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the soil during an earthquake. Since the goal is protection of the quay-wall, this is not considered a problem. The procedure is to drill a hole in the ground using a casing auger. Gravel is carried to the auger by a front-end loader. It is dropped into a hopper, lifted to the top of the auger, and poured into the casing. The casing is then removed from the ground leaving a sand drain. The gravel is fairly uniform. The casing has replaceable steel teeth to help it cut through soil and push away rocks. The gravel drains are placed close enough together to form a grid that will effectively drain out all the water. This project consisted of 3997 gravel drain piles in an area of 2770 m2 for 1.4 piles/m2 (the drains are 0.8 m apart). The drains are 0.5 m in diameter and 17 m long and cost about 50,000 Yen ($500) per pile or about 200 million Yen for the project. It takes less than an hour to make a gravel drain and there were four augers at the job site.

18.5.1.2 Deep Mixing Method: Kawaguchi City

The area along the Arakawa River has poorly consolidated soil. This project used deep soil mixing to improve the unconfined compressive strength of the ground (Figure 18.71). Without the DMM the soil would be expected to settle 1.5 m after the embankment is placed. With the DMM the settlement should be less than 0.03 m.

On this project, a modified pile-driving machine rotates a pair of rods with stirring wings for mixing the soil. The distance between piles can be changed by moving the rods closer together or further apart. The pile diameter is 1 m on this project. First, the machine pushes the stirring wings down 30 m,

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