# Water Retention Curve of Biocemented Sands Using MIP Results
## 1 Introduction
Because the water retention curve is dependent on the pore size distribution, the information on pore size can naturally be used for its determination, and the data from mercury intrusion porosimetry (MIP) tests earn relevance. Data from mercury intrusion porosimetry tests can be used as an alternative to direct suction measurement for drying paths that use data from the intrusion of non-wetting mercury, considering it to be equivalent to air entry into the soil. This has been investigated by others [15; 28; 29; 30; 31; 32; 33; 34] mainly for clayey soils and is explored in this paper for sandy soils. Although it is assumed that the soil volume remains constant during mercury intrusion, for active clayey soils, the consideration of some deformation helps in regard to adjusting the WRC from MIP to experimental data [35]. As far as the authors know, the studies using MIP data to estimate the WRC were performed for soils with a significant fine fraction, and the adjustment was very successful for the small suctions range, below the air entry value [16]. However, for the entire suction range, the curve had to be corrected to consider soil deformation occurring during the measurement of WRC due to soil-water interaction, namely volume changes, which are not occurring during MIP tests because mercury is used instead of water [19; 36]. In fact, in clayey soils, the volume changes occur when mobilizing the water in the inter-aggregates (free, macrostructural water), which is between the air entry value and the residual water content, while almost no volume changes occur above the residual water content because it is when the water in the aggregates (adsorbed water) is mobilized, and the energy required is very high. For sandy soils, there is no adsorbed water by the sand particles (mainly quartz), and therefore no deformations are expected to occur as a result of the water-soil interaction explained by expansibility. However, sandy soils can also experience marked deformations due to changes in capillary forces, for example, when collapse occurs because suction is providing stability to their open structure. Anyway, the perfect adjustment of the curves from MIP and WRC is not expected, because some simplifications are adopted in MIP tests, such as (i) no deformations occur during the intrusion, (ii) pore geometry is characterized by a series of capillary cylindrical pores, (iii) all pores are connected and accessed by the mercury, and (iv) there is no influence of the air trapped in the pores or the presence of adsorbed water in the case of clay aggregates. To take some of these limitations into consideration, the model for the water retention curve presented in this paper considers the deformability of the soil during the intrusion, assuming an isotropic elastic behavior, until a minimum void ratio defined by the maximum volume of mercury intruded. The model was tested in this study to find the WRC of a sandy soil extracted from a slope before and after being treated by using biocementation. The model was calibrated by using data from oedometer tests performed to measure the saturated and unsaturated compressibility indexes of the soil. The definition of this model explores alternative ways to find information about the WRC when the equipment available is not able to measure low suctions. Therefore, the water retention curve was measured by using WP4 (suctions above 1 MPa) and mercury intrusion porosimetry tests, MIP. Complementary tests were also performed, such as permeability tests (saturated permeability), mineralogical analysis by X-Ray diffractometry, XRD, and visualization by using Scanning Electron Microscope, SEM), to confirm that biocementation occurred.