Prediction of Compressibility Characteristics of In-situ Cohesive Soil using Reconstituted Sample

Md. Kausar Alam, Naveel Islam, Md. Zoynul Abedin, Rajib Dey, Mohammad Shariful Islam

In the proceedings of: GeoSt. John's 2019: 72nd Canadian Geotechnical Conference

Session: Laboratory Testing

ABSTRACT: Collecting undisturbed soil samples are essential in determining the compressibility of cohesive soils. The challenges of collecting good quality soil samples at significant depths has been well documented in the literature. However, reconstituted samples can be prepared using disturbed samples which can provide an insight on the compressibility nature of this cohesive soil. Limited research has been carried out focusing on preparation of reconstituted soil cakes in the laboratory which could simulate in-situ stress conditions. A modified oedometer mould has been developed to prepare the reconstituted soil cakes for this purpose. Soil slurries were prepared mixing natural clay powder specimens thoroughly with fixed portions of sand or bentonite clay (as an admixture) and water (near liquid limit). A number of test specimens with varying liquid limits were prepared. The prepared soil slurry samples were placed in the modified oedometer mould and consolidated applying varying effective stresses. The soil cakes prepared were used as consolidation test specimens for one dimensional consolidation tests. A number of consolidation tests were performed as per ASTM D2435/D2435M-11. The consolidation behavior and parameters obtained from these test results were compared to the undisturbed samples as well as established relationships from the literature.

RÉSUMÉ: Le prélèvement d'échantillons de sol non perturbés est essentiel pour déterminer la compressibilité des sols cohérents. Les difficultés rencontrées pour collecter des échantillons de sol de bonne qualité à des profondeurs significatives ont été bien documentées dans la littérature. Toutefois, les échantillons reconstitués peuvent être préparés à partir d'échantillons perturbés, ce qui permet de mieux comprendre la nature de compressibilité de ce sol cohérent. Des recherches limitées ont été menées sur la préparation en laboratoire de tourteaux reconstitués qui pourraient simuler des conditions de stress in situ. Un moule oedométrique modifié a été mis au point pour préparer les tourteaux reconstitués à cette fin. Les boues de sol ont été préparées en mélangeant soigneusement les échantillons de poudre d'argile naturelle avec des portions fixes de sable ou d'argile bentonite (en mélange) et d'eau (près de la limite de liquidité). Un certain nombre de spécimens avec des limites de liquidités variables ont été préparés. Les échantillons de boue de sol préparés ont été placés dans le moule à oedomètre modifié et consolidés en appliquant diverses contraintes effectives. Les tourteaux préparés ont été utilisés comme éprouvettes de consolidation pour des essais de consolidation unidimensionnels. Un certain nombre d'essais de consolidation ont été effectués selon les normes ASTM D2435/D2435M-11. Le comportement de consolidation et les paramètres obtenus à partir des résultats de ces tests ont été comparés aux échantillons non perturbés ainsi qu'aux relations établies dans la littérature. 1. INTRODUCTION The performance of foundations constructed over compressible clay soils may experience excessive settlements when not properly designed. In order to support the design process, it is critical that the compressibility properties of the clay material be well known. Therefore, undisturbed (UD) soil samples should be collected from field and tested in the laboratory to obtain the appropriate consolidation parameters (i.e. compression index, swell index, preconsolidation pressure etc.). Collecting and transporting UD soil samples can be challenging, costly and depending the soil sensitivity, samples are often subjected to varying degrees of disturbance during transportation and extraction. To overcome these problems, the concept of a reconstituted (RC) soil sample was introduced in the past to simulate the behavior of a normally consolidated clay sample. RC samples were used to assess the influence of soil structure on mechanical behaviour of natural sedimentary clays (e.g. in Nagaraj & Srinivasa Murthy, 1986; Burland, 1990; Hong & Tsuchida, 1999; Liu & Carter, 1999; Chandler, 2000; Cotecchia & Chandler, 2000). The quality of a RC soil sample is greatly influenced by the method of sample preparation and size of the mould used to prepare soil samples (i.e. the mould diameter). A number of studies were recently completed (e.g. Cerato & Lutenegger, 2004; Yin & Miao, 2015; Shi & Herle 2015), where advanced setups for the preparation of RC soil samples are discussed. However, the equipment used is prohibitively expensive for typical geotechnical studies. The present study introduces a simplified sample preparation method, which can be successfully used to prepare good quality RC clay samples. UD clay samples

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Cite this article:
Md. Kausar Alam; Naveel Islam; Md. Zoynul Abedin; Rajib Dey; Mohammad Shariful Islam (2019) Prediction of Compressibility Characteristics of In-situ Cohesive Soil using Reconstituted Sample in GEO2019. Ottawa, Ontario: Canadian Geotechnical Society.

@article{Geo2019Paper232,author = Md. Kausar Alam; Naveel Islam; Md. Zoynul Abedin; Rajib Dey; Mohammad Shariful Islam,title = Prediction of Compressibility Characteristics of In-situ Cohesive Soil using Reconstituted Sample,year = 2019}