Unconfined Compressive Strength Testing of Bio-cemented Weak Soils: A Comparative Upscale Laboratory Testing
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RESEARCH ARTICLE-CIVIL ENGINEERING
Unconfined Compressive Strength Testing of Bio‑cemented Weak Soils: A Comparative Upscale Laboratory Testing K. M. N. Saquib Wani1 · B. A. Mir1 Received: 28 January 2020 / Accepted: 14 May 2020 © King Fahd University of Petroleum & Minerals 2020
Abstract Bio-cementation of soils has gained a lot of attention on a global level owing of its ability to improve strength characteristics of weak or marginal soils. In this study, two urease producing bacteria namely Bacillus subtilis (B.S) and Bacillus pasteurii (B.P) along with a cementation media have been used to enhance the unconfined compressive strength (UCS) of dredged soils. Maintaining an optimum temperature of 18–23 °C, treatment was provided using cementation media molarity (CMM) of 0.5 and 1.0 in full contact moulds (FCM) having a diameter of 38, 76 and 114 mm respectively for 8 cycles (6 h each). The extruded samples were further tested for UCS with the test results indicating that as the sample size increased, the UCS value increased irrespective of the bacteria used. Maximum values of UCS for both the bacteria’s were observed at 0.5 CMM. An increase in UCS from 280 kN/m2 in the untreated state to 735 and 820 kN/m2 for B.S and B.P respectively was noticed. The enhancement in UCS is attributed to the formation of calcite crystals which was further supported by elemental and mineral analysis. The main goal of this study was to improve weak soils and to explore the potential of a green ground improvement technique in field applications. Keywords Bio-cementation · Weak soils · Bacteria · Unconfined compressive strength · Ground improvement techniques
1 Introduction Reduced strength and increased compressibility are the major characteristics of weak soils [1, 2]. There are a number of ground improvement techniques (GIT) that improve the engineering properties of soils which is then required either as a foundation, backfill, landfill or as a sub-grade material [3–10]. GIT’s at large follow either mechanical or chemical approaches, thus making a particular technique applicable based on the site conditions and materials availability whereas the purpose and amount of work being the other affecting factors. In the last few decades, chemical additives have been increasingly used for soil stabilization. Chemical grouts, deep mixing, soil–cement micro-piles, etc., have been incorporated in many studies related to GIT [11–18]. Although the use of chemicals gives appreciable * K. M. N. Saquib Wani [email protected]; [email protected] B. A. Mir [email protected] 1
Department of Civil Engineering, National Institute of Technology, Srinagar, J&K 190006, India
results, but the harmful effects of their use on the environment and during their production prove very fatal for the ecosystem and ground water [19–21]. Alternatives to such methods are a dire need for researchers worldwide and as such a more eco-friendly, green technique would be the best solution. A substitute to conventional GIT’s was given by Mitchelle and Sa
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