Showing papers on "Settlement (structural) published in 2012"

Tunnels in sands: the effect of size, depth and volume loss on greenfield displacements

Abstract: This paper examines the effect that tunnel size, depth and volume loss have on greenfield soil displacements above tunnels in sandy ground. The results of a series of plane-strain centrifuge tests ...

Performance of pile-supported embankment over soft soil: full-scale experiment.

Abstract: This paper describes a full-scale experiment of pile-supported embankments on soft soil, which is conducted within the French national research project, Amelioration des Sols par Inclusions RIgides (ASIRI), to provide a new design method. This experiment shows the great influence of a granular platform reinforced with geosynthetics in load-transfer mechanisms. The measurements of geosynthetic strains highlight that the maximum strain takes place at the vicinity of pile heads during the construction of an embankment. Measurements also show that the load-transfer behavior of a platform reinforced by a single geotextile is different from that of a platform reinforced by two geogrids, although the final settlement is the same in both sections. From the important measurement data of this full-scale experiment, some considerations on the design and the efficiency evaluation have been proposed.

Field Investigations on Performance of T-Shaped Deep Mixed Soil Cement Column–Supported Embankments over Soft Ground

Abstract: The soil cement deep mixing method has been used to improve soft clayey soils under embankment loading conditions. A compacted granular fill layer or geosynthetic reinforcement layer is placed over the top of soil cement deep mixed (DM) columns to reduce differential settlement between DM soil and the surrounding untreated soil, which, in turn, increases embankment stability. Typically, in conventional deep mixing methodology, the soil cement columns are closely spaced, indicating large area replacement ratios in the con- struction projects. Such practice could increase construction costs substantially. In this research, a new type of DM column, called a T-shaped DM (TDM) column, was designed and used as an alternative to the large-area-replacement-ratio DM columns employed in the field. Unlike in the conventional column, the cross section of the new column varies along the installation depth. Large amounts of cement slurry are injected and thoroughly mixed with the native shallow soil using specially designed mixing blades. At greater depths, deep mixing methodology is applied only to smaller-diameter columns, resulting in large-diameter columns near the surface and smaller-diameter columns deeper. Field trials were conducted to investigate the performance of TDM column-supported soft ground under embankment loading. For comparison, performance of conventional DM column-supported soft ground under similar embankment loading is presented. Differences in quality control studies and in situ plate loading tests on TDM and conventional DM columns are discussed. Under field embankment loading con- ditions, stress concentration ratio, excess pore water pressures generated in the soft clays, total monitored settlement, and lateral soil dis- placement near embankment toes are analyzed and discussed for both treatments. It is concluded that TDM columns have considerable advantages over conventional DM because they both mitigate settlement and enhance the performance of the embankments while reducing construction costs. DOI: 10.1061/(ASCE)GT.1943-5606.0000625. © 2012 American Society of Civil Engineers. CE Database subject headings: Embankments; Cement; Field tests; Pore pressure; Settlement; Soil mixing; Soft soils. Author keywords: Embankment; Cement; Field tests; Pore pressure; Settlement; Soil mixing; Soft soils.

A simplified nonlinear approach for single pile settlement analysis

Abstract: A simple analytical approach for nonlinear analysis of the load–displacement response of a single pile is presented. Two models are adopted in the proposed approach. One model uses a softening nonl...

Remedying embankment thaw settlement in a warm permafrost region with thermosyphons and crushed rock revetment

Abstract: Due to the special engineering geology characteristics of permafrost, construction in permafrost regions tends to result in serious permafrost-related engineering problems. Thaw settlement induced by permafrost degradation is the principal challenge for railway construction on the Qinghai-Tibetan Plateau. It threatens the stability and safety of the railway system, especially in warm and ice-rich permafrost regions. Thaw settlement in section DK1139+780 along the Qinghai-Tibetan railway is a potential risk to the safety of the railway, and a combination of closed thermosyphons and crushed rock revetment was used to remedy permafrost warming and thaw settlement of the embankment. Based on ground temperatures and embankment deformations observed at this site since 2002, the effects of the remedial measures were evaluated. The results show that the remedial measures lowered the ground temperature and raised the permafrost table. The crushed rock slope protection acted as an insulation layer and reduced heat ...

Trekking the Shore: Changing Coastlines and the Antiquity of Coastal Settlement

Abstract: This volume provides a sample of current archeological research exploring the importance of maritime adaptations in colonization and cultural development. It is the outgrowth of two independent symposia, one organized by Loren Davis at the 2007 annual meeting of the Society for American Archaeology and the other organized by Nuno Bicho and Jonathan Haws at the 2006 Union Internationale des Sciences Préhistoriques et Protohistoriques (UISPP) inLisbon,Portugal. The volume is comprised of 20 articles organized geographically in two parts: (a) North America and Eurasia, and (b) South America, Africa, and Oceania. Following a prologue by the editors, the first section begins with a contribution by Davis. He emphasizes the important role of the sea and ancient coastal zones in human colonization and stresses the significance of ancient habitation sites on the continental shelves submerged by post Pleistocene sea

Surface settlement caused by twin-parallel shield tunnelling in sandy cobble strata

Abstract: City metro tunnels are usually constructed as twin-parallel tunnels and their adjacent construction may lead to surface deformation, affecting the surface environment and the safety of the tunnels. Due to its strong dispersion, sandy cobble strata can be easily disturbed by shield tunneling. Based on the project of the Chengdu Metro Line 1, field and model tests were carried out to study the surface settlement caused by shield tunneling in sandy cobble strata by measuring surface settlement curves, ground loss ratios and construction influence zones. The discrete element method (DEM) was used to study the factors affecting the formation of ground arches in sandy cobble strata at the microscopic level. Results show that the shape of the surface settlement curve in sandy cobble strata is different from that in soft soil. The buried depth and clear spacing of the two tunnels had a significant impact on the formation of ground arches.

Settlement analysis of viscoelastic foundation under vertical line load using a fractional Kelvin-Voigt model

Abstract: Soil foundations exhibit significant creeping deformation, which may result in excessive settlement and failure of superstructures. Based on the theory of viscoelasticity and fractional calculus, a fractional Kelvin-Voigt model is proposed to account for the time-dependent behavior of soil foundation under vertical line load. Analytical solution of settlements in the foundation was derived using Laplace transforms. The influence of the model parameters on the time-dependent settlement is studied through a parametric study. Results indicate that the settlement-time relationship can be accurately captured by varying values of the fractional order of differential operator and the coefficient of viscosity. In comparison with the classical Kelvin-Voigt model, the fractional model can provide a more accurate prediction of long-term settlements of soil foundation. The determination of influential distance also affects the calculation of settlements.

Settlement evaluation of soft clay reinforced with stone columns using the equivalent secant modulus

Abstract: A method is proposed to evaluate settlement of soft clay reinforced with stone columns. Finite element analyses were carried out using 15-noded triangular elements with PLAXIS. A drained analysis was carried out using Mohr–Coulomb’s criterion for soft clay, stones, and sand. The stress due to column installation has been considered in the analysis. At the interface between the stone column and soft clay, interface elements have been used. The settlement ratio (SR) of the soil has been estimated using the equivalent secant modulus. The results are compared with those available in the literature, and the advantages of the numerical analysis were highlighted. Based on the results of this analysis, the SR decrease with compaction surrounding soft soil, but decrease of SR is mainly due to a stiffer column material in soft clay.

Evaluation of subsidence due to underground coal mining: an example from the Czech Republic

Abstract: This paper presents a case study dealing with variations on the ground surface due to the underground mining activities in the Ostrava–Karvina Coal District (Czech Republic) over the last 25 years. During this period, some of the areas have experienced settlements of up to 11 m. Seven settlement intervals were used to indicate the varying degrees of subsidence over time. Maps were prepared to show the spatial relationship of the subsidence and to assist in land use planning in this rapidly developing area.

Railway Tracks - Habitat Conditions, Contamination, Floristic Settlement - A Review

Abstract: Apart from roads, railways are one of the principal means of transportation. The specificity of rail transportation causes some environmental problems.

Where to settle--settlement preferences of Mytilus galloprovincialis and choice of habitat at a micro spatial scale.

Abstract: The global mussel aquaculture industry uses specialised spat catching and nursery culture ropes made of multi-filament synthetic and natural fibres to optimise settlement and retention of mussels for on-growing. However, the settlement ecology and preferences of mussels are poorly understood and only sparse information exists in a commercial context. This study quantified the settlement preferences of pediveligers and plantigrades of Mytilus galloprovincialis on increasingly complex surfaces and settlement locations at a micro spatial scale on and within ropes under commercial hatchery operating conditions using optical microscopy and X-ray micro-computed tomography (µCT). M. galloprovincialis has clear settlement preferences for more complex materials and high selectivity for settlement sites from the pediveliger through to the plantigrade stage. Pediveligers of M. galloprovincialis initially settle inside specialised culture ropes. Larger pediveligers were located close to the exterior of ropes as they increased in size over time. In contrast, smaller individuals were located deeper inside of the ropes over time. This study demonstrates that X-ray µCT is an excellent non-destructive technique for mapping settlement and attachment sites of individuals as early as one day post settlement, and quantifies the number and location of settled individuals on and within ropes as a tool to understand and optimise settlement in complex multi-dimensional materials and environments.

Settlement prediction and back analysis of Young’s modulus and dilation angle of stone columns

Abstract: Ground improvement using stone columns is one of the most suitable methods for deformation control of soft soils. The use of stone columns can improve the bearing capacity, reduce settlement, accelerate consolidation process and enhance slope stability as well as resistance to liquefaction. Settlement prediction of the ground influenced by the large stiffness difference between the columns and the surrounding soil and the induced arching is discussed in this paper. Plate load test is one of the common methods to be used for quality control of stone column reinforced ground. The test results can be used to back calculate some of the design parameters of the stone column. A finite element based procedure to estimate the Young's modulus and dilation angle of stone column material using plate load test results is proposed. The employed finite element model is axisymmetric and suitable for a cylindrical stone column. The field measurements after calibration have been in good agreement with numerical results for predicting deformations. The procedure developed in this study can be adopted by practicing engineers to estimate the Young's modulus and dilation angle of stone columns by conducting a plate load test.

New Findings from Centrifuge Modeling of Rocking Shallow Foundations in Clayey Ground

Abstract: Rocking foundations have shown performance advantages that may benefit the seismic performance of structures. Previous centrifuge tests have well characterized the behavior of rectangular rocking foundations on sand, but few results are available for clayey ground. In this study a series of centrifuge model tests of shear walls and single-degree-of-freedom (SDOF) structures with rocking foundations supported on clay of medium strength are conducted. Vertical bearing failure, slow cyclic loading, and dynamic shaking tests were performed at three different levels of centrifugal acceleration. The moment capacity, settlement, and rotation of each loaded model were tracked and then compared to previous published results. The measured moment capacity is found to match the theoretical values. The settlement vs. rotation behavior was characterized, and it is found that settlement is somewhat smaller than previous results for similar models tested on sand.

Vegetation productivity consequences of human settlement growth in the eastern United States

Abstract: In this study, we investigated the impact of human settlement growth on vegetation carbon uptake in the eastern United States between 1992/1993 and 2001. Human settlement growth was measured by changes in the density of housing units. Vegetation carbon uptake was estimated with gross primary production (GPP) based on the light-use efficiency approach applied to satellite imagery. Annual GPP was found to increase by approximately 140 g C m−2 on average for the entire study area in 2001 compared to 1992/1993, accompanied by region-wide increases in downward shortwave radiation and minimum daily temperature. Changes in GPP, however, varied significantly by different types of settlement growth. Exurbanized areas, where the rural settlement (less than 0.025 units per acre) converted to exurbs (0.025–0.6 units per acre), were associated with approximately 157 g C m−2 increase in GPP due to high vegetation proportions. Suburbanization, the conversion from exurban settlement to suburbs (0.6–4 units per acre), was related with a decline of GPP by 152 g C m−2 due to progressive development of built-up land cover. Results help to understand the potential of carbon mitigation in the human-dominated landscapes using vegetation as a natural store of carbon dioxide. This in turn has implications for the low-carbon development planning along the gradient of human settlement densities.

Study on optimized piled-raft foundations (PRF) performance with connected and non-connected piles- three case histories

Abstract: It has been realized that the raft (mat) foundations are capable of bearing very large loads when they are assisted with a pile group. The contribution of both raft and piles to carry the surcharge loads is taken into account, considering the stiffness and strength of involved elements in the system, i.e. piles, raft and surrounding soil. The piles are usually required not to ensure the overall stability of the foundation but to act as settlement reducers. There is an alternative design in which, the piles are nonconnected from the raft to reduce the settlement, which are then known to be "settlement reducer non-connected piles" to increase the system stiffness. In this paper, two and three dimensional finite element analysis of connected and non-connected pile-raft systems are performed on three case studies including a 12-storey residential building in Iran, a 39-storey twin towers in Indonesia, and the Messeturm tower, 256m high, in Frankfurt, Germany. The analyses include the investigation of the effect of different parameters, e.g. piles spacing, embedment length, piling configuration and raft thickness to optimize the design. The role of each parameter is also investigated. The parametric study results and comparison to a few field measurements indicate that by concentrating the piles in the central area of the raft foundation the optimum design with the minimum total length of piles is achieved, which is considered as control parameter for optimum design. This can be considered as a criterion for project cost efficiency. On the other hand, non-connected piled-raft systems can significantly reduce the settlements and raft internal bending moments by increasing the subsoil stratum stiffness. Finally, the comparison indicates that simple and faster 2D analysis has almost similar results to the time consuming and complicated 3D analysis.

FLAC Based Numerical Studies on Dynamic Interference of Two Nearby Embedded Machine Foundations

Abstract: This paper emphasizes on the dynamic interaction of two closely spaced embedded square or rectangular foundations under the action of machine vibration. One of the foundations is excited with a known vibration source placed on the top of it, called the active foundation. The objective is to study the effect of dynamic motion of the active foundation on the nearby passive foundation through a layered soil medium. The analysis is performed numerically by using the explicit finite difference code FLAC 3D . The soil profile is assumed to obey the Mohr–Coulomb yield criteria with non-linear failure envelope. The analysis is performed under sinusoidal dynamic loading with varying amplitude. Under the dynamic excitation, the settlement behavior of the interacting foundations is studied by varying the spacing between the foundations. In addition, the variation of vertical normal and shear stress developed beneath the interacting foundations is also explored. The present theoretical investigation indicates that the settlement and vertical normal stress below the active foundation is generally found to be higher than that obtained for the passive foundation, whereas the shear stress response below the foundations follows the reverse trend.

Bearing capacity and settlement of strip footing on geosynthetic reinforced clayey slopes

Abstract: 在忍受在 georeinforced 上放松粘土似的斜坡的长带地位的能力上增强的 geosynthetic 的效果被调查。用长带地位在之上上的有限元素分析的一系列数字学习的结果增强并且 unreinforced 粘土似的斜坡被介绍。这个工作的目的到：1 ) 在长带地位的熊能力上决定加强的影响邻近的斜坡， 2 ) 建议加强的一个最佳数字并且 3 ) 在 geogrids 增强的粘土似的土壤调查磨擦角度的效果。调查被从斜坡改变地位的边距离执行。geosynthetic 层的另外不同的数字被用于获得最大的适用能力和最小的解决。完成第三个目的，二个不同磨擦角度被使用。结果证明负担解决行为和地位的最终的适用能力能被增强层的包括更加改进。但是使用超过一层加强，最终的适用能力不更加变化。它也被看那为增强并且 unreinforced 斜坡，有边距离的增加的适用的能力增加。另外，当土壤磨擦角度被增加，增强的效率减少。

Predicting Leakage-induced Settlement of Shield tunnels in Saturated Clay

Abstract: This paper suggests a new set of analytical solutions for predicting leakage-induced seepage field and ground settlement in saturated clay. A unique feature of the solutions presented is considering the effect of the tunnel lining through the relative permeability between the tunnel and the soil. Through the superposition method, the proposed method can be easily extended to twin parallel tunnels. The accuracy of the analytical solutions are verified with numerical simulations. Parametric studies reveal that the decrease of pore pressure and the consequent settlements of ground and tunnel is proportional to the relative permeability. Over 20% of the initial hydrostatic pore pressure will dissipate when the relative permeability exceeds 0.01. The pore pressure decreases more significantly within the zone of 1.3D above the tunnel crown, 2.5D underneath the tunnel invert and 2.0D from the tunnel springline horizontally when the relative permeability is less than 0.01. Consequently, 62% of the total settlement of the ground occurs within this zone, which is called the main compression zone. It also shows that the tunnel leakage will result in very significant tunnel settlement because 78% of the total settlement occurs in the ground underlying the shield tunnel. Thus, the mechanism of the leakage-induced settlements of the ground and the tunnel can then be explained. For a typical shield tunnel in Shanghai, the leakage-induced settlement accounts for 1/6 of the total post-construction settlement.