Experimental study on strength and deformation characteristics of polymers treated sand
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摘要: 基于高聚物加固砂土展开抗剪和抗压试验，分析了高聚物掺量、养护时间和干密度对加固砂土强度和变形特征的影响，并阐明其相关性，最后结合SEM图像揭示了高聚物加固砂土的破坏机理。结果表明：(1)三个研究变量对加固砂土抗压和抗剪强度有显著促进作用，其中高聚物含量和养护时间对抗剪强度的影响主要体现在黏聚力上，并且强度与养护时间强正相关，与高聚物含量和干密度中等正相关，可用对数函数(或线性函数)表示其关系；(2)三个研究变量增加时，试样剪切特征由剪切硬化型转变为剪切软化型、破坏位移逐渐减小(干密度减小时)，轴向应力-应变曲线表现明显的峰后缓和现象并产生明显的变化，破坏模式以鼓胀并伴有裂缝为主，形态由E型逐渐变为G型(干密度减小时)；(3)加固砂土变形特征与养护时间强正相关，与干密度中等负相关，而与高聚物含量相关性不显著，峰值应变与三个研究变量呈多项式(或线性)关系；(4)对于高聚物加固砂土，最佳掺量为约2%，养护24h及以上时效果显著；(5)高聚物通过吸附、黏结和填充作用在砂粒间形成有效稳定的三维网状膜结构，从而改良砂土微观结构，高聚物在荷载下的变化类型占比决定了加固砂土的变形能力和破坏模式，而这与高聚物掺量、养护时间和干密度密切相关。Abstract: Polymer has broad application prospects in soil stabilization. However, there is currently little research on the strength and deformation characteristics of polymer treated soil, as well as the degree of influence of different influencing factors. In this work, a series of unconfined compression strength and shear strength tests were performed on a water-soluble polymer treated sand, and subsequently, the effects of polymer content, curing time and dry density on the strength and deformation characteristics of the treated sand were analyzed. Also, the degree of influence of the three research variables was elucidated using correlation analysis. And finally, the related mechanism of treated sand was revealed using electron microscopy scanning (SEM) observations. The results show that, (1) The three studied variables significantly enhance the unconfined compression strength and shear strength, and the influence of polymer content and curing time on shear strength was mainly reflected in the cohesion. The strength of polymer treated sand is significantly and positively correlated with curing time, and moderately and positively correlated with polymer content and dry density. In addition, these relationships can be represented by a logarithmic function or linear function. (2) As the polymer content, curing time and dry density increase, the shear characteristics of treated sand change from shear hardening type to shear softening type, and the shear failure displacement of treated sand decreases gradually (as dry densities decreases). Also, its axial stress-strain curve shows obvious post-peak easing phenomenon and then produces obvious changes, and the compression failure pattern is dominated by bulging and accompanied by cracks, what’s more, this pattern gradually changes from E-type to G-type (as dry densities decreases). (3) The deformation capacity of treated sand is strongly and positively correlated with curing time, moderately and positively correlated with dry density, while the correlation with polymer content is not significant. Additionally, the peak strain has a polynomial (or linear) relationship with three studied variables. (4) For this polymer treated sand, the optimum mixing content is about 2%, and when the curing time reaches 24h and above, it shows a better treatment effect. (5) The polymer forms an effective and stable three-dimensional membrane structure in the sand particles by adsorption, bonding and filling effects, and thus effectively improves the microstructure of sand. The proportion of changes in the types of polymers under load determines the strength, deformation capacity, and failure mode of treated sand, which is closely related to polymer content, curing time and dry density.
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Key words:
- polymer /
- sand /
- strength properties /
- deformation characteristics /
- correlation analysis /
- micro-mechanism
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图 3 不同高聚物含量下加固砂土剪切应力-位移曲线
Figure 3. Shear stress-displacement curves of polymer treated soil with different polymer contents
图 4 高聚物固化砂土抗剪强度与高聚物含量的关系
Figure 4. Relationship between shear strength and polymer content of treated sand
图 5 高聚物加固砂土试样剪切破坏形态
Figure 5. Shear failure pattern of untreated and polymer treated sand sample
图 6 不同高聚物含量下加固砂土剪切破坏位移
Figure 6. Shear failure displacement of treated sand with different polymer contents
图 7 不同高聚物含量下加固砂土轴向应力-应变曲线
Figure 7. Axial stress-strain curves of treated sand with different polymer contents
图 8 不同高聚物含量下加固砂土试样养护48 h破坏形态
Figure 8. Failure patterns of polymer treated sand with different polymer contents after curing 48 h
图 10 高聚物固化砂土抗剪强度与养护时间的关系
Figure 10. Relationship between the shear strength of polymer treated sand and curing time
图 11 不同养护时间下高聚物固化砂土剪切破坏位移
Figure 11. Shear damage displacement of polymer treated sand at different curing times
图 12 不同养护时间下高聚物固化砂土轴向应力-应变曲线
Figure 12. Axial stress-strain curves of polymer treated sand under different curing times
图 13 不同养护时间下3%高聚物固化砂土试样破坏形态
Figure 13. Compressive failure patterns of treated sand under different curing times
图 14 不同干密度下高聚物固化砂土抗剪强度
Figure 14. Shear strength of polymer treated sand under different dry densities
图 15 不同干密度下高聚物固化砂土剪切破坏位移
Figure 15. Shear damage displacement of treated sand under different dry densities
图 16 不同干密度下高聚物加固砂土轴向应力-应变曲线
Figure 16. Axial stress-strain curves of polymer treated sand under different dry densities
图 17 不同干密度下3%高聚物加固砂土破坏形态
Figure 17. Compressive failure patterns of 3% polymer treated sand under different dry densities
图 23 高聚物加固砂土剪切变形示意图
Figure 23. Schematic diagram of shear deformation of modified sandy soil
图 24 养护时间对高聚物加固砂土水分分布影响示意图
Figure 24. Schematic diagram of the effect of curing time on moisture distribution of polymer treated sand
表 1 砂土基本物理参数
Table 1. Basic physical parameters of sand
Type Specific
gravityMaximum dry density/(g·cm−3) Minimum dry density/(g·cm−3) d10/
mmd30/
mmd50/
mmd60/
mmNonuniform
coefficient CuCurvature
coefficient CcClassifications Sand 2.65 1.69 1.33 0.12 0.23 0.31 0.36 3.00 1.23 Graded poor sand Notes: d10, d30, d50, d60 refer to the grain size at which 10%, 30%, 50% and 60% of the total mass of the sample is contained, respectively, on the distribution curve. 
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表 2 高聚物基本物理参数
Table 2. Basic physical parameters of used polymer
Appearance Gs η/(MPa∙s) Ws /% pH Cw Light yellow
transparent emulsion1.15 700-800 ≥88 7 ≥40 Notes: Gs η, Ws and Cw are the specific gravity, viscosity, sloid content and water holding capacity of the used polymer.
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表 3 不同高聚物含量下加固砂土抗剪强度参数(c：kPa，φ：°)
Table 3. Shear strength index of improved sandy soils with different polymer contents (c: kPa, φ: °)
T/h ρd/(g·cm−3) Wp /% 0 0.5 1 2 3 4 c φ c φ c φ c φ c φ c φ 6 1.5 0.79 29.67 2.79 30.85 7.79 31.09 19.91 30.83 52.69 27.49 71.65 29.95 48 1.5 2.03 29.41 31.17 30.63 78.53 32.08 127.03 36.43 139.25 36.98 183.52 33.27 Notes: T is the curing time, ρd is the dry density of sample and Wp refers to the polymer content.
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表 4 不同高聚物含量下加固砂土抗压强度(kPa)
Table 4. Unconfined compressive strength of polymer treated sand with different polymer contents (kPa)
T/h ρd/(g·cm−3) Wp /% 0.5 1 2 3 4 6 1.5 24.40 67.03 172.31 242.90 360.98 48 1.5 159.21 301.86 458.40 581.37 662.58
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表 5 不同养护时间下高聚物加固砂土抗剪强度参数(c：kPa，φ：°)
Table 5. Shear strength parameters of polymer treated sand cured at different times (c: kPa, φ: °)
Wp /% ρd/(g·cm−3) T/h 1 3 6 12 24 48 72 c φ c φ c φ c φ c φ c φ c φ 1 1.5 3.43 24.12 6.15 26.36 7.79 31.09 13.09 31.26 32.20 31.01 78.53 32.08 133.27 31.00 3 1.5 33.18 28.10 45.19 28.24 52.69 27.49 54.27 28.37 59.47 34.74 139.25 36.98 200.19 37.39
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表 6 不同干密度下高聚物加固砂土抗剪强度参数(c：kPa，φ：°)
Table 6. Shear strength parameter of polymer treated sand under different dry densities (c: kPa, φ: °)
T/h Wp /% ρd/(g·cm−3) 1.4 1.45 1.5 1.55 1.6 c φ c φ c φ c φ c φ 48 1 62.10 28.12 68.73 28.69 78.53 32.08 85.58 34.20 102.94 35.58 48 3 90.96 28.93 122.90 33.51 139.25 36.98 146.55 38.06 160.92 39.30
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表 7 不同因素与高聚物固化砂土强度和变形的相关系数
Table 7. Correlation coefficients of different factors with the strength and deformation capacities of treated sand
Item Wp /% T/h ρd/(g·cm-3) Strength 0.514** 0.698** 0.245* Deformation capacity −0.009 0.730** −0.456** Notes: * indicates P<0.05, and ** indicates P<0.01; 0.2-0.4, 0.4-0.6, 0.6-0.8, 0.8-1 indicate weak correlation, moderate correlation, strong correlation and very strong correlation, respectively.
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