Showing papers on "Settlement (structural) published in 2007"
TL;DR: In this article, the pore fluid of SRA-containing mortar has lower surface tension, which can result in lower crackinducing stresses at the mortar's topmost layer, reduced capillary tension, reduced settlement, and less evaporation.
Abstract: Cracking that forms between concrete placement and concrete setting is generally described as plastic shrinkage cracking The authors discuss how concave menisci may form on fresh concrete surfaces due to water evaporation Potential development of plastic shrinkage cracks may occur when concrete surface tensile stress and concrete settlement develop because of the menisci The authors focus on how mortars containing a shrinkage-reducing admixture (SRA), which is commercially available, develop plastic shrinkage cracks When exposed to the same environmental conditions, fewer and narrower plastic shrinkage cracks are shown in SRA-containing mortar than plain mortar The authors propose that pore fluid of SRA-containing mortar has lower surface tension, which can result in lower crack-inducing stresses at the mortar's topmost layer, reduced capillary tension, reduced settlement, and less evaporation
181 citations
TL;DR: In this paper, a conceptual framework for the analysis of settlement and other processes in landfilled waste in relation to coupled hydraulic, biodegradation and mechanical behaviour is presented, which includes an innovative interpretation of the mechanical consequences of decomposition combined with established formulations of load and creep-induced effects to predict settlement under load and over time.
164 citations
TL;DR: In this article, a superposition technique was proposed to describe surface settlement troughs over twin tunnels, where the effect of ground conditions, tunnel size, and depth on the surface settlement was considered.
Abstract: It has been observed in many tunneling projects that surface settlement troughs caused by twin tunnels have a variety of shapes unlike single tunnels, where symmetric surface settlement troughs are usually observed. The surface settlement troughs observed over twin tunnels can be symmetric with respect to the midpoint between the two tunnels or symmetric but shifted toward either side or they can also be asymmetric. Settlement troughs both over single and twin tunnels (when symmetric) can often be described by a Gaussian curve. Most of the cases reported in the literature do consider the effect of ground conditions, tunnel size, and depth on the surface settlement. However, these cases do not consider the effect of construction operation. A study of settlements above tunnels driven with earth pressure balance shields in Bangkok made it possible to include operational parameters such as face pressure, penetration rate, and grouting pressure. This is possible by comparing the effect of twin tunnels which are geometrically and geologically identical but differ in the operational characteristics. These operational differences make it, however, more difficult to describe the resulting settlement troughs over twin tunnels using existing methods. Therefore, this paper introduces a superposition technique to describe surface settlement troughs over twin tunnels. It appears that one can construct settlement curves induced by the first shield and the second shield using the Gaussian function and combine the curves to obtain a total settlement trough as a result of the twin tunnels. Using extensive data from the Bangkok Subway Tunnel project, this approach was found to be suitable both for twin tunnels excavated side-by-side and also for stacked twin tunnels. Right now this superposition technique is basically descriptive. Eventually it will be possible to use this approach to predict settlement troughs over twin tunnels.
115 citations
TL;DR: It is shown that the GP model is able to learn the complex relationship between foundation settlement and its contributing factors, and render this knowledge in the form of a function.
Abstract: In this paper, a new genetic programming (GP) approach for predicting settlement of shallow foundations is presented. The GP model is developed and verified using a large database of standard penet...
111 citations
TL;DR: In this article, the prediction of ground movements above single tunnels in soft ground is well established and can be estimated using semi-empirical methods based on the Gaussian curve.
Abstract: The prediction of the ground movements above single tunnels in soft ground is well established and can be estimated using semi-empirical methods based on the Gaussian curve. However, the prediction...
102 citations
TL;DR: In this article, the performance of the geocell-reinforced soft clay foundations under circular loading was evaluated using a laboratory model test carried out to develop an understanding of the behaviour of geocell reinforced soft clay foundation.
Abstract: This paper presents the results of laboratory model tests carried out to develop an understanding of the behaviour of geocell-reinforced soft clay foundations under circular loading. Natural silty clay was used in this study. The geocells were prepared using biaxial polymer grid. The performance of the reinforced bed is quantified using non-dimensional factors i.e., Bearing capacity improvement factor (If) and Percentage reduction in footing settlement (PRS). The test results demonstrate that the geocell mattress redistributes the footing load over a wider area thereby improving the performance of the footing. The load carrying capacity of the clay bed is increased by a factor of up to about 4.5 times that of unreinforced bed. From the pressure-settlement responses, it is observed that the geocell-reinforced foundation bed behaves as a much stiffer system compared to the unreinforced case indicating that a substantial reduction in footing settlement can be achieved by providing geocell reinforcement in the soft clay bed. The maximum reduction in footing settlement obtained with the provision of geocell mattress of optimum size placed close to the footing is around 90%. Further improvement in performance is obtained with provision of an additional planar geogrid layer at the base of the geocell mattress.
85 citations
TL;DR: In this article, the authors present settlement mechanisms and the methods for estimating settlements of municipal solid waste landfills, including bioreactors, based on results of field monitoring and data in published literature, coefficients of secondary compression for solid waste due to self-weight and external load.
Abstract: This paper presents settlement mechanisms and the methods for estimating settlements of municipal solid waste landfills, including bioreactor landfills. Based on results of field monitoring and data in published literature, coefficients of secondary compression for solid waste due to self-weight and external load are estimated. Special considerations are given to bioreactor landfills. Uses of these coefficients for long-term settlement estimation and their application to postclosure maintenance and development plans are discussed. Four case histories illustrating the use of these coefficients are presented. Methods of landfill treatment to reduce settlements are also presented.
84 citations
TL;DR: A computer program was developed to numerically predict the settlements and gas pressures in a bioreactor landfill using landfill geometry and waste properties, and produced satisfactory trends of the settlement and the landfill gas pressure profiles.
62 citations
TL;DR: In this paper, the authors reviewed the basic methodologies and their limitations for set-set estimation of permafrost embankments and showed that these three processes are interactive, which makes any attempts at calculation very difficult.
Abstract: Settlement of embankments in permafrost regions results from several simultaneous processes, each with a different mechanism. The first is the well-known process of thaw settlement due to the degradation of permafrost underneath. This has been considered to be the most problematic and has attracted great attention in previous studies. The second process is that of creep. Field observations show that due to the construction of embankments, the temperature in permafrost layers may rise remarkably, forming a large ‘warmer’ frozen layer with a higher tendency to creep. At the same time, creep of unfrozen soils can take place in the active layer in warm seasons under new loading conditions. Third, because freeze-thaw cycling in the active layer can change the soil properties, additional settlement would also take place in the first years. These three processes are interactive, which makes any attempts at calculation very difficult. The article first reviews the basic methodologies and their limitations for set...
60 citations
TL;DR: In this article, three-by-three pile groups with varying pile spacing were driven into a layer of soft ground and used as reinforcement over each pile group, and a 2D numerical analysis has been conducted using the computer program FLAC 2D.
Abstract: The effectiveness of constructing a geogrid-reinforced and pile supported embankment on soft ground to reduce differential settlement has been studied by pilot scale field tests and numerical analysis. Three-by-three pile groups with varying pile spacing were driven into a layer of soft ground, and a layer of geogrid was used as reinforcement over each pile group. Further, a 2-D numerical analysis has been conducted using the computer program FLAC 2D. The mechanisms of load transfer can be considered as a combination of embankment soil arching, geogrid tension, and stress transfer due to the difference in stiffness between pile and soft ground. Based on the pilot scale field tests and results of numerical analysis, we find that the geosynthetic reinforcement slightly interferes with soil arching, and helps reduce differential settlement of the soft ground. Also, the most effective load transfer and vertical stress reduction at the midspan between piles occurs when the pile cap spacing index D/b (D: pile c...
55 citations
TL;DR: The behavior of foundations on geosynthetic-reinforced clay-ey soil of low to medium plasticity using laboratory model footing tests was investigated in this paper, which showed that the inclusion of reinforcement could significantly improve the soil's bearing capacity and reduce the footing settlement.
Abstract: The behavior of foundations on geosynthetic-reinforced clayey soil of low to medium plasticity using laboratory model footing tests was investigated. The model footing was made of a steel plate with dimensions of 152 mm (6 in.) x 152 mm (6 in.). The parameters investigated in this study included the top layer spacing, the number of reinforcement layers, the vertical spacing between layers, and the stiffness and type of reinforcement. The effect of reinforcement on the vertical stress distribution in the clay and the strain distribution along the reinforcement were also investigated. The test results showed that the inclusion of reinforcement could significantly improve the soil's bearing capacity and reduce the footing settlement. With three or more layers of reinforcement, the settlement could be reduced by approximately 50% at a relatively medium surface pressure. The geogrids with higher stiffness performed better than geogrids with lower stiffness. The test results also showed that the induced vertica...
01 Jan 2007
TL;DR: In this paper, the authors present findings of a railroad ballast Discrete Element Modeling (DEM) research study focused on investigating ballast settlement under repeated wheel loading, where the ballast layer is modeled as an assembly of aggregate particles, with different shapes and angularities and rough surface textures.
Abstract: This paper presents findings of a railroad ballast Discrete Element Modeling (DEM) research study focused on investigating ballast settlement under repeated wheel loading. In this approach, the ballast layer is modeled as an assembly of aggregate particles, AREMA No. 24 ballast gradation with different shapes and angularities and rough surface textures. The study matrix considered three different wheel load magnitudes applied on a crosstie at three different load frequencies. Varying load frequencies helped account for different load pulse durations realized under different trafficking speeds. For each DEM solution, the load was applied for up to 100 cycles and the plastic deformations were recorded to indicate resulting ballast settlement. As expected, greater load magnitudes produced larger plastic deformations at one loading frequency. Yet, at a constant applied load magnitude, lower loading frequencies often yielded higher plastic deformations. DEM simulations also conducted with two other aggregate shapes indicated similar impacts of the frequency on ballast settlement.
TL;DR: This paper reports the first results of mapping informal settlement areas obtained using QuickBird high‐resolution images and a new semi‐automatic building extraction approach using snakes and a radial casting algorithm.
Abstract: Recent advances in sensor technology have promoted the mapping communities to investigate the potential and information contents of recent very high-resolution satellite images. In this paper, we report our new semi-automatic building extraction approach and our first results of mapping informal settlement areas obtained using QuickBird high-resolution images. We implemented our mapping approach using snakes and a radial casting algorithm, and assessed the results both qualitatively and quantitatively and compared them with ground truth data from a similar area. Finally, we summarized the potential and limitations of the second-generation commercial high-resolution satellite images to extract buildings using existing software.
TL;DR: In this article, the effects of varying artificial substrata, size of replicates and method of deployment were determined on a shallow reef in Eilat, Israel, while the effect of size of replica replicates was also investigated in Sharm El Sheikh, Egypt, where significant differences were found between materials used, tile size and methods of deployment.
Abstract: The choice of substrata and the methods of deployment in analyses of settlement in benthic communities are often driven by the cost of materials and their local availability, and comparisons are often made between studies using different methodologies. The effects of varying artificial substratum, size of replicates and method of deployment were determined on a shallow reef in Eilat, Israel, while the effect of size of replicates was also investigated on a shallow reef in Sharm El Sheikh, Egypt. When statistical power was high enough, that is, when sufficient numbers of settlers were recorded, significant differences were found between materials used, tile size and methods of deployment. Significant differences were detected in total coral settlement rates and for the two dominant taxonomic groups, acroporids and pocilloporids. Standardisation of tile materials, dimensions, and method of deployment is needed for comparison between coral and other epibiont settlement studies. However, a greater understanding of the effects of these experimental variables on settlement processes may enable retrospective comparisons between studies utilising a range of materials and methods.
TL;DR: In this paper, an improved back-propagation (BP) neural network was proposed for the correction of soil parameters in numerical prediction of embankment settlement, and the proposed numerical back-analysis framework is used in practical engineering applications to calculate highway settlement.
TL;DR: In this paper, a 1.8 m (6 ft) diameter concrete footing was statically load tested and the results of the static load test showed settlements were over predicted by all methods.
Abstract: The purpose of this study was to critically examine insitu test methods as a means for predicting settlement of shallow foundations. Accordingly, a 1.8 m (6 ft) diameter concrete footing was statically load tested. Prior to construction, insitu [standard penetration test (SPT), cone penetration test (CPT), dilatometer (DMT), and pressuremeter (PMT)] and laboratory tests were performed to determine engineering properties of the soil. Predictions of the footing settlement were made by traditional as well as finite element methods. The results of the static load test showed settlements were over predicted by all methods. However, the traditional methods provided reasonable settlement estimates using either SPT- N or back computed CPT(N) as input. Finite element analyses using either DMT or CPT derived input parameters provided reasonable settlement estimates. Finite element analyses using SPT or PMT derived input parameters provided poor settlement estimates. The Mohr–Coulomb (elastoplastic) model, accountin...
TL;DR: In this article, the mechanism of wheel load variation that results from changes in railroad track stiffness, loose railroad ties on ballasted trackside, and other factors was investigated, showing that resilient and larger railroad ties are the most effective in reducing ballast vibration and settlement.
Abstract: This paper describes a study which looked at the mechanism of wheel load variation that results from changes in railroad track stiffness, loose railroad ties on ballasted trackside, and other factors Results are presented from a field inspection, a cyclic-movement loading test, and dynamic analysis performed on the ballasted trackside of the end portion of a slab track, as well as on a precast and prestressed concrete crossing The paper also presents an evaluation of countermeasures against differential settlement occurring at track transitions Resilient and larger railroad ties are shown to be the most effective in reducing ballast vibration and settlement
Dissertation•
01 Jan 2007
TL;DR: In this paper, the development of low-cost sensors and wireless sensor network (WSN) platform aimed at characterizing problematic rail beds (subgrade) is described, which is installed at a busy high-speed Northeast Corridor (NEC) railway site that is experiencing recurring mud pumping problems and requires frequent (bi-monthly) track maintenance.
Abstract: This thesis describes the development of low cost sensors and wireless sensor network (WSN) platform aimed at characterizing problematic rail beds (subgrade) The instrumentations are installed at a busy high-speed Northeast Corridor (NEC) railway site that is experiencing recurring mud pumping problems and requires frequent (bi-monthly) track maintenance The field instrumentation program addresses some of the challenges faced with designing and installing the subgrade sensors: adoption of new low-cost sensor technologies, fabrication for harsh railway environment, ease of installation with minimal traffic disruption; adoption of advances in WSN for remote data gathering, two-way communications, back-end processing, and near real-time viewing of data The subgrade sensors consist of piezometers, accelerometers, liquid-based settlement probes, and temperature sensors (thermistors) The piezometers measure the long-term variation in the ground water table and short-term load induced pore pressures The accelerometers measure the dynamic wheel-induced accelerations at the tie and the top subgrade The liquid-based settlement probes are designed for long-term settlement measurements although they are not important at this particular site that exhibits greater track vibrations than long-term settlement The temperature sensors installed at three different levels are able to track the atmospheric, top subgrade, and deep subgrade temperatures The field instrumentation installed at the problematic NEC site provides valuable insights into factors causing mud pumping The field data suggest that water, widely acknowledged one of the causes of mud pumping, is not derived from the in-situ ground water table, perched water table at the top subgrade (that is under hydrostatic matrix suction), or rain (merely replenished the matrix suction in the ground) An energy-based method, modeled after the Arias Intensity, is used to characterize the response of the track to train loadings based on measured acceleration This method is able to track the serviceability of the rail track (effect of maintenance and gradual build-up of track deterioration), investigate the damage factor of trains on the track (high-speed Acela is found to be most damaging), and establish that the track is extremely stable during winter due to frozen soil but dramatically deteriorates during ice thaw Thesis Supervisor: John T Germaine Title: Principal Research Associate in Civil and Environmental Engineering Thesis Supervisor: Andrew J Whittle Title: Professor of Civil and Environmental Engineering
TL;DR: In this article, a method of reducing the settlement of shallow circular foundations on sand is presented, which involves the use of structural skirts fixed to the edges of foundations and a settlement reduction factor (SRF) is proposed, which takes into account the influence of various parameters that affect settlements.
Abstract: This paper presents the findings of an experimental study concerning a method of reducing the settlement of shallow circular foundations on sand. It involves the use of structural skirts fixed to the edges of foundations. The experiments were performed in a large tank setting and the footing was instrumented in order to measure normal stresses and settlement. A series of tests were conducted to study the settlements of a circular footing with and without structural skirts. Test results indicate that this type of reinforcement reduces the settlement of subgrade and modifies the stress-displacement behaviour of the footing. A settlement Reduction Factor (SRF) was proposed, which takes into account the influence of various parameters that affect settlements. Results show that the use of structural skirts can produce enhanced settlement reduction in the range of 0.1 to 1.0 depending on stress applied and skirt depth. Given these levels of settlements reduction, it is concluded that the use of structural skirts to reduce the settlement of shallow foundations on dense sand is of practical significance. Further testing is recommended for different foundation shapes with structural skirts resting on different soil types.
TL;DR: In this paper, a model for the analysis of granular foundation beds reinforced with several geosynthetic layers is presented, where the soft soil is represented by a series of nonlinear springs.
Abstract: The paper presents a model for the analysis of granular foundation beds reinforced with several geosynthetic layers. Such reinforced granular beds are often placed on soft soil strata for an efficient and economical transfer of superstructure load. The granular bed is modeled by the Pasternak shear layer and the geosynthetic reinforcement layers by stretched rough elastic membranes. The soft soil is represented by a series of nonlinear springs. The reinforcement has been considered to be extensible and it is assumed that the deformation at the interface of the reinforcements and soil are same. The nonlinear behavior of the granular bed and the soft soil is considered. Plane strain conditions are considered for the loading and reinforced foundation soil system. An iterative finite difference scheme is applied for obtaining the solution and results are presented in nondimensional form. The results from the proposed model are compared to the results obtained for multilayer inextensible geosynthetic reinforcement system. Significant reduction in the settlement has been observed when the number of reinforcement layer is increased. In case of inextensible reinforcements as the number of reinforcement layer is increased the settlement is decreased with a decreasing rate, but in case of extensible reinforcement the reduction rate is almost constant. Nonlinear behavior of the soft soil decreases as number of reinforcement layer is increased. The effect of the stiffness of the geosynthetic layer on the settlement response becomes insignificant for multilayer reinforced system, but the mobilized tension in the reinforcement layers increases as the stiffness of the geosynthetic layers increases.
01 Jan 2007
TL;DR: In this paper, the authors describe the development and application of design charts for piled embankment designs, which address the issues of pile capacity, settlement, and settlement due to a temporary piling construction platform, and lateral response of piles near the edge of the embankments.
Abstract: This paper describes the development and application of design charts for piled embankment designs. It outlines the computational approach adopted, the geotechnical profiles used, and the application of the design procedure using the charts. The soil profile used for the charts is representative of a Malaysian soft clay profile, involving a more or less normally consolidated soil, with a strength and stiffness that varies linearly with depth. Such a profile is typical of the ground conditions in a variety of countries in the Southeast Asian region. The design charts address the issues of pile capacity, settlement due to embankment load, settlement due to a temporary piling construction platform, and lateral response of piles near the edge of the embankment. The charts consider variations in ground conditions, embankment height, pile length, and pile spacing. An illustrative example is given to demonstrate the use of the charts.
Journal Article•
TL;DR: In this paper, the authors investigated the dynamic characteristic of track settlement by combining the vehicle-track coupling vibration model and the track settlement model, and the dynamic response parameters of track structure and the irregularity in the vertical profiles of track were taken as a connection between the two models.
Abstract: Dynamic characteristic of track settlement was investigated by combining the vehicle-track coupling vibration model and the track settlement model,and the dynamic response parameters of track structure and the irregularity in the vertical profiles of track were taken as a connection between the two models.The results of investigation show that,track settlement accumulates gradually with an increase in action times of dynamic loads on tracks,the initial track irregularity has a strong impact on track settlement,and the wheel-rail forces and track responses increase with the increase in accumulated settlements.
TL;DR: In this paper, the results from various geophysical methods (electrical resistivity tomography, seismic refraction, multichannel analysis of surface waves, cross-hole seismic surveys) were integrated and correlated to give an overall picture of the subsoil geometry and characteristics in the area under investigation.
Abstract: We present a case history in which several geophysical methods were used to investigate a five-floor residential building, constructed from reinforced concrete, which has been seriously damaged by differential
settlement. The results from various geophysical methods (electrical resistivity tomography, seismic refraction, multichannel analysis of surface waves, cross-hole seismic surveys) were integrated
and correlated to give an overall picture of the subsoil geometry and characteristics in the area under investigation, with particular regard to the stiffness properties and the degree of saturation. The ability of geophysics to investigate non-invasively has proven successful for dealing with buildings affected by foundation instability. The resolution of the results obtained from experimental data provides
additional insight into the geological scenario and the causes of the settlement. Moreover, geophysical
data may be used as a guide to optimize borehole locations for coring and soil specimen collection, which are necessary steps in designing the restoration intervention.
TL;DR: In this article, the authors investigated the application of a group of 1072 piles for controlling settlement of an important and sensitive structure founded on weak rock and concluded that numerically efficient 2D axi-symmetrical FEM model is capable of simulating the behaviour of this complicated 3D problem with reasonable accuracy.
Book•
01 Dec 2007TL;DR: In this paper, a supplementary information related to No. 29 in the Occasional Papers in Anthropology series is provided, along with a review of the papers in the series. But they do not discuss the authorship of these papers.
Abstract: This volume includes supplementary information related to No. 29 in the Occasional Papers in Anthropology series.
Journal Article•
TL;DR: In this article, a compilation of documented case histories including comparisons of DMT-predicted vs observed settlements is presented, in order to review the available experience in the use of MDMT for settlement calculations and to evaluate the accuracy of settlement predictions based on DMT.
Abstract: This paper presents a compilation of documented case histories including comparisons of DMT-predicted vs observed settlements, in order to review the available experience in the use of DMT for settlement calculations and to evaluate the accuracy of settlement predictions based on DMT. The available data indicate that, in general, the constrained modulus obtained by DMT (MDMT) can be considered a reasonable “operative modulus” (relevant to foundations under “working conditions”) for settlement predictions based on the traditional linear elasticity approach. Attention is also given to the determination of the strain range appropriate to MDMT, in view of the possible use of MDMT for settlement predictions based on non-linear methods taking into account the decay of soil stiffness with strain level.
TL;DR: In this paper, a computational method for the simulation of three-dimensional granular bed responses under long term cyclic loading is presented, which sequentially uses a molecular dynamics scheme, a time averaging technique, and a relaxation method in order to predict the long term flow.
TL;DR: In this article, a dynamic response analysis to Man-Vehicle-Road system is carried out by means of the Laplace transform in which the vehicle is modeled as a three-degree-of-freedom system and the bridge approaches with and without approach-relative slopes are simplified as broken lines model and step model, respectively.
Abstract: The differential settlement between the bridge abutment and the approach embankment produces the common “bump at the end of the bridge.” This paper conducts a theoretical study on the determination of the allowable differential settlement. The maximum transient vibration value of the acceleration is recommended as the vibration comfort index. A dynamic response analysis to Man-Vehicle-Road system is carried out by means of the Laplace transform in which the vehicle is modeled as a three-degree-of-freedom system, and the bridge approaches with and without approach-relative slopes are simplified as broken lines model and step model, respectively. Parametric studies are carried out to find out what kind of effects some parameters such as the driving direction and running speed may have on the allowable differential settlement. Finally, the method and computational procedures to determine the allowable differential settlement are presented.
Journal Article•
TL;DR: Wang et al. as mentioned in this paper found that, even though the permafrost table under the embankment moved up after the railway was built, it still suffered quite a lot of settlement.
Abstract: According to the in-situ experiment results of embankment settlement and deformation at Beiluhe test site along Qinghai—Tibet Railway in permafrost regions,it was found that,even though the permafrost table under the embankment moved up after the railway was built,the embankment has suffered quite a lot of settlement,and the settlement was mainly from the compression of the warm and ice-rich frozen soils under the original permafrost table caused by increasing the temperature of the permafrost.The greater is the increase of temperature,the thickness of ice-rich permafrost and the height of embankment,the more the settlement of embankment will be.Numerical calculation indicates that,even if the thickness of the filled soil meets the critical height,the settlement of the railway embankment at Beiluhe test site in permafrost regions will reach the value of 30 cm in the coming 50 years against the annual average temperature increase year after year on the Qinghai—Tibetan Plateau.Therefore,if the settlement of embankment is to be controlled,the active cooling measures must be taken to lower the ground temperature under the embankment.The traditional method to raise the height of the embankment is ineffective and even worse for the stability of the railway subgrade in permafrost regions.