: Developed ground cavity due to leakage of decrepit old sewer pipe causes ground surface settlement and brittle fracture of pavement. Recently, for 5 years, frequency of occurrence of ground subsidence phenomenon tends to increase rapidly and/or steadily. It is difficult to investigate ground surface settlement and/or subsidence in urban area because most ground surfaces are covered with asphalt or concrete pavement. In this research, therefore, ground surface settlement, influence zone and settlement of sewer pipe were analyzed using finite element method. Not only reinforced effect of pseudo-plastic backfill that is applied to prevent ground surface settlement or subsidence spot, was compared and analyzed using numerical analysis program, but also direct shear test was carried out to determine strength parameters of pseudo-plastic backfill.

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A reinforced soil retaining wall is a structure that suppresses displacement of the soil by horizontal insertion of a reinforcing material having a large tensile force and frictional force, such as a metal band, a metal rod, and a geotextile on a back fill. It is economical and has been widely used [6]. Generally, the reinforcing soil retaining wall needs to be 5 m high or more, and the economic efficiency of the retaining wall improves as the retaining wall height increases (about 9 m or more). In this study, blocks of 0.4 × 0.5 × 0.4 m (length × width × height) were stacked. Failure behaviours were predicted according to heights of 3.2, 5.2, 7.2, and 9.2 m, as shown in Table 1. The collapse form of the reinforced soil retaining wall can be divided into external and internal factors, as shown in Figs. 1 and 2. The factors of extrinsic destruction are base sliding, overturning, and bearing capacity. The factors of internal destruction are tensile overstress, pull-out, internal sliding, bulging, connection failure, local overturning, and crest toppling. The collapse of these various reinforced soil retaining walls has been reported in Korea. Figure 3 shows a case in which the front wall has fallen because of

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