The use of structural asphalt layers inside ballasted railway tracks is attractive because it can increase track bending stiffness. Therefore, for the first time, this paper investigates the long-term settlement characteristics of asphaltic track in the presence of a subgrade stiffness transition zone. Phased load cyclic compression laboratory tests are performed on a large-scale hybrid asphaltballast track, supported by subgrade with varying stiffness. It is found that an asphaltic layer acts as a bridge to shield the subgrade from high stresses. It is also found that the asphalt reduces track settlement, and is particularly effective when subgrade stiffness is low.

This work describes a series of novel experimental tests to determine the potential of geogrids to confine granular layers within ballasted railway lines operating at speeds close to critical velocity. This is important because at low train speeds, vertical stresses are dominant, but when approaching critical velocity conditions, dynamic horizontal stress levels are magnified. Therefore the majority of previous geogrid investigations have been performed assuming constant horizontal stress levels, thus making them more relevant for lower speed lines. To investigate settlement under high relative train speeds, ballasted railway track samples were subject to combined vertical-horizontal cyclic loading. Three areas were explored: 1) the performance benefit from placing geogrid at the ballastsubballast interface, 2) the performance benefit from placing geogrid at the subballast-subgrade interface, 3) the effect of subgrade stiffness on geogrid performance at the subballast-subgrade interface. Testing was performed using a unique large-scale true triaxial apparatus which had the ability to vary stress levels in three Cartesian directions. Compared to the control conditions, the geogrid offered a settlement improvement of approximately 35% when placed at the ballastsubballast interface, and 10-15% when placed at the subballast-subgrade interface. Regarding subgrade CBR, it was found that the geogrid offered the greatest performance benefits when the subgrade was soft. Therefore it was concluded that for the ballasted rail structures under test, when subject to elevated levels of horizontal stress, geogrids reduced settlements compared to nongeogrid solutions.

This paper presents a desiccation crack monitoring campaign conducted on a full-scale, vegetated infrastructure embankment subjected to one-year of seasonally variable weather. The field survey involved direct measurement of naturally developed, annually reoccuring cracks in a heavily instrumented, clay fill embankment (BIONICS, Newcastle University). Transient crack morphology was captured in terms of opening width, length and depth, in addition to meteorological and near-surface soil hydrological conditions. In order to assess any correlation between crack development and weatherdriven changes in near surface soil conditions, the volume of cracks was estimated using an empirically derived equation. This work identified crack behaviour in four stages: initiation, expansion, contraction and closure. These stages and the distribution of cracks on the slope are closely related to prevailing atmospheric conditions, namely wind direction, relative humidity, precipitation and potential evapotranspiration. These ultimately govern the soil hydrological conditions in the near-surface, as manifested in the presented matric potential and volumetric water content data. Linearly descrete cracks are shown to form under such conditions in contrary to the polygonal patterns typically reported under laboratory conditions. Crack length growth terminates prior to full volumetric maturation with crack depth dominating the dynamic response regardless of overall crack size. Keywords chosen from ICE Publishing listField instrumentation; Expansive soils; Embankments; Full-scale tests;  is mean daily slope vapour pressure curve (kPa/°C)  is mean daily psychrometric constant (kPa/°C)

This is a repository copy of Railway ballast anisotropy testing via true triaxial apparatus.