Advanced testing apparatuses for unsaturated soil

Extensive advanced apparatuses are developed for testing unsaturated soil, including full-suction triaxial apparatus and direct shear box, one-dimensional instantaneous soil permeability apparatus, stress controlled pressure plate extractor (1D and 3D), and double cell volume measuring system. These apparatuses are adopted to investigate unsaturated soil behaviour with various applications, e.g., loose fill slopes in Hong Kong, expansive soil slope stability in the South–North Water Transfer Project, high-speed railway embankments and landfill covers. The above mentioned apparatuses have also been awarded patents. In particular, the double cell volume measuring system was adopted by the manufacturer GDS and is now a standard method to measure the volume change of unsaturated soils. It has been adopted by over 100 universities and scientific institutions. 

Full suction triaxial apparatus 
(Ng & Menzies 2007)

Full-suction direct shear box for 
unsaturated soil 
(Ng 2014)

Stress-dependent 1D soil column 
(Ng & Leung 2011)

Stress-controlled 1D pressure plate 
(Ng & Pang 2000)

Stress-controlled 3D pressure extractor 
(Ng et al. 2012)

Double cell total volume 
measuring system 
(Ng et al. 2002)

Temperature-controlled testing apparatuses

Various apparatuses are equipped with heating and cooling system, which are able to control soil temperature in a wide temperature range of -10 to 80C. Using these thermal apparatuses, the cyclic thermo-mechanical behaviour of saturated and unsaturated soils are systematically investigated, with application to energy pile, high-speed railway embankment, landfill cover and frozen ground. 

Temperature controlled 
cyclic triaxial cell 
(Ng & Zhou 2014)

Temperature controlled double 
cell triaxial cell 
(Ng et al. 2016a)

Temperature controlled direct 
shear box 
(Ng et al. 2017)

Advanced apparatuses enabling complex loading conditions

This laboratory possesses the hollow cylinder torsional shear device and true triaxial apparatus. Compared with the conventional triaxial apparatus, these apparatuses are much more versatile and powerful. They are used to simulate many complex loading conditions for constitutive model verifications as well as to test soil behaviour under various field loading conditions such as seismic loading, wave loading and traffic loads.

Hollow cylinder torsional shear device 
(Yang et al. 2007)

True triaxial apparatus

Mechanical and electromagnetic wave-based characterizations of soil properties

Mechanical and electromagnetic wave-based systems are developed to investigate the anisotropic soil stiffness, which is important for analysing ground response under dynamic loads and the serviceability of civil engineering structures. Some examples are given here: (a) Resonant column designed to determine shear moduli and damping ratios of soil specimens at small strains; (b) Unsaturated triaxial apparatus equipped with three pairs of bender elements for measuring anisotropic stiffness; (c) True triaxial apparatus with bender element system and I-scan system (tactile pressure sensors) for multi-purposes, e.g., measuring stiffness and associated anisotropy changes during soil aging, monitoring the evolution of contact forces during the aging process; (d) Multi-functional oedometer cell with mechanical and EM wave-based sensing system for characterizations of soil behaviour, e.g., monitoring the formation of clay fabric associations during the sedimentation process, and characterizing clay fabric associations using the spectral dielectric responses. 

Energy-injecting virtual mass resonant column 
(Li et al. 1998)

True triaxial apparatus with bender element and I-scan system 
(Wang et al. 2016)

Bender element for measuring anisotropic stiffness 
(Ng & Yung 2008)

Multi-functional oedometer cell 
(Wang & Dong 2008)

Geotechnical testing based on 3D printing technique

The geotechnical group in HKUST benefits from the application of 3D printing techniques on innovation of geotechnical testing devices and sensing techniques. Examples include (a) A biaxial system with flexible boundaries is designed to characterize the features of particle motion and associated contact movement in response to shearing, using the particle image velocimetry (PIV) technique. The 3D printing technique is applied to ease manufacture of the testing device and testing sample with very high accuracy. (b) 3D printed portable oedometer and tailor-made oedometer ring with a needle probe to measure pore water pressure and film-like sensor to measure K0.

Biaxial system with flexible boundaries 
(Yuan et al. 2016)

3D printed portable oedometer with film-like 
sensors and the needle probe 
( Chow and Wang 2017; Gao et al. 2017)

Geo-environmental room

The geo-environmental room (4 m  4.5 m  2.8 m) is designed to control various atmospheric parameters, including air temperature, relatively humidity, rainfall intensity and light intensity within a particular waveband favourable for plant photosynthesis and plant growth. This room is adopted to investigate the mechanisms of atmosphere-plant-soil interactions. The results provide a scientific basis for a wide range of applications, such as the stabilization of shallow slope, erosion control, design of earthen landfill cover, phytoremediation, and promoting the growth of Chinese medicinal plants. 

Geo-environmental room 
(Ng et al. 2016b)

Soil conditioning for promoting the growth of 
Chinese medicinal plants 
(e.g. ginseng)

Apparatuses for studying internal erosion and surface erosion

The stress-controlled internal erosion testing apparatus control hydraulic gradient and stress state independently. It allows a systematic investigation of the initiation and development of internal erosion subjected to complex stress states. In addition, a great benefit of this apparatus is its capability to investigate the stress-strain behaviour of the soil immediately after the internal erosion test. The Jet index erodibility test apparatus was modified from the ASTM standard D5852-00 apparatus, to allow testing the erodibility of relatively coarse soils and to eliminate turbulent effects of water inflow. The apparatus provides an important means for investigating the initiation of debris flows, soil and water conservation, and sediment transport.

Stress-controlled internal erosion testing apparatus 
(Chang & Zhang, 2011)

Jet index erodibility testing apparatus 
(Chang et al. 2011)

Physical models with innovative instrumentations

Various physical models with innovative instrumentations are built. The first example is a water flume with innovative instrumentation. In particular, low-cost and small-size MEMS (Micro-Electro-Mechanical-Systems) accelerometers and a MEMS sensing package, termed the Smart Soil Particle (SSP, first generation), is used to monitor movements of the slope body. Another example is a new pressure chamber with advanced sensing devices for model pile test. It allows for characterizing stress evolution in the soil surrounding the model pile during pile installation and setup, using the tactile pressure sensors and mechanical wave-based tomography imaging.

Figure 47. Water flume with Smart Soil Particle 
(Ooi et al. 2014)

Figure 48. Pressure chamber with advanced 
sensing devices for model pile test 
(Zhang & Wang 2015)

Data-enabled Scalable Research Laboratory

The Data-enabled Scalable Research Laboratory (DESR Lab) is the Makerspace specialized in the applications of Geotechnical Internet of Things (Geo-IoT), Deep Learning, and Big Data Analytics on the sustainable city development, e.g., critical infrastructure monitoring and slope health monitoring, and an open platform for geotechnical industries to collaborate and share resources.

Figure 49. Smart Soil Particle sensor for slope health monitoring 
(Geo-IoT sensor node)

Figure 50. The Smart Soil Particle installed at field

Figure 51. Big data server farm at the DESR Lab.


Chang, D.S., Zhang, L., Xu, Y. & Huang, R. (2011). Field testing of erodibility of two landslide dams triggered by the 12 May Wenchuan earthquake. Landslides 8, No. 3, 321-332.

Chang, D.S. & Zhang, L.M. (2011). A stress-controlled erosion apparatus for studying internal erosion in soils. Geotechnical Testing Journal, ASTM 34, No. 6, 579-589.

Chow, J.K. & Wang, Y.H. (2017). Preparation of high-quality load-preserved fabric clay samples for microstructural characterizations: a pragmatic guide featuring a 3D-printed oedometer. Geotechnical Testing Journal, ASTM (accepted for publication).

Gao, Y., Wang, Y.H. & Chow, J.K. (2017). Application of film-like sensors for K0 and pore water pressure measurement in clay during 1D consolidation. Geotechnical Testing Journal, ASTM 40, No. 1, 134-143.

Li, X. S., Yang, W. L., Shen, C. K. & Wang, W. C. (1998). Energy-injecting virtual mass resonant column system. Journal of Geotechnical and Geoenvironmental Engineering, ASCE 124, No. 5, 428-438.

Ng, C.W.W. (2014). Humidity and osmotic suction-controlled box. US Patent, 8 800 353 B2.

Ng, C.W.W., Cheng, Q., Zhou, C. & Alonso, E.E. (2016a). Volume changes of an unsaturated clay during heating and cooling. Géotechnique Letters 6, No. 3, 192-198.

Ng, C.W.W., Lai, C.H. & Chiu, C.F. (2012). A modified triaxial apparatus for measuring the stress path-dependent water retention curve. Geotechnical Testing Journal, ASTM 35, No. 3, 490-495.

Ng, C.W.W. & Leung, A.K. (2011). Measurements of drying and wetting permeability functions using a new stress-controllable soil column. Journal of Geotechnical and Geoenvironmental Engineering, ASCE 138, No. 1, 58-68.

Ng, C.W.W. & Menzies, B. (2007). Advanced unsaturated soil mechanics and engineering, Taylor & Francis, London and NY.

Ng, C.W.W., Mu, Q.Y. & Zhou, C. (2017). Effects of soil structure on the shear behaviour of an unsaturated loess at different suctions and temperatures. Canadian Geotechnical Journal 54, No. 2, 270-279.

Ng, C.W.W., Ni, J.J., Leung, A.K., Zhou, C. & Wang, Z.J. (2016b). Effects of planting density on tree growth and induced soil suction. Géotechnique 66, No. 9, 711-724.

Ng, C.W.W. & Pang, Y.W. (2000). Influence of stress state on soil-water characteristics and slope stability. Journal of Geotechnical and Geoenvironmental Engineering, ASCE 126, No. 2, 157-166.

Ng, C.W.W. & Yung, S.Y. (2008). Determination of the anisotropic shear stiffness of an unsaturated decomposed soil. Géotechnique 58, No. 1, 23-35.

Ng, C.W.W., Zhan, L.T. & Cui, Y.J. (2002). A new simple system for measuring volume changes in unsaturated soils. Canadian Geotechnical Journal 39, No. 3, 757-764.

Ng, C.W.W. & Zhou, C. (2014). Cyclic behaviour of an unsaturated silt at various suctions and temperatures. Géotechnique 64, No. 9, 709-720.

Ooi, G.L., Wang, Y.H., Tan, P.S., So, C.F., Leung, M.L., Li, X. & Lok, K.H. (2014). An instrumented flume to characterize the initiation features of flow landslides. Geotechnical Testing Journal, ASTM 37, No. 5, 748-768.

Wang, Y.H. & Dong, X.B. (2008). Complementary wave-based characterizations of sedimentation processes. Journal of Geotechnical and Geoenvironmental Engineering, ASCE 134, No. 1, 47-56.

Wang, Y.H., Gao, Y. & Ooi, G.L. (2016). Experimental characterizations of an aging mechanism of sands. Journal of Geotechnical and Geoenvironmental Engineering, ASCE 142, No. 2, DOI: 10.1061/(ASCE)GT.1943-5606.0001413.

Yang, Z.X., Li, X.S. & Yang, J. (2007). Undrained anisotropy and rotational shear in granular soil. Géotechnique 57, No. 4, 371-384.

Yuan, Q., Wang, Y.H., Tam, P.O., Li, X. & Gao, Y. (2016). Making a biaxial testing system with the aid of 3D printing technique to examine the kinetic behavior of particulate media. Geotechnical Testing Journal, ASTM 39, No. 2, 264-281.

Zhang, Z.T. & Wang, Y.H. (2015). Examining setup mechanisms of driven piles in sand using laboratory model pile tests. Journal of Geotechnical and Geoenvironmental Engineering, ASCE 141, No. 3, DOI: 10.1061/(ASCE)GT.1943-5606.0001252.