Experimental investigation on the mechanical and hydraulic properties of urease stabilized fine sand for fully permeable pavement

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Experimental investigation on the mechanical and hydraulic properties of urease stabilized fine sand for fully permeable pavement


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Experimental investigation on the mechanical and hydraulic properties of urease stabilized fine sand for fully permeable pavement

Abstract

A growing body of evidence suggests that the increase of permeability results in  reduced   strength  and bearing capacity of  subgrade. A new microbiological stabilizing method,        known as  microbial induced calcite precipitation (MICP),  was induced into stabilization        of  the subgrade for  fully permeable  pavement  in  this study. This   study explored the       mechanical and hydraulic properties of unsaturated and saturated fine  sand soil  stabilized   by  MICP technology. Instead of bacteria, urease was directly induced into fine  sand with modulus of unsaturated urease stabilized soil  were lower under the same CaCO3  or cement  content. What stands out in  this study is that the saturated urease stabilized soil  was not  sensitive to water and had relatively higher strength. In addition, the hydraulic conductiv- ity of urease stabilized soil  was significantly higher than that of cement stabilized soil.  This study developed a potential subgrade improvement technology for  possible application in fully permeable pavement. Urease stabilizing method could be  used to help increase the strength and maintain a high hydraulic conductivity

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  1. Introduction

Recently, with the development of urbanization, more and more areas are  covered by impermeable pavements or other

۵۰         buildings (Turco et al., 2017). The  weak infiltration and evaporation capacity of urban cities lead to  the increase of surface

۵۱         runoff and the decrease of groundwater recharge. Moreover, due to  the climate change, the extremely short-term strong

۵۲         rainstorms happen frequently, which is a grand challenge to  the drainage system of the urban cities (Min  et al., 2011). As

۵۳        a low  impact development (LID) technology, permeable pavement can  reduce impermeable surfaces and lower the adverse

۵۴         effects on the environment (Scholz and Grabowiecki, 2007). One of types of permeable pavement, fully permeable pavement

۵۵         allows rainwater to infiltrate into its  surface, base and subgrade. The infiltration and scour of water to  pavement structure

۵۶         result in  reduced stability, and the subgrade is mostly affected by  water (Zhao,  ۲۰۱۰). Under the influence of water and

۵۷       repetitive load,  the subgrade will  easily lose  its strength and stability, resulting in the damage of the entire pavement struc-

۵۸          ture. Therefore, it is necessary to explore the stabilizing methods of permeable soil  for fully  permeable pavement. Previous

۵۹         studies have reported that soil  stabilization techniques mainly include adding natural or synthetic materials (Iyengar et al.,

۶۰         ۲۰۱۳; Zhao  et al., 2019), chemical grouting method or deep mixing with cement or lime (Bagheri et al., 2013; Bessa  et al.,

۶۱         ۲۰۱۵; Falayi  et al., 2016), sand pile  or gravel pile  reinforcement, etc.  Among these methods, cement stabilizing method is

۶۲        one  of the most effective methods to  reinforce the soil.  Although the cement stabilized soil  has  the characteristics of high

۶۳         strength and low shrinkage, its low permeability obviously cannot meet the functional requirement of drainage through sub-

۶۴         grade of fully  permeable pavement.

۶۵               In 1973, Boquet (Boquet et al., 1973) isolated bacteria from soil and found that bacteria could induce carbonate deposition

۶۶         during metabolism. Subsequently, the researchers used microorganism Sporosarcina pasteurii (S.  pasteurii) producing

۶۷         urease to  carry out  experimental research (Sharaky et al., 2018). By providing them with nutrients with calcium ions  and

۶۸         nitrogen sources, calcium carbonate crystals with cementitious effect were precipitated rapidly. The  microbial mineraliza-

۶۹         tion technology is known as  Microbial Induced Carbonate Precipitation technology (MICP) (Whiffin, 2004). The  chemical

۷۰         reaction process can  be  expressed by the following chemical reaction equations (Eqs. (1)  and (2))

۷۱

۲þ               þ

۷۳                         COðNH2 Þ۲  þ H2 O ! CO3    þ ۲NH4                                                                                                                                                                                                                              ð۱Þ

۷۴

۳

۷۶                         Ca2þ  þ CO2    ! CaCO3                                                                                                                                                                                                                                                            ð۲Þ

۷۷                Several studies have documented that the unconfined compressive strength of the soil  stabilized by MICP method could

۷۸         reach 150  kPa–۳۴ MPa  (Whiffin, 2004). Recently investigators have examined the relationship between calcium carbonate

۷۹         precipitation produced by  MICP  and the unconfined compressive strength, shear strength  and internal friction angle

۸۰         (Harkes et al.,  ۲۰۰۸; Van  Paassen, 2009; Van  Paassen et al.,  ۲۰۰۹; Airey  and Duraisamy, 2012; Montoya and DeJong,

۸۱         ۲۰۱۵). It has  been noted that the MICP method is more effective to  maintain the original permeability of the natural soil.

۸۲        A number of studies have demonstrated that the biologically stabilized sand could maintain a high hydraulic conductivity

۸۳        of  ۱٫۰     ۱۰    ۶–۵٫۰    ۱۰–۳  cm/s (Cheng and Cordruwisch, 2014; Chou  et al.,  ۲۰۱۱; Keykha et al.,  ۲۰۱۵). Cheng and Cord-

۸۴          Ruwisch (2013) suggested that CaCO3  produced by the MICP also  affected the hydraulic conductivity whereas induced a rel-

۸۵         atively small volume change of soil  pores compared with other methods.

۸۶               It has  been reported that it is more effective when bacteria are directly used to treat soil. However, the bacteria are easy to

۸۷         decrease sharply and die  due to  many factors, such as  temperature,  urea concentration, pH,  etc.  (Ma,  ۲۰۱۳a; Zhao,  ۲۰۱۴;

۸۸         Gunjo et al., 2018) According to  the reaction mechanism of the MICP, urease plays a vital role  in  the process of bacteria-

۸۹         catalyzed urea hydrolysis (Zhao,  ۲۰۱۴). Few  studies have focused on  the experimental methods mainly including grouting

۹۰         injection method and premixing method (Mujah et al., 2016). The reaction process of grouting injection method is control-

۹۱         lable and the utilization rate of materials is higher (Ma, 2013a; Whiffin et al., 2007; Cheng et al., 2013; DeJong  et al., 2006).

۹۲        However, it suffered from uneven precipitation distribution of CaCO3. The premixing method caused a low  strength whereas

۹۳         produced the uniform distribution of CaCO3  (Yasuhara et al., 2012).

۹۴                Taken together, these studies support the notion that MICP technology is an effective approach to improve the stability of

۹۵         the subgrade. However, previous studies have failed to  demonstrate effective stabilization on  fine  sand and suffered from

۹۶         poor integrality. Mitchell (Mitchell and Santamarina, 2005) found that bacteria have a certain volume of 0.3–۰٫۵ µm. There-

۹۷        fore,  when the particle size  was  less  than 0.4 µm,  it was  not  conducive to  the flow  of bacterial solution resulting in lower

۹۸        CaCO3  content and poor stability. Rebatalanda (2007) found that the CaCO3  content increased with the particle size.  Zhao

۹۹        et al. (2014) demonstrated that the UCS of soil sample with a particle size  of 0.46  mm could reach 1320 kPa, the UCS of soil

۱۰۰         sample with a particle size  of 0.33  mm reduced to  ۵۱۰  kPa, and the UCS only  reached 150  kPa using tinier particle size.  In

۱۰۱         addition, the research to date has  not  been able  to applied into fully permeable pavement. The specific objective of this study

۱۰۲        was  to develop a potential subgrade improvement technology for possible application in fully  permeable pavement. In this

۱۰۳         study, plant enzymes by artificial extraction was  used to conduct experimental study. The mechanical and hydraulic prop-

۱۰۴         erties of unsaturated and saturated specimens were investigated. In addition, ordinary Portland cement was  mixed into fine

۱۰۵         sand and compared with urease stabilized method.

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