Compression behavior of MICP-treated sand with various gradations

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RESEARCH PAPER

Compression behavior of MICP-treated sand with various gradations Yang Xiao1,2,3 • Chang Zhao3 • Yue Sun3 • Shun Wang4 • Huanran Wu1,2,3 Hanlong Liu1,2,3



Hui Chen3



Received: 10 July 2020 / Accepted: 6 November 2020 Ó Springer-Verlag GmbH Germany, part of Springer Nature 2020

Abstract One-dimensional compression tests on quartz sands treated by microbially induced carbonate precipitation (MICP) were carried out to evaluate the effects of gradation and calcium carbonate (CaCO3) content on compression behaviors. The experimental results reveal that the compressibility of specimens increases with increasing coefficient of uniformity or decreasing CaCO3 content. The evolution of void ratio with vertical stress could be generally characterized into three stages based on the underlying mechanisms. The initiation of bond breakage occurs around vertical stress of 0.036 MPa, and the dominating mechanism transits to particle breakage around vertical stress of 8.3 MPa. Scanning electron microscope analyses demonstrate that bonding effect and coating effect of CaCO3 precipitation are responsible for the lower compressibility of MICP-treated specimen. The presence of small particles leads to more interparticle CaCO3 bonds whose breakage would still allow the small particles to fill the intercoarse-grain voids. Keywords Calcium carbonate  Compression index  Gradation  MICP  SEM

1 Introduction In recent years, microbially induced calcite precipitation (MICP), a new soil improvement technique, has attracted intense attention from scholars worldwide [12, 18, 72]. Sporosarcina pasteurii (UPB) produces urease during metabolism, and urea can be hydrolyzed by the enzyme to form carbonate and ammonium ions [7]. When calcium ions are supplied, they can combine with carbonate ions in solution to form crystals of calcium carbonate [13]:

& Huanran Wu [email protected] 1

Key Laboratory of New Technology for Construction of Cities in Mountain Area, Chongqing University, Chongqing 400045, China

2

State Key Laboratory of Coal Mine Disaster Dynamics and Control, Chongqing University, Chongqing 400030, China

3

School of Civil Engineering, Chongqing University, Chongqing 400045, China

4

Institute of Geotechnical Engineering, University of Natural Resources and Life Sciences, Vienna, Austria

2 NH2 CONH2 þ 2H2 O ! 2NHþ 4 þ CO3

ð1Þ

Ca2þ þ CO2 3 ! CaCO3 #

ð2Þ

MICP treatment has a wide range of improvement in soil behaviors, including stiffness enhancement [21, 33, 37, 40, 52], settlement control [18, 73], liquefaction reduction [27, 48, 54, 65, 66], etc. Moreover, MICP could also be used to restrain particle breakage [72], increase strength [11, 13, 16, 18, 23, 34, 42, 53, 60, 77], and decrease permeability for soils [1, 11, 12, 27, 29, 37, 61]. Previous researches suggested that the effects of MICP treatment might be influenced by many factors, such as strains of microbes [19, 76], concentration of urease [8, 43, 58], concentration of bacterial cell [4, 59], oxyg