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Results of an extensive series of repeated load triaxial test on Dublin Brown glacial till are reported. Charts are presented relating the relevant parameters of the till to dry density and moisture content. The effect of stress history is studied. The results indicate that modifications are required to the Kirwan-Snaith nomograph and suggest that the subgrade strain design criterion should vary with the stiffness of the soil. A recently developed low cost pneumatic repeated loading test apparatus is described. Skempton's A and B pore parameters have been used to interpret the response of samples under repeated loading. A method of determining a stress-dependent resilient modulus by prepared charts from in situ tests on a subgrade is described. Results of laboratory pavement simulator tests on subgrade are compared with those obtained on undisturbed samples and with these results of the repeated loading, testing program. Modifications to DEFPAV which are required in order to include horizontally layered anisotropy are described. Initial results from a testing program to investigate the properties effecting the behaviour of natural gravels in road pavements are presented. Two computer subroutines for optimization of road pavement design are described. (Author)

A rational design procedure for flexible pavements is presented. The analysis of pavement structures is demonstrated using an improved computer program. Test tracks from other centres of research are used to test the ability of the program to predict permanent surface deformation under traffic loading. The creep characteristics of a dense bitumen macadam are analysed and a relationship suggested that links the permanent strain behavior under static and dynamic loading., See also report dated Apr 74, AD-A008 099.

In the report repeated load test results for bituminous mixes, granular and cohesive soils are presented. The results of the laboratory tests were used to check theoretical predictions of stress and surface deflection of a three-layer experimental pavement. Field measurements for commercial vehicles loading were obtained over a period of nine months. A study of the impedance method of vibration testing was undertaken; the application of the method to evaluation of existing flexible pavements is reviewed. (Author)

A finite-element program has been developed to the stage that, given adequate material characterization, it may be used to analyse the effect of passing wheel loads on any proposed pavement structure. Until now such programs have examined the induced stresses and transient deflections of the pavement system. This program has the capability to predict the permanent strain accruing in any element of the pavement. It will then take these values and produce the surface profile of the pavement after any specified number of wheel loads has passed. To further this work a laboratory pavement simulator has been used to obtain load-deformation-time data for the program. Also the concepts of threshold and critical stresses to permanent deformation prediction have been examined together with two creep laws for boulder clays.

The main objectives of the research are the elucidation of environmental factors governing the behavior of flexible pavements, as they relate to civil and military engineering construction, with the aim of producing a new design procedure. This Report is mainly concerned with two approaches, namely the dynamic method based on laboratory repeated load tests on the pavement materials, and the impulse loading technique. (Author)

The findings of a field and laboratory investigation into the causes of distress in flexible pavements are presented. Three pavements where distressed zones occurred adjacent to sound sections were tested. An attempt has been made to explain the causes of localized failures on the basis of elasticity theory. In the case of two of these roads it was found possible to predict the causes of the distress noted. The concept of threshold stress, put forward in the earlier report, is examined from the standpoint of linear viscoelastic theory. The difficulties of applying viscoelastic theory to multilayer systems where one or more layers possess a threshold stress is discussed. It is shown that viscoelasticity is a cumbersome theory to apply in practice. An alternative rate theory is developed for estimating the permanent displacements in a stress pavement. The theory is based on the formulation of a stress-strain law for clays in repeated loading. The predictions of the rate theory are shown to be in satisfactory agreement with some data obtained in the A.A.S.H.O. Road Test. The construction and instrumentation of an experimental road is described. Some experiences gained in the investigation of this full-scale experiment is presented. (Author)

Five soils, with liquid limits in the range 25 to 75, were subjected to pulsed deviator stresses applied in increments until a limiting permanent deformation was reached, or alternatively an axial stress of 18 p.s.i. was sustained without failure within 100,000 stress applications. Resilient moduli, covering a practical range of moisture contents and densities, were determined for each soil. The threshold stress, which separates the regimes of mainly elastic from the inelastic behaviour was established by an analytical procedure. The application of the threshold stress concept to flexible pavement performance is discussed. The compaction characteristics and the C.B.R. vs moisture content and density relationships were determined, and were correlated where practicable with the results of the repeated load tests. Conventional shear tests, slow undrained triaxial and unconfined compression, were performed. These test results are reported in abbreviated form. (Author)