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Foundation analysis and design
01 Jan 1968-
TL;DR: In this paper, Fondation de soutenagement et al. presented a reference record for Dimensionnement Reference Record created on 2004-09-07, modified on 2016-08-08.
Abstract: Keywords: Fondation ; Mur de soutenement ; Pieux ; Capacite portante ; Ancrage ; Dimensionnement Reference Record created on 2004-09-07, modified on 2016-08-08
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TL;DR: In this article, the influence of different geotechnical characteristics of compacted clays of wide plasticity range on the compaction induced yield stress, and also to develop the correlational models to quickly predict the yield stress.
Abstract: Artificial compaction is a commonly practiced ground improvement technique around the world. Yield stress is an important parameter to quantify and analyze the strength and compressibility behavior of the artificially compacted clays; such materials are indeed of practical significance in various projects, e.g., engineered landfills, clay liners, etc. The present study aims to investigate the influence of different geotechnical characteristics of compacted clays of wide plasticity range on the compaction induced yield stress, and also to develop the correlational models to quickly predict the yield stress. Three natural clayey soil samples of different geotechnical properties were collected from different sites; 27 more samples of varying index properties were prepared by mixing bentonite with natural soil samples at varying rates. Series of one-dimensional consolidation tests were performed to determine compressibility parameters like yield stress, compression index, and coefficient of volume compressibility. Atterberg’s limits, grain size, compaction characteristics, and compressibility have a significant influence on the compaction induced yield stress. Predictive models of yield stress are also developed by using the plasticity index, optimum water content, and maximum dry unit weight as independent variables. Moreover, developed models are validated based on the independent data.
22 citations
TL;DR: In this article, the authors examined the effect of dynamic soil structure interaction (DSSI) on the distribution of forces at various elements of the pile foundation and supported structure and showed significant change in response at different elements of piled raft supported structure when DSSI effects are considered.
Abstract: Traditionally seismic design of structures supported on piled raft foundation is performed by considering fixed base conditions, while the pile head is also considered to be fixed for the design of the pile foundation. Major drawback of this assumption is that it cannot capture soil-foundation-structure interaction due to flexibility of soil or the inertial interaction involving heavy foundation masses. Previous studies on this subject addressed mainly the intricacy in modelling of dynamic soil structure interaction (DSSI) but not the implication of such interaction on the distribution of forces at various elements of the pile foundation and supported structure. A recent numerical study by the authors showed significant change in response at different elements of the piled raft supported structure when DSSI effects are considered. The present study is a limited attempt in this direction, and it examines such observations through shake table tests. The effect of DSSI is examined by comparing dynamic responses from fixed base scaled down model structures and the overall systems. This study indicates the possibility of significant underestimation in design forces for both the column and pile if designed under fixed base assumption. Such underestimation in the design forces may have serious implication in the design of a foundation or structural element.
22 citations
Cites background or methods from "Foundation analysis and design"
...A conservative design of the pile groups is made with an assumption of shear strength (su) and Young’s modulus (Es) of 0.98 kN/m 2 and 2500 kN/m2 (based on the correlation available in Bowles (1997), respectively, for the homogenous, very soft clay layer....
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...Assuming a Poisson’s ratio of 0.35 for saturated clay (Bowles, 1997), the estimated value of Es is 4550 kN/m 2....
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...…value for known PI and OCR values, as follows: For su = 2.5 kN/m 2, PI = 24 and IR = 700 considering OCR = 1.0 (i.e. normally consolidated clay), Gmax = su × IR = 2.5 × 700 = 1750 kN/m 2 (4) The value of Es is estimated as (Bowles, 1997), s max 2 (1 )E G (5) where is Poisson’s ratio of clay....
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...35 for saturated clay (Bowles, 1997), the estimated value of Es is 4550 kN/m 2....
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TL;DR: In this paper, the authors investigated the influence of soil suction on subgrade behavior with measurements made using the filter paper technique, whilst subgrade modulus was measured using the plate load test.
Abstract: Railway track is constructed on compacted soil which is, characteristically, unsaturated. The performance of the subgrade, both in the short- and long-term, is dependent on environmental factors, in particular, an increase in subgrade moisture content due to high rainfall can result in subgrade distress or shear failure under cyclic loading (i.e. train passage). Furthermore, due to varying climatic conditions, subgrade soil may fluctuate between a saturated and unsaturated condition. It is necessary, therefore, to understand such soil behaviour to ensure a safe and economical design and in the planning of maintenance work. Previous research has focused on the effect of water on the superstructure, but not the substructure. This paper outlines a full-scale testing programme to study track performance after flooding and, subsequently, during a 2, 4 and 6 week recovery (drying) period. The study investigated the influence of soil suction on subgrade behaviour with measurements made using the filter paper technique, whilst subgrade modulus was measured using the plate load test. The results show that subgrade behaviour is influenced by changes in water content associated with soil suction; particularly, when wetted from a dry state. It is also found that tamping is less effective in the presence of wet/low-stiffness subgrade soil.
22 citations
TL;DR: In this paper, two variants for modeling pipe, a beam model and a beam-shell hybrid model, were examined and a suitable boundary condition was introduced at the ends of the system to simulate the far field.
Abstract: A buried pipe extends over long distances and passes through soils with different properties. In the event of an earthquake, the same pipe experiences a variable ground motion along its length. At bends, geometrically a more complicated problem exists where seismic waves propagating in a certain direction affect pipe before and after bend differently. Studying these different effects is the subject of this paper. Two variants for modeling of pipe, a beam model and a beam-shell hybrid model are examined. The surrounding soil is modeled with the conventional springs in both models. A suitable boundary condition is introduced at the ends of the system to simulate the far field. Effects of angle of incidence in the horizontal and vertical planes, angle of pipe bend, soil type, diameter to thickness ratio, and burial depth ratio on pipe strains at bend are examined thoroughly. It is concluded that extensional strains are highest at bends and these strains increase with the angle of incidence with the vertical axis. The pipe strains attain their peaks when pipe bend is around $$135^{\circ }$$
and exceed the elastic limit in certain cases especially in stiffer soils, but remain below the rupture limit. Then equations for predicting the seismic response of the buried pipe at bend are developed using the analytical data calculated above and regression analysis. It is shown that these semi-analytical equations predict the response with very good accuracy saving much time and effort.
22 citations
Journal Article•
TL;DR: A literature survey was conducted and fracture influences on engineering behavior of glacial till are summarized, specifically with regard to saturated hydraulic conductivity, consolidation potential, and shear strength as mentioned in this paper.
Abstract: A literature survey was conducted and fracture influences on engineering behavior of glacial till are summarized, specifically with regard to saturated hydraulic conductivity, consolidation potential, and shear strength. Saturated hydraulic conductivity is increased by fractures, in some cases by two or more orders of magnitude. This in turn results in larger values for the coefficient of consolidation, cv, governing the rate of consolidation. A larger cv corresponds to faster settlement. Modest increases in total settlement occur only if fractures are open. Fractures also have the overall effect of reducing shear strength. Upon removal of surface material by excavation or erosion, stress release and water infiltration lead to further decreases in shear strength. This strength loss process, called softening, is due mostly to a decrease in effective cohesion and usually takes years to complete. Once failure occurs, there is another substantial drop in shear strength to a residual value. This residual strength is a result of realignment of particles along the failure plane during shear, which decreases the effective angle of internal friction. The fracture impact magnitude on glacial till saturated hydraulic conductivity, consolidation potential, and shear strength is determined largely by aperture and spacing characteristics. As the number and/or size of fractures increase, changes in these geotechnical properties become more pronounced. OHIO J SCI 100 (3/4):63-72, 2000 INTRODUCTION Greater than 30% of the Earth's land surface was covered by glaciers during the Pleistocene Epoch. Sediments deposited by glacial processes cover large areas of North America, Europe, and Asia. Till is the geologic term most frequently used in reference to these sedimentary deposits. Fractures of one form or another have been observed within tills from around the world. These fractures substantially influence the bulk hydraulic and mechanical behavior of this material. Within Ohio, fractured glacial tills are particularly common, and as a consequence, their geotechnical properties need to be carefully considered in design and before initiation of many construction projects, including landfills, open channels, building foundations, and roadway embankments to list a few. Classification of Glacial Till Glacial till classification is generally based on mode of deposition. Basal till, also referred to as lodgement till, is deposited in the subglacial environment beneath the ice sheet. Two mechanisms have been proposed for release of sediment found in basal till: 1) a \"plastering on\" effect and 2) melting of debris-rich ice along the base of the glacier (Milligan 1976; Edil and Mickelson 1995; Benn and Evans 1998). Ablation tills are compromised of material accumulated in the supraglacial environment on the top of the ice and later deposited during melting associated with glacial retreat. Basal and ablation tills are both poorly sorted and commonly include grain sizes ranging from clay to gravel. Supraglacial environments typically contain an abundance of water capable of washing, transporting, and redepositing 'Manuscript received 8 June 1999 and in revised form 20 December 1999 (#99-15). sediment. This glacial material, called flow till, tends to be much better sorted than either basal or ablation tills (Benn and Evans 1998). Fracture Formation Listed below are some of the natural mechanisms by which fractures (also known as joints, fissures, cracks, and so forth) are produced within glacial till (Boulton 1976; Kirkaldie and Talbot 1992): 1) vertical stress release caused by overburden reduction, 2) horizontal tensional stresses resulting from isostatic crustal rebound, 3) contraction from freezing, 4) shrinkage due to drying, and 5) induced failure from applied shear forces. Sediment erosion along with removal or thinning of the glacial ice sheet are two ways to reduce overburden, thereby diminishing vertical stress and in turn producing horizontal fractures. Surficial, horizontally oriented tension stresses, resulting from isostatic crustal rebound, are most likely to generate vertical joints. Freezing and drying processes induce contraction, forming vertical fractures that exhibit a polygonal pattern in plan view. Till shrinkage due to drying can be caused by climate change and/or lowering of the water table. Horizontal ice flow generates substantial shear stress within the rock and sediment material beneath the glacier. If the ice flow induced shear stress exceeds rock/sediment shear strength, fractures are formed. The orientation of these fractures can be either vertical or sub-horizontal. OBJECTIVES AND PURPOSE This paper was written with the goal of providing a compilation of previous research conducted on fractured glacial till geotechnical properties. To accomplish this 64 FRACTURED TILL GEOTECHNICAL PROPERTIES VOL. 100 task, an exhaustive literature search was conducted. Sources derived from books, journal articles, and conference proceedings came from a number of different disciplines including civil engineering, geology, and soil science. RESULTS AND DISCUSSION Fractures can substantially influence the hydraulic and mechanical behavior of glacial till. Some of the characteristics most affected include hydraulic conductivity, consolidation potential, and shear strength. Construction projects within areas covered by glacial till often require careful consideration of fracture-induced changes in these soil characteristics. Perloff and Baron (1976) define soil in the engineering sense as all uncemented accumulations of solid particles produced by mechanical or chemical disintegration of rocks. The following three subsections provide a general discussion regarding fracture influence on glacial till hydraulic conductivity, consolidation potential, and shear strength. Saturated Hydraulic Conductivity The saturated flow of water through a porous material, such as glacial till, is governed by Darcy's law:
22 citations