Part 1: Physical and flow charcteristics of unsaturated soil 1 Basic physics, phases and stress state variables 2 Measurement and control of suction: methods and applications 3 Flow laws, seepage and state-dependent soil-water characteristics Part 2: Collapse, swelling, strength and stiffness of unsaturated soils 4 Collapse and swelling caused by wetting 5 Measurement of shear strength 6 Measurement of soil stiffness Part 3: State-dependent elasto-plastic modelling of unsaturated soils 7 A state-dependent elasto-plastic critical state-based constitutive model Part 4: Field trials and numerical studies in slope engineering of unsaturated soil 8 Instrumentation and performance: A case study in slope engineering 9 Engineering applications for slope stability Appendix A: Definitions Appendix B: Notations

Advanced Unsaturated Soil Mechanics and Engineering

Test data to compare the resulting behavior with that observed under cyclic loading triaxial test conditions are presented. It is concluded that the liquefaction characteristics observed in the two types of tests are qualitatively similar. However, under cyclic simple shear conditions, which provide a close simulation of the stresses induced under field conditions, the cyclic shear stresses required to cause liquefaction were only about 35% of those determined by more approximate triaxial test procedures. It is suggested, however, that limitations of the simple shear test procedure induce liquefaction at stress levels perhaps 40% to 50% lower than those corresponding to actual field conditions, and that a correction factor of this order of magnitude should be applied to laboratory simple shear test data intended for use in the analyses of field problems. The test program also showed that frequency effects, within the range from 1/6 cps to 4 cps, are small.

Closure to “Sand Liquefaction Under Cyclic Loading Simple Shear Conditions”

Influence of curing under stress on the triaxial response of cemented soils

Bender element (BE) testing is a powerful and increasingly common laboratory technique for determining the shear S-wave velocity of geomaterials. There are several advantages of BE testing, but there is no standard developed for the testing procedures or for the interpretation of the results. This leads to high degree of uncertainty and subjectivity in the interpretation. In this paper, the authors review the most common methods for the interpretation of BE tests, discuss some important technical requirements to minimize errors, and propose a practical framework for BE testing, based on the comparison of different interpretation techniques in order to obtain the most reliable value for the travel time. This new procedure consists of the application of a methodical, systematic, and objective approach for the interpretation of the results, in the time and frequency domains. The use of an automated tool enables unbiased information to be obtained regarding variations in the results to assist in the decision of the travel time. Two natural soils were tested: residual soil from Porto granite, and Toyoura sand. Specimens were subjected to the same isotropic stress conditions and the results obtained provided insights on the effects of soil type and confining stress on the interpretation of BE results; namely, the differences in testing dry versus saturated soils, and in testing uniform versus well-graded soils.

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A Framework Interpreting Bender Element Tests, Combining Time-Domain and Frequency-Domain Methods

Tunnel driving inevitably induces changes in stress and deformation in the ground, which could cause ultimate and serviceability problems to an adjacent tunnel. The effects of induced stress on an ...

Three-dimensional centrifuge and numerical modeling of the interaction between perpendicularly crossing tunnels

This paper summarizes the results of an experimental site investigation and characterization survey, on a residual (saprolitic) soil from granite, in the framework of a research project led by the Faculty of Engineering of the University of Porto (FEUP). This project aims at characterizing these unusual soils in the context of the development of an International Prediction Event (Class A) on the behaviour of different types of piles. A very extensive site characterization campaign, including a large variety of in-situ tests and field methods, has been held. These investigations comprised the application of several geophysical borehole and surface methods, namely P- and S-wave seismic refraction, reflection, cross-hole (CH), down-hole (DH), electrical resistivity imaging and ground probing radar (GPR), as well as mechanical tests, namely SPT, CPT and DMT, among others. The site is geologically formed by an upper layer of heterogeneous residual granitic soil, overlaying rather weathered granite contacting a gneissic migmatite. Direct and indirect results from some of the referred surveys were compared between them and with some of the available geological and geotechnical information, namely those obtained from seismic, electrical and GPR profiles, conducted adjacent to three boreholes in which undisturbed soil samples were collected previously to geophysical data acquisition. In addition, a comprehensive laboratory testing program was carried out using the collected undisturbed samples. A discussion of the obtained results is hereby presented, giving emphasis to the correlations encountered between the different tests, specific of saprolitic soils with weak relic structures.

Characterization of a profile of residual soil from granite combining geological, geophysical and mechanical testing techniques

In the north-western region of Portugal residual soils from granite are dominant. Their porous cemented structure leads to a complex geotechnical behaviour, quite distinct from that of transported soils with a similar grain size distribution. The paper describes some of the studies carried out at an experimental site on which a fairly homogeneous saprolitic soil 6m thick was encountered. These studies included: (i) a full-scale load test of a circular concrete footing (1·20m diameter), under carefully controlled conditions and with extensive monitoring; (ii) in situ testing techniques (SPT, CPT, SBPT, CH) and (iii) laboratory testing on high-quality block samples, including triaxial tests with local strain measurement. The discussion is concentrated on the interpretation of the pressure—settlement curve from the footing load test, for a range of pressures typical of working conditions, by means of linear and non-linear elastic analyses based on stiffnesses from the laboratory and in situ tests. Some pract...

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Interpretation of a footing load test on a saprolitic soil from granite

Bender elements are used to measure the low-strain shear-wave velocity of soils in many geotechnical laboratories worldwide. Despite their popularity, the method remains without a standard, mainly ...

Time and frequency domain evaluation of bender element systems

Comparison of shear wave velocity measurements in different materials using time and frequency domain techniques

Ultrasonic and bender element tests in the laboratory are typically used to measure elastic modulus and damping ratio. However, interpretation of the results is challenging for a variety of reasons, including the influence of experimental details, geometrical effects and the analytical techniques used for data processing. It is therefore convenient to cross-check results by performing several independent measurements. Three different types of measurements were performed on cemented-sand specimens. Longitudinal waves or constrained compressional waves in a cylindrical specimen were generated in a high-frequency range (20–70 kHz) using a newly designed transducer interface. Full dynamic characterisation was made possible by independent measurement of the transducer response. Pure unconstrained compressional waves or simply compression waves were measured in the same specimens with high-frequency transducers. The shear modulus was computed and used to predict the arrival of shear waves on independent bender ...

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A. Viana da Fonseca

Papers

Characterization of a profile of residual soil from granite combining geological, geophysical and mechanical testing techniques

Interpretation of a footing load test on a saprolitic soil from granite

Time and frequency domain evaluation of bender element systems

Comparison of shear wave velocity measurements in different materials using time and frequency domain techniques

Compression and shear wave propagation in cemented-sand specimens