Louis Ngai Yuen Wong

The University of Hong Kong | HKU · Department of Earth Sciences

Rock images play a vital role in providing data for engineering geological studies. However, low-light (a.k.a. dark) rock images are often obtained, and the existing methods for image enhancement, whether they are software-based, algorithm-based, or data-driven-based, are incapable of addressing the issue. This paper establishes a novel unsupervise...

The damage of rock joints or fractures upon shear includes the surface damage occurring at the contact asperities and the damage beneath the shear surface within the host rock. The latter is commonly known as off-fault damage and has been much less investigated than the surface damage. The main contribution of this study is to compare and contrast...

Fracture Index (FI), which represents the count of fractures over an arbitrary length of core with similar intensity of fracturing, provides insight into the fracture state of rock masses. Manual interpretation of core is not only time-consuming but also prone to human error. To address these challenges, this study develops a computational algorith...

The brittle failure of rock material is closely related to crack propagation and coalescence. Wing crack is the most common manifestation of crack propagation subject to compression. Previous studies proved that under uniaxial compression, 2D wing cracks were able to propagate extensively and split the rock specimen. In contrast, the propagation of...

Rock classification provides vital information to geosciences and geological engineering practices. Reaping the benefits of the advances of computer vision-based deep learning artificial intelligence (AI) technology, this study aims to develop a next-generation convolutional neural network (CNN) to perform automatic rock classification. Two major c...

Deep cement mixing is a typical ground improvement technique, and has recently been introduced in some large-scale reclamation projects in Hong Kong. There is a lack of internationally recognised testing standard for determining the tensile strength of cement stabilised soil. Owing to its low tensile strength and strain at failure, the practical di...

Natural faults or discontinuities in general are usually rough at different scales, and the roughness of fault surfaces plays a dominant role in determining the mode of sliding (stable or unstable). Understanding the frictional behavior of rough fractures is important for investigating the mechanics and nucleation of earthquakes, and other dynamic...

Rock classification provides vital information to geosciences and geological engineering practices. Reaping the benefits of the advances of computer vision-based deep learning artificial intelligence (AI) technology, this study aims to develop a next-generation convolutional neural network (CNN) to perform automatic rock classification. Two major c...

It is well documented that temperatures higher than 400 ℃ can significantly lower rock strength due to thermally induced decomposition and microcracks. However, rock strength increase under temperatures 25–400 ℃ has also been reported. It remains elusive whether thermal strengthening does exist or it is just an illusion caused by rock heterogeneity...

Thermo-hydro-mechanical (THM) coupling prevails in all sorts of underground activities, and numerical simulation is an effective tool to understand THM coupling. The essence of performing THM coupling simulation lies in solving a system of partial differential equations (PDEs) with displacements (U), pore pressure (P) and temperature (T) as the pri...

Underground engineering is becoming increasingly sophisticated in recent years, exemplified by shale gas recovery, nuclear waste disposal and enhanced geothermal systems. Displacement Discontinuity Method (DDM) and Fictitious Stress Method (FSM) are two branches of boundary element method which can efficiently and accurately simulate fractures and...

Despite a large number of studies examining the effects of high temperature on the physical and mechanical properties of various rock types, few studies have addressed the effects of high temperature on the frictional behavior of rough fractures. As a benchmark of high temperature effects on rock integrity, we measure the uniaxial compression stren...

Thermally induced microcracks alter the mechanical properties of rocks. Mode I loading prevails in nature, while rocks are typically weak in tension. Understanding the effects of pre-existing thermal microcracks on the microcracking mechanisms of granite under mode I loading is of both scientific and practical value. We conducted three-point bendin...

Enhanced geothermal systems (EGS) is currently the most efficient method to mine heat from hot dry rock (HDR) reservoirs. The coupled thermo-hydro-mechanical (THM) effect therein is of critical importance to predict the long-term performance of EGS. A novel 3D THM coupling model integrating displacement discontinuity method (DDM), finite volume met...

Cracks at various scales in rock masses are often subjected to mixed-mode I-II loading in Earth’s dynamic processes and geotechnical engineering works. Insightful understanding of the macroscopic and microscopic cracking mechanisms of rocks under this loading condition is of far-reaching significance. To investigate the effect of the loading condit...

Crack growth and coalescence from discontinuities is the fundamental process that underlies the majority of rock mass failures. Still, however, numerical simulation of this process remains a formidable challenge. The main reasons include that tensile and shear fractures are often mixed in the cracking process, that the cracking patterns depend stro...

Intelligently predicting the frequency and volume of natural hazards, including boulder falls, attracts widespread attention in earth science and engineering communities. Taking Hong Kong, China, which is a highly developed and densely populated city, as a research example, the present paper statistically studies the occurrence of boulder falls bas...

The accurate measurement of joint roughness is the premise for the development of reliable shear strength models and prediction of joint shear strength, the prerequisite of which is a proper choice of a reference plane for the calculation of joint roughness parameters. The plane perpendicular to the direction of the applied normal load and the best...

Grain size effect on rock strength is a topic of great interest in geotechnical engineering. A consensus obtained from earlier laboratory tests is that rock strength generally decreases with the increase of grain size for both silicate and carbonate rocks; however, some recent numerical results conflict with such laboratory test results. To address...

We present a two-dimensional conceptual model to investigate the mechanisms of brittle fracturing in low-porosity rock. Biaxial compression tests are simulated on rock specimens containing preexisting fractures, in which the local fracturing processes leading to fault nucleation are closely observed. The impact of fracture configuration and applied...

An in-depth understanding of the thermomechanical properties of rocks is fundamentally important in many fields of geotechnical engineering. However, the microcracking mechanisms of thermally-treated granite under mode I loading are very complex. To investigate the effect of thermal treatment on the microcracking behavior, we perform mode I three-p...

Pore is a common type of microdefect or flaw in rock or rock-like material. Predicting the influence of pore-like flaw on the deformation, strength, and failure behavior of a brittlematerial is a topic of great interest in the field of geomechanics and geotechnical engineering. In this study, the influences of a group of twodimensional circular por...

Brittleness is an important parameter controlling the mechanical behavior and failure characteristics of rock under loading and unloading, such as the fracability, cutability, drillability and rockburst proneness. As such, it is of high practical value to correctly evaluate the rock brittleness. However, the definition and measurement method of roc...

The mineralogy and texture of granite, which is a common host rock in geotechnical engineering practices such as tunneling, enhanced geothermal systems and nuclear waste disposal, significantly affect its microcracking behavior. However, the effects of these two attributes on the microcracking behavior of granite are not entirely understood. We stu...

Fire safety is one of the most important concerns in underground engineering projects. Exposure to high temperature can weaken rocks and potentially cause catastrophic failure of the rock mass, either during the fire, or after the fire. In this study, Brazilian tensile tests were conducted on unheated and heat-treated Bukit Timah Granite. The micro...

Pore-like flaws, which are commonly encountered in brittle rock, play an important role in the engineering performance of structures constructed in or on rock. Experimental and numerical investigations of micro-cracking mechanism of rock containing a pore-like flaw can enhance our knowledge of rock damage/failure from a microscopic view. In this st...

Circumferential strain-control tests were suggested to obtain the complete stress–strain curves (SSCs) of intact rock. However, compression test performed by the axial strain-control loading is mostly used to obtain the strength parameters and the SSCs. The influences of load control modes on the mechanical behavior of rock have not been fully inve...

Overcoming two inherent limitations presented by the standard bonded‐particle model (BPM), the flat‐jointed model still lacks extensive application. This study hereby conducts a comprehensive investigation on the application of the flat‐jointed model in rock mechanics study. First, after a careful examination on the mechanical behavior of the flat‐...

Shear failure of rock masses along pre-existing discontinuities is one of the predominant failure modes of rock slopes and underground tunnels. The monitoring and prediction of the impending shear failure is of great significance to ensure the stability of the rock structures and the safety of the workers. In this study, direct shear tests under no...

Mode I fracture toughness is an important material parameter of rock. To date, a number of laboratory methods have been developed to measure the mode I fracture toughness. Although the fracture toughness values measured by different methods have been compared in many previous studies, the effect of the specimen configuration and pre-existing notch...

Growth and connection of preexisting fractures have been recognized as the driving mechanism of rock fracturing. This paper aims at throwing light on the geological implications of the fracturing behavior in pre‐cracked rock observed in rock mechanics‐oriented experiments, by numerical interpretation on the interaction of en echelon fractures. To p...

Understanding the physics of earthquakes is a crucial step towards improving the prediction accuracy of earthquakes. Scale invariance or fractal features are often reported in earthquakes, such as the size distribution of earthquakes, the spatial distribution of hypocenters, and the frequency of aftershocks. Here we assess whether other key paramet...

Rock joints may be sheared at different rates under quasi-static or dynamic loading. Understanding the mechanical response of rock joints at different shear rates is of great importance for the mitigation of dynamic geo-hazards such as earthquakes, fault slip rockbursts and landslides. In this study, direct shear tests at various shear rates (0.001...

In this study, the cohesive element-based numerical manifold method with Voronoi grains is extended by incorporating a coupled hydro-mechanical (HM) model to investigate hydraulic fracturing of rock at micro-scale. The proposed hydraulic solving framework, which explicitly calculates the flow rate and fluid pressure of a compressible viscous fluid...

This paper, not properly checked by the authors when receiving the proofs.

In this paper, the quantitative Geological Strength Index (GSI) for Singapore’s sedimentary rock mass is determined by applying four different approaches proposed by Hoek et al. (Quantification of the geological strength index chart, 2013), Cai et al. (Int J Rock Mech Min Sci 41(1):3–49, 2004), Sonmez and Ulusay (Int J Rock Mech Min Sci 36:743–760,...

The first commercial underground rock caverns for hydrocarbon storage in South East Asia, the Jurong Rock Caverns Project (JRC Project), have recently been completed in Singapore. The storage capacity of 5 caverns is 1.47 million cubic meters and 3.5 million cubic meters of rocks were excavated in this project. Geologically, it was excavated in low...

Reliable prediction of the rock fracturing process is a challenging issue in exploitation of deep earth resources in which artificial creation of complex fracture networks is employed. The grain-based modeling (GBM) approach is a promising numerical technique for its unique capability to simulate the fracturing behavior of crystalline rocks. An ext...

Previously, the stability analysis of seismically induced landslides was investigated by the factor of safety of the entire sliding body, which provided no information on the displacements of the analyzed seismically induced landslides. The landslides are assessed to be dangerous when the minimum value of the factor of safety (Fs) is less than a cr...

The Ayer Chawan Facies is one of the volcano-sedimentological facies belonging to the Jurong Formation in Singapore. The geology of the south-western Jurong Island had never been documented before the island was reclaimed in 1998. The present geological, sedimentological and geochronological study of the Ayer Chawan Facies was undertaken as part of...

Hydraulic fracturing is a favorably used technique to measure in-situ rock stress orientation and magnitude for the design of underground excavations. In Hong Kong, studies prior to 2000 revealed a general WNW-ESE maximum horizontal stress orientation and established stress ratio depth profile. However, there is a paucity of geological assessment o...

Uniaxial compressive strength (UCS) is often an indispensable parameter for the engineering geological assessment. The specimen geometry has a significant influence on such determination in the laboratory. Previous laboratory test results confirm that the laboratory-determined rock strength generally decreases with the increase in the slenderness r...

Acoustic emission (AE) is a technique which has been widely used in geomechanics to study the progressive micro-cracking behavior of rocks in response to different loadings. However, the study of the combined effects of thermal damage and specimen size on the performance of rocks using the AE technique is still limited, which needs further investig...

The structural stability of rock masses is dictated by the inherent geological structures present, most notably joints. Joint spacings are one of crucial parameters to control the block volume, permeability, deformability as well as strength of rock masses. While extensive rock engineering projects have been carried out in Hong Kong in the last cen...

This paper presents a method for continuous multiscale observation of uniaxial compressive tests of Carrara marble specimens containing a single preexisting artificially created flaw. The experiments aim at analyzing the associated mesoscale-macroscale phenomena in the fracture process of the specimens. In the macroscale, the crack types are observ...

Rocks inherently contain some micro-cracks. The existence of initial micro-cracks introduces weakness to the rock specimen and hence affects the strength and deformation behavior of rocks. This paper numerically investigates the influence of initial micro-crack damage on the strength and deformation behavior and the associated micro-cracking proces...

Fracturing behavior of ductile multi-flawed rock mass is very different from those of brittle multi-flawed rock mass. However, there is a very vague distinction of the fracture mechanism of ductile multi-flawed rock mass from that of brittle multi-flawed rock mass due to the absence of quality experimental data. To evaluate the fracturing behavior...

The crack initiation, growth, wrapping and coalescence of two 3D pre-existing cross-embedded flaws in PMMA specimens under uniaxial compression are investigated. The stress–strain curves of PMMA specimens with 3D cross-embedded flaws are obtained. The tested PMMA specimens exhibit dominant elastic deformation and eventual brittle failure. The exper...

This paper details a method for investigating the stability of a layered slope that combines random field theory with horizontal integration. Both the cohesion and friction coefficient are treated as a Gaussian random field. The closed-form solution of the factor of safety and the probability of failure of the layered slope are derived, in which th...

Both thermal damage and specimen size have a significant influence on the rock strength and deformation behavior. This study experimentally investigates the combined influences of thermal damage and specimen size on the strength and deformation behavior of a fine-grained marble. Uniaxial compression tests on specimens with different specimen sizes...

Rock strength and deformation behavior has long been recognized to be closely related to the microstructure and the associated micro-cracking process. A good understanding of crack initiation and coalescence mechanisms will thus allow us to account for the variation of rock strength and deformation properties from a microscopic view. This paper num...

The first underground rock caverns for hydrocarbon storage in South-East Asia has recently been completed in Singapore. The storage capacity of 5 twin-caverns is 1.47 million cubic meters with total volume of rock excavation is about 3 million cubic meters. Geologically, it was excavated in low-angled bedded meta-sedimentary rocks, namely Jurong Fo...

Compression-induced tensile and shear fractures were reported to be the two fundamental fracture types in rock fracturing tests. This study investigates such tensile and shear fraturing process in marble specimens containing two different flaw configurations. Observations first reveal that the development of a tensile fracture is distinct from shea...

A large number of layered slopes with complex lithological units and complex sliding surfaces exist in nature. The conventional Sarma method, which was originally developed for slopes comprised of relatively homogeneous and isotropic geomaterials, is not applicable for analysis of the stability of such layered slopes. In this paper, a modified Sarm...

The closure behavior of rock joints remains a problem of interest with applications in many practical engineering problems. Based on a comprehensive assessment of realistic closure behavior, we developed a Hertz-based theoretical model to predict the closure behavior of a rock joint under compressive loading. In the present study, special attention...

Tunnels and caverns excavated for the purpose of mining tend to be designed for short term use and would usually be unlined. Fire hazard within a mining cavern or tunnel poses concerns on the structural integrity of the surrounding rock. Hence, a fast, non-destructive method for assessing the strength of a rock mass after a fire would be useful in...

... reliable sensor calibration is highly warranted to ensure the AE information is readily usable in moment tensor analysis. This paper presents and compares the calibration attempts by three types of sources, namely, breaking pencil lead source, ball drop source, and the source generated by the electrically energized piezoelectric sensor. By com...

Failures of the surrounding rock mass have been identified as the most serious threat to the stability of underground water-sealed petroleum storage depots. To elucidate the effects of petroleum on the deformation and failure patterns of sandstone, a series of uniaxial compression experiments have been conducted. The experimental results show that...

Useable land is a finite space, and with a growing global population, countries have been exploring the use of underground space as a strategic resource to sustain the growth of their society and economy. However, the effects of impact loading on rocks that have been heated, and hence the integrity of the underground structure, are still not fully...

In this paper, the stability of base circle slopes is analyzed based on the theory of random fields. The closed-form solution of the safety factor and the failure probability of base circle slopes are obtained using the integration method. The effects of the spatial variation of the mechanical parameters of soils on the stability of base circle slo...

The stability analysis of toe circle slopes is studied using random field theory from the perspective of probability, and the relationship between the failure probability of toe circle slopes and the correlation length is analyzed. The closed-form solutions of the safety factor and the failure probability of toe circle slopes are derived using the...

This study numerically investigates the influence of material heterogeneity on the strength and deformation behavior and the associated micro-cracking process of a felsic crystalline rock using a grain-based modeling approach in two-dimensional Particle Flow Code (PFC2D). By using a heterogeneity index defined in this study, the heterogeneity induc...