We have developed various types of geotechnical tests: (1) scaled model testing, in which we aim to address the reclamation related geotechnical problems, such as sedimentation and consolidation of marine deposits, marine reclamation by super-fast consolidation methods, FRP pile behaviour filled with sand or cemented sand, and clay-FRP pile interaction under static and cyclic loadings; (2) advanced soil element testing, in which the soil element performance can be clarified by several advanced testing apparatuses, including multi-functional soil-structure interface testing apparatus, PolyU-patented true triaxial apparatus, dynamic hollow cylinder apparatus, and biaxial testing apparatus; and (3) soil microstructural testing, in which the soil microstructure can be well identified by X-ray computed micro-tomography, scanning electron microscope (SEM) and mercury intrusion porosimetry (MIP) test, with the relevant apparatus in PolyU and CEE.

Topic 1: Scaled model testing

Related PhD students | Yu PanKai LOUNuman MALIKJing-Cheng TENGShao-Qun LIN

1.1 Sedimentation and consolidation of marine deposits for reclamation

Hong Kong faces severe scarcity of construction land and reclamation is an effective solution. To reduce the expense of filling material and the environmental impact, sometimes the marine clays on the neighboring seabed would be used as filling material. However, the poor engineering properties of marine clay would induce difficulties for construction. Another problem is that there are two stages during the whole reclamation process: sedimentation and consolidation. Traditional research focuses on primary consolidation only. In addition, conventional tests use different devices to study sedimentation and consolidation separately. However, the soil deformation is a continuous process. This study is to development a novel apparatus for simulating the complete reclamation process in a continuous way; to propose a unifying model for linking sedimentation and consolidation; and to find a fast and effective way for soil improvement in reclamation.

1.2 Marine reclamation by super-fast consolidation methods

Ground improvement methods are usually introduced to accelerate the consolidation process of the dredged soil. Prefabricated vertical drains (PVDs) with vacuum preloading and surcharge preloading are commonly used in reclamation projects. Considering the problems existed in PVDs method, like time-consuming, limited vacuum pressure, prefabricated horizontal drains (PHDs) with vacuum preloading is jointly studied to increase the efficiency. This study is to investigate the combined efficiency of PVDs and PHDs, providing a critical support to the application of this proposed new super-fast consolidation method in practical reclamation projects. The application of multiple layers of PHDs, and its effective treating height will be studied. A new theory for the PHDs and PVDs with vacuum preloading in Hong Kong marine deposit will be proposed based on the large-scale physical model test.

1.3 FRP pile filled with sand or cemented sand

Steel is commonly adopted for the pile-wall in reclamation engineering, but its corrosion poses a great challenge to the service life. By contrast, a new type of corrosion-resistant material, fiber-reinforced polymer (FRP), is getting increasing attention as an alternative of steel in marine environment. The FRP material directly eliminates the corrosion issue, thereby bringing sustainability benefits to marine infrastructures. In addition, in reclamation engineering, sand or cemented sand will be filled into the FRP pile to increase its stability. Therefore, the flexural behavior and compressive behavior of the FRP pile should be clearly understood. Some findings can be summarized that: (1) sand filling in the FRP piles can increase its ductility in terms of flexural behavior but cannot increase its stiffness, and cemented sand filling in the FRP pile can increase the stiffness of the FRP pile; (2) filling sand in FRP piles can improve the ductility of piles and avoid buckling problem in the compression test, and the ultimate compressive stress of cemented sand-filled FRP pile is lower than sand-filled FRP pile.

1.4 Clay-FRP pile interaction under static and cyclic loadings

The interface shear behaviour between pile materials (steel, concrete, and wood) and marine clay is not sufficient known. To design reliable and cost-effective pile foundation in the coastal areas, it is essential to understand the mechanical behaviour at the interface of the pile and marine clay. Since the studies show that the application of FRP or composites with other construction materials, such as steel, concrete, etc., can sufficiently improve the engineering properties of pile foundation, it is crucial to study the marine clay-FRP interface behaviour in details for better engineering designs and applications. This study is to design and develop a new physical model for the study of the marine clay-FRP interface behaviour under complex static and cyclic loadings; and to study the variations of interface pore pressure and soil stresses.


Topic 2: Advanced soil element testing

Related PhD students | Bidur PATHAKNa YANG

2.1 Multi-functional soil-structure interface testing apparatus

The apparatus has the following features: (1) constant normal stress and constant normal stiffness can be applied; (2) in the shear direction, both monotonic and cyclic loadings can be applied; and (3) temperature control can be fulfilled for the testing sample.

2.2 PolyU-patented true triaxial apparatus

The true triaxial apparatus was developed by Prof. Jian-Hua Yin, and is a laboratory testing equipment to study the soil behaviour under three-dimensional stress state, which is the real state of in-situ soils. The sliding loading plates are patented by PolyU.

2.3 Dynamic hollow cylinder apparatus

Capable of controlling 4 independent loadings for studying behaviour of a hollow soil specimen under (a) pure shearing; (b) plane strain; (c) rotation of the principal stress; (d) influence of the middle principal stress.

2.4 Biaxial testing apparatus

Capable of simulating plain strain testing condition of soils (1 direction confining pressure, 1 direction fix end, 1 direction deviator stress).


Topic 3: Soil microstructural testing

Related PhD students | Kai LOU

3.1 X-ray computed micro-tomography apparatus

Except for the macro-scale laboratory test and the large-scale model test, the microstructural identification for soils is also important to understand the underlying mechanisms for complex geotechnical problems. Recently, an X-ray computed microtomography apparatus XT H 225 ST (Nikon) has been installed in our department, with a minimum focal spot size of 1 μm, maximum energy of 225 kV, maximum power of 450 W for the X-ray source and minimum pixel size of 150 μm for the detector. The relevant microstructural investigation of soils can be completed using this facility with satisfactory resolution.

3.2 SEM and MIP testing

In the Department of the PI, we have the necessary testing apparatuses to clarify the soil microstructure by scanning electron microscope (SEM) and the soil pore size distribution by mercury intrusion porosimetry (MIP) test.