Zhiye Zhao

Nanyang Technological University | ntu · School of Civil and Environmental Engineering

Data related to the pre-grouting work of a large underground project are systematically analyzed to reveal the mechanism behind, to shed some light on the execution of practical grouting, and to enrich the theory of engineering geology. Grouting is generally taken as an effective way for controlling non-ignorable water seepage during underground ro...

What hinders current models for fluid transportation in three-dimensional (3D) fracture system from considering fracture roughness is model complexity, which makes it hard to get convergent results. Therefore, we propose an electrical circuit (EC) model to simulate fracture flow, with each rough rock fracture taken as an EC with distributed electri...

Layered rock masses with joints are widely found in nature. Their mechanical behavior plays a key role in rock engineering applications. However, previous studies have concentrated on the single lithologic layer, and few studies have reported the crack coalescence mechanism in layered rock masses with joints. In this study, uniaxial compression tes...

Fracture deformation during grouting is a hydro-mechanical coupled dynamic process. Some studies indicated that an increase in grouting pressure can accelerate the grouting process, while some other investigations concluded that a high grouting pressure would weaken the grouting effect for fine fractures due to fracture deformation. Though the assu...

Underground projects are typically performed in nonpersistent jointed rock masses. Excavation of tunnels or chambers causes crack initiation, propagation and coalescence, resulting in the instability and destruction of surrounding rocks. The failure behaviour of rocks is complicated owing to the interaction between holes and joints. Therefore, unde...

The existence of highly complex and heterogeneous geological and hydrogeological conditions makes it cumbersome to determine grouting parameters for a cost-efficient grouting process. Although many empirical, numerical and analytical models have been proposed previously, there are still some gaps between the existing predictive models and practical...

The existence of highly complex and heterogeneous geological and hydrogeological conditions makes it cumbersome to determine grouting parameters for a cost-efficient grouting process. Although many empirical, numerical and analytical models have been proposed previously, there are still some gaps between the existing predictive models and practical...

To prevent large tunnel deformations caused by rock bursts or squeezing ground conditions, rockbolts need to satisfy both strength capacity and the required deformability. Currently, energy-absorbing rockbolts, such as the cone bolt and the D-bolt, have been successfully used in deep mining to avoid sudden tunnel collapses. This paper proposes a ne...

Opening holes in rock including their size and distribution can affect the performance of rock-related structures. A good understanding on this will contribute to, for example, rock cavern design, and construction, tunnelling, and mining engineering. To improve the understanding, a comprehensive investigation of the opening hole effect on the rock...

This paper presents a 3D coupled Smoothed Particle Hydrodynamics (SPH) and Finite Element Method (FEM) model, which was developed to investigate the extent of damage zone and fracture patterns in rock due to blasting. The RHT material model was used to simulate the blasting-induced damage in rock. The effects of discontinuity persistence and high i...

A complete understanding of the fracture behaviour of anisotropic rocks under elevated temperatures is fundamentally important for rock and reservoir engineering applications. This paper shows a three-dimensional numerical investigation of the fracture behaviour of anisotropic sandstone, with consideration of the effects of temperature and material...

Apertures of rock fractures is frequently considered as one of the most important factors affecting grouting characteristics. The real fracture distribution, however, is inaccessible due to its complex intrinsic properties, making it cumbersome to directly assess its impact on on-site grouting. In this paper, we argued that investigation of the gro...

Conventional tunnelling methods (i.e., the drill and blast tunnelling method or the new Austrian tunnelling method) have been frequently applied for the construction of tunnels/caverns under a high overburden and with a large cross section. Under such adverse conditions, tunnel support materials may yield because of ground pressure and tunnel defor...

The bonding condition at the rock and rockbolt interface is one of the most important factors to determine the load transfer mechanism of a CMC rockbolt element. The two-dimensional Discontinuous Deformation Analysis (2D-DDA) method is used in this paper to investigate the pullout performance of the CMC rockbolt element which is modeled as three co...

Cryptocrystalline flint is an extremely hard siliceous rock that is embedded in chalk formations, which in recent decades is often used as a host for underground rock caverns and tunnels in Europe and North America. A reliable estimation of the uniaxial compressive strength (UCS) of the extremely strong flint, with an average UCS of about 600 MPa w...

Blasting has been widely used in mining and construction industries for rock breaking. This paper presents the results of a series of field tests conducted to investigate the ground wave propagation through mixed geological media. The tests were conducted at a site in the northwestern part of Singapore composed of residual soil and granitic rock. T...

Most existing models for fluid transportation within a single rock fracture tend to use a channel with two smooth parallel plates, whereas real fracture surfaces are usually rough and tortuous, which can produce a flow field significantly different from the smooth plate model. For fluid flow in a rough fracture, there are surface concave areas (SCA...

A 3D particle-based DEM model was established taking into account the geometries of rock bridges. The model was used to investigate the shear behaviour of incipient rock joints. Fifty-seven direct shear tests were conducted under constant normal load (CNL) boundary conditions using the established model, in which rock bridges with nineteen differen...

Due to scarce land resources in Singapore, it is imperative to increase water storage capacities to meet the increasing demand of water to secure a sustainable development, which can be achieved in the underground by rock caverns. In this paper, a preliminary study on the effects of cavern span, height and radius on the cavern stability is presente...

This paper presents a series of field test results conducted at a site in the north western part of Singapore to investigate blast-induced ground vibration propagation through mixed geological media which comprised of residual soils and granitic rock. In total, six blast tests were carried out. Tri-axial accelerometers were placed at different stan...

Excavation in rock may change the stress field and induce excavation damaged zones (EDZ) in the surrounding rock mass. To consider the development of the EDZ, the support design could be evaluated using the convergence-confinement method (CCM). In this paper, an efficient approach is proposed to evaluate the support design based on rock cavern perf...

A series of field tests using controlled blasting was conducted at a location in the North Western part of Singapore to assess the behaviour of pile foundations subjected to ground excitation. The field tests involved three piles with different pile head fixity conditions. The piles were instrumented with strain gauges to evaluate the bending momen...

In this paper, a testing methodology was developed in the laboratory to measure the tensile strength of large-scale incipient rock joints. In the test, an expansive grout was used to develop the tensile force. Each test comprises two phases: Phase i test and Phase ii test. The Phase i test identified sample failure time, while the Phase ii test mea...

The high‐order approximation with regularly patterned flat‐top partition of unity mesh in one‐ and two‐dimensional cases has been proven linearly independent. However, for problems with stress concentration or stress singularity, local refinement within the regular mesh is necessary to improve the accuracy and efficiency. This paper introduces loca...

This figure is related to the article entitled "3D particle-based DEM investigation into the shear behaviour of incipient rock joints with various geometries of rock bridges" which has been published in RMRE 2018, https://doi.org/10.1007/s00603-018-1531-0

This figure is related to the article entitled "3D particle-based DEM investigation into the shear behaviour of incipient rock joints with various geometries of rock bridges" which has been published in RMRE 2018, https://doi.org/10.1007/s00603-018-1531-0

Rockbolts have been used to minimize the deformation of underground excavations where the surrounding rock masses contain weak planes such as fractures, joints or faults. Rockbolts installed across rock joints are able to resist the opening and shearing movements of rock joints. One of the rockbolt failure modes encountered in the field is caused b...

Stresses induced by a demolition agent in non-explosive rock fracturing was analysed using the theory of elasticity and the thick-walled cylinder principle. Circumferential and radial stresses in rock induced by an internally pressurized hole was first analysed under plane strain condition. Stresses perpendicular to the line connecting two adjacent...

The flat-top partition of unity method can obtain a stiffness matrix with a small condition number and avoid the linear dependence problem. We aimed to extend the flat-top partition of unity method to rock dynamic analyses to simulate the influence of discontinuity and dynamic loading. Therefore, the flat-top partition of unity method was coupled w...

Persistence of geological discontinuities is of great importance for many rock-related applications in earth sciences, both in terms of mechanical and hydraulic properties of individual discontinuities and fractured rock masses. Although the importance of persistence has been identified by academics and practitioners over the past decades, quantifi...

In this paper, a unified rock bolt model is proposed and incorporated into the two-dimensional discontinuous deformation analysis. In the model, the bolt shank is discretized into a finite number of (modified) Euler–Bernoulli beam elements with the degrees of freedom represented at the end nodes, while the face plate is treated as solid blocks. The...

Numerical modelling of a field soil desiccation test is performed using a hybrid continuum-discrete element method with a mix-mode cohesive fracture model and Voronoi tessellation grain assemblages. The fracture model considers material strength and contact stiffness degradation in both normal and tangential directions of an interface. It is found...

This paper presents a numerical investigation of the effects of boundary conditions, i.e., constant normal load (CNL) and constant normal stiffness (CNS), on the failure mechanism of incipient rock discontinuities in direct shear. A series of numerical simulations were performed using the particle-based discrete element method (DEM), in which rock...

A rockbolt model has been implemented into the 2-dimensional discontinuous deformation analysis (DDA-2D) code to analyze the performance of the fully grouted rockbolts installed in the jointed rock mass. Parametric studies are also conducted to investigate the effects of the rock properties, joint orientations, rockbolt lengths and in-plane spacing...

This paper relates to thermal effect on the fracture toughness of a Midgley Grit sandstone. A 3D semi-circular bend (SCB) model of the rock incorporating thermal responses of different minerals was established using the particulate Discrete Element Method (DEM). The particulate DEM model was calibrated against a laboratory programme. The results re...

As the free field geological condition is usually complex, the conventional wave attenuation law established for the homogeneous open field may not be applicable for actual field situations. Thus, to understand the impact of the attenuation law and the geological features on the blast wave propagation, a field rock blasting test is conducted and th...

The anisotropic direct tensile behaviour of laminated and transversely isotropic Midgley Grit sandstone (MGS) was investigated in this paper using a particle-based discrete element method (DEM) with consideration of the incipiency of bedding planes. Laboratory experiments were conducted to quantify the direct tensile strength of the incipient beddi...

For rockbolts subjected to tensile loads, there exists a unique local slip–strain relationship as well as a unique bond–slip relationship between rockbolts and rock mass. An analytical model is presented in this study for fully grouted rockbolts under tension, based on the slip–strain relationship of rockbolts. This analytical model takes into acco...

Simulation of rock grouting plays an important role for improving grouting technology and practice. Most of the current models for simulating grouting of fracture channels assume that grout flow between two parallel plates is in a state of static equilibrium, neglecting the influence of inertia forces, thus the average velocity obtained from the go...

Openings including their size, shape and distribution in rock play a significant role in the performance of rock related structures. The well-established knowledge in this area can contribute to the engineering practices, for example, underground space design, planning and optimisation in Civil and Mining Engineering and wellbore stability in Drill...

Discontinuous deformation analysis (DDA) has been widely applied in analyzing various rock engineering problems. As the joint strength play a vital role in the stability of jointed rock mass, this paper makes an attempt to implement the Barton-Bandis rock joint model into the DDA code to replace the original Mohr-Coulomb joint model. The developed...

Since conventional tunnelling method has frequently been utilised for many tunnels under severe conditions such as high overburden, extremely shallow depth, excavation close to existing structures, a large cross-section, tunnel support should be carefully designed under those adverse conditions. The authors have been studying about the rock bolt wh...

The shear strength of rock joints is an important factor to be considered when analyzing the stability of jointed rock mass. Rock joints tend to have smaller shear resistances in the reverse shearing than that of the forward shearing. A conceptual model describing the general shear behavior of rock joints under cyclic loading and the Barton–Bandis...

Blasting has been widely used in mining and construction industries for rock breaking. Ground vibration induced by blasting is an inevitable side effect that may cause damage to nearby structures, if not properly controlled. In this study, response and possible damage of rock-socketed pile near soil-rock interface subjected to ground shock excitati...

Discontinuous deformation analysis (DDA) method is a newly developed discrete element method which employs the implicit time-integration scheme to solve the governing equations and the open-close iteration (OCI) method to deal with contact problem, its computational efficiency is relatively low. However, spherical element based discontinuous deform...

Water control is highly concerned for underground facilities, and rock grouting has been used over decades to reduce the water inflow. The performances of grouting are influenced by many factors such as rock type, joint distribution and grouting materials. In this paper, the effects of water related factors are focused, from the engineering perspec...

This paper characterized the observed low frequency acoustic signals generated by rock falls, thunderstorm, and wind turbulence in large rocky landslide. A digital infrasonic recording system was deployed on site to capture real-time low frequency acoustic signals associated with rock falls. An advanced non-stationary signal analysis method, i.e. E...

In this paper, a cohesive fracture model is applied to model P-wave propagation through fractured rock mass using hybrid continuum-discrete element method, i.e. Universal Distinct Element Code (UDEC). First, a cohesive fracture model together with the background of UDEC is presented. The cohesive fracture model considers progressive failure of rock...

Recent attempts to couple discontinuous deformation analysis (DDA) blocks with finite element meshes have been regarded as fruitful. The hybrid model has been proven to be reliable in modeling continuum–discontinuum problems. In this paper, a hydraulic crack initiation–propagation extension complete with a coupled hydro-mechanical analysis algorith...

A comprehensive investigation of grain effect (size and distribution) in discrete element modelling of intact rock is carefully conducted through simulating Brazilian disc and uniaxial compressive tests on an intact rock using Universal Distinct Element Code. All the investigations are performed based on the same group of material parameters. Six s...

A numerical model of fully grouted bolts is proposed in this study by implementing the tri-linear bond–slip relationship of bolts into the numerical framework presented by Hyett et al. (1996). The bond–slip relationship of bolt–rock interface is simplified and represented by the tri-linear model. The proposed numerical model is characterized by (1)...

This paper formulates the flat-top partition of unity (PU)-based numerical manifold method (NMM). Through modifying the finite element PU into the flat-top PU, the linear dependence problem involved in finite element PU-based high-order polynomial approximations has been successfully alleviated. Moreover, the procedure to construct the flat-top PU...

Energy absorption of graded foam subjected to blast is investigated, in which the high velocity crushing of foam is modeled with shock theory and rigid-perfectly-plastic-locking idealization. The characteristics of a typical blast are taken into account when determining the foam density profile. Different from the homogeneous foam, the graded foam...

The dynamic behavior of gradient cellular solids subjected to high velocity impact is investigated, with shock theory and rigid-perfectly-plastic-locking idealization. The impact is induced by the fragments of a cased charge explosion in near field, sufficiently high to progressively crush the cellular solids from the loading part, regardless of th...

In this paper, a discontinuous numerical model, namely SDDARF3D (three-dimensional spherical discontinuous deformation analysis for rock failure), is proposed for simulating the whole process of rock failure. Firstly, within the framework of the classical discontinuous deformation analysis (DDA) method, the formulation of three-dimensional spherica...

The subsea rock cavern project is an underground storage facility. For cost-effective and safe excavation, the risk caused by the groundwater seepage into the rock cavern must be addressed. As one of the essential steps of the assessment work, the hydraulic conductivities of the fractured rock masses should be reliably determined based on the limit...

Rock cavern stability has a close relationship with the uncertain geological parameters, such as the in situ stress, the joint configurations, and the joint mechanical properties. Therefore, the stability of the rock cavern should be studied with variable geological conditions. In this paper, the coupled hydro-mechanical model, which is under the f...

In order to reduce the risk associated with water seepage in an underground rock cavern project in Singapore, a reliable hydro-geological model should be established based on the in situ investigation data. The key challenging issue in the hydro-geological model building is how to integrate limited geological and hydro-geological data to determine...

Computer modeling can be used to explore and gain new insights into the impacts of rock bolt intersecting joints in rock masses, and to estimate the effectiveness of the rock reinforcement system. In order to achieve this goal, we couple a rock bolt element into the two-dimensional discontinuous deformation analysis (DDA(2D)) program. The coupling...

The response of a blast mitigation cladding consisting of a face sheet and metal foam core subjected to a close-range blast is predicted. Whereas the cladding is sufficiently wide compared to the standoff distance between the explosion center and the cladding, the boundary of the blast induced bulge is released. The face sheet is considered as a ri...

In this study, numerical modeling on the damage of existing circular tunnel subject to blast-induced shock wave was carried out with DEM-based code UDEC. The disturbed zones including failure zones, open zones and shear zones around circular tunnel and peak particle velocities (PPVs) at tunnel surface are employed to analyze the damage of tunnel. T...

SUMMARY As a hybrid method, the nodal-based discontinuous deformation analysis (NDDA) greatly improves the stress accuracy within each DDA block by coupling a well-defined finite element mesh inside the DDA block; at the same time, the NDDA inherits the unique block kinematics of the standard DDA method. Each finite element mesh line inside the DDA...

This paper analytically investigates the performance of fully grouted rock bolts in typical scenarios, including pullout test, suspending loosened block, and increasing joint aperture, respectively. The interface shear stress distribution follows the model proposed by Li and Stillborg (Int J Rock Mech Mining Sci 36:1013-1029, 1999), while the axial...

The discontinuous deformation analysis (DDA) is a discontinuum-based method, which employs a penalty method to represent the contact between blocks. The penalty method is easy to be implemented in the program, but the contact constraint is only approximately satisfied. Penetrations between contacting blocks are unavoidable even if the penalty value...

To understand the response of rockbolts under various loads is an important part in the design of rock reinforcement. In this paper, the rockbolt models are developed within the frame work of the two-dimensional discontinuous deformation analysis (DDA). The rockbolt material is modeled by the elastic, linear strain-hardening behavior. To simulate t...

In this study, numerical modeling of a large-scale decoupled underground explosion test with 10 tons of TNT in Älvdalen, Sweden is performed by combining DEM and FEM with codes UDEC and AUTODYN. AUTODYN is adopted to model the explosion process, blast wave generation, and its action on the explosion chamber surfaces, while UDEC modeling is focused...

This paper customizes a contact detection and enforcing scheme to fit the three-dimensional (3-D) numerical manifold method (NMM). A hierarchical contact system is established for efficient contact detection. The mathematical mesh, a unique component in the NMM, is utilized for global searching of possible contact blocks and elements, followed by t...

This paper presents a three-dimensional numerical manifold method (NMM) for jointed rock slope stability analysis. The main barriers for realistic rock slope stability analysis are discussed, and the unique features of the NMM which make it stand out in slope analysis are emphasized. The framework of the 3-D NMM is established via a regularly-patte...

Stability charts for homogenous soil slopes are still routinely used in practice to determine the safety factor. A new graphical approach is employed to produce a set of stability charts that eliminates any iterative process when calculating the safety factor and can provide the type of failure mode. Stability charts are presented based on the limi...

In-structure shock of underground structures subjected to ground shocks is investigated, both theoretically and experimentally. In the theoretical prediction, the ground shock is simplified to a triangular pulse with a rise time. It is found that the acceleration time history of the structure when the rise time of the ground shock is considered is...

SUMMARY An extensive examination of the discontinuous deformation analysis (DDA) in block dynamic sliding modeling is carried out in this paper. Theoretical solutions for a single block sliding on an arbitrarily inclined plane by applying the horizontal/vertical seismic loadings to the sliding block as acceleration time histories or to the base as...

This paper proposes a numerical model for jointed rock masses within the 3-D numerical manifold method (NMM) framework equipped with a customized contact algorithm. The strength of rock sample containing a few sets of discontinuities is first investigated. The results of models with simple geometries are compared with the available analytical solut...

Underground structures are sometimes threatened by ground shocks induced by subsurface detonations. This paper proposes one possible method to mitigate the subsurface blasts by attaching a cladding consisting of a face sheet and cellular solid core to the exterior of the structure; the cellular core is foam made from relatively strong materials, su...

In this paper, explosion-induced stress wave propagations in jointed rock in a small-scale underground explosion field test is modeled by the Discontinuous Deformation Analysis (DDA) method. Two application approaches of explosion loadings including the pressure input and the displacement input are used and verified for the modeling of explosion-in...

Mining goes deeper and deeper, more rock bursts, deformation problems and safety issues are exposed. Although the concept of dynamic (or energy-absorbing) rock bolts were raised in early 1990s and quite a few products (e.g. cone bolt, Roofex and D-bolts) have been developed, their performances in various scenarios are not clear and the current dyna...