Dynamic centrifuge modeling of an isolated footing for transmission line tower

Parameters which influence the settlement of the tower of transmission line are evaluated. Dynamic centrifuge tests and tests for obtaining fundamental properties of sand satured with different pore fluids (water, 50cst silicon oil) are carried out. The letter tests indicate:(i) In cyclic triaxial tests, there is no difference between the samples satured with water and silicon oil:; (ii) To satisfy the law of similarity, it is preferable to use silicon oil instead of water in centrifuge tests.(AU)

Evaluation of deformation characteristics of model ground during shaking using laminar box

Damage to lifeline facilities is common during earthquakes. Efforts to understand ground behavior during dynamic losding so as to minimize damage or to apply suitable counter measures has been made over years. This paper is an attempt to show the ground behavior during shaking and to evaluate deformation characteristics of ground in a laminar box at normal gravitational environment. Tests were conducted at a low confining pressure of less than 1m depth of ground. Results of the tests on dry and satured sandy ground models are presented. Methodology used for the evaluation of stress-strain response has been briefly discussed. It was possible to study cycle-wise stiffness degradation in satured ground due to the generation of excess pore water pressure. Ground showed some increase in strength after reaching a minimum value. It was understood that frequency of excitation and inertia of the mass affected the calculated modulus and damping ratio in the strain range of 0.01 to 1

showing lower stiffness and higher damping during shaking and the frequency effect reduced with depth.(AU)

Theory and model tests on mitigation measures against lateral flow of liquefied ground

This paper describes first the shaking table tests which were conducted to study the possibility of mitigation of lateral soil flow induced by seismic liquefaction. The present study used two types of embedded walls which were made of a sheetpile or compacted sand. Both types of walls were shown to be able to reduce the ground movement. The study then proceeded to develop an analytical method by which mitigated soil displacement can be predicted. The authors developed a closed-form solution of the lateral displacement which is based on the principle of the minimum potential energy at the state of stability as well as the Lagrangean equation of motion. The presnet study added the strain energy to the formerly-developed theory and the effects of mitigation walls were combined with the analytical metod of prediction.(AU)

Assessment of the behavior of quay walls using 1G shaking table tests

Behavior of caisson type quay walls during earthquakes is studies using the results obtained from a nimber of 1G shaking table model tests. Different modes of failure, i.e., slip, rotation and overturning are observed as the consequence of different input acceleration, weight of caison and different soil properties in subsoil and backfill area. Wall moves faster immediately after excess pore pressure increases at subsoil. This movement slows down in a later stage and reaches a constant velocity. This characteristic of wall movement is in a good correlation with subsoil density as well as magnitude and direction of input acceleration. Excess pore water pressure is not 100

of initial confining stress in subsoil probably due to the presence of initial shear stress. The absolute value of excess pore water pressure in subsoil is higher when a heavier model caisson is employed. In the case of a heavier wall, as a result of drastic change of vertical effective stress in front of the caisson, pore water pressure reaches 100

of initial confining stress, whereas it is lower beneath the wall. Excess pore water pressure in backfill is lower near the wall probabli due to the presence of a gravelly filter and also decreases of confining stress caused by outward movement of the wall. Analyses of response accelerations together with earth and pore water pressures show a complicated interaction pattern between wall, water and saturated backfill and subsoil.(AU)

Post - liquefaction ground flow in shaking table tests

The behavior of liquefied ground in lateral flow was studied in shaking table using a smaller and a larger container. Tests were conducted in a submerged model slope made with Toyoura sand. The dilatancy characteristics were considered to be very important. Since the shear deformation behavior of model ground at low confining pressure is dilative, the flow created in regular1-G shaking table tests is limited and cannot continue after shaking stops. However, this problem was solved by using a very loose model ground with contractive behavior. The model ground was prepared by moist placement and wet tamping methods. In order to trigger free flow an impact load was applied in the direction perpendicular to the slope (Transverse direction). Some tests were conducted with continuous shaking applied in the direction parallel to the slope (Longitudinal direction). In order to observe the soil deformation in detail, markers made from dyed sand were placed in contact with the transparent side wall of container. The displacement obtained from markers and a transducer placed in the center of the ground were compared. A relationship between the velocity of flow and the void ratio was obtained. Results of experiments with free flow triggered by an impact load and flow applied by continuous shaking were also examined.(AU)

Dynamic analysis of lateral flow of liquefied ground

A theory of dynamic analysis was derived in order to make it possible to follow the time history of lateral ground motion triggered by seismic liquefaction. This theory obtains a single-degree-of-freedom differential equation, by solving which the time history is calculated. Since the equation have a viscous term and a residual strenght that need a detailed study to understand, model shaking tests were perfomed. Those tests revealed that liquefied sand has a rate-dependent nature that is viscous as well as that the magnitude of the residual strength of liquefied sand is strongly affected by the presence of inertia force. Consequently, several cases were analyzed and compared with observation. Their agreement seems to be good.(AU)

Analysis on development of permanent displacement with time in liquefied ground

A predictive method for the temporal development of permanent displacement is hereby proposed. This method considers the transient displacemnt as a fraction of the ultimate one which can be predicted by using the principle of the minimum potential energy. The fraction varies with time and is predicted in turn in this text by solving the Lagrangian equation of motion. Since this equation gives a simple second-order differential equation in terms of time, its closed-form solution is easily derived. Therefore, the computation time is very short. When a mechanism of energy dissipation, as suggested by a shaking table test, is combined with the analysis, the agreement between calculation and observation is satisfactory. The amount of soil data is very limited for a practical convenience.(AU)

Prediction of liquefaction - induced permanent ground displacements : A three - dimensional approach

This paper deals with the three-dimensional extension of the above model for predicting the magnitude and spatial distribution of ground displacemnts caused by liquefaction.(AU)