# Effects of Cement Treatment on Mechanical Properties and Microstructure of a Granite Residual Soil
## 3 Results and Analysis
### Compressibility and Vertical Yielding Pressure  
Oedometric compression curves of the saturated untreated and cement-treated GRSs cured to 7 d and 28 d are shown in Figures 9 and 10, respectively. The \(e-\)log\(\sigma_{\rm{v}}\) relationship is nonlinear in all the cases, indicating initial over-consolidation states of the specimens due to compaction. The untreated specimen entered the normal consolidation state as the vertical pressure exceeded 400 kPa (see Figure 9). However, the states of the treated specimen cannot be confirmed due to the moderate stress level (see Figure 10). Nevertheless, the compression index (\(C_{\rm{c}}\)) of the specimens was determined via linear fitting of the \(e-\)log\(\sigma_{\rm{v}}\) relationship in the range of \(\sigma_{\rm{v}}>400\) kPa (for \(C_{\rm{vi}}=0\)-4%) or \(\sigma_{\rm{v}}>800\) kPa (for \(C_{\rm{vi}}=5\%\)). The unloading-reloading cycle yielded a hysteresis loop of the \(e-\)log\(\sigma_{\rm{v}}\) relationship; its diagonal slope (absolute value) was accepted as the rebound index (\(C_{\rm{r}}\)) of the specimen. Given the subjectivity of Casagrande method [36], an alternate approach was employed to determine the vertical yielding pressure (\(\sigma_{\rm{y}}\)) of the specimen [37]. As all the compression curves are horizontal in the case of \(\sigma_{\rm{v}}<12.5\)-25 kPa, the vertical pressure at which the intrinsic compression line (ICL) intersects the initial void ratio was deemed to be the vertical yielding pressure of the specimen (see Figures 9 and 10).  
Figure 8: Secant modulus (\(E_{50}\)) of saturated untreated and cement-treated GRSs at various cement contents and curing times. (**a**) Changes in \(E_{50}\) with cement content at various curing times; (**b**) Changes in \(E_{50}\) with curing time at various cement contents.  
Figure 9: \(e-\)log\(\sigma_{\rm{v}}\) relationship of saturated untreated GRS.  
The dependence of the compression index, rebound index, and vertical yielding pressure on the cement content and curing time is shown in Figure 11. It is observed that, for a given cement content, the specimen cured to 28 d has a slightly larger compression index compared with the case of 7 d (see Figure 11a). As the volumetric cement content increased to 2%, the compression index of the specimens cured to 7 d and 28 d dropped sharply from 0.17 to 0.03 and 0.04, respectively. As the volumetric cement content exceeded 2%, the variation of the compression index with the cement content became less significant. The rebound index of the treated specimens is much smaller than that of the untreated one (0.003-0.01 versus 0.028) and changes in the rebound index with the cement content and curing time are less significant (see Figure 11a). For a given cement content, the vertical yielding pressure of the specimens cured to 28 d is much higher than that of those cured to 7 d (see Figure 11b). For a given curing time, the vertical yielding pressure of the specimens decreased successively and was followed by a continuous increase as the volumetric cement content increased. The volumetric cement content at which the tendency reversed is 2-3%.