PERMEATION OF POLYMER FLUIDS IN SOILS (POPFS)

当修建铁路隧道或高层建筑的深基础时，第一步是在地面上挖一个大洞。一个关键的挑战是在插入最终的永久结构之前防止开挖的洞坍塌。要做到这一点，一种方法是将一种名为支撑液的特殊液体泵入开挖的孔中。目前，最常用的流体是膨润土粘土悬浮液。当这种液体流入土层周围的土壤时，粘土堵塞了开挖面上土壤中的孔隙空间，形成了一层称为滤饼的层，防止了液体和土壤的运动，并支持了开挖。出现了一种新技术，它使用的流体是聚合物溶液，而不是小粘土颗粒的悬浮液。这些聚合物流体的工作方式与膨润土粘土悬浮液非常不同。正是流体的高粘度防止了孔的坍塌；这些流体可以在不需要形成滤饼的情况下保持挖掘的支撑和安全。使用聚合物流体的支撑系统比使用膨润土悬浮液的系统更便宜，对环境的影响更小。然而，聚合物流体与土壤的相互作用比土壤与膨润土悬浮液的相互作用要复杂得多。因此，设计这些支撑系统的工程师更难准确预测它们将如何工作，这减缓了建筑业对它们的接受。我们的总体目标是提供所需的基础科学，以减少任何技术不确定性，从而使这些材料能够得到更广泛的使用。在这个项目中，拥有实验室和建筑工地聚合物流体工作经验的工程师将与擅长研究多孔材料中流体流动细节的工程师合作，以更好地了解聚合物流体支撑系统的工作原理。这个新组建的团队成员拥有土木工程、机械工程和石油工程的背景，并在伦敦帝国理工学院(ICL)、剑桥大学(UoC)和牛津大学(Oxf)任职。为了提供这项研究，我们将把先进的数值模拟(在ICL)与详细的实验测量(在UOC和Oxf)联系起来。计划中的研究将分为4个工作包(WPS)。在WP1中，ICL的研究人员将使用计算机模型来模拟孔隙空间中的流动，这些计算机模型是使用实际孔隙空间的高分辨率3D X射线图像创建的。这些模型将提供大量详细信息，但由于它们使用大量计算机能力，因此只能考虑较小的体积。因此，在WP2中，ICL将使用一种更简单的模型，称为孔隙网络模型，来运行更大规模的模拟，以查看土壤模型中聚合物前沿的迁移。在WP3中，UOC将使用一种名为渗透仪的特殊开发的实验室设备来研究聚合物流体在真实土壤样本中的流动；将考虑不同类型的聚合物流体。在WP4中，Oxf将开发和执行特殊的2D流动实验，以便我们可以看到聚合物流体流经土壤中的孔隙。我们将使用实验数据来确认计算机模型的工作，计算机模型将产生实验室无法测量的数据，我们将为设计挖掘机的工程师回答的关键问题包括：(1)聚合物流体穿过土壤中的孔隙(我们称之为土壤中聚合物流体的导电性)有多容易？(2)当非常粘性的聚合物流体流入土壤时，对土壤颗粒施加了多大的稳定压力？(3)悬浮在流体中的聚合物链如何与土壤颗粒相互作用？

When tunnels for railways or deep foundations to high rise buildings are built, the first step is to excavate a large hole in the ground. A key challenge is to prevent the excavated hole from collapsing before inserting the final, permenant structure. One way to do this is to pump a special liquid called a support fluid into the open excavated hole. Currently the fluid that is most often used is a suspension of bentonite clay. When this fluid flows into the soil around an excabayion the clay clogs the pore space in the soil at the open face, forming a layer called a filter cake, which prevents fluid and soil movement, and supports the excavation. A newer technology has emerged that uses fluids that are polymer solutions rather than suspensions of small clay particles. These polymer fluids work in a very different way to the bentonite clay suspensions. It is the high viscosity of the fluid that prevents collapse of the hole; these fluids can keep the excavation supported and safe without the need to form a filter cake. Support systems that use polymer fluids are cheaper and have a lower environmental footprint than systems using bentonite suspensions. However the interaction of the polymer fluids and the soil is more complex than the interaction between the soil and the bentonite suspensions. It is therefore more difficult for engineers designing these support systems to predict exactly how they will work and this has slowed their uptake by the construction industry. Our overall aim is to provide the fundamental science needed to reduce any technical uncertainty and therefore enable wider use of these materials. This will have both environmental and economic benefits.In this project engineers with experience of working with polymer-based fluids in the laboratory and on construction sites will team up with engineers who are experts at studying the detail of fluid flow in porous materials to get a much better understanding of how polymer-fluid based support systems work. Members of this newly formed team have backgrounds in civil engineering, mechanical engineering, and petroleum engineering and are based at Imperial College London (ICL), the University of Cambridge (UoC) and the University of Oxford (Oxf). To deliver the research we will link advanced numerical modelling (at ICL) with detailed experimental measurements (at UoC and Oxf ). The planned research will be divided into 4 work packages (WPs). In WP1, researchers at ICL will simulate flow in the pore space using computer models that are created using high resolution 3D X-ray images of the actual pore space. These models will provide a lot of detailed information, but only small volumes can be considered as they use a lot of computer power. Therefore, in WP2 ICL will use a simpler type of model, called a pore network model, to run larger scale simulations to look at the migration of the polymer front in a model of the soil. In WP3, UoC will use a specially developed laboratory apparatus called a permeameter to study the flow of the polymer fluids in real samples of soils; different types of polymer fluids will be considered. In WP4, Oxf will develop and carry out special 2D flow experiments so that we can see the polymer fluid as it flows through the pores in the soil. We will use the experimental data to confirm the computer models work and the computer models will generate data that can't be measured in the laboratory, such as the flow profiles in the 3D voids and the forces on the soil grains.The key questions we will answer for engineers designing excavations will include: (1) How easy it is for the polymer fluid to move through the pores in the soil (we call this the conductivity of the polymer fluid in the soil)?(2) How much stabilizing pressure is exerted on the soil grains as the very viscous polymer fluid flows into the soil?(3) How do the polymer chains suspended in the fluid interact with the soil grains?