表面波震測應用於地盤改良率檢測之數值模擬探討

Abstract

地盤改良可增加土壤的工程性質（剪力強度、承載力等），然而施工後改良場址的高度不均質性，使傳統單點檢核方式（如鑽探取樣）較不具整體代表性，反之使用表面波震測法，其有取樣範圍大、施作快速和經濟等優點，並可提供改良後整體複合土體的彈性力學行為，但表面波震測於改良前後，所測得之剪力波速提升，反映出的工程性質為何？是否可做為量化分析之依據？對此文獻中未曾探討提及。本研究以數值模擬的方式，進行量化數據的處理，以評估剪力波速與改良率的關係。 研究成果顯示，表面波於改良後場址之行為，主要受到波長λ與改良柱間距t影響，當λ/t>4時，其波速之均質化可由其等效波速決定，當 λ/t<4時，則為等效串聯模數行為。透過對表面波震測 λ/t 的計算，判斷表面波均質化之行為模式，可有效得將表面波震測應用做為改良率的檢核工具，經與現場實測資料初步比對驗證後顯示，此檢核方法具有可行性且極具潛力。

Ground improvement can improve the engineering properties of soil, such as shear strength, stiffness, and bearing capacity. But after construction, the improved site is highly heterogeneous. Experimental methods ( Standard Penetration Test, Sampling, etc.) used to assess such ground improvement are not effective due to small sampling volume. Surface wave method as a non-invasive and direct method for assessing the overall quality of the ground improvement is characterized by large sampling volume, efficiency, and cost effectiveness. However, how to interpret the shear wave velocity increase measured by the surface wave method remained to be discussed. In this study, numerical simulations were conducted to quantitatively investigate the relationship between shear wave velocity and improving rate (i.e. replacement ratio of ground improvement). Research shows that surface wave behavior in the improved site is mainly affected by the wavelength(λ) and column spacing( t ). When λ/ t > 4, the homogenization of shear wave velocity can be derived based on the equivalent velocity. When λ/ t < 4, the homogenization should be derived based on the equivalent modulus in series. Through the calculation of λ/ t to determine the homogenization behavior of surface wave, the surface wave method can be effectively used to inspect the improving rate. By comparison with field measurement data, the hypothesis is further verified and shows that the surface wave method has great potential and feasibility in assessment of improving rate.