Introduction
The Laboratory explores and addresses issues associated with the use of high performance materials, especially high strength steel materials or composite structural elements, in various aspects of foundation engineering and underground construction. In particular, the stress mobilizations and strain developments in soil-structure interaction problems.
Research Team of the Lab
- Laboratory-in-charge
- Dr Andy Leung
- Members
- Dr Horace Lo (Postdoctoral researcher)
- Mr A. Abdullah (PhD student)
Lab details
1.Strain developments in composite structural elements
Composite structural elements, such as concrete-filled steel tube utilizes the confinements provided by steel tube to enhance the performance of concrete column, and can have wide range of applications in superstructures and substructures. The strain developments and interaction between these two elements are, however, not well understood.
With the high-resolution optical fibre optic sensors and analyser (housed at Z520 Smart Geotechnology Laboratory), the composite structural elements can be instrumented during experiments, in such a way that the strain developments can be accurately captured. This provides a new means to understand the interaction between concrete and steel tubular structures of different geometries (circular, hexagonal, etc.)
The strain sensing technique is based on based on Optical Frequency Domain Reflectometry (OFDR), and the analyser (Semicon OSI-S) is an ultra-high precision diagnostic and distributed optical fibre sensing instrument, with spatial resolution of 1 mm and measurement accuracy of ±1.0 micro strain (με). The main advantage lies on the continuous strain profile that can be obtained from these measurements, which reveals more detailed features of the response than discrete measurements by conventional strain gauges. The photos of the optical fibre and sensing instruments are shown in Figure 1.
2.Effective use of high-strength steel material in foundations and lateral support system of deep excavation
The use of high-strength steel as foundation elements is associated with some clear benefits, as it entails higher (structural) capacity compared with H piles with normal grade steel, and is easier to handle and construct compared with other large-diameter concrete piles (bored piles). This project/task involves investigation, together with industrial partners, on the application of such high strength steel in foundation elements, such as socketed H piles or driven piles. The benefits and precautions associated with these applications will be explored, through numerical simulations of soil-structure interaction of the piles embedded in soils and rocks, laboratory testing of the structural elements, etc. Focused working group/meetings will be held with industrial partners and authorities to explore potential sites for the application.
Apart from utilizing the H sections as foundation piles, there are also benefits on their applications as lateral support elements (struts, walers, king posts) in deep excavation projects or other underground construction scenarios. Another direction to be explored involves the application of high strength threadbars as foundation or geotechnical elements, such as micropiles, ground anchors and soil nails. This would involve laboratory testing and numerical simulations of these elements embedded in soils with various conditions. The high accuracy, continuous strain measurement technique mentioned above also plays an important role in the experimental investigations.
3.Installation and pile driving in high strength steel materials
Various aspects of pile engineering, including the installation (e.g., welding and pile driving) process and the performance in soil-structure interactions involving the high strength materials have not been thoroughly understood. While the welding process will be investigated in considerable details by another laboratory of CNERC, this project will analyse the potential pile driving effects in H sections of high strength steel materials.
This project objective aims to extend the wave equation analysis for pile driving process to enhance understanding of the compressive and tensile stresses generated in the high strength steel material during pile installation. Recommendations will then be made associated with pile driving stress and allowable working stress, so that more specific guidance can be applied to foundation designs with high performance steel./p>
Expected deliverables:
- Research publications in reputed journals on the foundation and geotechnical applications of high strength steel and composite structural elements
- Focused workshops/meetings to discuss with key stakeholders the benefits/precautions of the applications
- A set of procedures for the installation of fibre optic sensors in foundation and excavation projects, to obtain high resolution and high accuracy strain measurements
