Pore Structure Characterization And Seepage Simulation Of Microbial Solidified Sand Column

Leakage is a common engineering problem,and microbial induced calcium carbonate deposition plugging is an emerging environmentally friendly leak management technology.In this paper,the combination of indoor sand column test and numerical simulation is used to study the effect of soil self-property on the cementation effect of sand column.At the same time,the microscopic pore structure of the sand column after sealing is quantitatively characterized,and the understanding of the meso-mechanism of microbial mineralization is deepened.The main conclusions are as follows:(1)Particle size and gradation are the main factors affecting the change of permeability of the solidified sand column.When the particle size is too large or too small,the permeability of the sand column decreases rapidly but the cementation integrity is poor.When the particle size is moderate,the bacterial liquid and the reaction liquid can flow smoothly and can remain in the pore space,and the cementation effect is good overall;the influence of the particle grading on the plugging effect is mainly due to the difference in the void ratio.The permeability of the sample with high initial void ratio decreases slower but the cementation uniformity is better.The sample with lower initial void ratio is easier to be cemented and plugged,so the decline in permeability is more obvious,but the reaction is concentrated in the slurry inlet,and the cementation uniformity is unsatisfactory.(2)The 6.5μm high-resolution synchrotron microscopy CT was used to scan the sand column plugging sample and the control sample for micro-CT scanning,and the three-dimensional reconstruction model was obtained.Three representative elementary volume(REV)were extracted at different height positions.The maximum ball algorithm was used to construct the pore network model.After quantitative analysis of the pore structure,it was found that the porosity of the plugged samples was significantly lower than that of the control samples,and the volume porosity decreased by 26.4%.The pore structure parameters changed significantly:pore radius,pore volume,pore coordination number,throat length,throat radius were significantly reduced,the seepage channel was blocked,the pore shape irregularity was reduced,the pore number increased,and the original single large pores were divided into several small pores that are not connected.(3)The three-dimensional percolation simulation of REV was performed using the lattice Boltzmann method,and the permeation rate of each REV was calculated.The results showed that compared with the control sample,the average permeability of the plugged sample decreased by 59.42%,which was consistent with the experimentally determined permeability reduction of 63.59%.