表面入渗法诱导碳酸钙沉积加固海相粉土研究

Improvement of marine silt by microbial induced calcite precipitation by surface percolation

目前利用微生物诱导碳酸钙沉积加固土体主要是采用注浆方式,处理对象主要是粒径较大的砂土。相比注浆胶结方法,表面入渗法具有操作简单、便于实施的优点,但容易受土中孔隙尺寸的限制。以海相粉土为处理对象,探讨将生物胶结同表面入渗法相结合加固土体。由于粉土粒径小,为解决孔喉尺寸与微生物尺寸相容性问题,采用上清液替代菌液同胶结液交替入渗的方法加固试样。结果表明,该方法可以避免生物封堵,处理后的试样上部能形成具有水稳定性的胶结层,但加固厚度有限。为了进一步提高加固深度,采用将菌液和粉土拌和制样,然后循环入渗胶结液的方法进行加固。水稳定性和碳酸钙测试结果均表明,采用该方法的加固深度明显增加,可以在整个试样高度上形成有效胶结。通过对比试验,验证了该方法对不同尺寸试样的有效性,并发现胶结液浓度对于加固效果有直接影响。研究结果可对实际工程中采用不同方法对粉土进行生物处理提供依据。

Grouting method is usually applied in the current soil improvement utilizing microbial induced calcite precipitation(MICP),and the main treated soil is coarse sand.Compared with sand,silty has the disadvantages in small particle size,small pore size,weak permeability,weak structure,etc.,which often lead to a series of problems such as early blockage of the soil sample end and the loss of silt particles when the MICP is applied to strengthen the silt.Compared with the grouting method,surface percolation method shows the advantages in simple operation and field application,but its application is usually limited by the void size of soil.Therefore,the surface percolation method combined with bio-cementation is studied to reinforce marine soil.In order to solve the compatibility between bacteria and pore throat of small silt particles,supernatant and cementation fluid are infiltrated into soil by turn to reinforce sample instead of bacteria fluid.Experiment results show that this method can avoid bio-plugging,and form water-stable cementation in the upper part of sample,but the reinforcing depth is limited.Thus the new method of mixing bacteria with silt particles before cementation fluid repeated percolation is carried out to improve reinforcing depth.After mixing the bacteria liquid and powder soil and then the cementing liquid is used to infiltrate soil,and the water stability of silt can be improved effectively.After 6 rounds of infiltration,the reinforcing thickness reaches almost the whole height of soil sample,and its effect is obvious.Tested results of water stability and calcium carbonate indicate the reinforcing depth treated by this method is increased notably and effective cementation is formed in the whole sample height.The availability of this method to treat samples in different dimensions is confirmed by comparison experiments and the result shows the concentration of cementation fluid has remarkable influence on the improvement.An effective method for strengthening silt is determined.The results of this study may provide convincing basis for reinforcing silt with different methods in practical projects.