1. The site

The construction of a new head barrage for the Muda Irrigation Project, in northwest Malaya, involved knowledge of the in-situ permeability of adjacent alluvial sands, in order to determine the extent of sheet pile cut-off needed on one side of the structure.

Figure 1 shows the geological conditions at the site extending from the proposed structure, through the river diversion to the permeability test site.

This profile was determined from a number of earlier boreholes and a seismic traverse made during the initial site investigation of the area. The layer of coarse sands with fine gravel seen on the figure was of particular interest in the test. Figure 2 shows the particlesize distribution of both this layer and the overlying layer of fine sands and clayey silty sands. The clays with sand lenses underlying the coarse granular layer were taken as an impermeable base.

Three 'wells' were used for the permeability tests. These are marked on Fig. 1 as kl, k2, k3. The spacing between kl and k2 was 38 ft and between k2 and k3, 54 ft. The wells were sunk in line and at right angles to the flow of the river.

2. Method of testing

The three permability test wells, each 6 inches in dia., were terminated in the clays below the coarse granular layer. Four-inch internal dia. p.v.c, tubing was inserted inside the cased holes down to the clay stratum and the casing was withdrawn. The bottom 20 ft of the tubes had

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