Abstract: For existing underground structures that could not be replaced with new ones under opencut, the rehabilitation can only be performed throughout the nonexcavation piled methods. However, due to the soft and highly compressible organic peat soil layer in the Dianchi Lake basin area, its special physical and chemical properties of subsurface soil prevents the applying of soilcement column method since the soil particles cannot effectively harden by the introduction of the cement slurries. Further, the organic peat soil turns into plastic paste when the water is encountered. Therefore, the soilcement method cannot be applied. To rehabilitate the defected municipal underground utility pipes in Dianchi Lake area, the isolation walls and columns formed by the jet grout method was proposed throughout the trial test in organic peat soils. The result by this improvement was prove to be satisfactory.

Key words: High Pressure Jet Grout Columns, Underground Utility Tunnel, Organic Peat Soil, Soil Improvement