Failure Of Soil Mass Research Articles

Photogrammetric Technique-Based Quantitative Measuring of Gravity Erosion on Steep Slopes in Laboratory: Accuracy and Application

Quantitative measuring of gravity erosion contributes to a better understanding of soil-mass failure occurrence and prediction. However, the measurement of gravity erosion requires the continuous monitoring of the objective terrain, due to its occurrence, usually within seconds, and combination with hydraulic erosion. The photogrammetric technique can quickly obtain terrain data and provide a new method for measuring gravity erosion. Based on a continuous high-overlapping image-acquisition equipment, a Structure-from-Motion-Multi-View-Stereo (SfM-MVS)-integrated workflow, and volume calculation, a new working methodology was established for measuring gravity erosion on steep granitic slopes in the laboratory. The results showed a good match between the digital point clouds derived from SfM-MVS-integrated workflow and terrestrial laser scanning (TLS), achieving millimeter-scale accuracy. The mean distance between the point clouds derived from TLS and SfM-MVS was 1.13 mm, with a standard deviation of 0.93 mm. The relative errors among the volumes calculated by SfM-MVS and TLS or the conventional oven-drying method were all within 10%, with a maximum error of 9.3% and a minimum error of 0.2%. A total of 213 gravitational erosion events were measured in the laboratory by using the SfM-MVS method, further confirming its feasibility.

Investigation of rocking mechanism of shallow foundations on sand via PIV technique

AbstractAdoption of the rocking isolation concept in foundation design is considered as an effective method in reducing seismic loads of structures. Despite much research conducted on the rocking behavior of foundations, concerns regarding the practical application of the rocking foundation design concept still prevail. The concerns primary stem from the lack of accurate understanding and knowledge associated with the soil‐foundation deformation mechanisms during rocking motions. Determination of deformation mechanisms and soil mass failure modes during foundation rocking helps to gain insight into the rocking behavior, recognize influential factors on foundation settlement or uplift, and propose appropriate improvement strategies to control foundation deformations. The primary objective of this study is to investigate the deformation behavior and failure modes of the soil mass beneath a rocking foundation with various initial static vertical factors of safety (F.S.v) and embedment depths. To this end, a series of reduced‐scale slow‐cyclic tests under 1g condition have been conducted using a single degree of freedom (SDOF) model. To determine soil deformation mechanisms, soil displacement fields have been measured using Particle Image Velocimetry (PIV) technique. Soil deformation mechanisms during loading and unloading paths, as well as causes leading to the foundation settlement or uplift have been evaluated and discussed. Additionally, changes in the effective soil‐foundation contact area in different loading cycles have been examined based on the PIV results. Based on the results, soil deformation mechanisms in the loading portions include soil densification, wedge deformation and scoop deformation. As the footing embedment depth increases, wedge deformation mechanism becomes limited, while scoop deformation mechanism becomes stronger. Additionally, as the foundation F.S.v increases, the depth of influenced zone of the rocking foundation decreases and the soil displacement occurs to a more limited depth.

Structure Degradation Induced by Wetting and Drying Cycles for the Hilly Granitic Soils in Collapsing Gully Erosion Areas

The hydrological and mechanical properties of granitic residual soils can be significantly altered by periodical wetting and drying (W-D) cycles. The soil structure degradation induced by W-D cycles can lead to soil mass failure and collapsing gully erosion in granitic hilly slopes in south China. However, limited attempts have been made at a comprehensive investigation of the effects of W-D cycles on the structure degradation of granitic residual soils, especially at the pedon scale. The purpose of this paper is to investigate the structural degradation of granite soils induced by W-D cycles and explore its potential influence on the development of collapsing gully erosion. The granitic soil properties, including hydraulic properties, shear strength, and disintegration characteristics, were performed after W-D cycles. The results indicated that the W-D cycles altered the soil pore structure, leading to variations in soil hydraulic properties. Specifically, with increasing alternate W-D cycles, the initial saturated water content and residual water content decreased, while the saturated hydraulic conductivity increased. Meanwhile, increasing W-D cycles contributed significantly to variations in cohesion and internal friction strength by decreasing the shear strength variables, especially the soil cohesion strength. Correspondingly, soil disintegration was increased during W-D cycles. Furthermore, most degradation of soil structure was recorded within the first two cycles of W-D. The obtained results indicate that the W-D cycles weaken soil structure, increase rainwater infiltration, decrease soil shear strength and disintegration resistance, and accelerate soil erosion. A vicious cycle of granitic slope failure induced by W-D cycles is eventually formed. This study provides useful information about the mechanism of soil mass failure and collapsing gully erosion in granitic hilly slopes.

Determining trigger factors of soil mass failure in a hollow: A study based in the Sichuan Province, China

Soil mass failure disasters are among the most destructive disasters in mountainous areas worldwide, and they continue to receive significant attention in the literature. However, factors that influence soil mass failure in hollows have not been explored via experimental approaches. In this study, we conducted a series of indoor hollow–flume experiments to exhibit how the three factors, namely, initial moisture content, slope angle, and clay content, influence the collapse of soil mass under surface runoff conditions. Our findings revealed that the major processes causing soil mass failure were internal seepage erosion resulting from subsurface runoff, migration of fine particles, development of tension cracks, increase in pore water pressure, and decrease in cohesion. Fluctuations in pore water pressure were characterized by two main trends: (1) an abrupt rise under static liquefaction and (2) a decrease before failure due to dilatancy. The time required for soil mass failure first decreased and then increased with the increase in moisture content. The soil mass with an initial moisture content of ∼12.5% was more critical to the failure. In addition, the time required for soil mass failure decreased with increasing slope angle, revealing a slope angle of 40° to be more prone to failure. The buildup of pore water pressure was found to increase with clay content; soil with a clay content of ∼7.5% required the shortest amount of time to initiate slides. Thus, our results provide a thorough insight into the processes and factors involved in the initiation and development of soil mass failure in hollow areas, which can be used by public agencies to improve monitoring, early warning, and forecasting systems. Notably, our study can help identify risk-prone source areas, and sensors can be installed to monitor potential mass failure locations.

Estimation of Critical Safety Thickness of the Base against Confined Water Inrush for a Rectangular Foundation Pit

Affected by confined aquifer, basal inrush accidents caused by excavation are common in foundation pits, and accurate estimation of the safety thickness of the base is a big concern of engineers. In this paper, a three‐dimensional failure mechanism of base inrush was constructed for a rectangular foundation pit. In this mechanism, the strength of the soil mass was assumed to be nonhomogeneous along the depth, and the soil‐mass failure satisfied the linear and nonlinear Mohr–Coulomb strength criteria. Then, based on the limit equilibrium theory, the prediction method for the safety thickness of the base against confined water inrush was deduced, and a comparison with existing research works was conducted. Furthermore, the influence laws of soil strength parameters, pit design parameters, and confined water pressure on the critical safety thickness were analyzed. The results show that the critical safety thickness of the base is positively correlated with nonlinear coefficient and confined water pressure but negatively correlated with cohesion, internal friction angle, nonhomogeneity coefficient, and unit weight. The soil strength is a key factor affecting the base safety thickness, which should be paid enough attention to in engineering design and construction. The research findings in this paper can provide a theoretical reference for the prevention and control of basal inrush accidents in confined water strata.

Variations of soil hydraulic properties along granitic slopes in Benggang erosion areas

As soil hydraulic characteristics, including near-saturated hydraulic conductivity and water retention, influence slope stability and erosion development, this study aimed at the spatial distribution patterns of hydraulic properties along the Benggang slopes for a better understanding of the development mechanisms of Benggang erosion in southern China. Near-saturated hydraulic conductivity and soil water retention at different slope positions in two typical Benggang erosional areas were determined by the in situ infiltration test using tension disk infiltrometer and laboratory test using the high-speed freezing centrifuge method. The soil hydraulic conductivity, effective macropore, and pore size parameter, Gardner α, in lower slopes were greater than those in upper and middle slopes. From upper to lower slope, the total water flow showed an increasing trend in pores > 1 mm in diameter, in contrast to a decrease in pores between > 0.33 mm and < 0.5 mm in diameter, and < 0.33 mm in diameter. The effective macroporosity values in measured soils were statistically greater (p < 0.05) in the lower slope than in the upper or middle slope. Meanwhile, the soil water retention of lower slopes was lower than that of upper and middle slopes, and the lower slope had higher unsaturated hydraulic conductivity than the upper or middle slope. Erosion degree showed significant (p < 0.05, p = 0.016) influence on the soil hydraulic conductivity and effective macropore. Moreover, the soils on the severe erosion slope drain faster than that on the slight erosion slope, and the unsaturated hydraulic conductivity decreased faster on the severe erosion slope than on the slight erosion slope. Vertical differentiation of granitic soil properties is the main factor influencing the soil hydraulic properties of the two slopes with a different erosion degree, while the macropores are the main factor influencing the soil hydraulic properties in different slope positions. Spatial variation may affect the rainwater infiltration during rainfall and soil water redistribution after the rainfall and finally affect the soil mass failure of the collapsing wall.

Influence of stress history, strain rate and end effects on undrained shear behaviour and strain localization of laterite soil

ABSTRACT Recognizing the abundant use of lateritic soils in the construction of embankments and their susceptibility towards extreme erosion, it is necessary to explore the influence of stress history and strain rate on their undrained shear behaviour. The mechanism of development of localized deformation and failure of soil mass are equally important for understanding the stability of laterite soils. Moreover, the use of porous stones in conventional triaxial testing for drainage to investigate the undrained shear behaviour of soils leads to the development of shear stresses near the ends and thereby influences the mechanical response of the soil. In the current research, the effect of stress history, strain rate and boundary effects on the shear strength behaviour and strain localization patterns of naturally available laterite soil is explored. The effect of end boundaries on the initiation and propagation of localized deformations of soil have been also evaluated in this study.

Granite residual soil properties in collapsing gullies of south China: spatial variations and effects on collapsing gully erosion

Collapsing gully erosion, a special erosion phenomenon in the hilly granitic regions, is an important factor responsible for the deterioration of the ecological environment in southern China. The granite residual soil properties tend to vary with soil depth and their spatial variations have an important impact on the formation and development of collapsing gullies. Here, two typical granitic soil profiles in the north boundary of collapsing gully erosion in south China were selected to investigated the spatial variations of soil physicochemical, hydraulic, and mechanical properties along the profile and their influences on collapsing gully erosion. The upper two soil layers (surface soil layer and red soil layer) were significantly different from the lower two soil layers (sandy soil layer and detritus layer) in the investigated properties. The soil texture performed a large variation along the profile, which might be a positive factor for the formation of secondary vertical joints, faults, and weak structural planes. Meanwhile, the lower soil layers had a lower value of PL, LL, organic matter, and iron‑aluminum oxides, demonstrating their poor structure and vulnerability to erosion under rainfall conditions. Additionally, the upper soil layers had a higher water-holding capacity, but a lower decreasing rate in the unsaturated coefficient of permeability, leading to the overburdening of the lower soil layers under rainfall conditions. And the low soil layers had a low shear strength, which could also lead to the sliding of the gully head and sidewall, especially under saturated conditions. Collectively, the special geological structure of the granite residual soil layers plays an important role in the occurrence and development of collapsing gully erosion. The data reported in this paper may facilitate a better understanding of soil mass failure on the gully head and the collapsing gullies.

Main types of soil mass failure and characteristics of their impact factors in the Yuanmou Valley, China

Gully erosion is a dominant process causing soil loss in the Yuanmou Valley of Yunnan Province, China. Soil mass failure is a common process involved in gully development. The development of the gully and the occurrence of mass failure are interdependent and mutually promotive, but mass failure types have not been very well understood. In this study, we identify the main types of soil mass failure and the characteristics of their impact factors in the Yuanmou Valley. A detailed field survey was conducted in May 2010 in a representative area of the studied region, and selected soil parameters were measured in the field and laboratory. Results showed that there are four different soil mass failure types: falling, sliding, exfoliating, and toppling, each having unique characteristics of geology, topography, soil, and climate. Examination of these characteristics indicates that the occurrence of mass failure is controlled by four factors: 1) the typical geological structure of the Yuanmou Group represented by alternating layers of sand and clay; 2) the different terrain and landforms; 3) the different gully development stages; and 4) the particular soil properties under special weather conditions, including a dry–hot climate with distinct wet and dry seasons.

Determine the Stress Calculating Mode of Sliding Failure of Soil Mass under the Push-Extend Multi-under-Reamed Pile

Through the analysis of the sliding failure form of soil mass under the bearing push-extend reamed of Push-extend Multi-under-reamed Pile, in the paper, the law of coulomb-Mohr is used to establish a stress function and the theory of the sliding line is used to establish Prandtl regional stress field, which determines the stress calculating mode of soil mass and provides a theoretical basis for a further study of this type of pile ultimate bearing capacity of soil mass.

The processes and mechanism of failure and debris flow initiation for gravel soil with different clay content

Clay content can influence gravel soil mass failure and debris flow initiation significantly. But quantification of the clay content influence in the published literature is lacking. This paper describes the experiments carried out to explore soil mass failure and debris flow initiation with different clay contents. The whole process of gravel soil mass failure and debris flow initiation can be grouped into five phases: (i) infiltration excess runoff, (ii) fracture extending, (iii) initial slip, (iv) large-scale slip, (v) debris-flow triggering. In the experiments, when the clay content of soil mass is lower than 2.5%, no soil failure and debris flow are triggered. Only the soil masses with moderate clay contents (5–10%) show the clear processes of the five phases that need the shortest rainfall duration among different clay contents. Soil masses with high clay content (> 10%) and low clay content (2.5–5%) need longer rainfall duration to cover the five phases for partially triggering soil failure and debris flows. Clay content is closely linked with the soil failure and debris flow initiation under rainfall. The key mechanism can be grouped into two reasons: (i) the clay particles absorb the moisture and dilate to fill the soil pores, and the content of the clay has a direct link with the filled pores, (ii) the gravel soil masses with different clay content differ in their structure. For the low clay content soil mass group (2.5–5%), the coarse grains of the gravel soil form large pores and saturated clay particles are too few to block most soil pores. As a result, pore water pressure of soil mass is released easily in the raining process. Therefore, inner friction holds strong and soil mass is hard to mobilize into slip and debris flows. On the other hand, for soil masses with high (> 10%) clay contents, soil failure and debris flow are triggered under the aid of surface runoff flux to reduce the cohesion of the soil. Whereas, only for the soil masses with moderate clay contents (5–10%), large-scale soil failure and debris flow can be triggered within the shortest duration. In this case, the debris flow is of the form of “soil mechanics,” which is triggered after soil masses slip and liquefaction. The others are of the form of “hydraulic mechanics.” The experiments provide valuable evidence for quantifying clay content impact on gravel soil failure and debris flow initiation. Because they were carried out in a flume, the research results are applicable to the soil failure and debris flow initiation in bedrock gully situations.

ANALYSIS OF AXISYMMETRIC BORE-TYPE FOUNDATION IN RESPECT OF PLASTIC DEFORMATION/AŠIAI SIMETRINIO GRĘŽININIO PAMATO ANALIZĖ ĮVERTINANT PLASTINES DEFORMACIJAS

ANALYSIS OF AXISYMMETRIC BORE-TYPE FOUNDATION IN RESPECT OF PLASTIC DEFORMATION/AŠIAI SIMETRINIO GRĘŽININIO PAMATO ANALIZĖ ĮVERTINANT PLASTINES DEFORMACIJAS

ANALYSIS OF AXISYMMETRIC BORE-TYPE FOUNDATION IN RESPECT OF PLASTIC DEFORMATION

Summary In order to design efficient foundations, it is necessary to know exact behaviour of them and surrounding soil under the load. At present various numerical methods [1–11] are used to determine such response. The behaviour of axi-symmetric bored foundation is described in this paper. The finite element method is utilized in analysis of the foundation. Linear and non-linear properties of material are taken into account. The investigation of properties of soil, predominating in Lithuania, and economical constructing of foundation gives preference to bored foundation [12]. Schematically this type of foundation can be depicted as a cylindrical body resting on soil (Fig 1). Geometrically the foundation can be described through the diameter d and the height h. F denotes the vector of the axisymmetric load. Such bored foundation has ratio h/d ≥ 2 and transmit part of the external load through their side surface to soil. It is very difficult to achieve a shear failure of soil mass for such a type of founda...

Cyclic variation in moldboard plow draft and its effect on implement control systems

The cyclic variation in a moldboard plow draft was studied to assess the response of the tractor draft control system. The experiments were conducted using a 32-cm Ransom mounted moldboard plow in heavy clay soil at a field moisture content of 24% dry basis (d.b). The tests were conducted in two implement control modes, i.e. depth of working and draft control. Three speeds, i.e. 0.45, 0.65 and 0.90 m s −1, and two depths of operation, 24 and 29 cm, were used to determine their effect on cyclic variation of draft. A cyclic variation in the plow draft was observed to show definite peak and trough values. The fracture length remained almost the same, i.e. 1 ± 0.2 m at all plowing speeds and depths. The total draft frequency range was divided into two groups. The lower frequency range corresponded to the actual soil failure frequency, whereas the higher frequency corresponded to the frequency of failure of soil mass over the moldboard surface into smaller sub-blocks. It was observed that the response of the draft control system was affected by the lower frequencies of the draft. The performance of the draft control system was better in low-speed third gear than in low first or second gear as the lower frequencies of the draft corresponded to the system response.