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Soil arching effect results from the non-uniform stiffness in a geosynthetic-reinforced and column-supported embankment system. However, most theoretical models ignore the impact of modulus difference on the calculation of load transfer. In this study, a generalized mathematical model is presented to investigate the soil arching effect, with consideration given to the modulus ratio between columns and the surrounding soil. For simplification, a cylindrical unit cell is drawn to study the deformation compatibility among embankment fills, geosynthetics, columns, and subsoils. A deformed shape function is introduced to describe the relationship between the column and the adjacent soil. The measured data gained from a full-scale test are applied to demonstrate the application of this model. In the parametric study, certain influencing factors, such as column spacing, column length, embankment height, modulus ratio, and tensile strength of geosynthetic reinforcement, are analyzed to investigate the performance of the embankment system. This demonstrates that the inclusion of a geosynthetic reinforcement or enlargement of the modulus ratio can increase the load transfer efficiency. When enhancing the embankment height or applying an additional loading, the height of the load transfer platform tends to be reduced. However, a relatively long column has little impact on the load transfer platform.
In this study, the effects of particle sphericity and initial fabric on the shearing behavior of soil-structural interface were analyzed by discrete element method (DEM). Three types of clustered particles were designed to represent irregular particles featuring various sphericities. The extreme porosities of granular materials composed of various clustered particles were affected by particle sphericity. Moreover, five specimens consisting of differently oriented particles were prepared to study the effect of initial fabric. A series of interface shear tests featuring varying interface roughnesses were carried out using three-dimensional (3D) DEM simulations. The macro-response showed that the shear strength of the interface increased as particle sphericity decreased, while stress softening and dilatancy were easily observed during the shearing. From the particle-scale analysis, it was found that the thickness of the localized band was affected by the interface roughness, the normal stress and the initial fabric while independent of the particle sphericity. The thickness generally ranged between 4 and 6 times that of the median particle equivalent diameter. A thicker localized band was formed in the case of rougher interface and in soil composed of inclined placed and randomly placed particles. The coordination number measured in the interface zone and upper zone suggested that the dilation mostly occurs inside the interface zone. Anisotropy was induced by the interface shearing of the initial isotropic specimens. The direction of shear-induced anisotropy correlates with the shearing direction. The evolutions of anisotropies for the anisotropic specimens depend on the initial fabric.
This study demonstrates the feasibility of nanoscale Zero-Valent Iron (nZVI) for simultaneous stabilization of Pb and improvement of soil strength via batch experiments. The soil samples were prepared using slurry and pre-consolidation method at nZVI doses of 0.2%, 1%, 5%, and 10% (by dry weight). The physicochemical and geotechnical properties of Pb-contaminated soil treated by nZVI were analyzed. The results indicate that the contamination of Pb(II) resulted in a notable reduction in the undrained shear strength of soil from 16.85 kPa to 7.25 kPa. As expected, the Pb in exchangeable and carbonate-bound fractions decreased significantly with the increasing doses of nZVI. Meanwhile, the undrained shear strength of Pb-contaminated soil enhanced substantially as the increase of nZVI, from 25.83 kPa (0.2% nZVI treatment) to 69.33 kPa (10% nZVI treatment). An abundance of bubbles, generated from the oxidation of nZVI, was recorded. The mechanisms for simultaneous stabilization of Pb and soil improvement primarily include: 1) the precipitation and transformation of Pb-/Fe-hydrated oxides on the soil particles and their induced bounding effects; 2) the increased drainage capability of soil as the occupation of nZVI aggregates and bubbles in the macropores space and 3) the lower soil density derived from the increase in microbubbles retained in the soil. This study is provided to facilitate the application of nZVI in the redevelopment of contaminated soil.
This study presents a practical consolidation solution for ground improvement used prefabricated vertical drains (PVDs) by incorporating the available time-dependent discharge rate around PVDs, which can be easily obtained by laboratory test and field monitoring. Only radial consolidation is taken into account in the derivation to significantly simplify the final expression as the vertical consolidation can be neglected in a typical soft ground improvement project. The proposed solution is verified by the finite element method (FEM) and two case histories, including vacuum preloading and surcharge loading. The verification results show that the proposed solution can predict the development of excess pore water pressure (EPWP) and the degree of consolidation (DOC) effectively and accurately. Design charts and framework are developed to assist geotechnical engineers in using this solution for field construction and performance prediction.
A non-orthogonal elastoplastic model for clay is proposed by combining the non-orthogonal plastic flow rule with the critical state concept, and the model framework is presented from the perspective of the magnitude and direction of the plastic strain increment. The magnitude is obtained based on the improved elliptical yield function and the plastic volumetric strain dependent hardening parameter. The direction is determined by applying the non-orthogonal plastic flow rule with the Riemann-Liouville fractional derivative to the yield function without the necessity of additional plastic potential function. The presented approach gives rise to a simple model for soil with five parameters. All parameters have clear physical meaning and can be easily identified by triaxial tests. The model performance is shown by analyzing the evolution process of the yield surface, the hardening rule and the plastic flow direction. The capability of the proposed model to capture the mechanical behaviours of clay with different stiffness is also confirmed by predicting test results from the literature.
Most slow-moving landslides in the Three Gorges Reservoir (TGR) region of China are characterized by pre-existing shear surfaces. The large deformation within the shear zones usually gives rise to clastic soil formation. The creep properties have large influence on the kinematic feature of landslides. In this paper, we report an in-situ direct shear creep test carried out in the shear zone of a reactivated slow-moving landslide in the TGR region. Correspondingly, some laboratory ring shear creep tests are carried out to interpret the movement pattern of this landslide. The shear zone soil exhibits similar non-attenuating creep responses in both the in-situ direct shear and laboratory ring shear creep tests. At the same stress level, however, the in-situ direct shear creep test yields a larger rate of creep displacement due to shearing along the landslide direction. In the ring shear creep tests, at the prepeak stage, the critical creep stress that triggers creep failure is slightly lower than the peak shear strength but much larger than the residual strength; at the postfailure stage, the critical creep stress of the shear-zone soil is equal to the residual shear strength. The rate-dependent residual shear strength may account for the stepwise movement pattern of the landslide.
To investigate the bearing mechanism of piles in inclined slope, this paper proposed an analytical method through geometric transformation to calculate the ultimate bearing capacity at the tip of a pile in inclined rocks based on the characteristic line method. It was found that there were five failure modes for piles in inclined rocks depending on the embedment ratios, slope angles, average overburden load and tensile strength parameter of the rock mass. When the pile failure mode was under the modes of deep pile with minor overburden (DL) and deep pile with major overburden (DH), the ultimate bearing capacity had no change as the slope angle and the pile embedment ratio changed. When the pile was under the failure modes of semi-deep pile with minor overburden (SL), semi-deep pile with major overburden (SH) or shallow pile (SS), the ultimate bearing capacity decreased with an increasing rate as the slope angles increased; and to get the same ultimate bearing capacity at the pile tip, the pile embedment ratio should increase. The proposed analytical method can be served as an efficient method to estimate the bearing capacity of piles in inclined slope with small slope angle (typically less than 40°).
A non-orthogonal elastoplastic constitutive model for sand with dilatancy is presented in the characteristic stress space. Dilatancy of sand is represented by the direction of plastic flow, which can be directly determined by applying the non-orthogonal plastic flow rule to an improved elliptic yield function. A new hardening parameter is developed to describe the contractive and dilative volume change during the shear process, which is coordinated with the non-orthogonal plastic flow direction. The combination of the non-orthogonal plastic flow rule and the proposed hardening parameter renders the proposed model with the ability to reasonably describe the stress-strain relationship of sand with dilatancy. The model performance is evaluated by comparing with the experimental data of sand under triaxial stress conditions.
In deep excavation designs, strut loads play a key role to ensure excavation safety. During the construction, temperature fluctuation inevitably leads to a variation in strut loads. Therefore, how to quantitatively estimate the effects of temperature on strut loads is a matter of concern. In this study, the incremental changes in wall deflection due to temperature fluctuation were assumed to be piecewise linear. Based on the beam-on-elastic-foundation (BEF) model, an empirical approach accounting for the variation in temperature-induced strut loads at all levels was established. This model was further calibrated against a reported case study for a more precise predictive performance.
In order to investigate the dynamic impact of a moving surface load on a shallow-buried tunnel, an analytical model of a tunnel embedded in an elastic half-space was proposed. The half-space and the tunnel structure were modeled as visco-elastic media and the moving surface load was simplified as a moving point load on the ground surface. Based on the fundamental solution for the isotropic elastic half-space system in Cartesian and cylindrical coordinates, the dynamic response of a shallowly-buried tunnel in a half-space generated by a moving surface load was obtained. The transformations between plane wave and cylindrical wave functions were used to facilitate the application of boundary conditions at the ground surface and the tunnel interface. It was found that the vibration of the shallowly-buried tunnel increases significantly as the load moving speed increases, and reaches a maximum value at a critical load velocity. The tunnel vibration can be greatly reduced as the buried depth increases, and can satisfy the requirement of vibration specification (ISO 04866-2010) after it exceeds the critical depth. The critical depth increases exponentially with the increase of the moving speed of the surface load.
High speed rail demands precision structural health monitoring in shallow underground environments near embankments. Traditional low frequency wireless channels can communicate with underground sensors, but its large antenna elements are prone to damage from geological stress. In this case study paper, we design a higher frequency compact system and experimentally characterize its performance in-situ, in different soil and moisture conditions that are representative of UK soil conditions near the planned HS2 rail site and weather conditions. Accurate 3D electromagnetic simulation results are also shown to support experimental results and a pathloss model sensitive to soil conditions is developed to inform upcoming high speed rail embankment monitoring deployment. The multi-disciplinary findings presented will also directly inform the depth and data reliability of current high speed rail sensor deployment.
Spalling (or slabbing) in the sidewalls of deep rectangular tunnels is a type of rock failure phenomenon under the three-dimensional stress environment, which often occurs on the surrounding rocks after the tunnel face excavation is completed and has a significant impact on the safety of construction and support. In order to investigate the spalling process in deep rectangular excavated tunnels under three-dimensional stress, a granite material was firstly processed into cubic specimens (100 mm × 100 mm × 100 mm) with prefabricated rectangular holes (40 mm × 40 mm). Simulation experiments were performed using a rock true-triaxial electro-hydraulic servo mutagenesis testing system under four different initial stress states. Meanwhile, a wireless micro-camera was used to record and monitor the damage process on the sidewalls of the rectangular tunnel in real time. The results showed that under the four stress conditions, an evident spalling failure occurred on the entire sidewalls of the rectangular hole. It was observed that the spalling-damaged zone gradually developed toward the deep part of the hole in a horizontal direction. Finally, it formed a penetrating symmetric arc-shaped groove along the axial direction, whereas the roof and bottom slab remained stable. The spalling failure process of the sidewalls had four stages: the calm period, particle ejection at the upper and lower shoulders, sidewall crack propagation, and crack penetration spalling failure. Compared with the dynamic failure (rockburst) of a circular tunnel under the same three-dimensional high stress conditions, the spalling failure of the rectangular tunnel sidewalls was of the static failure mode. Under the three-dimensional stress condition, the radial stress had a greater effect on the spalling failure than the axial stress, by increasing the radial stress can be significantly reduced the degree of spalling failure and effectively improved the stability of the surroundings.
The cascading failure of underground pillar sections poses a risk to miners and surface structures. Assessing the risk of underground mining panels contributes to the prevention and control of the catastrophic failure. To resolve the challenge in quantifying the effect of failure of a single pillar on the risk of an entire pillar section, a new risk assessment model incorporating the stability of individual pillars and the load transfer between pillars was proposed to investigate the cascading failure of pillar sections. The load transfer process from failed pillars to adjacent ones was effectively quantified by the relationship between transferred incremental load and transferring distance. The influence of uncertainties of pillar strength, caused either by intrinsic strength variability of a single pillar (quantified by coefficient of variation COV) or the non-uniform deterioration process of pillar sections (quantified by correlation coefficient ρ), was investigated on the probability of cascading failure. Risk mapping was also performed on two representative historical collapsed pillar sections using the risk evaluation method proposed to illustrate the risk level of each pillar to trigger cascading failure. The proposed model could represent realistic load transfer process and provide reliable risk assessment results for pillar sections. The results showed that the reliability of pillar sections is significantly influenced by both intrinsic variability in pillar strength and intercorrelation of strength between pillars. The probability of cascading failure increases with increasing COV, which verifies that geological uncertainties increase the risk of collapse in pillar sections. The impact of COV on probability gradually decreases to negligible levels as ρ increases to 1, which means that the synchronous variation of pillar strength among a pillar section can significantly compensate for the impact of COV. The proposed approach provides a distinct perspective on understanding sudden failure of high-risk pillars and contributing to the risk control for abandoned pillar sections.
Geohazard——landslide
Geohazard——landslide
Landslide is a type of common geohazard which occurs to the region with many mountains and slopes. The ground movement of a landslide involves rock falls , slops slippage and debris flows. The landslide can be induced by the long term soil erosion, earthquake, floods, human activities, and so on. Every year, the landslide may cause billions of damage and thousands of deaths.
Geohazard——earthquake
Geohazard——earthquake
The earthquake is dreadful natural geohazards deriving from the strain energy release beneath the ground. when the intense stress break the rocks, the ground undergoes strong movements and deformation. Examples of huge earthquakes in recent years are the magnitude 9 Tohoku-oki earthquake in Japan (2011) and the magnitude 8 Wenchuan earthquake in China (2008). Many other disasters, such as landslide, sinkhole, tsunami, can be triggered and cause secondary damages.
Geohazard——coastal erosion
Geohazard——coastal erosion
This project is funded by European Union's Horizon 2020 research and innovation programme Marie Skłodowska-Curie Actions Research and Innovation Staff Exchange (RISE) under grant agreement No 778360)
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