Shear strength comparison of the natural and reconstituted form of Upper Globigerina Limestone in the undrained state using triaxial testing

Abstract

The Upper member of the Globigerina limestone formation is a peculiar sedimentary ground material found within the Maltese stratification, which poses difficulties in classification as it can be considered both a hard soil and a soft rock. Geologically, the Upper Globigerina Limestone is one of the weakest layers in the Maltese stratigraphy. However, currently there is very limited literature on the geotechnical engineering behaviour of this material. Such material is well-known for causing foundation issues, and many areas across Malta and Gozo are surmounted on this ground material. Leroueil and Vaughan (1990) and Burland (1990) outlined that natural sedimentary deposits have a bonded structure and that the strength and stiffness of these deposits cannot be fully explained by void ratio and stress history alone. They emphasized that the soil's structure plays an equally significant role in influencing the material’s mechanical behaviour. This theory will be further explored by comparing the mechanical behaviour of the soil in both its intact state, which retains structure, and its destructured state, which lacks such structure. This comparison will highlight the impact the soil's structure has on this material’s mechanical properties. Multiple triaxial tests were conducted to compare the shear strength and the mechanical behaviour of the Upper Globigerina Limestone in both its natural state and its reconstituted equivalent, under undrained conditions. These comparisons enabled determination of how the observed results align with the theory mentioned by Leroueil and Vaughan (1990) and Burland (1990). Additionally, this analysis will offer valuable insights into the mechanical behaviour of this unique facies within the Maltese stratigraphy when subjected to load under isotropic, undrained conditions.