摘 要 採用動力壓密工法進行土質改良施工時，地層將因夯錘夯擊而產生體波與表面波，其中體波能穿透地層，使土壤架構趨於緊密，但表面波對土壤改良並無助益，且可能造成結構物之損害。 為降低表面波對結構物之影響，本研究以鋼板與槽溝作為阻隔振波傳遞之複合式隔振設施，並進行模型試驗。藉由模型試驗探討複合式隔振設施中，鋼板埋入深度、鋼板寬度、鋼板與振源距離及槽溝之挖掘對於不同相對密度砂土隔振效果之影響。 由試驗結果可知，以鋼板之埋入深度為0.3倍振波波長及槽溝之深度為0.2倍、寬度為0.74倍振波波長所組成的複合式隔振設施，對相對密度較小之砂土能阻隔較多波傳能量，即複合式隔振設施對相對密度較小之砂土有較佳隔振效果。由不同鋼板寬度或鋼板埋入深度之試驗可知，鋼板寬度愈寬或鋼板埋入深度愈深，則隔振效果愈佳，若以面積大於試體斷面之鋼板完全截斷試體，其隔振效果可達99%以上。 ABSTRACT When improving soil layer by using dynamic consolidation method, the body wave and surface wave occur in soil layer because of the impact. The body wave can go through the soil layer and make the structure of soil denser. But the surface wave can not improve the soil strength, and it may damage the structure. To realize the acceleration amplitude of surface wave can be reduced by composed wave barriers, which were composed of steel plate and open trench, this research carried out a series of simulated dynamic compaction tests with small-scale sandy ground models in laboratory. The relationships between the effect of isolation and test parameters, which included the embedded depth of steel plate, the width of steel plate, the distance between impact source and steel plate, the depth of open trench, and the relative density of sandy ground model were discussed in this research. From the result of experiments, it was revealed that the composed wave barriers whose embedded depth of steel plate was 0.3 times of wavelength, depth of open trench was 0.2 times of wavelength and width of open trench was 0.74 times of wavelength could reduce more energy of wave when the relative density of soil is small, that is to say, the effect of isolation by using the composed wave barriers can be found for small relative density. The result of experiments also revealed that the effect of isolation can be obtained while the embedded depth of steel plate or the width of steel plate increased. The amplitude reduction factor could be less than one percent while the steel plate totally cut off the specimen.
