Collapse Settlement Research Articles

Constructing Structures on Backfilled Opencast Mine Spoil for Better Sustainability

In this study we collate existing knowledge and suggest a possible methodology for construction on environmentally challenged backfilled mines to restore the sustainability of human settlement. The possibility of reconstruction on a backfill soil with a sustainable solution has been explored. The study highlights the issue of subsidence in backfilled opencast mines through a meticulous understanding of different case studies of construction on mine spoil. The prime focus of the study apart from structural and construction aspects includes the behaviour of heterogeneous mine spoil. Collapse settlement and hydrocompression are discussed to develop an understanding of failure in backfill. The study also incorporates the proposition of possible effective ground improvement treatment for improving soil behaviour through effective utilization of demolished concrete waste material. Further, ground improvement through demolished waste stone column has also been discussed. Finally, a feasible method for constructing a low-rise building on back-filled soil is proposed with available experimental data on bearing capacity. This study along with a comprehensive list of references may prove useful for conducting further research and a thorough understanding of the issues faced by the mining sector in India and other developing countries.

Influence of Pressure and Water Content on Loess Collapsibility of the Xixian New Area in Shaanxi Province, China

More than 40% area of the Xixian New Area is a loess deposit region, and most of the loess landform is tableland and terrace where the thickness of loess is very large. Therefore, loess collapsibility will be the most important geotechnical problem in future foundation investigation and construction. To explore loess collapsibility in the Xixian New Area, we conducted the K0 compression test, based on the collapsibility mechanism, which has different combinations of pressure (0~1.2 MPa) and water content (4%~Sat). Based on the σ-ε curve under different water content, we calculated the generalised collapse settlement and collapsibility coefficient of every water content under every pressure by subtracting the relevant curve from the saturated curve, and analysed the cross action of pressure and water on loess compressibility. The results show that the average collapsibility level of the northern Xixian New Area is self-weight collapsible level Ⅱ, with a lower limit of 14 m. Compressibility of loess is proportional to pressure and water content. Under low water content, the collapsibility coefficient δs increased while the pressure increased, but under medium and high water content, δs will reach peak with increasing pressure and after that, δs will decrease until its value is close to constant. When under the same pressure, δs decreases when water content increases. If set the additional strain 1.5% as collapse start criterion, then the initial collapse pressure Pi will linear proportional to water content. The initial collapse water content wi will increase sharply when pressure increases under low pressure, but wi will reach a constant value of 26% when pressure is larger than 200 kPa. This consequence will be meaningful for future geotechnical investigation and design in the Xixian New Area.

Rapid remediation using polyurethane foam/resin grout in Malaysia

Consolidation and collapse settlements are common threats to existing highways and buildings around the world. With the emergence of various ground improvement technologies, lightweight materials are alternative solutions for filling embankment settlement, ground repair and resolving settlement issues of roadways and building structures. This alternative solution has become effective and rapid in terms of performance and time. In the polyurethane resin (PUR) injection method, the liquids, polyol and isocyanate, are injected in small drilled holes without the need for excavation. This method is fast and provides additional strength to the ground with reduction in the void ratio, hence reducing the compressibility of the soil. In fact, its lightweight and impermeable characteristics are advantageous to ground experiencing inundation and groundwater table fluctuation where it triggers the buoyancy effect. This paper presents the chemistry of PUR, the concept of PUR grouting, the properties of PUR and case studies conducted in Malaysia for rapid ground remediation.

A new approach for prediction of collapse settlement of sandy gravel soils

Collapse settlement of the granular soils has become one of the main concerns of geotechnical engineers since their increased usage for constructing rockfill dams. Behavioral characterization of soil collapse settlement is a challenging task because this phenomenon is influenced by several parameters. In this study, a multi-gene genetic programming (MGGP) approach is proposed for the prediction of the collapse settlement of sandy gravel soils. The main goal is to formulate the collapse settlement and coefficient of stress release (CSR) in terms of sand content, normal stress, shear stress level, and relative density. The proposed models are compared with linear regression and ANN models. The results indicate that the MGGP models have superb accuracy and efficiency while they are simple and practical. The contribution of each parameter is evaluated through a sensitivity analysis. A parametric study is performed, and the obtained results are discussed.

The mineralogy and fabric of ‘Brickearths’ in Kent, UK and their relationship to engineering behaviour

Mineralogical and petrographical investigation of two loessic brickearth profiles from Ospringe and Pegwell Bay in north Kent, UK have differentiated two types of brickearth fabric that can be correlated with different engineering behaviour. Both sequences comprise metastable (collapsing) calcareous brickearth, overlain by non-collapsing ‘non-calcareous’ brickearth. This study has demonstrated that the two types of brickearth are discretely different sedimentary units, with different primary sedimentary characteristics and an erosional junction between the two units. A palaeosol is developed on the calcareous brickearth, and is associated with the formation of rhizolithic calcrete indicating an arid or semi-arid environment. No evidence has been found for decalcification being responsible for the fabric of the upper ‘non-calcareous’ brickearth. Optically-stimulated dates lend further support for the calcareous and ‘non-calcareous’ brickearth horizons being of different age or origins. The calcareous brickearth is metastable in that it undergoes rapid collapse settlement when wetted under applied stresses. It is characterised by an open-packed arrangement of clay-coated, silt-sized quartz particles and pelletised aggregate grains (peds) of compacted silt and clay, supported by an inter-ped matrix of loosely packed, silt/fine-grained sand, in which the grains are held in place by a skeletal framework of illuviated clay. The illuviated clay forms bridges and pillars separating and binding the dispersed component silt/sand grains. There is little direct grain-to-grain contact and the resultant fabric has a very high voids ratio. Any applied load is largely supported by these delicate clay bridge and pillar microfabrics. Collapse of this brickearth fabric can be explained by a sequence of processes involving: (1) dispersion and disruption of the grain-bridging clay on saturation, leading to initial rapid collapse of the loose-packed inter-ped silt/sand; (2) rearrangement and closer stacking of the compact aggregate silt/clay peds; (3) with increasing stress further consolidation may result from deformation and break up of the peds as they collapse into the inter-ped regions. Smectite is a significant component of the clay assemblage and will swell on wetting, further encouraging disruption and breaking of the clay bonds. In contrast, the ‘non-calcareous’ brickearth already possesses a close-packed and interlocking arrangement of silt/sand grains with only limited scope for further consolidation under load. Minor authigenic calcite and dolomite may also form meniscus cements between silt grains. These have either acted as “scaffolds” on which illuviated clay has subsequently been deposited or have encrusted earlier-formed grain-bridging clay. In either case, the carbonate cements may help to reinforce the clay bridge fabrics. However, these carbonate features are a relatively minor feature and not an essential component of the collapsible brickearth fabric. Cryoturbation and micromorphological features indicate that the calcareous brickearth fabric has probably been developed through periglacial freeze–thaw processes. Freezing could have produced the compact silt/clay aggregates and an open porous soil framework containing significant inter-ped void space. Silt and clay were remobilised and translocated deeper into the soil profile by water percolating through the active layer of the sediment profile during thawing cycles, to form the loosed-packed inter-ped silt matrix and grain-bridging meniscus clay fabrics. In contrast, the upper ‘non-calcareous’ brickearth may represent a head or solifluction deposit. Mass movement during solifluction will have destroyed any delicate grain-bridging clay microfabrics that may have been present in this material.

Simulation of collapse settlement of first filling in a high rockfill dam

In this paper, a new collapse prediction framework is proposed, involving an introduction of a stress dependent collapse coefficient which is directly obtained from results of triaxial tests. Within the proposed framework, the collapse settlement of rockfill dams can be simulated for first impoundment analysis. To make an appropriate choice of the model parameters, some large-scale triaxial collapse tests are numerically modeled employing the proposed framework and the parameters are used for simulation of collapse settlement of Gotvand, 178m high rockfill dam, and verified by field measurements and monitoring data. The influence of first filling rate on the deformation field of the dam body is discovered using a different number of stages for the impoundment. A parametric study has been undertaken with regard to the newly introduced collapse coefficient which contributes to the better understanding of collapse phenomenon.

Effect of Soil Replacement on Collapsibility of Footing Resting on Calcareous Sand- A Prototype Study

Soil replacement technique is not a new method to improve a soil stratum possessing poor strength properties. Before, such a problem of facing a location with weak soil properties is simply solved by changing that spot of estate by another one. Nowadays, such a proposal is no longer valid as a solution since the finance of real estates is rising considerably so that altering a location to the favor of other is not a choice. Calcareous soils are soils rich of calcium carbonate which occur manly in the semiarid subtropics for both hemispheres. This soil is one of the famous collapsible soils similar to the well-known gypseous soils. It has very good strength properties when dry, but once wetted it undergoes large and almost instantaneous settlement, potential collapse of productivity, even if there is no additional load applied on it. This research is concerned in studying the effect of soil replacement technique in reducing collapse settlement. A laboratory prototype model is used in study using SW soil mixed with different percentages of calcium carbonates, and gradual replacement of calcareous soil with sand is carried out in terms of width of footing B. Each model is leached for continuous seven days, and time-settlement data are recorded. This is done again for different percentages of calcium carbonate ratios mixed with sand. Laboratory tests revealed that the degree of improvement in terms of settlement for replacing B/2 depth by sand is 0.36 (B is footing width), that for replacing B is 0.65, for replacing 2B is 0.88, and for replacing 3B is 0.92. The amount of CaCO3 in soil does not affect the degree of improvement observed. An empirical formula is derived using finite differences for relating degree of improvement with depth of soil to be replaced.

Collapse settlement of dump soils revealed by studies on soil samples of modelled lithology and lump-size distribution

Collapse settlement of dump soils revealed by studies on soil samples of modelled lithology and lump-size distribution

The influence of the geological origin on soil volume change through collapse settlement

Partially saturated soils are often dense with a high bearing capacity and will subsequently only suffer small amounts of compression under normal foundation loads. However, when wetted under load many such soils undergo a marked and sudden increase in settlement, the phenomenon that is known as collapse settlement.It was originally assumed that the collapse phenomenon is largely restricted to loose aeolian deposits, with the result that most of the research and work dealt almost exclusively with such deposits. However, the collapse phenomenon has since been identified in a number of different transported soils as well as residual soils, most notably the residual granitic soils associated with the Basement Complex of South Africa.Recent studies suggest that the geological origin of the material plays an important role in the collapse mechanism of the particular material. This paper highlights the differences between the collapse process in transported and residual soils by focusing on the geological origin of the material.

Effectiveness of granular columns in containing settlement

Laboratory-based research studies and full-scale evaluations of the behaviour of ground improved with granular columns are ample regarding bearing capacity, but limited in respect to the settlement response. This paper presents a laboratory model study that considers the settlement performance of isolated pad footings bearing on reinforced sand deposits under the influence of a fluctuating groundwater table. This is a particularly onerous condition for loose sand deposits in coastal areas, which may undergo significant collapse settlement over time. Loose and dense experimental sand beds were constructed, and the performance of rigid footings under a maintained load and bearing on sand incorporating different column configurations was monitored under cycling of the water table over a period of 28 d, with one filling/empting cycle every 18 h. It was found that settlement, while greatly reduced compared with that for unreinforced footings, was ongoing, and typically occurred at a much greater rate for loose sand than for dense sand. Also, settlement rates were slightly higher for fully penetrating than partially penetrating columns, and also for footings reinforced by a column group rather than a single column. This was attributed to the migration of sand grains into the larger column voids.

Collapse Cause Analysis and Treatment Research of West Slope Tunnel

Abstract: West Slope Tunnel's surrounding rock is broken. A positive step method is used in the reconstruction process of collapsed West Slope Tunnel. During tunnel construction process, heavy rain cause a landslide failure of tunnel (Located in DK51+175- DK51+195). The mainly collapsed area is located in the position of DK51+180. According to collapsing, we executed the settlement observation, cross-section deformation detection and upper crack observation.When collapse settlement is basically stable, the collapse is segmented to settle. The previous board of Secondary lining for the collapse need to add steel reinforcement and tunnel collapse cavity backfill C30 concrete. When concrete strength is expected ,it need to be excavated and must keep the core soil. The advanced small pipe is needed to stabilize the soil before the excavation section. In invasion of secondary lining collapse, girdle previous Primary Support and reform Primary Support.. Add I16 steel frame where necessary. We must strengthen the tunnel monitoring to ensure the safety during tunnel construction process.

Geotechnical design in the presence of loess cover of the Nałęczów Plateau

An analysis of the diagnosis and design solutions of road viaduct foundation in the presence of dense loess cover of the Nałęczów Plateau. The analysis was conducted with regard to the provisions and the requirements of Eurocode 7 regulations: Geotechnical design. Studies on selected physical and mechanical characteristics of soil samples taken at the time of the object foundation were performed with the use of index analysis. In the light of the tests, parameters defined very carefully were established, and the leading borderline state resulting from the very term loess and its structural sensitivity was adopted without establishing the parameter of collapse settlement (imp) or/and the value of yield stress (YSR). Design solutions of foundation resulting from the recognition, settled parameters and properties of the substrate were reconsidered to be as very careful and expensive.

Using artificial neural network (ANN) in prediction of collapse settlements of sandy gravels

Collapse settlement is one of the main geotechnical hazards, which should be controlled during first impoundment stage in embankment dams. Imposing large deformations and significant damages to dams makes it an important phenomenon, which should be checked during design phases. Also, existence of a variety of contributing parameters in this phenomenon makes it difficult and complicated to well predict the potential of collapse settlement. Thus, artificial neural networks, which are commonly applied by majority of geotechnical engineers in predicting various perplexing problems, can be efficiently used to calculate the value of collapse settlement. In this paper, feedforward backpropagation neural networks are considered. And three-layered FFBPNNs with the architectures of 4–6–2 and 4–9–2 accurately predicted the coefficient of stress release and collapse settlement value, respectively. These networks were trained using 180 datasets gained from large-scale direct shear test, which were carried out on gravel materials. High correlation between measured and predicted values for both collapse settlement and coefficient of stress release can be easily understood from the coefficient of determination and root mean square error. It is shown that sand content and normal stress applied to the specimens, respectively, are most effective parameters on the collapse settlement value and coefficient of stress release.

Collapse settlement behaviour of remoulded and undisturbed weathered quartzite

The behaviour of semi arid residual soils derived from the weathering of Johannesburg quartzite are difficult to predict because of their heterogeneous particle constitution and weakly bonded structure. The collapse behaviour of undisturbed and remoulded weathered Johannesburg quartzite was investigated; and the reliability of the collapse settlement data was also evaluated. The results showed that a combination of low initial saturation of 13% and consolidation stress of 200 kPa result in the greatest collapse and that in order to avoid collapse, at any stress range, the soil must be compacted at a degree of saturation higher than 26%. The effect of desiccation on the magnitude of collapse settlement is dependent on the fines content and clay minerals. The collapse settlement of the undisturbed and remoulded quartzite was more sensitive to changes in dry density than changes in moisture content. Statistical analysis of collapse settlement test data of 15 undisturbed and remolded samples inundated at consolidation stress of 200 kPa revealed a mean, covariance and 95.5% reliability of 4.75%, 13.65±1.477% for undisturbed samples and 6.82%, 7.57±1.17% for remolded samples. The implications are that the higher values of collapse settlement associated with remolded samples should be recommended for geotechnical design. Key words: Collapse settlement, desiccation, weathered quartzite, soil structure.

A Numeric Analyses Method and Application of Loess Collapse Deformation

The collapse settlement of loess foundation is one of issues in engineering which need to be solved. Firstly, a finite element program was developed and the computational function of collapse deformation was implemented based on chord modulus method. Then, the comparison of the measured collapse settlement in a loading plate test and the computational collapse settlement based on the finite element were analyzed. The computational results show that the nonlinear finite element method based on the chord modulus should be recommended to evaluate the collapse deformation, owing to its potential application that it may consider the collapse deformation field of the whole collapsible loess foundation.

Effects of hydraulic shear stress and rate of erosion on the magnitude, degree, and rate of collapse

Arid regions worldwide are plagued by collapsible soils. Collapsible soil is characterised by the sudden decrease in volume that occurs when it is subjected to inundation under constant stress. This volume change manifest itself as drastic and unpredicted foundation settlement, which may lead to further catastrophic failure of the supported structures. Collapse settlement is the term applied to the additional settlement of a foundation due to wetting of the underlying soils. The results of an experimental investigation of the effects of the saturation of soil with water, kerosene, and crude oil, and of the effects of the fluid head on the magnitude, degree, and rate of collapse of the underlying soil are presented in this paper. Soil erodibility is presented in terms of the applied hydraulic shear stress and the rate of erosion. The relationship between soil erosion and the magnitude and rate of collapse is examined. Empirical methods for the prediction of the magnitude and rate of collapse of a soil saturated with the test fluids and subjected to a hydraulic constant head are proposed.

A review of Beliche Dam

Beliche Dam, a zoned earthdam with rockfill shoulders and a central clay core, experienced large collapse settlements due to reservoir impounding and direct action of rainfall. Long-term field records of vertical and horizontal displacements are available as well as a set of large-scale laboratory tests on rockfill specimens. It has been the subject of several numerical analyses that failed to capture the relevant effect of weather conditions on the behaviour of the dam. Recent developments in the constitutive modelling of rockfill allow a substantial improvement of modelling capabilities, and this is illustrated in the paper. Laboratory test results under dry and flooded conditions were interpreted, and material parameters were identified. The complete history of dam construction, impoundment and rainfall was then simulated by means of a coupled flow–deformation model. Deformations during construction and impoundment have been reproduced. Long-term deformations have consistently been related to rainfall records. In general, long-term deformations are controlled by the varying wetting history of the dam shoulders and by an intrinsic deformation component. The wetting action comes to an end when the relative humidity of the rockfill reaches 100% for the first time. The paper also discusses scale effects and the role of rockfill permeability in the development of deformations.

A review of Beliche Dam

Beliche Dam, a zoned earthdam with rockfill shoulders and a central clay core, experienced large collapse settlements due to reservoir impounding and direct action of rainfall. Long-term field records of vertical and horizontal displacements are available as well as a set of large-scale laboratory tests on rockfill specimens. It has been the subject of several numerical analyses that failed to capture the relevant effect of weather conditions on the behaviour of the dam. Recent developments in the constitutive modelling of rockfill allow a substantial improvement of modelling capabilities, and this is illustrated in the paper. Laboratory test results under dry and flooded conditions were interpreted, and material parameters were identified. The complete history of dam construction, impoundment and rainfall was then simulated by means of a coupled flow–deformation model. Deformations during construction and impoundment have been reproduced. Long-term deformations have consistently been related to rainfall records. In general, long-term deformations are controlled by the varying wetting history of the dam shoulders and by an intrinsic deformation component. The wetting action comes to an end when the relative humidity of the rockfill reaches 100% for the first time. The paper also discusses scale effects and the role of rockfill permeability in the development of deformations.

Performance of a steel structure on Ar-Rayyas Sabkha soils

Sabkha deposits cover extensive areas along the Red Sea and the Arabian Gulf shores. They are the site of huge industrial complexes in spite of their low bearing capacity of its upper part. The strength of the Sabkha soil is controlled by several factors, among them are the evaporatic salts that cement the grains. The Standard Penetration Test (SPT) is used extensively in this terrain but its results are misleading. The Sabkha soil that may give high N value will lose most of its strength upon wetting as part of the salts are dissolved. Therefore, the design N value was adjusted for Sabkhas to account for salt migration, by relating the SPT (N) value to the Sabkha moisture and salt content. A steel structure factory that was placed in an eastern Saudi Arabian virgin Sabkha deposits was considered. After a few years of operation fresh water leaked through the ground and caused signi.cant differential collapse settlement which threatened the functional integrity of the superstructure. The differential settlement was con.ned to one area of the structure indicating that localized conditions must have contributed to the observed settlement. The subsurface conditions and the geotechnical properties of the site are presented. A statistical model was developed that quanti.es the effect of the moisture and salt content on SPT (N) values. A simple site procedure is suggested to correct the design N value in similar cases. It was found that the increase in the moisture content could reduce the SPT (N) values by as much as 60, good agreements were found between the measured and predicted N values.

An analysis of stress–strain behaviour and wetting effects on quarried rock shells

The analysis of stress–strain behaviour and the effects of submergence on quarried rock shells, used mainly in dams but also in road construction, is of major importance from both economic and safety points of view. The research work presented here starts with an in-depth review of the nonlinear elastic procedure widely used in rockfill analyses since 1970, its later application to simulate wetting effects, and the latest published modifications to the so-called hyperbolic stress–strain model. An update of the existing wetting simulation procedure has been formulated, calculation routines to analyze constructional behaviour and wetting effects on rockfills have been implemented, and the methodology developed has been applied to a structure 100 m high. Calculation routines have been written to run in FLAC, a finite difference based code that incorporates a programming language. The analyzed structure is part of a road rockfill located at the Contreras Reservoir in Spain and consists specifically of two shell-shaped cross sections subjected to the influence of submergence. The results are expected to be useful in estimating collapse settlements in the upstream shells of earth-core dams.Key words: elasticity, stress–strain, rockfills, behaviour, numerical, dams.