PIEZOMETERS FOR PORE PRESSURE MEASUREMENTS IN CLAY

EQUIPMENT AND MATERIALS REQUIRED FOR INSTALLATION OF PIEZOMETERS ARE DESCRIBED. SARAN OR POLYETHYLENE PLASTIC TUBING IS RECOMMENDED FOR THE RISER PIPE. FOR THE POROUS POINT, A CERAMIC TUBE IS RECOMMENDED. A TAMPING HAMMER, HAMMER-CABLE ASSEMBLY IS USED TO: (1) TAMP THE BENTONITE LAYERS AND ASSURE A WATER-TIGHT SEAL BETWEEN THE CASING AND THE PLASTIC TUBING, (2) CENTER THE PLASTIC TUBING WHILE THE BENTONITE SEAL IS BEING TAMPED INTO PLACE, AND (3) MEASURE DEPTHS AT VARIOUS STAGES OF THE INSTALLATION. THE ASSEMBLY OF THE POROUS POINT IN PLASTIC TUBING IS DESCRIBED. ONE END OF THE POROUS TUBE SHOULD BE PLUGGED WITH THE NEOPRENE OR RUBBER STOPPER, AND THE PLASTIC TUBING SHOULD BE ATTACHED TO THE OTHER END BY MEANS OF THE NEOPRENE OR RUBBER BUSHING. A CASED HOLE SHOULD BE ADVANCED TO THE ELEVATION OF THE BOTTOM OF THE PERVIOUS SPACE THAT WILL CONTAIN THE POROUS TUBE EMBEDDED IN SAND. AFTER THE CASING IS ADVANCED TO THE DESIRED DEPTH, THE INSTALLATION OF THE POROUS POINT AND SEAL IS DESCRIBED. FINALLY, THE BENTONITE SEAL CONSISTS OF FIVE LAYERS OF BENTONITE BALLS, EACH ONE PLACED AND COMPACTED. WHEN THE WATER LEVEL IS BELOW THE TOP OF THE PLASTIC TUBING, AN ELECTRIC SOUNDING DEVICE IS USED, CONSISTING OF A SHIELDED MICROPHONE CABLE AS SOUNDING WIRE AND AN OHMMETER TO WHICH THE UPPER END OF THE SOUNDING WIRE IS CONNECTED. WHEN THE PIEZOMETRIC HEAD IS ABOVE THE TOP OF THE STANDPIPE, READINGS CAN BE MADE EASILY WITH A RELIABLE BOURDON GAUGE ATTACHED FIRMLY TO THE STANDPIPE, OR A MERCURY MANOMETER. DIRECTIONS ARE GIVEN FOR IMPROVISING A SATISFACTORY MERCURY MANOMETER. IT IS EMPHASIZED THAT IT IS IMPORTANT TO PROTECT THE TOP OF THE PIEZOMETER PIPE, AND ANY INSTRUMENTS ABOVE THE GROUND, AGAINST DIRECT RAYS OF THE SUN. TO MINIMIZE ERRORS DUE TO TEMPERATURE VARIATIONS, THE READING SHOULD PREFERABLY BE MADE AT THE SAME HOUR EARLY IN THE MORNING.

  • Supplemental Notes:
    • 13 Pp, 7 FiG
  • Corporate Authors:

    Harvard University

    Division of Engineering and Applied Science, 29 Oxford Street
    Cambridge, MA  USA  02138
  • Authors:
    • Casagrande, A
  • Publication Date: 0

Subject/Index Terms

Filing Info

  • Accession Number: 00229141
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Oct 5 1970 12:00AM