Sunday, November 11, 2007

Effect of boring method on bearing capacity of short cast-in-place piles

1. Bored-hole/cast-in-place piles 4–10 m long tend to retain a constant value of the unit bearing capacity, irrespective of soil moisture. Driven piles, and piles cast in punched holes, undergo a loss unit bearing capacity (up to 20%) as their length is increased.
2. With the saturation of high-porosity collapsible soils, the unit bearing capacity of bored-hole/cast-in-situ piles up to 10 m long diminishes two to three times, on average. For cast-in-place piles installed in a punched hole, and for driven piles, this reduction ranges up to only 30%. This trend is characteristic of soil layers whose collapsibility properties diminish with depth, from 2–3% to 1–1.5%.
3. The unit bearing capacity of cast-in-place piles installed in punched holes is equal to that of driven piles, both for saturated and dry soil conditions.
4. Following soil compaction, the unit bearing capacity of concrete cast-in-place piles installed in punched holes is higher than for bored-hole/cast-in-place piles, in the ratio of up to 2 for slightly moistened soils and 3–3.5 for saturated soils.
5. All other conditions being equal, the unit bearing capacity is greater for driven piles, and somewhat smaller (by 10–15%) for piles cast in punched holes. The smallest unit bearing capacity is observed in bored-hole/cast-in-place piles (1.5–2 times less than for driven piles).
Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 4, pp. 14–15

making a low distortion frame construction

A method of making a low distortion frame construction, the construction having joint regions formed by first and second overlapping members defining a lapped interface, the joint regions being comprised of material that can be converted to a solid state deformable plastic condition by friction heat, comprising:

(a) providing a stir friction welding tool having
(i) a rotatable thermally conductive body presenting a shoulder to engage the joint region for storing friction-generated heat, and
(ii) a friction generating pin rotatable with said body about a pin axis and selectively extendable from the shoulder to progressively penetrate the overlapping members as the joint region in contact with the pin becomes plastic;

(b) placing the tool shoulder against the joint region with the pin axis transverse to the lapped interface and spinning the body while progressively extending the pin at a rotational speed effective to generate friction heat that converts the adjacent material of the joint to a plastic condition allowing the spinning of the probe to stir such plastically converted material; and

(c) controlling the depth of penetration of the spinning probe while translating the tool across the joint region to perfect a friction stirred welded zone that extends through the interface and between the overlapping members to provide a welded joint that is exceptionally strong in shea