Browsing by Author "Pan, YW"

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A field study of induced slope failure in poorly cemented rock
(2003)
Pan, YW
;
Lin, CP
;
Liao, JJ
;
Huang, AB
;
土木工程學系
The paper presents the results of afield study of an induced slope failure and accompanied laboratory and in-situ tests of a poorly cemented soft rock. The project was aimed to examine the full-scale deformation/strength characteristics of soft rock within reservoir bank with geology of poorly cemented rock. Comparison of the results of various tests enabled the clarification of the true properties of the poorly cemented rock. Effect of disturbance was quantitatively investigated. An in-situ study of induced slope failure with well-planed instrumentations looked into the full-size deformation and strength properties of the geomaterial.
A micromechanics-based methodology for evaluating the fabric of granular material
(1999-12-01)
Pan, YW
;
Dong, JJ
;
交大名義發表
;
National Chiao Tung University
A micromechanics approach can successfully model the stress-strain-strength relation of a granular material once the microcharacteristics of the material have been obtained. However, it is usually difficult to determine the fabric of natural granular materials, Using a stress-dependent micromechanics model, the elastic properties can become a function of the geometric and kinetic fabric. Also, the wave velocity can be related to the elastic properties, Consequently, this paper proposes a methodology for evaluating the fabric of a granular assembly from a set of measured wave velocities. The methodology contains three elements: (a) stress-dependent micromechanics elastic model, (b) an anisotropic elastic wave propagation theory and (c) an optimization procedure. It is verified by calibrating available wave velocity data of a glass bail assembly and washed mortar sand, The methodology is further applied to study the microstructural evolution of the washed mortar sand under biaxial stresses. Two aspects of fabric change can be observed: (a) concentration of contact normals in the major principal direction and (b) a residual fabric after subsequent loading/unloading.
Characterization of soft rocks in Taiwan
(2000)
Huang, AB
;
Liao, JJ
;
Pan, YW
;
Cheng, MH
;
Hsieh, SY
A research project was carried out to enhance our capabilities in establishing the engineering properties of the weak sedimentary rocks in northern and central regions of Western Taiwan. Improved field sampling and testing techniques were developed and a series of in situ and laboratory experiments were performed. These included modifications of rock coring procedure, field pressuremeter, PS logging, Lugeon tests and laboratory triaxial tests. A test site was developed where rock cores were taken and a series of field experiments performed. The results from the field and laboratory experiments were analyzed and compared. An interpretation procedure in establishing the rock properties was proposed. This paper describes the experience gained in this series of experiments and discusses its implications in the characterization of the soft rocks.
Constitutive model for the continuous damage of brittle rock
(2001-03-01)
Pan, YW
;
Wen, BH
;
土木工程學系
;
Department of Civil Engineering
Degradation of weak sandstone and continuum damage model
(1998)
Pan, YW
;
Lee, JY
;
土木工程學系
;
Department of Civil Engineering
The study experimentally simulates in-situ degradation mechanisms to investigate the degradation of weak sandstone. Following different artificial degradation processes, the specimens are subjected to uniaxial compression. From the experimental results, it is noted that degradation of the tested weak sandstone results in a marked reduction in strength and elastic modulus and an increase in the failure strain. On the basis of the experimental results, a constitutive model is proposed to describe the mechanical behavior of weak sandstone. The presented constitutive model-contains a hyperbolic pore/crack closure model and a continuum damage mechanics model. By comparing the simulated and experimental results, it is demonstrated that the proposed model can closely simulate the stress-strain relation of weak sandstone with very limited material parameters.
Development of a multiple-purpose borehole testing device for soft rock
(2002-09-01)
Huang, AB
;
Fang, CK
;
Liao, JJ
;
Pan, YW
;
土木工程學系
The authors developed a versatile in situ testing device specifically for soft rock. The main purpose of this device was to provide design parameters for shallow or deep foundations in soft rock. The new. device, referred to as the Borehole Testing Device (BTD) consisted of four radial curved platens at the top and a circular steel plate at the bottom. The BTD was designed to be used in a 200-mm-diameter borehole. Driven by a high stress pressure-meter and a hydraulic piston, the BTD, can be used to perform a borehole jacking test, plate-loading test, and borehole sheaf test in the same borehole. A multistage testing procedure was proposed to perform the BTD test. This paper describes the design and operation of the BTD and presents a set of test data to demonstrate the capabilities of the BTD.
Developments in the characterization of soft rocks in Taiwan
(2003)
Huang, AB
;
Liao, JJ
;
Pan, YW
;
Cheng, MH
;
土木工程學系
Local Experience has indicated that the weak sedimentary rocks in northern and central regions of Western Taiwan were poorly cemented. Sampling in these types of rock formations has been difficult and test results on recovered samples were often scattered. The authors have been developing improved field sampling and testing techniques to enhance our capabilities in characterizing the soft rocks. These included modifications of rock coring procedure, development of a high stress pressuremeter, a borehole testing device, and laboratory triaxial tests with local strain measurements. These techniques have been applied for various construction and research projects. The paper describes the development of these new or modified techniques and experience gained in the characterization of the soft rocks in this region.
Estimating coefficients of volume compressibility from compression of strata and piezometric changes in a multiaquifer system in west Taiwan
(2004-09-01)
Liu, CH
;
Pan, YW
;
Liao, JJ
;
Hung, WC
;
土木工程學系
This paper estimates the coefficients of volume compressibility from variation in compressible! layer thickness and changes in piezometric heads by using detail ground surface surveys and a multilayer monitoring well at a selected site (Shigang) within the Choshui River alluvial fan in west Taiwan. The paper integrates various types of in situ monitoring tools, including leveling surveys, continuous global position system (GPS) stations, multilevel layer compression and groundwater pressure head-monitoring wells, to investigate the situation and progress of the subsidence problem in the region. The results from the cross-analyses of the measured data show that surface settlement caused by the compression of strata is between the depths of 60 and 210 m where the clayey stratum within 120-180 m was most pronounced and contributes up to 53% of the total compression. The results indicate that the clayey stratum is under normal consolidation. The results also reflect the fact that 20% of settlement contribution comes from the sandy stratum within 90-120 m; the elasto-plastic behavior of this sandy stratum is clear. The coefficients of volume compressibility of the clayey and sandy stratum analysed from the stratum's compression records; they were 6.38 x 10(-8) and 5.71 x 10(-9) m(2)/N, respectively. Ultimately, this parameter estimation would permit to control and predict land subsidence based on change in pressure head which are related to groundwater extraction. (C) 2004 Elsevier B.V. All rights reserved.
Fabric evolution of granular assembly under K-0 loading/unloading
(2003-11-01)
Liou, JC
;
Pan, YW
;
土木工程學系
;
Department of Civil Engineering
This study attempted to investigate the fabric evolution in K-0 loading/unloading. The work made use of a field simulator to control K-0 loading/unloading in large specimens prepared by air-pluviation. In each loading stage, wave velocities along various propagation directions were measured. On the basis of the theories of micro-mechanics and wave propagation, the microscopic parameters of the granular assembly were back calculated to investigate the fabric evolution of granular soil during K-0 loading/unloading. In this study, the Geometric fabric was modelled by fabric tensors of ranks 2 and 4. The comparison of calibrated results using ranks 2 and 4 revealed the advantage of the usage of rank-4 fabric tensor in modelling fabric evolution in spite of its complexity. By comparing relative magnitudes of vertical and horizontal components of geometric fabric, it was demonstrated that relative constraint in lateral directions increased during K-0-unloading in order to maintain a K-0 condition. It revealed that fabric evolution was responsible for a higher K-0 in unloading than K-0 in loading. Copyright (C) 2003 John Wiley Sons, Ltd.
Hierarchical model of rough rock joints based on micromechanics
(1996-02-01)
Dong, JJ
;
Pan, YW
;
土木工程學系
;
Department of Civil Engineering
A rough rock joint model is proposed in this study on the basis of micromechanics concepts. In the model, the global behavior of a rough joint depends on the microfeatures of the contact planes on the joint. The contact mechanics on contact planes controls the mechanical behavior of the joint via a homogenization process. Also, the complex mechanical behavior of a joint is associated with simple microfeatures of the joint, including the frictional properties and the structure of contact planes. To capture the feature of scale dependency of joint roughness, a hierarchical representation of a joint profile is proposed in the form of a multi-level-asperity model. Moreover, the constitutive relation of the multi-level-asperity model is derived through a recursive homogenization process. The proposed model's framework is general and systematic. Furthermore, major deformation mechanisms of joint asperities, i.e. interlocking, wearing, shearing-off sliding, separation and degradation, are taken into account.
Improved design and data interpretation of a multi-purpose borehole testing device for soft rock
(2006-06-01)
Pan, YW
;
Liao, JJ
;
Huang, AB
;
Chang, JC
;
Liao, HJ
The authors previously developed a multi-purpose borehole testing device (BTD). The purpose of the BTD was designed for obtaining mechanical properties including anisotropic elastic modulus and interface shear strength properties for soft rock that may be easily disturbed during sampling. Since the creation of the previous BTD, a few minor problems were experienced during in situ testing operation. In the present work, improvements both in equipment design and data interpretation were made. Improved design of BTD successfully reduced the chance for pressure meter test (PMT) membrane breakage, allowed larger expansion of borehole jack test (BJT), improved the waterproof of the bottom compartment and made easy for the whole equipment setup. The refined design has improved the in situ performance of BTD. New approach of data interpretation was also proposed. A series of BTD tests, including BJTs, borehole plate loading tests and borehole shear tests were carried out to demonstrate the capability of the refined borehole test device. (c) 2005 Elsevier Ltd. All rights reserved.
K-0 estimation in level granular soil from anisotropic wave velocities on the basis of micromechanics
(2004-12-10)
Pan, YW
;
Liou, JC
;
土木工程學系
;
Department of Civil Engineering
This study aims to explore the possibility for estimating K-0 in a level ground of granular soil by seismic methods on the basis of micromechanics theory. The idea was to simulate in situ cross-hole seismic method for the measurement of wave velocities along various directions of wave-propagation. This work made use of a field simulator to control a K-0 condition (zero lateral strain condition) in specimens. A series of vertical loading containing subsequent loading and unloading were applied to the specimen prepared by pluviation. In general, the K-0 values determined experimentally in this work agreed with the exiting empirical relations. K-0 value was also calibrated from measured anisotropic wave velocities using an optimization procedure. From the comparison of the back-calculated and measured results of K-0, it revealed the feasibility for the determination of the in situ lateral stress in granular soil by seismic methods and on the basis of micromechanics theory as long as enough wave-velocity measurements along various directions of wavepropagation were available. The potential for the usage of the presented methodology for the determination of the in situ lateral stress in level-ground of granular soil by seismic methods seems encouraging. Copyright (C) 2004 John Wiley Sons, Ltd.
Loading behavior of shallow foundation on poorly cemented sandstone
(2004)
Liao, JJ
;
Chang, JC
;
Pan, YW
;
Huang, AB
;
Lin, CP
This paper aims to investigate the load bearing behavior and failure mechanism of a shallow foundation on poorly cemented rock. A series of laboratory material and model tests with specimens made of artificial soft rock were conducted. The results of material tests show that the properties of the artificial material are quite close to natural poorly cemented sandstone. The results of model bearing test indicate that a load-settlement curve can be roughly divided into the incipient stage, the linear stage, the yielding stage, and the final stage. The failure zones and mechanism were also identified. Failure zones were divided into the active zone, the transitional zone, and the passive zone. It was found that the bearing behavior on poorly cemented sandstone is distinct from the cases on hard rock or soil, with both plasticity and brittle characteristics. The bearing capacity formulas commonly used for soil or hard rock is not necessarily suitable for the case of poorly cemented soft sandstone.
Micromechanics model for elastic stiffness of non-spherical granular assembly
(1999-09-01)
Dong, JJ
;
Pan, YW
;
土木工程學系
;
Department of Civil Engineering
This paper presents a micromechanics model for the elastic stiffness of a non-spherical granular assembly. The microstructural continuum model of ideal spherical assembly is extended for non-ideal assembly. The presented work takes the effects of gradation, shape, and preferred orientation into account by introducing a directional distribution function of branch-vector length. The microstructure of a granular assembly is described by the distributions of packing structure, branch-vector length, and particle number per unit volume. These distributions account or the random nature of a realistic granular material. The microfeatures relevant to the description of non-deal particle assembly are elaborated. The influences of various direction-dependent and direction-independent microfeatures on the elastic stiffness are demonstrated. Hypothetical non-ideal granular assemblies are used to study the effects of gradation, shape and preferred orientation. Based on the proposed model, the paper discusses the inherent anisotropy in a non-ideal granular assembly. The presented work also makes use of a generalized static hypothesis to estimate the contact-force distribution for specific microstructure and stress state. With the estimated contact-force and the Hertz-Mindlin contact theory, the elastic stiffness of a particulate assembly can be evaluated. Hence, the effects of geometric fabric and anisotropic stress state on the elastic stiffness can be deliberated. Consequently, the effects of geometric fabric and kinetic fabric of a natural granular material can be evaluated independently. It is shown that the proposed model can reasonably capture the phenomena of inherent anisotropy and stress-induced anisotropy of a non-spherical granular assembly under small strain. Copyright (C) 1999 John Wiley & Sons, Ltd.
Numerical model for estimating underground temperature distribution
(1999)
Pan, YW
;
Wu, PK
;
土木工程學系
;
Department of Civil Engineering
Engineering projects, such as deep tunnel and nuclear-waste repository, may involve very deep overburden. As the depth at the project site increases, the underground temperature tends to elevate. This study aims to develop a reasonable methodology for estimating underground rock temperature under deep overburden. This paper proposes a methodology of modular analysis for estimating deep underground rock temperature. The proposed methodology involves the finite-element method and nonlinear optimization method. The proposed analysis assumes that the distribution of underground temperature is solely due to two-dimension thermal conduction. After verification, numerical experiments:demonstrate that the distribution of underground temperature significantly depends on the thermal conductivity of underground rock. Parametric study illustrates that the anisotropy of thermal conductivity and the topography of ground surface also affect the distributions of temperature and thermal gradient. This study also discusses the sources of error for estimating the underground temperature.
The influence of surface ruptures on building damage in the 1999 Chi-Chi earthquake: a case study in Fengyuan City
(2004-01-01)
Dong, JJ
;
Wang, CD
;
Lee, CT
;
Liao, JJ
;
Pan, YW
In addition to the main surface rupture along the Chelungpu fault associated with the 1999 Chi-Chi, Taiwan earthquake, numerous secondary or branch ruptures on hangingwall were also observed. These secondary surface ruptures are parallel or sub-parallel to the main rupture within a distance of a few meters to 1-2 km. The rupture length of these secondary ruptures varies from a few tens of meters up to 5 km. The surface deformation resulted in serious damages of buildings. The present work studied the features of surface deformation on the hangingwall around the Chung-Cheng Park, Fengyuan, Taichung. Three distinct surface ruptures, minor ruptures and tension cracks were observed in this area. The observed distribution and types of building damage on the hangingwall are demonstrated. Due to the difference in geological condition and complex pattern of surface deformation, the resulted building damages on the hangingwall vary. A series of site investigation including field survey, drilling, seismic prospecting, P-S logging tests and laboratory tests were carried out in the interested area. A geological structure model was proposed on the basis of the results of site investigation. Numerical simulation was carried out to model the surface deformation as well as subsurface potential damage zone of an active fault. It reasonably explains the observed pattern of surface deformation and indicates that the surface deformation zone during a catastrophic earthquake is predictable. (C) 2003 Elsevier Science B.V. All rights reserved.