Reducing differential settlements of approach embankments

Abstract

This paper presents a case history of an approach road remediation project on a low embankment over soft Ariake clay, located in the coastal Saga Plain of Japan. After the road had been opened to traffic for two-anda-half years, large settlements were observed, and there was significant differential settlement between piled structures and approach road embankments on soft clay. This differential settlement had a significant impact on vehicle ride quality, and necessitated a remediation programme. In the remediation project, a new method called the column approach (CA) method was adopted to support a transitional zone at the interfaces of piled structures and road embankment. With the CA method a transitional zone was designed at these interfaces to be supported by soil-cement columns of varying lengths to smooth out the settlement profile within these zones. Field monitoring was conducted following completion of remediation. The CA method was also compared with two other Japanese code-designated methods: overlaying a new pavement on the existing pavement at a certain time interval, and constructing a concrete cushion slab under the road pavement. Both practical and economic aspects are examined in the case study presented. This study shows that, when the differential settlement is over 0 . 3 m, overlay remediation is not economic, and the approach cushion method does not perform well. The CA method not only reduces the differential settlement effectively, but also reduces the total construction cost, although the initial investment is relatively high. NOTATION a, b, m, and n 1 constants B spacing of columns CA column approach CBR California bearing ratio C c compression index e 0 initial void ratio EPS expanded polystyrene EQ empirical equations ESL equivalent static loading H col length of columns H em height of embankment i approach slope L a extension of approach L s slab length N number of repeated load P 0 effective overburden pressure q d traffic-load-induced dynamic deviator stress q f static failure deviator stress of soil q s initial static deviator stress S da allowable differential settlement S R differential settlement S s consolidation settlement due to static load S T consolidation settlement due to ESL t s thickness VD vertical drains Z T influential depth H thickness of soft clay under columñ P E static load of embankment P T traffic loading å p cumulative plastic strain (%) Ł inclining angle of pavement INTRODUCTIONFor a road on a low embankment over soft subsoil, permanent deformation of the subsoil due to traffic load is one of the most important factors that controls both the design life and the serviceability and maintenance cost of the road. Deformation induced by traffic load causes large differential settlement between the approach embankments (transitional zone) on soft ground and piled structures such as bridge abutments and box culverts. This differential settlement affects the comfort of the vehicle ride, and can even obstruct vehicle movement. In conventional design considerations two...

Ground Vibration Induced by Moving Vehicle on Soft Soil

“…There are several explanations why bridge approach settlement was previously examined by other researchers before and one of the issues is a disparity between the height of the bridge and road on the connection. A study of previous research revealed various potential causes of bridge approach distress and that the settlement of the bridge approach is primarily a site specific problem [7,8,9,10,11,12,13,14].…”