Case Histories of Damage of Foundations Near Sliding Slopes

The paper studies the effect of large slope movements on foundations through case histories. More than 30 well-documented case histories of damaged buildings near the tip of slopes due to excessive movement caused by either heavy rain or earthquakes were collected. The case histories showed that a critical factor affecting the level of damage of buildings, is the coefficient Ι, that is defined as the ratio of the width below the foundation that settles by the total width of the foundation: (a) When Ι \u3c 0.2, collapse does not occur, even if settlement is very large, (b). When 0.2 \u3c Ι \u3c 1.0, the level of damage depends both on settlement and the factor l. (c) When Ι=1, buildings may not collapse, even if the settlement is very large, about 1m, but damage and rotation may be high. The above hold regardless of the cause of the slide: heavy rain or earthquake

Constitutive Models Predicting the Response of Clays Along Slip Surfaces

The paper proposes and validates a constitutive model simulating the change of resistance along clay slip surfaces under both undrained and drained conditions. The proposed model is based on (a) the critical state theory and (b) the assumption that the critical state changes once failure is reached, in terms of the further shear displacement. Under undrained conditions, the proposed model simulates the excess pore pressure generation and subsequently the continuous change of clay resistance along the slip surface from its initial value to the peak strength and then at large displacement the residual value measured in constant-volume ring shear tests. Under drained conditions, the model simulates the normal displacement change and subsequently the change of clay resistance along the slip surface in clays as measured in drained ring shear tests

Lateral Stress Ratio on Retaining Structures after Earthquake loading

Equations are derived by analysis g1vmg the earthquake-induced change in the permanent horizontal stress acting on frictionless vertical walls retaining dry sand. These equations exhibit a limit in the coefficient of lateral pressure that depends only on the slope of the critical state line and the Poisson\u27s Ratio of the backfill. The horizontal stress after dynamic shaking increases or decreases towards this limit. Predictions agree qualitatively with results of laboratory tests

The Effect of Geometry Changes on Sliding-Block Predictions

The sliding-block model is often used for the prediction of permanent co-seismic displacements of slopes and earth structures. This model assumes motion in an inclined plane but does not consider the decrease in inclination of the sliding soil mass as a result of its downward motion, which is the usual state in the field. The paper studies the above effect and proposes an empirical equation correcting the predictions of the sliding-block model. The investigation is performed using the recently-developed multi-block model

Accuracy of Empirical Equations Predicting Sliding-Block Displacement

The sliding-block model forms the basis of simple models predicting permanent co-seismic shear displacements of soils. For excitations consisting of actual accelerograms, different parameters of the applied motion have been used and different expressions have been proposed by researchers. Recently, many accelerograms have been recorded and these accelerograms are available in internet sites. These accelerograms allow the investigation of the accuracy of the expressions described above, some of which were based in a small number of accelerograms. In the present work the accuracy of empirical equations predicting sliding-block displacement is studied thru the application of 101 accelerograms covering a wide range of magnitudes, maximum accelerations, maximum velocities and dominant periods. The analysis illustrated that the accuracy of the methods vary. The Whitman and Liao (1984) method was found to produce the best predictions

Geotechnical Factors in Recent Earthquake-Induced Structural Failures in Greece

A review is made of geotechnical factors that played an important role in three recent earthquake-induced failures, two of which were deadly. The first two catastrophes concern two five-storey hotels that collapsed during the “Alkyonides earthquake” of 24 February 1981 (M=6.7) and the “Egion earthquake” of 15 June 1995 (M=6.2). The third failure is the collapse of a multi-storey factory caused by the “Athens earthquake” of 7 September 1999 (M=5.9). In the first two catastrophes, ground subsidence was estimated by two different methods and was found to be of the order of 0.13 to 0.46 m. These estimates are based on tentative assumptions that should be reviewed and possibly revised. Considerable differential settlements must have existed before the earthquake, as there were no basements that would have attenuated vertical loading and so even a moderate additional differential settlement could cause failure. In the third case, the structure was built near the edge of a steep slope of clayey soil. The co-seismic shear displacement caused the footings resting on the sliding mass to settle, thus causing severe distortions to the structure

Back Analysis of the Malakassa Landslide Using the Multi-Block Model

During the early hours of 18-02-1995 a landslide occurred at Malakasa, on the 36th kilometer of the highway joining Greece\u27s main cities, Athens and Thessaloniki. The computed deformed geometry using this model agrees reasonably well with that measured. The back-estimated soil strength of 16o is in the range of the measured values (8-19o). Finally, state-of-the-art stability analyses, using the back-estimated residual soil strength, illustrated that the location of the slip surface can be predicted if it is assumed that only the saturated soil below the water table loses its strength

Back Analysis of the Liquefaction Failure at King Harbor Redondo Beach, California

During recent earthquakes small dams and embankments suffered large settlements as a result of earthquake-induced liquefaction. One such case is the mole embankment that settled about 1.2m and was displaced horizontally by about 2m at King Harbor Redondo Beach, California as a result of the Northridge earthquake of 1994 (Kerwin and Stone, 1997). The conventional sliding-block model has shortcomings in back-estimating the critical acceleration and corresponding strength of such earthquake-induced slides when seismic displacement is large. The reason is that the change on geometry of the sliding mass, that greatly affects the seismic displacement, is not modeled. Stamatopoulos et al (2000) proposed a two-body sliding system that models this change in geometry. In the present paper, the Stamatopoulos et al (2000) sliding system model is used to back-estimate the residual shear strength of the mole embankment at King Harbor Redondo Beach. Then, the correlation of the residual soil strength and the blow count resistance of the SPT of this case is compared to the relationship that has been proposed by Seed and Harder (1990)

Critical Acceleration and Seismic Displacement of Vertical Gravity Walls By a Two Body Model

Under the assumption that as a result of earthquake loading the backfill behind a gravity wall reaches an active state, and with further increase in the earthquake acceleration the wall slides outwards, the soil-wall system consists of two bodies, each sliding along a different inclination: (a) the active soil wedge that slides with the inclination of least resistance in the backfill, and (b) the wall that slides along the soil-wall boundary at the base. This paper first gives the equation of motion of the 2-block sliding system described above that models the seismic response of vertical gravity walls retaining dry sand. Then, using the principle of limit equilibrium it gives analytical expressions giving (a) the angle of the prism of the active soil wedge, and (b) the corresponding value of the critical acceleration. Finally, differences between the predicted displacement by the new model and those of Newmark’s sliding-block model are detected and discussed