| Structural clay of Zhanjiang Formation is the most widely distributed soil body in the Beibu Gulf coastal area,which is exposed on the surface or beneath the Quaternary Holocene or Middle Pleistocene soils,and is the main carrier of various engineering activities.Structural clay of Zhanjiang Formation in Beibu Gulf coastal area has thixotropy,which causes serious engineering problems.Although people have a deep and systematic understanding of thixotropy of soil,the formation mechanism of thixotropy in the process of structural clay disturbance remains unsolved.On the basis of previous research results,taking structural clay of Zhanjiang Formation in Beibu Gulf coastal area as the research object,this paper analyzed the influencing factors of thixotropy formation mechanism from the perspective of mineral composition and macro-micro structure of soil through regional engineering geological survey and macro-micro test,established a reasonable thixotropy model of structural clay of Zhanjiang Formation,and interpreted the thixotropy mechanism of structural clay of Zhanjiang Formation.The main research work and results are as follows:(1)the physical properties of Zhanjiang Formation structural clay undisturbed soil are tested in laboratory,and its basic physical properties are tested.Providing basic data for subsequent experiments.(2)thixotropic Micro-properties of Zhanjiang Formation structural clay were tested,including X-ray diffraction(XRD),Scanning Electron Microscope Combined with X-ray Energy Dispersion Spectrometry(SEM-EDS),mercury intrusion porosimetry test(MIP)and nuclear magnetic resonance(NMR),and the change of mineral composition,chemical element and microstructure and pore evolution characteristics of undisturbed and stationary remolded soils at different ages were analyzed and compared,and thixotropic properties of Zhanjiang clay were studied from the microscopic point of view.The results show that the thixotropic mode of structural clay in Zhanjiang Formation is that the mineral composition remains unchanged during thixotropic process.In the early stage of thixotropy,the flocculation structure is mainly loose.In the middle stage of thixotropy,the micro-pore develops continuously,structural stability is enhanced relative to initial thixotropic stability,the bond strength between particles is enhanced,at the later stage of thixotropy,the micro-pore is relatively developed,and the structural stability is enhanced relative to the stability in the early and middle stages.The cementation strength between particles reaches the maximum at this time,and the flocculation degree of microstructures is higher,and flocculation structure with aggregates appears.(3)through the unconfined compressive strength test and penetration resistance test,the thixotropic macro-characteristics were studied from the macro point of view.The test results are as follows: in the early thixotropic period(0-20 days),the strength recovery is slow,in the middle thixotropic period(20 days-150 days),the thixotropic strength recovery is rapid,and in the late thixotropic period(150 days later),the strength recovery speed is slow.The variation of unconfined compressive strength and penetration resistance with time in thixotropic process conforms to the power function growth relationship. |
