The goal of this article is to revise several aspects of the well-known classification of landslides, developed by Varnes (1978). The primary recommendation is to modify the definition of landslide-forming materials, to provide compatibility with accepted geotechnical and geological terminology of rocks and soils. Other, less important modifications of the classification system are suggested, resulting from recent developments of the landslide science. The modified Varnes classification of landslides has 32 landslide types, each of which is backed by a formal definition. The definitions should facilitate backward compatibility of the system as well as possible translation to other languages. Complex landslides are not included as a separate category type, but composite types can be constructed by the user of the classification by combining two or more type names, if advantageous.

The Varnes classification of landslide types, an update

Soils can rarely be described as ideally elastic or perfectly plastic and yet simple elastic and plastic models form the basis for the most traditional geotechnical engineering calculations. With the advent of cheap powerful computers the possibility of performing analyses based on more realistic models has become widely available. One of the aims of this book is to describe the basic ingredients of a family of simple elastic-plastic models of soil behaviour and to demonstrate how such models can be used in numerical analyses. Such numerical analyses are often regarded as mysterious black boxes but a proper appreciation of their worth requires an understanding of the numerical models on which they are based. Though the models on which this book concentrates are simple, understanding of these will indicate the ways in which more sophisticated models will perform.

Soil Behaviour and Critical State Soil Mechanics

RELATIONSHIPS of soil water tension and hydraulic conductivity with soil water content are needed to quantify plant available water and to model the move-ment of water and solutes in and through soils. Field and laboratory measurement of these hydraulic soil proper-ties is very difficult, laborous, and costly. To provide the best estimates possible from previous analyses, a com-prehensive search of the literature and data sources for hydraulic conductivity and related soil-water data was made in 1978. From this search, data for 1,323 soils with about 5,350 horizons from 32 states were assembled. From the data, the Brooks and Corey water retention parameters, soil water retention volumes at 0.33 bar and 15 bar, total porosity, and saturated conductivities for the major USDA soil textures classes were developed. Also, relationships for predicting water retention volumes for particular tensions and saturated hydraulic conductivities based on soil properties are presented.

Estimation of Soil Water Properties

Two aspects of seismically-induced liquefaction are discussed which are of vital engineering significance: the triggering condition and the consequences of liquefaction. The triggering condition is examined with respect to liquefaction analysis, note being taken of the onset condition which is governed by cyclic strength. Consequences of liquefaction are discussed with respect to post-seismic stability analysis, in which the residual strength plays a major role. Procedures used for liquefaction analysis based on the results of in situ sounding tests are introduced, and the applicability of this method for estimating associated ground settlements is discussed. The evaluation of residual strength requires a better understanding of undrained sand behaviour. Results of extensive laboratory rests on Japanese standard sand are examined and new index parameters are proposed to quantify undrained sand behaviour better. The results of laboratory tests on silty sands are examined in the same way. AH the results are...

Liquefaction and flow failure during earthquakes.

The dilatancy and strength of an assembly of individual particles in contact when subjected to a deviatoric stress system is found to depend on the angle of friction $\phi\_\mu$ between the particle surfaces, on the geometrical angle of packing, $\alpha$, and on the degree of energy loss during remoulding. The Mohr-Coulomb criterion of failure which is strictly applicable to a continuum is shown not to have general application to a discontinuous assembly of particles. A theoretical and experimental study of ideal assemblies of rods and uniform spheres establishes expressions for the relation between the rate of dilatancy and the maximum stress ratio for any ideal packing. The solution is extended to the case of a random assembly of irregular particles by investigating the conditions under which the mass dilates such that the rate of internal work absorbed in frictional heat is a minimum. Experiments on random masses of steel, glass, and quartz in which all the physical properties are measured independently show that the minimum energy criterion is closely obeyed by highly dilatant dense over-consolidated and reloaded assemblies throughout deformation to failure. An additional rate of energy has to be supplied to account for losses due to rearranging of loose packings, when the value of $\phi$ to satisfy the theory increases to $\phi\_f$ by an amount dependent on the degree of remoulding. The external stresses applied to an assembly are to be integrated over the $\alpha$-plane defined with reference to figure 14(a) as a plane of repetition of pattern over which the particles interlock, and the resulting forces are to be in equilibrium for sliding on particle interfaces at (45-$\frac{1}{2}\phi_f$) to the direction of the major principal stress. For the special case of no volume change these two planes are identical and the solution agrees then with that based on the Mohr-Coulomb theory. The well-known slip plane in drained discontinuous assemblies is proved to be the result of failure and nothing whatsoever to do with the peak strength. The findings are discussed in the light of previous contributions to the subject.

The stress-dilatancy relation for static equilibrium of an assembly of particles in contact

PHYSICAL PROPERTIES OF SOILS Index Properties of Soils Soil Exploration Hydraulic and Mechanical Properties of Soils THEORETICAL SOIL MECHANICS Hydraulics of Soils Plastic Equilibrium in Soils Settlement and Contact Pressure PROBLEMS OF DESIGN AND CONSTRUCTION Ground Improvement Earth Pressure and Stability of Slopes Foundations Settlement Due to Extraneous Causes Dams and Dam Foundations References Indexes

Soil mechanics in engineering practice

Synopsis The observational method, used so successfully by Terzaghi in applied soil mechanics, often permits maximum economy and assurance of safety, provided the design can be modified as construction progresses. The essential features of the method are set forth and examples are given of its application. The method is not without its pitfalls and limitations. It should not be used unless the designer has in mind a plan of action for every unfavourable situation that might be disclosed by the observations. The observations must be reliable, must reveal the significant phenomena, and must be so reported as to encourage prompt action. The possibility of progressive failure may introduce a serious element of uncertainty. In spite of the limitations, the potential for savings of time and money without sacrifice of safety is so great that every engineer who deals with applied soil mechanics needs to be informed of its principal features. La methode d'observation, utilisee avec tant de succees par Terzaghi pou...

Advantages and Limitations of the Observational Method in Applied Soil Mechanics

The significance of progressive failure in slides of natural or cut slopes is reviewed and qualitative methods for taking it into account are discussed. Nevertheless, it is concluded that present procedures do not permit reliable assessment of the factor of safety of natural or cut slopes under most conditions encountered in practice. This conclusion is illustrated by the history of a landslide that destroyed the Lower Baker Power Plant near Seattle. The failure occurred while the sliding mass was thought to be temporarily under control although remedial measures were being planned. The reliability of predictions is enhanced in old landslide areas, provided the existence of the old slide material is recognized.

Ralph B. Peck

Papers

Soil mechanics in engineering practice

Advantages and Limitations of the Observational Method in Applied Soil Mechanics

Stability of Natural Slopes

Stability of Natural Slopes

From Theory to Practice in Soil Mechanics