Proceedings of the Thirty-second (2022) International Ocean and Polar Engineering Conference
Shanghai, China, June 5–10, 2022
Copyright © 2022 by the International Society of Offshore and Polar Engineers (ISOPE)
ISBN 978-1-880653-81-4; ISSN 1098-6189

www.isope.org

Mechanical Characteristics of MICP-treated Calcareous Sand and Natural Coral RockZhang Baofeng1,2, Li Yujie2,*,Yu Huafeng1, Zhou Hu1
1PowerChina Huadong Engineering Corporation Limited, Hangzhou, China
2Zhejiang University, Hangzhou, China

ABSTRACT

strength and stiffness of the calcareous sand increase. To date, thistechnology has been utilized in numerous geotechnical applications
such as ground reinforcement, liquefaction mitigation, settlement
reduction, dust suppression, erosion control, gaining well stability toimprove oil and gas extraction (Van Paassen et al., 2010; Burbank et al.,2011; DeJong et al., 2009; DeJong et al., 2010; Jiang and Soga, 2017;
Latil et al., 2008; Salifu et al., 2016; Kumar et al., 2019.). Khan used
MICP technology to reinforce coral sand, and the UCS strength of thetreatment sample can reach 20 MPa after 28 days (Khan et al., 2015).
Liu et al (2018) studied the microscopic mechanism of MICP
cementation and the dynamic characteristics of MICP cemented
calcareous sand columns. Zhao (2014) considered the various factors
on engineering properties of the MICP-treated sand and the results ofunconfined compression test show that the bacteria concentration,
cementation media concentration, reaction time, and type of sand havea significant impact on the engineering properties of MICP-treatedsamples. Rebata-Landa (2007) believes that particle size mainly has thefollowing impacts on MICP process:(1) the MICP is inhibited by low
permeability in very fine soil particles; (2) a thin coating layer ofprecipitation cannot bond particles together in coarse soils. These
researches evaluated the potential for using MICP technique toreinforce calcareous sand. However, only the mechanical properties of
MICP-treated calcareous sand samples were studied, and there are few
literatures about systematic comparison of mechanical characteristics
and microstructure of the MICP-treated calcareous sand samples andthe natural coral rocks.
The objective of this paper is to study the mechanical behavior andmicrostructure of the MICP-treated samples, and compare thesecharacteristics between MICP-treated samples and natural coral rocks.

With the developments of the reclamation projects, the physicaland mechanical properties of the reef limestone have become a hotspot
in the ocean engineering. However, it is difficult to obtain natural reef
limestone samples. MICP (Microbially Induced Calcium Carbonate
Precipitation) was used to cement the calcareous sands in this paper.
The sand sample was immersed in the bacterial solution and cementsolution successively, leading to precipitation of calcium carbonate tobond sand particles. The mechanical characteristics and microstructureof artificial cementing samples were compared with the natural reef
limestone.

KEY WORDS: Calcareous sand; reef limestone; MICP; UCS;
Microstructure; Calcium carbonate

INTRODUCTION
A large number of coral reefs are dispersed in the South China Sea.
In general, the shallow layer of the coral reef is uncemented calcareoussand and the deep layer is the natural coral rock. Calcareous sands havedifferent physical and mechanical properties from the terrigenous sand,such as obvious internal void, irregular particle shape, significant
particle breakage, and weakly cemented structure (Shahnazari et al.,2013; Wang et al., 2011; Wang et al., 2017). These characteristics maylead to the instability of foundation during the process of construction.
In order to solve these problems, the loose calcareous sand layer needs
to be reinforced. Chemical grouting techniques are generally used in
the ground improvement of soil layer, but they are harmful to theecological environment and may lead to the coral bleaching. It isneeded to seek a kind of environmentally friendly technique for thereinforcement of the calcareous sand.
MICP (Microbially Induced Calcium Carbonate Precipitation) is abiomineralization process that exists widely in nature. The MICP basedon urea hydrolysis mainly relies on Sporosarcina pasteurii to produce
urease, which hydrolyses urea to produce a large amount of carbonateion. Calcium carbonate precipitation cannot occur until ion activity
product (IAP) in the environment exceeds the solubility constant, whichis 4.8×10-9 at 25℃ (Morse, 1983; Muynck et al., 2010; Helmi et al.,2016). The new-formed calcium carbonate can coat sand particles,cement the sand matrix, and fill the void space. Therefore, both the

1. MATERIALS AND METHODS
1.1 Calcareous Sand and Coral Rocks
In this study, the calcareous sand was taken from the lagoon basin
and the coral rock was taken from the stratum of 17.9m~36.6m below
the surface, as shown in Figs. 1(a). Intraparticle pores and irregularshapes may promote the formation of MICP cementation between theparticles from Fig. 1(b). In order to ensure dried completely, theretrieved calcareous sand was cleaned by deionized water and kept
being in an oven at 102 °C until no further reduction in its weight was2850