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Relying on the application of the artificial freezing method on subway tunnel construction, a series of triaxial creep tests were carried out to study the creep behavior changes of Shanghai soft clay subjected to artificial freeze–thaw action. On this basis, MIP tests were conducted with the soil samples before and after creep for comparison to investigate the microstructure changes. The results indicate that freeze–thawed soil produces smaller creep deformation and instantaneous deformation than the unfrozen soil. On a micro-level, during the creep process, the soil skeleton reaches a new structure balance with smaller pore volume and pore area. But the diameter of the maximum pore increases. The change rate of total intrusion volume is a pivotal micro-parameter to evaluate creep strain as there is a good linear relationship between them. [ABSTRACT FROM AUTHOR]

With the rapid development of subway transportation systems, the problem of uneven settlement around tunnels cannot be ignored. The soil around the tunnel near the Guoquan Road Station of Shanghai Metro Line 10 was investigated in this study. Through a dynamic triaxial test using a global digital systems, the factors affecting the accumulated plastic strain, such as frequency, dynamic stress amplitude, consolidation ratio, and other factors were considered. The experimental results showed that the accumulated plastic strain on silty soil was related to the vibration times, the amplitude of dynamic stress, and the frequency. Moreover, when the vibration times were constant, the accumulated plastic strain increased with an increase in the amplitude of dynamic stress. In contrast, the accumulated plastic strain decreased with an increase in the frequency. Scanning electron microscopy (SEM) was used to qualitatively and quantitatively analyze the microscopic characteristics of silty soil before and after cyclic loading. Through the introduction of the plane fractal dimension, the relationship between the microstructure parameters of silty soil and macroscopic deformation were established. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Geotechnical Journal is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Featured Application: This paper provides the valuable instructions for the incoming large-area utilization of GSHP system in soft clay area in coastal cities in China and the characteristic of the thermal balance in muddy soil in Shanghai should be taken account into the design and development of the operation of the GSHP system. Geothermal energy resources, such as a green and clean renewable energy, are utilized all over the world, especially in soft clay areas along coastal cities in China, such as Shanghai. However, the operation of the ground-buried heat exchanger potentially affects the initial temperature field and the thermal balance, which will probably result in some potential engineering or environmental problems. This paper presents results from a series of large-scale laboratory modeling experiments which were conducted to study the thermal balance in saturated soft clay during the operation of the ground source heat pump (GSHP) system. In experiments, thermal phenomena are induced by a heat exchanger which is embedded in the testing soils and investigated by temperature sensor arrays. It summarizes the experimental methodologies and presents the time-dependent temperature distribution within the testing soils both in operation stage and the re-stabilization duration. Characteristics of thermal balance are discussed in two specific parameters of relative time ratio and temperature factor by comparing summer and winter cases. The thermal mattress effect is proposed to provide valuable guidelines for the utilization and operation of the GSHP system in soft clay areas. [ABSTRACT FROM AUTHOR]

Cyclic triaxial test by means of the geotechnical digital system is conducted for the soil near the Guoquan Road Station of Metro Line 10 in Shanghai to analyze the strain characteristics and the variation law of saturated silty soil under subway loading. Orthogonal design method is used to arrange the experiment, considering the following factors: frequency ratio f , cyclic stress ratio σ , vibration time ratio N , and the interaction function among them. Results show that the cyclic stress ratio σ , the frequency ratio f , the vibration time ratio N , and the interaction between the cyclic stress ratio σ and the vibration time ratio N have a significant effect on the axial strain of the subway tunnel. The effect of the interaction between the cyclic stress ratio σ and the vibration time ratio N is also significant. From the analysis of variance and regression theory, the nonlinear regression equation of the cumulative plastic strain of silty soil under subway loading is established. Residual analysis proves that the equation is ideal and credible. The results have important value for the design of subway tunnels. [ABSTRACT FROM AUTHOR]

Relying on the application of the artificial freezing method on subway tunnel construction, a group of cyclic triaxial tests were carried out to study the dynamic behavior of freezing-thawing saturated muddy clay under step cyclic loading. In terms of practical engineering, the freezing temperature and loading frequency were taken into account to indicate how the influencing factors affect the dynamic elastic modulus. The results indicate that the dynamic elastic modulus displays ladder-type drops with the increasing dynamic step loading amplitude. The dynamic elastic modulus increases with the growth of loading frequency. Freezing temperature has slight influence on dynamic elastic modulus, but the freezing and thawing cycles can lead to rearrangement of the soil structure. The dynamic elastic modulus increases with the growth of loading frequency. The fluctuation of dynamic elastic modulus is the most serious in the first stage and tends to be stable in the following steps. The fluctuation of dynamic elastic modulus of unfrozen soil is greater than freezing-thawing soil in the first stage. Based on a hyperbolic model, the dynamic constitutive behavior of freezing-thawing soil was investigated. [ABSTRACT FROM AUTHOR]

With the development and exploitation of geothermal energy ground source heat pump (GSHP) systems are being utilized all over Shanghai due to its unique energy advantages. A model experiment is designed and carried out to simulate an alternately-running GSHP system in summer and winter. It aims to study the characteristics of thermal conductivity and moisture migration of saturated soft clay (Shanghai mucky clay) with respect to thermal balance during the operation of a GSHP system by a series of laboratory modeling experiments. Thermal conductivity is an essential thermo-physical parameter for designing a GSHP system and is calculated [1.3680 W/(m °C)] rather than obtained via the expensive and time consuming in situ thermal response test. The value measured in laboratory experiments [1.1200 W/(m °C)] by transient probes did not comply well with in situ data. The Thermal conduction and moisture migration characteristics of Shanghai mucky clay indicate it is a geo-material with good heat storage but poor heat release based on a comparison between summer and winter conditions. All results provide reference for further discussion regarding the environmental effect of thermal balance surrounding a GSHP system. They are essential and valuable for the development of GSHP systems in Shanghai. [ABSTRACT FROM AUTHOR]

To determine the influence of load and drainage on the engineering consolidation characteristics of hydraulic fill soil in Shanghai, a detailed study has been carried out using three controlled model tests under different conditions. The governing equation of one-dimensional large strain consolidation with the load and self-weight was also quoted to discuss the influence. Three consolidation settlement stages and two consolidation periods of growth in strength were observed. The effect of applying load was more obvious than improving drainage condition in the first consolidation time. Prolonging consolidation time had no significant influence on increasing strength. It is shown that the increase in strength is concentrated in the first period of consolidation and the load and drainage play their different roles in different consolidation periods. Conclusively, some relevant recommendations are offered for the construction of hydraulic fill soil. [ABSTRACT FROM AUTHOR]

Copyright of Bulletin of Engineering Geology & the Environment is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this paper, the results of the instantaneous dynamic response of saturated soft clay under the subway vibration loading are presented. Based on the assumption of soil as viscoelastic medium, wave equation under forced vibration of three-dimensional anisotropy is derived, and time-space domain semi-analytical solution is given through Laplace and Fourier transform and their inverse transform using MATALB. Taking Shanghai metro line No. 2 for example, the dynamic monitoring is conducted with embedded earth pressure gauges and pore piezometers around the tunnel, and the horizontal response amplitude of dynamic stress of soil around the tunnel is calculated by the method presented in this paper with the laboratory Global Digital System test apparatus to determine the related calculation parameters. Then, a comparative analysis is made between calculation result and continuous field monitored data, and it is found that the attenuation trend of the two cases agree well with each other both in the horizontal and vertical direction, which indicates that the method presented in this study is reasonable. [ABSTRACT FROM AUTHOR]

Abstract: Shanghai is a typical area of soft soil distribution, Metro railway construction is now being developed in Shanghai City on a large scale and the planning of Metro stations are often located in densely populated districts with tall buildings. Metro station constructions are mostly taking pit dewatering measures, while the dewatering of aquifer may cause soil layer compression, land subsidence, foundation''s deformation, cracking and tilting of the buildings, and so on. In order to control the land subsidence effectively, the underground continuous concrete wall is often used in the deep foundation pit dewatering. The depth of underground continuous concrete wall and the filter tube position of pumping well affect drawdown outside the pit and land subsidence directly. This study refers to the deep foundation pit dewatering project of Hangzhong Road station of Shanghai Metro Line No.10. The excavation depth of foundation pit is 15.60–17.60m, and the design depth of underground continuous wall is 28m in the standard part and 30 or 31m in the end well. Three-dimensional finite differences method is used to simulate the pit dewatering through the inversion of permeability parameters based on the field pumping tests. The hydraulic barrier function of the underground continuous wall is simulated at four different depths including primary design depth, increasing 3m, 4m and 6m. The result of the numerical simulation indicates that the drawdown of the aquifer decreases with the increase of the underground continuous concrete wall depth. When the underground continuous concrete wall increases 4m on primary design basis, the drawdown outside the pit and land subsidence can be controlled effectively. The monitored results indicate that the drawdown outside the pit at a distance of 1–5m to the wall is less than 2m, while the maximum land subsidence is 7.97mm, which is of nearly no influence on the environment around the pit during dewatering. [Copyright &y& Elsevier]