Analysis of Face Stability during Excavation of Double-O-Tube Shield Tunnel

This paper focuses on the face stability analysis of Double-O-Tube shield tunnel. This kind of analysis is significant to ensure the safety of workers and reduce the influence on the surrounding environment. The key point of the stability analysis is to determine the supporting pressure applied to the face by the shield. A collapse failure will occur when the supporting pressure is not sufficient to prevent the movement of the soil mass towards the tunnel. A three-dimensional collapse failure mechanism was presented in this paper. Based on the mechanism of a single circular shield tunnel, the mechanism of Double-O-Tube shield tunnel was established by using the fact that both of the mechanisms are symmetrical. Then by means of the kinematic theorem of limit analysis, the numerical results were obtained, and a design chart was provided. The finite difference software FLAC3D was applied to investigate the face failure mechanism of DOT shield tunnel established in this paper; the critical supporting pressures of the collapse failure mechanism in different strata (sand and silt) were calculated. Through comparative analysis, the theoretical values were very close to the numerical values. This shows that the face failure mechanism of DOT shield tunnel is reasonable, and it can be applied to the sand and silt strata

Effect of Foam Parameters on Cohesionless Soil Permeability and Its Application to Prevent the Water Spewing

Water spewing from the screw conveyor often occurs in cohesionless soil strata below the groundwater level during tunnel excavation with earth pressure balanced (EPB) tunnel boring machines (TBM). Foaming agents have been extensively employed as soil conditioner during the use of EPB TBMs to change the properties of soil, and the conditioned soil, with its low permeability, was the key to reduce the frequency of water spewing. To determine effect of foam parameters on cohesionless soil permeability, the conditioned sand permeability under different foam liquid half-lives ( T hl ) foam expansion rates (FERs), and foam injection rates (FIRs) was tested. To verify the permeability test results, a case study was carried out to optimize the foam parameters for preventing water spewing. Based on these results, this paper suggests that high-stability foaming agents with a medium FER and FIR represent an effective way to reduce cohesionless soil permeability and to prevent water spewing

Field Study on the Waterstop of the Rodin Jet Pile Method in a Water-Rich Sandy Gravel Stratum

Due to the increasing depths of underground urban construction, the surrounding environment and hydrogeological conditions are becoming increasingly complex, and conventional high-pressure rotary jet grouting has become unable to meet construction needs. At present, Rodin jet pile (RJP) ultra-high-pressure rotary jet grouting has been widely used as a grouting reinforcement method for deep and large foundations in silty soils, fine sands and clay strata; however, there have been no successful applications in a sandy gravel stratum with high water content (namely, water-rich sandy gravel stratum). Therefore, this paper uses the ventilating shaft in a section of the Beijing Metro as the construction background to carry out field tests on the RJP ultra-high-pressure rotary jet grouting method and waterstop in a water-rich sandy gravel stratum. Through a series of experiments monitoring the formation deformation and pore water pressure and exposing the pile diameter, pile occlusion, pile strength, and permeability of the test pile construction process, it is believed that, for the RJP ultra-high-pressure construction method in a water-rich sandy gravel stratum, reliable jet solidification can occur, the joint between jets can be achieved, the solid strength can reach 10 MPa or higher, and the permeability coefficient can reach 10−8 cm/s. Therefore, RJP ultra-high-pressure rotary jet grouting can be applied as a waterstop method in water-rich sandy gravel stratum

Comparative Study on Mechanical Properties of Sealing Grease Composed of Different Base Oils for Shield Tunnel

This study proposes a novel sealing grease with improved mechanical properties and environmental performance. A series of sealing grease samples were made with different base oils, including mineral oil and renewable oil (vegetable oil and lard). In this study, thermogravimetric analysis (TGA) was conducted to study the adsorption capacity of the thickener to the base oil. The fluidity of the sealing grease was also tested at different temperatures. Furthermore, an exponential function was proposed for the flow rate of the sealing grease and the temperature. Moreover, a cone penetration test was conducted to study the consistency of the sealing grease. The results indicated that the capacity of the thickener to adsorb vegetable oil was greater than that of mineral oil, but less than that of lard. Additionally, the flow rate of the sealing grease increased with an increase in temperature. At a fixed temperature, the flow rate of the sealing grease increased with the base oil content. According to the exponential function, the composition of the base oil is the key factor that determines the temperature sensitivity of the sealing grease. In addition, the sealing grease made of vegetable oil has the minimum temperature sensitivity coefficient

ATG5 regulates type Ⅱ collagen expression by modulation of autophagy

Objective To explore the regulative effect of autophagy-related protein ATG5 on the expression of type Ⅱ collagen in human chondrocytes through affecting autophagy function. Methods Transcriptome data of 13 human cartilage tissue samples were downloaded from GEO database to analyze the correlation between ATG5 and COL2A1 expression.Western blotting and immunofluorescence assay were used to detect the expression of type Ⅱ collagen (Collagen Ⅱ, COL2) in human chondrocytes C28/I2 after rapamycin (Rapa) and bafilomycin A1(BafA1) treatment.Human COL2A1 promoter plasmid was constructed, and dual-luciferase reporter assay was applied to detect the effect of overexpression of ATG5 on COL2A1 promoter activity.mRFP-GFP-LC3 autophagy dual fluorescent virus was used to dynamically monitor the changes in autophagic flux of C28/I2 cells with overexpression and knockdown of ATG5.Western blotting was used to detect the effects of Rapa and BafA1 on COL2, LC3Ⅱ/LC3Ⅰ expression levels after overexpression or knockdown of ATG5. Results The results of correlation analysis showed a positive correlation between the mRNA expression of ATG5 and COL2A1 in human chondrocytes samples.Rapa and BafA1 significantly promoted and inhibited the expression of COL2 in C28/I2 cells (P < 0.05), respectively.The human COL2A1 promoter plasmid was successfully constructed, and the transcriptional activity of the COL2A1 promoter was up-regulated by the overexpression of ATG5(P < 0.01).Treatment with autophagy dual-fluorescence virus resulted in LC3-GFP fluorescence quenching after overexpression of ATG5(P < 0.01), suggesting autophagy activation; and a greater fluorescence intensity of LC3-GFP was observed after knockdown of ATG5(P < 0.05), demonstrating autophagy inhibition.Rapa obviously promoted the expression of COL2 and LC3Ⅱ/LCⅠ, which were up-regulated by ATG5(P < 0.05), but BafA1 showed the opposite effect of Rapa (P < 0.05). Conclusion Overexpression of ATG5 up-regulates the expression of type Ⅱ collagen, and the regulation of ATG5 on the expression of type Ⅱ collagen depends on autophagy in chondrocytes

Understanding Free Volume Characteristics of Ethylene-Propylene-Diene Monomer (EPDM) through Molecular Dynamics Simulations

Understanding the underlying processes associated with the viscoelasticity performance of ethylene-propylene-diene monomer (EPDM) during its service life is essential for assessing and predicting its waterproofing performance in underground infrastructure. The viscoelasticity of the polymer is closely related to its free volume, and both of these properties depend on multiple factors, such as temperature, stress magnitude, and strain level. To explore the fundamental viscoelastic behavior of EPDM using free volume as a proxy for viscoelasticity, this article investigates the influence of temperature, stress magnitude, and strain level, as well as their combined effect, on the free volume through molecular dynamics (MD) simulations. An EPDM cross-linked molecular model was built and verified by comparing the simulation values of glass transition temperature, mechanical properties, and gas diffusivity with the experimental results reported in the literature. Then, the dependence of EPDM&#8217;s fractional free volume on temperature, strain, and their combined effect was investigated via MD simulations, on the basis of which the applicability of various superposition principles was also evaluated

A New Soil Conditioner for Highly Permeable Sandy Gravel Stratum in EPBs

Full-face water-rich gravel stratum is a large challenge during tunnel excavation with earth pressure balance shields (EPBs) because of accidents such as water spewing from the screw conveyor and ground collapse. Slurry and polymer have been used as conditioning agents to avoid such problems and thus ensure a successful tunneling. However, limited improvement of sandy gravel was achieved when traditional soil conditioner were applied. This study proposes a new conditioner (modified slurry) consisting of bentonite slurry, viscosity modifier, sodium silicate and polymer, which will enhance the properties of sand gravel stratum. Low reaction time, high apparent viscosity, good plastic behavior and low permeability were employed for investigating the optimum ratio of the ingredients. The proposed modified slurry has a good performance in conditioning sandy gravel soils and can be the reference for EPBs’ excavation in highly permeable, non-adhesive coarse-grained soil stratum

A New Soil Conditioner for Highly Permeable Sandy Gravel Stratum in EPBs

Full-face water-rich gravel stratum is a large challenge during tunnel excavation with earth pressure balance shields (EPBs) because of accidents such as water spewing from the screw conveyor and ground collapse. Slurry and polymer have been used as conditioning agents to avoid such problems and thus ensure a successful tunneling. However, limited improvement of sandy gravel was achieved when traditional soil conditioner were applied. This study proposes a new conditioner (modified slurry) consisting of bentonite slurry, viscosity modifier, sodium silicate and polymer, which will enhance the properties of sand gravel stratum. Low reaction time, high apparent viscosity, good plastic behavior and low permeability were employed for investigating the optimum ratio of the ingredients. The proposed modified slurry has a good performance in conditioning sandy gravel soils and can be the reference for EPBs’ excavation in highly permeable, non-adhesive coarse-grained soil stratum

Impact of Plant Root Morphology on Rooted-Soil Shear Resistance Using Triaxial Testing

Mechanical reinforcement by plant roots increases the soil shearing strength. The geometric and distribution characteristics of plant roots affect the soil shearing strength. Current research on the shear strength of rooted-soil is mostly based on direct shear tests with a fixed shear surface and thus cannot reflect the actual failure state of the rooted-soil. In this study, Golden Vicary Privet was used to create a rooted-soil, and a triaxial test method was used for soil mechanical property analysis. The influence of the root geometry (root diameter and individual root length) and distribution characteristics (root density and root distribution angle) on the rooted-soil shearing strength was studied by controlling the root morphology in the specimens. According to the results, both the root geometry and distribution characteristics affect the rooted-soil shearing strength. For a fixed total length of the roots, the longer the individual root length is, the better the soil shearing strength is. In addition, the reinforcement effect of the root system increases as the angle between the root and the potential failure surface increases. The results also show that the root system significantly enhances the soil cohesion while only minimally affecting the internal friction angle. The maximum rooted-soil cohesion is 2.39 times that of the plain soil cohesion, and the maximum internal friction angle of rooted-soil is 1.24 times that of plain soil. This paper provides an approach for the determination of the rooted-soil strength and a rationale for vegetation selection in ecological slope reinforcement applications