The Pinhole Test for Dispersive Soil Identification

Abstract

The dispersion of sodium-rich clay soils in water and its influence on the stability of various engineered structures has been a topic of concern in various engineering projects for many years. One of the main problems is the seeming inability to positively identify such soils and thereby to reduce the potential for failure of many engineering structures. Recent research has revealed that deficiencies in the identification and classification of dispersive soils are most commonly related to inconsistencies in the test methods and testing protocols. A study was carried out to determine the repeatability, reproducibility and reliability of the pinhole test as an indicator of dispersive soil behaviour. Initial testing allowed for the identification of shortcomings in the pinhole test method and some modifications to the method were made. The modified method was then used to assess the dispersivity of 12 samples as well as the repeatability of the test itself. Results of this study showed the pinhole test (both before and after modifications) to be a highly unreliable test. The test method is ambiguous and time consuming and addresses very little of the fundamental properties that characterise dispersive soils. This paper summarises the problems identified during the testing of the samples, the modifications made to overcome them and the results obtained. The overall conclusion is that the test should no longer be incorporated into the rating systems currently being employed for identifying dispersive soils in South Africa.