Prior research has shown that a well-drained base is a very important requirement for preserving the soundness of a highway pavement. Although adequate knowledge exists to guide an engineer in the design of a new pavement with good drainage characteristics, there are no established methods to estimate the quality of drainage under an existing pavement and therefore to estimate its life expectancy or to properly design its overlay. A summary is presented of research efforts aimed at investigating and adapting existing techniques from the geotechnical area for the development of methods for measuring the permeability of pavement bases. 1\vo geotechnical methods were adapted, and one new technique was developed. The first two methods were used to conduct permeability tests near the middle of thepavement slabs, using either constant head or falling head setups. These were named the Midslab Constant Head Test Permeability Test and the Midslab Falling Head Permeability Test, respectively. The third method was designed for conducting permeability tests near the edge of a slab. This method was named the Edge-of-Slab Constant Head Permeability Test. Numerous permeability tests were conducted under a jointed reinforced concrete test pavement in Chillicothe, Ohio, using these three methods. It was found that the tests conducted near the edge of the slab held the most promise, even though the method needs further refinements. However, the results of the edge-of-slab test were quite different from those of the midslab test, partly because of the erosion of fines from the base in the edge-of-slab test. In addition, it became clear from the tests that the field test results were considerably different from laboratory test results.

A well-drained base is of utmost importance for highway pavements. Cedergren (J) in 1978 estimated that the lack of proper drainage of infiltrated water from the nation's highway pavements would cost US taxpayers more than $2 QO billion in just 15 years. The AASHTO design guide (2) recognizes the importance of pavement drainage in its thickness design procedures by accounting for the quality of drainage and for the period of time during which the pavement section is exposed to moisture. However, the design guide does not help the engineer with criteria to establish what good quality drainage entails, especially when the rehabilitation of an existing pavement is in question. Nonetheless, engineering judgment points to the permeability of the base as one of the most important factors in pavement drainage. The literature survey on the permeability of bases found several articles and references on the subject. Moulton and Seals (3, 4) presented permeability testing methods applicable to the field measurement of permeability of newly placed bases and subbases before the pavement is placed on them. They designed a special