Experimental Study On Mechanical And Permeability Properties Of Fiber-Reinforced Bio-cemented Sand With Different Gradations

This paper adopts the microbial induced calcium carbonate precipitation(MICP)technology to cement the quartz sand.A series of studies of the mechanical properties and inner mechanism of bio-cemented quartz sand were carried out.The main contents are as follows:A series of unconfined compression tests were performed to study the influence of sand gradation,relative density,calcium carbonate content and fiber content on the unconfined compression strength of quartz sand.The results show that:(1)the unconfined compression strength of the bio-cemented sand increases with the increase of the coefficient of uniformity,calcium carbonate content and relative density;(2)for fiber contents used in this study,the unconfined compression strength of the bio-cemented sand increases with the increase of the fiber content firstly.Then the unconfined compression strength decreases with more fiber added;(3)an empirical formula was put forward to integrate the unconfined compression strength of the sand with porosity and calcium carbonate content,which can be used to predict the unconfined compression strength of the sand under different gradations,porosity and calcium carbonate contents.It is shown that the predicted value achieved by empirical formula is in good consistence with the test data.A series of splitting tensile tests were performed to study the influence of sand gradation,relative density,calcium carbonate content and the fiber content on the splitting tensile strength of quartz sand.The results show that:(1)the splitting tensile strength of the sand increases with the increase of the coefficient of uniformity and calcium carbonate content;(2)the splitting tensile strength of the fiber reinforced bio-cemented sand generally keeps increasing with the increase of the fiber content,although the effectiveness of the fiber gets less obvious;(3)an empirical formula was put forward to integrate the splitting tensile strength of the sand with porosity and calcium carbonate content,which can be used to predict the splitting tensile strength of the fiber reinforced bio-cemented sand under different gradations,porosity and calcium carbonate contents.According to the scanning electron microscope tests,it can be concluded that:(1)with the increase of the coefficient of uniformity,the number of contact points between sand particles increases while the pore size between sand particles decreases;(2)with the increase of the relative density,the pore size between sand particles decreases while the number of particle contact points is on the contrary,which causes the calcium carbonate bonding points increasing correspondingly;(3)the pore volume of the sample decreases with the increase of calcium carbonate content;(4)with the increase of the fiber content,there are increasing contact points between sand particles as well as sand particles and the fiber.The binding effect is much more obvious.However,the fiber could gather together with the fiber content keeping increasing.In addition,the effect of gradation,relative density,calcium carbonate content and fiber content on the permeability of bio-cemented sand and fiber reinforced bio-cemented sand were studied by variable water head permeability tests.The results show that:(1)the permeability coefficient of two types of specimens decreases with the increase of calcium carbonate content;(2)with the increase of the relative density,the permeability of bio-cemented sand decreases slightly;(3)the permeability coefficient of two types of sand decreases obviously with the increase of the coefficient of uniformity,and the influence of gradation on the permeability coefficient of the samples is more obvious than the calcium carbonate content and dry density;(4)the permeability data of bio-cemented sand and fiber reinforced sand can be well fitted by the empirical formula.The cementing factor index integrating the porosity and calcium carbonate content of the specimen is also suitable for the analysis of permeability coefficient of bio-cemented sand and fiber reinforced sand.