摘要
使用胶结型高聚物对粉土进行固化,研究了高聚物掺量、粉土含水率、养护龄期对固化粉土力学特性的影响及其固化机理.结果表明:高聚物对粉土具有良好的固化效果,高聚物掺量越高,粉土含水率越低,养护龄期越长,固化土的强度越高;高聚物能够有效附着在粉土表面,并填充于粉土颗粒之间,主要通过“包裹”、“填充”、“桥接”作用,减小粉土的孔隙比,提高粉土的密实度,从而提升粉土的强度和抗渗性,但在此过程中没有生成新的化合物.
粉土具有孔隙率高、容易吸水引发翻浆、动荷载作用下易液
本文研发了一种可固化粉土的胶结型高聚物,通过室内试验从宏观方面探究含水率、高聚物掺量及养护龄期对固化粉土力学特性的影响,并借助扫描电子显微镜(SEM)、X射线衍射(XRD)以及压汞试验(MIP),从微观方面揭示粉土的固化规律和改良机理,旨在为粉土的加固提供新的思路,并为高聚物类固化剂的研究提供一定的科学依据.
试验用土取自郑州某建设工地,取土深度为3 m,土的物理性能如

图1 粉土的颗粒分布曲线
Fig.1 Particle size distribution of silt soil
试验用高聚物为本课题组研发的一种胶结型聚氨酯类材料,由A、B双组分构成:A组分基本组成为多元醇、表面活性剂和阻燃剂等,密度为1.26 g/c

图2 高聚物抗压强度随龄期的变化
Fig.2 Compressive strength of polymer varies with age
使用无侧限抗压强度来表征固化土的强度特性,主要研究高聚物掺量(质量分数,文中涉及的掺量、水固比等除特别说明外均为质量分数或质量比)、粉土含水率和养护龄期对固化土力学特性的影响.无侧限抗压强度试验方案设计如
抗渗性是固化土的关键性能之一,根据已有的试验结果,设置高聚物固化土的渗透系数影响因素取值水平.渗透系数试验方案设计如

图3 不同含水率下高聚物掺量与固化土无侧限抗压强度的关系
Fig.3 Relationship between polymer content and UCS of solidified silt soil at different water contents
从

图4 固化土无侧限抗压强度与养护龄期的关系
Fig.4 Relationship between UCS and curing time of solidified silt soil

图5 固化土无侧限抗压强度与粉土含水率的关系
Fig.5 Relationship between UCS of solidified silt soil and moisture content of silt soil
从

图6 含水率为8% 时固化土渗透系数与高聚物掺量的关系
Fig.6 Relation ship between k values of the solidified silt soil and polymer contents under 8% water content
(1)在相同龄期下,随着高聚物掺量的增加,固化土的渗透系数逐渐减小.这是因为在相同条件下,高聚物掺量增大,反应后产物会增多,这会导致土的密实度增加,从而使固化土的渗透系数逐渐减小.
(2)随着高聚物掺量的增加,渗透系数下降曲线的趋势并不相同,在高聚物掺量处于较低水平时,渗透系数下降较为“陡峭”,在高聚物掺量处于较高水平时,渗透系数下降较为“平缓”.这是因为高聚物掺量较少时,土颗粒间的大孔隙是主要的渗流通道,掺入粉土中的高聚物基本填充于土颗粒间的较大孔隙.随着高聚物掺量的增多,大孔隙基本被填充后,土颗粒间的微孔隙将被继续填充,而小孔隙对渗透系数的影响较小,因而在高聚物掺量较高时,渗透系数随高聚物掺量的变化就较小.这一结论与水泥土试验规律相近,且高聚物固化土与水泥土的渗透系数基本处于同一数量
前文分别讨论了高聚物掺量、粉土含水率、养护龄期对固化土无侧限抗压强度及渗透系数的影响,这些宏观性能的改变往往由微观特性引起,因此从微观角度分析固化土的性质具有重要意义.

图7 高聚物对粉土不同作用形式的SEM图像
Fig.7 SEM images of different polymer interaction forms
(1)含水率8%、未掺高聚物的粉土中土颗粒分布松散,孔隙较大,土颗粒在震动、挤压等外力作用下仍具有可压缩变形的能力.
(2)高聚物固化土的作用形式分为3种:一是如

图8 素土及高聚物固化土试样的EDS测试结果
Fig.8 EDS test results of pure and solidified silt soil samples

图9 素土及高聚物固化土的XRD图谱
Fig.9 XRD patterns of pure silt soil and solidified silt soil
孔隙结构特征对粉土的强度有着重要的影响,而高聚物的掺入会改变粉土的孔隙特征,因此研究高聚物掺入前后粉土孔隙结构的变化,对揭示高聚物固化机制有重要的意义.

图10 含水率为8% 时不同高聚物掺量试样的孔隙直径分布图
Fig.10 Pore diameter distribution diagram of samples with different polymer contents under 8% water content
由
由以上分析可知,高聚物固化土高效可行,可以通过降低土体孔隙率进而明显提高土体的强度.
(1)高聚物能够对粉土进行有效固化,明显提升粉土的无侧限抗压强度.固化土的无侧限抗压强度随着高聚物掺量的增加而提高,随粉土含水率的增加而减小,随着养护时间的延长而提高.高聚物掺量为15%、粉土含水率为8%固化土的28 d无侧限抗压强度为6.24 MPa.
(2)高聚物掺入粉土中后,并没有与粉土颗粒发生化学反应,而是通过“覆盖”、“填充”和“桥接”等作用来填充、挤密、连接粉土,形成较大的土颗粒团聚体,提高了粉土的密实度,充分填充了大孔隙,从而提高了粉土的强度.
(3)当粉土含水率为8%、高聚物掺量为15%时,固化土的性能优异,为较优的固化土配合比.
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