This paper includes a numerical study of the seismic behavior of tunnels constructed in liquefiable soils. It is carried out using finite element modeling based on the (u-p) formulation (displacement for the solid phase and pore-pressure for the fluid phase). The behavior of the soil material is modeled using a cyclic elastoplastic constitutive relation involving both isotropic and kinematic hardening. The paper is composed of three parts. The first part includes a brief presentation of the numerical model used in this study; the second concerns the analysis of a reference example; the last part presents a parametric study of the influence of both loading and soil characteristics on the seismic response of tunnels constructed in saturated soils.

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Compensation grouting involves making grout injections at close neighboring locations so as to replace ground loss, due to tunnelling for example. Since the objective of the technology is to match volume changes so as to eliminate subsidence, the tendency of ground to dilate or compress around the injection becomes a very significant consideration. Furthermore, the effects of different sequences of grout injection, and the zoning of injection relative to the tunnel centreline, are of interest when devising grouting schemes. This paper investigates these issues using centrifuge and numerical modelling in dense and loose dry sand. It is found that the profile of surface heave and the tunnel lining deformation is dependent on the relative injection position, as well as injection history. Ground stiffening due to the compaction arising from previous injection permits larger pressures to be developed from a given injection volume. These larger pressures eventually cause upward heaving and lining deformation. In conclusion, the most favourable and unfavourable injection sequence are identified in relationship to the induced centre surface heave and tunnel lining deformation.

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An experimental study on the behaviour of reconstituted samples of sand reinforced with geotextile layers is presented using standard triaxial and plane strain tests. After describing the main features of the plane strain device and of the data acquisition system, details are provided on the procedure developed for preparing plane strain samples containing inclined reinforcements with respect to the principal stress directions. Comments are also made on the influence of the preparation procedure on the overall behaviour observed during loading. Finally, the results of the experimental investigation are described with reference to standard triaxial tests with horizontal reinforcements, and to plane strain tests with horizontal and inclined reinforcements. The study complements data already available in the literature, for the development of constitutive laws applicable to the numerical analysis of reinforced earth structures.

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Efficient lumped-parameter models recently developed by the authors for generally representing the vibrations of foundations are applied in this study to perform simplified soil-structure interaction (SSI) analysis for seismic excitations. A number of important computational issues, especially the determination of an appropriate input motion modified from the foundation input motion, are discussed for effectively incorporating the lumped-parameter models with the structural parameters to represent the whole structure-foundation-soil system. It is found that the modification of the foundation input motion is dependent on the frequency and may increase to a significant level in the high frequency range. It is also demonstrated that the application of the lumped-parameter models can accurately represent the time responses of the actual SSI system. More specifically, since the adopted lumped-parameter models exhibit better accuracy in approximating the translational foundation vibrations than in the cases of rotational foundation vibrations, results from the numerical example indicate that relatively more significant error can be induced in conducting the simplified SSI analysis for the slender system.

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The Darcy's experimental law is valid in the case of linear laminar steady flows through saturated porous media. Although this law is still widely used, it is not valid in the case of laminar unsteady or cyclic flows due, for instance, to the action of short waves within soils and earth structures, which can affect their behaviour and durability. The present paper presents a new extension of Darcy's law particularly suitable to these unsteady flows. The model is first derived from the Navier-Stokes equations combined with a capillary-type model. For validation of the model, an experimental device simulating flows due to short waves within soils was developed. 95 unsteady tests conducted on five different sands have confirmed the validity of the law identified. The results of the tests show the effects of acceleration, which generates an increase of the interstitial pressure within the soils.

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Characteristics of the maximum and minimum void ratios of sands and their possible use for material characterization have been investigated in this study. Data of over 300 natural sandy soils including clean sands, sands with fines and sands containing small amount of clay-size particles have been used to examine the influence of fines, grain-size composition and particle shape on e_max, e_min and void ratio range (e_max - e_min). A set of empirical correlations are presented which clearly demonstrate the link between these void ratios and material properties of sands. The key advantage of (e_max - e_min) over-conventional material parameters such as Fc and D₅0 is that (e_max - e_min) is indicative of the overall grain-size composition and particle characteristics of a given sand and that it shows off the combined influence of relevant material factors. The void ratio range provides a general basis for comparative evaluation of material properties over the entire range of cohesionless soils. Important issues related to the laboratory procedures used for determination of e_max and e_min as well as their applicability to fines-containing sands are also addressed. Three distinct linear correlations were found to exist between e_max and e_min for clean sands, sands with 5-15% fines and sands with 15-30% fines respectively, thus illustrating that the standard JGS procedures for minimum and maximum densities of sands can provide reasonably consistent e_max and e_min values for sands with fines content of up to 30%. The importance of the grain-size distribution and presence of gaps in the grading of composite soils or mixtures of sands with fines produced in the laboratory is also discussed.

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Microbial activities can be enhanced by organic rich leachate occurring in solid waste landfills, which possesses the potential to alter the barrier capacity of clay liners. Flexible-wall hydraulic conductivity tests are conducted to investigate the effect of the microbial activities on the hydraulic conductivity of Osaka marine clay used for clay liners of offshore solid waste landfill sites in Japan. Permeants with different redox potentials are employed to investigate the redox effect; and, permeants with high nutrients are used to check the effect of the microbial production in soil specimens. Test results indicate that there are no obvious changes in the free swell index, the liquid limit, or the hydraulic conductivity of the marine clay when a strong reducing agent is used. When nutrients are applied for the growth of microorganisms, however, a decrease in hydraulic conductivity, ranging from greater than two orders of magnitude to less than one order of magnitude, is observed. The formation of biofilm and anaerobic inorganic precipitation on the surface of the soil particles is considered to be responsible for this reduction in hydraulic conductivity. Test results reveal that microbial activities, enhanced by landfill leachate, may not cause an increase in the hydraulic conductivity of natural clay liners of offshore landfill sites.

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In order to examine the liquefaction resistance of partially saturated sand, a cyclic triaxial test apparatus was manufactured, with which it was possible to first measure the longitudinal and shear wave velocities and then to conduct cyclic triaxial tests on the same specimens under p-constant conditions. A series of the tests indicated that the longitudinal wave (P-wave) velocity could be used to identify the degree of saturation of near-saturated samples, and its effect on the liquefaction resistance could be clarified by conducting cyclic loading tests immediately following measurement of P-wave velocity. The results of the P- and S-wave measurements indicated that the velocity of P-wave propagation, V_p, tends to increase from about 500 m/sec to about 1800 m/sec when the B-value increases from 0 to 0.95 corresponding, respectively, to the saturation ratio S_r of about 90 and 100%. Simple theoretical consideration indicated, on the other hand, that V_p could be expressed as a function of two factors, that is, the B-value and what may be termed "skeleton Poisson's ratio" which is defined for the small-strain level of soil deformation, based on the measured V_p and the propagation velocity, V_s, of the shear wave (S-wave). The theoretically derived simple formula as above was shown to be in good coincidence with the relations obtained in the tests. For the cyclic phase of triaxial tests, the cyclic resistance to liquefaction was shown to increase with a decrease in the B-value and hence with a drop in the saturation ratio S_r. It was also shown that when the B-value drops practically to zero with a V_p-value of about 500 m/sec, the cyclic strength of the specimen becomes twice as much as that at full saturation with B = 0.95 and V_p = 1800 m/sec.

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Formulations based on finite strain theory are introduced to develop an analytical procedure for determining volume changes and volumetric strains in the elastic and plastic zones, and average volumetric strain, Δ, in the plastic zone during expansion of the cylindrical and spherical cavities. Vesic's cavity-expansion theory requires the value of Δ to be determined from triaxial shear tests. This requirement can be relaxed by use of an analytical procedure proposed herein. Δ significantly decreases with increase of the rigidity index, I_r, and slightly decreases with increase of friction angle, Φ. The analysis shows that volumetric strains are about 5 to 7 percent near the face of the cavity and rapidly reduce to less than 0.1 percent at the interface of the elastic and plastic zones. Dimensionless cavity expansion factors (F'_q, F'_c, F_q, F_c) versus Φ curves for various values of I_r and Poisson's ratio, v, are prepared on the basis of analytically calculated value of Δ. Depending on I_r and Φ values, these factors increase by about 2.5 to 12.5 percent with increase of v from 0.2 to 0.4.

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Bearing capacity factors, N_q and N_c, for deep foundations have been determined using the dimensionless cavity expansion factors, F_q and F_c. Both angle of friction, Φ, and rigidity index, I_r have significant effect on N_q and N_c. N_q - Φ curves for various values of I_r are prepared on the basis of analytically calculated value of F_q, Vesic's, λ_v, and Yasufuku and Hyde's, λ_YH, factors. Meyerhof (1976) N_q - Φ charts are within upper half of the envelope of N_q - Φ curves. Hannigan et al. (1996) and Fellinuos (1991) N_q - Φ charts are within envelopes of N_q - Φ curves for I_r. = 100 to 1000, while API (1993) N_q- Φ charts are within envelopes of N_q - Φ curves for I_r = 10 to 100. Using F_q and λ_YH or F'_q and λ_v or λ_SMJ factors, the study shows that the cone tip resistance, q_c, can be estimated, on average, with an accuracy of ±15 percent.

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