海洋工程装备导论

外文及翻译

case, the measured force to extract a pile driven 60 m into these calcareous sands was little more than

the weight of the pile! These calcareous sands are relatively impermeable but grout under pressure may

crush the grains at the contact surface, and hence lock to the fabric behind. Calcarenite, which is a calcareous "sandstone; and calcirubfite, which is calcareous conglomerate, while having initial rigidity and strength, are also subject to crushing of their constituent calcareous sands, resulting in sudden loss

of strength and large deformations. Calcareous sands are relatively impermeable~ so that the potential

for liquefaction exists.

Sampling techniques inevitably crush some of the grains. Scale effects appear to be important in any

testing and evaluation. Methods of constructing suitable pile foundations in such soils are given in Chapter 8.

2.4 Boulders on and near the Seafloor Surface; Glacial Till

Boulders on and near the seafloor are typically found in sub-Arctic areas where they may have been deposited by ice rafting. Another widespread process is that of erosion, occurring when the sea was shallower than at present. The weaker deposits eroded away, dropping the boulders down and concen-

trating them. A third process occurs in granitic soils such as those of the east coast of Brazil and west coast of Africa, as well as in Hong Kong. As these rocks have weathered into residual soils, resistant cores

have remained firm, thus becoming "boulders" formed in place. Borings made in such residual soils usually miss most of the boulders. When they do encounter one, they often erroneously report it as "bedrock." The practice in Hong Kong, after much distress due to excessive settlement, is to core 5 m below the top of "bedrock" in order to confirm validity.

Boulders also exist in clay deposits. Some of these arose as morainal deposits from glaciers, discharging

their bed load into shallow water muds, which have since been overconsolidated by subsequent advances

of the glaciers. These are the boulder clays of the North Sea. GlaciaI till is a term used to describe these

unstratified conglomerate deposits of clay, gravel, cobbles, and boulders found in many Arctic and sub-Arctic regions. The term is very nonspecific; some glacial tills have little binder and may be largely

composed of gravel, and cobbles, whereas others may contain large boulders. Perhaps the most difficult

are the well-graded fills, with all the interstices filled with silts and clays, so that there is a very low percentage of voids. These deposits are usually heavily overconsolidated, resulting in a high unit weight

and a structure superficially resembling that of weak concrete. Thus unit weights have reached 2400 kg/m3.

Geotechnical explorations, unless very carefully planned and carried out, often find only the finer sediments, and the samples will have been highly disturbed, resulting in the indication of much weaker

material than that actually encountered. Wash borings bring back mud and sand. These tills are hard to

drill; the material is very abrasive and hard, yet the bond is weak. However, high-pressure jets have proved