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Bermed excavation (deep excavation supported by an excavation wall and a berm) can be an economical method for basement construction in urban areas if ground movement around the excavation is not the primary concern and the excavation site is large and (or) irregular in shape. This paper reviews three bermed excavation projects carried out in the Taipei Basin. One project was successful, one was successful after near failure, and one was a failure. Ironically, extensive ground improvement work had been done for the near-failure and failure cases; but no ground improvement was done for the successful case. It is of interest to find the similarities and differences among these bermed excavation projects. The causes of instability that result in unsuccessful bermed excavation projects and the applications of limit equilibrium analysis to the stability of bermed excavation are also discussed here. These three cases show that the existence of grout columns does not help to effectively increase the stability of the berm if the original safety factor against sliding of a berm slope is less than 1.0 and the improvement ratio of grout columns is low (say <20%). [ABSTRACT FROM AUTHOR]

In this paper the authors present an analysis of the seismic records of the Liyutan dam, which is a zoned compacted earth dam. It is 96 m in height, and it suffered some minor cracks and settlement during the 1999 Chi-Chi earthquake. A large amount of seismic motion has been recorded for 42 past earthquake events. These records were used to analyze the vibration characteristics of the dam. The fundamental frequency and nonlinear amplification of the peak ground motion of the dam body have been clearly identified. Based on the fundamental frequency identified from the small earthquake data, the seismic motion of the dam during the Chi-Chi earthquake could be well simulated by an equivalent linear dynamic procedure. An empirical decomposition method was used to decompose the Chi-Chi earthquake motion histories, from the top and the bottom of the dam, into several orthogonal and complete intrinsic mode functions (IMFs). These IMFs show that the low frequency parts of the seismic motion at the top and bottom of the dam are nearly the same, however, the high frequency parts are significantly amplified when the seismic motion propagates from the bottom to the top of the dam. [ABSTRACT FROM AUTHOR]

This paper examines the liquefaction performance of soils at the site of a partially completed ground improvement project at the Chang-Hwa Coastal Industrial Park during the 1999 Chi-Chi earthquake in Taiwan. The site is on land reclaimed by hydraulic filling. To meet the need of a planned construction, site characterization was carried out with standard penetration tests (SPTs) and cone penetration tests (CPTs) at 13 locations. Dynamic compaction was later performed to mitigate the potential liquefaction hazards at this site. Before completion of the ground improvement work, the site experienced a major earthquake, the Chi-Chi earthquake (magnitude M[sub w] = 7.6). Evidence of liquefaction was observed in this earthquake in the unimproved area but not in the improved area. After the earthquake, additional site exploration was carried out using SPTs and CPTs. The data from these in situ tests carried out before and after the earthquake and in areas with and without ground improvement are analyzed and the results are reported.Key words: ground improvement, in situ tests, liquefaction, earthquake.Cet article examine la performance en liquéfaction d'un site partiellement traité dans le Chang-Hwa Coastal Industrial Park durant le séisme de Chi-Chi à Taiwan en 1999. Le site est sur un terrain qui a été préparé par remblayage hydraulique. Pour rencontrer les exigences de la construction prévue, la qualité du site a été évaluée par des essais SPT et CPT à 13 différents endroits. Par la suite, du compactage dynamique a été exécuté pour réduire les risques de liquéfaction potentielle sur ce site. Avant l'achèvement des travaux d'amélioration du terrain, le site a subi un séisme majeur, le séisme de Chi-Chi (M[sub w] = 7,6). Au cours de ce séisme, on a observé des signes de liquéfaction dans la superficie non traitée, mais non dans la partie traitée. Après le séisme, des investigations additionnelles ont été réalisées sur le site au moyen du SPT et du CPT. On a analysé ces données des essais in situ réalisés avant et après le séisme, et sur les superficies traitées et non traitées, et on présente les résultats.Mots clés : amélioration du terrain, essais in situ, liquéfaction, séisme.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]