Stability and durability of polymers and clay-polymer composites in geotechnical environments

聚合物在许多岩土工程和岩土环境应用中被用来取代膨润土或改善其性能，例如，在土工合成粘土衬里中作为支撑液，在机械化隧道施工中作为润滑剂和土壤改良剂。然而，聚合物在其使用寿命期间会发生降解。在土壤中，聚合物的降解是由机械和化学压力或由于生物活动引起的。降解会改变相关的聚合物性质，如聚合物的摩尔质量、电荷分布和组成。随后，发现聚合物的相关工程性质渗透性、强度和体积特性也发生了变化。甚至在文献中也有关于有毒降解产物释放的报道。这导致了岩土工程应用中聚合物的稳定性和耐久性方面的重大不确定性。稳定性降低，流动性增加，耐久性不足可能意味着土壤可能受到污染。目前的研究建议集中在土工应用中由相关的水力、力学和生物影响引起的聚合物和聚合物增强土壤的变化。合成聚合物和生物聚合物都被考虑。该项目分为以下几个部分：(1)用于土力学实验室测试的聚合物表征技术的发展；(2)聚合物和聚合物改性土在摩擦流、机械应力和生物活性作用下的降解实验研究；(3)利用数值模拟评估聚合物及其降解产物的迁移性。电荷性质将与已知的盐浓度变化引起的粘度变化有关。使用Hagen-Poiseuille方程根据流变仪测试结果校准简单的流出测试，以确定粘度，并计划用于各种聚合物的快速表征。在第二部分中，将通过充分的实验研究阴离子聚合物溶液的摩擦流动、作用于阳离子聚合物改性干(脆)或湿(韧)土上的机械剪应力，或阳离子和阴离子聚合物-土壤混合物中具有生物活性的微生物所引起的降解。退化将根据测量的塑性特性、渗透率、粘度、峰值强度、应力应变行为和不排水剪切强度以及各自退化影响前后的膨胀指数来量化。研究项目的第三部分包括(使用PLAXIS 3D PlaxFlow)以粘度为主要参数对聚合物和降解产物的流动性进行数值研究。为此，将对早期开发的针对聚合物溶液的数值方法进行修改。

Polymers are used in numerous geotechnical and geoenvironmental applications to replace bentonite or improve its performance, e.g. as support fluids, in geosynthetic clay liners, as lubrification agent and soil conditioner in mechanized tunnelling. However, polymers are subjected to degradation during their service life time. In soils, degradation of the polymer is caused by mechanical and chemical stresses or due to biological activities. Degradation alters the relevant polymer properties, such as molar mass, charge distribution and composition of the polymer. Subsequently, also the relevant engineering properties permeability, strength, and volumetric behaviour of the polymer are found to alter. Even the release of toxic degradation products has been reported in literature. This leads to significant uncertainties with respect to the stability and durability of polymers within geotechnical applications. A reduced stability, thus increased mobility, and an insufficient durability can imply possible pollution of the soil.The current research proposal focuses on the alteration of polymers and polymer enhanced soils caused by relevant hydraulic, mechanical and biological impacts in geotechnical applications. Both synthetic polymer and biopolymer are considered. The project is divided in the main parts: (1) development of techniques for the characterization of polymers adopted to soil mechanics laboratory testing, (2) experimental investigation on degradation of polymers and polymer-modified soils subjected to frictional flow, mechanical stresses and biological activity, (3) assessment of the mobility of polymers and their degradation products using numerical modelling.In the first part, by an extensive experimental program, correlations between the molar mass and the viscosity are established. The charge properties will be related to a change in viscosity by the known change in salt concentration. A simple outflow test is calibrated against rheometer test results for determining viscosity using Hagen-Poiseuille equation and is planned to be used for quick characterisation of the various polymers. In the second part, the investigation of degradation induced by frictional flow of anionic polymer solutions, by mechanical shear stresses acting on dry (brittle) or wet (ductile) soil modified with cationic polymers, or by biologically active microorganisms in cationic and anionic polymer-soil mixtures will be performed using adequate experiments. Degradation will be quantified based on measured plasticity properties, permeability, viscosity, peak strength, stress-strain behaviour and undrained shear strength, and swell index prior and after the respective degradation impact. The third part of the research project covers a numerical study (with PLAXIS 3D PlaxFlow) on the mobility of polymers and degradation products using viscosity as the main parameter. For this, an earlier developed numerical approach will be modified with respect to polymer solutions.