Design, construction and performance of buildings foundations on soft clays in the Brisbane region

Abstract

[Abstract]: This project is a study on the various methods used to construct buildings on soft clays in the Brisbane region which is located in the South Eastern corner of Queensland, Australia. This location enjoys long summers and relatively mild winters, especially compared to those found in the northern hemisphere. The study also compares them to world’s best practice and explains the many different ways of constructing buildings on soft clay. Consideration is also given to new techniques and developments in the area of soft clay foundation design. As the population of the Brisbane region and South East Qld grows the amount of quality land available for buildings declines. This makes the prospect of building in areas once thought too expensive, due to poor soil conditions, more appealing. Large areas of Brisbane, particularly around the mouth of the Brisbane River are underlain by soft clays. The Brisbane region has a diverse range of geology, ranging from volcanic rock formations through to soft estuarine deposits. As would be expected the majority of the soft clay deposits are along the Brisbane River and its tributaries. The objectives of this thesis are to show the various methods for building foundations used in the Brisbane region in soft clays. The advantages and disadvantages of these are discussed as well as other potential methods that could possibly be adopted. The predominant foundation type used in the soft clays in the Brisbane region are deep foundations. These transfer the load from the structure to suitable material beneath the soft clay, typically rock and they generally comprise a concrete pier bored through this upper soft clay material and socketed into the underlying rock. Variations of this method are also found in the form of driven piers and Continuous Flight Auger (CFA) piles. Other methods that are utilised include lime stabilisation, heavy impact, bridging and ground replacement. The testing that is used to determine what foundation option would be suitable usually consists of a borehole with insitu-testing. Cone Penetration Testing (CPT) testing may also be undertaken as another form of insitu-testing. Samples collected from the borehole drilling may be tested for consolidation and strength. There are many techniques that are now readily available that can be used to support buildings founding in soft clays. This thesis aims to highlight the current techniques used in the Brisbane region and compare them to those used in other areas of the world.