Subsoil Model Research Articles

Drop-weight test based identification of elastic half-space model parameters

A method enabling the conversion of dynamic drop-weight test results into a statical substitute is presented. Owing to this substitution, statical models, instead of complex dynamical models, can be used for subsoil elastic moduli identification. An elastic half-space was adopted as the subsoil model. Identification was limited to the determination of the subsoil's modulus of elasticity. The results were verified in two ways. One way consisted in the simulation of experimental results on the basis of theoretical results. The latter were obtained by analytically solving the problem of half-space vibrations caused by an impact pulse. The elastic moduli identified on the basis of the simulated results were compared with the assumed elastic moduli. In the other verification method, the results obtained by the proposed identification method were compared with the result yielded by the standard statical identification method. The load and displacement values used were from tests carried out on actual soils.

Liquefaction induced lateral spread analysis using the CIP method

Abstract This paper presents a CIP (cubic interpolated pseudoparticle) based numerical method for liquefaction induced lateral spread analysis in the framework of fluid dynamics. Previously, the authors presented similar methods using a SIMPLE-VOF based commercial code but were not able to extend such a code to simulate lateral spread of liquefied ground with an overlaying non-liquefied layer, which is the most common and more practical post liquefaction problem. In this study, the CIP method is used because it is able to treat solid, liquid and gas together, can correctly define the flow behavior at interfaces of multi-fluids and can also be used as a unified scheme for both compressible and incompressible materials. A Bingham model that takes the undrained strength of soils into account is used as the basic constitutive model. A CIP based numerical scheme, which has been successfully used in fluid dynamics problems, is modified by incorporating the Bingham viscosity and an implicit calculation procedure for pressure terms. The Poisson equation is used to compute the pressure over the whole domain. The current numerical method is validated and good agreement is produced in comparison with experimental results. A previously verified similitude for liquefied ground flow is also reproduced by this method. The method is, finally, used to simulate shaking table tests on a liquefied subsoil model with an overlaying non-liquefied layer. From the results of simulations, the numerical method is found to satisfactorily reproduce the time histories of ground surface velocity and displacement and depth distribution of displacement.

A modular algorithm for linear, periodic train-track models

An algorithm is presented which can be used for the investigation of a large variety of train-track models. These models only have to fulfil the requirements of linearity and periodicity with respect to the track length direction. A steady-state solution is obtained for a vehicle moving on a tangent track with constant velocity. The algorithm itself can be split into three modules: one for the whole train-track system, one for the track, and one for a single rail support. These modules and their interfaces are described in detail. The article demonstrates the applicability of the algorithm by means of four examples. The first example shows the influence of the sleeper elasticity on the sleeper motion. The second one illustrates the effect of an advanced subsoil model on the wheel/rail contact force. Subsequently, as a further example, the compliance frequency-response functions of a ballasted track and a rigid track are compared. The last example deals with the sleeper passing excitation. Here, it is shown that even in the case of resonance, the wheel/rail contact-force fluctuations remain below ten percent of the static value.

An improved visual acuity test object

The area located inside the São Sebastião volcanic crater, at the southeast end of Terceira Island (Azores), is characterized by an important amplification of ground motion with respect to the surrounding area, as clearly demonstrated by the spatial distribution of the damage that occurred during the Terceira earthquake (the strongest earthquake felt in the Island during the recent decades — 01/01/1980 — M = 7.2). Geological and geophysical studies have been conducted, to characterize the volcanic crater and understand the different site effects that occurred in the village of São Sebastião. The complexity of the subsurface geology, with intercalations of compact basalt and soft pyroclastic deposits, is associated to extreme vertical and lateral velocity contrasts, and poses a serious challenge to different geophysical characterization methods. The available qualitative model did not allow a complete understanding of the site effects. A new seismic campaign has been designed and acquired, and a single, geologically consistent geophysical model has been generated integrating the existing and new data. The new campaign included two cross-line P-wave seismic refraction profiles, four short SH-wave seismic reflection profiles, and seven multichannel surface wave acquisitions. The integration and joint interpretation of geophysical and geological data allowed mutual validation and confirmation of data processing steps. In particular, the use of refraction, reflection and surface wave techniques allowed facing the complexity of a geology that can pose different challenges to all the methods when used individually: velocity inversions, limited reflectivity, and lateral variations. It is shown how the integration of seismic data from different methods, in the framework of a geological model, allowed the geometrical and dynamic characterization of the site. Correlation with further borehole information, then allowed the definition of a subsoil model for the crater, providing information that allowed a better understanding of the earthquake site effects in the São Sebastião village. The new near-surface geological model includes a lava layer within the soft infill materials of the crater. This new model matches closely with the damage distribution map, and explains the spatial variation of building stock performance in the 1980 earthquake.