The success of a tunnel-boring machine （TBM） in a given project depends on the functionality of all components of the system, from the cutters to the backup system, and on the entire rolling stock. However, no part ...The success of a tunnel-boring machine （TBM） in a given project depends on the functionality of all components of the system, from the cutters to the backup system, and on the entire rolling stock. However, no part of the machine plays a more crucial role in the efficient operation of the machine than its cutterhead. The design of the cutterhead impacts the efficiency of cutting, the balance of the head, the life of the cutters, the maintenance of the main bearing/gearbox, and the effectiveness of the mucking along with its effects on the wear of the face and gage cutters/muck buckets. Overall, cutterhead design heavily impacts the rate of penetration （ROP）, rate of machine utilization （U）, and daffy advance rate （AR）. Although there has been some discussion in commonly available publications regarding disk cutters, cutting forces, and some design features of the head, there is limited literature on this subject because the design of cutter- heads is mainly handled by machine manufacturers. Most of the design process involves proprietary algorithms by the manufacturers, and despite recent attention on the subject, the design of rock TBMs has been somewhat of a mystery to most end-users. This paper is an attempt to demystify the basic concepts in design. Although it may not be sufficient for a full-fledged design by the readers, this paper allows engineers and contractors to understand the thought process in the design steps, what to Look for in a proper design, and the implications of the head design on machine operation and life cycle.展开更多
The study of transient heat conduction in multilayered slabs is widely used in various engineering fields. In this paper, the transient heat conduction in multilayered slabs with general boundary conditions and arbitr...The study of transient heat conduction in multilayered slabs is widely used in various engineering fields. In this paper, the transient heat conduction in multilayered slabs with general boundary conditions and arbitrary heat generations is analysed. The boundary conditions are general and include various combinations of Dirichlet, Neumann or Robin boundary conditions at either surface. Moreover, arbitrary heat generations in the slabs are taken into account. The solutions are derived by basic methods, including the superposition method, separation variable method and orthogonal expansion method. The simplified double-layered analytical solution is validated by a numerical method and applied to predicting the temporal and spatial distribution of the temperature inside a landfill. It indicates the ability of the proposed analytical solutions for solving the wide range of applied transient heat conduction problems.展开更多
The wide engineered application of compacted expansive soils necessitates understanding their behavior under field conditions.The results of this study demonstrate how seasonal climatic variation and stress and bounda...The wide engineered application of compacted expansive soils necessitates understanding their behavior under field conditions.The results of this study demonstrate how seasonal climatic variation and stress and boundary conditions individually or collectively influence the hydraulic and volume change behavior of compacted highly expansive soils.The cyclic wetting and drying(CWD)process was applied for two boundary conditions,i.e.constant stress(CS)and constant volume(CV),and for a wide range of axial stress states.The adopted CWD process affected the hydraulic and volume change behaviors of expansive soils,with the first cycle of wetting and drying being the most effective.The CWD process under CS conditions resulted in shrinkage accumulation and reduction in saturated hydraulic conductivity(k sat).On the other hand,CWD under CV conditions caused a reduction of swell pressure while has almost no impact on k sat.An elastic response to CWD was achieved after the third cycle for saturated hydraulic conductivity(k sat),the third to fourth cycle for the volume change potential under the CV conditions,and the fourth to fifth cycle for the volume change potential under the CS conditions.Finally,both swell pressure(s s)and saturated hydraulic conductivity(k sat)are not fundamental parameters of the expansive soil but rather depend on stress,boundary and wetting conditions.展开更多
Compacted layers of expansive soils are used in different engineering projects,such as subgrades,engineered clay barriers,and buffers for radioactive waste disposal.These layers are exposed to a variety of stresses an...Compacted layers of expansive soils are used in different engineering projects,such as subgrades,engineered clay barriers,and buffers for radioactive waste disposal.These layers are exposed to a variety of stresses and wetting conditions during field serviceability.Coupling between hydraulic and mechanical repeated loading provides insight understanding to the induced progressive deformation of expansive clay.This study was conducted to investigate the hydromechanical behavior of unsaturated compacted expansive clay under repeated loadingeunloading(RLU)conditions.Two series of onedimensional(1D)oedometer tests were conducted under controlled matric suction up to 1500 kPa using the axis translation technique(Fredlund soil-water characteristic curve device,SWC-150).The first test series was carried out at different levels of controlled matric suction for non-repeated loading eunloading(NRLU)cycles.RLU cycles were applied in the second test series at different repetitivestress levels and under different levels of matric suction.The results indicated increasing axial wetting strainε_(a)(s),axial swell pressure ss(s),compression index C_(c)(s),and swell index C_(s)(s)with suction reduction.The estimated loadecollapse(LC)curves obtained from NRLU series(LCN)and RLU series(LCR)indicated increasing yield stress sy(s)with increasing suction.This is attributed to the developed apparent cohesion between soil particles,which in turn rigidifies the material response.Applying repetitive loading induced a notable reduction of compression index C_(c)(s)at the same level of suction,whereas swell index C_(s)(s)seems to be independent of repetitive loading.Finally,repetitive loading exceeding initial yield stresses results in plastic hardening and,hence,enlargement of yield stress locus(i.e.LCR curve).展开更多
This article discusses the flyash mechanical properties and analyzes stability of two flyash dams under earthquake by finite element methods. It is studied whether the mixture of flyash and clay can be used as the fil...This article discusses the flyash mechanical properties and analyzes stability of two flyash dams under earthquake by finite element methods. It is studied whether the mixture of flyash and clay can be used as the fill for a dam located in an earthquake region.展开更多
According to the results of cyclic triaxial tests, a linear correlation is presented between liquefaction resistance and elastic shear modulus, which shows the relation of Gmax (kPa) with (σd/2)1/2(kPa)1/2. When appl...According to the results of cyclic triaxial tests, a linear correlation is presented between liquefaction resistance and elastic shear modulus, which shows the relation of Gmax (kPa) with (σd/2)1/2(kPa)1/2. When applied to soils from different sites, the correlation can be normalized in reference to its minimum void ratio (emin). Accordingly, an improved method is established to evaluate the liquefaction potential with shear-wave velocity. The critical shear-wave velocity of liquefaction is in linear relation with 1/4 power of depth and the maximum acceleration during earthquakes, which can be used to explain the phenomenon that the possibility of liquefaction decreases with the increment of the depth. Compared with previous methods this method turns out simple and effective, which is also verified by the results of cyclic triaxial tests.展开更多
文摘The success of a tunnel-boring machine （TBM） in a given project depends on the functionality of all components of the system, from the cutters to the backup system, and on the entire rolling stock. However, no part of the machine plays a more crucial role in the efficient operation of the machine than its cutterhead. The design of the cutterhead impacts the efficiency of cutting, the balance of the head, the life of the cutters, the maintenance of the main bearing/gearbox, and the effectiveness of the mucking along with its effects on the wear of the face and gage cutters/muck buckets. Overall, cutterhead design heavily impacts the rate of penetration （ROP）, rate of machine utilization （U）, and daffy advance rate （AR）. Although there has been some discussion in commonly available publications regarding disk cutters, cutting forces, and some design features of the head, there is limited literature on this subject because the design of cutter- heads is mainly handled by machine manufacturers. Most of the design process involves proprietary algorithms by the manufacturers, and despite recent attention on the subject, the design of rock TBMs has been somewhat of a mystery to most end-users. This paper is an attempt to demystify the basic concepts in design. Although it may not be sufficient for a full-fledged design by the readers, this paper allows engineers and contractors to understand the thought process in the design steps, what to Look for in a proper design, and the implications of the head design on machine operation and life cycle.
基金Projects(41530637,41877222,41702290)supported by the National Natural Science Foundation of China
文摘The study of transient heat conduction in multilayered slabs is widely used in various engineering fields. In this paper, the transient heat conduction in multilayered slabs with general boundary conditions and arbitrary heat generations is analysed. The boundary conditions are general and include various combinations of Dirichlet, Neumann or Robin boundary conditions at either surface. Moreover, arbitrary heat generations in the slabs are taken into account. The solutions are derived by basic methods, including the superposition method, separation variable method and orthogonal expansion method. The simplified double-layered analytical solution is validated by a numerical method and applied to predicting the temporal and spatial distribution of the temperature inside a landfill. It indicates the ability of the proposed analytical solutions for solving the wide range of applied transient heat conduction problems.
文摘The wide engineered application of compacted expansive soils necessitates understanding their behavior under field conditions.The results of this study demonstrate how seasonal climatic variation and stress and boundary conditions individually or collectively influence the hydraulic and volume change behavior of compacted highly expansive soils.The cyclic wetting and drying(CWD)process was applied for two boundary conditions,i.e.constant stress(CS)and constant volume(CV),and for a wide range of axial stress states.The adopted CWD process affected the hydraulic and volume change behaviors of expansive soils,with the first cycle of wetting and drying being the most effective.The CWD process under CS conditions resulted in shrinkage accumulation and reduction in saturated hydraulic conductivity(k sat).On the other hand,CWD under CV conditions caused a reduction of swell pressure while has almost no impact on k sat.An elastic response to CWD was achieved after the third cycle for saturated hydraulic conductivity(k sat),the third to fourth cycle for the volume change potential under the CV conditions,and the fourth to fifth cycle for the volume change potential under the CS conditions.Finally,both swell pressure(s s)and saturated hydraulic conductivity(k sat)are not fundamental parameters of the expansive soil but rather depend on stress,boundary and wetting conditions.
文摘Compacted layers of expansive soils are used in different engineering projects,such as subgrades,engineered clay barriers,and buffers for radioactive waste disposal.These layers are exposed to a variety of stresses and wetting conditions during field serviceability.Coupling between hydraulic and mechanical repeated loading provides insight understanding to the induced progressive deformation of expansive clay.This study was conducted to investigate the hydromechanical behavior of unsaturated compacted expansive clay under repeated loadingeunloading(RLU)conditions.Two series of onedimensional(1D)oedometer tests were conducted under controlled matric suction up to 1500 kPa using the axis translation technique(Fredlund soil-water characteristic curve device,SWC-150).The first test series was carried out at different levels of controlled matric suction for non-repeated loading eunloading(NRLU)cycles.RLU cycles were applied in the second test series at different repetitivestress levels and under different levels of matric suction.The results indicated increasing axial wetting strainε_(a)(s),axial swell pressure ss(s),compression index C_(c)(s),and swell index C_(s)(s)with suction reduction.The estimated loadecollapse(LC)curves obtained from NRLU series(LCN)and RLU series(LCR)indicated increasing yield stress sy(s)with increasing suction.This is attributed to the developed apparent cohesion between soil particles,which in turn rigidifies the material response.Applying repetitive loading induced a notable reduction of compression index C_(c)(s)at the same level of suction,whereas swell index C_(s)(s)seems to be independent of repetitive loading.Finally,repetitive loading exceeding initial yield stresses results in plastic hardening and,hence,enlargement of yield stress locus(i.e.LCR curve).
文摘This article discusses the flyash mechanical properties and analyzes stability of two flyash dams under earthquake by finite element methods. It is studied whether the mixture of flyash and clay can be used as the fill for a dam located in an earthquake region.
基金State Natural Science Foundation(59678020) Natural Science Foundation of Zhejiang Province(RC9609).
文摘According to the results of cyclic triaxial tests, a linear correlation is presented between liquefaction resistance and elastic shear modulus, which shows the relation of Gmax (kPa) with (σd/2)1/2(kPa)1/2. When applied to soils from different sites, the correlation can be normalized in reference to its minimum void ratio (emin). Accordingly, an improved method is established to evaluate the liquefaction potential with shear-wave velocity. The critical shear-wave velocity of liquefaction is in linear relation with 1/4 power of depth and the maximum acceleration during earthquakes, which can be used to explain the phenomenon that the possibility of liquefaction decreases with the increment of the depth. Compared with previous methods this method turns out simple and effective, which is also verified by the results of cyclic triaxial tests.
