Tunnel excavation in mountainous region frequently encounters high local inflows as a consequence of hydraulic head and multiple faults geology, which may adversely affect the serviceability of ...tunnel structures. Previous researches, however, paid very little attention to the seepage field of rocks around deep buried tunnels adjacent to water-bearing faults under high hydraulic head. In this paper, a new close-form analytical method is proposed to investigate the combined effect of high far-field hydraulic head and head generated by water-bearing faults on mountain tunnel structures. First, the virtual image technique and conformal mapping theory are employed to evaluate the water discharge and the head variation at concerned locations of deep circular tunnel embedded in water-rich zone, such as the lining, grouting ring and surrounding rocks. Second, the head difference is introduced as a new parameter to predict the uneven distribution of hydraulic head on tunnel structures. Then this paper contrasts to the classical Harr analytical solution and implements numerical simulation on the fault geological conditions to examine the presented analytical method, receiving reasonable agreements. Furthermore, sensitivity analyses are preformed to investigate the performance of concerned parameters on the distribution of hydraulic head on tunnel structure adjacent to water-bearing fault, including the magnitude of head induced by water-bearing fault, spacing between fault and tunnel, water discharge after drainage ditch installed and fault dip. The interesting point and ingenious approach are tracing the corresponding analytic functions for not only the influence of vertical fault adjacent to the tunnel but also the fault with an inclined angle, which enhances the engineering applicability of presented method. In general, this work contributes to the preliminary design of tunnels in water-rich fault zones and provides a theoretical basis on the tunnel excavation and operation in the mountainous area and other adverse geological environments with faults.
Abstract
The three-parameter Weibull distribution has a strong ability to fit many kinds of experimental data, which provides a solution for using a unified expression to characterize the ...elastic-brittle, strain softening, elastic-plasticity, and other constitutive behaviors of rocks. Therefore, a statistical damage constitutive model based on three-parameter Weibull distribution was constructed through theoretical analysis and derivation. Its expression ability was verified by combining with the conventional triaxial compression test data of marble. Meanwhile, the application effect of this statistical damage constitutive model on granite and sandstone was analyzed. The results show that the statistical damage constitutive model of rock based on three-parameter Weibull distribution can well express elastic-brittle, elastic-plastic, strain softening behaviors of rock by setting reasonable constitutive parameters, which lays a theoretical foundation for constructing a unified rock constitutive model. Conventional triaxial tests of marble show that with the increasing of confining pressure (σ3= 5, 15, 25, 35 MPa), the plastic deformation increases and the failure mode gradually changes from brittle tensile failure to shear failure, showing brittle-ductile and brittle-plastic transition characteristics. And its constitutive behaviors are characterized by elastic-brittleness, strain softening, and elastic-plasticity, which can be well expressed by the statistical damage constitutive model. When σ3 is 25 and 35 MPa, sandstone samples show elastic-brittle behavior. And for granite samples, they show strain softening behavior when σ3 is 5 MPa. The statistical damage constitutive model is also suitable for describing both sandstone elastic-brittle behavior and granite strain softening behavior. It is concluded that the three-parameter Weibull distribution provides a useful approach to characterize various constitutive behaviors of rock, and the model has a wide potential in numerical simulation for mining engineering, geoengineering, and other rock engineering.
Due to the uncertainty in soil landslide failure mechanisms, lack of early warning systems for soil landslides and adoption of improper excavation configurations, soil landslides accidents triggered ...by highway excavation in Chinese mountainous areas generally require expensive remedial measures. This paper describes a soil landslide associated with excavation through integrating field reconnaissance and finite element method simulation. According to the obtained results, the adoption of toe excavation and the presence of a silty clay layer are the two main factors contributing to the failure of the soil landslide, and a strong negative correction was observed between the toe excavation and surface displacement and the safety factor of the investigated cut slope; therefore, a four-level early warning system for this excavation-induced soil landslide was established by employing toe excavation and surface displacement thresholds as the warning indicators. Lastly, a preferable excavation configuration was proposed to facilitate excavation designs in similar landslide-prone areas.
Many slabbing rock masses have emerged in hydropower slopes and underground engineering, with the construction of basic engineering and resource development projects along the zone of the Belt and ...Road. The anti-dip slabbing rock mass is prone to toppling and the degree of slabbing controls the development of toppling deformation. There are a few reports on the mechanical mechanism of rock mass toppling deformation after slabbing. Based on the analysis of the genetic conditions of rock mass slabbing, the influence of rock mass after slabbing on toppling deformation was explored by means of the mechanics method. The toppling bending deflection (TBD) and the toppling fracture depth (TFD) were selected as the analysis indexes, and the response regularity of slabbing on toppling rock mass was analyzed with examples. The results show that the width and thickness of the slabbing rock mass become narrower and thinner, the toppling bending deflection (TBD) increases, the toppling fracture depth (TFD) decreases, and the toppling deformation and failure intensify. The TBD is independent of the width of rock mass slabbing under self-weight, and the change of TBD is slow when the slab beam slabbing number (
n
) of thickness is <4 and fast when the slabbing number is above 4. The first TFD decreases fast when
w
is <2.0 m and it tends to be stable when
w
is above 2.0 m. The first TFD reduces relatively fast with the decrease in the thickness (
t
) of the slab beam. The result of this study can provide a reference for the treatment and evaluation of slabbing rock mass toppling deformation.
Slope deformation and failure is an inevitable engineering problem in highway construction and operation in mountainous areas. Its essence is a continuous–discontinuous gradual failure process of ...slope under the action of unbalanced force. Slope deformation and failure mechanism is the basis and key content of its emergency treatment and comprehensive treatment. In this study, the continuous–discontinuous element method (CDEM) and finite difference method are used to analyze the deformation mechanism and support the effect of a scattered slope in the Biwei Expressway. The results showed that the change in the local geological environment caused by roadbed excavation leads to slope slippage along the surface and then pulls the upper rock mass gradually to produce slippage failure, resulting in the stability gradually decreasing. The mechanism is traction sliding–tensile cracking. The continuous–discontinuous element method can effectively simulate the formation process of the main and sub sliding planes during excavation and can better display the phenomenon of slope failure and gradual disintegration. The emergency disposal of the gravity anti-sliding retaining wall in front of the slope can effectively control further deformation and ensure temporary stability. In comprehensive treatment, step-type slope excavation, gravity anti-sliding retaining wall, and anchor frame beam are adopted to control the deformation and failure of slope and ensure long-term stability. The numerical simulation results are consistent with the actual results, which effectively explains the rationality of this study. The research results of this study can provide some reference for the emergency treatment and comprehensive treatment of slopes in mountainous areas and for the construction and operation of highways and other infrastructure in mountainous areas.
From June 10 to 13, 2019, continuous heavy rainfall occurred in Longchuan County, Guangdong Province, yielding a cumulative rainfall of nearly 270 mm. The heavy rainfall triggered a large number of ...landslide disasters and formed three hardest-hit areas. In this paper, Mibei village, Beiling town, Longchuan County, is chosen as the research object; detailed field investigation data, satellite remote sensing images, rainfall monitoring data, and artificial rainfall physical model test results are integrated; the temporal and spatial distribution characteristics of rainfall-induced group-occurring landslides in the study area are obtained; and the rainfall instability mechanism of granite residual soil slopes is explained. Under the influence of continuous heavy rainfall from June 10 to 13, 2019, 327 landslides developed in Mibei village, Beiling town, and these landslides were mainly distributed in low mountainous areas, of which the sections at elevations from 300 ~ 400 m and slopes ranging from 35 ~ 45° were the most susceptible to landslide disasters. Continuous rainfall on June 10 and 11 was the controlling factor leading to these large number of landslides, with numerous landslides occurring from 20:00 on June 11 to 04:00 on June 13. These group-occurring landslides exhibited the characteristics of a considerable rainfall lag. The deformation and failure characteristics of the numerous observed landslides within the study area were highly similar, mainly involving traction sliding failure, and the sliding mass thickness ranged mostly from 1.5 ~ 3 m. The flow pattern characteristics of unconsolidated deposits after landslide instability were significant. According to the deformation and failure characteristics of landslides and the rainfall infiltration pattern, the development of landslides was divided into stages in this paper. Due to the difference between the rainfall intensity and permeability of granite residual soil, the main influence depth of heavy rainfall was limited to the superficial zone of slopes, which is the main reason why the shallow surface zone was damaged by landslides. Under the action of continuous heavy rainfall, a saturated seepage field was established in the shallow surface zone of slopes. Driven by gravitational potential energy, this led to an uneven distribution of the slope saturation zone. Attenuation of the mechanical strength of saturated soil reduced the slope stability, and sliding failure consequently occurred in the shallow surface saturation zone. In regard to excavated slopes, anti-sliding force reduction and free face formation enhanced the slope’s susceptibility to sliding failure under the influence of heavy rainfall, which is also the reason for the large-scale distribution of landslides along the X158 county road.
•Propose the experimental and particle flow numerical models for tunnel leakage.•Predict the settlement of sand layer and laws of water and sand loss.•Explore the distribution of seepage fields by ...the design of a seepage tracer device.•Discuss the migration and soil arching effect of sand particles from the fine scale.•Conduct the parametric analyses for different influencing factors of tunnel leakage.
Most of urban ground collapses and tunnel failures are caused by joint leakage of shield tunnel lining. This paper conducts a series of model tests and particle flow simulations aiming to investigate the geo-hazards and explore the associated failure mechanism due to tunnel leaking. Based on critical width of leaky joint, taking leaky joint location, overburden depth and height of overlying water level as influencing factors, the settlement of the sand layer and the law of the water and sand loss is effectively predicted. Then, the focus is on designing a seepage tracer device to explore the distribution of the seepage field and its flow line variation. Finally, the particle flow numerical model of tunnel-sand is employed for the soil arching effect and flow line changes during seepage erosion to discover the fine scale influences of sand particle migration and loss around the shield tunnel on the surrounding environment.
Limited mathematical analytical studies for tunnel leakage-induced surface and subsurface soil movements and tunnel responses incorporated the distribution of excess pore water pressure, in which the ...concrete lining was often assumed perfectly permeable or impermeable. This mechanical closed-form model will bring calculation errors and inconsistencies in engineering practice. This article introduces a new set of mathematical model for analyzing tunnelling-induced dissipation of excess pore water pressure and ground consolidation settlement considering long-term leakage influence through a semi-permeable lining, in which the soil-lining permeability ratio is used as the relative parameter to measure the influence of lining permeability on consolidation settlement. The interesting point is that the theoretical model conducts coupling with the Terzaghi-Rendulic consolidation theory through solving of the conformal mapping technique in complex variable theory and the separation variable method in classical mathematical physics equation. The accuracy of presented solutions is verified by comparisons with numerical simulation and in-situ measurements of engineering profiles and reasonable agreements are obtained. Furthermore, a sensitivity analysis is implemented on the subsurface consolidation settlement and the distribution of excess pore water pressure, and the results indicate that the soil-lining permeability and the soil Young's modulus notably affect the tunnel leakage-induced ground responses.
