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To address the low drainage efficiency and insufficient consolidation typically encountered during the vacuum preloading of low-permeability soft soil,this study introduces a pre-vacuum freeze-thaw disturbance aimed at enhancing the soil structure and improving drainage performance.Vacuum drainage tests were conducted on specimens subjected to various disturbance modes,with continuous monitoring of the coupled thermal-hydraulic-mechanical responses,settlement evolution,and energy consumption throughout the artificial freeze-thaw and vacuum stages.Post-consolidation measurements of water content and shear strength were also performed.The results indicate that ice crystallization and fissure development during freezing significantly increased soil permeability by approximately 10%-40%.Upon thawing,the newly formed pore channels facilitated accelerated vacuum drainage.During vacuum preloading,the freeze-thaw disturbed specimens exhibited faster water content reduction,more rapid dissipation of pore-water pressure,greater strength enhancement,and larger settlement compared to the undisturbed specimens,indicating a significant improvement in overall consolidation efficiency.Although the disturbed group consumed more total energy,its energy-consumption ratio throughout the process displayed a stage-dependent pattern:an initial sharp rise,a rapid mid-stage decline,and a slight late-stage increase.Notably,the late-stage energy consumption ratio of the disturbed specimens was lower than that of the undisturbed group,demonstrating superior full-cycle energy performance.This study provides a novel technical pathway for achieving efficient dewatering and consolidation of soft soil.
Using the self-developed one-dimensional visual horizontal freezing device,one-way horizontal freezing tests are conducted on soft clay under various temperature gradients.The development of the cryostructure in the longitudinal section of the soil is observed.The results indicate that the water migration during the horizontal freezing process induces thermal responses,including variations in the temperature,water content,pore-water pressure and soil pressure,with the temperature gradient being the primary driver of water migration.During the horizontal freezing process,bidirectional water redistribution occurs in the soil due to the gravitational effects.However,the horizontal water migration is significantly greater than the vertical one.After freezing of 120 h,the water content within the freezing zone is markedly higher than the initial water content,with the maximum often observed at 1～3 cm from the freezing front.Conversely,the water content in the unfrozen area is generally lower than the initial value,indicating the dehydration consolidation in this region.Additionally,the longitudinal section of the soft clay exhibits a distinct and pronounced cryostructure during the horizontal freezing process,primarily resulting from the increased tensile stress due to low-temperature suction and crystallization stress.Based on the shape,density and distribution characteristics of the cryostructure,it can be qualitatively categorized into whole,fibrous layered,thin layered,and thick layered structures.The findings of this study provide preliminary insights into the water-heat-force-structure response processes of soft clay during the horizontal freezing,whole,fibrous layered,thin layered,and thick layered structures providing a theoretical basis for understanding horizontal frost heave mechanisms.
The new Yichang—Zhengwan high speed railway connection line crosses the eastern edge of the Dabashan arc tectonic belt in the Qinling orogenic belt, with strong neotectonic movement, mixed stratigraphic lithology, large topographic relief, and a large number of perilous rocks developed on the upward slopes of tunnel entrances, which poses a serious threat to the safety of the construction and operation of the connection line. On the basis of the preliminary evaluation during the survey phase, this paper takes 35 risky slopes screened out in the preliminary evaluation as research objects to carry out re-evaluation. Considering the efficacy of temporary construction protective measures, we narrowed down two high risk tunnels using stereographic projection analysis and the fuzzy mathematical analytic hierarchy process. Subsequently, the predictive analysis was conducted to assess the dynamic characteristics of falling rocks by Rockpro3D simulation based on GIS and probability models. The results show that: (1) The exit of the Weijiashan tunnel has a low probability of being impacted by falling rocks, while the exit of the Laolingang tunnel has an extremely high probability of being impacted by falling rocks; (2) The probability of the perilous rock of Laolingang tunnel impacting directly on the tunnel opening is 24.73%, with the maximum impact energy of 6 693 kJ and the maximum speed of 26.2 m/s, and the impact points are concentrated in the right side of the tunnel entrance; (3) According to the factors of impact probability, impact energy, impact velocity, woods and topography, there is an urgent need for engineering management of perilous rock zone 3. The research results can provide reference for the effective prevention and control of perilous rocks in the tunnel of Zheng-Wan high speed railway connection line.
The high-temperature frozen soil is prone to creep deformation under long-term load.In order to explore the influence of its internal pore structure on the creep deformation of high-temperature frozen soil,static triaxial creep tests under different temperatures,dry densities and axial stresses were carried out on the high-temperature frozen soil.At the same time,CT scanning and pore extraction were carried out on the air-dried triaxial samples after the creep test.The results show that:Avizo was used to conduct 3D modeling and pore extraction on CT scan images.After conducting pore equivalence analysis on the extracted pores using three different methods,it was found that sphere equivalent error was the smallest.Therefore,sphere equivalent was selected for microscopic pore analysis,and the pores were divided into four categories:0～200 μm,200～500 μm,500～1 000 μm and＞1 000 μm.Under the given test conditions,the pore size of the sample is mainly distributed in the range of 200～500 μm,and the creep deformation is positively correlated with the number of pores with the pore size＞500 μm.The creep deformation increases with the increase of temperature,the decrease of dry density and the increase of axial stress,and the temperature,dry density and axial stress all have significant effects on the creep deformation and the number of pores with pore size＞500 μm.The number of pores with pore size＞500μm increases with increasing temperature,decreasing dry density and increasing axial stress.
In order to optimize the waterproof and drainage design of the lining of a high-water pressure karst tunnel,taking the New Yuanliangshan Tunnel as the research background,based on the differential equation of the plane radial stable seepage of pressurized water,considering the water pressure reduction effect of shotcrete,a calculation formula for the water pressure of the tunnel lining is derived.The influence of factors such as the drainage capacity of the drainage pipe,the thickness and impermeability of the grouting ring on the water pressure of the lining was analyzed.The results indicate that:The magnitude of water pressure on the lining varies exponentially with the tunnel drainage capacity,grouting ring thickness and permeability coefficient.The drainage capacity of the tunnel has the greatest impact on the water pressure of the lining.Once the drainage pipe is blocked,the water pressure reduction coefficient becomes 1,and the lining will withstand static water pressure.Increasing the thickness of the grouting ring is beneficial for reducing the water pressure loaded on the lining,but the reduction effect gradually weakens.Strictly controlling the quality of grouting operations,improving the homogeneity of the grouting circle,and reducing the permeability coefficient of local short plate grouting bodies can effectively improve the water pressure resistance of the grouting circle and reduce the permeability pressure of the lining.
