Shaking Table Tests on Transient Flow of Liquefied Ground

An attempt was made to predict the time history of the lateral displacement of ground that liquefied due to earthquakes. The study was initiated by model tests to examine the nature of liquefied sand. The knowledge thus obtained was combined with the theory of Lagrangean equation of motion in order to develop a method of prediction. Comparison was then made between prediction and observation

Sensing, measuring and modelling the mechanical properties of sandstone

We present a hybrid framework for simulating the strength and dilation characteristics of sandstone. Where possible, the grain-scale properties of sandstone are evaluated experimentally in detail. Also, using photo-stress analysis, we sense the deviator stress (/strain) distribution at the microscale and its components along the orthogonal directions on the surface of a V-notch sandstone sample under mechanical loading. Based on this measurement and applying a grain-scale model, the optical anisotropy index K0 is inferred at the grain scale. This correlated well with the grain contact stiffness ratio K evaluated using ultrasound sensors independently. Thereafter, in addition to other experimentally characterised structural and grain-scale properties of sandstone, K is fed as an input into the discrete element modelling of fracture strength and dilation of the sandstone samples. Physical bulk scale experiments are also conducted to evaluate the load-displacement relation, dilation and bulk fracture strength characteristics of sandstone samples under compression and shear. A good level of agreement is obtained between the results of the simulations and experiments. The current generic framework could be applied to understand the internal and bulk mechanical properties of such complex opaque and heterogeneous materials more realistically in future

Silent boundary for time domain wave motion analyses based on direct energy deletion

A new specialized method to simulate the radiation condition of unbounded domains is developed. This method is of the so called 'local type' and it is designed for semi-discretized finite models analysed in the time domain, considering linear elastic behaviour of the exterior unbounded domain and arbitrary nonlinear behaviour of the interior. The principle of the proposed method is based on erasing the wave energy in an extended boundary region so that the front of reflected waves is continually held back from the interior of the finite model. This is achieved via a simple numerical scheme which maintains a wave field continuity that can be handled by the discretized system without creating numerical wave shocks. It has turned out that the accuracy of the method is a function of the size of the extended boundary region; the larger the boundary region, the better the accuracy.Les auteurs proposent une nouvelle m\ue9thode sp\ue9cialis\ue9e permettant de simuler la condition de radiation des domaines non born\ue9s. Cette m\ue9thode, dite 'de type local', s'applique aux mod\ue8les finis semi-discrets analys\ue9s dans le domaine temporel, compte tenu du comportement \ue9lastique lin\ue9aire de l'ext\ue9rieur du domaine non born\ue9 et du comportement non lin\ue9aire arbitraire de l'int\ue9rieur. La m\ue9thode propos\ue9e repose sur l'effacement de l'\ue9nergie des ondes dans une r\ue9gion limite \ue9tendue de sorte que le front des ondes r\ue9fl\ue9chies soit constamment emp\ueach\ue9 de revenir \ue0 l'int\ue9rieur du mod\ue8le fini. On utilise \ue0 cette fin une proc\ue9dure num\ue9rique simple qui entretient un champ d'ondes continu qui peut \ueatre trait\ue9 par le syst\ue8me discret sans cr\ue9er d'ondes de choc num\ue9riques. Il s'est av\ue9r\ue9 que la pr\ue9cision de la m\ue9thode est fonction de la taille de la r\ue9gion limite \ue9tendue; plus la r\ue9gion limite est grande, plus la m\ue9thode est pr\ue9cise.Peer reviewed: YesNRC publication: Ye

Preface

10.1016/j.soildyn.2005.04.006Soil Dynamics and Earthquake Engineering257-10471

Dynamic Response of Underground Structures in Sand: Experimental Data

A densely instrumented system of large-scale underground structures consisting of two vertical shafts connected through a cut-and-cover tunnel and two independent shield tunnels was installed in an 8 m-diameter laminar soil box at the E-Defense shake table in Miki, Japan. The system was subjected to step-sine sweeps and scaled ground motion records of the Kobe (1995) earthquake. The underground structures were embedded in Albany Silica Sand with an average relative density of 54%. System instrumentation consisted of over 800 sensors, including strain gauges, accelerometers, displacement transducers, bender elements and pressure sensors. A U.S.-Japanese research collaboration was established to instrument the vertical shaft elements and record seismic soil pressures. Data records are archived at the NHERI DesignSafe Data Depot_and can be used to analyze the structural response, soil-structure interaction and other response parameters of individual subsurface components as well as the entire system. The DOI for the data set is 10.17603/DS21C78

Water-induced granular decomposition and its effects on geotechnical properties of crushed soft rocks

The widespread availability of soft rocks and their increasing use as cheap rockfill material is adding more to geotechnical hazards because time-dependent granular decomposition causes significant damage to their mechanical properties. An experimental study was conducted through monotonic torsional shear tests on crushed soft rocks under fully saturated and dry conditions and compared with analogous tests on standard Toyoura sand. Due to the sensitivity of material to disintegration upon submergence, saturated conditions accelerated granular decomposition and, hence, simulated loss of strength with time, whereas, dry test condition represented the response of the soil with intact grains. A degradation index, in relation to gradation analyses after each test, was defined to quantify the degree of granular decomposition. Possible correlations of this index, with strength and deformation characteristics of granular soils, were explored. Enormous volumetric compression during consolidation and monotonic loading of saturated specimens and drastic loss of strength parameters upon submergence were revealed. It is revealed that the observed soil behaviour can be critical for embankments constructed with such rockfill materials. Moreover, the enhanced ability of existing soil mechanics models to predict time-dependent behaviour by incorporating water-induced granular decomposition can simplify several in situ geotechnical problems