Shear strength characteristics of sand solidified by enzyme-induced carbonate precipitation with waste face mask reinforcement
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摘要: 为进一步提升酶诱导碳酸盐沉淀(EICP)固化砂土的抗剪强度特性，改善固化砂土的脆性破坏特征，向未固化砂土中添加废弃的一次性口罩进行改良。基于三轴压缩试验等，研究不同口罩纤维掺量对EICP固化砂土抗剪强度的影响，并分析改变EICP滴注轮次和砂土初始相对密实度后，改良砂土的抗剪强度特性和口罩加筋效益的变化情况。结果表明：口罩最优掺量为0.2%，不同围压下可以使改良砂土的峰值偏应力提高59.9%~34%，黏聚力提高188%，内摩擦角提高14.5%，且能有效减少峰后强度损失，改善固化砂土的脆性破坏特征；增加滴注轮次和相对密实度可以提高峰值偏应力、黏聚力和内摩擦角，但口罩的加筋效果略微减弱；碳酸钙生成率随滴注轮次增加而增大，随相对密实度增加而减小，加筋可以提高碳酸钙生成率。Abstract: To further enhance the shear strength characteristics of sandy soils cured by enzyme-induced carbonate precipitation (EICP) technology, and to improve the brittle damage characteristics of the cured sandy soils, the abandoned disposable masks were blended into the sandy soils for improvement. Based on the triaxial compression test, the influence of different contents of the mask on the shear strength of EICP solidified sand was studied. However, the change of the shear strength characteristics of improved sand and the benefit of mask reinforcement were analyzed after changing the EICP drip rounds and the initial relative compactness of sand. The results show that the best content of the mask is 0.2%. At this time, the peak partial stress of improved sandy soil increases by 59.9%-34% under different confining pressures, the cohesive force increases by 188%, and the internal friction angle increases by 14.5%. The post-peak strength loss is effectively reduced and the brittle damage of cured sand is improved. However, increasing the number of drip rounds and relative compactness could increase the peak partial stress, cohesive force and internal friction angle, but the effect of mask reinforcement is slightly weakened. Finally, mask reinforcement can improve the calcium carbonate generation rate, and the calcium carbonate generation rate increases with the increase of drip rounds, but decreases with the increase of relative compactness.
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图 2 不同口罩纤维掺量的酶诱导碳酸盐沉淀技术(EICP)固化砂土在不同围压下的应力-应变曲线
Figure 2. Stress-strain curves of EICP solidified sand with different mask fiber content under different confining pressures
图 3 EICP固化砂土的初始弹性模量Ei与口罩纤维掺量、围压的关系
Figure 3. Initial elastic modulus Ei of EICP solidified sand affected by mask fiber content and confining pressure
图 4 不同口罩纤维掺量下EICP固化砂土的峰值偏应力和残余偏应力
Figure 4. Peak deviator stress and residual deviator stress of EICP solidified sand varying with mask fiber contents
图 5 加筋前后EICP固化砂土的SEM微观图像
Figure 5. SEM microscopic images of EICP solidified sand before and after reinforcement
图 6 不同口罩纤维掺量下EICP固化砂土的强度损失率
Figure 6. Strength loss rate of EICP solidified sand varying with mask fiber contents
图 7 EICP固化砂土的黏聚力和内摩擦角随口罩纤维掺量变化曲线
Figure 7. Variation of cohesion and angle of internal friction of EICP solidified sand with mask fiber contents
图 8 不同滴注轮次(l)的EICP固化砂土在围压300 kPa时的应力-应变曲线
Figure 8. Stress-strain curves of EICP solidified sand affected by different reinforcement times (l) under confining pressure of 300 kPa
图 9 不同滴注轮次下EICP固化砂土的初始弹性模量
Figure 9. Initial elastic modulus of EICP solidified sand affected by different reinforcement times
图 10 滴注次数对EICP固化砂土的碳酸钙生成率的影响
Figure 10. Effect of reinforcement times on calcium carbonate formation rate of EICP solidified sand
T—Top part; M—Middle part; B—Bottom part
图 11 不同滴注轮次下EICP固化砂土的峰值偏应力和残余偏应力
Figure 11. Peak deviator stress and residual deviator stress of EICP solidified sand varying with reinforcement times
图 12 不同滴注轮次下EICP固化砂土的强度损失率
Figure 12. Strength loss rate of EICP solidified sand varying with reinforcement times
图 13 EICP固化砂土的黏聚力和内摩擦角随滴注轮次变化曲线
Figure 13. Variation of cohesion and angle of internal friction of EICP solidified sand with reinforcement times
图 14 不同初始相对密实度的EICP固化砂土在围压300 kPa时的应力-应变曲线
Figure 14. Stress-strain curves of EICP solidified sand with different initial relative densities under confining pressure of 300 kPa
图 15 不同初始相对密实度下EICP固化砂土的初始弹性模量
Figure 15. Initial elastic modulus of EICP solidified sand affected by different initial relative densities
图 16 初始相对密实度对EICP固化砂土碳酸钙生成率的影响
Figure 16. Effect of initial relative density of EICP solidified sand on calcium carbonate formation rate
图 17 不同初始相对密实度下EICP固化砂土的峰值偏应力和残余偏应力
Figure 17. Peak deviator stress and residual deviator stress of EICP solidified sand varying with initial relative densities
图 18 不同初始相对密实度下EICP固化砂土的强度损失率
Figure 18. Strength loss rate of EICP solidified sand varying with initial relative densities
图 19 EICP固化砂土的黏聚力和内摩擦角随初始相对密实度变化曲线
Figure 19. Variation of cohesion and angle of internal friction of EICP solidified sand with initial relative densities
表 1 标准砂的物理力学性质
Table 1. Physical-mechanical properties of sand
Effective particle size/mm Specific gravity Curvature coefficient Nonuniformity coefficient D10 D30 D60 0.13 0.3 0.66 2.65 1.05 5.07 Note: Dn means the mass of particles smaller than this particle size accounts for n% of the total mass of soil particles. 
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表 2 口罩的物理力学性质
Table 2. Physical-mechanical properties of face masks
Nonuniformity
coefficientMelting point/
℃Water absorption/
%Tensile strength/
MPaElongation at break/
%Tensile strength at break/
MPa0.91 160 9.5 4.25 118.9 4.18
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表 3 工况设置
Table 3. Working conditions setting
Test Mask fiber content/% Number of EICP drops/drop Relative density/% Confining pressure/kPa C1 0 4 50 100, 200
300, 400C2 0.1 4 50 C3 0.15 4 50 C4 0.2 4 50 C5 0.25 4 50 C6 0.3 4 50 L1 0 3 50 L2 0 5 50 L3 0.2 3 50 L4 0.2 5 50 D1 0 4 30 D2 0 4 80 D3 0.2 4 30 D4 0.2 4 80 Note: EICP—Enzyme-induced carbonate precipitation.
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