Based on polarization mechanisms, such as electronic, ionic and orientational polarizations, a new equation for dielectric permittivity of soil is proposed to interpret the dielectric behavior of a mixture like soil, ...Based on polarization mechanisms, such as electronic, ionic and orientational polarizations, a new equation for dielectric permittivity of soil is proposed to interpret the dielectric behavior of a mixture like soil, in terms of polarization process of its components and the interactions between its components. The dielectric permittivity is expressed in terms of a fre-quency-dependent part and a frequency-independent part. These two parts correspond to polarizations occurred at different fre-quency range. It is a new volumetric mixing model with theoretical background. Based on time domain reflectometry (TDR) measurements of saturated soil samples and test data from literature, comparisons of this model with some well established mixing models show that the curves for saturated sand soils and slurries resulted from the new equation, which agree well with TDR measurements, are close to those calculated from Birchak's model.展开更多
Groundwater leakage in shield tunnels poses a threat to the safety and durability of tunnel structures. Disturbance of adjacent constructions during the operation of shield tunnels frequently occurs in China, leading ...Groundwater leakage in shield tunnels poses a threat to the safety and durability of tunnel structures. Disturbance of adjacent constructions during the operation of shield tunnels frequently occurs in China, leading to deformation of tunnel lining and leakage in joints. Understanding the impact of adjacent constructions on the waterproofing performance of the lining is critical for the protection of shield tunnels. In this study, the weakening behavior of waterproof performance was investigated in the joints of shield tunnels under transverse deformation induced by adjacent construction. First, the relationship between the joint opening and transverse deformation under three typical adjacent constructions (upper loading, upper excavation, and side excavation) was investigated via elaborate numerical simulations. Subsequently, the evolution of the waterproof performance of a common gasket with a joint opening was examined by establishing a coupled Eulerian-Lagrangian model of joint seepage, and a formula describing the relationship between waterproof performance and joint opening was proposed. Finally, the weakening law of waterproofing performance was investigated based on the results of the aforementioned studies. It was determined that the joints with the greatest decline in waterproof performance were located at the tunnel shoulder in the upper loading case, tunnel crown in the upper excavation case, and tunnel shoulder in the side excavation case. When the waterproof performance of these joints decreased to 50% and 30%, the transverse deformations were 60 and 90 mm under upper loading, 90 and 140 mm under upper excavation, and 45 and 70 mm under side excavation, respectively. The results provide a straightforward reference for setting a controlled deformation standard considering the waterproof performance.展开更多
Shield tunneling and post-tunneling steady seepage are accompanied by stress and displacement variations,which could induce and influence the soil arching effect.Although there are many studies on the tunneling-induce...Shield tunneling and post-tunneling steady seepage are accompanied by stress and displacement variations,which could induce and influence the soil arching effect.Although there are many studies on the tunneling-induced soil arching effect,the research about the effect of seepage on soil arching effect is extremely lacking.In this study,a numerical model is firstly established and verified by field data.Then,a series of numerical models,whose simulation method of steady seepage is verified by adopting the conformal mapping technique,are established to study the soil arching evolution of deep-buried tunneling and post-construction steady seepage.The results indicate that seepage leads to an increase in effective vertical stress,which is consistent with the existing theory.The seepage weakens the soil arching effect resulting in the height of the arch zone reducing from 2.38D(D is the tunnel diameter)to 1.25D.The seepage leads to the further development of ground consolidation settlement,but the differential displacement in the soil mass decreases.The ground reaction curve in the steady seepage condition shows a bigger value than that after excavation.It is reasonable to control the ground loss ratio in the range of 0.5–1.0%,which can minimize overburden pressure with moderate ground deformation.展开更多
Pressurized bentonite slurry is applied on a tunnel face to form a filter cake to stabilize the tunnel face when the slurryshield excavates through the sandy soil. Failure of the tunnel face may be caused by a high pe...Pressurized bentonite slurry is applied on a tunnel face to form a filter cake to stabilize the tunnel face when the slurryshield excavates through the sandy soil. Failure of the tunnel face may be caused by a high permeable filter cake, which commonlyhas a long penetration distance of slurry in sands. A column system with a height of 680 mm and a diameter of 300 mm was de-veloped to model pressurized slurry infiltration in sands. Pressure transducers were installed to estimate the hydraulic conductivityof the filter cake during slurry infiltration. The electrical conductivity of the leachate of collected samples was measured. Resultsshow that the majority of fine particles in slurry are within the range 100-300 mm into the sand specimen. The time for forming animpermeable filter cake is about 300 s, which indicates the impermeable filter cake is hard to form during the excavation.展开更多
In this paper,a semi-analytical method for the analysis of pile-supported embankments is proposed.The mathematic model describes the cooperative behavior of pile,pile cap,foundation soil,and embankment fills.Based on ...In this paper,a semi-analytical method for the analysis of pile-supported embankments is proposed.The mathematic model describes the cooperative behavior of pile,pile cap,foundation soil,and embankment fills.Based on Terzaghi's 1D consolidation theory of saturated soil,the consolidation of foundation soil is calculated.The embankments with two different types of piles:floating piles and end-bearing piles are investigated and discussed.The results of axial force and skin friction distributions along the pile and the settlements of pile-supported embankments are presented.It is found that it takes a longer time for soil consolidation in the embankment with floating piles,compared with the case using end-bearing piles.The differential settlement between the pile and surrounding soil at the pile top is larger for the embankment with end-bearing piles,compared with the case of floating piles.展开更多
In the past decades,we have witnessed the rapid development of high-speed transportation infrastructure,such as high-speed railways,urban subways,expressways,and airfields worldwide.As a major effort in transportation...In the past decades,we have witnessed the rapid development of high-speed transportation infrastructure,such as high-speed railways,urban subways,expressways,and airfields worldwide.As a major effort in transportation infrastructure development,China plans to build 20 000 km of high-speed rail network by the year of 2020 with design speed up to 500 km/h.With such a fast pace,ensuring the safe and comfortable high-speed transportation presents major technical challenges to the design,construction,and maintenance of high performance infrastructure.展开更多
基金Project (Nos. 50278087 and 50308026) supported by the NationalNatural Science Foundation of China
文摘Based on polarization mechanisms, such as electronic, ionic and orientational polarizations, a new equation for dielectric permittivity of soil is proposed to interpret the dielectric behavior of a mixture like soil, in terms of polarization process of its components and the interactions between its components. The dielectric permittivity is expressed in terms of a fre-quency-dependent part and a frequency-independent part. These two parts correspond to polarizations occurred at different fre-quency range. It is a new volumetric mixing model with theoretical background. Based on time domain reflectometry (TDR) measurements of saturated soil samples and test data from literature, comparisons of this model with some well established mixing models show that the curves for saturated sand soils and slurries resulted from the new equation, which agree well with TDR measurements, are close to those calculated from Birchak's model.
基金The present study was conducted with the support of the Youth Science and Technology Innovation Talent Project of Hunan Province(No.2021RC3043)National Natural Science Foundation of China(Grant Nos.52090082,51878267,52122807,and 51938005)the High-level Talent of Innovative Research Team of Hunan Province,China(No.2019RS1030).We gratefully acknowledge their financial support.
文摘Groundwater leakage in shield tunnels poses a threat to the safety and durability of tunnel structures. Disturbance of adjacent constructions during the operation of shield tunnels frequently occurs in China, leading to deformation of tunnel lining and leakage in joints. Understanding the impact of adjacent constructions on the waterproofing performance of the lining is critical for the protection of shield tunnels. In this study, the weakening behavior of waterproof performance was investigated in the joints of shield tunnels under transverse deformation induced by adjacent construction. First, the relationship between the joint opening and transverse deformation under three typical adjacent constructions (upper loading, upper excavation, and side excavation) was investigated via elaborate numerical simulations. Subsequently, the evolution of the waterproof performance of a common gasket with a joint opening was examined by establishing a coupled Eulerian-Lagrangian model of joint seepage, and a formula describing the relationship between waterproof performance and joint opening was proposed. Finally, the weakening law of waterproofing performance was investigated based on the results of the aforementioned studies. It was determined that the joints with the greatest decline in waterproof performance were located at the tunnel shoulder in the upper loading case, tunnel crown in the upper excavation case, and tunnel shoulder in the side excavation case. When the waterproof performance of these joints decreased to 50% and 30%, the transverse deformations were 60 and 90 mm under upper loading, 90 and 140 mm under upper excavation, and 45 and 70 mm under side excavation, respectively. The results provide a straightforward reference for setting a controlled deformation standard considering the waterproof performance.
基金supported by the National Natural Science Foundation of China(Grant Nos.52090082,51938005,52122807,and 52108318)China Hunan Provincial Science&Technology Department(Grant Nos.2021RC3043 and 2021JJ30119).
文摘Shield tunneling and post-tunneling steady seepage are accompanied by stress and displacement variations,which could induce and influence the soil arching effect.Although there are many studies on the tunneling-induced soil arching effect,the research about the effect of seepage on soil arching effect is extremely lacking.In this study,a numerical model is firstly established and verified by field data.Then,a series of numerical models,whose simulation method of steady seepage is verified by adopting the conformal mapping technique,are established to study the soil arching evolution of deep-buried tunneling and post-construction steady seepage.The results indicate that seepage leads to an increase in effective vertical stress,which is consistent with the existing theory.The seepage weakens the soil arching effect resulting in the height of the arch zone reducing from 2.38D(D is the tunnel diameter)to 1.25D.The seepage leads to the further development of ground consolidation settlement,but the differential displacement in the soil mass decreases.The ground reaction curve in the steady seepage condition shows a bigger value than that after excavation.It is reasonable to control the ground loss ratio in the range of 0.5–1.0%,which can minimize overburden pressure with moderate ground deformation.
基金supported by the National Natural Science Foundation of China(Nos.51225804,U1234204,and 41472244)the Doctoral Fund of the Ministry of Education of China(No.20120101110027)+1 种基金the Research Fund from the China Railway Corporation(No.2014G003-B)the Zhejiang Provincial Communication Department(No.2014H07),China
文摘Pressurized bentonite slurry is applied on a tunnel face to form a filter cake to stabilize the tunnel face when the slurryshield excavates through the sandy soil. Failure of the tunnel face may be caused by a high permeable filter cake, which commonlyhas a long penetration distance of slurry in sands. A column system with a height of 680 mm and a diameter of 300 mm was de-veloped to model pressurized slurry infiltration in sands. Pressure transducers were installed to estimate the hydraulic conductivityof the filter cake during slurry infiltration. The electrical conductivity of the leachate of collected samples was measured. Resultsshow that the majority of fine particles in slurry are within the range 100-300 mm into the sand specimen. The time for forming animpermeable filter cake is about 300 s, which indicates the impermeable filter cake is hard to form during the excavation.
基金supported by the National Natural Science Foundation of China(Nos.51225804,U1234204,51178418,and 51222803)the Research Fund by China Railway Corporation(No.2014G006)
基金Project supported by the Research Committee of the University of Macao (Nos. MYRG189(Y2-L3)-FST11-ZWH and MYRG067(Y1-L2)-FST12-ZWH),Macao SAR,China
文摘In this paper,a semi-analytical method for the analysis of pile-supported embankments is proposed.The mathematic model describes the cooperative behavior of pile,pile cap,foundation soil,and embankment fills.Based on Terzaghi's 1D consolidation theory of saturated soil,the consolidation of foundation soil is calculated.The embankments with two different types of piles:floating piles and end-bearing piles are investigated and discussed.The results of axial force and skin friction distributions along the pile and the settlements of pile-supported embankments are presented.It is found that it takes a longer time for soil consolidation in the embankment with floating piles,compared with the case using end-bearing piles.The differential settlement between the pile and surrounding soil at the pile top is larger for the embankment with end-bearing piles,compared with the case of floating piles.
文摘In the past decades,we have witnessed the rapid development of high-speed transportation infrastructure,such as high-speed railways,urban subways,expressways,and airfields worldwide.As a major effort in transportation infrastructure development,China plans to build 20 000 km of high-speed rail network by the year of 2020 with design speed up to 500 km/h.With such a fast pace,ensuring the safe and comfortable high-speed transportation presents major technical challenges to the design,construction,and maintenance of high performance infrastructure.
