GROUND IMPROVEMENT FOR INFRASTRUCTURE ON PROBLEMATIC SOILS

Key Researchers: Shanyong Wang, John Carter, Stephen Fityus, Jubert Pineda

PROBLEM DESCRIPTION

Soft problematic soils are common along Australia’s coastal fringes, and often increase the cost of building transport infrastructure significantly. Strategies used to support structures on this type of soil include ground treatment, load transfer to deeper and stronger strata, or combinations of both. The design of such measures is currently based on empirical methods.

INNOVATION

This theme will focus on developing advanced ground treatment and deep load-transfer techniques for large projects such as the $5B Pacific Highway upgrade in NSW. This will demand a better understanding of the fundamentals underpinning cost-effective improvement solutions such as static and dynamic compaction grouting (DCG) which, in turn, will lead to the development of a fully coupled soil-grout-pile interaction model ; optimisation of the dynamic compaction frequency for specific mechanical properties of the soil; and inclusion of strain rate effects. A key advantage of DCG over static compaction grouting is that it gives greater densification for the same grout volume, static pressure and compaction effort. Another focus of this work will be a new form of soil nailing, pioneered by Prof. Shanyong Wang, which employs a novel design with multiple confined grout bulbs to maximise the pull-out capacity and minimise uncontrolled grout leakage. This will entail a detailed study of grout-induced fracture in soils as well as the formulation and implementation of robust grout diffusion models in three-phase media.

SCIENTIFIC AND ENGINEERING APPROACHES

  • Seek a method for predicting the soil fracture direction of single and multiple injections through laboratory experiments.
  • Investigate grouting behavior, the influence of the grouting operation on existing structures, and the ground surface displacement pattern under a working stress level by conducting centrifuge tests. These tests will be simulated numerically.
  • Investigate the fundamental mechanism of hydraulic fracturing in heterogeneous soils, due to grout penetration, using the newly developed numerical model. The coupled effects of seepage, damage and stress will be considered.
  • Reveal the grout diffusion characteristics and corresponding soil responses during the grouting and pull-out process in various types of soil;
  • Provide a systematic experimental and theoretical understanding of the effects of a variety of factors (e.g., grout injection pressure, injection volume, grout viscosity, soil types, initial soil density, degree of saturation, ground stress conditions and effective confining pressure) on the grout-soil interactions.

APPLICATIONS

  • Establish a cost effective fracture-controlled compensation grouting design criteria which optimizes the compensation efficiency and minimizes the grouting cost and the risk of damage to nearby structures.

Figure 1

Figure 1: Ground improvement with DCG

Figure 2

Figure 2: Capturing of photographs and the generated 3D grout model