Man-made Slopes Research Articles

Review of Quantifying Slope Stability and Assessing Landslide Susceptibility in Sabah, Malaysia

Landslides affect 3.7 million square kilometers of land and affect around 5% of the global population. In Malaysia, 21,000 locations are prone to landslides, with 16,000 in Peninsular Malaysia, 3,000 in Sabah, and 2,000 in Sarawak. Factors contributing to landslides include geological factors, weather conditions, slope steepness, vegetation, and human activities. Rainfall and geological conditions are significant external and internal causes. Landslides can be mitigated using various construction techniques, such as contagious bored pile, guniting, and rock anchoring. Rainfall and landslides are closely related, with rainfall affecting soil stability and causing slope failure. Prolonged rainfall can decrease slope stability due to increased water infiltration, leading to landslides. Analysis of slope stability is crucial in geotechnical engineering, assessing the stability of natural and man-made slopes. It involves assessing soil properties and identifying potential failure surfaces. Limit Equilibrium (LEM) and finite element (FE) methods are commonly used for slope stability assessments. LEM divides failure mass into slices, while FEM maintains global equilibrium until failure occurs. Both methods offer advantages, such as revealing working stress deformations with realistic soil compressibility data and tracking progressive failure to shear failure.

Mechanical and hydraulic characteristics of unvegetated or vegetated loess soils amended with xanthan gum

With the development of western and central China, the increasing construction of transportation infrastructures (e.g., roads, railways, etc.) has been producing a large number of man-made slopes in loess regions. Biopolymer as an eco-friendly stabilizing material, has a great potential to amend soils for the purpose of ground improvement and slope stabilization, with its application in vegetated soils particularly at the initial growing stage to support vegetation growth as well as offer reinforcement to unprotected soils being reported recently. In the current study, the contribution of xanthan gum (XG) to both mechanical and hydraulic behaviors of the unvegetated and vegetated loess soils subjected to climatic wetting–drying cycles under the impacts of degree of compaction and biopolymer content are explored, whilst the effectiveness of the two XG-based soil reinforcing methods (with and without vegetation) are compared. Results indicate that XG treatment improved the water-retention capacity of loess soils to an extent that even the degradation of water retention upon initial wetting–drying cycles could be mitigated particularly at higher degrees of compaction. The strengthened shear resistance of loess soils was observed, mainly attributed to the increased soil cohesion, whilst the friction angle remained almost constant. The unvegetated loess soils basically had an increased cohesion proportional to the XG content up to 1.00% of the dry soil mass, whilst the vegetated soils had the highest soil cohesion at a fixed XG content of 0.50% which corresponded to the mostly promoted vegetation growth. Although a dense soil structure inhibited the seed germination and growth of sprouts and roots, it contributed to the overall shear strength of the vegetated soils similar to its effect on the unvegetated soils. XG amendment outperformed planting vegetation at enhancing soil shear strength at a degree of compaction of 95% (comparable to those adopted for design of highway subgrade), whilst providing XG in combination with vegetation was able to result in a more sizable strength increment over the summation of gains in strength by utilizing XG and vegetation separately, suggesting the considerable potential of XG in assisting vegetated soils for ecological slope stabilization. The results obtained from the current research support the broader usage of biopolymers (either used alone or in combination with vegetation) as reliable geotechnical engineering materials in practical implementations.

Overview of watershed development and river sedimentation condition in Sorong, Papua, Indonesia

Sorong Regency is developed to be a special economic zone, for enhancing economic in the eastern part of Indonesia. Few studies or investigations, which are related to river sedimentation due to the development, are rarely available. In September 2023, we conducted field investigation to four watersheds in Sorong (Remu, Mariat, Klasaman, and Warsamson Watersheds), in which each of them has different services. The normal flow at the upstream of Remu River was not visually turbid, and the watershed was well conserved for drink water purposes. The Mariat River was visually turbid as the watershed was developed for transmigration and agriculture area, which is likely related to siltation at the downstream segment of the river and sedimentation in the irrigation facilities. The sand mining and washing activities in the Klasaman Watershed are likely related to the difference of visual turbidity of the upstream and downstream river flows relative to the mining site. We think that the erosion protection of manmade slopes are needed to reduce the amount of sediment entering the Warsamson River. Erosion and sedimentation monitoring efforts are crucial and urgent toward sustainable water resources development in Sorong, Papua, Indonesia.

New insights into the catastrophic slope failures at Sau Mau Ping: the role of antecedent rainfall pattern

Climate change is increasing the frequency and intensity of extreme rainfall events, which aggravate the threat to the safety of natural and man-made slopes. There is growing interest in the role of rainfall characteristics in these slope failures. Most of previous studies treated the rainfall individually or as cumulative value and used hypothetical rainfall temporal patterns with no association with actual physical failures. In this study, the two deadly landslides in Sau Mau Ping, Hong Kong, in June 1972 and August 1976, which caused 165 casualties, are revisited. An intriguing question that has long been overlooked is posed: why the slopes that withstood the 1972 rainfall failed in the 1976 rainfall, given that the rainfall intensity of the latter event was only half of the former? Based on an extensive review of the forensic reports and relevant studies on the failure events, numerical modeling is carried out by a combination of seepage analysis with stability analysis and unsaturated shear strength theory. Focus is placed on the geological and hydrological settings and the rainfall characteristics, particularly the temporal pattern of the antecedent and main rainfall, to look into the causes and mechanisms for these failures. Implications of the new findings for future research and practice are also highlighted.

Forensic Analysis of a Distressed Railroad Embankment

Land subsidence is becoming a prevalent worldwide occurrence, perhaps with a devastating impact on civilian lives. Moreover, natural and man-made slopes formed are susceptible to damage unless there is adequate stability. The bulk of the slope failures is due to intensive rains. Examination of slope stability due to massive rains is an important issue to inspect in the area with high precipitation. This study is aimed at exploring the effects of severe flooding on the stability of the slope. A 30 m long railroad embankment failure that happened on May 25, 2011, in the city of Ann Arbor, Michigan, is introduced. The collapse happened due to the rainy season that brought about ponding water against the embankment and sufficiently high-water pressures that brought about the instability of the railroad embankment. The back investigation is a much more dependable and predictable strategy to evaluate the shear parameters in situ. The back investigation of a slope is solved using the Resistance Envelope method wherein the embankment is divided through a certain number of slices. Forces on each slice are estimated and the potential failure surface is identified. The shear parameters are extracted employing the resistance envelope method for the actual failure plane and are verified with the initial condition. This study aims to find the impact of precipitation on slope stability using Geostudio 2012 software.

A Feasibility Study of Thermal Infrared Imaging for Monitoring Natural Terrain—A Case Study in Hong Kong

The use of infrared thermography (IRT) technique combining other remoting sensing techniques such as photogrammetry and unmanned aerial vehicle (UAV) platforms to perform geotechnical studies has been attempted by several previous researchers and encouraging results were obtained. However, studies using time-lapse IRT survey via a UAV equipped with a thermal camera are limited. Given the unique setting of Hong Kong, which has a high population living in largely hilly terrain with little natural flat land, steep man-made slopes and natural hillsides have caused significant geotechnical problems which pose hazards to life and facilities. This paper presents the adoption of a time-lapse IRT survey using a UAV in such challenging geotechnical conditions. Snapshot and time-lapse IRT studies of a selected site in Hong Kong, where landslides had occurred were carried out, and visual inspection, photogrammetry, and IRT techniques were also conducted. 3D terrain models of the selected sites were created by using data collected from the photogrammetry and single (snapshot) and continuous monitoring (time-lapse) infrared imaging methods applied in this study. The results have successfully identified various thermal infrared signatures attributed to the existence of moisture patches, seepage, cracks/discontinuities, vegetation, and man-made structures. Open cracks/discontinuities, moisture, vegetation, and rock surfaces with staining can be identified in snapshot thermal image, while the gradient of temperature decay plotted in ln(T) vs. ln(t) enables quantifiable identifications of the above materials via time-lapse thermography and analysis.

Grain-scale modeling of shear responses of dilative granular packings under stress path pertinent to rainfall-induced slope failures

Slope failures frequently occur under storm rainfall, for which the constant shear drained (CSD) stress path is more pertinent to the soil element underneath the slope surface. Soil mass in man-made slopes or other compacted slopes is often at medium-dense or even dense state. Evaluating the stability of such slopes entails a comprehensive understanding of the behavior of dilative granular packings under the CSD stress path. Here we use a robust grain-scale model to simulate responses of dilative granular packings along the CSD, constant-volume (CDCV), and conventional drained (CD) stress paths. We show that the behavior under the CSD stress path complies with the critical state theory at both macro- and micro-scale. When the second-order work becomes nonpositive, a substantial plastic strain starts to develop under the CSD loading, while a significant drop of shear strength happens along the CDCV stress path for medium-dense packing and along the CD stress path for dense packings. In these conditions, the second-order work vanishes at an almost identical stress ratio which marks the onset of strength reduction or large deformation, and such stress ratio is well correlated with the initial state parameter of the granular packing. Furthermore, we show that the CSD stress path drives an intensified fabric anisotropy and there exists a quantitative correlation between anisotropy parameters and mobilized shear strength.

Experimental study on the influence of embankment slope direction on near-surface thermal conditions in permafrost region, Qinghai-Tibet Plateau

Heterogeneous ground thermal conditions caused by slope orientation are significant in Qinghai-Tibet Plateau because of the high altitude and strong solar radiation. Variation in solar radiation may result in contrasting thermal and upper boundary conditions, causing engineering problems at infrastructure with sloped embankments. Quantitative research on conditions on different man-made slopes is insufficient in permafrost regions, and consequently, planning for long-term effects on linear infrastructure is challenging. Net radiation, heat flux, near-surface temperature, soil moisture content, were recorded for one whole year (2021) at a field platform with eight slopes. Slope orientation affected net radiation (Rn) and ground heat flux (G), resulting in different energy balances between slopes. The north facing slope had a lowest Rn (174 W m-2), while the south slope had a maximum (239.8 W m-2). The north slope had a negative annual heat flux (-0.7 W m-2), while a maximum positive flux (1.5 W m-2) was recorded on the southeast slope. The annual mean surface temperature (Ts) was highest on the south slope and lowest on the north slope. The maximum difference of ground temperatures (within 30 cm depth) (Tg), was close to differences in Ts of over 4 °C. The maximum difference in soil moisture content during the thawing season (May–October) was 11% between the W and E slopes. Due to the different ground temperatures and soil moisture conditions, the annual number of freeze-thaw cycles was variable, and the maximum freeze-thaw cycles were 106 times in south slope and the minimum were 18 times in west slope. Those different thermal conditions between different slope orientations were significant, and pertinent to planning and maintenance of infrastructure. The results provide accurate boundary conditions for modeling to support development of new infrastructure that have embankment slopes in any direction, and for ensuring the stability of existing structures on Qinghai-Tibet Plateau.

Pre and Post Earthquake Slope Stability Analysis Using Equivalent Linear Method – a Case Study of Jure Landslide

Slope stability analysis is one of the most important tools to determine the stability of both natural as well as man-made slopes. The main objective of this study is to compare safety factor of the Jure landslide before and after an earthquake occurrence using Geostudio QUAKE/W module. Three different positions of water table (top, middle and bottom of debris) were considered for the study. The safety factors of both deterministic and probabilistic case are determined. The Gorkha Earthquake's time history data were taken into consideration. Both the bedrock and debris are modeled using the equivalent linear approach for dynamic analysis. The findings indicate that the slope was on the verge of failing prior to the earthquake and is predicted to fail following the earthquake event that was taken into account.

Effect of initial failure geometry on the progress of a retrogressive seepage-induced landslide

Natural and man-made slopes can undergo a retrogressive landslide when subjected to seepage. Studying the mechanism of retrogressive landslides contributes greatly to the employment of effective mitigation approaches. A multi-stage limit equilibrium-based study was performed to explore how the geometry of initial failure affects the progress of a retrogressive, multiple-rotational landslide caused by seepage flow. Seepage-stability analyses were carried out on two silty sand slopes which were previously found to experience successive rotational failures upon raising the water table in centrifuge tests. Analyzed in prototype dimensions were the slope models with the height of 24 cm and inclinations of 45° (1V:1H) and 63.4° (2V:1H) tested at different centrifugal accelerations. According to the tests, the initial shallow failures were assumed to be circular initiating from the face and emerging from the toe of the slopes in the stability analyses. The impact of curvature and length of the initial failure surface (referred to as IFS) as well as the height of the scarp shaped at each failure episode were investigated. The results show that the landslide continues until the slope profile finds a stable curvature. For the landslides that occur in the 45° inclined slope, when the initial failure initiates at a higher elevation on the slope face, the landslide retrogresses further. In addition, with an increase in the length or curvature of IFS, the final retrogression distance decreases. Further, it was observed that the progress of landslides depends on the height of the scarp exposed at each failure episode.

Soil Detachment Rate of a Rainfall-Induced Landslide Soil

In recent decades, the number of rainfall-induced landslides has increased significantly in many parts of Malaysia, especially in the urbanized and hilly areas. The disturbance of hilly morphology as a result of human activities has increased the potential for erosion on man-made slopes, especially during extreme rainfall during rain events. Most hilly areas in Malaysia are covered by a thick layer of soil, which is known to have a significant impact on soil erosion. However, little is known about how soil erosion and rainfall could be the driving force behind landslide initiation, especially on stabilized slopes. Therefore, this study focuses on the soil detachment rate of landslides triggered by rainfall at different rainfall intensities. A sandbox model is used to represent real slope conditions. The relationship between the soil detachment capacity, soil properties (water content, slope, clay layers and soil compaction), hydraulic parameters (flow shear stress and stream power) and rainfall intensities (low, medium and high) was investigated. The results showed that the hydraulic parameters and the rainfall intensity are directly proportional to the detachment rate of the soil. Water content and slope show a higher soil detachment rate and a lower critical flow shear stress than other soil properties. It can be concluded that high saturation and steep slope increase the risk of soil erosion because the cohesion and friction of the soil are significantly reduced, leading to a weakening of the soil structure at the surface. The results of this study can feed into the existing analysis of slope stability and formulate the onset of a landslide triggered by rainfall, especially in eroded soils.

Vegetation management and monitoring on man-made slopes

Vegetation management and monitoring on man-made slopes

Parametric Design and Field Behavior of Earthen Structures

The stability of earthen structures is governed by field uncertainties arising from material properties, environment loading, and slope geometry. This research devised a systematic approach to capture the effects of field uncertainties on the stability of natural and manmade slopes. New design charts were developed by incrementally changing slope geometry and randomly generating shear strength parameters. Subset simulation was used to determine the safe range of soil properties for various slopes. The charts were applied to three published case studies with distinct triggering mechanisms resulting from complex field settings. All of the investigated slopes were found to be stable (factor of safety (FOS) > 1.0) under the reported geometry and shear strength parameters while assuming no water table. The effects of soil properties’ variation and environmental conditions on fluctuating water table were captured through history matching. Results indicated three distinct failure mechanisms: foundation settlement of a glacial moraine till (Vernon, British Columbia) due to an increased pore water pressure during construction of the compacted fill (FOS = 1.45 without berms and 2.24 with berms); instability in the natural cut (FOS = 0.98) comprising layered glacio-lacustrine clays (Labret, Saskatchewan) due to saturation of the entire slope resulting from a long duration rainfall; and collapse of a compacted fill (FOS = 0.98) on a glacial moraine till (Hamelin Creek, Alberta) due to soil saturation arising from thawing of a frozen layer in the slope. This validation illustrates that the new approach fully captures environmental loading (resulting in water table variation in the slope) and partly captures construction practice and site geology via soil properties.

Mitigation Strategy for Low-frequency Large-magnitude Debris Flows in Hong Kong

Potential hazards arising from low-frequency large-magnitude debris flows have become apparent under the adverse impact of climate change and extreme weather. Hong Kong has systematically managed landslide risks arising from man-made slopes and natural hillsides since 1977, owing to its unique geographic location, steep terrain, deep weathering profile and post-war rapid urban development. In recent years, evaluation of potential hazards arising from low-frequency large-magnitude debris flows and their possible dire consequences has developed into a key part of the landslide mitigation effort in Hong Kong in light of the occurrence of more frequent and more severe extreme rainfall events. Valuable experience is gained in identifying potential low-frequency large-magnitude debris flow hazards, assessing their potential impacts to the public located at the densely populated foothills and developing a holistic strategy to mitigate against potentially catastrophic consequences. This paper sets out the mitigation strategy for mitigating low-frequency large-magnitude debris flows in Hong Kong and gives a case study to demonstrate the approach.

Slope Stability Analysis for the Phosphogypsum Stockpiles: A Case Study for the Sustainable Management of the Phosphogypsum Stacks in Aqaba Jordan

The process of making phosphates fertilizer involves taking the soft rock phosphate and mixing it with sulphuric acid. This process creates a gypsum by-product (phosphogypsum). Although gypsum is a widely used material in the construction industry, most of the produced phosphogypsum is not processed around the world and is stacked into large piles over the land, especially near coastal areas, which raised concerns about their stability. Such a disposal scheme creates man-made slopes in the surrounding areas which are prone to failure, which represents a common challenge for engineers. A slope failure will lead to a significant risk not only to human lives and activities but to the topographic and geological location of the stacks. In this paper, the geotechnical properties of the phosphogypsum in Aqaba, Jordan are determined and embankment stability analysis is carried out, as the purpose of this study is to evaluate the phosphogypsum stockpiles’ stability, and therefore, avoid any possible environmental disasters. Limit equilibrium methods and finite element methods were utilized in the analysis of this study. The required topographic and geological characteristics were obtained during the site visits and the contour plot of each phosphogypsum pile was produced by the Jordan Phosphate Mines Company (JPMC). Several laboratory tests were conducted to estimate the geotechnical properties of the stacked material due to the limited information on the Jordanian Phosphogypsum characteristics. Based on the results of this study, the above-ground slopes for the stacking of Phosphogypsum in Aqaba were found to be stable under both static and earthquake loading. Therefore, this study proved that the disposal process of the current stockpiles in Aqaba is sustainably managed for providing stable stockpiles and that the process has a generally low environmental risk.

Intelligent Control of Groundwater in Slopes with Deep Reinforcement Learning.

The occurrence of landslides has been increasing in recent years due to intense and prolonged rainfall events. Lowering the groundwater in natural and man-made slopes can help to mitigate the hazards. Subsurface drainage systems equipped with pumps have traditionally been regarded as a temporary remedy for lowering the groundwater in geosystems, whereas long-term usage of pumping-based techniques is uncommon due to the associated high operational costs in labor and energy. This study investigates the intelligent control of groundwater in slopes enabled by deep reinforcement learning (DRL), a subfield of machine learning for automated decision-making. The purpose is to develop an autonomous geosystem that can minimize the operating cost and enhance the system's safety without introducing human errors and interventions. To prove the concept, a seepage analysis model was implemented using a partial differential equation solver, FEniCS, to simulate the geosystem (i.e., a slope equipped with a pump and subjected to rainfall events). A Deep Q-Network (i.e., a DRL learning agent) was trained to learn the optimal control policy for regulating the pump's flow rate. The objective is to enable intermittent control of the pump's flow rate (i.e., 0%, 25%, 50%, 75%, and 100% of the pumping capacity) to keep the groundwater close to the target level during rainfall events and consequently help to prevent slope failure. A comparison of the results with traditional proportional-integral-derivative-controlled and uncontrolled water tables showed that the geosystem integrated with DRL can dynamically adapt its response to diverse weather events by adjusting the pump's flow rate and improve the adopted control policy by gaining more experience over time. In addition, it was observed that the DRL control helped to mitigate slope failure during rainfall events.

Mechanical properties of Bermuda grass roots towards sandy and clay soil for slope reinforcement

Natural and man-made slope failure has been a phenomenon that has caused many deaths, destruction, and environmental damage. The use of bioengineering technique (grasses) has been widely approached for slope remediation work. However, slope failure still occurs even though it has been protected by a few grasses. Many previous findings have reported on root pull out and root tensile strength for different plant species. However, the type of soil was not taken into account. Therefore, this research was carried out to investigate the function of root mechanical properties in different types of soil. The dry and wet sieve analysis tests were performed to know the classification of the soil. In addition to that, the soil mineralogy test was also conducted to support the soil classification. Root tensile strength tests were carried out on well-grown and poorly-grown Bermuda grass toward sandy and clay soil in dry and wet conditions. The dry condition is considered the condition of Bermuda grass in hot weather, while the wet condition is the condition after the raining season. Bermuda grass was chosen since this type of grass is widely applied for slope stabilization. The site locations were chosen in Temerloh, Maran which consist of clay soil. The other locations chosen were Karak, Gambang, Kuantan, Dengkil, Batang Kali, Ulu Yam, Kuala Pilah, Gombak and Sabak Bernam consist of sandy soil. The results show that the single root of Bermuda grass has higher tensile strength in sandy soil with range values from 0.47 to 185 Mpa compared to clay soil with range values from 0.12 to 159.10 Mpa. In conclusion, the results indicate that soil is one of the factors that influence the growth of bioengineering techniques for slope reinforcement.

Development of a monitoring and warning system based on optical fiber sensing technology for masonry retaining walls and trees

Hong Kong has a long history of applying masonry retaining walls to provide horizontal platforms and stabilize man-made slopes. Due to the sub-tropical climate, some masonry retaining walls are colonized by trees. Extreme weather, such as typhoons and heavy rains, may cause rupture or root failure of those trees, thus resulting in instability of the retaining walls. A monitoring and warning system for the movement of masonry retaining walls and sway of trees has been designed with the application of fiber Bragg grating (FBG) sensing technology. The monitoring system is also equipped with a solar power system and 4G data transmission devices. The key functions of the proposed monitoring system include remote sensing and data access, early warning, and real-time data visualization. The setups and working principles of the monitoring systems and related transducers are introduced. The feasibility, accuracy, serviceability and reliability of this monitoring system have been checked by in-site calibration tests and four-month monitoring. Besides, a two-level interface has been developed for data visualization. The monitoring results show that the monitored masonry retaining wall had a reversible movement up to 2.5 mm during the monitoring period. Besides, it is found that the locations of the maximum strain on trees depend on the crown spread of trees.

Analytical solution for coupled hydro-mechanical modeling of infiltration in unsaturated soils

Simulating water infiltration in unsaturated soils is an important step in analyzing a wide range of engineering and geosciences applications. The infiltration problem inherently possesses a coupled hydro-mechanical problem in which the unsaturated flow and the soil deformation interact and affect each other. This hydro-mechanical coupling, however, has been ignored in the majority of existing analytical solutions, mainly due to the complexity associated with the mathematical derivation. This paper presents a novel analytical solution for coupled hydro-mechanical modeling of one-dimensional (vertical) infiltration in unsaturated soils. We present an analytical solution for two problems where infiltration is applied at the top boundary as a constant pressure head (first problem) or as a constant flow rate (second problem). A parametric study was performed to examine the effects of hydro-mechanical coupling and various soil parameters on pressure head and strain profiles versus depth. Results reveal that the coupling effect can be pronounced for various values of saturated hydraulic conductivity, Gardner’s α parameter, and Young’s Modulus. The solution can be readily incorporated into site-specific (e.g., groundwater modeling, slope stability) or regional-scale (e.g., landslide mapping) analyses of unsaturated natural and man-made slopes and earthen structures subject to infiltration. Further, the presented analytical framework offers a benchmark for the validation of numerical methods.

Numerical Studies on Stability of Sand Slopes

Stability analysis of slopes is generally performed to assess the safe design of man-made or natural slopes. Choice of analysis depends on both site conditions and the probable mode of failure with consideration being given to the varying strengths and limitations involved in each method. Numerical techniques provide an approximate solution to field problems which otherwise cannot be solved by conventional methods due to complex geometry, anisotropic material, non-linear behavior, and in-situ stresses. Present study presents results of stability of unreinforced and reinforced model slopes using GEOSTUDIO 2020 and stability calculations were performed using SLOPE/W module and factor of safety of slopes with and without reinforcement is computed by considering various methods. Soil is modeled as a Mohr-Coulomb material in the analysis. The soil properties obtained from laboratory investigation was given as input parameters and analysis was carried out for different types of model slopes. The results from analysis are presented and discussed in detail.