Strength characteristics of biopolymer modified sand under dry-wet cycle
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摘要: 通过无侧限抗压强度试验和三轴剪切试验对生物聚合物(XG)/砂土复合材料强度特性进行研究，分析不同XG含量(与砂土质量比)和不同干湿循环次数对XG/砂土的强度特性的影响，并利用扫描电子显微镜和低场核磁共振分析仪对不同XG/砂土的微观结构进行分析与研究。研究结果表明：随着XG含量的增加，XG/砂土的无侧限抗压强度、峰值偏应力和黏聚力均发生增强，内摩擦角在27°~32°范围内变化。随着干湿循环的次数的增加，XG/砂土的无侧限抗压强度、峰值偏应力和黏聚力均发生一定的减小。当经历4次干湿循环时，XG/砂土的强度降幅为28.57%。随着干湿循环次数的继续增加，强度的降幅趋于平缓。生物聚合物可以在砂土表面和孔隙中形成大量的网状结构，大量的网状结构相互连接为网状膜将砂土连接为一个整体。环境中水分的变化会使得网状膜产生一定的损伤，使得XG/砂土的力学性质降低。但相较于未经改良的砂土，XG/砂土仍然拥有较强的结构性能和力学性能。Abstract: The strength characteristics of biopolymer (XG)/sand composites were studied by unconfined compres-sive strength test and triaxial shear test. The effects of different XG contents (mass ratio to sand) and different dry-wet cycles on the strength characteristics of XG/sand were analyzed. The microstructure of different XG/sand was analyzed and studied by scanning electron microscope and low field NMR analyzer. The results show that with the increase of biopolymer content, the unconfined compressive strength, peak deviator stress and cohesion of XG/sand increase, and the internal friction angle varies in the range of 27°-32°. With the increase of the number of dry-wet cycles, the unconfined compressive strength, peak partial stress and cohesion of XG/sand decrease. The strength of XG/sand decreases about 29% after 4 dry-wet cycles. With the continuous increase of the number of dry-wet cycles, the decrease of strength is stable at about 20%. Biopolymers can form a large number of network structures on the surface and pores of sand. A large number of network structures are connected to each other as a network membrane, connecting the sand as a whole. The change of water in the environment will cause some damage to the reticular membrane, which reduces the mechanical properties of XG/sand. However, XG/sand still has strong structural and mechanical properties compared with the unmodified sand.
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Key words:
- biopolymer /
- sand /
- strength characteristics /
- dry-wet cycle /
- microstructure
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图 3 不同生物聚合物(XG)含量XG/砂土试样典型应力-应变曲线
Figure 3. Typical stress-strain curves of XG/sand samples with different biopolymer (XG) contents
图 4 干湿循环次数对不同XG含量XG/砂土试样抗压强度的影响
Figure 4. Effect of dry-wet cycles on compressive strength of XG/sand samples with different XG contents
图 5 100 kPa围压不同XG含量XG/砂土试样偏应力-应变曲线
Figure 5. Partial stress-strain curves of XG/sand samples with different XG contents under 100 kPa confining pressure
图 6 XG/砂土峰值偏应力随干湿循环次数的变化曲线
Figure 6. Variation curves of peak partial stress of XG/sand with different dry-wet cycles
图 7 XG/砂土黏聚力(a)和内摩擦角(b)随干湿循环次数的变化曲线
Figure 7. Variation curves of cohesion (a) and internal friction angle (b) of XG/sand with different dry-wet cycles
图 9 改良前后砂土的能谱测试结果
Figure 9. Energy spectra test results of sand before and after modification
图 10 不同干湿循环次数下XG含量2%的XG/砂土试样的孔径分布曲线
Figure 10. Pore size distribution curves of XG/sand samples with 2%XG content and different dry-wet cycles
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