A Combination Method for Testing the Mechanical Properties of Ultra-Soft Fine-Grained Soils

Abstract

Abstract With the consumption of land resources and a shortage of land space, the exploration and use of the ocean have increased. However, a new type of geotechnical engineering problem has been encountered in the development of marine engineering: the problem of ultra-soft soils, such as the dredger fills extracted from sediments in coastal reclamation projects and submarine landslides formed by the movement of sediments. Ultra-soft soils usually have very low strength with high water content, and flow easily. These features enable ultra-soft soils with high water content to exhibit physical properties of both solids and fluids. Reliably testing their mechanical properties presents new challenges for the traditional geotechnical test methods. To address these problems, a test method is proposed that combines a full-flow penetrometer test for soils and a rheological test for fluids. Kaolin samples with water content between 110 % and 157 % (approximately two to three times the liquid limit of kaolin) are tested as an example, and a detailed description and verification of the combination test method are presented. The results show that the combination test method can reliably measure the undrained shear strength of an ultra-soft soil at a wide range of shear strain rates in a short time, which is difficult for traditional methods. The combination test method proposed in this study provides a new reference for mechanical property testing of ultra-soft soils and hazard assessments related to ultra-soft soils.