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Development and Redevelopment
Published in F.G.H. Blyth, M. H. de Freitas, A Geology for Engineers, 2017
F.G.H. Blyth, M. H. de Freitas
The intensity of loading that causes shear failure to occur beneath a foundation is termed the bearing capacity of the ground. This capacity is governed by the fabric of the rocks and soils beneath a foundation and by the reaction of this fabric to changes in effective stress. Such changes will accompany periods of construction that change the total stress on the ground and are described in Chapter 9. Thus the behaviour of a soft to firm compressible clay will not only be that of an inherently weak sediment but also that of an undrained material: the clay will have a low bearing capacity. A hard boulder clay will be stronger and have a higher bearing capacity, but will also behave as an undrained material. Dense deposits of sand and gravel have their particles packed closely together yet retain a permeability that is sufficient to readily dissipate any increase in pore pressure that may accompany an increase in total stress. These sediments can have a high bearing capacity and behave as a drained material. Loose sands and gravels have an open texture and a lower bearing capacity than their denser varieties. Strong rocks have a saturated strength that exceeds the safe working stress of concrete (around 4000 kNm-2) and are therefore not loaded to their bearing capacity. But even strong rocks contain weak surfaces, such as joints and soft horizons interbedded with stronger strata, and the load from a large foundation can cause movement to occur along these planes. The bearing capacity of weak rocks, especially porous sedimentary rocks and weathered igneous and metamorphic rocks, can be exceeded by foundation loads from structures of moderate size.
Fill materials
Published in A.A. Balkema, Building on Soft Soils, 2017
Boulder clay is material produced during the penultimate Ice Age from glaciers; it consists of a mixture of clay, silt, sand, gravel, stones, cobbles and boulders. The most prevalent boulder clay has a sand content of 60–70% and according to NEN 5104 [6.24] must be classified as slightly to moderately sandy clay. General indications about a number of relevant properties of boulder clay are listed in Table 6.7. The plastic properties, in particular, appear to show comparatively large disparities which are probably ascribable to differences in mineralogical composition or site.
Investigation of the interaction of the construction of building S1 on underlying Thameslink
Published in Geomechanics and Geoengineering, 2021
Jonathan Foster, Chrysothemis Paraskevopoulou, Richard Miller
Figure 19 shows the total displacements of the northbound tunnel’s crown at each stage of construction. The increased stiffness parameters of the Dublin Boulder Clay (DBC) shows a clear and expected decrease in tunnel displacement from the London Clay (LC) at the excavation stage and the reverse is seen for the Shanghai Clay. Each of the soil types shows similar trends but at different scales. The LC and DBC both show similar total displacements between stages 5 and 12 when the ground has been unloaded and reloaded previously. In contrast with the monitoring data, the DBC shows a better prediction than the LC. This is particularly evident with the predicted settlement at the pile installation Phase (2–3). It should be noted that this is not a recommendation to use stiffer parameters than what is observed from laboratory testing, as that is counter-intuitive to the philosophy of numerical modelling. The implications of these observations are that significant changes in the soil’s parameters are needed to replicate realistic behaviour of the soil within finite element software.
Influence of groundwater level fluctuation on lateral deformation of cantilever enclosure structure of pit-in-pit
Published in Marine Georesources & Geotechnology, 2020
Yuke Wang, Bin Li, Can Chen, Heyang Jia
In the past decades, there are many studies on the subject of wall and ground movements associated with deep excavation. Clough (1969) was among the first to use the finite element (FE) method in the analysis of excavation, and then the soil deformation and wall deflections were studied by many researchers with using FE method (Finno and Harahap 1991; Finno, Blackburn, and Roboski 2007; Gourvenec and Powrie 2000; Ng, Leung, and Lau 2004; Ou, Chiou, and Wu 1996; Orazalin, Whittle, and Olsen 2015; Hsieh et al. 2015; Hsiung et al. 2016). FE analysis could estimate the wall deflections of excavations by simulating complex construction steps. Among the walls, cantilever walls are ideal solution for temporary or permanent excavation works. The excavation area can be kept free of internal struts, then the construction process can be continued easily. Long et al. (2012) suggested that cantilever walls of 7.5 m high have been successfully constructed in Dublin boulder clay. Such walls showed smaller movements than expected. Parametric study were performed considering excavation depth, pile embedded depth, and wall stiffness. However, cantilever walls used in pit-in-pit have not been considered in the previous studies.
Evaluation for intrinsic compressibility of reconstituted clay using liquid limit, initial water content and plasticity index
Published in European Journal of Environmental and Civil Engineering, 2019
Ming-Zhi Zhao, Qiang Luo, Ming Wei, Liang-Wei Jiang
Comparisons of predicted compression curves and measured ones for (a) two Lianyungang clay samples at w0 = 2.0wL and w0 = .7wL, respectively; (b) two Baimahu clay samples at w0 = 2.0wL and w0 = .7wL, respectively; (c) two Lianyungang clay samples at w0 = 1.5wL and w0 = wL, respectively; (d) two Wuqing clay samples at w0 = .8wL and w0 = 1.4wL, respectively; (e) two Zhuozi clay samples at w0 = .8wL and w0 = 1.4wL, respectively; (f) two Boston Blue clay samples at w0 = 1.75wL and w0 = wL, respectively; (g) Severn R. alluvium clay and Boulder clay at w0 = wL; (h) Red earth and Glacial silty clay at w0 = wL.