Dynamic characteristics of polyurethane reinforced sea sand under traffic loads
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摘要: 采用聚氨酯型固化剂对我国某地海砂进行改良处理，以快速提升其浅层地基承载能力，为定量评价其固化性能，研发适用于聚氨酯固化海砂的空心圆柱制样方法，开展了不同动应力比及加载频率下的固化前后海砂的空心圆柱扭剪试验，并结合SEM结果分析微观加固机制。试验表明：未固化试样的应变及孔压发展随动应力比的变化呈现3种形式，试验所得围压频率一定时临界动应力比η'=0.33。固化前的海砂在不同频率条件下，频率f越小，循环荷载的累积效应越明显，应变与孔压的发展速率越快，并以f=1.5 Hz为界，呈现两种发展趋势。固化后的海砂抗变形能力大大加强，在改变动应力比及频率两组加载条件下的轴向累积应变均不超过0.7%，且孔压发展限制均不超过20 kPa，部分加载条件孔压出现负值，产生剪胀现象。SEM结果分析表明，固化剂反应后占据了砂土内部的部分孔隙，反应生成的固化膜联结在一起，与砂颗粒形成了一种“砂粒嵌裹于固化膜”的稳定的空间结构，同时增加了试样的相对密实度，使颗粒重新排列阻力增大，从而极大提升了固化试样的力学性能。Abstract: In order to improve the bearing capacity of sea sand foundation in China, a treatment method for curing of sea sand foundation using polyurethane has been studied. The cyclic traffic load tests on the pure sand and reinforced sand were carried out by using hollow cylinder apparatus under different dynamic stress ratios and loading frequencies. A hollow cylindrical sample preparation method which is suitable for polyurethane rapid and efficient curing sea sand was innovatively designed for the study. And the micro-reinforcement mechanism was analyzed based on SEM results. The experimental results show that: The strain curve and pore pressure development of pure sand are divided into three development trends with the change of dynamic stress ratios, the critical dynamic stress ratio η' obtained by the test is 0.33. The smaller the frequency f under different frequency conditions is, the more obvious the cumulative effect of cyclic load is, the more obvious the development of strain and pore pressure are, bounded by the condition f=1.5 Hz, showing two development trends. The axial cumulative strain of the cured sea sand under the two sets of loading conditions did not exceed 0.7%, and the pore pressure development limit did not exceed 20 kPa. In some conditions, pore pressure eventually turned to be negative, resulting in shear dilatation. The analysis of SEM results shows that the curing agent takes up part of the pores in the sand after reaction. And as a consequence, the curing agent and sea sand forms a stable spatial structure, which leads to an increase of the resistance of particle rearrangement, thereby greatly improving the mechanical properties of the cured sample.
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Key words:
- polyurethane /
- sea sand /
- traffic loads /
- axial cumulative strain /
- pore pressure development
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图 4 空心圆柱试样薄壁单元体受力状态
Figure 4. Force acting on a hollow cylindrical specimen
pi—Internal confining pressure; po—External confining pressure; W—Axial force; MT—Torque; $ {\sigma _z} $—Axial stress; $ {\sigma _r} $—Radial stress; $ {\sigma _\theta } $—Ring stress; $ {\tau _{z\theta }} $, τθz—Torsional shear stress, same quantity, different directions; $ \theta $—Torsion angle; $ \alpha $—Angle at which the large principal stress deviates from the original direction; $ {\sigma _1} $, $ {\sigma _2} $, $ {\sigma _3} $—Large, medium and small principal stresses
图 5 双组分聚氨酯：(a) 双组分聚氨酯A组分与B组分；(b) 双组分A、B混合固化后的聚氨酯
Figure 5. Two-component polyurethane: (a) Two-component polyurethane A component and B component; (b) Polyurethane cured by mixture of component A and component B
图 7 模拟加载波形
Figure 7. Simulated loading waveforms
W/Wmax—Axial force; M/Mmax—Torque; t/T—Cycle
图 8 空心圆柱试样不同循环动应力比下的实际应力路径
Figure 8. Actual stress path diagrams of hollow cylindrical sample under different cyclic dynamic stress ratios
$ ({\sigma _z} - {\sigma _\theta })/2 $—Half the difference between axial stress and ring stress; The different cyclic dynamic stress ratios of the internal to external are 0.25, 0.31, 0.33, 0.35, 0.36 and 0.41, respectively
图 9 空心圆柱试样不同动应力比下轴向累积应变曲线
Figure 9. Axial cumulative strain of hollow cylindrical sample under different dynamic stress ratios
图 10 空心圆柱试样不同动应力比下孔压增量曲线
Figure 10. Pore pressure increment curves of hollow cylindrical sample under different dynamic stress ratios
图 11 空心圆柱试样破坏振次与初始动应力比关系曲线
Figure 11. Curves of destructive cycles and initial dynamic stress ratio of hollow cylindrical sample
图 12 空心圆柱试样不同频率下轴向累积应变曲线
Figure 12. Axial cumulative strain of hollow cylindrical sample under different frequencies
图 13 空心圆柱试样不同频率下孔压增量曲线
Figure 13. Pore pressure increment curves of hollow cylindrical sample under different frequencies
图 14 空心圆柱试样固化后不同动应力比下轴向累积应变曲线
Figure 14. Axial cumulative strain of the reinforced sand of hollow cylindrical sample under different dynamic stress ratios
图 16 空心圆柱试样固化后不同动应力比下孔压增量曲线
Figure 16. Pore pressure increment curves of the reinforced sand of hollow cylindrical sample under different dynamic stress ratios
图 17 空心圆柱试样固化后不同频率轴向累积应变曲线
Figure 17. Axial cumulative strain of the reinforced sand of hollow cylindrical sample under different frequencies
图 18 空心圆柱试样固化后不同频率孔压增量曲线
Figure 18. Pore pressure increment curves of the reinforced sand of hollow cylindrical sample under different frequencies
图 19 聚氨酯固化海砂不同倍数SEM图像
Figure 19. SEM images of reinforced sea sand by polyurethane with different magnifications
表 1 海砂的物理性质指标
Table 1. Physical parameters of the sea sand
Specimen Gs Cu Cc D50 D10 D30 D60 ρdmax/(kg·cm−3) ρdmin/(kg·cm−3) Sea sand 2.66 1.47 0.95 0.174 0.122 0.155 0.184 1654 1410 Notes：Gs—Specific gravity of solid particles; Cu—Coefficient of uniformity; Cc—Compression index; Dx—Particle size corresponding to the cumulative distribution percentage reaching x, x is the cumulative distribution percentage; ρdmax—Maximum dry density; ρdmin—Minimum dry density. 
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表 2 试验采用的应力路径加载
Table 2. Stress paths used in tests
p0/kPa f/Hz Number η0 p0/kPa η0 Number f/Hz 100 1 (G)HSRA1025 0.25 100 0.36 (G)HSRB0536 0.5 HSRA1031 0.31 (G)HSRB1036 1 (G)HSRA1033 0.33 (G)HSRB1536 1.5 HSRA1035 0.35 (G)HSRB2036 2 HSRA1036 0.36 (G)HSRB2536 2.5 (G)HSRA1041 0.41 Notes: The addition of "G" before the number indicates the number of the cured sample; HSRA stands for the heart stress ratio loading test group A, HSRB stands for heart stress ratio loading test group B, the last four numbers represent the frequency and dynamic stress ratio; p0—Effective confining pressure; f—Frequency; η0—Initial dynamic stress ratio.
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