Effect of cementation on the small-strain parameters of sands A.L. Fernandez and J.C. Santamarina Abstract: Natural cementation affects the properties of soils, the interpretation of in situ and laboratory test results, and the selection of criteria for geotechnical design. In this paper, published experimental studies are reviewed, a microscale analysis is presented of the effect of cementation on small-strain stiffness for distinct stress–cementation histories, and the effect of cementation on small-strain velocity and damping is experimentally studied. Observations include the prevailing effects of cementation over effective stress, the coexistence of frictional and viscous losses, and the effects of decementation when the medium is unloaded from the level of confinement prevailing during cementa- tion. Key words: wave velocity, seismic response, stiffness, damping, sampling effects, loading history. Résumé : La cimentation naturelle affecte les propriétés des sols, l’interprétation des résultats des essais in situ et en laboratoire, et la sélection de critères pour la conception géotechnique. Dans cet article, des études expérimentales publiées sont passées en revue, suivies par une analyse de l’effet de la cimentation sur la rigidité à faible déformation pour les histoires distinctes de cimentation de contraintes. Ensuite, on étudie expérimentalement l’effet de la cimentation sur la vitesse à faible contrainte et sur l’amortissement. Les observations comprennent les effets de la cimentation prévalant sur la contrainte effective, la coexistence des pertes visqueuse en frottement, et les effets de la cimentation lorsque le milieu est déchargé par rapport au niveau de confinement prévalant durant la cimentation. Mots clés : vitesse d’ondes, réponse sismique, rigidité, amortissement, effets de l’échantillonnage, histoire des contraintes. [Traduit par la Rédaction] Notes 199 1. Introduction Diagenesis begins at the time of soil deposition and con- tinues while the sediment becomes a sedimentary rock. It may involve changes in the surface texture of the material, changes in fabric, the formation of interparticle bonds, and the change in internal distribution of contact forces. Most natural soil deposits possess some degree of cementation re- sulting from the deposition or precipitation of cementing agent around and at particle contacts. Some of these agents lithify the soil without any modification of the detrital grains. However, other agents produce more complex physicochemical reactions, including changes in the original sediment (Mitchell 1993; Larsen and Chilingar 1979; Blatt 1979). Cementation, caused by either natural or artificial soil sta- bilization processes, can have a remarkable influence on the small- and large-strain behavior of soils. Hence, cementation effects should be taken into account in the design of founda- tions, analysis of the dynamic response of the subsurface, and evaluation of stability problems (see, for example, Arkin and Michaeli 1985; and Poulos 1988). The study of cemented soils in the laboratory demands special specimen preparation and testing procedures. Natu- ral, lightly cemented soils can undergo partial and even com- plete decementation during sampling. On the other hand, the preparation of artificially cemented specimens in the labora- tory can be a challenging task; ideally, artificial specimen preparation and testing should simulate the in situ processes that caused cementation and its history. Two distinct stress– cementation histories can be identified: either the soil stra- tum is loaded first and cemented afterwards, or the soil is first cemented and then loaded. This paper reviews published experimental results related to the mechanical behavior of naturally and artificially ce- mented sands, presents a micromechanical analysis of the small-strain stiffness for different stress–cementation histo- ries, and presents an experimental study on the evolution of small-strain stiffness and damping during cementation and loading. Small-strain parameters do not affect ongoing ce- mentation–decementation processes. Furthermore, the em- phasis on small-strain parameters reflects the increased interest for near-surface characterization with seismic waves, and the potential identification of lightly cemented sites with seismic methods. 2. Mechanical properties: prior studies The small- and large-strain behavior of soils are affected by cementation. A brief review of published data follows. Can. Geotech. J. 38: 191–199 (2001) © 2001 NRC Canada 191 DOI: 10.1139/cgj-38-1-191 Received March 3, 1999. Accepted June 1, 2000. Published on the NRC Research Press Web site on February 19, 2001. A.L. Fernandez and J.C. Santamarina. Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0355, U.S.A.