| The coal reserves in northern Shaanxi are abundant in China.Due to the rough mining method in the past and improper maintenance after mining,a large number of secondary geological disasters and surface cracks have been caused.The generation of surface cracks not only has a huge impact on mining safety,but also is not conducive to the recovery of the subsequent ecological environment.Therefore,an economic,environmental protection and effective surface crack repair method is urgently needed.In recent years,with the in-depth study of microbial induced calcium carbonate precipitation(MICP)technology,solidification of sandy soil and repair of concrete have gradually become a hot research direction in the field of geotechnical engineering.Reinforcement and improvement of soil based on MICP curing technology combined with the excellent mechanical properties of fiber itself is an environmentally friendly and effective repair method.In this study,MICP fiber reinforcement technology was used to repair the two types of soil cracks.Through rapid consolidation direct shear test,unconfined compressive strength test,triaxial compression test,penetration test,erosion test,combined with scanning electron microscopy observation,X-ray diffraction,calcium carbonate quality measurement and other technical means,the repair mechanism of MICP reinforcement technology in the treatment of fractured soil was revealed and the best fiber ratio of two types of fractured soil samples in laboratory research was determined.(1)Firstly,according to the geometric,filling and environmental characteristics of surface cracks in field investigation data,surface cracks can be divided into two types,namely internal cracks and edge cracks.Activation of Bacillus megaterium was carried out.After the activation of the strain,it was subjected to three times of overlapping culture,and the change of the bacterial concentration was measured.It was found that the bacterial concentration gradually increased with the increase of overlapping times,and the bacterial concentration reached 3.32.After low-temperature acclimation,the bacterial concentration reached 3.28 after 14 days,which met the requirements of subsequent experiments.The above contents prepared the materials for the subsequent experiments.(2)Secondly,the rapid consolidation direct shear test was carried out on two types of fissured soil samples.The test results show that the optimal curing time for MICP to repair the two types of fissured soil samples is 48 h.The best ratio of repairing internal cracks is 1 : 1.5,and the best ratio of repairing edge cracks is 1 : 2.The optimal ratio of Baode laterite to standard sand in the internal fissure filling of soil sample is 1 : 1,and the optimal ratio of Baode laterite to standard sand in the edge fissure filling of soil sample is 1 : 3.(3)Thirdly,the unconfined uniaxial compression test was used to test the soil samples with edge cracks.The uniaxial compressive strength of MICP fiber reinforced soil samples was increased by about 41 % compared with that of non-fiber MICP soil samples,and was increased by about 180 % compared with that of non-cured soil samples.Triaxial compression was used to test the internal fissured soil sample.The maximum deviatoric stress of MICP fiber reinforced soil sample increased by about 74.3 % compared with that of non-fiber MICP soil sample,and increased by 103.3 % compared with that of non-cured soil sample.(4)From then on,variable head penetration test and scouring test were carried out on two types of fractured soil samples.The minimum permeability coefficient of soil samples with edge cracks decreased by about 79.2 % compared with that of soil samples without fiber MICP,and decreased by about 85.7 % compared with that of soil samples without curing.The minimum permeability coefficient of internal fissure soil samples decreased by about 85.3 %compared with that of non-fiber MICP soil samples,and decreased by about 89.7 % compared with that of non-cured soil samples.Different erosion time,slope and rainfall intensity tests were carried out on the soil samples by using the self-made Baode laterite erosion model.It was found that the erosion mass of soil samples was significantly reduced after adding basalt fiber into the filling.The erosion mass of soil samples with edge cracks decreased by about 60.2 %,and that of soil samples with internal cracks decreased by about 59 %.Although the repaired soil samples affected the repair effect under different rainfall intensity conditions,the experimental results still showed that MICP repair technology reinforced by basalt fiber had good modification effect on the surface cracks of soil samples.(5)Finally,the MICP fiber reinforced soil samples were observed by scanning electron microscopy,X-ray diffraction and calcium carbonate quality determination.X-ray diffraction test results showed that there was calcite diffraction peak,indicating that there was calcium carbonate crystallization precipitation in soil samples.Under the electron microscope,calcium carbonate crystal cements between soil particles and partially covers the surface of soil particles.Calcium carbonate crystal plays a ’ bridge ’ role in the soil sample,and basalt fiber provides a planting range for microorganisms.The results of calcium carbonate crystal quality determination are consistent with those of physical and water.In this paper,the basalt fiber ratio suitable for filling was obtained by repairing the two kinds of fissured soil samples,that is,0.4 % basalt fiber content of 12 mm was added to the internal fissure of soil sample;add 12 mm basalt fiber 0.8 % to the soil sample edge crack.In this indoor experimental study,MICP basalt fiber reinforcement technology has been verified from both physical and water aspects,which proves the feasibility of this technology for surface crack repair and provides theoretical support for field tests in mining areas in the future. |
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