Compressibility characteristics of clays in the Red River Delta

Abstract

The Red River Delta (RRD) is the second largest delta in Vietnam and is a significant economic zone in the country, encompassing important cities and economic zones. Geologically, the delta consists of clay layers distributed all over its area, which strongly impact the foundation designs of the infrastructure system (e.g., highways, industrial parks, harbors). However, up to date, there were no comprehensive studies on the compressibility characteristics of the clays in the delta. This study presents a primary study on some compressibility characteristics of clays in the whole delta with an emphasis on the use of CPTu data in the interpretation. For this, high-quality field and laboratory test results obtained from four research test sites and eight project sites were analyzed to depict the characteristics. The results indicate that the clays in the delta are typically soft to medium stiff and normally consolidated to slightly overconsolidated, which represent typical characteristics of young Holocene deposits. The compression index (Cc) of the clays was found to have good correlations with natural water content (Wn) or in-situ void ratio (e0). The ratio of radial coefficient of consolidation from a consolidation test with a central drain (CD) to the vertical coefficient of consolidation from the standard consolidation test (i.e., cr,CD/cv) from the 4 research test sites is on average 2.76 (log t method) and 2.32 (root t method) and these average ratios are found typical for deltaic soil deposits. The correlations for the remolded samples indicate that the drainage type has a strong influence to the induced coefficients of homogeneously remolded soils. Results from this study help geotechnical engineers have a general view on the compressibility characteristics of the clays in the delta, which in turn helps secure optimal foundation design solutions.