Effects of halloysite on compaction behavior of saprolite soils in Palau

The Palau archipelagos are of volcanic and tectonic origin, and most parts of the islands are covered with residual and saprolite soils to substantial depths. The saprolite soil is formed from extreme weathering of volcanic base rocks and ashes under tropical humid climate. It contains a variable amount of halloysite minerals which are also produced from such weathering and leaching of volcanic materials. Construction of a new road of 85 km is currently underway in Palau, and the saprolite soils, generated from excavations of the slope cuts of the alignment, are used as embankment fill material. Existence of halloysite, along with abundant rainfalls all the year round, has created extreme difficulties in the field in achieving the compaction degree required. This paper presents engineering properties and compaction behavior of the halloysitic clays in Palau. The nature of the field compaction problems is evaluated in terms of characteristic behaviors of halloysite, and effects of dehydration characteristic of halloysite on the soil properties are also investigated.