| Popis: |
Buildings, utility services, and transportation links in towns and cities built on expansive clay soils often suffer distortion and/or structural damage. This damage is caused by shrinkage and/or expansion of expansive soils through water extraction or absorption. Movement of clay may be estimated using testing protocols, with results depending on the method employed and sample preparation. Communities throughout the world continue to spend billions of dollars annually on rectification works due to the “unpredictable” movement of these soils. The aim of this chapter is to provide a summary of current literature and suggest a pathway to ensure constructed design meets its expected design life. Specific focus is on scenarios with combinations of expansive clays, tree species and root architecture (type and distribution of roots), chemical soil stabilization additives, and infrastructure materials. Deeply rooted trees growing in expansive clay suburban residential environments are known to exacerbate shrinkage movement through soil desiccation as the tree roots extract soil water. However, vegetation can provide a stabilizing effect, particularly, for example, for the usually wet subgrades underlying rail tracks and for sloped embankments built on moist to wet clay soils. The destabilization and/or stabilization of clay soils due to tree roots extracting and/or redistributing moisture in soil profiles in both suburban residential and rail track environments is yet to be reliably quantified through modeling, as conceded in the design standards in Australia for construction of residential footings. The distribution and interaction of the roots with the soil of various tree species in an expansive clay profile, particularly specific environments such as streets and rail corridors, is not predictable with current knowledge. The environment will impact on the tree root architecture. Numerical modeling of the influence of vegetation on soil requires an understanding of where the roots will be. Without this knowledge, prediction of either expansive clay ground movements or ground improvement due to trees growing next to buildings, roads, rail tracks, and sloped embankments will be misguided. The design of buildings and infrastructure on expansive clays may be undertaken with an understanding of trees and their root architecture and the soil suctions that are likely to be developed within and around the root zone. In conjunction with knowledge of the structural capacity of the materials of construction and, in some cases, the possibility of mitigating expansive soil movement with chemical additives, considerable savings may ensue through minimizing rectification during the operational life of the structure. |
