Liquefaction and Deformation of Soils and Foundations Under Seismic Conditions

A summary of significant developments in seismic liquefaction research and applications is presented for the period 1985-1995. It is concluded that rapid progress is being made, especially in evaluating ground deformation and straining and their effects on constructed facilities. Four topics illustrating these developments are selected and discussed in more detail

Comparison Between Clean Sand Liquefaction Charts Based on Penetration Resistance and Shear Wave Velocity

A comparison is conducted between clean sand liquefaction charts based, respectively, on normalized point penetration resistance in CPT static cone tests (qc1N) and shear wave velocity (Vs1). Examination of the shape of these field-calibrated curves, review of the factors influencing liquefaction resistance in the laboratory, field correlations between qc1N and Vs1, and field and laboratory evidence related to some of the factors influencing cone penetration resistance and shear wave velocity in sands, are all used in the discussion. It is concluded that the difference between the shapes of the two charts at the high end may be due - at least partially - to lateral stress effects associated with overconsolidation and preshaking, which are known to increase liquefaction resistance, and specifically to the higher sensitivity of the penetration resistance to the value of the coefficient of lateral stress at rest, K0

Recent Studies on Seismic Centrifuge Modeling of Liquefaction and Its Effects on Deep Foundations

The effects of liquefaction on deep foundations are very damaging and costly, and they keep recurring in many earthquakes. The first part of the paper reviews the field experience of deep foundations affected by liquefaction during earthquakes in the last few decades, as well as the main lessons learned. The second part of the paper presents results of physical modeling of deep foundations in the presence of liquefaction conducted mostly in the U.S. and Japan in the 1990’s, with emphasis on the work done by the authors and others at the 100 g-ton RPI centrifuge. Centrifuge models of instrumented single piles and pile groups embedded in both level and sloping liquefiable soil deposits have been excited in-flight by a suitable base acceleration. End-bearing and floating piles with and without a pile cap, with or without a mass above ground, free at the top or connected to a lateral or rotational spring to simulate the superstructure\u27s stiffness, with the foundation embedded in two- or three-layer soil profiles, have been tested. Tests with a mass above ground have allowed backfiguring the degradation of the lateral resistance of the loose saturated sand against the pile as the soil liquefies, while tests in sloping ground without a mass have allowed studying the effect of lateral spreading. Interpretations of these centrifuge experiments and their relation to field observations, soil properties, theory and analytical procedures are also discussed

Recent Studies on Seismic Centrifuge Modeling of Liquefaction and Its Effects on Deep Foundations

The effects of liquefaction on deep foundations are very damaging and costly, and they keep recurring in many earthquakes. The first part of the paper reviews the field experience of deep foundations affected by liquefaction during earthquakes in the last few decades, as well as the main lessons learned. The second part of the paper presents results of physical modeling of deep foundations in the presence of liquefaction conducted mostly in the U.S. and Japan in the 1990’s, with emphasis on the work done by the authors and others at the 100 g-ton RPI centrifuge. Centrifuge models of instrumented single piles and pile groups embedded in both level and sloping liquefiable soil deposits have been excited in-flight by a suitable base acceleration. End-bearing and floating piles with and without a pile cap, with or without a mass above ground, free at the top or connected to a lateral or rotational spring to simulate the superstructure\u27s stiffness, with the foundation embedded in two- or three-layer soil profiles, have been tested. Tests with a mass above ground have allowed backfiguring the degradation of the lateral resistance of the loose saturated sand against the pile as the soil liquefies, while tests in sloping ground without a mass have allowed studying the effect of lateral spreading. Interpretations of these centrifuge experiments and their relation to field observations, soil properties, theory and analytical procedures are also discussed

Inelastic Seismic Response of San Fernando and Santa Felicia Dams

A simplified method of inelastic seismic analysis of earth dams developed by the authors is used to study the response of the San Fernando and Santa Felicia dams to accelerograms recorded in the 1971 San Fernando Earthquake. The method involves two separate stages. In stage I, the dam is discretized into finite elements and is subjected to horizontal static inertia-like forces; its nonlinear deformation is computed using a plane strain code, while the applied horizontal forces are gradually increased until large enough strains develop in most elements of the dam. The results of this analysis are utilized to derive realistic nonlinear stress-strain relationships for layer super-elements consisting of horizontal rows of finite elements. Then, in stage II of the analysis, the dam is discretized as a one-dimensional layered triangular shear beam, in which each layer\u27s constitutive relation stems from the nonlinear stress-strain super-element relation determined in the previous stage. The dynamic response of the dam is then computed using (with small modifications) existing nonlinear shear beam formulations. The results of the analysis for San Fernando and Santa Felicia Dams are presented and compared with the results of two-dimensional equivalent-linear and kinematic-plasticity methods. Considerable insight is gained into the nature of the nonlinear seismic response of embankment dams

Foundation-Soil-Inclusion Interaction Modelling for Rion-Antirion Bridge Seismic Analysis

The Rion-Antirion Bridge in Greece will span a total length of 352 1 m, which includes a five span cable-stayed bridge 2252m in length and two approach viaducts. Upon completion in 2004, the bridge will be the longest cable-stayed bridge in the world. The main factors affecting the foundation design involve high seismicity, poor in-situ soil conditions, deep sea water (65m) and high ship impact force. These factors called for an innovative foundation design for each of the 90m diameter piers by the foundation designer, Geodynamique et Structure (GDS) from France. The proposed design consists of vertical open-ended steel cylinders (called “inclusions”), 25 to 30m long and 2m in diameter, which will reinforce the in-situ soils. The inclusions are to be spaced at 7 to 8m beneath each pier footing supporting a 230m tall pier and pylon structure. These inclusions are not connected structurally to the footing. Beneath each footing is to be placed a layer of gravel in which the inclusion heads are to be embedded. The interface between the pier base and gravel is to serve as a sliding shear fuse under extreme earthquake loading, involving a base isolation concept. This design was checked independently by the Checker - Buckland & Taylor Ltd. (B&T), using nonlinear finite element analyses of the foundation and soil subjected to equivalent seismic or ship impact loading consisting of a horizontal monotonic or cyclic force acting at a representative height (lever arm) above the seabed. The failure mechanisms observed in centrifuge model tests and in field sliding tests of the footing were closely examined and compared with the failure behavior predicted by the finite element soil-structure interaction modeling. The hysteretic damping characteristics of the foundation under horizontal cyclic loading obtained from the above analyses were used in the dynamic global bridge seismic analysis. The Checker’s independent analyses confirmed the viability of the proposed design