# Water Retention Curve of Biocemented Sands Using MIP Results
## 4 Results and Discussion  
### Oedometer Tests  
The compressibility curves of the oedometric tests are presented in Figure 3 for the samples with and without treatment (bacteria and water, respectively). The elastoplastic and elastic compressibility indexes, Cc and Cs, are presented in Table 1 for the saturated and unsaturated tests (when wetting until full saturation was applied 1200 kPa). The initial suction of the samples after drying in the laboratory environment is also presented in Table 1, confirming that they were very similar before and after the treatment.  
It is worth noting that the high collapse deformation observed for the untreated soil after full saturation is highlighted in Figure 3a. The biochemical soil behaves like the untreated soil because the Cc is larger for the full saturated state than for the unsaturated one [39]. The relationship between Cc for the saturated and unsaturated samples is 4.0 for the untreated samples and 1.5 for the biochemical ones. For the treated soil, both suction and the biocement bonds maintain the metastable structure during loading in the unsaturated state [44; 45; 46], while the biocement continues playing this role in the saturated sample; this explains the lower amount of contrast in the Cc values for the treated soil. The presence of the bioemented bonds also increases the values of the yielding stresses, \(\sigma^{\prime}y\) (see Table 1).  
The values of Cc found are larger for the bioemented soil than for the untreated soil independently from suction--a result also found by others [47; 48; 49]. It was explained by structure loss caused by bond breakage during the increment of vertical stress. This is also observed in structured soils when progressive bond breakage is occurring during loading [50]. There is also the possibility of bioement dissolution after full saturation if vaterite is precipitated [51].  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & **Sample** & \(\delta\epsilon_{\text{vol}}\) **(\%)** & **Cc** & **Cs** & \(\kappa\) & \(\lambda\)**(s)** & \(\sigma^{\prime}y\) **(kPa)** \\ \hline Untreated soil—water (initial suction s = 67.5 MPa) & Saturated & – & 0.137 & 0.014 & 0.034 & 0.316 & 80 \\ \hline Bioemented soil—bacteria (initial suction s = 62.7 MPa) & Saturated & – & 0.162 & 0.013 & 0.031 & 0.372 & 100 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Results of the oedometer tests.  
Figure 3: Oedometric curves: (**a**) untreated samples and (**b**) bioemented samples.  
The elastic compressibility indexes, Cs, computed for all cases are almost the same--a result expected for the untreated soil [39]. For the biocemented soil, the presence of structure is not marked probably because the amount of biocenter precipitated was small.  
With Cc and Cs, it was possible to determine the elastoplastic and elastic compressibility index for changes in the net mean stresses, \(\lambda\) and \(\kappa\), respectively [39]. The collapse deformations when full saturation was applied under 1200 kPa are also present in Table 1. Their value decreases with the treatment, proving its efficiency to treat the collapsible soils [9; 10]. The elastic compressibility index for suction changes, \(\kappa\)s, was not computed, because these collapse deformations are not elastic.