Product Description
DENISON CORE BARREL
Triple tube core barrel Denison
The Denison core barrel is a triple-tube swivel type corebarrel, with a shoe with a sharp cutting edge threaded onto the inner barrel and extending below the cutting teeth of a tungsten corebit.
The length of the corebit must be changed to alter the amount by which the shoe extends below the corebit. According to Hvorlev (1949) and Lowe (1960) a 50-75 mm inner barrel protrusion is suitable for relatively loose or soft soils, whilst the cutting edge should be flush with the corebit in'very stiff, dense and brittle'soils. The Denison corebarrel uses a "basket" type spring core catcher, where a number of curved, thin, flexible springs are fixed to a base ring by rivets, or by welding.
FEATURES
Essentially a double tube, swivel type of core barrel, the Denison is capable of producing undisturbed samples from soft materials as well as hard soils where the pressures required to push or even drive thin wall samplers might produce undesirable results. The Denison has several important distinctions from a double tube core barrel:
1. The inner tube of the sampler contains a plastic liner designed to retain the sample during sampling and to protect the sample once it is removed for its trip to the laboratory.
2. The inner tube show precedes the cutting bit into the formation to prevent torsional disturbance of the sample by the circulating drill fluid.
3. Three interchangeable hard faced cutting bits are provided for variation in materials, allowing undisturbed sampling to be accomplished.
OPERATION:
The Denison Sampler is rotated while being pressed into the soil in either a cased hole or a hole stabilized by drilling mud. The soil sample or core is retained in the sampler by wall friction or by a basket type of retainer. Three different lengths of saw tooth cutter bits are provided to aid sampling in soft, medium or hard materials. When extremely hard and compacted formations are encountered, the Denison can be fitted with a cutter bit is recommended for average conditions. The intermediate cutting bit is recommended for average conditions. Standard length Denisons recover two foot (0.6 m) samples. Optional conversion parts are available if 5 ft. (1.5 m) samples are required. The Denison Sampler can be operated by any standard drill rig. The Sampler is designed for use with either clear water, drilling mud or air.
HOW THE DENISON CORE BARREL OPERATES
In operation, the Denison Core Barrel is rotated into the soil either in a cased hole or a hole stabilizer with drilling mud. The inner barrel is a full swing type mounted on anti-friction bearings. The inner tube protrudes below the cutting bit carried by the outer barrel. Purpose of this protrusion is threefold:
1. To insure that the sample is recovered from material undisturbed by cutting action of the rotating bit,
2. To seal off the sample from water or drilling fluid discharged at the bit face, and
3. To protect the sample from deformation by preventing any rotative drag on the inner barrel. The inner tube remains stationary at all times.
As the Denison Core Barrel is forced down with gradually increased pressure, the sample passes through the core retainer into the inner barrel and its plastic liner. The plastic liner serves as a permanent container for the sample. Two types of core retainers are used - a split ring type for harder materials or a basket spring type with thin flexible springs for soft soils. In the smaller size Denison Core Barrels (2-15/16" & 3-1/2"), it is sometimes possible to omit the core retainer altogether and rely on the skin friction of the inner tube to retain the sample. The shoe of the inner tube is made to provide a slight clearance so that the sample swells after entering the barrel, it will tend to be retained by wall friction.
As the sample pushes upward in the barrel, drill fluid or water on top of it is vented through a disk valve to the low pressure area on the outside of the core barrel itself. With soft materials the pressure differential thus created is instrumental in helping to retain the sample. During the sampling operation, fluid flow is reduced to the point of keeping the bit clean and return cuttings slowly flowing out of the hole. When the full length of sample has been run and the core barrel removed from the hole, the inner tube liner is removed with the sample intact and sealed with paraffin in the standard manner for delivery to the laboratory as a true undisturbed sample.
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