Journal of Geotechnical and Geoenvironmental Engineering

This paper considers two stochastic models for a soil-structure interaction problem with vertical propagation of P waves during strong earthquake motion. These models include the horizontal and vertical spatial variability of stiffness of the soil medium. The first model involves a two-dimensional stochastic Winkler foundation, which takes into account the horizontal variability of the soil. This model elucidates some experimental results obtained on a nuclear power station physical model built in Hualien (Taiwan). The second model is developed as a continuum system of random columns involving, this time, horizontal and vertical random characteristics of the soil medium. For both models a statistical analysis was performed with respect to determining probabilistic properties resonance frequencies and amplitudes of the corresponding transfer functions. The theoretical development and numerical results demonstrate the importance of considering soil variability for geotechnical design applications.

The mechanical behavior of many soils such as stiff clays depends on their current effective-stress states and stress history. For improving design and analysis of soil-structure interaction associated with deep excavations in these soils, it is important to understand effective-stress changes around excavations caused by both horizontal and vertical stress relief. In this paper, total and effective-stress variations adjacent to a diaphragm wall during construction of a 10-m-deep excavation in stiff fissured clay are reported and discussed. Interpreted field stress paths are compared with some relevant laboratory triaxial stress path tests, which simulate the horizontal and vertical stress relief in the field at an appropriate stress level. The interpreted field effective-stress paths in front of the wall are found to be similar to laboratory stress paths determined in undrained extension tests. Field stress paths behind the wall do not correspond particularly well with those from laboratory undrained compression tests, except when the stress state approaches active failure. The conventional undrained assumption does not seem to hold for the soil located immediately behind the wall during a relatively rapid excavation in the stiff clay.

A 3.5-km (2.2 mi) section of a road in Georgia developed unexpected transverse bumps within 6 months after construction. The source of the bumps appeared to be expansion within the cement-stabilized base course. Laboratory examination of samples from areas showing distress revealed the presence of ettringite, a calcium sulfoaluminate the formation of which can be accompanied by severe expansion. This expansive material was the probable cause of the volume changes causing the transverse bumps. The calcium and alumina needed to form ettringite were available from the portland cement and the stabilized soil's clay minerals. The source of the sulfur was identified as the well water that was mixed with the cement-stabilized base. Sulfate attack of cement-stabilized soils is a relatively infrequent problem, but it is highly destructive when it occurs. Currently, there are no firm criteria for identifying when sulfate attack of a cement-stabilized soil is a potential problem nor are there established methods of preventing the attack.

Shallow spread footings on soil are becoming an attractive choice for supporting highway bridge structures. However, to encourage their utilization, well-documented, comprehensive case histories must be established and made accessible to practicing bridge and geotechnical engineers. In addition, performance prediction methods for spread footing foundations must be verified further using carefully compiled field data. This paper is the writers' attempt toward achieving these goals, presenting details of a recently completed research project on 30 bridge spread footings in Ohio. The project data show that spread footings can be used successfully to support highway bridge structures on both cohesionless and cohesive soils, provided that the subsoil conditions are suitable and that the existing performance prediction methods are accurate.

This paper deals with anisotropic elastic properties of large-size tire shreds used as lightweight fills in road and embankment construction. The anisotropy is a result of compaction and overburden pressure, which induce a layered structure of the shreds. Laboratory experiments conducted in a novel biaxial apparatus revealed a difference in Young's moduli perpendicular and parallel to the layered structure; also, Poisson's ratios differ although their values could not be determined accurately. The out-of-plane shear modulus not readily determined from the tests was assessed by means of a layered material model. The results were used for determining the settlement of two road structures containing a layer of tire shreds modeled as either an isotropic or an anisotropic elastic material. Numerical calculations using the code CIRCLY indicated that the effect of tire shreds' anisotropy on road structure settlements is moderate, and the traditional isotropic elastic analysis overestimates the actual settlements.

A database consisting of 85 full-scale compacted clay liners was assembled to evaluate field hydraulic conductivity K_F. Large-scale field hydraulic conductivity tests were conducted on each liner. All of the clay liners were intended to achieve K_F ≤ 1 × 10⁻⁷ cm/s, but only 74% succeeded in meeting this objective. The important factors affecting K_F are the soil wetness relative to the line of optimums and the number of lifts or the thickness of the liner. Poor correlation exists between K_F and hydraulic conductivities measured in the laboratory (K_L) on field-compacted samples (especially for liners with K_F > 10⁻⁷ cm/s compacted at lower water contents relative to the line of optimums), percent compaction, and index properties representative of composition (e.g., Atterberg limits and particle size fractions). The findings indicate that (1) compacted clay liners having K_F ≤ 10⁻⁷ cm/s can be constructed with a broad variety of clayey soils; (2) the primary emphasis should be ensuring compaction is primarily wet of the line of optimums; (3) less emphasis should be placed on other traditional measures such as percent compaction, K_L, and index properties; and (4) liners that are thicker or have a greater number of lifts tend to have lower K_F.

During the reconstruction of a state highway in 1991, a full-scale test section was established at a site with a history of poor pavement performance, most likely because of a soft silty clay subgrade, high ground-water table, and heavy logging truck traffic. Five different separator geotextiles and a soil-only control section were installed in each lane. Excavations were made in the test section 5 years after installation, and samples of geotextiles, subgrade, and base course materials were exhumed for visual observation and laboratory testing. In addition, in situ soil tests were performed on the exposed subgrade soils. This paper summarizes these observations and test results. Although some fines from the subgrade had migrated through the geotextiles into the bottom of the base course, there was no evidence after 5 years of any adverse effect on the pavement itself. Minor geotextile damage that apparently occurred during construction had little effect on the pavement performance. In all of the sections with geotextiles, the subgrade soils were found to have consolidated significantly in comparison with the soil-only sections. Overall, the geotextiles performed their intended function well.

This paper is concerned with the problem of soil amplification and structural damage due to local site conditions in sedimentary valleys during earthquakes. It focuses on a small valley in Kirovakan, for which 1D wave propagation analyses have failed to provide adequate answers for the large extent and spatial distribution of damage during the 1988 Armenia earthquake. A more realistic 2D finite-element analysis is performed herein in search of an explanation for the observed behavior. Using as input an inferred rock accelerogram, the response of the valley is calculated for a vertically incident SH-wave. Synthetic accelerograms of the surface ground motion are presented for different sites; these accelerograms are then used to determine the amplification ratios of the surface response with respect to that of the free-field motion of the rock outcrop, for different frequencies and for a continuous set of sites. In addition, response spectra are evaluated for simple oscillators representing structures located at various sites. Results of the 2D simulations show striking differences with respect to those from 1D analyses. In particular, (1) while the resonant frequencies exhibited by a 1D model for a given site also appear in the 2D model, the peak ground response and structural response are almost twice as large for the 2D as for the 1D model; (2) the 2D model exhibits, in addition, a new set of resonant frequencies and concomitant “mode shapes” across the valley, which are directly related to its finite width; and (3) due to these additional resonances the ground amplification ratio tends to oscillate very rapidly, both spatially and with frequency, leading to the observation that two identical structures located in the same vicinity or two slightly different structures located essentially on the same site can be subjected to significantly different seismic forces, even if the underlying soils have very similar characteristics. These results provide a meaningful explanation for the observed damage, and thus serve to exemplify a situation in which site effects caused by the finite lateral extent of a valley must be taken into consideration in order to model satisfactorily seismic behavior.