Showing papers on "Settlement (structural) published in 2016"

Ground Response to Multiple Parallel Microtunneling Operations in Cemented Silty Clay and Sand

Abstract: This paper presents a case history of the successful application of observational method to instruction microtunneling with successive pipe-jacking. The microtunneling project is the construction of four parallel pipes under Guan River in Jiangsu, China. Four parallel tunnels with external diameter of 4,160 mm and horizontally spaced at 4.8 m apart were jacked over 450 m in cemented silty clay and sand by two slurry-balance microtunnel boring machines (MTBM) at a depth of 4.6 m under the river bed. Since the overburden soil is very thin, proper control of tunneling operations was of utmost importance for maintaining the stability of the river bed. In order to optimize the operation parameters prior to construction under the river bed, a field trial was conducted, which included measurement of ground surface settlement, subsurface settlement, and lateral displacement of the subsurface soils, as well as excess pore water pressure and earth pressure. The relationship between ground response and const...

Numerical and Centrifuge Modeling of Seismic Soil–Foundation–Structure Interaction on Liquefiable Ground

Abstract: The effective mitigation of the liquefaction hazard requires an improved understanding of the consequences of liquefaction in terms of ground shaking, permanent displacement, and building performance. In this paper, results from centrifuge experiments of a shallow-founded structure on liquefiable sand are used to evaluate the predictive capabilities of a state-of-the-art numerical tool. Solid-fluid, fully-coupled 3D nonlinear numerical simulations were performed using the PDMY02 soil model implemented in a software modeling domain. The numerical model captured excess pore pressures and accelerations well in the free-field, but largely underestimated volumetric settlements due to loss of water during shaking. This was associated with the drastic increase in soil hydraulic conductivity when approaching liquefaction, which was not taken into account numerically, as well as the underestimation of soil volumetric compressibility. The contribution of volumetric strains to total building settlement was, ...

Seismic Performance of Shallow Founded Structures on Liquefiable Ground: Validation of Numerical Simulations Using Centrifuge Experiments

Abstract: The results of fully coupled, three-dimensional (3D), nonlinear finite-element analyses of structures founded on liquefiable soils are compared with centrifuge experiments. The goal is to provide insight into the numerical model’s capabilities in predicting the key engineering demand parameters that control building performance on softened ground for a range of structures, soil profiles, and ground motions. Experimental and numerical observations will also guide future analyses and mitigation decisions. The numerical model captured excess pore pressures and accelerations, the dominant displacement mechanisms under the foundation, and therefore building’s settlement, tilt, and interstory drift. Both experimental and numerical results showed that increasing the structure’s contact pressure and height/width (H/B) ratio generally reduces net excess pore pressure ratios in soil but amplifies the structure’s tilting tendencies and total drift. The settlement response of a structure with a greater pressu...

Mechanical behaviour of a small-scale energy pile in saturated clay

Abstract: The mechanical behaviour of an energy pile in saturated clay under thermo-mechanical loading was studied using a model pile. Axial load was first applied to the pile head in steps to determine the resistance of the pile under mechanical load. Afterwards, thermo-mechanical tests were performed by applying a heating/cooling cycle to the pile under constant axial load. The results show pile head heave during heating and settlement during cooling. Irreversible settlement was observed after the thermal cycles. Tests performed with various axial loads show that the thermal irreversible settlement is greater under a higher axial load.

Pile-Soil Interaction and Settlement Effects Induced by Deep Excavations

Abstract: Deep excavations may cause settlement and damage to adjacent buildings, even if they are found on piles. The corresponding pile deformations are determined by axial and lateral effects. This paper describes an analytical model relating axial pile deformation to the vertical soil displacement resulting from the deep excavation and also suggests ways to determine the pile response to lateral displacements. The axial pile-soil interaction is clearly different for end-bearing and friction piles. Common generalizations that end-bearing piles settle the same as the soil settlement at the base level and friction piles with the ground surface settlement present lower and upper bounds, which are only valid for certain idealized cases. The settlement of piles with a large component of shaft friction is determined mainly by the actual load on the pile relative to the pile ultimate capacity. The lateral pile response is governed mainly by the relative stiffness of the pile to the soil. The proposed model was ...

Jointed pipeline response to tunneling-induced ground deformation1

Abstract: This paper focuses on the effect of tunneling-induced ground deformation on the response of jointed cast iron and ductile iron pipelines that (i) cross the settlement profile perpendicular to the t...

Differential Settlement and Induced Structural Damage in a Cut-and-Cover Subway Tunnel in a Soft Deposit

Abstract: This study investigated the differential settlement and induced structural damage in the west extension of Nanjing Metro Line 1. The minimum and maximum cumulative settlements measured over the course of four years of operation were 1 mm and 122 mm, respectively. Four settlement troughs in the longitudinal direction of the line, as well as a periodic variation of differential settlement between the stations and the tunnel, were observed. Approximately 10% of the vertical radius of curvature of the line violates the safety limit of 15,000 m, and three typical kinds of cracks (i.e., transverse cracks in the tunnel roof and in the track bed, and inclined cracks in the outer wall) and leakage have occurred. The differential settlement of the line was mainly caused by the nonuniform distribution of underlying soft soil. The periodic variation of differential settlement between the stations and tunnel was attributed to the structural characteristics and the seasonal variation in the groundwater level. T...

A Laboratory Investigation to Assess the Functioning of Railway Ballast with and without Geogrids

Abstract: Understanding the complex load transfer mechanism and the subsequent accumulation of deformation in ballast and subballast layers under repeated wheel loading is essential to design resilient rail tracks. Large-scale cyclic tests have been conducted on railroad ballast instrumented with optical based fibre Bragg grating (FBG) sensors, LVDTs, pressure plates and the settlement pegs to explore the role of geogrid and its interaction with ballast in improving the track performance. Latite basalt and geogrids with different aperture sizes were used for the investigations. The laboratory experimental results indicate that the geogrid inclusions enhance track performance by arresting the lateral spreading of ballast and thereby significantly reducing the extent of its vertical settlement. In contrast, the reinforcement of ballast with geogrid has only a marginal effect on reducing the settlement in the subballast layer. The results also show that geogrid minimises the amount of particle breakage, the effectiveness of which is governed by its placement position, with lowest breakage occurring when the geogrid is placed at a location 130 mm above the subballast. In addition, geogrids also reduce the extent of vertical stress in the subgrade soil. The laboratory test results establish beyond doubt the effectiveness of FBG sensing system in capturing the ballast movement under cyclic loading.

Long-Term Settlement of Buildings Erected on Driven Cast-In-Situ Piles in Loess Soil

Abstract: Results are presented for long-term geodetic observations of the settlement of residential buildings erected on driven cast-in-situ piles that are part of foundation frames on loess soil. Stabilized deformations of building foundation beds are compared to the results of analysis using normative methods and simulation of the stress-strain state of the system using two- and three-dimensional versions of the finite element method and a plasticelastic soil model.

Settlement Analysis of Saturated Tailings Dam Treated by CFG Pile Composite Foundation

Abstract: Cement fly ash gravel (CFG) pile composite foundation is an effective and economic foundation treatment approach, which is significant to building foundation, subgrade construction, and so forth. The present paper aims at investigating the settlement behaviors of saturated tailings dam soft ground under CFG pile composite foundation treatment, in which FEM and laboratory model test were utilized. The proposed findings demonstrate that CFG pile treatment is effective in reinforcing saturated tailings dam and loading has little influence on settlement of soil between piles. The variation of soil between piles settlement in FEM has a good agreement with the laboratory model test. Additionally, the cushion deformation modulus has a small effect on the composite foundation settlement, although the cushion thickness will generate certain influence on the settlement distribution of the composite foundation.

Centrifuge and Numerical Models to Investigate Liquefaction-Induced Response of Shallow Foundations with Different Contact Pressures

Abstract: Currently, there is no reliable design procedure which considers all aspects of liquefaction effects on shallow foundations. There are many light and heavy structures resting on saturated sand with high liquefaction potential in seismic areas. The aim of this experimental and numerical study is to evaluate the performance of two shallow foundations with different contact pressures in liquefaction. The results of the centrifuge experiment of shallow foundations with surcharges of three-story and nine-story buildings on liquefiable sand are presented in detail. Although entire soil profile is liquefied, no liquefaction is observed under the foundations. There is a clear difference in settlement mechanisms observed beneath the shallow foundation and in the free-field. The heavy foundation fluctuated more strongly compared with the lighter one. The effect of soil permeability and contact pressure on foundation response is investigated during numerical study. Subsequently, the experiment is simulated two dimensionally using a fully coupled nonlinear constitutive model (UBCSAND) implemented in a finite-difference program, FLAC-2D. The results show that settlement of foundations increased with the increase of soil permeability. Trends of excess pore water pressure are captured reasonably by the soil model, but the settlement mechanisms are different. The soil model underestimates total liquefaction-induced settlement of shallow foundation, especially for light foundation.

Radar interferometry based settlement monitoring in tunnelling: Visualisation and accuracy analyses

Abstract: The accurate, efficient and economical monitoring of settlements caused by tunnel boring machines, especially in regions of particular interest such as critical inner city areas, has become an important aspect of the tunnelling operation. Besides conventional terrestrial based methods to capture settlements, satellite based techniques that can accurately determine displacements remotely, are increasingly being used to augment standard terrestrial measurements. However, not much attention has been paid to analyse the accuracy of satellite based measurement data. In addition, there is also a lack of studies on how to visualise the resulting huge amount of data in the context of both the tunnel advancement and the existing building infrastructure. This paper introduces the basics of settlement monitoring using radar interferometry methods, in particular showing the results obtained by processing radar images from the TerraSAR-X satellite to monitor a downtown construction site in Dusseldorf, Germany, where a new underground line (“Wehrhahn-Linie”) is being built. By comparing terrestrial measurements with remote satellite based settlement data in temporal and spatial corridors, the accuracy of the radar interferometry method is shown. Moreover, a 4D visualisation concept is presented that correlates satellite and terrestrial based settlement data correlated with above-ground buildings and boring machine performance parameters within a Virtual Reality (VR) environment. By comparing up to 23,000 pairs of satellite and terrestrial based settlement data points of a real tunnelling project an accuracy of about ±1.5 mm in the measurement of deformation using the method of radar interferometry in urban areas can be stated. In addition, providing a visual analysis of data sources within a VR environment, the accuracy of terrestrial and satellite-based measurements can be visualised in different time steps. Sources of error that affect the degree of accuracy, such as atmospheric conditions, systematic errors in the evaluation of radar images and local events in the spatial corridor, can be quantified. In addition, the 4D visualisation can help reveal direct interdependencies between settlement data and boring machine performance data. The Persistent Scatterer Interferometry (PSI) based on high resolution radar images of the TerraSAR-X satellite, in combination with conventional ground-based terrestrial measurements, provides a new settlement monitoring approach in tunnelling. For example, due to minimized surveying works and disruptions of construction activities on site and due to the large settlement area coming with a high magnitude of settlement data points, this combined monitoring approach is very practical and economical. Moreover, by visualizing the settlement data properly, the risk of damage of surface structures can be analysed and understood more precisely, which increases the safety of underground works.

Effect of Footing Shape and Embedment on the Settlement, Recentering, and Energy Dissipation of Shallow Footings Subjected to Rocking

Abstract: From results of a recent series of centrifuge model tests, this paper investigates the effects of shape and embedment on the performance of rocking footings. Rectangular and H-shaped footin...

An investigation of subgrade differential settlement on the dynamic response of the vehicle–track system

Abstract: The construction of non-ballasted slab railway track on existing subgrade soils, or on embankments, is at an early stage of development on Chinese railways. Developing appropriate standards for the...