Miguel P. Romo

Neurofuzzy mapping of CPT values into soil dynamic properties

Ever since the early days of soil mechanics there has been a strong tendency to develop correlations between easy-to-obtain parameters and mechanical properties of geotechnical materials. This interest has not decreased as more elaborated methods have been proposed. On the contrary, once a method under development reaches certain degree of sophistication, researchers usually devote a great deal of time to establish simplified procedures. The study presented in this paper follows a similar path in the sense that a data-based knowledge procedure instead of mathematically based methods is used to develop a manner to estimate soil dynamic properties directly from cone-tip penetration resistances. This method is based on a hybrid system integrated by merging artificial neural networks and fuzzy logic. The procedure is evaluated comparing its results with actual measurements of cone-tip penetration resistances and shear wave velocities done in twin borings.

Influence of earthquake frequency content on soil dynamic properties at CAO site

The installation of vertical downhole arrays in the field that record the soil behavior during earthquakes, has opened the opportunity of exploring another alternate method for assessing the soil dynamic properties by solving the inverse problem. This article proposes a methodology for solving this problem using spectral analysis of downhole arrays records. The one-dimensional shear wave propagation model was used, considering a homogeneous-viscoelastic medium. This methodology was applied at the site known as Central de Abasto Oficinas (CAO), which is located in the lake zone of the Mexico City. The results indicate that even relatively low frequencies have a noticeable effect on dynamic soil properties. Shear modulus increases and damping ratio lessens when the frequency rises.

Characterization of ground motions using recurrence plots

The current analysis of earthquakes is typically based on linear mathematical models that may fail to describe and forecast particular behaviors, because in many cases the data complexity may induce a highly non linear behavior. In this paper the implementation of an alternative method for seismic time series analysis is presented. The RPs (Recurrence Plots) enables recognition and treatment of measured accelerations. An RP obtained from seismic data allows a more efficient interpretation of the ground motions and this explanation contributes to characterize materials and responses. The nonlinear attributes from RPs analysis can be used as filters to reveal patterns or be combined to predict a seismic property. Automated seismic data characterization, based on nonlinear seismic attributes, could rewrite the rules of earthquake phenomena interpretation. The objective of this work is to establish a new methodology for practical application of nonlinear dynamics in seismic pattern/attributes recognition, an evolving and challenging engineering field.

P–Y Curves for Piles Under Seismic Lateral Loads

This paper describes an experimentally based procedure for building dynamic P–Y curves for clays from the Campeche sound in the Gulf of Mexico and for Mexico City clays. Cyclic triaxial and resonant column tests were used to derive hyperbolic stiffness–strain and damping–strain functions that depend on soil plasticity and on relative consistency. The dynamic P–Y curves incorporate these functions and also include hysteretical and geometrical damping characteristics of the pile–soil system; they can be used directly in dynamic interaction analyses of structure–pile–soil systems in the time or the frequency domains. Usual practice relies on pseudo static formulations and a simplified alternative to include P–Y curves in this kind of analysis is also proposed, which is essentially the same as the dynamic ones but does not include radiation or hysteretical damping.

Advanced 3-D Seismic Soil-Structure Interaction Analysis of a Cellular-Raft Foundation in Soft Clay

Seismic soil-structure interaction performance evaluations of projects located in deep soft clay deposits warrant special attention, particularly when designing strategic infrastructure that must remain operating after a major earthquake. The development of numerical analytical platforms in recent decades, along with faster computing tools, have made possible to include in the state of practice quite sophisticated solution techniques aimed at better representing the physics of the problem at hand. This paper presents the application of a 3-D finite difference model for evaluating the static and dynamic response of a 118 by 100 m cellular-raft foundation to be built in soft clay. The raft foundation is a 2.5 m high box-type foundation embedded 1 m and supported by a grid of peripheral and internal walls, 2.5 m long and 0.40 m thick, which integrates a cellular structure. The model is used to obtain first the static behavior exhibited by the foundation for the construction stages, including long term consolidation, and then the design earthquake is considered and the equation of motion is solved in time domain.

Modeling soil-pile interaction under axial loading using a bilinear Mohr-Coulomb based model

It is common practice to rely on traditional relationships to compute the bearing capacity of deep foundations. In particular, when dealing with piles is essential to calibrate the load-displacement response, both for axial and lateral loading and to define the load transfer mechanism at the pile tip and along the shaft. These calibrations allow to reduce uncertainties and to design less expensive and safer foundations. The objective of this paper is to simulate the mechanical response obtained from a load test performed in a real scale cast in place concrete pile embedded in alluvial sand, using a 3D finite differences model. The pile was instrumented to monitor directly the reaction along its shaft and tip. The interface was modeled using a shear coupling-spring with frictional resistance. Both the soil and the pile were represented with four nodes axi-symmetric elements. The stress-strain behavior of the soil and soil-pile interface was described with a bilinear MohrCoulomb constitutive law. Although the simplicity of the bilinear model, good agreement was observed between the measured and computed responses when monotonic increasing loading was applied (i.e. static conditions). However, the bilinear constitutive model largely underestimates the measured permanent deformations prevailing in the pile-soil system after unloading. This should be accounted for when analyzing the dynamic response of the soil-pile system.