A vector sum analysis method for stability evolution of expansive soil slope considering shear zone damage softening

Slope stability analysis is a classical mechanical problem in geotechnical engineering and engineering geology.It is of great significance to study the stability evolution of expansive soil slopes for engineering construction in expansive soil areas.Most of the existing studies evaluate the slope stability by analyzing the limit equilibrium state of the slope,and the analysis method for the stability evolution considering the damage softening of the shear zone is lacking.In this study,the large deformation shear mechanical behavior of expansive soil was investigated by ring shear test.The damage softening characteristic of expansive soil in the shear zone was analyzed,and a shear damage model reflecting the damage softening behavior of expansive soil was derived based on the damage theory.Finally,by skillfully combining the vector sum method and the shear damage model,an analysis method for the stability evolution of the expansive soil slope considering the shear zone damage softening was proposed.The results show that the shear zone subjected to large displacement shear deformation exhibits an obvious damage softening phenomenon.The damage variable equation based on the logistic function can be well used to describe the shear damage characteristics of expansive soil,and the proposed shear damage model is in good agreement with the ring shear test results.The vector sum method considering the damage softening behavior of the shear zone can be well applied to analyze the stability evolution characteristics of the expansive soil slope.The stability factor of the expansive soil slope decreases with the increase of shear displacement,showing an obvious progressive failure behavior.

Study on Soil Erosion Model Under Different Slopes in Southwest Karst Mountain Area

The aim was to further research soil erosion characteristics and accurately predict soil erosion amount in karst areas. Based on field surveys and research achievements available, yellow soils, which are widely distributed, were chosen as test soil samples and slope, rain intensity, vegetation coverage and bare-rock ratio were taken as soil erosion factors. Artificial rain simulation instruments （needle-type） were made use of to simulate correlation of rain intensity, vegetation coverage, and bare-rock ratio with soil erosion quantity. Furthermore, multiple-factor linear regression analysis, stepwise regression analysis and multiple-factor non-linear regression analy- sis were made to establish a multiple-factor formula of soil erosion modulus with dif- ferent slopes and select regression models with high correlation coefficients. The re- sults show that a non-linear regression model reached extremely significant level or significant level （0.692〈FF〈0.988） and linear regression model achieved significant lev- el （0.523〈FF〈0.634）. The effects of erosion modulus changed from decreasing to in- creasing and the erosion factors from high to low were rain intensity, vegetation cov- erage and bare-rock ratio when slope gradient was at 6~, 16~, 26~ and 36~. The mod- el is of high accuracy for predicting gentle slope and abtupt slope, which reveals correlation of erosion modulus with erosion factors in karst areas.

Stability analysis of unsaturated soil slope during rainfall infiltration using coupled liquid-gas-solid three-phase model

Generally, most soil slope failures are induced by rainfall infiltration, a process that involves interactions between the liquid phase, gas phase,and solid skeleton in an unsaturated soil slope. In this study, a loosely coupled liquid-gas-solid three-phase model, linking two numerical codes,TOUGH2/EOS3, which is used for water-air two-phase flow analysis, and FLAC^(3D), which is used for mechanical analysis, was established. The model was validated through a documented water drainage experiment over a sandy column and a comparison of the results with measured data and simulated results from other researchers. The proposed model was used to investigate the features of water-air two-phase flow and stress fields in an unsaturated soil slope during rainfall infiltration. The slope stability analysis was then performed based on the simulated water-air two-phase seepage and stress fields on a given slip surface. The results show that the safety factor for the given slip surface decreases first, then increases, and later decreases until the rainfall stops. Subsequently, a sudden rise occurs. After that, the safety factor decreases continually and reaches its lowest value, and then increases slowly to a steady value. The lowest value does not occur when the rainfall stops, indicating a delayed effect of the safety factor. The variations of the safety factor for the given slip surface are therefore caused by a combination of pore-air pressure, matric suction, normal stress, and net normal stress.

Failure behavior of soil-rock mixture slopes based on centrifuge model test

The stability of soil-rock mixtures(SRMs) that widely distributed in slopes is of significant concern for slope safety evaluation and disaster prevention. The failure behavior of SRM slopes under surface loading conditions was investigated through a series of centrifuge model tests considering various volumetric gravel contents. The displacement field of the slope was determined with image-based displacement system to observe the deformation of the soil and the movement of the block during loading in the tests. The test results showed that the ultimate bearing capacity and the stiffness of SRM slopes increased evidently when the volumetric block content exceeded a threshold value. Moreover, there were more evident slips around the blocks in the SRM slope. The microscopic analysis of the block motion showed that the rotation of the blocks could aggravate the deformation localization to facilitate the development of the slip surface. The high correlation between the rotation of the key blocks and the slope failure indicated that the blocks became the dominant load-bearing medium that influenced the slope failure. The blocks in the sliding body formed a chain to bear the load and change the displacement distribution of the adjacent matrix sand through the block rotation.

Coupled hydro-mechanical analysis of slope under rainfall using modified elasto-plastic model for unsaturated soils

Two modifications for the basic Barcelona model(BBM) are present. One is the replacement of the net stress by the average skeleton stress in unsaturated soil modeling, and the other is the adoption of an expression for the load-collapse(LC) yield surface that can match flexibly the normal compression lines at different suctions. The predictions of the modified BBM for the controlled-suction triaxial test on the unsaturated compacted clay are presented and compared with the experimental results. A good agreement between the predicted and experimental results demonstrates the reasonability of the modified BBM. On this basis, the coupled processes of groundwater flow and soil deformation in a homogeneous soil slope under a long heavy rainfall are simulated with the proposed elasto-plastic model. The numerical results reveal that the failure of a slope under rainfall infiltration is due to both the reduction of soil suction and the significant rise in groundwater table. The evolution of the displacements is greatly related to the change of suction. The maximum collapse deformation happens near the surface of slope where infiltrated rainwater can quickly reach. The results may provide a helpful reference for hazard assessment and control of rainfall-induced landslides.

Effectiveness of Fiber Bragg Grating monitoring in the centrifugal model test of soil slope under rainfall conditions

Centrifugal model testsare playing an increasingly importantrolein investigating slope characteristics under rainfall conditions. However, conventional electronic transducers usually fail during centrifugal model tests because of the impacts of limitedtest space, high centrifugal force, and presence of water, with the result that limited valid data is obtained. In this study, Fiber Bragg Grating(FBG) sensing technology is employed in the design and development of displacement gauge, an anchor force gauge and an anti-slide pile moment gauge for use on centrifugal model slopes with and without a retaining structure. The two model slopes were installed and monitored at a centrifugal acceleration of 100 g. The test results show that the sensors developed succeed in capturing the deformation and retaining structure mechanical response of the model slopes during and after rainfall. The deformation curvefor the slope without retaining structure shows a steepresponse that turns gradualfor the slope with retaining structure. Importantly, for the slope with the retaining structure, results suggest that more attention be paid to increase of anchor force and antislide pile moment during rainfall. This study verifies the effectiveness of FBG sensing technology in centrifuge research and presents a new and innovative method for slope model testing under rainfall conditions.

Novel protection systems for the improvement in soil and water stability of expansive soil slopes

To improve the soil and water stability of expansive soil slopes and reduce the probability of slope failure,novel protection systems based on polymer waterproof coatings(PWC)were used in this study.Herein,three groups of expansive soil slope model tests were designed to investigate the effects of polyester nonwovens and PWC(P-PWC)composite protection system,three-dimensional vegetation network and PWC(T-PWC)composite protection system,and nonprotection on the soil and water behavior in the slopes under precipitation–evaporation cycles.The results showed that the moisture change of P-PWC and T-PWC composite protected slopes was significantly smaller than that of bare slope,which reduced the sensitivity of slope moisture to environmental changes and improved its stability.The soil temperature of the slope protected by the P-PWC and T-PWC systems at a depth of 70 cm increased by 5.6℃ and 2.7℃,respectively.Using PWC composite protection systems exhibited better thermal storage performance,which could increase the utilization of shallow geothermal resources.Moreover,the maximum average crack widths of the bare slopes were 7.89 and 3.17 times those of the P-PWC and TPWC protected slopes,respectively,and the maximum average crack depths were 6.87 and 3 times those of the P-PWC and T-PWC protected slopes,separately.The PPWC protection system weakened the influence of hydro–thermal coupling on the slopes,inhibited the development of cracks on the slopes,and reduced the soil erosion.The maximum soil erosion of slopes protected by P-PWC and T-PWC systems was 332 and 164 times lower than that of bare slope,respectively.The P-PWC and T-PWC protection systems achieved excellent"anti-seepage and moisture retention"and anti-erosion effects,thus improving the soil and water stability of slopes.These findings can provide important guiding reference for controlling rainwater infiltration and soil erosion in expansive soil slope projects.

STRUCTURAL DAMAGE MODEL OF UNSATURATED EXPANSIVE SOIL AND ITS APPLICATION IN MULTI-FIELD COUPLE ANALYSIS ON EXPANSIVE SOIL SLOPE

Focused on the sensitivity to climate change and the special mechanical characteristics of undisturbed expansive soil, an elasto-plastic damage constitutive model was proposed based on the mechanics of unsaturated soil and the mechanics of damage. Undisturbed expansive soil was considered as a compound of non-damaged part and damaged part. The behavior of the non-damaged part was described using non-linear constitutive model of unsaturated soil. The property of the damaged part was described using a damage evolution equation and two yield surfaces, i.e., loading yield （LY） and shear yield （SY）. Furthermore, a consolidation model for unsaturated undisturbed expansive soil was established and a FEM program named UESEPDC was designed. Numerical analysis on solid-liquid-gas tri-phases and multi-field couple problem was conducted for four stages and fields of stress, displacement, pore water pressure, pore air pressure, water content, suction, and the damage region as well as plastic region in an expansive soil slope were obtained.

Comparison of Slope Length Factor Extraction in Hillslope Soil Erosion Model with Different DEM Resolutions

In this study, non-cumulative slope length(NCSL) calculation method and spatial analytical calculation(SAC) method were respectively applied to extract slope length and slope length factor from 10 sample areas, which are located in Ansai County, north Shaanxi Province. The comparison of computation precision between variable DEM resolutions showed that NCSL was superior to SAC entirely. And the results were best when the DEM resolutions were 5 and 10 m. Besides, the results of slope length factor were nearly the same under the two conditions. So DEM of 10 m resolution can be used to extract slope length.

Determination of a Mathematical Model of Erosion Taking into Account the Intensity of Rainfall and Soil Slopes from the Global MNT Model

Our study is being carried out in the Wouri Estuary more precisely in the Nylon area, Douala. This area is influenced by abundant rainfall which promotes the phenomenon of rain erosion. This erosion contributes to the degradation of structures and soils. To better understand and predict this phenomenon of rainfall erosion, we set out to establish a mathematical model that takes into account precipitation and topography. To this end, the data collected in the field and in the laboratory made it possible. First, we graphically modeled the variation of the potential as a function of the intensity of rainfall and the slope of the ground. Next, we identified a mathematical model from cubic spline surface interpolation. Finally, we obtained the mathematical model which makes it possible to evaluate and predict the erosion potential. The results obtained allowed to have an erosion potential of 153.67 t/ha/year with field data and 153.94 t/ha/year with laboratory data. We compared the results obtained with those existing in the literature on the same study site. This comparison made it possible to validate the established mathematical model. This mathematical model is a decision support tool and can predict problems related to water, erosion and the environment.

Application of transparent soil model tests to study the soil-rock interfacial sliding mechanism

When transparent soil technology is used to study the displacement of a slope, the internal deformation of the slope can be visualized. We studied the sliding mechanism of the soil-rock slope by using transparent soil technology and considering the influence of the rock mass Barton joint roughness coefficient, angle of the soil mass, angle of the rock mass and soil thickness factors on slope stability. We obtained the deformation characteristics of the soil and rock slope with particle image velocimetry and the laser speckle technique. The test analysis shows that the slope sliding can be divided into three parts: displacements at the top, the middle, and the bottom of the slope; the decrease in the rock mass Barton joint roughness coefficient, and the increase in soil thickness, angles of the rock mass and soil mass lead to larger sliding displacements. Furthermore, we analyzed the different angles between the rock mass and soil thickness. The test result shows that the displacement of slope increases with larger angle of the rock mass. Conclusively, all these results can help to explain the soil-rock interfacial sliding mechanism.

Bearing capacity of foundation on slope determined by energy dissipation method and model experiments

To determine the ultimate bearing capacity of foundations on sloping ground surface in practice, energy dissipation method was used to formulate the beating capacity as programming problem, and full-scale model experiments were investigated to analyze the performance of the soil slopes loaded by a strip footing in laboratory. The soil failure is governed by a linear Mohr-Coulomb yield criterion, and soil deformation follows an associated flow rule. Based on the energy dissipation method of plastic mechanics, a multi-wedge translational failure mechanism was employed to obtain the three bearing capacity factors related to cohesion, equivalent surcharge load and the unit gravity for various slope inclination angles. Numerical results were compared with those of the published solutions using finite element method and those of model experiments. The bearing capacity factors were presented in the form of design charts for practical use in engineering. The results show that limit analysis solutions approximate to those of model tests, and that the energy dissipation method is effective to estimate bearing capacity of soil slope.

Simplified method for analyzing soil slope deformation under cyclic loading

Reasonable assessment of slope deformation under cyclic loading is of great significance for securing the safety of slopes. The observations of centrifuge model tests are analyzed on the slope deformation behavior under cyclic loading conditions. The potential slip surface is the key for slope failure and follows two rules:(i) the relative horizontal displacement along the potential slip surface is invariable at an elevation, and(ii) the soil along the slip surface exhibits the same degradation pattern. These rules are effective regardless of the location of the potential slip surface throughout the entire deformation process of a homogeneous slope, ranging from the initial deformation stage to the failure process and to the post-failure stage. A new, simplified method is proposed by deriving the displacement compatibility equation and unified degradation equation according to the fundamental rules. The method has few parameters that can be determined through traditional element tests. The predictions from the proposed method agree with the centrifuge test results with vertical loading and shaking table loading. This result confirms that the proposed method is effective in predicting the full deformation process of slopes under different cyclic loading conditions.

Critical Assessment of Slope Stability: A Case Study on the Toffo-Lalo Road Project

This article systematically delves into a comprehensive analysis of the latest and most advanced techniques for the assessment of slope stability. It particularly focuses on strategies aimed at enhancing slope stability in road construction. In addition to this analysis, the article presents an illustrative case study centered on the Toffo-Lalo Road Project. The core objective of this paper is to scrutinize the stability of large embankments in road construction, with a specific emphasis on the development and asphalt overlay of the Toffo-Lalo road. This scrutiny is conducted through the utilization of stability calculation software, GEOSTUDIO2018, specifically its SLOPE/W module. Within this framework, a detailed model of the cutbank located at KP1+750-2+250 was meticulously developed. This model takes into account the physical-mechanical characteristics of the soil at the site, as well as the topographic layout. Its attributes include a cohesion value of 11.3 Kpa, a density of 16.57 KN/m3, and a friction angle of 27˚. The modeling results, employing the Morgenstern-Price method—an approach renowned for its adherence to equilibrium conditions and provision of precise results—conclude that the safety coefficient (Fs = 1.429) prior to any reinforcement signifies a critical state of slope stability. To address this, the article explores the implementation of reinforcement techniques, particularly focusing on rigid inclusions like nailing and piles. The modeling exercises reveal a noteworthy enhancement in the safety coefficient (Fs) post-reinforcement. Furthermore, the article undertakes a parametric study to optimize the reinforcement strategies. This analysis highlights that anchoring at 0˚ downward relative to the horizontal plane and employing a pile angle of 90˚ represent the most favorable approaches. These measures yield safety coefficients of 3.60 and 2.34, respectively, indicating substantially improved slope stability.

三维土工网边坡防护水土保持能力研究

路基边坡防护工程可减轻降雨对坡面土体的侵蚀作用,为深入研究坡面防护材料水土保持能力的定量表征方法,通过室内人工降雨边坡侵蚀模型试验,分析不同降雨强度和不同三维土工网防护下路基边坡的降雨侵蚀规律,提出三维土工网水土保持能力的试验测定方法及相关系数计算公式。研究结果表明:三维土工网防护边坡泥沙流失干质量明显小于相同条件下不设防边坡泥沙流失干质量,土工网防护在减少边坡侵蚀量的同时,有利于边坡侵蚀进程的快速稳定,但土工网的水土保持能力随雨强增大急剧下降。泥沙流失速度随着降雨的持续而逐渐减小,后期趋于收敛稳定,侵蚀历程采用指数函数拟合具有较好的相关性。建议设防边坡的试验降雨时间不少于70 min,不设防的边坡试验降雨时间不小于100 min。水土保持能力系数随雨强的增大呈对数函数关系减小,雨强超过100 mm/h时水土保持能力系数实测值与对数函数拟合值差异较大,建议在测定材料水土保持能力系数时雨强取20~100 mm/h,可取50 mm/h作为标准试验雨强。泡面类三维土工网水土保持能力显著优于普通三维土工网,而双泡面的三维土工网优于单泡面三维土工网。试验条件下凹凸泡面三维土工网的水土保持能力系数主要分布在1.71~3.03,建议50 mm/h雨强三维土工网水土保持能力系数不应小于1.5。

稻草加筋土边坡稳定性模型试验

为了研究稻草加筋土边坡的稳定性及变形破坏特征,先后开展了稻草加筋土无侧限抗压强度试验与边坡稳定性模型试验.通过无侧限抗压强度试验得出,在土体中加入稻草,可有效抑制土体的变形,且当稻草加筋率为0.2%、筋材长度为25 mm,即最优加筋条件时,加筋土无侧限抗压强度最大,对试样变形的抑制效果最好.在此基础上,开展了最优加筋条件下的稻草加筋土边坡稳定性模型试验,试验结果表明,相较于素土边坡,稻草加筋可有效提高边坡极限承载力,减小竖向位移;素土边坡与加筋土边坡的水平位移变化趋势均可分为稳定、等速变形和加速变形(包括弱加速变形阶段与强加速变形阶段)三阶段演化,稻草的加筋作用在弱加速变形阶段发挥明显,能显著提高坡体抵抗变形能力;加筋土边坡完全破坏后产生的滑面深而广,且滑面周围小裂隙相对较多,整体性与稳定性均优于素土边坡.

黑土区坡耕地水土保持耕作措施对土壤理化性状的影响

为探寻黑土区坡耕地不同水土保持耕作措施对土壤理化性状的影响机理,开展了田间小区试验。设置横坡耕作(TP)、垄向区田(RF)、深松(SF)、横坡耕作+垄向区田(TP-R)、横坡耕作+深松(TP-S)、垄向区田+深松(RF-S)3种水土保持耕作措施及3种组合耕作措施,并以常规顺坡耕作(CK)为对照,分析了土壤孔隙度、土壤机械组成、水稳性土壤团聚体稳定性、土壤养分含量等指标,并采用TOPSIS模型对不同水土保持耕作措施进行了综合评价,筛选了土壤稳定性强且蓄水保肥效果良好的水土保持耕作措施。结果表明:在玉米的全生育期内,深松、垄向区田、横坡耕作均能提高土壤体积含水率。TP-S处理体积含水率最大,0~40 cm土层平均体积含水率较CK处理增加29.47%;RF-S处理平均孔隙度最大,TP-S处理次之,平均孔隙度较CK处理分别增大10.68%、9.25%;TP-S处理能够显著提高土壤稳定性,其中平均质量直径(MWD)、几何平均直径(GMD)和大团聚体含量(R0.25)较CK处理分别增加12.30%、19.57%、13.97%;TP-S处理能够改善土壤机械组成,TP-S处理粗砂粒、粉粒、黏粒含量较CK处理增加15.40%、26.89%、1.90%,细砂粒含量较CK处理降低31.56%;TP-S处理IN(无机态氮)、AP(有效磷)、AK(速效钾)含量最高,较CK处理IN、AP、AK含量分别增加42.81%~55.32%、39.69%~40.68%、20.41%~25.45%。由TOPSIS模型综合评价结果可知,TP-S处理贴合度最高,土壤结构更稳定,且蓄水保肥效果更好,为适宜该地区的水土保持耕作措施。

基于失稳模量理论的降雨条件下非饱和边坡流滑与滑移失稳机理研究

基于经典塑性理论,利用失稳模量(HIN)的概念建立了非饱和土的渗流稳定性准则;针对非饱和土边坡常出现的失稳形式(即有限滑移失稳和快速流动失稳),通过引入考虑基质吸力依赖性的弹塑性本构模型,给出了识别边坡不同失稳模式的HIN表达式;对于具有潜在液化能力的松散火山灰土给出了理论模型参数的标定方式;在此基础上,预测了火山灰土边坡出现的失稳模式以及相应的失稳含水率,通过与室内水槽试验结果对比验证了理论模型的正确性和合理性,结果显示,结合无限边坡模型与失稳模量理论可进一步推导出不同失稳模式下的边坡安全系数表达式,二者互为验证;最后,通过参数分析研究了各模型参数对边坡在不同边界条件下失稳模式的影响.研究结果可进一步明晰降雨条件下非饱和土边坡出现不同失稳模式的内在机理,以便为渗流边坡稳定性的评估与设计提供相应的指导.

RUSLE模型对黄土高原退耕植被恢复坡面土壤侵蚀的模拟效果分析

[目的]为了探究RUSLE模型对黄土高原退耕植被恢复坡面土壤侵蚀模拟的效果。[方法]基于陕北安塞区坊塌小流域内10个径流小区2016-2022年的降雨产流产沙监测资料,通过RUSLE模型中各因子在黄土高原的不同常用算法之间的变换组合,模拟144种因子组合下各退耕植被恢复坡面的土壤侵蚀量,采用纳什效率系数(NSE)和均方根误差(RMSE)评价模型模拟结果的有效性。[结果]利用RUSLE模型144种因子组合模拟的退耕植被恢复坡面土壤侵蚀量,NSE范围为-38.47~0.19,RMSE范围为1.92~12.65 t/(hm 2·a),模拟效果较差,所选各因子算法难以适应退耕植被恢复坡面上的土壤流失量的评估,还需要对RUSLE模型各因子进一步改进。运用RUSLE模型对黄土高原退耕植被恢复坡面土壤侵蚀模拟时,建议尽可能采用时间分辨率高的数据减小对R因子的计算误差,综合考虑土壤有机质含量、土壤粒径与团粒结构组成和容重等土壤理化性质对K因子的影响,以及植被覆盖度、植被高度、枯落物、生物结皮等对C因子的影响,充分考虑10°以上的坡度,细化其LS因子的算法。[结论]RUSLE模型无法很好地适用于黄土高原退耕植被恢复坡面土壤侵蚀的模拟。研究结果为土壤侵蚀模型的研发及RUSLE模型在黄土高原植被恢复坡面的应用提供一定参考依据。

Movement Properties of Pipe Flow Along Granite Slope of Three Gorges Area of Yangtze River in China

It is well known that, in most cases, soil water doesn't move in the form of laminar flow as described by Darcy law. Only when Reynolds number ( Re ) is no more than 10, does water movement follow Darcy law. A soil profile with 2 9 m long and 2 13 2 60 m deep was excavated on a lower slope located at Zigui County, Hubei Province, China. Field observation found that soil pipes were mainly distributed in the transient layer between horizon B with higher degree of granite weathering and horizon C with lower degree of granite weathering. At the foot of the slope, about 5 7 soil pipes per meter were observed along the vertical direction of the slope. The observed results, obtained by continuous observation of soil pipes and pipe flow processes at granite slope for many rainfall events, indicate that the relationship between velocity of pipe flow and hydraulic gradient along the pipe is parabolic rather than linear. Based on the investigated data of soil, landform, and land use etc., combined with observed data of pipe flow derived from many rainfall events, a pipe flow model was developed. For velocity V p, discharge Q p of pipe flow and radius r of soil pipe, great similarity was found between simulated and observed values. Particularly, the simulated length of soil pipes reflects the great difference among soil pipes as a result of its different position in the soil profile. The length values of 4 soil pipes were estimated to be 98 1%, 27 6%, 11 0% and 3 0% of the longest distance of the catchment, respectively. As a special case of water movement, soil pipe flow follows Darcy Weisbach law. Discharge of pipe flow is much greater than infiltration discharge in common. Only when the depth of groundwater is more than the diameter of soil pipe and water layer submerges soil pipes during rainfall, may pipe flow occur. Under these circumstances, discharge of pipe flow is directly proportional to the depth of groundwater.