This is a study about the stress, displacement and factor of safety of Mae Ngat Dam. According to the field study and the analysis by finite element method in a 2D nonlinear plane strain, using the Elasto-Plastic soil model with Mohr-Coulomb failure criteria to analyze acceleration, pores water pressure, deformation and factor of safety. The analysis was done using dynamic method with the intensity that had happened according to the earthquake in Phan, Chiangrai, in northern part of Thailand, where the earthquake measured 6.3 Richter. The location of Mae Ngat Dam is 150 kilometers away from the epicenter. It was found from the model under seismic force, that the acceleration had even diffusion. The highest acceleration was at the crest of the dam. There was mostly horizontal displacement, analyzing 5.7 centimeters and the most vertical displacement was analyzed at 3.3 centimeters. According to the earth zone dam seismic force, the factor of safety was 1.856, which was higher than the minimum criteria of the safety factor by the Department of Irrigation 1.500. The seismic force had not much effected to the dam. It can be concluded that Mae Ngat Dam is still safe from this earthquake.

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Recently, the number of earthquakes has been rapidly increasing on a global scale; reports of severe earthquakes are becoming more and more frequent. Dam movements are identified in real-time with measuring instruments for dam maintenance. However, for dams that have aged, the measuring instruments that were installed during the dam construction are frequently malfunctioning or completely failing altogether. Precision safety diagnosis is being executed for dams that are national facilities Type 1. During the diagnosis, a safety assessment is conducted for the dam body. Normally, during the analysis of dam safety, the widest cross-section is selected and a two-dimensional numerical analysis is taken place for the cross-section. However, numerous researchers have recently looked into applying the 3-dimensial numerical analysis program developments to precisely analyze the structure of the dam, as well as the surrounding strata, and the lower dam strata. In this study, PLAXIS 3D, a geotechnical generic FEM analysis program, was used to conduct dam safety assessments for earthquakes. The following were compared and analyzed: 1) considering the seismic properties of the dam body with all zoned structures reflected as one rock-fill zone together with the dam body, 2) considering the dam body as the rock-fill zone and the core zone, and 3) the numerical analysis results. Thus, the study was aimed to analyze the impact properties of seismic waves according to the different zones.

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Shear modulus and damping ratio which are important parameters in any dynamic analysis of soil are related to the frictional behavior at inter particle contacts and rearrangement of grains. The strength loss of granular soil when subjected to cyclic loading is affected by particle size, shape and its distribution. Soil structure also termed as fabric which encompasses grains/particle distribution, particle orientation and arrangement, the voids and the fluid present in between the voids, continually changes during cyclic loading. Such changes are imperative of mechanisms that result in liquefaction of saturated sands and compaction of dry sands. Unlike, experimental and analytical testing methods, numerical methods are equipped to provide insight into these underlying mechanisms. To understand the interactions between particles that influence the dynamic behavior of soil, modeling of cyclic triaxial test was conducted using 3D DEM for different particle shapes and sizes. Before the testing, validation of the generated soil sample is conducted by checking the pressure dependent behavior and dilative response of the sample. Contact normals and contact forces were also used to validate the sample at different stages. From the cyclic testing, normalized shear modulus curves, contact normal and force distributions were plotted. It was observed that the rounded particles had more shear stiffness compared to other shapes. This behavior was not evident when the shear modulus was normalized and the spherical particles had the highest stiffness. The effect of particle shape was verified with the change in the coefficient of uniformity (C_u) with stiffness and it was observed that shear modulus decrease with an increase of C_u. Micromechanical expression for the same was also been discussed.

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Low amplitude repeated loading can cause soil particles to rearrange into a denser and more stable state. When the number of load cycles exceeds the threshold, it results in overstressed soils. This results in accumulation of plastic strains and reduction in shear strength. In some cases, failure planes begin to develop within the soils. Magnitude, duration and the type of loading, all affect strain accumulation and, this needs to be well understood. This paper investigates the effect of multiple loading cycles followed by drainage. This step was repeated a few times before testing the sample up to critical state. In this setup, 100 mm diameter and 200 mm long cylindrical soil samples were arranged on the cyclic triaxial frame. Thousands to a million of sinusoidal loading and unloading cycles were then imposed on the samples. In each case, liquefaction failure was prevented by maintaining low amplitude cyclic stress ratios. In some cases, the samples were allowed to drain in between the cycles e.g. to simulate rail and road embankments. This enabled dissipation of pore pressures from the sample to reach a new state before repeating the cyclic loading. In each case, the rate-of-accumulation of pore pressures and axial-strains reduced with the increase in the number of cycles. The samples were then subjected to undrained shearing at 100 kPa effective stress to investigate the change in strength with the number of load and drainage cycles. The results show that there was a remarkable increase in the stress-strain response of the samples when subjected to recompression. This change was dependent on the number of cycles and cyclic stress amplitude.

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The determination of shear wave velocity (Vs) in soil and the associated small-strain shear modulus (G0) plays an important role in many geotechnical applications. In the last decades extensive laboratory experiments have been carried out to study these two properties for clean quartz sands. Often natural sands are not clean but contain some amount of fines (referred to as silty sand in practice). The effect of fines on the shear wave velocity and shear modulus is therefore a matter of concern. This paper presents an experimental study on mixtures of clean quartz sand and crushed silica fines at different percentages of fines. A series of resonant column (RC) and bender element (BE) tests were carried out for a range of confining stresses and void ratios. It is found that G0 values obtained from the BE tests are significantly greater than the ones obtained from the RC tests, indicating the importance of testing method for silty sand. For either method, however, the G0 value of the mixture always decreases with an increase of fines content. An empirical model is proposed for estimating G0 which allows for both the effect of fines and the stress and density dependence, and it is shown to possess a reasonably good performance.

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This paper describes an experimental results for effect of wall flexibility on the dynamic earth pressure for cantilevered retaining wall. Three centrifuge tests were performed on reduced models with different flexibility. The retaining walls were fixed on the container to clear boundary condition except wall flexibility. This condition was far from assumption of limit state analysis, which allow sufficient yield displacement in the backfill soil such as Mononobe-Okabe method, but this paper focused on the change of dynamic earth pressure with wall flexibility. The phase difference between wall and soil reduced the dynamic earth pressure and dynamic moment has a same phase with wall inertia for flexible retaining wall. Position of dynamic thrust is H/3 for ordinary retaining wall and upper bound is 0.5H. Seed and Whitman method overestimate the dynamic thrust when surface PGA was used as a kh, and using wall base PGA as a kh agrees with Seed and Whitman estimation.

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