Abstract: A series of small scale dynamic experiments have been carried out on 2 × 1 model aluminum batter pile group embedded in soft clay. The batter angles vary from 0 to 20 degrees. The pile group is subjected to sinusoidal lateral loads of different magnitudes (20–90 N), constituting 20–40% of its static ultimate capacity with the frequency in the range of 1–120 Hz. The time history of pile head displacement and bending strain along the length of pile are measured. It is found that the peak lateral displacement and peak bending strain at resonance region decrease with an increase in the batter angle, particularly for higher magnitude of lateral loads.

Evaluation of seismic hazard and potential of earthquake-induced landslides of the Nilgiris, India

Abstract: The Nilgiris district in the Tamilnadu state of India is frequented by many landslides in the recent past. Though many of these landslides are rainfall-induced, there is a need to evaluate the potential of earthquake-induced landslides considering seismicity of the region. In this paper, deterministic seismic hazard of Nilgiris is carried out by considering a study area of 350 km radius around Nilgiris. Seismotectonic map of the Nilgiris, showing the details of faults and past earthquakes, is prepared. The peak ground acceleration (PGA) at bed rock level and response spectrum are evaluated. The potential sources for Nilgiris are Moyar and Bhavani shears. The PGA at bed rock level is 0.156 g corresponding to maximum considered earthquake 6.8. Ground response analysis for seven sites, in the Nilgiris, is carried out by one-dimensional equivalent linear method using SHAKE 2000 program after considering the effect of topography. PGA of surface motion got amplified to 0.64 g in Coonoor site and 0.44 g in Ooty site compared to 0.39 g of the input motion. The bracketed duration of time history of surface acceleration has increased to 20 s in Coonoor site and 18 s in Ooty site compared to that of 8 s of input motion. Results from seismic displacement analysis using Newmark’s method revealed that out of seven sites investigated, five sites have moderate seismic landslide hazard and two sites (Coonoor and Ooty) have high hazard.

Integrated computational and full-scale physical simulation of dynamic soil-pile group interaction

Abstract: Three dimensional dynamic soil-pile group interaction has been a subject of significant research interest over the past several decades, and remains an active and challenging topic in geotechnical engineering. A variety of dynamic excitation sources may potentially induce instabilities or even failures of pile groups. Employing modern experimental and numerical techniques, the dynamics of pile groups is examined in this study by integrated physical and computational simulations. In the physical phase, fullscale in-situ elastodynamic vibration tests were conducted on a single pile and a 2×2 pile group. Comprehensive site investigations were conducted for obtaining critical soil parameters for use in dynamic analyses. Broadband random excitation was applied to the pile cap and the response of the pile and soil were measured, with the results presented in multiple forms to reveal the dynamic characteristics of the pile-soil system. In the computational phase, the BEM code BEASSI was extended and modified to enable analysis of 3D dynamic pile group problems, and the new code was validated and verified by comparison to reference cases from the literature. A new theoretical formulation for analysis of multi-modal vibration of pile groups by accelerance functions is established using the method of sub-structuring. Various methods for interpreting the numerical results are presented and discussed. Case studies and further calibration of the BEM soil profiles are conducted to optimize the match between the theoretical and experimental accelerance functions. Parametric studies are performed to quantify the influence of the primary factors in the soil-pile system. It is shown that the new 3D disturbed zone continuum models can help improve the accuracy of dynamic soil-pile interaction analysis for pile groups in layered soils. This study therefore helps to advance the fundamental knowledge on

Comparison on the Horizontal Behaviors of Lattice-Shaped Diaphragm Wall and Pile Group under Static and Seismic Loads

Abstract: Lattice-shaped diaphragm wall (hereafter referring to LSDW) is a new type of bridge foundation, and the relevant investigation on its horizontal behaviors is scant. This paper is devoted to the numerical study of the comparison on the static and seismic responses of LSDW and pile group under similar material quantity in soft soil. It can be found that the horizontal bearing capacity of LSDW is considerably larger than that of pile group, and the deformation pattern of LSDW basically appears to be an overall toppling while pile group clearly shows a local bending deformation pattern during the static loading process. The acceleration response and the acceleration amplification effects of LSDW are slightly greater than that of pile group due to the existing of soil core and the difference on the ability of energy dissipation. The horizontal displacement response of pile group is close to that of LSDW at first and becomes stronger than that of LSDW due to the generation of plastic soil deformation near the pile-soil interface at last. The pile body may be broken in larger potential than LSDW especially when its horizontal displacement is notable. Compared with pile group, LSDW can be a good option for being served as a lateral bearing or an earthquake-proof foundation in soft soil.

Simplified procedure for evaluating soil liquefaction potential

Abstract: Significant factors affecting the liquefaction (or cyclic mobility) potential of sands during earthquakes are identified, and a simplified procedure for evaluating liquefaction potential which will take these factors into account is presented Available field data concerning the liquefaction or nonliquefaction behavior of sands during earthquakes is assembled and compared with evaluations of performance using the simplified procedure It is suggested that even the limited available field data can provide a useful guide to the probable performance of other sand deposits, that the proposed method of presenting the data provides a useful framework for evaluating past experiences of sand liquefaction during earthquakes and that the simplified evaluation procedure provides a reasonably good means for extending previous field observations to new situations When greater accuracy is justified, the simplified liquefaction evaluation procedure can readily be supplemented by test data on particular soils or by ground response analyses to provide more definitive evaluations

Pile Foundation Analysis and Design

Abstract: This book deals with methods of analysis that may be useful in design of pile foundations. The aims are to: 1) present a consistent theoretical approach to the prediction of pile deformation and load capacity, 2) present parametric solutions for a wide range of cases, 3) demonstrate how such solutions can be used for design purposes, and 4) review the applicability of these approaches to practical problems. (TRRL)

Semi-empirical procedures for evaluating liquefaction potential during earthquakes

Abstract: Semi-empirical procedures for evaluating the liquefaction potential of saturated cohesionless soils during earthquakes are re-examined and revised relations for use in practice are recommended. The stress reduction factor ( r d ), earthquake magnitude scaling factor for cyclic stress ratios (MSF), overburden correction factor for cyclic stress ratios ( K σ ), and the overburden normalization factor for penetration resistances ( C N ) are discussed and recently modified relations are presented. These modified relations are used in re-evaluations of the SPT and CPT case history databases. Based on these re-evaluations, revised SPT- and CPT-based liquefaction correlations are recommended for use in practice. In addition, shear wave velocity based procedures are briefly discussed.

Behavior of Laterally Loaded Piles: I-Single Piles

Abstract: An analysis is presented for the horizontal displacement and rotation of a vertical pile subjected to lateral loading and moment, and situated in an ideal elastic mass. Influence factors are presented for a wide range of pile flexibilities and length-to-diameter ratios, for both free-head and fixed-head piles. Comparisons between the elastic solutions and the corresponding solutions obtained from the subgrade reaction theory show that the latter considerably overestimates the displacement and rotation of the pile, but gives a reasonable estimate of the moments in the pile. The elastic analysis is extended to include the effect of local yield between the soil and the pile; the load-displacement relationship for relatively flexible piles is found to be markedly influenced by local yield. The characteristics of behavior indicated by the theoretical solutions agree reasonably well with those reported from measurements on full-scale piles.

Lateral Load Behavior of Full-Scale Pile Group in Clay

Abstract: A static lateral load test was performed on a full-scale pile group to determine the resulting pile-soil-pile interaction effects. The 3 × 3 pile group at three-diameter spacing was driven into a profile consisting of soft to medium-stiff clays and silts underlain by sand. The piles were instrumented with inclinometers and strain gages. The load carried by each pile was measured. A single pile test was conducted for comparison. The pile group deflected over two times more than the single pile under the same average load. Group effects significantly reduced load capacity for all rows relative to single pile behavior. Trailing rows carried less than the leading row, and middle row piles carried the lowest loads. Maximum moments in the group piles were 50–100% higher than in the single pile. P-multipliers were 0.6, 0.38, and 0.43 for the front, middle, and back row piles, respectively. Good agreement between the measured and computed pile group responses was obtained using the p-multiplier approach. Design c...