ABSTRACT
The utilization of clayey soils as the backfill of a reinforced retaining wall is of environmental and economic significance. A pioneer study on the behavior of 5-m-high reinforced walls using volcanic ash clay (Kanto loam) as the backfill has been performed in Japan since 1982 (Tatsuoka and Yamauchi, 1986). In this study, a nonwoven, lowstiffness geotextile was used as the reinforcing material. A relatively low degree of compaction was obtained because the compaction was conducted under natural water content (ω≈100%). Large deformations were measured for the reinforced clay walls
during the long-term monitoring. In this study, Tatsuoka and Yamauchi (1986) found that the nonwoven geotextile may effect degree of compaction and provide drainage function during the rainfall. In the subsequent studies on the reinforced clay wall for railway test embankment (Tatsuoka et al., 1992), relatively stiff geogrid and geosynthetic composite for soil reinforcement were used. In addition, layers of sand filter and cast-in-place rigid RC facing (namely, RRR method) were used to provide drainage and lateral confinement of the soil mass. Consequently, the deformation of the reinforced wall under intensive rainfalls was significantly reduced. Wu (1992) reported a 3-m-high timber-faced steep wall using a clayey sand (classified as SC based on USCS) reinforced with a heat-bonded nonwoven geotextile. In this study, a clayey soil was air-dried, crushed, sieved through a No. 4 sieve (4.76-mm opening), and mixed with silt and sand under carefully controlled conditions. The soil was subsequently mixed with water to achieve a 2% wet optimum water content and was cured in a constant moisture room. The compaction effort was provided by a vibration plate compactor weighted 700 N under 76-mm soil lift to achieve 95% relative compaction of the Standard Proctor test. A reinforced wall backfilled with medium-dense sand (relative density≈67%) was also built for comparison purposes. The result of loading tests showed that the ultimate load of the clay wall was larger than the sandy wall. However, a conclusion regarding the feasibility of using clay as the backfill has not been reported. Itoh et al. (1994) also reported a 7.5-m-high steep reinforced wall using a high-plasticity clay (classified as CH based on USCS, approximately on the Aline) formed by weathered mudstone. The compaction was provided by a vibrating roller weighted 70 kN under 0.25-m lift and 4 to 8 passes. In this study, the control of the clod size of clay before compaction, the water content of soil during compaction, and the relative compaction achieved were not reported. Large horizontal and vertical deformations (≈0.4m and 0.6 m, respectively) of the wall face were measured in the five months since completion. Inadequate compaction conditions might account for the large deformation of the wall face. So far, clayey soils have not yet been widely accepted for permanent soil structures because the engineering properties of the compacted clay could be susceptible to various factors. Therefore, a systematic employment of clays as the backfill of reinforced walls requires more studies on the relationship between the performance of reinforced clay walls and the factors that control the quality of the compacted clay. This report covers the design and construction of the reinforced walls, the long-term monitoring, and the results of seepage analyses.
