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Compressibility characteristics of bio-cemented calcareous sand treated through the bio-stimulation approach

Journal of Rock Mechanics and Geotechnical Engineering 2023年第2期15卷 510-522页

作者： Yijie Wang Ningjun Jiang Alexandra Clarà Saracho Ogul Doygun Yanjun Du Xiaole Han Institute of Geotechnical Engineering Southeast UniversityNanjingChina Department of Civil and Environmental Engineering University of Hawaii at ManoaHonoluluUSA Department of Engineering Cambridge UniversityCambridgeUK Geosyntec Consultants Inc.Huntington BeachUSA

calcareous sand is widely present in coastal areas around the world and is usually considered as a weak and unstable material due to its high compressibility and low strength.Microbial-induced calcium carbonate precipitation(MICP)is a promising technique for soil improvement.However,the commonly adopted bio-augmented MICP approach is in general less compatible with the natural soil environment.Thus,this study focuses on the bio-stimulated MICP approach,which is likely to enhance the dominance of ureolytic bacteria for longer period and thus is deemed more efficient.The main objective of this paper is to investigate the compressibility of calcareous sand treated by bio-stimulated MICP approach.In the current study,a series of one-dimension compression tests was conducted on bio-cemented sand pre-pared via bio-stimulation with different initial relative densities(D r).Based on the obtained compression curves and particle size distribution(PSD)curves,the parameters including cementation content,the coefficient of compressibility(a v),PSD,relative breakage(B r),and relative agglomeration(A r)were discussed.The results showed that a v decreased with the increasing cementation content.The bio-cemented sand prepared with higher initial D r had smaller(approximately 20%e70%)a v values than that with lower initial D r.The specimen with higher initial D r and higher cementation content resulted in smaller B r but larger A r.Finally,a conceptual framework featuring multiple contact and damage modes was proposed.

关键词： calcareous sand Bio-cementation Bio-stimulation Compressibility

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Responses of calcareous sand foundations to variations of groundwater table and applied loads

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Journal of Rock Mechanics and Geotechnical Engineering 2022年第4期14卷 1266-1279页

作者： Dingfeng Cao Sanjay Kumar Shukla Linqing Yang Chengchao Guo Jinghong Wu Fuming Wang School of Civil Engineering Sun Yat-sen UniversityGuangzhou510275China Southern Marine Science and Engineering Guangdong Laboratory(Zhuhai) Zhuhai519082China Discipline of Civil and Environmental Engineering School of EngineeringEdith Cowan UniversityPerth6027Australia School of Architectural Engineering Guangzhou Institute of Science and TechnologyGuangzhou510540China School of Civil Engineering Suzhou University of Science and TechnologySuzhou215011China

The long-term settlement of calcareous sand foundations caused by daily periodic fluctuations has become a significant geological hazard,but effective monitoring tools to capture the deformation profiles are still rarely reported.In this study,a laboratory model test and an in situ monitoring test were conducted.An optical frequency domain reflectometer(OFDR)with high spatial resolution(1 mm)and high accuracy(10-6)was used to record the soil strain responses to groundwater table and varied loads.The results indicated that the fiber-optic measurements can accurately locate the swelling and compressive zones.During the loading process,the interlock between calcareous sand particles was detected,which increased the internal friction angle of soil.The foundation deformation above the sliding surface was dominated by compression,and the soil was continuously compressed beneath the sliding surface.After 26e48 h,calcareous sand swelling occurred gradually above the water table,which was primarily dependent on capillary water.The swelling of the soil beneath the groundwater table was completed rapidly within less than 2 h.When the groundwater table and load remain constant,the compression creep behavior can be described by the Yasong-Wang model with R2¼0.993.The daily periodically varying in situ deformation of calcareous sand primarily occurs between the highest and lowest groundwater tables,i.e.4.2e6.2 m deep.The tuff interlayers with poor water absorption capacity do not swell or compress,but they produce compressive strain under the influence of deformed calcareous sand layers.

关键词： Distributed fiber optic sensing(DFOS) calcareous sand Optical fiber Optical frequency domain reflectometer (OFDR) Soil foundation settlement

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Shear Strength and Dilatancy of calcareous sand in the South China Sea

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China Ocean Engineering 2022年第5期36卷 781-790页

作者： PEI Hui-min WANG Dong Shandong Provincial Key Laboratory of Marine Environment and Geological Engineering Ocean University of ChinaQingdao 266100China Qingdao National Laboratory for Marine Science and Technology Qingdao 266100China

The shear strength and dilatancy of typical uncemented calcareous sand from the South China Sea are investigated by soil lab tests.According to drained triaxial tests at various relative densities and confining stresses,it is found that the constant volume friction angle is approximated as 39°and the traditional Bolton’s equations can be modified to estimate the peak friction angle and dilation angle.The reliability of the equation proposed for the peak friction angle is verified in terms of calcareous sands from more onshore and offshore sites worldwide,while the errors of the predicted dilation angles scatter in a relatively large range.Totally,the dilation angles of sands in the South China Sea are estimated by the equation presented with an error of±30%.The peak friction angle measured by the undrained is similar to that by the drained tests as the relative density smaller than 60%,while the former is slightly lower for denser samples.

关键词： calcareous sand triaxial tests friction angle dilatancy drained South China Sea

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Coupling effects of morphology and inner pore distribution on the mechanical response of calcareous sand particles

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Journal of Rock Mechanics and Geotechnical Engineering 2023年第6期15卷 1565-1579页

作者： Xin Li Yaru Lv Yuchen Su Kunhang Zou Yuan Wang Wenxiong Huang College of Mechanics and Materials Hohai UniversityNanjing210098China College of Energy and Electrical Engineering Hohai UniversityNanjing210098China

calcareous sand is typically known as a problematic marine sediment because of its diverse morphology and complex inner pore structure.However,the coupling effects of morphology and inner pores on the mechanical properties of calcareous sand particles have rarely been investigated and understood.In this study,apparent contours and internal pore distributions of calcareous sand particles were obtained by three-dimensional(3D)scanning imaging and X-ray micro-computed tomography(X-mCT),respectively.It was revealed that calcareous sand particles with different outer morphologies have different porosities and inner pore distributions because of their original sources and particle transport processes.In addition,a total of 120 photo-related compression tests and 4923D discrete element simulations of four specific shaped particles,i.***.bulky,angular,dendritic and flaky,with variations in the inner pore distribution were conducted.The macroscopic particle strength and Weibull modulus obtained from the physical tests are not positively correlated with the porosity or regularity in shape,indicating the existence of coupling effect of particle shape and pore distribution.The shape effect on the particle strength first increases with the porosity and then decreases.The particle crushing of relatively regular particles is governed by the porosity,but that of extremely irregular particles is governed by the particle shape.The particle strength increases with the uniformity of the pore distribution.Particle fragmentation is mainly dependant on tensile bond strength,and the degree of tensile failure is considerably impacted by the particle shape but limited by the pore distribution.

关键词： calcareous sand Coupling effects Outer shape Internal pore distribution Particle strength Failure mode

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Effect of stress path on the mechanical properties of calcareous sand

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Underground Space 2023年第2期9卷 20-30页

作者： Houzhen Wei Hao Liu Xiaoxiao Li Zhao Tao Yongjie Wu Jianhua Shen Mei Yin State Key Laboratory of Geomechanics and Geotechnical Engineering Institute of Rock and Soil MechanicsChinese Academy of SciencesWuhan 430071China College of Civil Engineering and Architecture Guilin University of TechnologyGuilin 541004China Guangxi Key Laboratory of Geomechanics and Geotechnical Engineering Guilin University of TechnologyGuilin 541004China Dept.of Civil and Environmental Engineering Brunel University LondonLondon UB83PHUK

calcareous sand is widely observed in the foundation of off-shore infrastructure.Although a lot of research has been carried out on the mechanical properties of calcareous sand,study into the influence of the stress–strain path on the mechanical behaviour of calcareous sand is very limited.In this study,a series of triaxial tests were performed on calcareous sand under three different stress paths.The particle morphology of calcareous sand before and after the tests,the stress–strain relationship under different stress paths,and the char-acteristics of shear strength and deformation were investigated.The results show that the consolidation pressure and stress path have significant effects on the volume strain,strength,and particle breakage of calcareous sand.In addition,the underlying mechanisms of the different behaviours of calcareous sand observed in this study were discussed.

关键词： calcareous sand Triaxial test Stress path Particle breakage

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Study on Triaxial Mechanical Properties and Micro Mechanism of Fly Ash Reinforced Cement calcareous sand

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Journal of Renewable Materials 2022年第6期10卷 1693-1710页

作者： Ben Li Na Li Chulei Fang Jun Hu Rong Yu Longxin Shu Kai Yao Fang Zhang School of Civil Engineering Shaoxing UniversityShaoxing312000China College of Civil Engineering and Architecture Hainan UniversityHaikou570228China School of Qilu Transportation Shandong UniversityJinan250002China

In order to study the mechanical properties and micro-mechanism of industrial waste fly ash-reinforced cement calcareous sand(FCS),the triaxial unconsolidated undrained(UU)test and scanning electron microscope tests(SEM)were carried out on it.The results of UU test show that the peak stress and energy dissipation of the FCS sample first increase and then decrease with the increase in fly ash content.Fly ash enhances the cement calcareous sand by increasing both the cohesion and internal friction angle,and adding 10%content of fly ash gives the largest values.The SEM test results shows that the hydration products of cement and fly ash filled the pores and cracks on the surface of the calcareous sand,which increased the compactness and structure of the FCS samples.The porosity of cement calcareous sand can be reduced from 27.6%to 12.8%by adding 10%fly ash.A brittleness evaluation index based on energy dissipation is proposed to quantitatively characterize the brittleness of FCS samples.The results show that when the content of fly ash is 5%,the brittleness of FCS samples is the lowest.This study shows that the mechanical properties of cement calcareous sand can be effectively enhanced by adding the appropriate amount of fly ash.

关键词： calcareous sand cement fly ash triaxial UU test SEM test

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