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1.
Slopes composed of stratified and poorly cemented rocks that fail during heavy rainfalls are typical in the outer zone of Taiwan's Western Foothills. This study investigates how hydraulic conductivity anisotropy influences pore water pressure (PWP) distributed in stratified, poorly cemented rock slopes and related slope stability through numerical simulation. The notion of representing thin alternating beds of stratified, poorly cemented rocks as an equivalent anisotropic medium for ground‐water flow analysis in finite slopes was validated. PWP was then derived in a modelled slope comprising an anisotropic medium with suitable boundary conditions. Simulation results indicate the significance of the principal directions of hydraulic conductivity tensor and the anisotropic ratio on PWP estimation for anisotropic finite slopes. For a stratified, poorly cemented rock slope, estimating PWP utilizing a phreatic surface with isotropic and hydrostatic assumptions will yield incorrect results. Stability analysis results demonstrate that hydraulic conductivity anisotropy affects the slope safety factor and slip surface pattern. Consequently, steady‐state groundwater flow analysis is essential for stratified, poorly cemented rock slopes when evaluating PWP distribution and slope stability. This study highlights the importance of hydraulic conductivity anisotropy on the stability of a stratified, poorly cemented rock slope. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
2.
The literature contains limited information on variations in the factors of safety (FOS) of riverbank stability associated with river water level (RWL) fluctuations. This paper analyses a case study on the portion of the Red River flowing through Hanoi using the finite element method and extending the mechanics of saturated and unsaturated soils to understand how the riverbank’s FOS varies with RWL fluctuations. The results show that hydrostatic force is one of the key parameters influencing the FOS when the soil’s hydraulic conductivity is less than 10−6 m/s. However, the pore-water pressure and rate of RWL change are the key parameters influencing the FOS when the hydraulic conductivity is greater than 10−6 m/s. The study also indicates that a surcharge of 50 kPa or higher significantly weakens the riverbank stability and influences the FOS when the RWL rises. The construction of residential or other structures without taking special protection measures within 50 m of the lateral riverbank should be avoided for safety reasons. 相似文献
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4.
A parametric study is performed to investigate hydraulic effect of vegetation on shallow slope stability with different root architectures in an infinite slope. Calculated results show during the first one hour of rainfall (181 mm/day), the exponential root architecture has higher ability to maintain shallow slope stability than the parabolic one. Under light rainfall (i.e., 20 mm/day) for 24 h, hydraulic effect of vegetation is more important inside root zone than outside root zone, while it is the opposite for rainfall intensities of 181 and 394 mm/day over the same duration. Parabolic rooted slope is more sensitive to rainfall pattern than bare one. 相似文献
5.
Earthquakes can trigger slope instability, especially in the case of slopes with cracks. Studies of slope stability rarely account for the presence of cracks. In this study, the upper bound limit analysis technique and the pseudo-static method were used to examine the stability of homogeneous slopes with cracks subjected to seismic loading. A series of stability charts for slope inclinations of 2:1 (β = 63.4°), 1:1 (β = 45°), 2:3 (β = 33.7°), and 1:2 (β = 26.6°) (vertical to horizontal) and internal friction angles, φ, of 10°, 20°, 30°, and 40° are presented. These charts should be useful for readily determining the stability number (critical slope height), the critical crack depth, and the region affected by cracks for cracks of known depth but unknown location, cracks of known location but unspecified depth, and cracks of unspecified depth and location. 相似文献
6.
The subalpine to montane zones within the Critical Zone (CZ) of the Colorado Front Range, USA outside Pleistocene glaciation limits are characterized by the abundance of stratified and multilayered slope deposits exhibiting depths >1 m. Initial luminescence dating for the upper sediment layers in different profiles give last glacial ages ranging between 40 and 12 ka. A periglacial origin by solifluction is hypothesized for these slope deposits, which is corroborated by geomorphic and sedimentologic parameters. The stratified slope sediments have a strong influence on the physical and chemical properties as well as on soil forming processes in the CZ. Examples are provided for the sediment derived contribution of some elements and common clay minerals together and the great importance of slope sediments as barriers and pathways for the interflow that runs in sediment layers are shown. 相似文献
7.
在岩质边坡的稳定性计算分析中,各向异性岩体抗剪强度参数的合理取值直接决定了分析成果的可靠性。为充分考虑岩体各向异性对边坡工程的影响,本文基于H-B强度准则,利用边坡岩体质量分类体系CSMR替代RMR,对参数mb、s进行修正,并由此进一步计算得到各向异性边坡岩体的等效M-C强度参数。通过工程实例,计算比较了金沙江某水电站导流洞出口边坡在相同基岩条件、不同开挖设计方案下强度参数修正前后的边坡稳定安全系数。研究结果表明,岩体各向异性对边坡稳定性影响较大,未考虑岩体各向异性的岩体参数用于边坡稳定性计算时不能准确反映边坡的实际稳定性状态;而经过各向异性修正后,导流洞出口边坡两种设计方案下的整体稳定安全系数计算结果分别为1.11和1.70,与工程地质定性、半定量评价结果基本相符。通过本文提出的方法对边坡各向异性岩体参数进行修正,并在此基础上对边坡整体稳定性进行计算分析是可行的。 相似文献
8.
Residual shear strength is generally considered in the design of preventive measures for slopes consisting of preexisting shear surfaces of large-scale landslides. Recent research suggests that the preexisting shear surface of a reactivated landslide can regain strength with the passage of time, which might also be considered in designing the slope stability measures. In this study, three reactivated landslide soils were tested in a ring shear apparatus for the discontinued shear periods of 1, 3, 7, 15, and 30 days with the following main objectives: (i) to understand the strength recovery behavior of landslide soils in a residual state of shear after as long as 30 days of discontinued shear, (ii) to understand the comparative pattern of strength recovery in highly plastic and less plastic soils, and (iii) to understand the mechanism involved in strength recovery at a residual state of shear. The results indicate that recovered strength measured in the laboratory is hardly noticeable after a rest period of 3 days, but recovered strength is lost after a small shear displacement. This paper primarily focuses on the effect of strength recovery from residual strength on preexisting shear surface soils and the mechanisms behind it. 相似文献
9.
考虑强度各向异性的边坡稳定有限元分析 总被引：1，自引：0，他引：1
天然沉积的土层总是表现出一定程度的强度各向异性,但现有的边坡稳定有限元分析极少考虑各向异性的影响。对大型有限元软件ABAQUS进行二次开发,使其能够考虑土体黏聚力随大主应力方向的变化,动态更新增量迭代求解过程中边坡不同位置处的抗剪强度,进而提出具备安全系数自动搜索功能的各向异性边坡稳定分析方法。计算结果表明,均匀边坡的有限元解与极限分析上限解相差很小。如果采用土体固结方向的黏聚力并按各向同性评价缓坡的稳定性,可能严重高估安全系数,尤其是在黏聚力较高的情况下。与极限分析不同,建立的强度更新有限元模型能够分析成层边坡的稳定性。 相似文献
10.
During filling in 1992 of the Tongjiezi reservoir, in Southwest China, it was noticed that the dam body and the rock masses on the right side of the valley were uplifted up to 22.2 mm and 24.3 mm respectively. After reservoir filling in 1993, the uplift continued, but the rate decreased, and the measured maximum uplift increased from 22.2 mm to 27.5 mm in the dam body and from 24.3 mm to 28.9 mm in the rock masses from 1993 to 2004. Based on the geological features of the dam site and observed geomechanics data, a numerical method is used to evaluate the representative elementary volume (REV) and to identify the parameters related to the mechanical and hydraulic properties of the rock mass. Furthermore, a coupled hydro-mechanical model is presented to describe the uplift process. The simulated results agree well with those measured. In addition, the time-dependent deformation is studied in the laboratory and numerically. It is concluded that, with the specific hydrogeological conditions at the Tongjiezi dam site, hydro-mechanical coupling during and after the reservoir impoundment is the main factor contributing to the uplift, and the time-dependent deformation is due to the rheological behavior of rock masses under seepage pressure. 相似文献
11.
This study investigates the hydraulic conductivity field and the groundwater flow pattern as predicted by a calibrated steady state groundwater flow model for the Keta Strip, southeastern Ghana. The hydraulic conductivity field is an important parameter in evaluating aquifer properties in space, and in general basin-wide groundwater resources evaluation and management. This study finds that the general hydraulic conductivity of the unconsolidated unconfined aquifer system of the Keta Strip ranges between 2 m/d and 20 m/d, with an average of 15 m/d. The spatial variation in horizontal hydraulic conductivity appears to take the trend in the variations in the nature of the material in space. Calibrated groundwater recharge suggests that 6.9–34% of annual precipitation recharges the shallow aquifer system. This amount of recharge is significant and suggests high fortunes in terms of groundwater resources development for agriculture and industrial activities in the area. A spatial distribution of groundwater recharge from precipitation is presented in this study. The spatial pattern appears to take the form of the distribution in horizontal hydraulic conductivity, and suggests that the vertical hydraulic conductivity takes the same pattern of spatial variation as the horizontal hydraulic conductivity. This is consistent with observations in other areas. The resulting groundwater flow is dominated by local flow systems as the unconfined system is quite shallow. A general northeast – southwest flow pattern has been observed in the study area. 相似文献
12.
A field experiment is being carried out at the Diavik diamond mine in northern Canada to investigate the influence of unsaturated flow behavior on the quality of drainage from mine waste rock piles in a region of continuous permafrost. This paper is part of a series describing processes affecting the weathering of waste rock and transport of reaction products at this site; here the focus is on unsaturated water flow and its role in mass loading. Two 15 m-high instrumented test piles have been built on 60 m by 50 m collection systems, each consisting of lysimeters and a large impermeable high-density polyethylene (HDPE) liner. Collection lysimeters are installed nearby to investigate infiltration in the upper 2 m of the waste rock. Porosity, water retention curves, and hydraulic conductivity functions are estimated from field measurements and for samples ranging in size from 200 cm3 to 16 m3. Net infiltration in 2007 is estimated to have been 37% of the rainfall for mean annual rainfall conditions. Early-season infiltration freezes and is remobilized as the waste rock thaws. Wetting fronts migrate at rates of 0.2–0.4 m d−1 in response to common rainfall events and up to 5 m d−1 in response to intense rainfall. Pore water and non-reactive solutes travel at rates of <10−2 to 3 × 10−2 m d−1 in response to common rainfall events and up to 0.7 m d−1 in response to intense rainfall. Time-varying SO4 mass loading from the base of the test piles is dictated primarily by the flow behavior, rather than by changes in solute concentrations. 相似文献
13.
The stability of the slope around a flood discharge tunnel is influenced by the space topography, the geological structure, the seepage of the flood discharge tunnel, the rainfall and so on, which introduce complexity and uncertainty to the problem of slope engineering. For slope stability analysis at the outlet of a flood discharge tunnel affected by high interior hydraulic pressure, the inner water exosmosis (IWE) phenomenon will become obvious, the rock’s mechanical properties will be changed, and the seepage effects of the flood discharge tunnel should be focused on. In this paper, a complicated three-dimensional (3D) numerical simulation and safety assessment of the slope around the flood discharge tunnel at Yangqu hydropower station is implemented in FLAC3D, and 3D slide arcs of good shape are obtained. When calculating the safety coefficient of slopes, the Shear Strength Reduction Technique (SSRT) is adopted, and a factor of safety (FOS) is then found. It is found that the FOS of the natural slope is 1.43 in its original condition, and in this case, the slope is in a stable state. The safety factor of the slope is 1.30 after the slope excavation without considering IWE. Under the condition of normal seepage from inside the tunnel to the outside, the safety factor is 1.29. For investigating the influence of IWE on the slope stability, we design three types of scenarios – minimal seepage, normal seepage and serious seepage – for the fluid–solid coupling calculation. Under the serious seepage condition, the safety factor of the slope is 1.26, and it is in a critical failure state. It should be pointed out that uncertainties in input parameters are not researched in this paper. There is not big difference among safety factors under different scenarios mainly because the maximum of inner water head of the flood discharge tunnel is only about 80 m. It still can be found that seepage action has an effect on the stability of the whole slope from calculation results. The stress concentrated region (SCR) near the surrounding rock grows from inside to outside as the seepage intensity increases. The surrounding rock will experience more water pressure and seepage pressure, and, at the same time, the area of the plastic zone grows. Suitable treatments and suggestions are discussed to eliminate the adverse effects of IWE. The research results in this paper can provide a reference for construction, reinforcement and drainage design of the slope in similar hydropower slope engineering scenarios. 相似文献
14.
This study was aimed at evaluating the mechanical and pH-dependent leaching performance of a mixed contaminated soil treated with a mixture of Portland cement (CEMI) and pulverised fuel ash (PFA). It also sought to develop operating envelopes, which define the range(s) of operating variables that result in acceptable performance. A real site soil with low contaminant concentrations, spiked with 3000 mg/kg each of Cd, Cu, Pb, Ni and Zn, and 10,000 mg/kg of diesel, was treated with one part CEMI and four parts PFA (CEMI:PFA = 1:4) using different binder and water contents. The performance was assessed over time using unconfined compressive strength (UCS), hydraulic conductivity, acid neutralisation capacity (ANC) and pH-dependent leachability of contaminants. With binder dosages ranging from 5% to 20% and water contents ranging from 14% to 21% dry weight, the 28-day UCS was up to 500 kPa and hydraulic conductivity was around 10−8 m/s. With leachant pH extremes of 7.2 and 0.85, leachability of the contaminants was in the range: 0.02–3500 mg/kg for Cd, 0.35–1550 mg/kg for Cu, 0.03–92 mg/kg for Pb, 0.01–3300 mg/kg for Ni, 0.02–4010 mg/kg for Zn, and 7–4884 mg/kg for total petroleum hydrocarbons (TPHs), over time. Design charts were produced from the results of the study, which show the water and/or binder proportions that could be used to achieve relevant performance criteria. The charts would be useful for the scale-up and design of stabilisation/solidification (S/S) treatment of similar soil types impacted with the same types of contaminants. 相似文献
15.
层状岩质边坡遍布节理模型的三维稳定性分析 总被引：5，自引：1，他引：4
采用遍布节理模型（ubiquitous-joint模型）描述层状岩体的各向异性特征,并探讨ubiquitous-joint准则中安全系数的计算方法,利用FLAC3D分析层理倾角、倾向与边坡稳定性之间的关系,结果表明：（1）对于顺层边坡,当岩层倾向与坡面倾向的夹角 较小时,边坡的安全系数随层理倾角 的增大呈现先减小后增大再减小的趋势; 20°～30°时,安全系数得到最小值, 60°时安全系数得到最大值;不同破坏型式导致安全系数变化规律之间的差异;当 较大时,曲线从先减小后增大的趋势转变为不断增大的趋势;根据 的大小将顺层边坡分为两类：当 45°时,为严格顺层边坡;当45° 90°时,为斜向层状边坡。（2）对于逆层边坡,当 45°时,曲线呈现先增大再减小然后又增大的趋势,各曲线随 的变化程度基本相同;但减小过程中,随着 的增大,曲线的斜率逐渐减小,边坡稳定性的各向异性程度减小;当 45°时,曲线随 的增大呈现非线性单调递增的趋势。（3）安全系数与 之间的关系表明,对于顺层坡,随着 的增大,边坡安全系数逐渐增大;对于逆层坡,当 较小时( 150°),边坡安全系数随 的增大而逐渐减小;随着 的增大( 120°),边坡安全系数与 呈现递增关系。 相似文献
16.
This study presents the crustal shear wave velocity structure and radial anisotropy along two linear seismic arrays across the North China Craton (NCC) from ambient noise tomography. About a half to one year long ambient noise data from 87 stations were used for obtaining the inter-station surface wave empirical Green's functions (EGFs) from cross-correlation. Rayleigh and Love dispersion curves within the period band 5–30 s were measured from the EGFs of the vertical and transverse components, respectively. These dispersion data were then used to determine the crustal shear wave velocity structure (VSV and VSH) and radial anisotropy (2(VSH ? VSV) / (VSH + VSV)) from point-wise linear inversion with constraints from receiver function analysis. Our results reveal substantial structural variations among different parts of the NCC. The Bohai Bay Basin in the eastern NCC is underlain by a thin crust (~ 30 km) with relatively low velocities (particularly VSV) and large positive radial anisotropy in the middle to lower crust. Such a crustal structure is no longer of a cratonic type and may have resulted from the widespread tectonic extension and intensive magmatism in this region since late Mesozoic. Beneath the Ordos Basin in the western NCC, the crust is relatively thicker (≥ 40 km) and well stratified, and presents a large-scale low velocity zone in the middle to lower crust and overall weak radial anisotropy except for a localized lower crust anomaly. The overall structural features of this region resemble those of typical Precambrian shields, in agreement with the long-term stability of the region. The crustal structure under the Trans North China Orogen (TNCO, central NCC) is more complicated and characterized by smaller scale velocity variations, strong positive radial anisotropy in the middle crust and rapid change to weak-to-negative anisotropy in the lower crust. These features may reflect complex deformations and crust–mantle interactions, probably associated with tectonic extension and magmatic underplating during the Mesozoic to Cenozoic evolution of the region. Our structural images in combination with previous seismic, geological and geochemical observations suggest that the Phanerozoic lithospheric reactivation and destruction processes may have affected the crust (especially the middle and lower crust) of the eastern NCC, and the effect probably extended to the TNCO, but may have minor influence on the crust of the western part of the craton. 相似文献
17.
The physicochemical processes that affect acid mine drainage (AMD) in unsaturated waste rock piles and the capabilities of small-scale laboratory experiments to predict AMD from waste rock are not well understood. An integrated laboratory and field study to measure and compare low sulfide waste rock and drainage characteristics at various scales has been initiated. This paper describes the design, construction and instrumentation of three field-scale experimental waste rock piles (test piles), and six active zone lysimeters at the Diavik diamond mine in the Northwest Territories, Canada. The test piles are comprised of granitic and sulfide-bearing metasedimentary waste rock excavated during open pit mining operations. One test pile contains waste rock with a target S content of <0.04 wt.% S; the second test pile contains waste rock with a target S content of >0.08 wt.% S; and the third test pile contains the higher sulfide waste rock (>0.08 wt.% S) and was re-sloped and capped with a low permeability till layer and a low sulfide waste rock cover. The first two test piles are approximately 15 m high with bases of 50 m by 60 m, and the re-sloped test pile has a larger base of 80 m by 125 m. Instrumentation was selected to measure matrix flow, geochemistry of pore water and drainage, gas-phase O2 concentration, temperature evolution, microbiological populations, waste rock permeability to air, and thermal conductivity, as well as to resolve mass and flow balances. Instrument locations were selected to characterize coupled physicochemical processes at multiple scales and the evolution of those processes over time. Instruments were installed at a density such that the number of instruments that survived construction (40% to >80% by instrument type) was sufficient to allow adequate characterization of the physicochemical processes occurring at various scales in the test piles. 相似文献
18.
《Computers and Geotechnics》2006,33(6-7):294-304
When the slope geometry, unit weight and pore water pressure distribution in a homogeneous soil slope are given, the location of the critical slip surface for a particular method of slices is related only to the ratio of c′ (cohesion) and tan ϕ′ (internal friction angle). To utilize this relationship in back calculating c′ and ϕ′ values, two slope models with circular slip mechanism are presented to represent shear failures in simple fill or cut slopes and long natural slopes, and for each of the models, two dimensionless parameters regarding c′/tan ϕ′ and maximum depth of the critical slip surface are introduced. Based on the new findings from limit equilibrium analysis of slope models, charts are plotted to show the relationships of the two dimensionless parameters and ϕ′ values for a safety factor of unity. Using the charts can make a rapid estimate of the magnitude of both c′ and ϕ′ from a known position of the failure surface in a homogeneous slope. 相似文献
19.
In recent years, spatial variability modeling of soil parameters using random field theory has gained distinct importance in geotechnical analysis. In the present study, commercially available finite difference numerical code FLAC 5.0 is used for modeling the permeability parameter as spatially correlated log-normally distributed random variable and its influence on the steady state seepage flow and on the slope stability analysis are studied. Considering the case of a 5.0 m high cohesive–frictional soil slope of 30°, a range of coefficients of variation (CoV%) from 60 to 90% in the permeability values, and taking different values of correlation distance in the range of 0.5–15 m, parametric studies, using Monte Carlo simulations, are performed to study the following three aspects, i.e., (i) effect of stochastic soil permeability on the statistics of seepage flow in comparison to the analytic (Dupuit′s) solution available for the uniformly constant permeability property; (ii) strain and deformation pattern, and (iii) stability of the given slope assessed in terms of factor of safety (FS). The results obtained in this study are useful to understand the role of permeability variations in slope stability analysis under different slope conditions and material properties. 相似文献
20.
The Northern Till is a thick (>65 m) deformation till underlying some 7500 km2 of Southern Ontario, Canada including the Peterborough Drumlin Field. It was deposited below the Lake Ontario ice stream of the Laurentide Ice Sheet. The till rests on glaciotectonized aquifer sediments and consists of multiple beds of till up to 6 m thick. These are separated by boulder lags, sometimes in the form of striated pavements, with thin (<30 cm) interbeds of poorly sorted waterlaid sand. The composite till stratigraphy indicates ‘punctuated aggradation’ where the subglacial bed was built up incrementally by the repeated ‘immobilization’ of deforming overpressured till layers. Boulders and sands indicate pauses in subglacial aggradation marked by sluggish sheet flows of water that reworked the top of the underlying till. Interbeds are laterally extensive and correlated using downhole electrical conductivity, core recovery and natural gamma data. A 3-D finite element model (FEFLOW) using data from 200 cored and geophysically logged boreholes, and a large digital water well dataset of 3400 individual records shows that the till functions as a ‘leaky aquitard’ as a consequence of water flow through interbeds. It is proposed that interbeds played a similar role in the subglacial hydraulic system below the Laurentide Ice Sheet by allowing drainage of excess porewater pressures in deforming sediment and promoting deposition of till. This is in agreement with theoretical studies of deforming bed dynamics and observations at modern glaciers where porewater in the deforming layer is discharged into underlying aquifers. In this way, the presence of interbeds may be fundamental in retarding downglacier transport of deforming bed material thereby promoting the build-up of thick subglacial till successions. 相似文献