Bappaditya Manna

Nonlinear Dynamic Response of Piles under Horizontal Excitation

This paper presents test results from cast-in situ reinforced concrete single and group piles subjected to strong horizontal excitation. The tests were conducted for different eccentric moments simulating different excitation levels to obtain the frequency-amplitude response of the pile. Moderate nonlinear behavior is observed in both horizontal and rocking components of vibration. The experimental results were compared with dynamic interaction factor approach using nonlinear solutions. The accuracy of the nonlinear analysis in predicting the dynamic response depends on the choice of parameters that best characterize the response of boundary zone around the pile and the realistic length of pile separation. It is shown in this study that by allowing for boundary zone and separation between pile and soil, close agreement between theoretical predictions and measured response curves can be achieved.

Dynamic vertical response of model piles — experimental and analytical investigations

Abstract Dynamic response characteristics of reinforced concrete model piles were investigated in the field under varying levels of vertical harmonic excitation. In the investigations single piles and 2 × 2 group piles with length to diameter ratios 10, 15 and 20. For group piles, spacing to diameter ratios of 2, 3 and 4 for each length to diameter ratio were used. In both the cases, two different conditions of pile cap — embedded into soil and above the ground surface, were considered in this investigation. The measured response was compared with the response obtained by different analytical methods. The stiffness and damping of piles under vertical vibration were computed by two different analytical approaches — (i) Novaks frequency independent solutions with static interaction factor for parabolic soil profile and (ii) Novaks complex frequency dependent analytical solutions with dynamic interaction factor approach for layered media. From the comparison of these theories with the experimental data it was found that the Novaks frequency dependent solutions with dynamic interaction factor approach produced reasonable estimates of the experimental results. In this study the influence of excitation intensity, static load on pile and different contact condition of pile cap with soil on the dynamic behaviour of pile foundation are reported.

Stability analysis of steep nailed slopes under seismic condition using 3-D finite element method

This paper presents the behavior of steep nailed soil slopes under seismic conditions by numerical studies. Three-dimensional solid numerical models have been developed to simulate steep nailed soil slopes by finite element (FE) method. The real-time history analyses are carried out to study the seismic response of steep-nailed soil slopes. The effect of various influencing parameters such as the nail inclination, nail length, frequency amplification factor, and the slope angles on the seismic resistance and failure mechanism of the nailed slopes is studied in details. All the numerical models developed have been used to examine the shaking table test results of steep nailed slopes (Hong et al., 2005). The numerical results such as maximum lateral displacements at various heights of the facing are compared with the test results for two different nail inclinations, nail lengths, frequency amplification factors, and the slope angles at various peak amplitudes of accelerations.

Seismic Behaviour of Buried Pipelines: 3D Finite Element Approach

This paper presents a numerical investigation on six pipeline models to study the seismic response of single and double buried pipelines using finite element method. Different depth and spacing of pipes are considered to investigate their prominent role in the seismic response of buried pipelines under an earthquake loading having PGA of 0.2468 g. In case of single pipeline, the maximum magnitude of final displacement as well as the stress at the end of the seismic sequence is found at the burial depth equal to the pipe diameter. In case of double pipeline, the maximum magnitude of final displacement is found when the spacing between pipes is equal to half the pipe diameter and there is an increasing tendency of developed stress with increase in spacing between pipes. In addition to the above results, the response of the buried pipelines with a particular bend angle (artificially induced bend/buckle) to the permanent ground deformation which is assumed to be the result of seismic wave propagation has also been studied. Remarkable differences in these results are obtained and with these results the designers can reduce seismic risk to their buried pipelines by taking proper precautionary measures.

The Nonlinear Coupled Response of Single and Group Piles under Various Horizontal Excitations: Experimental and Theoretical Study

Dynamic response characteristics of reinforced concrete single piles and 2 × 2 group piles subjected to varying levels of horizontal harmonic excitation are investigated by both experimental and analytical study. Two different types of coupled vibration tests, namely, type 1—horizontal exciting force above the center of gravity (c.g.), and type 2—horizontal exciting force below the c.g. of the pile cap-loading system, are conducted in the field. The tests are conducted for different eccentricities to determine the frequency-amplitude response of piles for horizontal and rocking motion separately. The influence of excitation intensity, static load on pile, spacing of piles in group, and different contact condition of pile cap with soil on the coupled dynamic response of piles are reported. The measured responses of type 1 and type 2 are compared with the results obtained by the continuum approach of Novak with nonlinear solution. For nonlinear analysis, the boundary zone concept, which accounts for yielding of soil around the pile, is incorporated into the linear elastic-based model and the allowance is made for the separation between the pile and soil. A reasonable match between the measured and predicted response by nonlinear analysis has been observed after introducing appropriate boundary zone parameters and soil–pile separation length. The differences between the dynamic characteristics of piles for coupled vibration type 1 and type 2 in terms of frequency response curves for amplitude, stiffness, and damping constants are also discussed.

Dynamic Response Characteristics of Hollow Steel Single Pile Under Vertical Excitations

In this present study, the nonlinear behavior of a single hollow steel pile having an outer diameter of 0.114 m and length of 3 m was investigated under vertical excitations of rotating machine. Forced vibration tests were performed in the field to determine the dynamic responses of the single pile for four different eccentric moments. First time-acceleration responses of the single pile were measured for different frequencies and finally from that the frequency-amplitude response curves have been obtained for different excitation forces. It is observed from the field test results that the measured frequency-amplitude response curves exhibit nonlinear behavior of the soil-pile system by showing the decrement in resonant frequencies and disproportional increment in resonant amplitudes with the increase of excitation intensities. Additionally, the inverse analytical method of Novak is used to quantify the variation of stiffness, damping, and effective mass of the pile for different excitation intensities using the measured response curves. It is observed that the calculated damping values are increased with the increase of excitation forces. However, the effective mass and average stiffness values are decreased with the increase of excitation forces. The frequency-amplitude response curves are also back-calculated using the theory of vertical vibration with the calculated parameters of the soil-pile system. The back-calculated response curves are compared with the field dynamic test results and it can be seen from the comparison curves that the dynamic nonlinear response obtained from the theoretical analysis have a very close match with the field test response curves.

Influence of Rock Joint Orientation on the Natural Frequency of Dam-Foundation System

The natural frequency of dam-foundation system is a function of its stiffness and the participating mass. In the present study, an attempt is made to understand the effect of rock joint orientation on the natural frequency of the dam-foundation system. Discrete element simulations are carried out using UDEC (1993) software for the intact rock foundation and rock foundations having joint inclinations of 0°, 30°, 60°, 90°, 120° and 150° with 20 m, 10 m, 5 m, 2.5 m and 1 m joint spacing in the rock mass. Results, confirm that the joint orientation affects the natural frequency of the system significantly. The natural frequency of the dam-foundation system is found higher for the intact rock foundation as compared to other jointed rock foundations. Results also reveal that the magnitude of the natural frequency of the system increases as the joint spacing increases in the rock mass.

Vertical Response of 2 × 2 Pile Group Under Rotating Machine Induced Vibrations

The dynamic behavior of 2 × 2 pile group has been investigated under rotating machine induced vertical vibration using both field testing and numerical analysis. Forced vibration tests have been performed in the field on a pile group (pile length = 3 m, pile diameter = 0.114 m) embedded in silty soil. The frequency-amplitude responses of the pile group are measured for four different eccentric moments. It is found that the measured response curves are nonlinear in nature. The numerical analysis has been performed using continuum approach and superposition method to determine the nonlinear frequency-amplitude responses of the pile group. From the analysis, the boundary parameters and soil-pile separation lengths are predicted for different eccentric moments. The analytical frequency-amplitude responses of the pile foundations are compared with the dynamic field test results and it is found from the comparison curves that the nonlinear frequency-amplitude responses obtained from the analysis have a very close match with the field nonlinear response curves.

Experimental and Theoretical Studies on the Nonlinear Characteristics of Soil-Pile Systems under Coupled Vibrations

AbstractThis study includes the determination of soil-pile separation lengths and frequency-amplitude responses of single and group piles under rotating machine-induced coupled (horizontal and rock...

STABILITY ANALYSIS OF STEEP NAILED SLOPES IN SEISMIC CONDITIONS: NUMERICAL APPROACH

Abstract. In this paper an attempt has been made to understand the seismic behavior and deformation characteristics of model steep nailed soil slopes by numerical studies. A twodimensional plane-strain numerical model has been developed to simulate steep nailed slopes by finite element software, MIDAS GTS. The real time-history analyses are carried out to study the seismic response of nailed-soil slopes. The effect of various influencing parameters such as the nail inclinations and the slope angles on the seismic resistance and failure mechanism of the nailed slopes are studied in details. The numerical model developed has been used to examine the shaking table test results of steep nailed slopes [1]. The nailed soil slopes are modeled in FE analysis as per the geometry of shake table testing and the numerical analysis are carried out for different seismic excitations. The numerical results such as maximum lateral displacements at various heights of the facing are compared with the test results for various slopes angles, nail inclinations and peak amplitude of accelerations. The failure pattern of nailed soil slopes for different seismic conditions obtained from the numerical analysis are studied and compared with the experimental failure patterns. A reasonable agreement between the finite element analysis and shaking table test results are obtained.