ABSTRACT
A typical ground investigation for characterizing geotechnical properties of soil requires sampling soils to test in a laboratory. Laboratory X-ray computed tomography (CT) has been used to non-destructively observe soils and characterize their properties using image processing, numerical analysis, or three-dimensional (3D) printing techniques based on scanned images; however, if it becomes possible to scan the soils in the ground, it may enable the characterization without sampling them. In this study, an in-situ X-ray CT scanning system comprising a drilling machine with an integrated CT scanner was developed. A model test was conducted on gravel soil to verify if the equipment can drill and scan the soil underground. Moreover, image processing was performed on acquired 3D CT images to verify the image quality; the particle morphology (particle size and shape characteristics) was compared with the results obtained for projected particles captured in a two-dimensional (2D) manner by a digital camera. The equipment successfully drilled to a target depth of 800 mm, and the soil was scanned at depths of 700, 750, and 800 mm. Image processing results showed a reasonable agreement between the 3D and 2D particle morphology images, and confirmed the feasibility of the in-situ X-ray CT scanning system.
ABSTRACT
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)
Subject(s)
Earthquakes , Soil , Acceleration , EngineeringABSTRACT
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)