Development Of Tension Cracks Research Articles

The study of the natural frequency evolution and numerical simulation of retrogressive landslides

A retrogressive landslide is influenced by the cyclical fluctuations in reservoir water levels is considered a common natural disaster. Tension cracks are important indicators for assessing landslide status in the case of retrogressive landslides. Displacement monitoring is a commonly used method and provides an intuitive reflection of the landslide deformation; however, it does not directly indicate the depth of the tension cracks. Based on the principles of vibrational dynamics, a retrogressive landslide is proposed to be initially classified as a single-mass spring oscillator model before the development of cracks. Following the development of tension cracks, the model can be classified as a double-mass spring oscillator model. The model patterns are verified through numerical simulations using ABAQUS. Based on the numerical simulations, with an increase in the number of reservoir water cycle fluctuations, the displacement and stress of the landslide exhibit periodic growth. However, during displacement growth, the tension cracks do not necessarily increase. As the tension cracks deepen, the landslide transitions from a single-mass spring oscillator model to a double-mass spring oscillator model, with the appearance of a second-order natural frequency. Moreover, as the tension cracks deepen, the numerical values of the natural frequency change. The maximum change in first-order natural frequency is 3.5 Hz. The maximum change in second-order natural frequency is 4.5 Hz. The variation in the natural frequency can reflect the depth of development of the landslide's tension cracks and, consequently, indicate changes in the stability state of the landslide.

Insight into the crack characteristics and mechanisms of retrogressive slope failures: A large-scale model test

Cracks in the crown area are one of the important indicators in the instability of the landslide headscarp, potentially offering early warnings for landslide hazards. Due to the complex causes of crack formation and numerous influencing factors, the understanding of crack development characteristics is still insufficient. In this paper, a large-scale soil slope model test is carried out through a large tilting platform to simulate the whole process of retrogressive slope failures including the first-time failure and the enlargement of the failure. The characteristics of crack development, the relations between internal slope parameters (e.g., internal strain and earth pressure) and cracks, and the evolutionary mechanisms of retrogressive failures are focused. The model test is monitored by high-tech equipment, including optical fibres, pressure gauges, and cameras. The results show that crack developments are divided into four stages based on crack location, quantity, and size. Optical fibre monitoring shows that the areas of tension crack development fall within the negative strain area in the slope model. In addition, the failure mode of the retrogressive landslides can be summarized in three stages: a deformation stage with sparse local cracks, a destabilizing stage with main cracks, and a retrogressive failure stage with dense secondary cracks. This study offers preliminary insights into the relations between crack development and the mechanisms in soil multiple retrogressive failures, which can be beneficial for better identifying and interpreting landslides at sites through crack monitoring.

Mechanical properties of polypropylene fibre reinforced recycled concrete aggregate for sustainable road base and subbase applications

There is limited research on the dynamic behaviour of soils reinforced with polypropylene (PP) fibres and a scarcity of literature on using PP fibres to improve the mechanical properties of recycled construction and demolition (C&D) waste subjected to dynamic wheel loads. To fill these research gaps, this study introduces varying proportions of PP fibres (0%, 0.1%, 0.2%, and 0.3% by dry weight of recycled concrete aggregate (RCA)) to enhance unbound granular RCA for pavement base/subbase applications. Incorporating PP fibres resulted in increased unconfined compressive strength, primarily attributed to the reinforcement effect of the fibres, which improved the tensile strength and resistance to stretching between aggregates and hindered the development of tension cracks through a bridging mechanism. Moreover, the enhanced stretching resistance between RCA particles, achieved by incorporating PP fibres, led to a 7% increase in Mr when the PP content was increased from 0 to 0.1%. Incorporating PP fibres into RCA also reduced permanent deformation and permanent strain rates. Notably, adding 0.1% PP fibres yielded the most favourable outcome in terms of permanent deformation response, transforming the behaviour of RCA from “Incremental Collapse” to “Plastic Creep.” This distinctive characteristic makes the blend of RCA with 0.1% PP fibres suitable for application as base and subbase layers.

Dynamic damage identification of tunnel portal and verification via shaking table test

Tunnel portals are seismically weak. Large-scale shaking-table tests of a tunnel portal were conducted. A method based on the Hilbert-Huang transform (HHT) for dynamic damage identification of tunnel portals was studied using the test results. The test preparation process and basic principles of the HHT are briefly described. The intrinsic-mode functions (IMFs) after empirical mode decomposition (EMD) were evaluated using multiple indicators, including the coefficient of determination (R2), root-mean-square error (Rmse), variance contribution rate (Mi), and energy moment (E). The time histories of the IMFs, marginal Hilbert spectrum, and Hilbert instantaneous energy spectrum were analysed. The results show that the damage development process of the lining and slope can be characterised by the marginal Hilbert spectrum and Hilbert Instantaneous energy spectrum. The slope had an obvious acceleration amplification effect with elevation and surface-trend amplification effect. Damage to the tunnel-portal slope is mainly caused by the development of tension cracks at the top of the slope, falling of scattered particles on the slope shoulder, development of cracks on the slope surface, and instability and collapse of the surrounding rock near the tunnel portal. Slope surface damage developed faster and to a greater extent than the interior of the slope. The lining of the portal section was dominated by longitudinal cracks, with some diagonal cracks. Damage to the invert at the tunnel portal occurs earlier than that of the crown, and the degree of injury is greater than that of the crown. The degree of damage and development speed of the tunnel portal were also greater than those of the tunnel body. The proposed method can serve as a guide for identifying the dynamic tunnel-portal damage.

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.

Modelling discontinuity control on the development of Hell\u2019s Mouth landslide

This paper focuses on numerical modelling and back analysis of the Hell’s Mouth landslide to provide improved understanding of the evolution of a section of the north coast of Cornwall, UK. Discontinuity control is highlighted through the formation of a ‘zawn’ or inlet, the occurrence of two successive landslides and evidence of ongoing instability through opening of tension cracks behind the cliff top. Several integrated remote sensing (RS) techniques have been utilised for data acquisition to characterise the slope geometry, landslide features and tension crack extent and development. In view of the structural control on the rock slope failures, a 3D distinct element method (DEM) code incorporating a discrete fracture network and rigid blocks has been adopted for the stability analysis. The onset and opening of tension cracks behind the modelled slope failure zones has also been studied by analysing the displacements of two adjoining landslide blocks, between which, a joint-related tension crack developed. In addition, a sensitivity analysis has been undertaken to provide further insight into the influence of key discontinuity parameters (i.e. dip, dip direction, persistence and friction angle) on the stability of this section of the coastline. Numerical modelling and field observations indicate that block removal and preferential erosion along a fault resulted in the formation of the inlet. The development of the inlet provides daylighting conditions for discontinuities exposed on the inlet slope wall, triggering the initial landslide which occurred on 23rd September 2011. Numerical modelling, and evidence from a video of the initial landslide, suggests that the cliff instability is characterised by a combination of planar sliding, wedge sliding and toppling modes of failure controlled by the discrete fracture network geometry.

Strength properties and durability of clay soil treated with mixture of nano silica and Polypropylene fiber

This article examined the effect of recycled polypropylene fiber (PPF), which is generated during manufacturing of plastic chairs, in addition to Nano-Silica as a novel technique to enhance the mechanical characteristics of clay soil. The main motive of this research is to investigate the optimal combination of Nano-Silica and Polypropylene fiber with clay soil. The engineering properties such as liquid limit, plastic limit, maximum dry density and unconfined compressive Strength (UCS) are analyzed with virgin soil, the soil with Nano-Silica and combination of soil with Nano-Silica and polypropylene fiber. The Durability test is performed to understand the durability of stabilized soil by analyzing wetting–drying cycles Also, Scanning Electron Microscopy (SEM) test is carried out and images are obtained to understand micro-structural modification towards mixture of Nano-SiO2 and PPF. Four different combinations of Nano-Silica at different percentages 1%, 3%, 5% and 7% are used in integration with polypropylene fiber is used in different percentages such as, 0.1%, 0.4%, 0.7%, 1%, and 1.3%. From these experiments, it has been analyzed that with the increase of PPF content in addition to Nano-Silica, the UCS increases and maximum value of UCS is obtained at 7% of Nano-Silica with 0.7% of PPF. The intermixing of PP fiber with the soil acts as a reinforcing material in binding the soil particles and the ‘bridge effect’ of fiber reinforcement in soil impedes the further development of tension cracks.

Centrifuge model studies on the performance of soil walls reinforced with sand-cushioned geogrid layers

This paper is to investigate the effectiveness of encapsulating geogrid layers within thin sand layers, for enhancing the deformation behavior of vertical reinforced soil walls constructed with marginal backfills. Centrifuge model tests were performed on vertical soil walls, reinforced with geogrid layers, using a 4.5 m radius large beam centrifuge available at IIT Bombay at 40 gravities. The backfill conditions, height of soil wall, reinforcement length, and reinforcement spacing, were kept constant in all the tests. A wrap-around technique was used to represent flexible facing. Three different geogrid types with varying stiffness were used in the present study. The walls were instrumented with vertical linear variable differential transformers to monitor surface settlements during the tests. Marker-based digital image analysis technique was used to determine face movements and distribution of geogrid strain along the wall height. The deformation behavior of soil walls, reinforced with geogrid layers encapsulated in thin layers of sand, were compared against a base model having no sand-cushioned geogrid layers. Provision of sand-cushioned geogrid layers and increase in geogrid stiffness were found to limit normalized face movements (Sf/H), normalized crest settlements (Sc/H), and change in maximum peak reinforcement strain (dεpmax). Sand-cushioned geogrid layers were also found to limit the development of tension cracks behind and within the reinforced zone. Significant reduction in rate of maximum face movement (dSfmax/dt) and rate of maximum peak reinforcement strain (dεpmax/dt) was observed, with an increase in value of normalized reinforcement stiffness (Jg/γH2) of geogrid layers. The analysis and interpretation of centrifuge model tests on soil walls, constructed with marginal backfills and reinforced with sand-cushioned geogrid layers, indicate that their performance is superior to the walls without sand-cushioned geogrid layers.

Flexural fatigue strength of demolition aggregates stabilized with alkali-activated calcium carbide residue

Replacing the base and subbase layers in flexible pavements and sub-ballast layer in railway tracks with recycled materials has attracted significant attention from industry and researchers alike. The semi-rigid stabilized layers in the flexible pavement structure and railway tracks sustain high flexural and tension stresses which reduces the serviceability life of the superstructure. The flexural and compressional modulus of the stabilized materials under repeated loads and at at-rest k0 condition is highly dependent on the specifications of the binder. Industrial by-products including calcium carbide residue (CCR), Fly Ash (FA) and Slag (S) were utilized to improve the compressional resilient modulus, flexural strength, durability and fatigue life of recycled aggregates. The variation of ductility in the blend with different precursors indicated that the service life of the stabilized layers not only depended on the strength but was also controlled by the deterioration rate of the flexural modulus and stiffness of the sample. The ductility of binder with aluminosilicate gels fabric can potentially absorb the stresses of the cyclic loading and postpones development of tension cracks.

Stress concentrations around voids in three dimensions: The roots of failure

We present stress concentration factors at the edges of 3D voids in uniaxial compression. Variations in these stress concentration factors due to Poisson's ratio of the host material, void shape, and void-void proximity are explicitly quantified. Voids loaded by a vertical compressive stress are hypothesised to fail in one or two ways: (1) tension crack development due to tensile stress concentrations at the void poles; or (2) compressive stress concentrations at the void sides causing the void wall to fail in shear. The stress concentration factors in this study are found using the numerical displacement discontinuity method. Equations are provided to assess the proximity of a void to the two hypothesised modes of failure. For 3D voids thinned in an axis that lies parallel to the compressive stress these have increasingly high stress concentrations at their sides. Changes in stress concentrations due to the Poisson's ratio of the matrix are minor, apart from for the intermediate stress at the void sides. Void shape, void separation, and void alignment are critical factors in the concentration of stresses. This suggests a significant departure from strength predictions for porous material that are based solely on scalar values of porosity.

Discrete element modeling of a mining-induced rock slide.

Slopes are subjected to stress redistributions during underground mining activities, and this may eventually cause deformation or landslide. This paper takes Madaling landslide in Guizhou Province, China as a case study to investigate the failure mechanism and its run-out behaviours by using discrete element method. Previous qualitative analysis indicated that the slope experienced four stages of failure mechanisms: (1) development of tension cracks, (2) development of stepped-like creep cracks, (3) development of potential rupture surfaces, and (4) occurrence of the landslide. PFC2D program was employed to model the pre-failure deformation characteristics in order to verify the failure mechanisms quantitatively. Subsequently, the run-out behaviours of the landslide were analyzed by PFC3D program. The results indicated that the movement could be summarized into four stages: acceleration stage, constant movement stage, rapid movement stage, and deceleration and deposition stage.

Tensile Strength of Fiber-Reinforced Soil

AbstractThe tensile strength of soil is an important mechanical parameter that controls the development of tension cracks. In this study, randomly distributed polypropylene fibers were employed to improve soil tensile behavior. Direct tensile tests were conducted on fiber-reinforced soil specimens with different fiber contents and compacted at different water contents and dry densities. Desiccation tests were also performed to evaluate the effectiveness of fiber reinforcement in improving soil tensile cracking resistance. The tensile test results showed that fiber inclusion significantly increased the soil peak strength, reduced the postpeak strength, and changed the brittle tensile failure behavior to a more ductile one. Soil tensile strength increased with the increase in fiber content. The tensile strength of both reinforced and unreinforced specimens decreased with increasing water content and increased with increasing dry density. Moreover, a higher soil dry density showed a more positive effect in m...

The hydrogeomorphic influences on alluvial gully erosion along the Mitchell River fluvial megafan

AbstractHydrogeomorphic processes influencing alluvial gully erosion were evaluated at multiple spatial and temporal scales across the Mitchell River fluvial megafan in tropical Queensland, Australia. Longitudinal changes in floodplain inundation were quantified using river gauge data, local stage recorders and HEC‐RAS modelling based on LiDAR topographic data. Intra‐ and interannual gully scarp retreat rates were measured using daily time‐lapse photographs and annual GPS surveys. Erosion was analysed in response to different water sources and associated erosion processes across the floodplain perirheic zone, including direct rainfall, infiltration‐excess runoff, soil‐water seepage, river backwater and overbank flood inundation. The frequency of river flood inundation of alluvial gullies changed longitudinally according to river incision and confinement. Near the top of the megafan, flood water was contained within the macrochannel up to the 100‐year recurrence interval, but river backwater still partially inundated adjacent gullies eroding into Pleistocene alluvium. In downstream Holocene floodplains, inundation of alluvial gullies occurred beyond the 2‐ to 5‐year recurrence interval and contributed significantly to total annual erosion. However, most gully scarp retreat at all sites was driven by direct rainfall and infiltration‐excess runoff, with the 24‐h rainfall total being the most predictive variable. The remaining variability can be explained by seasonal vegetative conditions, complex cycles of soil wetting and drying, tension crack development, near‐surface pore‐water pressure, soil block undermining from spalling and overland flow, and soil property heterogeneity. Implications for grazing management impacts on soil surface and perennial grass conditions include effects on direct rainfall erosion, water infiltration, runoff volume, water concentration along tracks, and the resistance of highly dispersible soils to gully initiation or propagation under intense tropical rainfall. Copyright © 2012 John Wiley & Sons, Ltd.

Implications of bank failures and fluvial erosion for gully development: Field observations and modeling

Gully erosion is most commonly triggered by fluvial erosion following natural and anthropogenic disturbances or as a response to changes in climate and tectonic forcing and base level drop. Field observations attribute the headward growth and widening of many gully systems to gravitational mass‐wasting processes of oversteepened sidewalls. Soil saturation, groundwater sapping, and tension crack development contribute to the instability. Recent landscape evolution models treat such mass failures as slope‐dependent continuous sediment transport processes, sometimes conditioned on a slope threshold or with nonlinear dependence on slope gradient. In this study we first present an explicit physically based theory for the stability analysis of gully heads and walls. The theory is based on the force balance equation of an assumed planar failure geometry of a steep gully wall, with a potential failure plane dipping into the incised gully bed and tension cracks developing behind the scarp face. Then, we test the theory against field data collected in our field site in Colorado and against other published data. Second, the theory is implemented in a one‐dimensional hillslope profile development model and the three‐dimensional channel‐hillslope integrated landscape development (CHILD) to study the effects of soil cohesion, erosion thresholds, and stochastic climate on the tempo of gully development and morphology. Preliminary results indicate that wider and shallower gullies develop and integrate, forming wide valleys, when soil cohesion is small. As soil cohesion increases, erosion slows down, gullies become deeper with vertical walls, and episodic mass failures occur. Differences in storm intensity‐duration characteristics and erosion thresholds are predicted to have a significant impact on gully development. Vertical gully walls develop rapidly, and gullies enlarge by slab failures in a climate characterized by high‐intensity, short‐duration storm pulses. However, under low‐intensity, long‐duration storms, gullies quickly stabilize, and vertical walls are eliminated and rounded, forming diffusion‐dominated hilltops. Erosion thresholds have a similar impact on the tempo of gully erosion but in the opposite direction. Lowering the erosion threshold enhances gully widening by slab failures. Gully walls stabilize when the erosion threshold is high due to a reduction in the erosion of the failure material on the toe of gully walls.

Assessment of sidewall erosion in large gullies using multi-temporal DEMs and logistic regression analysis

Although in the last decades gully erosion has been a thriving research field, few studies have specifically addressed the contribution and location of sidewall erosion processes in gullies. In this paper, sidewall erosion in some large gullies in a Mediterranean area (Anoia-Penedès, NE Spain) is mapped and assessed for two time intervals (1975–1995 and 1995–2002), using detailed digital elevation models derived from aerial photographs at a scale of 1:5000 to 1:7000. Logistic regression analysis is applied to compute the probability of occurrence of gully sidewall erosion from terrain variables. The results confirm the complex nature of sidewall processes, whose intensity is most probably related to rainfall characteristics. Prolonged wet soil conditions in the period 1995–2002, together with the large and high-intensity rainfall of an extreme event occurred on 10th June 2000, help to explain the different sediment production rates: 16±0.4 Mg ha −1 year −1 in 1975–1995 and 83±6.3 Mg ha −1 year −1 in 1995–2002. The logistic regression analysis revealed that gully-wall slope angle was the main factor controlling gully sidewall failure. In gully walls with high slope angles, tension crack development is the main process promoting wall collapse. The application of the logistic regression model showed a high overall accuracy (87%) but over 50% of commission and omission errors for the class of interest (sidewall erosion), in agreement with the variance explained by the model.

Centrifuge Modeling of Geotextile-Reinforced Cohesive Soil Retaining Walls

Twenty-four reduced scale models of vertical and steeply sloping (1\iH:6\iV) reinforced soil walls were built using kaolin as the backfill, reinforced with a nonwoven geotextile simulant, and loaded to failure under increasing self-weight in the geotechnical centrifuge. Models were constructed on either firm or rigid foundations, and different lengths of reinforcement were tested. No pullout failures were observed in any models. In vertical walls failure developed entirely within the reinforced zone when \iL/\iH ≥0.75; in the steeply sloped walls this threshold occurred when \iL/\iH≥0.67. Models on firm foundations showed better performance than identical models built on rigid foundations. A stability analysis using the simplified, two-dimensional limit-equilibrium simplified Bishop method incorporating reinforcement was found to be a good predictor of the behavior of the models based on calculated factors of safety at failure. The development of tension cracks in the backfill as walls underwent prefailure deformations led to stress concentrations in the geosynthetics and should be avoided in practice.

An unusual diagenetic structure in the Precambrian banded iron formation (BIF) of Orissa, India, and its interpretation

An unusual type of late diagenetic tectonic and compaction structure simulating boudinage phenomena is described and documented from the Precambrian banded iron formation (BIF) of Orissa, India. The structure was seemingly initiated by the development of tension cracks in the hydroplastic stage followed by rotation and imbrication of the segments of the iron (magnetite) bands. The tension cracks were subsequently filled up by finely crystalline diagenetic quartz veins.

Tension crack development in soils : Fook-Hou Lee; Kwang-Wei Lo; Seng-Lip Lee J Geotech Engng Div ASCEV114, N8, Aug 1988, P915–929

Tension crack development in soils : Fook-Hou Lee; Kwang-Wei Lo; Seng-Lip Lee J Geotech Engng Div ASCEV114, N8, Aug 1988, P915–929

Tension Crack Development in Soils

A model is proposed for finite‐element modeling of tension crack propagation in soils. The essential features of this model are the splitting of a single node into two distinct nodes in the wake of an advancing crack tip to replicate separation of material on either side of the crack, and the use of a fracture mechanics criterion to predict crack propagation. The material parameter employed in this criterion, the critical energy release rate, is determined experimentally and shown to be reasonably constant over a range of crack lengths, thereby supporting the adoption of this parameter as a material constant for tension cracking in soils. The model is then applied to two classes of problems in which tension cracking is known to exercise significant influence, a stiff embankment on soft soil and an excavated slope. For both problems, stable and reasonable solutions are obtained, suggesting that fracture mechanics offers a feasible approach to the analysis of tension cracking in soils.

Pore-Space Reduction in Sandstones

In two deep wells in Wyoming three types of pore-space reduction occur. These are simple pore filling, solid flow, and solution and redeposition or removal of the dissolved material. Five sands, ranging in depth from 2,885 to 8,343 feet, and sections of randomly packed sand grains were studied. Sand-grain contacts, as they appear in the plane of a random thin section, are classified. The number of contacts per grain and types of contacts due to pressure increase with depth, and each type of contact has its individual trend with increasing depth. Development of tension cracks and crushing of fragile grains are other features due to pressure. Some cementation and replacement occur, but no depth relationship can be established.