2 results for Phillips, Christopher J.

  • Rheological investigations of debris flow materials

    Phillips, Christopher J.

    Lincoln University

    A 2.0 m diameter viscometer/rheometer was designed, constructed, and used to test the behaviour of coarse grained debris flow materials. A 1/5 scale model was also constructed and used to test fluid-only and grain-fluid mixtures. The 30° inverted cone-and-plate viscometric system produced results comparable to those obtained from more standard viscometric systems. Internal flow behaviour was shown to be similar to standard cone-and-plate geometries and values of internal shear rate were close to those predicted from theory. The behaviour of highly concentrated fine suspensions (clay slurries) confirmed the findings of previous workers that these materials have a plastic or Bingham plastic rheology. Clay slurries containing coarse grains, and artificial grain-fluid mixtures, display many features of granulo-viscous behaviour such as stick-slip phenomena, structural changes, and fluctuations in torque values. Flow curves displaying dilatant behaviour occurred almost universally in coarse grain-fluid mixtures at shear rates greater than about 5 s⁻¹. Flow curves for fresh concrete were similar to those identified by others and might well fit the Bingham plastic model. Flow curves for debris flow materials were extremely sensitive to water content. Debris flow materials that have a bimodal grain size distribution are likely to have a dilatant plastic rheology while those which have a low content of coarse material and a unimodal grain size distribution are likely to have a plastic or viscoplastic rheology.

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  • Sedimentation in an artificial lake -Lake Matahina, Bay of Plenty

    Phillips, Christopher J.; Nelson, Campbell S. (1981)

    Journal article
    University of Waikato

    Lake Matahina, an 8 km long hydroelectric storage reservoir, is a small (2.5 km2), 50 m deep, warm monomictic, gorge-type lake whose internal circulation is controlled by the inflowing Rangitaiki River which drains a greywacke and acid volcanic catchment. Three major proximal to distal subenvironments are defined for the lake on the basis of surficial sediment character and dominant depositional process: (a) fluvial-glassy, quartzofeld-spathic, and lithic gravel-sand mixtures deposited from contact and saltation loads in less than 3 m depth; (b) (pro-)deltaic-quartzofeldspathic and glassy sand-silt mixtures deposited from graded and uniform suspension loads in 3-20 m depth; and (c) basinal-diatomaceous, argillaceous, and glassy silt-clay mixtures deposited from uniform and pelagic suspension loads in 20-50 m depth. The delta face has been prograding into the lake at a rate of 35-40 m/year and vertical accretion rates in pro-delta areas are 15-20 cm/year. Basinal deposits are fed mainly from river plume dispersion involving overflows, interflows, and underflows, and by pelagic settling, and sedimentation rates behind the dam have averaged about 2 cm/year. Occasional fine sand layers in muds of basinal cores attest to density currents or underflows generated during river flooding flowing the length of the lake along a sublacustrine channel marking the position of the now submerged channel of the Rangitaiki River.

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