Stability Of Residual Soil Slopes Research Articles

Revealing the Effect of Typhoons on the Stability of Residual Soil Slope by Wind Tunnel Test

Typhoon-induced slope failure is one of the most important geological hazards in coastal areas. However, the specific influence of typhoons on the stability of residual soil slopes still remains an open issue. In this study, the Feiyunjiang catchment in Zhejiang Province of SE China was chosen as the study area, and a downscaling physical model of residual soil slopes in the region was used to carry out the wind tunnel test. Our aim was to answer the question, How does the vegetation on the slope and slope stability respond during a typhoon event? For this purpose, multiple aspects were monitored and observed under four different wind speeds (8.3 m/s, 10.3 m/s, 13.3 m/s, and 17 m/s), including vegetation damage on the slope, macrocracks on the slope surface, wind pressure, wind load, permeability coefficient of the soil layer, and slope stability. The results showed that the plants on the slope could restore to their original states when the wind speeds ranged from 8.3 m/s to 13.3 m/s, but were damaged to the point of toppling when the wind speed increased to 17 m/s. Meanwhile, evident cracks were observed on the ground under this condition, which caused a sharp increase in the soil permeability coefficient, from 1.06 × 10−5 m/s to 6.06 × 10−4 m/s. The monitored wind pressures were larger at the canopy than that at the trunk for most of the trees, and generally larger at the crown of the slope compared with the toe of the slope. Regarding the wind load to the slope ground, the total value increased significantly, from 35.4 N under a wind speed of 8.3 m/s to 166.5 N under a wind speed of 17 m/s. However, the wind load presented different vector directions at different sections of the slope. The quantitative assessment of slope stability considering the wind load effect revealed that the safety factor decreased by 0.123 and 0.1 under the natural state and saturated state, respectively, from no wind to a 17 m/s strong wind. Overall, the present results explained the mechanism of slope failure during typhoon events, which provided theoretical reference for revealing the characteristics of residual soil slope stability under typhoon conditions.

Behavior of Stabilizing Piles to Increase Stability of Residual Soil Slope

The use of one-row of piles for stabilization of an unstable slope has been employed for many years. However, when one-row of piles are not able to stabilize complex slopes then multiple rows of piles should be adopted. This paper presents the feasibility of using multiple rows of stabilizing minipiles to increase the residual soil slope stability. Consolidated undrained triaxial (CIU) tests were conducted on reconstituted saturated samples of residual soil to determine the shear strength behavior. The response of residual soil slope stabilized with minipiles was carried out using a simplified pile-slope analysis method. The influencing factors on the behavior of residual soil slope stabilized with multiple rows of stabilizing minipiles were investigated. A parametric study was performed for utilizing the use of multiple rows of stabilizing minipiles mainly includes the pile row number, pile row position and slope geometry. The computed stabilizing minipile response shows that the residual soil slope stability with one-row of stabilizing piles is different from that with multiple rows of stabilizing piles. The present study could provide useful insight into the use of multiple rows of minipiles to increase the stability of residual soil slope.

Role of Actual Evaporation on the Stability of Residual Soil Slope

Role of Actual Evaporation on the Stability of Residual Soil Slope

Influence of changes in extreme daily rainfall distribution on the stability of residual soil slopes

ABSTRACT Many landslides triggered by intense rainfall have occurred in mountainous areas in Thailand, causing major economic losses and infrastructure damage. Extreme daily rainfall is a significant trigger for hillslope instability. Increases in extreme daily rainfall intensity due to climate change may be one of the key factors responsible for the increased landslides. Thus, in this context, changes in the intensity of extreme daily rainfall in Chiang Mai Province in North Thailand and their effects on hillslope stability are analyzed. Extreme rainfall is modeled using a generalized extreme value distribution and estimated for various return periods. A numerical analysis of seepage and an infinite slope stability model are combined to understand the hillslope response under extreme rainfall conditions. The analysis period is divided into two periods of 34 years: 1952 to 1985 and 1986 to 2019. According to the analysis results, the distribution of extreme daily rainfall changes in terms of location. The average annual daily maximum rainfall increased by approximately 11.13%. The maximum decrease in the safety factor is approximately 4.5%; therefore, these changes in extreme daily rainfall should be considered in future landslide prevention policies.

Stability analysis and improvement evaluation on residual soil slope: building cracked and slope failure

A case study of the building and road utilities which was loading directly on the slope at IIUM, Kuantan campus was damaged due to slope failure and landslide. This research are conducted to investigate and analyze the soil properties and parameters which affected the stability of residual soil slope against failure by conducting a comprehensive laboratory testing and software analysis. The properties of soil are determined from several physical index tests and shear strength tests. Numerical simulation model from engineering software SLOPE/W were performed to show the stability analysis (Factor of Safety - FOS) of typical residual soil slope without reinforcement and new innovative design of slope with reinforcement. This paper presents two types of slope design which are single reinforcement load and combination reinforcement loads. Through this research it is proved that both single and combination reinforcement load can improve the soil properties and parameters of the residual soil slope. The new slope design successfully proved to produce positive results by achieving up to 82.49% of stability improvement (FOS) within the correct position of reinforcement load added at failure slip surface on the slope.

Effect of hysteresis on the stability of residual soil slope

Soil-water characteristic curve (SWCC) is an essential parameter in unsaturated soil mechanics. Matric suction in unsaturated residual soils changes with varying climatic conditions associated with cyclic drying-wetting conditions that result in hysteresis in the SWCC. The soil mechanical behaviour under wetting is crucial since numerous rainfall-induced slope failures occur during the wetting process. However, many slope stability analyses were carried out using drying SWCC. Consequently, the factor of safety (FoS) calculation may not represent the actual field condition. This paper presents the effect of hysteresis in SWCC on the stability of unsaturated residual soil slopes from Bukit Timah Granite in Singapore. The study focused on the analyses considering the differences in pore-water pressure and water content variations under drying and wetting conditions by performing numerical seepage and stability analyses. Each analysis was carried out on a slope subjected to dry and rainy periods under three different conditions: i) using only drying SWCC; ii) using only wetting SWCC; iii) using combined drying and wetting SWCCs. The results indicated that the FoS variations obtained from the numerical analyses incorporating combined SWCC matched more closely those obtained by incorporating only wetting SWCC than those obtained by incorporating only drying SWCC, regardless of the wetting or drying processes that the soil experienced. Moreover, the numerical analyses under high rainfall intensity by incorporating only wetting SWCC gave a more conservative FoS as compared to those obtained by incorporating combined SWCC. Numerical analyses incorporating only drying SWCC gave the most conservative FoS regardless of rainfall intensity.

Effect of drag force on stability of residual soil slopes under surface runoff

ABSTRACTTo investigate the effect of drag force on stability of residual soil slopes, a modified approach based on the limit equilibrium method is proposed by establishing a nonlinear coupled mathematical model to calculate the seepage velocities in soils and the runoff velocities at a fluid–solid interface. In this mathematical model, the Navier–Stokes equation and Brinkman-extended Darcy equation are used to describe the incompressible surface runoff and seepage in soils, respectively. Then, the drag force can be derived by adopting Newton's law of internal friction, and the factor of safety (FOS) of residual soil slopes considering drag force can be calculated based on the limit equilibrium method. The modified approach was applied to analyse the stability of rainfall-induced landslides in residual soils in Nanjiang, Sichuan, China, 2011. We found that the runoff depth can significantly control the FOS of the residual soil slopes and cause slope failures. The results of sensitivity analysis highlight the significance for considering drag force due to surface runoff when calculating the FOS of the residual soil slope. The FOS obtained from the modified approach is more reasonable, and this modified approach also can be used for evaluating or predicting rainfall-induced slope instability in residual soils.

Variability in unsaturated hydraulic properties of residual soil in Singapore

Residual soil covers most of the land in Singapore and is commonly found in unsaturated conditions due to the deep ground water table. Matric suction in residual soil plays an important role on the stability of residual soil slopes against rainfall. Matric suction in the soil will change due to infiltration during rainfall, and infiltration is mainly controlled by the unsaturated hydraulic properties (i.e., soil-water characteristic curve (SWCC) and hydraulic conductivity) of the residual soil. Variability in SWCC and hydraulic conductivity of residual soils in Singapore, such as Jurong Formation, Bukit Timah granite and Old Alluvium, were quantified and compared with the uncertainty of saturated soil properties. A new framework for the estimation of SWCC from the saturated hydraulic conductivity, ks, is proposed in this paper. The upper bound from the proposed framework is recommended for the infiltration analyses and the lower bound from the proposed framework is recommended for the slope stability analyses.

Finite-Element Simulation for Contribution of Matric Suction and Friction Angle to Stress Distribution during Pulling-Out Process

AbstractIn slope engineering, soils are ordinarily in an unsaturated state. Today the application of unsaturated soil mechanics theory to slope stability analysis has become an essential point in geotechnical engineering research. To explain the relationship between matric suction and soil structure with slope stability (via the pulling-out effect), reasonable finite-element (FE) modules can be created. By using FE analysis (which includes the existing soil parameters), the stability of residual soil slope can be simulated under different water contents (via changes in matric suction) and soil structures (via different Φ values). Inferring from the soil-water characteristic curve obtained from previous work, the influence of matric suction on unsaturated soil slope is determined. The importance of matric suction and soil structure is discovered during the root pulling-out analysis. The results show that because of increasing matric suction in unsaturated soil (which is the result of the decreasing degree ...

Performance of Horizontal Drains in Residual Soil Slopes

ABSTRACT In tropical and subtropical regions, shallow landslides often occur in residual soil slopes. Short-duration, high-intensity rainfall will increase the pore-water pressure. As a result, the shear strength of the soil in the slopes decreases and the stability of the slopes is affected. In this study, horizontal drains were installed in a residual soil slope in Singapore in order to improve the stability of the slope. The slope was instrumented with tensiometers and piezometers to investigate the effectiveness of the horizontal drains as a slope stabilization method against rainfall-induced slope failures. The variations in water table elevation and matric suction in the slope due to rainfall events were monitored. In addition, numerical analyses of the seepage into the slope brought about by the rainfall were carried out, and the results showed a reasonably good agreement with the data obtained from field measurements. The field measurement results indicated that horizontal drains were indeed effective for lowering the water table and for increasing the stability of the investigated slope. Therefore, horizontal drains are considered to be a useful and economical method for improving the stability of residual soil slopes against rainfall.

Stability Analysis and Stability Chart for Unsaturated Residual Soil Slope

In tropical residual soils most hill slope failures are caused by rainfall. It is therefore important to consider dynamic hydrological conditions when attempting to analyze the stability of residual soil slopes. This paper describes a coupled hydrology/stability model that has been developed to overcome the limitations of the standard method of analysis used to investigate stability of tropical soil slopes. A computational hydrology – limit equilibrium stability analysis model is outlined and examples are provided of the model output capabilities in terms of design charts. Although nowadays most realistic problem should be analyzed by computer and stability charts are mainly used to analyze simple slopes, they can be useful for preliminary analysis and enable the designer to quickly assess the sensitivity of a problem to changes in different input parameters.

Instrumentation of an Unsaturated Residual Soil Slope

Abstract The stability of slopes has become a major concern in areas that experience frequent periods of heavy rainfall such as the tropical areas of Southeast Asia. Previous research has indicated that rainfall has a detrimental effect on the stability of residual soil slopes. The reason for this is that the additional shear strength that exists in unsaturated soils due to negative pore-water pressures is lost as a result of rainwater infiltration into the soil. To study the infiltration characteristics in slopes, a residual soil slope in Singapore was instrumented. The instruments were used to determine the changes in the pore-water pressure distribution throughout the slope in response to evaporation and infiltration. Tensiometers were used to measure negative pore-water pressures, piezometers were used to measure the groundwater level, and a rain gage was used to measure rainfall intensities on the slope. An automated data acquisition system was used to collect the data from the slope. This paper describes the instrumentation program and the procedures associated with the installation of the instruments into the slope. Typical measurement data collected from the slope are presented, and their interpretations are discussed.