RESEARCH INTO THE STRESSING OF PAVEMENT STRUCTURES. PART 3: THE EFFECT OF ADJOINING AXLES ON SOIL COMPRESSIVE STRESS UNDER FLEXIBLE PAVEMENTS

IN WORK BY SIEBEL IN 1971, THE STRESS ARISING IN STANDARDISED FLEXIBLE PAVEMENTS WAS STUDIED IN RELATION TO THE NATURE OF CONSTRUCTION AND ARRANGEMENT OF LORRY TYRES. THE AIM OF THE STUDY WAS TO DETERMINE THE EFFECTS OF WHEELS WITH DOUBLE TYRES IN COMPARISON TO SINGLE TYRES AND THE EFFECTS OF DOUBLE AXLES ON THE STRESS IN THE FLEXIBLE PAVEMENT. IN THIS PAPER, THE STRESS IN UNBOUND ROAD BASES, FROST BLANKET AND SUBSOIL IS ANALYSED, THE STUDY BEING EXTENDED TO THE STANDARDISED TYPE OF FLEXIBLE PAVEMENT CONSTRUCTION. SCIENTIFIC AIDS USED WERE AN APPROXIMATION METHOD BASED ON THE EQUIVALENCE THEORY OF ODEMARK AND THE MULTI-LAYER THEORY USING THE BISTRO PROGRAM. FROM THE RESULTS OF AASHO TESTS AS WELL AS THEORETICAL STUDIES CARRIED OUT, IT IS RECOMMENDED, THAT WHERE THE AXLE SPACING IS 1.3 M, THE ALLOWABLE DOUBLE AXLE LOAD NOW USED OF 16 MP SHOULD BE MAINTAINED AND WITH HYDRO PNEUMATIC SHOCK ABSORBERS SHOULD BE RAISED TO 18 MP AND IN ADDITION WITH AN AXLE SPACING OF 1.7 M, AN INCREASED AXLE LOAD ON THE DOUBLE AXLE OF 20 MP IS ALLOWABLE. WITH AN AXLE LOAD OF 20 MP AND USING HYDRO PNEUMATIC SHOCK ABSORBERS, THE AXLE SPACING CAN BE REDUCED TO 1.5 M. FOR AXLE SPACINGS LYING WITHIN THE RANGES MENTIONED ABOVE, STRAIGHT LINE INTERPOLATION MAY BE EMPLOYED.