Solifluction Research Articles

Modeling the Formation of Topographic Asymmetry by Aspect‐Dependent Erosional Processes and Lateral Channel Migration

AbstractSome landscapes exhibit the intriguing characteristic that the steepness of hillslopes varies systematically with the direction they face, even where there is no bias introduced by bedrock structure. This topographic asymmetry has inspired numerous explanations. In the simplest scenario, insolation‐driven microclimatic differences lead to different erosion rates on opposing slopes and topographic asymmetry develops. Alternatively, lateral channel migration and the corresponding steepening of undercut slopes have also been suggested as a dominant cause of topographic asymmetry. To examine these proposed origins of asymmetric topography, we adapted a numerical landscape evolution model to include lateral channel migration as well as aspect‐induced variations in soil creep, regolith strength, and runoff. We compared the resulting topography and erosional response produced by each mechanism and found that the model with lateral channel migration produces unique signatures in erosion rates and the ridgetop Laplacian of elevation. To further investigate lateral channel migration, we developed a model of hillslope profile evolution in which sediment fluxes from opposing slopes control lateral channel migration rate and direction. We find that topographic asymmetry in this system can be self‐sustaining. All else being equal, we find that the aspect‐dependent models with variable regolith strength or runoff predict that less topographic asymmetry should develop as slope length decreases. These two models also predict that weaker asymmetry should develop as rock strength increases, whereas the lateral channel migration model predicts that greater rock strength should lead to weaker asymmetry only if lateral channel migration efficiency increases faster than fluvial incision efficiency.

Late Holocene geomorphodynamics in the vicinity of Göbekli Tepe, SE Turkey

This study traces the geomorphological development in the environs of the Pre-Pottery Neolithic site Göbekli Tepe by means of radiocarbon dated sediment profiles from its close vicinity. Based on facies interpretation we identify different depositional environments and discuss the involved process dynamics. Our results show that the sediments from the foot slopes are characterized by soil creep and slope wash. Further downstream, in the proximal piedmont zone, fluvial deposition prevails forming a channel and an overbank facies. The sediments at the foot slopes were mainly deposited during Roman and Byzantine times, while those from the proximal piedmont zone cover the period from the Bronze Age to the Roman times. Phases of geomorphological activity and stability can be distinguished in the course of the later Holocene, where organic rich topsoils were buried at c. 4750, 4200, and 3650 cal. a BP documenting phases of landscape stability followed by enhanced geomorphodynamics. These phases fall into the Bronze Age in Anatolia and coincide with an increasing population, pronounced human impact, and climatic aridization that occurred in Turkey around 5.3–4.1 ka BP. Our findings provide among the first insights into the environmental development including the involved process dynamics in the vicinity of the UNESCO World Heritage site of Göbekli Tepe during the later Holocene, also allowing to further develop hypotheses for the period of its occupation.

Semianalytical Solution for Evaluating Viscoelastic Consolidation of Saturated Soils with Overlying Dry Layers

Saturated soils with overlying dry layers are frequently encountered in geotechnical engineering. In urban construction works, the underground water level is usually influenced by the extraction of water or complex fluid for industrial uses or oil exploitation tasks. The creep and consolidation behavior of saturated soils with overlying dry layers is drastically different from that of completely saturated soils. This paper presents an investigation on the creep and consolidation behavior of the layered saturated soils with overlying dry layers under the vertical load. With the aid of the Laplace–Hankel transform, typical viscoelastic models (e.g., the Kelvin, the Maxwell, or the standard linear solid model), and the correspondence principle, a semianalytical solution is presented for this investigation. Detailed comparisons between the present results with the published numerical and analytical results are given to confirm the solution, followed by an extensive parametric study examining the effect of types of viscoelastic models, thickness of the overlying layer, and viscosity. This paper aims to present a semianalytical solution to describe the time-dependent consolidation of layered saturated soils with the overlying layer accurately and to provide useful implications for foundation design on those soils.

Constitutive Model of Lateral Unloading Creep of Soft Soil under Excess Pore Water Pressure

Presented in this paper is a study on the lateral unloading creep tests under different excess pore water pressures. The marine sedimentary soft soil in Shenzhen, China, was selected in this study. The results show that the excess pore water pressure plays a significant role in enhancing the unloading creep of soft soil. Higher excess pore water pressure brings more obvious creep deformation of soft soil and lower ultimate failure load. Meanwhile, the viscoelastic and the viscoplastic modulus of soft soil were found to exponentially decline with creep time. A modified merchant model and a combined model of the modified merchant model and plastic elements are used to simulate the viscoelastic and the viscoplastic deformation, respectively. Therefore, a lateral unloading creep model of soft soil is developed based on the modified merchant model. The accuracy and applicability of this model were verified through identifying the parameters in the model. Research results are of particular significance to the numerical simulation of underground space excavation in soft soil areas which considers the effects of excess pore water pressure.

A Bounding Surface Viscoplasticity Model for Time-Dependent Behavior of Soils Including Primary and Tertiary Creep

Abstract A viscoplastic model is presented for creep and strain rate behavior of soils with particular reference to capturing drained, undrained, primary, and tertiary creep. The model is formulate...

Experimental Investigation of Creep Behavior of Bayer Red Mud in Guizhou Aluminum Factory's Red Mud Disposal Field

Long-term stability and safety of red mud disposal field is very important for the local residents’ life, which necessitates the knowledge of its creep behavior. Through the improved triaxial creep apparatus, a series of triaxial drained creep tests were conducted. The results indicate that the creep behavior of BRM is significant with confining and deviatoric stresses being critical factors. The soil creep occurs in two stages of transient creep and the steady creep, and a larger deviator stress will lead to a larger creep strain. The main failure mechanism of BRM is plastic shear, accompanied by a significant compression and ductile dilatancy. The Burgers model and the Singh–Mitchell model are used to describe the creep behavior of BRM, and four parameters of these two models are estimated by the nonlinear regression. The deformations predicted by this model are in reasonable agreement with experimental data.

GEOPHYSICAL STUDIES AND STRENGTHENING A LAYERED AND WATER-SATURATED SOIL MASS IN THE KYIV METRO CONDITIONS

Purpose. An urgent issue for shallow underground tunnels in difficult engineering and geological conditions is the determination of the physical and mechanical properties of soils not only during engineering surveys, but also when they are studied using geophysical methods for studying ground conditions. In addition, it is important to choose ways to improve the properties of soils by strengthening, especially in areas where their strength characteristics are reduced. This ensures the efficient operation of tunnels with the elimination of hazardous phenomena such as vibration creep of soils and deformations of the track and lining. Methodology. Using the existing provisions on geophysical research, in order to identify the weaknesses of the layered and water-saturated massif and justify ways to strengthen it, the basics of a comprehensive study and production implementation have been developed to increase the level of safe operation of metro tunnels. Findings. Geophysical studies were carried out to identify weaknesses in the soil stratum along the route of the running tunnels of the Syretsko-Pechersk line of the Kyiv metro (the left bank of the Dnipro) and it was established that in present conditions, to strengthen weak water-saturated and layered soils, it is necessary to use methods of mixing soils with binders that are injected under pressure. Originality. Based on the performed analytical studies, the dependence of the porosity of weak water-saturated soils on the ratio of the acceleration of vibrations to the acceleration of gravity at certain frequencies of the path vibration caused by the movement of metro trains was obtained, and the parameters of soil strengthening on the sides and the bottom of the rim of the running tunnels were determined. Practical value. The use of geophysical methods for determining weak spots in the soil massif allowed them to be strengthened in the existing shallow underground tunnels and reduce the risk of their dangerous operation.

INTERACTION OF POST FOUNDATIONS AND FROZEN SOILS

The frozen soils’ stress-strain state varies with time due to the internal soil rheological processes. Those processes become active within the thawing period of the active soil layer causing increase in settlement of the engineering structures’ foundations. Hence, creep processes and thawing of frozen soils should be considered when designing the transportation facilities for regions of the Far North and Siberia.The objective of the research is to develop a procedure for evaluating the variation in time of the stress-strain state of the frozen soil under the post footing of a bridge pier’s foundation considering the frozen soil creep and thawing. The interaction of the bridge pier post foundations and frozen silt-loam soil is modelled and studied. The research is based on the example of an existing overpass over the M‑56 Lena motor road situated at Amga–Samyrdah stage of Tommot–Yakutsk section of the Berkakit–Tommot–Yakutsk railway line. This overpass has piers with post foundations. The above railway line is in the area of hard frozen soils.The study focuses on changes in principal normal compressive stresses with the course of time, as well as on the frozen soil movements under the post footing. The time allotted for the above system behavior study is limited to five months. There are two design cases: a) considering the frozen soil thawing up to a depth range of 1,5 to 4 m; b) without considering the frozen soil thawing.The research has shown that the thawing of the frozen soil up to a comparatively low depth as compared to natural level results in a significant increase (by 2÷2,5 times) in the values of post foundation settlement as compared with the design case without thawing. At the same time, it was found that small values of thawing have a subtle effect on the frozen soil’s stress state under the post footing. Besides, all reviewed design cases (with / without thawing revealed that stress of the frozen soil under the post footing decreases with time (stress relaxation).

Paleotopography controls weathering of Cambrian-age profiles beneath the Great Unconformity, St. Francois Mountains, SE Missouri, U.S.A.

ABSTRACT Precambrian (1.4 to 1.5 Ga) granite and rhyolite in the St. Francois Mountains at the northeast corner of the Ozark Plateau in Missouri has been altered down to a depth up to 8 meters below the Great Unconformity (the contact between Paleozoic sedimentary rock and underlying Precambrian). Petrographic, geochemical, and mineralogic data indicate that at least two events generated this alteration: 1) surficial weathering due to subaerial exposure of the granite before Cambrian burial—this material is preserved as a paleosol; and 2) alteration due to reaction with basinal fluids channeled along the unconformity from nearby sedimentary basins long after burial by Paleozoic strata. To assess the variation between surficial weathering and basinal fluid alteration, we measured and sampled for petrologic, geochemical, and mineralogic data in the rock at and just below the Great Unconformity at three paleoelevations. Whole-rock geochemical oxide and X-ray diffraction data indicate that K-metasomatism and highly crystalline illite occurred in each profile. The K increase reflects crystallization of authigenic feldspar and illite from basinal fluids that were channeled along the Great Unconformity during younger Paleozoic fluid-flow events. Each profile also exhibits an upward increase in altered feldspar crystals and highly crystalline kaolinite, and an upward decrease in Ca and Na. Such changes reflect soil formation due to reaction with meteoric water before Cambrian burial, indicating that the altered granite was a paleosol before Paleozoic basinal fluid-flow events. Notably, the paleosol at the highest paleoelevation displays the least amount of paleoweathering and the paleosol at the lowest displays the greatest amount of paleoweathering. These results demonstrate that not only can characteristics of the paleosol just below the Great Unconformity be recognized in the St. Francois Mountains, despite subsequent alteration, but also it is possible to detect variations in soil thickness that were controlled by slope steepness and, therefore, water availability and/or soil creep or failure. This spatial relationship is compatible with studies of modern soils which indicate that soil character varies with position on a slope.

An Applicability of Vyalov’s equations to ice wall strength estimation

A simple analytical relations are commonly used in engineering practice to calculate ice wall thickness. One of them is Vyalov’s relation that takes into account the features of a real technological process of tubing lining and the inelastic deformation associated with frozen soil creep. An estimation of applicability and margin of safety of this equation is an issue of engineering mechanics. In this paper, we propose a mathematical model for description of ice wall deformation under natural external loading and present the results of the computational experiments in which an optimal thickness for the ice wall is determined. Based on this simulation, we modify the existing analytical relation, which makes it possible to calculate the thickness of an ice wall of unlimited height.

Experimental Study of Compression Behavior of Indian Black Cotton Soil in Oedometer Condition

The clayey soil containing montmorillonite minerals exhibits both time-dependent compression called creep and swelling behavior, which is time-dependent expansion. Both the creep and swelling characteristics of the clayey soils have a significant influence on the deformation and failure of geotechnical structures. Study of time-dependent stress–strain behavior of a clayey soil is a great concern for construction purposes. In this paper, the long-term time-dependent behavior of Indian Black Cotton (BC) soil is investigated under a series of test in Oedometer apparatus at different loading pattern. The experimental result shows that non-linear function is suitable for prediction of long-term creep and swelling behavior of BC soil. Using the non-linear function, the behavior of the strain rate with time and the effective stress is studied. The strain rate, after the end of primary consolidation, decreases non-linearly to attain an equilibrium after reaching an equilibrium condition, and it is independent of the loading. The experimental result indicates that BC soil shows the repeated ability to swell at different stages of loading–reloading cycles. The experimental results along with the performance evaluation of the analytical model to predict long-term consolidation and creep behavior of BC soil are presented and discussed in details.

Interaction of a long barrette with three-layer base taking into account elastic and elastic- viscous properties of hereditary creep

The formulation and solution for the problem of interaction of a single barrette with the surrounding inhomogeneous massif are considered, taking into account the elastic property and elastic-viscous hereditary creep of soils on the basis of mathematical functions and models of the soil environment. In this case, determining the stress-strain state (SSS) of a single barrette with surrounding and underlying soil is complexity. It is shown that when the elastic-viscous hereditary creep of soils is available, there is a redistribution of effort on the barrette between the side surface and the lower end of the barrette in time. Resulting solution can be used to predict the sediment of a single barrette, as well as to determine the limit of the long-term load capacity of a single barrette.

Integrated geophysical methods for determination of lithology and unstable slope, case study: Cipogor area, PSK-1 mini hydro power plant

Cipogor is an area in PSK-1 Power Plant located at West Java. This area has a damaged flushing canal due to landslides at 2018. Therefore, integration of two-dimensional resistivity (ERT), one-dimensional resistivity (VES), and Digital Elevation Model is conducted to determine lithology and unstable slope that characterized by water saturated weak zone. Resistivity models from ERT and VES method are integrated with elevation data from DEM. Lithologies from interpreted VES model are as follows: Alluvial (6 – 70.06 Ωm), Tuff sediments (12 – 28.44 Ωm), sandstone sediments (1.96 – 9 Ωm) and Breccia (42.07 – 88.6 Ωm) from Koleberes Formations. There is an anomaly (12 – 28.98 Ωm) within sandstone layer. From ERT model, there is low resistivity zone (2-5 Ωm) interpreted as weak zone and moderate resistivity zone (16-24 Ωm) around 9-17 m in depth, interpreted as sediments transported during previous landslide. From the interpretation, it can be concluded that there is weak zone in depth 5-6.91 m and 17-20 m which is a weathered sandstone of Koleberes Formation and a sediment layer that transported from previous landslide in depth 9-17 m. Heaving is occurred in this layer and preventing any large landslide to occur but cannot prevent soil creeping in the area.

Decreasing Landslide Erosion on Steeper Slopes in Soil‐Mantled Landscapes

AbstractSlope‐stability models predict that steeper hillslopes require smaller hydrological triggers for shallow landslides to occur due to the added downslope pull of gravity, which should result in more frequent landslides and faster erosion. However, field observations indicate that landslide frequency does not consistently increase on steeper hillslopes. Here, we use measurements of 1,096 soil landslides in California and Switzerland, and a compilation of landslide geometries, to show that steeper hillslopes typically have thinner soils and that thin soils inhibit landslides due to enhanced roles of cohesion and boundary stresses. We find that the landscape‐averaged landslide erosion depth peaks near the threshold slope for instability, and it drops to half that value on hillslopes that are just 5° to 10° steeper. We propose that faster rates of soil creep on steeper slopes cause thin and more stable soils, which in turn reduces landslide erosion, despite the added pull of gravity.

Settlement of a railway embankment on PVD-improved Karakore soft alluvial soil

This paper presents a case history of the settlement performance of a railway embankment built on a Prefabricated Vertical Drain (PVD) improved soft alluvial soil of Karakore area, Wollo province, north-east of Ethiopia. The embankment was constructed on Awash - Kombolcha - Haragebaya (AKH) railway project for the purpose of preloading so as to facilitate the consolidation settlement in a short period of time; and it was monitored for more than 750 days. Numerical predictions of Class A and Class C (based on back-calculation procedure) were performed using Plaxis 2D. The soft soil creep (SSC) model was employed for the soft soil layers, while the Mohr-Coulomb (MC) model was used for the drainage and fill layers. The predictions were compared with the field monitoring settlement data. Quite a reasonable agreement was achieved from the finite element modelling of Class C prediction when the prediction was compared with the actual field settlement values. Parametric sensitivity studies were carried out to examine the influence of parameters on the rate and magnitude of settlements. The results of the numerical predictions and parametric studies have been discussed in detail. The soil on the flood plain area of Karakore is found to be very soft to soft alluvial deposit and formed over Tertiary Eocene stiff clay. The variable conditions of the soil formation and deposition highly dictated the deformation and excess pore water pressure behaviour of the soft subsoil sediment. The parametric sensitivity study showed that, following the compression index, the initial void ratio, the hydraulic conductivity, and the OCR highly influenced the settlement responses of PVD-improved soft alluvium soil respectively.

Evaluation on the behavior and contributing factors of subsidence in the intersection area of Expwy 78 and Taiwan High Speed Rail based on in situ monitoring and numerical simulations

This paper discusses the behavior and contributing factors of land subsidence in the intersection area of Expressway (Expwy) 78 and Taiwan High Speed Rail (THSR), located on Choshui River alluvial fan-delta (CRAFD) to the midwest of Taiwan. Since the CRAFD has been suffering a long-time problem of land subsidence, the transportation safety of THSR and Expwy 78 thus has become a major concern. The subsidence of CRAFD can be attributed to several factors, including overexploitation of groundwaters for area development. However, additional loadings of Expwy 78 and THSR structures would appear to deteriorate the problem. It would be of interest to know the influence of various factors on subsidence of the study area where the subsidence has now become most serious along the entire THSR route. It would also be advisable to provide information on the potential effects of subsidence on the integrity of THSR structure. With these aims, we perform analyses on the subsidence of the area based on 8-year on-site monitoring and numerical simulations. Results indicate, in a period started approximately from Expwy 78 construction, the average subsiding rate would be 10.53 cm/year, with relative contributions of 14.1%, 55.2%, 11.8%, 11.6%, and 7.3%, respectively, by the factors of soil creeping, previous overpumping, groundwater fluctuations, and loadings of Expwy 78 and THSR. We also estimate 23% and 77% of total subsidence occurred as the compressions of soils within and beyond the installation depth of THSR piles, which might impair pile bearing capacity and vertical alignment, respectively, of THSR.

Consolidation and creep phenomena in a sand-bentonite mixture under controlled suctions

ABSTRACT Investigating the creep of expansive unsaturated soils is necessary to simulate the long-term deformations that can cause structural failures. Hence, this paper presents a laboratory investigation of the consolidation and creep of an artificially prepared sand-bentonite mixture consisted of 40% commercial bentonite at controlled suction levels of zero, 100 kPa, 200 kPa, 400 kPa, and 800 kPa. A modified osmotic oedometer was utilised to apply vertical net stress and the desired matric suctions. After conducting the consolidation tests on samples, the last loading step was kept for extra 72 h to assess the creep behaviour of expansive unsaturated samples, and the creep coefficients (Cα) at different suctions were calculated. The results showed that the swelling index (Cs) gradually decreased with an increase in the amount of suction and a negligible value of the parameter is observed at higher levels of suction. Also, the creep coefficient decreased with an increase in the amount of suction value.

Model-Based Assessment of Long-Term Serviceability and Fire Resistance for Underground Reinforced Concrete Ducts

The collapse simulation of underground reinforced concrete (RC) ducts surrounded by soil foundations in a fire is conducted using multi-scale finite element analysis. The underground RC ducts are found to be deteriorated by both long-term soil subsidence and creep and shrinkage of concrete. The long-term shear crack risk is clarified by site inspection of some underground RC ducts. To conduct the structural risk assessment, the multi-scale simulation is applied and its performance upgraded to 1000°C. The release of chemically bound water from hardened cement paste is developed in the scheme of micropore structural modelling. It is linked with the mesoscale thermodynamics of vapour and the mechanics of the solid skeleton, and its fracture is integrated with the macroscopic cracked concrete constitutive models. This framework is upgraded to include the spalling of concrete cover in the event of a fire, and the exposure of reinforcing bars to high temperatures during a fire is reproduced. As the moisture dynamics inside the micropores of concrete can be used to determine the creep and shrinkage of concrete, long-term RC deformation can also be consistently taken into account for its normal use.

Channelization cascade in landscape evolution

The hierarchy of channel networks in landscapes displays features that are characteristic of nonequilibrium complex systems. Here we show that a sequence of increasingly complex ridge and valley networks is produced by a system of partial differential equations coupling landscape evolution dynamics with a specific catchment area equation. By means of a linear stability analysis we identify the critical conditions triggering channel formation and the emergence of characteristic valley spacing. The ensuing channelization cascade, described by a dimensionless number accounting for diffusive soil creep, runoff erosion, and tectonic uplift, is reminiscent of the subsequent instabilities in fluid turbulence, while the structure of the simulated patterns is indicative of a tendency to evolve toward optimal configurations, with anomalies similar to dislocation defects observed in pattern-forming systems. The choice of specific geomorphic transport laws and boundary conditions strongly influences the channelization cascade, underlying the nonlocal and nonlinear character of its dynamics.

Soil production and the soil geomorphology legacy of Grove Karl Gilbert

AbstractGeomorphologists are quantifying the rates of an important component of bedrock's weathering in research that needs wide discussion among soil scientists. By using cosmogenic nuclides, geomorphologists estimate landscapes’ physical lowering, which, in a steady landscape, equates to upward transfers of weathered rock into slowly moving hillslope‐soil creep. Since the 1990s, these processes have been called “soil production” or “mobile regolith production”. In this paper, we assert the importance of a fully integrated pedological and geomorphological approach not only to soil creep but to soil, regolith, and landscape evolution; we clarify terms to facilitate soil geomorphology collaboration; and we seek a greater understanding of our sciences’ history. We show how the legacy of Grove Karl Gilbert extend across soil geomorphology. We interpret three contrasting soils and regoliths in the USA's Southern Piedmont in the context of a Gilbert‐inspired model of weathering and transport, a model of regolith evolution and of nonsteady systems that liberate particles and solutes from bedrock and transport them across the landscape. This exercise leads us to conclude that the Southern Piedmont is a region with soils and regoliths derived directly from weathering bedrock below (a regional paradigm for more than a century) but that the Piedmont also has significant areas in which regoliths are at least partly formed from paleo‐colluvia that may be massive in volume and overlie organic‐enriched layers, peat, and paleo‐saprolite. An explicitly integrated study of soil geomorphology can accelerate our understanding of soil, regoliths, and landscape evolution in all physiographic regions.