CASE STUDIES OF IN-SITU STRUCTURE OF NATURAL SEDIMENTARY CLAYS
2000 年 40 巻 3 号 p. 87-100
詳細
2000 年 40 巻 3 号 p. 87-100
Natural sedimentary clays exhibit ageing effects on their behaviour when subjected to both consolidation and shearing. Attempts to characterising the in-situ 'structure'of soft marine clays have been made in case studies performed in Ariake (Japan) and in Bangkok (Thailand), each showing a typical profile of aged clay-structure with depth reflecting its site-specific geological consolidation history. In each site, profiles of Atterberg limits, natural water content, overconsolidation ratio (OCR), quasi-elastic shear modulus Gmax and the undrained shear strength cu with depth were attained from various laboratory tests, together with the a comparable profile of quasi-elastic shear modulus from insitu seismic survey Gf. Quantitative assessment of the aged clay-structure was made by using two different measures, metastability index MI (G) and the soil constant reflecting structure S (Jamiolkowski et al., 1994). The profiles of MI (G) and the S-value with depth were both determined based on the corresponding Gmax behaviour of the reconstituted sample. "Disturbance"of laboratory samples retrieved by using two different samplers (i.e., Laval and Japanese thin-walled samplers) with two different sampling techniques (i.e., pre-boring and displacement methods) was discussed. A new approach to estimate cu"in the ground", termed by the authors the MILK (Metastability Index coupled with Laboratory Ko test) method, is proposed. A trial of the MILK-method is demonstrated in soft Bangkok clay, the texture of which is similar to "soft cheese".
