REPEATED LOAD TESTS ON SUBGRADE MATERIALS

THE AUTHOR GIVES AN ACCOUNT OF REPEATED LOAD TESTS CARRIED OUT ON TWO TYPES OF SUBGRADE MATERIALS WITH THE OBJECT OF PREDICTING THEIR BEHAVIOUR UNDER TRAFFIC. THE REPEATED LOAD TEST APPARATUS USED WAS BASED ON THAT DEVELOPED BY H.B.SEED OF THE UNIVERSITY OF CALIFORNIA AND HAS ALSO BEEN USED BY BRITISH RAIL. IT MAKES USE OF A LOAD CELL PLACED IN THE HEAD OF A TRIAXIAL CELL AND A LINEAR VARIABLE DIFFERENTIAL TRANSFORMER TO MEASURE DEFORMATION. THE REPEATED LOAD CYCLE WAS A CONSTANT DEVIATOR LOAD APPLIED FOR ONE SECOND AND REMOVED FOR THREE SECONDS. THE SOILS USED WERE A HIGHLY PLASTIC LACUSTRINE CLAY AND LEIGHTON BUZZARD SAND. RESULTS SHOWED THAT THE AMOUNT OF PERMANENT DEFORMATION WAS HIGH IN THE EARLY STAGES OF LOADING, AND AT LOW STRESS LEVELS THE RATE OF INCREASE IN PERMANENT STRAIN SLOWED TO A TERMINATING VALUE, WHEREAS ABOVE A CRITICAL STRESS LEVEL THE INCREASE CONTINUED AT A HIGH RATE UNTIL SHEAR FAILURE TOOK PLACE. RESULTS ARE GIVEN FOR THE TWO SOILS AT TWO CELL PRESSURES (70KN/M2 AND 100KN/M2). THE PERMANENT DEFORMATION WAS DETERMINED WITH IN SITU SAMPLES, AS INITIAL VALUES OF PERMANENT STRAIN AT UP TO 10-100 CYCLES TEND TO BE VARIABLE AND NEGATIVE PORE PRESSURES AFFECT THE RESULTS WITH SOME SAMPLES. IT WAS FOUND THAT VALUES OF RESILIENT DEFORMATION AT LESS THAN 100 CYCLES WERE NOT VERY INFORMATIVE AND THAT RESULTS WERE LESS CONSISTENT WITH THE SAND. FURTHER WORK WITH CLAY SOILS WITH A GREATER NUMBER OF CYCLES SHOWS THAT SAMPLES MAY APPEAR TO STIFFEN UP TO 60,000 CYCLES, BUT THAT A FURTHER 10,000 LOAD CYCLES MAY CAUSE SOFTENING AND EVENTUAL BREAKDOWN BY SHEAR.

  • Corporate Authors:

    IPC Building and Contract Journals Limited

    32 Southwark Bridge Road
    London SE1 9EX,   England 

    IPC Building and Contract Journals Limited

    32 Southwark Bridge Road
    London SE1 9EX,   England 
  • Authors:
    • Clarke, J D
  • Publication Date: 1974-10

Media Info

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Filing Info

  • Accession Number: 00083394
  • Record Type: Publication
  • Source Agency: Transport and Road Research Laboratory (TRRL)
  • Files: ITRD, TRIS
  • Created Date: Apr 8 1975 12:00AM