RESULTS AND DISCUSSION The structure of compacted soils plays an important role in their mechanical behaviour (Barden & Sides, 1970; Sridharan et al., 1971; Gens et al., 1996; Romero et al., 2003). Compacted fine silt-clay materials have a bimodal pore size distribution that may be viewed as aggregates of particles in an essentially saturated condition, surrounded by air-filled voids. The size of the aggregates is largely dependent on the sample preparation prior to compaction. The size of aggregates and the compaction pressure both determine the actual pore size distribution. Increase in compactive effort reduces the inter-aggregate voids, but it has no notable influence on the intra-aggregate pore size distribution (Lloret et al., 2003). The data reported here were obtained on statically compacted samples of kaolin prepared using three different compaction pressures: 1300 kPa, 800 kPa and 400kPa. In all cases, the material for compaction was prepared in a similar manner with an identical initial water content so that the pore size distribution of the raw material was the same for all tests. Mercury intrusion tests were performed to establish the nature of the bimodal pore size distribution. Fig. 2 shows the results obtained on samples compacted to three different compaction efforts. The results show a clear indication of bimodal pore size distribution, where inter-aggregate pore spaces reduce with increasing compactive effort. The influence of compactive effort on the intra-aggregate voids was less significant as the compaction water content was similar for all three compaction pressures.

Wetting As the initial suction in the samples was significantly higher than the suction values applied subsequently, the samples drew in water during the equalisation process (paths BC, BD or BE in Fig. 1 (a) and path BC in Fig. 1 (b)). During this process, the reduction in suction in the individual aggregates will be associated with an increase in aggregate sizes. Assuming no significant distortion of the aggregates, an increase in overall voids ratio can be expected (Alonso et al., 1995; Lloret et al., 2003). However, when the