# Undrained Behavior of Microbially Induced Calcite Precipitated Sand with Polyvinyl Alcohol Fiber
## 1 Introduction  
Microbially induced calcite precipitation (MICP) has received considerable attention in recent years because it has the potential to replace ordinary Portland cement in geotechnical stabilization practices. In addition, significant environmental benefits might be achieved by reducing the carbon dioxide (CO\({}_{2}\)) otherwise required for manufacturing cement. MICP processing with ureolytic bacteria is a process based on the use of enzyme ureases and complementary chemicals (typically urea and calcium chloride). This is illustrated by the following reactions [1]:  
1. CO(NH\({}_{2}\))\({}_{2}\) + 2H\({}_{2}\)O \(\rightarrow\) 2 NH\({}_{4}\)\({}^{+}\) + CO\({}_{3}\)\({}^{2-}\)
2. CO\({}_{2}\) + H\({}_{2}\)O \(\rightarrow\) H\({}_{2}\)CO\({}_{3}\)
3. Ca\({}^{2+}\) + CO\({}_{3}\)\({}^{2-}\)\(\rightarrow\) CaCO\({}_{3}\)  
Intent on promoting pragmatic geotechnical applications of these biochemical conversions, a number of researchers [2; 3; 4; 5] have published studies on biocementation using MICP methods over the past two decades. At the same time, the engineering properties of MICP biocementation have also been investigated on multiple levels. For example, several investigations [6; 7; 8] have confirmed thatthe unconfined compressive strength (UCS) increases with the MICP-derived calcite content (CC). However, it has also been found that the hydraulic conductivity decreases as the CC increases [5; 9; 10]. Other researchers have evaluated bioccmentation using shear wave velocity [2; 11; 12], while yet another group of researchers have confirmed the levels of bioccmentation using triaxial [12; 13] and dynamic testing [1; 14]. In addition to MICP treatment, artificial fiber can be combined to improve the physical properties beyond those achieved with either cement-based processing (which typically shows brittleness and low strength [15]) or standard MICP treatment (which similarly tends to show brittleness [16]).  
[PERSON] et al. [17] recently published an article that addresses a similar addition of co-blended fibers to improve the MICP performance of sand bioccmentation, and reported on the use of homopolymer polypropylene multifilament fiber. This addition showed that suitable engineering properties were obtained with fiber additions of up to 0.3% fiber content by weight of sand. [PERSON] et al. [18] also reported similar MICP enhancements using polyvinyl alcohol (PVA) fiber. Their work revealed that the addition of PVA fiber increased the UCS and tensile strength of the MICP-treated sand by 30% and 160%, respectively. However, despite the various analyses of the engineering properties of bioccentations, bioccentations with fiber are not clearly understood.  
In this study, two different effects, calcite precipitation and fiber inclusion, were investigated in order to understand the engineering properties of bioccmentation by the MICP method using triaxial and permeability tests. The effect of calcite precipitation was evaluated for different CCs (0%, 2%, and 4%). The effect of fiber inclusion was compared for specimens with four different fiber contents (0%, 0.2%, 0.4%, and 0.6%) and the same CC (4.0%).