Collapse Settlement Research Articles

Influence of different mining locations on deformation characteristics of overlying strata on gently anti-dip high-steep mining slope.

High-steep gently inclined mining slopes, prevalent globally, often suffer significant deformation, leading to landslides due to numerous goafs. This research investigates the critical role of goaf location in controlling deformation, failure mechanisms, and disaster evolution, vital for safe mining practices. Through field investigations and model generalization in Guizhou, a physical model test method was used to study three positions of goafs: under the shoulder and foot of the slope, under the slope shoulder, and within the slope. Findings highlight the stronger influence of the goaf's mutual position with the slope shoulder on slope and overburden deformation and failure compared to the slope toe. Deformation and failure modes evolve from collapse toppling to collapse slip and collapse settlement as the goaf shifts from the near slope surface to inside of the slope. Statistical analysis of fracture distribution in the goaf's overlying strata reveals damage increase with larger goafs, following a Gaussian distribution, with concentrated damage in the middle. The study identifies the maximum damage area, influenced by the horizontal distance between the goaf center and slope shoulder. These insights advance understanding of overburden rock deformation in gently inclined high-steep mining slopes.

A Coupled Effect of Eccentric Loading and Upward Seepage on Collapse Settlement of Strip Footings on Reinforced Sand

A Coupled Effect of Eccentric Loading and Upward Seepage on Collapse Settlement of Strip Footings on Reinforced Sand

The Wetting Deformation Model of Rockfill and Its Two Methods for Simulating Rockfill Dam Collapse Settlement.

The wetting deformation of the upstream dam shell material during the impoundment of the core wall rockfill dam seriously affects the safety of the dam. Based on the proposed Ew - νw wetting model, this paper proposes its corresponding two methods to simulate the collapse settlement of the rockfill dam: the initial strain method and the initial stress method. By simulating the collapse settlement of the Guanyinyan core wall rockfill dam, it is found that the simulated result using the initial stress method is in good agreement with the field monitoring data, while the displacement simulated using the initial strain method is larger. The distribution of displacement contours simulated using the initial strain method is obviously inconsistent in the area where the wetting deformation occurs, and the simulation results of the initial stress method are more reasonable. With the rise in the water level, the wetting deformation of the upstream dam shell material causes the tensile stress zone at the top of the dam. Therefore, the wetting deformation is the direct cause of the crack at the top of the dam, and the initial stress method should be preferred in the simulation of the wetting deformation of rockfill materials.

Study on collapse settlement and cracks of core wall rockfill dams under wetting deformation

AbstractThe safety and stability of core wall rockfill dams during impoundment are threatened by the wetting deformation of up‐stream shell materials. The serious wetting deformation not only aggravates the collapse settlement of upstream rockfill but also intensifies differential settlement of the dam crest during impoundment, and then causes cracks on the dam crest. On the basis of the proposed wetting deformation model and its simulation method of wetting deformation, this paper simulated the impoundment process of Guanyinyan core wall rockfill dam and studied the deformation characteristic of the dam during impoundment. In addition, the smeared cracking model was used to simulate the crack propagation on the dam crest, and the crack develop and spread mechanism was analysed. The results show that the simulated deformation can fit the in‐situ data well, and the simulated crack propagation is in good agreement with the actual situation. Once watered, the upstream rockfill and core wall have significant settlement, and the whole dam crest has obvious horizontal displacement towards the upstream. It is on the same order of magnitude that the increment of horizontal displacement and settlement at the top of the dam during impoundment. In the process of impoundment, the upper part of the dam tends to deform towards the reservoir area, which will lead to tensile cracks appearing in the rockfill areas on both upstream and downstream sides of the core wall of the dam crest, and the propagation direction of the cracks is basically parallel to the adjacent core wall surface. With the water level rising, the cracks on the downstream side of the dam crest mainly extend vertically, and the cracks on the upstream side of the dam crest not only extend vertically, but also extend horizontally.

Developing Predictive Models of Collapse Settlement and Coefficient of Stress Release of Sandy-Gravel Soil via Evolutionary Polynomial Regression

The collapse settlement of granular soil, which brings about considerable deformations, is an important issue in geotechnical engineering. Several factors are involved in this phenomenon, which makes it difficult to predict. The present study aimed to develop a model to predict the collapse settlement and coefficient of stress release of sandy gravel soil through evolutionary polynomial regression (EPR). To achieve this, a dataset containing 180 records obtained from a large-scale direct shear test was used. In this study, five models were developed with the secant hyperbolic, tangent hyperbolic, natural logarithm, exponential, and sinusoidal inner functions. Using sand content (SC), normal stress (σn), shear stress level (SL), and relative density (Dr) values, the models can predict the collapse settlement (∆H) and coefficient of stress release (CSR). The results indicated that the models developed with the exponential functions were the best models. With these models, the values of R2 for training, testing, and all data in the prediction of collapse settlement were 0.9759, 0.9759, and 0.9757, respectively, and the values of R2 in predicting the coefficient of stress release were 0.9833, 0.9820, and 0.9833, respectively. The sensitivity analysis also revealed that the sand content (SC) and relative density (Dr) parameters had the highest and lowest degrees of importance in predicting collapse settlement. In contrast, the Dr and SC parameters showed the highest and lowest degrees of importance in predicting the coefficient of stress release. Finally, the conducted parametric study showed that the developed models were in line with the results of previous studies.

Effect of Time History on Long-Term Deformation of Gypseous Soils

Abstract The time-dependent behavior of three gypseous soils was investigated. The soils had gypsum content of 66%, 44%, and 14.8%. The mineralogical and chemical properties of the soils were determined. Two series of tests were performed. In the first, collapsibility characteristics were investigated for a long period (60 days) by conducting single and double oedometer tests. In the second series, the effect of relative density on collapse with time was investigated. The samples were compacted to 40%, 50%, and 60% relative density and then tested. The results of collapse tests showed that the relationship between the strain and logarithm of effective stress has two vertical lines. The first one represents the collapse settlement taking place within 24 h, while the second one represents the long-term collapse. The collapse potential (CP) in both single and double oedometer tests increases when the gypsum content increases from 14.8% to 66% and when the initial void ratio increases. The CP–logarithm of time relationship for soaked samples prepared at different relative densities under 800 kPa indicated that the CP increased with time for the soil sample compacted at 60% relative density and the increase was higher than those compacted at 40% and 50% relative density. The curves started with a straight line and then a concave downward curve was observed with a high strain. For samples compacted at 40% and 50% relative densities, the curves were interrupted by little soil collapses, while the third curve exhibited smooth relation following the collapse.

Improvement of chalk solution feature infill by rapid impact compaction

This paper provides upper- and lower-bound limits of stiffness improvement observed from the treatment of infilled solution features in chalk as part of the Central 1 contract being delivered by the Align JV, which is part of the UK's High Speed 2 Phase 1 rail link. Infilled solution features were treated using rapid impact compaction (RIC) to achieve a sufficiently stiff subgrade beneath a wide range of temporary foundations and reduce the risk of collapse settlement. Improvement by RIC treatment was sufficient to ensure subsequent foundation performance or reduce the extent of compaction grouting subsequently required beneath the most heavily loaded foundations. The depth of improvement observed was up to 10 m and the improvement in elastic modulus observed was up to five times the pre-treatment value. Over 40 cone penetration tests were conducted before and after RIC. Typical lower- and upper-bound improvement curves are presented based on the observed minimum and maximum post-treatment stiffness. The degree of stiffness improvement was observed to generally reduce at greater than 5 m depth.

Wet and dry installation effects on the capacity of helical piles in loess deposits

ABSTRACT Vast land areas in northeastern Iran are covered with loess soils being susceptible to collapse and excessive settlement after moistening. Different improvement techniques were developed for loess soils, including compaction, immersion, or reinforcement. However, the shortcomings, such as limited improvement depth and lack of control over the treated area restrict these techniques’ effectiveness. The present study suggests the installation and application of helical piles as a combination of improvement techniques. About 13 uniform triple-helix piles of 3 m length, 250 mm blade diameter, and 750 mm blade spacing were installed via two different dry and wet installation methods. Static pile load tests were performed for all the helical piles. The results showed that the pile load tests were highly dependent on the moisture content at the testing time, the crowd force and the injected water pressure. Eventually, wet installed piles led to a more stable structure of loess soils than dry installed piles subjected to water.

Loess collapsibility characteristics of railway engineering sites using large-scale trial immersion pit experiments

Estimating and preventing loess collapsibility are important for the design and construction of the Xi’an North–Airport Intercity Railway. Laboratory tests and large-scale in situ immersion experiments were carried out to assess the collapsibility characteristics, seepage field, and deformation properties of loess at sites located on the third terrace of the Wei River (Bai Qi Zhai village) and the Xianyang loess tableland (Bu Li village). The calculated and measured in situ self-weight collapsibility are 363.0 mm and 3.0 mm for the Bai Qi Zhai village experimental site (the third terrace with loess covering permeable alluvium) and 306.0 mm and 318.5 mm for the Bu Li village experimental site (loess tableland), respectively. The presence of underlying highly permeable strata inhibits the in situ collapsibility characteristics of the loess at the third terrace site. Along the project route, the third terrace of the Wei River and the loess tableland can be assessed as non-self-weight and self-weight collapsible sites, respectively, for which relevant foundation treatment methods can be suggested to alleviate the collapse settlement of the foundation of the project.

An experimental investigation on collapsible behavior of dry compacted phosphate mine waste rock in road embankment

Prescribing compaction at optimum water content in arid and semi-arid climate regions generally leads to unjustified ecological practices. Indeed, to achieve optimum densities for road embankment compaction, significant volumes of water are required, which is perceived as a very scarce resource in drought-prone areas. Dry compaction with the promotion of the use of materials at their natural moisture content can be a promising alternative that could save water resources. Nevertheless, dry compaction can affect the infrastructures’ stability under flooding conditions.This paper presents field and laboratory tests carried out to investigate the effect of dry compaction on Phosphate Mine Waste Rocks (PMWR) behavior. In situ tests were conducted and the PMWR dry compaction protocol has been defined. Furthermore, the collapse deformation and the shear strength properties were evaluated through double oedometer and triaxial tests, respectively. The microstructural evolution on wetting was evaluated using mercury intrusion porosimetry (MIP) and 3D X-Ray computed tomography techniques. The water retention curve and mineralogical quantification tools were used to explain the influence of hydraulic hysteresis and clay minerals properties on the hydro-geotechnical behavior of PMWR. The results show a significant effect of applied stress level and dry density in addition to the type and amount of clayey expansive minerals on the structural deformation of PMWR on wetting. PMWR showed a maximum collapse settlement of 5.33% under a pressure of 1500 kPa, while no collapse is expected for stress less than 100 kPa. Low content of clays was identified as well as the swelling shrinkage potential within PMWR. The ability of using PMWR as embankment materials at dry moisture content under total overburden stress below 200 kPa ensuring a dry density of at least 95%.σd max is confirmed. The results of this work can also be applied to standard materials with similar hydro-geotechnical characteristics.

Intrusion of Geomesh in Gypseous Soil Under Single Footing

Methods to improve bearing capacity of footing resting of collapsing soil can, in fact, take two approaches, improving soil strength properties and intrusion of reinforcing sorces into soil. The footing is modeled by a square steel plate 0.1 by 0.1 m. The footing is loaded as to have a stress of 40 kPa and settlement is receded in dry and in soaking conditions. Two depths of the geo-mesh reinforcement are used, one B (B is width of footing) and 0.5B. For one B depth, three different square sizes of geo-mesh are used, 4B, 6B, and 8B. For the reinforcement depth of 0.5B the three sizes of the geo-mesh used are, 3.5B, 5.5B, and, 7.5B. Results reveal that the best improvement obtained is the case of square geo-mesh width of 7.5B and located at depth of B/2 under footing, with an improvement in terms of collapse settlement of 35%, and a settlement reduction in dry condition of 50%. The least improvement is the case of square geo-mesh with width of 4B and depth of one B, and it was really negligible, about 4% decrease in collapse settlement. Other cases varied between the two mentioned ratios. For findings of study, author recommends not to use geomesh size less than size of footing and not to place it in a depth more than half footing width. As such, in a whole, the effectiveness of geomesh in reducing the settlement of collapsing soil is obvious if used in proper way.

Vertical and Inclined Lime Injected Piles Under Footing Resting on Collapsing Soil

Gypseous soil, as one type of collapsible soils, is widely separated in Iraq. Gypsum concentrations of more 60% are not uncommon, and such soils are present in the western and northern parts of this country. Distresses in engineering facilities resulting from high collapse settlements are well known by the locals and as such causing much financial problems in government and private sectors. Soil improvement and replacement techniques are used as a result of tackle the large collapse of the soil. This laboratory research is directed in using lime piles to reduce the collapse potential of the gypseous soil. A comparison study is conducted between vertical lime piles and inclined lime piles. The inclination angle is chosen arbitrarily to be 30° to the vertical. A plain strain footing is used to simulate the separate foundation having length-to-width ratio (L/B) of 4. Three spacing patterns are used for each case of lime piles, namely B/3, B/2 and B. Test results reveal that inclined lime piles have much advantage over the vertical ones in reducing the collapse potential. Measured improvements in reducing settlement for inclined over vertical lime piles are 42% for spacing of B/3, 46% for spacing of B/2 and 27% for B. Unfortunately, the presence of lime piles has been found experimentally to increase the settlement in case, the collapsing soil is in dry condition compared to the untreated soil.

Study on wetting deformation characteristics of coarse granular materials and its simulation in core‐wall rockfill dams

SummaryThe wetting deformation of coarse granular materials is often considered to be an important cause of the core wall rockfill dam cracks during impounding. By analyzing existing research results, this paper proposes a hyperbolic relationship between the wetting axial strain and wetting stress level and puts forwards a warped surface relationship among spherical stress, shear stress, and the ratio of wetting volumetric strain to wetting axial strain. To illustrate its practicability, the wetting strain model's parameter determination process is introduced and the rockfill materials wetting parameters are determined using the triaxial wetting test data. Moreover, the collapse settlement of Guanyinyan rockfill dam during first impounding is numerically simulated using the proposed method to calculate rockfill wetting deformation and verified by field measurements and monitoring data. The results show that the calculative method of wetting deformation proposed in this paper is reasonable and practical; the wetting deformation of upstream rockfill materials would cause an adverse deformation trend, which may lead to crack occurrence at the upstream slope and dam crest; and the Guanyinyan rockfill dam cracks on the top of junction mainly caused by the wetting deformation of upstream rockfill.

A semi-analytical framework for one-dimensional collapse analysis of partly saturated soils

Despite the increasing interest to understand the behavior of collapsible soils, a very limited number of procedures have been proposed to perform analyses in order to predict collapse settlements. Hence, simple models that would enable engineers to undertake analyses within the one-dimensional and two-dimensional frames are still desirable. The present paper proposes an efficient semi-analytical framework where it is shown that collapse settlements can be estimated with a very reasonable computational effort. A semi-analytical procedure is developed within a one-dimensional framework and can be extended to two-dimensional and three-dimensional problems. In this procedure, the analytical solution of the infiltration problem is combined to a collapse model in a semi-analytical process where the soil layer and time period are divided into regular increments. Each increment over the soil layer depth is considered as a small soil element for which parameters such as moisture content and pressure head are estimated as functions of time. Local volumetric strain caused by soil collapse is estimated using a collapse model and integrated numerically to find the total settlement. The soil collapse settlement can be analyzed in conjunction with volumetric moisture content. Effects of parameters such as permeability and collapse modulus can be analyzed as will be shown.

A new wetting deformation simulation method based on changes in mechanical properties

This paper proposes a new simulation framework for wetting deformation of rockfill materials, in which wetting deformation is caused by changes in mechanical properties and simulated by using the modulus softening method. To study the difference in mechanical properties between dry and saturated rockfill, some conventional triaxial tests of dry and saturated rockfill are simulated using a plastic constitutive model with double yield surfaces. The elastic modulus of dry rockfill is found to be substantially higher than that of saturated rockfill, and the plastic hardening parameters of rockfill in these two states are substantially different. Then, a single-line triaxial wetting test that the wetting of sample was carried out after loading was numerically modelled. In the modelling process, the associated flow rule is found to be no longer appropriate, and the simulation results and test data fit well after the plastic potential function changed during wetting. Finally, the collapse settlement of the Guanyinyan rockfill dam is simulated and verified by field measurements and monitoring data. The research shows that wetting deformation of upstream rockfill materials would cause an adverse deformation trend, which may lead to cracking on the dam crest and upstream and downstream dam slopes near the dam crest.

A typical Earth fissure resulting from loess collapse on the loess plateau in the Weihe Basin, China

Earth fissures are major geological hazards that frequently occur in the Weihe Basin in northwestern China and can cause severe damage to infrastructure. This paper reports a case study of earth fissures resulting from loess collapse in the village of Xibai, in the Weihe Basin. A series of geological investigations, consisting of a site investigation, trench excavation, geological drilling, exploratory well drilling, and geotechnical testing, were conducted to determine and analyze the characteristics of the Xibai Village earth fissures, as well as the physical characteristics of the loess in the earth fissure development area. The earth fissures were parallel to the village sewage pit and had a total length of 800 m. With a maximum depth of 8.5 m, the Xibai Village earth fissures were nearly vertical. Comparing the results of self-weight collapsibility coefficient and three parameters (void ratio, dry density, and water content) of loess at different distances from the sewage pit, the collapsibility of Malan loess in this area and the effects of leakage from the sewage pit were determined. The results revealed that a tilted seepage line was generated, and the loess below this seepage line underwent varying degrees of self-weight collapse deformation. The nonuniform collapse settlement and rotation deformation of loess above the seepage line were thus generated, while tensile stress was created in the upper part of the loess. This rotation of loess, similar to the deformation of the cantilever beam, caused the formation of the earth fissures at the site with higher tensile stress. Based on the rotation mechanism, this study explained the development process of collapse earth fissures and predicted that the Xibai Village earth fissures would continue to develop outward in the future.

Collapse settlement of unsaturated soil from effective stress and shear strength interaction of soil

Consolidation settlement is the volume change behaviour due to dissipation of excess pore water pressure in saturated conditions. However, in a partially saturated condition, suction plays an important role in governing settlement behaviour. Besides, it also influences the shear strength of the soil by providing additional cohesion (termed apparent cohesion, cs) due to the existence of suction in the shear strength against suction axis. The shear strength decreases as the soil becomes fully saturated i.e. suction is reduced to zero, thence causes the apparent cohesion reduced to zero. Apparently, the shear strength has strong influence on the volume change behaviour. Therefore, a comprehensive review of the effective stress and shear strength interaction was conducted to verify this. The objective of this research is to verify the effective stress and shear strength interaction for both saturated and unsaturated soil conditions and to evaluate the complex settlement behaviour due to inundation at constant net stress, which has puzzled geotechnical practitioners. These conditions are tested and verified using the double wall triaxial test apparatus to determine the unsaturated shear strength of soil, the pressure plate extractor to produce Soil Water Characteristic Curve (SWCC) and modified large Rowe’s cell apparatus to simulate the loading and wetting collapses of partially saturated soils.

Treatment of collapsible soils by mixing with iron powder

Collapsible soils are meta-stable soils which present a potential for a large deformation and a complete change to the whole particle structure after wetting, with or without loading. Such soils can show high apparent strength in its natural state but collapse takes place as the bonds between grains break down when the soil is wetted or loaded. There are several techniques for treatment of collapsible soils such as chemical stabilization and dry mixing the soil with other material/materials which improve the soil's mechanical properties. This paper discusses a new proposed technique for treating the collapsible soils by dry mixing with iron powder in a specified percentage proportional to the weight (Ad). Experimental tests program was performed on collapsible soils with/without the addition of iron powder. The analysis of results showed the effect of the initial unit weight of soil γd, and the percentage of the weight-related additives on collapse potential (CP). The testing program also presents the effects of the amount of induced rainfall water (Qw), the applied stress on footing model (q), the ratio between depth of improved soils and the footing width (di/B), as well as the degree of compaction (Rc) of the improved portion of collapsible soils. This study presents the obtained results and shows in detail the positive effect of using iron powder for treating the collapsible soils and subsequently reducing the expected collapse settlement.

The Deformation Mechanism of a High Rockfill Dam during the Construction and First Impoundin

The Masjed-e-Soleyman dam is a high rockfill dam with clay core, located in Iran. During construction and first impounding, a considerably high excess pore water pressure has been developed inside the core and has been being dissipated with a very slow rate, so the consolidation deformations have been insignificant. However, there have been reports of noticeable internal deformations in the dam, the crest has also exhibited quick settlements during the first impounding. The main objective of this paper was to identify the deformation mechanism of this dam. For this purpose, the data recorded by its instruments were carefully studied and then a three-dimensional numerical model of the dam was developed. The mechanical behavior of materials was idealized by a hardening strain constitutive model. A numerical method was proposed, based on this constitutive model and Rowe’s stress–dilatancy theory, to simulate the deformation behavior of coarse-grained materials, like rockfills, due to particle size distribution, particle breakage, rotation, and rearrangement under shearing. The results show that significant development of pore pressure in the core and its insignificant dissipation, plastic shear deformations inside the core and extensive collapse settlements of the upstream shell are the main causes influencing the deformation mechanism.

Constitutive Modelling of Wetting Deformation of Rockfill Materials

In this paper, the constitutive framework of hypoplasticity is used to model long-term deformations and stress relaxations of weathered and moisture sensitive rockfill materials. The state of weathering of the material is represented by a so-called solid hardness in the sense of a continuum description. The time-dependent degradation of the solid hardness is a result of progressive weathering caused for instance by hydro-chemical reactions of fluid with the solid material. The degradation of the solid hardness can lead to collapse settlements and creep deformations, which are also called wetting deformations. In contrast to a previous version, a new evolution equation for a more refined modelling of the degradation of the solid hardness is proposed. With respect to a pressure-dependent relative density, the influence of the pre-compaction of the material and also the influence of the pressure level on the stiffness can be modelled in a unified manner using a single set of constants. The performance of the new model is validated by comparison of the numerical simulations with experiments data.