Analysis of the Effect of Pore Water Pressure on a Small Radius Curve Section of a Fine Sand Layer under Cyclic Metro
2. Materials and Methods
2.1. Experimental Design
2.1.1. Experimental Site Overview
2.1.2. Experimental Measurement Point Layout
2.1.3. Experimental Content and Programme
2.2. Field Data Analysis
2.2.1. Pore Water Pressure Response Analysis under Cyclic Loading
2.2.2. Variation of Pore Water Pressure with Depth of Burial
2.2.3. Excess Pore Water Pressure Response Analysis
2.2.4. Ground Settlement Monitoring Analysis
2.2.5. Liquefaction Predictions for Silty Soils
- The ratio decreases under 0.8 for all monitoring points with increasing time, and the ratio decreases with increasing time for monitoring points with greater burial depths (e.g., K3-4, K11-4, K3-3, K11-3), indicating that the possibility of sand liquefaction is low.
- Working conditions 1 and 2 represent K3-1 to K3-4 and K11-1 to K11-4, where the closer working condition 2 is to the tunnel, the greater the value found, which indicates that the closer to the tunnel the greater the dynamic response generated. At the same time, the ratio slowly increases and then decreases as the distance increases, remaining between 0.6 and 0.8, indicating that liquefaction is less likely to occur with increasing distance.
2.3. Constitutive Model
- It is assumed that all soil bodies in the same rock formation are elastic-plastic, isotropic materials and conform to the Moore-Coulomb yielding criterion.
- The construction phase group, consolidation analysis module, performs initial ground stress calculations considering only the effect of self-weight stresses and ignoring the effect of tectonic stresses.
- The train is considered to be running at a constant speed.
2.3.1. Numerical Model Development
2.3.2. Boundary Conditions and Model Parameters
- Boundary conditions.
- Model parameters
2.3.3. Determination of Vibration Loads
2.3.4. Calibration of the Model
3. Results and Discussion
3.1. Excess Pore Water Pressure Response Pattern of the Soil at the Bottom of the Tunnel
3.2. Soil Deformation Development Pattern during Train Operation
3.3. Analysis of Straight Versus Curved Sections
4. Conclusions and Discussion
- The pore water pressure and excess pore water pressure generated by the initial vibration of the train are not easily dissipated and transferred, resulting in a larger pore pressure in the silty sand layer at the beginning of the train operation. During this, the pore pressure fluctuates due to peak commuting periods and climatic problems, while the fine particles of the powdered sand soil have a small amount of cohesive particles, making the soil layer have a certain strength and cohesion. The pore pressure and excess pore water pressure gradually decrease and stabilise at a later stage under the action of the train vibration.
- Under the action of cyclic train load, the response of the powder sand soil around the tunnel to train vibration is closely related to the location. The closer to the tunnel, the more sensitive the response is. The upper part of the tunnel arch waist beyond a certain burial depth range with the disappearance of the vibration force pore pressure also decreases rapidly. The soil layer in the lower part of the tunnel arch waist with the disappearance of the vibration effect pore pressure in the short term is not easy to dissipate.
- Soil liquefaction is related to the type of soil and is less likely to occur in silty soils compared to other soil layers in this tunnel shield section.
- Under the action of cyclic loading, the greater the horizontal distance from the tunnel, the more slowly the super-pore water pressure decays, and along the vertical direction decays faster, indicating that the soil beneath the tunnel vibrates mainly in the vertical direction. The area where the soil settles more is mainly concentrated on the surface of the soil 3 m from the lining on the right side of the tunnel, in the silt layer on the upper side of the tunnel and 3 m at the bottom of the tunnel, mainly in a “V” shape; i.e., the displacement settlement is large in the middle and small at the ends.
- The tunnel settlement is reduced from 2 mm to 1 mm during train operation and the resulting track unevenness is more moderate. The deteriorating effect on wheel-rail dynamics is weaker, so the displacement caused by vibration is safe for vehicle operation.
Institutional Review Board Statement
Data Availability Statement
Conflicts of Interest
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|Strata||GS||Moisture Content (w)||Porosity (e)||Clay Content (%)|
|fine medium sand||2.63||18.1||0.525||12.3|
|Monitoring Points||Clearance of the Monitoring Point from the Outer |
Profile of the Interval Tunnel/m
Between the Bottom of the Hole and the Tunnel Floor/m
|Monitoring Points |
|Strata||E (Mpa)||μ||γ (KN/M3)||Φ (°)||C (KN/M3)||K|
|Miscellaneous fill||/||0.37||17||18||10||5.8 × 10−6|
|Silt||13.6||0.3||18.4||23||15||5.8 × 10−6|
|Silty clay||8.1||0.3||19||15||20||5.8 × 10−7|
|Silty sand||17||0.3||18||31.3||2||1.2 × 10−4|
|Silt||12||0.25||20.6||25||18||5.8 × 10−6|
|Fine Medium Sand||30.5||0.25||18||35.9||0||2.4 × 10−4|
|Silty clay||10.5||0.3||20.2||18||28||5.8 × 10−7|
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Wang, X.; Liu, X.; Lin, Y.; Tan, F. Analysis of the Effect of Pore Water Pressure on a Small Radius Curve Section of a Fine Sand Layer under Cyclic Metro. Water 2023, 15, 981. https://doi.org/10.3390/w15050981
Wang X, Liu X, Lin Y, Tan F. Analysis of the Effect of Pore Water Pressure on a Small Radius Curve Section of a Fine Sand Layer under Cyclic Metro. Water. 2023; 15(5):981. https://doi.org/10.3390/w15050981Chicago/Turabian Style
Wang, Xiaorui, Xu Liu, Yunhong Lin, and Fei Tan. 2023. "Analysis of the Effect of Pore Water Pressure on a Small Radius Curve Section of a Fine Sand Layer under Cyclic Metro" Water 15, no. 5: 981. https://doi.org/10.3390/w15050981