PERFORMANCE OF REPAIRED SLOPE USING A GEONET OR GEOPIPE DRAIN TO LOWER GROUND-WATER TABLE

A 70 m long by 5 m high slope with gradient of 1(v):2(H) was cut into a medium-stiff residual soil of undrained shear strength better than 60kPa, with drained strength parameters of about c = 10kPa, and o = 22 degrees, to form the bank for an effluent pond used for irrigation of a racetrack turfing. Both drained and undrained slope stability analysis indicates stable slopes under reasonable ground-water (GW) levels expected in the cut slope. However, after a period of intense rainfall during construction, the slope suffered a shallow slip of about 1 m to 1.5 m depth over a 30m stretch of the slope length with a vertical scarp near the top of the cut slope. This paper examines the cause of slope failure, and the strategy adopted for a permanent repair of the slope by providing internal geosynthetic drains beneath the re-compacted slope, using a GEONET or closely spaced geo-pipe inclusions in the slope. For design, the GEONET or geo-pipe drains used must have adequate factored transmissivity to conduct expected heavy rainfall condition of 150 mm/h on the racetrack, it is demonstrated by the Finite Element Method (FEM) analysis, that GEONET must be provided to at least as far back as the mid-depth of the slope (about 4 m depth) to produce sufficient GW lowering to give stable slopes. The construction method of the slope repair to avoid further failure is described briefly, and the performance of the sub-soil drains in enhancing slope stability is demonstrated in the field project.

Language

  • English

Media Info

  • Features: Figures; References; Tables;
  • Pagination: p. 3-14

Subject/Index Terms

Filing Info

  • Accession Number: 00801020
  • Record Type: Publication
  • ISBN: 0803128606
  • Report/Paper Numbers: STP 1390
  • Files: TRIS
  • Created Date: Oct 16 2000 12:00AM