The Casagrande thread-rolling method for determining the plastic limit of fine-grained soil is heavily dependent on operator judgement and can often give inconsistent or unreliable results. This paper presents an energy-based approach used in the development of an improved testing procedure for the plastic strength limit. A 0·727 kg cone is allowed to fall freely through 200 mm before contacting the surface of the test specimen, with the plastic strength limit determined for a cone penetration depth of 20 mm. For ten mineral clays of intermediate to very high plasticity tested, the plastic limits deduced using the cone were in good agreement with the measured Casagrande plastic limits. The values deduced using an 8 kg contacting cone were consistently lower than the Casagrande limits.
Granular anchors are a relatively new concept in ground engineering with relatively little known regarding their load–displacement behaviour, failure modes, ultimate pullout capacity, and also potential applications. A granular anchor consists of three main components: a base plate, tendon, and compacted granular backfill. The tendon is used to transmit the applied load to the base plate, which compresses the granular material to form the anchor. A study of the load–displacement response and ultimate pullout capacity of granular anchors constructed in intact lodgement till and made ground deposits is reported in this paper. Parallel tests were also performed on cast in situ concrete anchors, which are traditionally used for anchoring purposes. A new method of analysis for the determination of the ultimate pullout capacity of granular anchors is presented and verified experimentally, with the dominant mode of failure controlled by the column length (L) to diameter (D) ratio. Granular anchors with L/D > 7 principally failed by bulging whereas short granular anchors failed on shaft resistance, with the latter mobilizing similar pullout capacities as conventional concrete anchors.
Laboratory-based research studies and full-scale evaluations of the behaviour of ground improved with granular columns are ample regarding bearing capacity, but limited in respect to the settlement response. This paper presents a laboratory model study that considers the settlement performance of isolated pad footings bearing on reinforced sand deposits under the influence of a fluctuating groundwater table. This is a particularly onerous condition for loose sand deposits in coastal areas, which may undergo significant collapse settlement over time. Loose and dense experimental sand beds were constructed, and the performance of rigid footings under a maintained load and bearing on sand incorporating different column configurations was monitored under cycling of the water table over a period of 28 d, with one filling/empting cycle every 18 h. It was found that settlement, while greatly reduced compared with that for unreinforced footings, was ongoing, and typically occurred at a much greater rate for loose sand than for dense sand. Also, settlement rates were slightly higher for fully penetrating than partially penetrating columns, and also for footings reinforced by a column group rather than a single column. This was attributed to the migration of sand grains into the larger column voids.
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