A conceptual model for loess in England: Principles and applications

PTD, an acronym for Provenance - Transport - Deposition, is a multilayer geomorphotechnical system, the combination of geomorphology, Quaternary Sciences, and geotechnical consequences of its implementation in groundworks and other crosscutting disciplines. Embedded in its three layers are geographical, geochemical, geophysical, mineralogy, dating, lithological and geotechnical inputs. In this state-of-the-art review contribution and for Loess in England, Syngenetic and Epigenetic mechanisms are drawn out and used to generate the three constitutive layers for three conceptual PTD models and the interrelationships among them. The developed models are then deployed to inform earthworks design for three HS2 embankments in Chiltern Hills

Stabilisation of peat with colloidal nano and micro silica

Peat occurs abundantly in wetlands across Iran, particularly around the disappearing Urmia Lake. Conventional chemical stabilisation has been widely used to tackle the high compressibility and shrinkage potential of peat. Whilst effective, this generally reduces the carbon storage capacity of peat. Exotic stabilisers such as nano-silica (NS) have been shown to be relatively less harmful and without any direct environmental risk. NS has proved effective in improving the mechanical properties (to some extent) and pH-dependent natural structure of peat, but is commercially nonviable. This article presents findings from an experimental study of Urmia Lake peat stabilised with composites of NS and cheaper micro-silica (MS). Unconfined compressive strength (UCS) and California Bearing Ratio (CBR) tests were conducted on untreated and treated compacted natural peat soil samples after 7, 14 and 28 days of curing. Nano-silica was varied from 3 % to 9 % (by dry mass) in 3 % increments and micro-silica was varied from 6 % to 24 % (by dry mass) in 6 % increments. The observations are explained in terms of micro-scale events using XRF spectroscopy and SEM imaging. The findings suggest that the UCS of peat can be increased by administration of NS-MS composites, and the effectiveness is dependent on the relative content and particle size of NS and MS. The UCS and elasticity modulus increase with curing time. As manifested in the CBR results, administration of the composites improves the bearing capacity of peat and transforms it into a sub-base with suitable engineering functions whilst safeguarding its ecosystem service provisions

Anisotropy in Sand–Fibre Composites and Undrained Stress–Strain Implications

Among the plethora of studies on anisotropy in fibre-reinforced sands, there exist conflicting views on effects on the steady-state deformations of initial packing. These conflicting views are further confused by strictly limited experimental evidence on flow in complex loading environments where the principal stresses rotate whereby shearing and torsional stresses combine, and when extension in soil relieves the compressive stresses. In the heuristic of intrinsically anisotropic nature of the soil and in recognition of the inability of placement methods to overcome such anisotropy, this paper aims to use the orientation of principal stress and soil initial packing state combined as proxy parameters to further the knowledge of plastic behaviour in fibre-reinforced sands. This study furthers the knowledge of the dependency of steady states on anisotropy in composite geomaterials. In doing so, the direction of principal stress orientation is varied from 15° to 60° (from vertical axis), taking an intermediate principal stress ratio of 0.5 and 1.0 and two initial confining pressures. Twenty-four undrained torsional shear tests are conducted using a hollow cylindrical torsional shear apparatus. Under compression and plain strain conditions, torsional stresses limit the improvements in soils’ undrained shear strength upon fibre reinforcement. Extension in soil remarkably increases fibres’ contribution to betterment of undrained strength. Fibres are least effective under low isotropic confining pressures and also for certain ranges of torsional stresses

Hepatobiliary scintigraphy with SPET in the diagnosis of bronchobiliary fistula due to a hydatid cyst

In this report, we present the application of hepatobiliary scintigraphy using Tc-99m mebrofenin in the diagnosis of bronchobiliary fistula caused by a liver hydatid cyst, which penetrated the diaphragm. Hepatobiliary scintigraphy noticeably depicted the leakage of the tracer from the biliary system of the liver to the bronchial tree. Hepatobiliary scintigraphy stands as a robust modality in the accurate diagnosis and treatment planning of bronchobiliary fistulas. © 2015, P.Ziti and Co. All rights reserved

Stabilisation of peat with colloidal nanosilica

Colloidal nanosilica hydrosols are electrochemically stabilised polymerised amorphous silica in low viscosity suspensions. They have no known adverse impact on soil health and ecosystem service functions, thereby having a scope for use in groundworks as an alternative low-viscose stabilising material. Six grades of colloidal nanosilica are synthesised through an in-house procedure and introduced to a natural peat soil. The peak and residual compressive strength of compacted and modified soils are measured immediately after treatment and in four strain levels post treatment. Findings suggest that, despite the direct correlation between the nanosilica content and compressive strength, an increase in nanosilica content does not necessarily offer stability at larger strains. This is a major limitation. The particle-level kinematics in modified peat is discussed to gain a new insight into the role played by silica flocs on the build-up of macro-mechanical quantities such as peak and critical state strength. Overall, modification of peat with nanosilica leads to improvements in strength and formation of composites with generally more dilative behaviour. When used as a single stabiliser, a design 15 % to 20 % grade nanosilica solution yields a reasonably high strength although precautions against excessive straining of modified peat soils need to be taken in the first seven days post treatment. At this optimum grade, the loss of strength on further straining is capped to 9 % at plastic strains 1.5 times the peak strain

Shear Strength in Terms of Coulomb C-Intercept

Foundation design is conventionally practiced by deriving the allowable bearing capacity in terms of shear strength and compressibility. Shear strength refers to the individual or combined contribution of drained angle of internal friction and undrained cohesion, at one of the three instances of peak (failure), residual, or critical (softened) states. Compressibility refers to the elastic and consolidation settlements; the predominance of which is a factor of soil permeability. Soil is conventionally examined by confined stressing on the wet stress-state surface, for the coefficient of volume compressibility to be determined. Ultimate bearing capacity is then reduced to a certain total settlement, and an arbitrary factor of safety of 3 is finally applied to cover uncertainties. Such a conservative approach however does not always successfully restrict the settlements beneath foundation. Although the shear strength has become a muchpracticed subject, there has been a certain lack of emphasis on a fundamental understanding of shear strength parameters, and even greater neglect of the correct choice of stress path for individual soil types so to derive such parameters in the most critical stress-hydraulic environment. For that reason, this work aims to critically review the shear strength literature for a better understanding of the internal angle of friction and c-intercept