**1. Introduction**

The study on the geomechanical behavior of bio-cemented Sydney sand was carried out using unconfined compression strength (UCS) tests and triaxial tests. To date there have been limited numbers of triaxial tests reported on soil cemented by microbes, and owing to differences in soil type and cementation methodology, these have provided variable results on the potential of bio-cementation. Part of the variability in behavior is a result of the widely used method of injecting bacterial solutions into sand to create the cementation. The injection process leads to heterogeneity in the distribution of calcite and hence to variability in the mechanical response and permeability of the bio-cemented soil. The mixing technique was used to create consistent and coherent bio-cemented samples and to overcome the difficulties of interpretation faced by previous researchers [1–3]. It has been suggested that the injection technique targets the contact points between the particles, which

is beneficial for cementing, and comparisons are made between mixed samples in this study and other studies where injection has been used to explore this hypothesis. The small strain shear stiffness has been used as an indicator to evaluate the success of bio-cementation [4], and shear wave velocity was monitored in this study to explore the influences of cement level and stress on the data and the ability to predict the success of bio-cementation.

The discussion in this chapter concentrates on:


iv.The influence of calcite content on the strength and stiffness
