Journal of Geotechnical and Geoenvironmental Engineering

Two major earthquakes (M= 6.2 and M= 7) with different characteristics took place in the eastern coast of Taiwan in 1986 within a 4-month period. A test site at Lotung was located near the epicenters of the two quakes. The site was instrumented with three-dimensional (3D) surface and downhole accelerometer arrays and pore-pressure transducers embedded at depths from 3 to 16 m below the ground surface. Field investigation of the site, including sampling “undisturbed” soils, was carried out before the two events, and followed by a laboratory test program aimed at gaining detailed soil properties. Based on the available information, numerical analyses were performed using a fully coupled, multidirectional dynamic procedure incorporating a bounding surface hypoplasticity model. The calculated responses for the two different events showed equally reasonable agreements with the field records in both 3D acceleration and pore-pressure time histories. This paper reports the methodology of the analyses and presents the recorded data and calculated results.

In this paper a new empirical relation between the unconfined compressive strength of intact rock and the end bearing capacity of drilled shafts in rock is developed. In addition, an analytical relation between rock mass strength and end bearing capacity is developed to explicitly consider the effect of discontinuities. Specifically, a database of 39 load tests is used in this paper to derive the new relation between end bearing capacity and unconfined compressive strength of intact rock. The derived relation indicates that the end bearing capacity factor, N_c, which is the ratio of the end bearing capacity, q_max, and the unconfined compressive strength, σ_c, of intact rock, decreases with increasing σ_c. This is in contrast to many existing relations assuming constant N_c values. Since this new empirical relation is derived from the results of load tests, the effect of discontinuities is implicitly considered. To explicitly study the effect of discontinuities, an analytical relation based on the Hoek-Brown strength criterion that considers the effect of discontinuities is developed. The new analytical and empirical relations are in good agreement and are thus combined in a simplified form for predicting the end bearing capacity of drilled shafts socketed into rock masses. A comparison with two examples from instrumented test shafts indicates that the recommended relation produces satisfactory predictions.

Cyclic tests were conducted to study damping properties of two reconstituted sands and three laboratory-made clays at small cyclic shear strain amplitudes of γ_c≈ 0.001–0.04%, employing a recently developed constant-volume equivalent-undrained direct simple shear device for small-strain testing. The tests were strain-controlled with an approximately sinusoidal shape of cyclic straining. The effects of cyclic strain amplitude (γ_c), frequency of cyclic loading (f), plasticity index (PI), silt content, vertical effective consolidation stress (${\sigma }_{\mathit{v}c}^{\prime }$) and overconsolidation ratio (OCR) on the equivalent viscous damping ratio, λ, were investigated. The results show that, for a given γ_c, λ decreases with ${\sigma }_{\mathit{v}c}^{\prime }$ and OCR, but both of these effects become smaller if PI increases. The effect of f on λ was not observed for f≈ 0.01–0.1 Hz. The results also show that below γ_c≈ 0.005%, λ for clays is larger than λ for sands, which is exactly the opposite of the trend above γ_c≈ 0.005% established previously. Such a reversal of the trend of λ with respect to the type of soil is explained by the relative contributions of soil nonlinearity and soil viscosity to the area of the hysteretic cyclic stress-strain loop at small versus large cyclic strains.

A basic step in analyzing the behavior of shallow foundations is to collect full-size structure data. This is important on the one hand to check the actual methods of evaluating displacements of shallow foundation and to carry out settlement predictions, and on the other hand to study the complex interaction between foundation settlements and superstructure damage. This problem is especially important when the foundations rest on a cohesionless soil, owing to the impossibility of having undisturbed samples. This paper reports the experimental data, collected during the construction of two residential buildings, regarding the monitoring of the shallow foundations supported on a gravelly-silty sand deposit. Moreover, in the present work this information was used to evaluate the accuracy and the reliability of the methods proposed by Schmertmann, Burland and Burbidge, and Berardi and Lancellotta; the classic theory of elasticity as regards the establishment of settlements caused by static loads; and the elastic approach proposed by Wolf to estimate foundation rotations. Therefore, the real-size data allowed the analysis of the tolerable settlements problem following the guidelines given by Holtz and the new guidelines reported by the European Committee for Standardization.

Characteristics of response spectra of free-field horizontal and vertical ground motion recorded by JMA-87 type accelerometers are examined. The database includes 2,166 response spectra of motions from 387 events recorded at 76 JMA sites (70% on hard soil or rock and 30% on medium to soft soil). Most of the ground motions are far-source records. Relative spectral velocities at 0, 2, and 5% critical damping for 22 periods in the range of engineering interest have been subjected to nonlinear regression procedures in terms of magnitude and hypocentral distance. The attenuation relations consider the effect of depth and the local site amplification. A numerical technique called iterative partial regression is used to apply Joyner and Boore's two-stage regression methodology while considering the effect of the recording site. Dependence of horizontal and vertical response spectra, and their ratio, on magnitude, site-to-source distance, and depth are investigated through the development of attenuation relationships for horizontal and vertical spectral ordinates. The horizontal-to-vertical (H/V) response spectral ratio is found to be strongly dependent on period. At short periods, the value of the H/V spectral ratio is 1.5, but with an increase in period from an intermediate to a longer range, the spectral ratio attains a value of 3. These characteristics of H/V spectral ratio are likely to be universal for far-source recordings. The frequency-dependent relative amplification of the sites are found to be distinctive from site to site, and it is found that stations with the same soil type classification show an apparent pattern. Because the local site characteristics are explicitly derived, the resulting predictive equations can be considered as site-specific response spectra for the 76 JMA stations examined here.

Experimental and theoretical studies on the pullout performance of inclined helical screw anchors are presented. Previous contributions are reviewed and compared. The experimental program was conducted on anchors inclined at 15, 30, and 45° with respect to the vertical and installed into dense, medium, and loose sands. Special tests on anchors inclined at 45 and 60° installed into colored-layered sands were conducted to define the failure mechanism and the associated rupture surface. The results of these tests confirmed that the rupture surface is unsymmetrical and of a very complex nature; however, it can be represented by segments of logarithmic spiral curves. These segments differ in shape and size along the anchor perimeter. The concept of a conjugate anchor and auxiliary rupture surface was developed and introduced to correlate the pullout capacities of inclined and vertical anchors installed to the same depth in identical sand conditions. A coefficient of embedment depth was established and expressed theoretically in terms of the relative depth and the angle of inclination to facilitate the calculation of the pullout capacity of inclined anchors. A comparison of theoretical and experimental as well as field results showed reasonable agreement and confirmed the validity of the proposed theory.

Fourteen full-scale field test plots containing five types of geosynthetic clay liners (GCLs) were constructed on 2H:1V and 3H:1V slopes for the purpose of assessing slope stability. The test plots were designed to simulate typical final cover systems for landfills. Slides occurred in two of the 2H:1V test plots along interfaces between textured geomembranes and the woven geotextile components of internally reinforced GCLs. One additional slide occurred within the unreinforced GCL component of a 2H:1V test plot, when the GCL unexpectedly became hydrated. All 3H:1V slopes have remained stable. Results of laboratory direct shear tests compared favorably with field observations, providing support for the current design procedures that engineers are using for assessing the stability of slopes containing GCLs.

Practicing engineers and researchers are becoming aware of the importance of ground movements and stress changes in the ground that may occur during the construction of a diaphragm wall type of retaining walls. In this paper, the construction sequence of a typical diaphragm wall panel in stiff clay is fully simulated using a three-dimensional finite difference program. Computed results are compared with some reported results of centrifuge model tests and relevant case histories. It has been found that the influence zone due to the diaphragm wall panel installation falls within a normal distance of approximately one panel depth, D, from the face of the panel, 1/3D below from the toe and 1/3L from the edge and along the length of the panel (L). Significant horizontal stress reduction behind the center of the panel is attributed to both the downward load transfer and the horizontal arching mechanisms. A settlement bowl appears behind the panel. The maximum settlement occurs at a distance of about 0.2D behind the wall and settlements beyond the influence zone are found to be insignificant.