為了檢驗現地土壤單位重與相對密度，通常採用砂錐法或橡皮膜法，但仍有諸多不便之處。本研究之目的在於探討衝擊加速度與砂土單位重及相對密度的相關性，以作為求取現地土壤單位重之依據。
本研究以西螺砂為試驗土樣，以霣降方式製作各種相對密度之砂土。於夯錘上裝置加速度計，連接資料擷取系統(TEAM 490)，夯擊試體後，可得加速度歷時曲線。此曲線之尖峰值即為衝擊加速度(Retardation或Impact acceleration, )。本研究對各種夯錘質量、落距、砂土試體之相對密度(單位重)以及不同尺寸試體之試驗結果做分析。試驗結果顯示，夯錘質量越大，對於相同緊密程度之試體，其衝擊加速度越小；夯錘落距越大時，所得衝擊加速度會越大；落距相同，貫入量越大者，其衝擊加速度越小；試驗結果受到邊界效應影響，CBR模所製作試體之試驗結果會高於大型土桶之試驗結果，但可藉由結果進行迴歸並加以修正。最後並以中央大學大型力學實驗室之大型土槽，驗證以室內大型土桶進行衝擊試驗已不受邊界效應所影響，並建立一預估公式，能以CBR模試驗預估該相對密度(單位重)之現場衝擊加速度。

In order to measure the unit weight and relative density of soil in field, the sand cone method or the rubber balloon method are used frequently, but it is still not convenient enough. This research used traveling pluviation assembly to prepare the Siluo sand specimens with different relative densities. By setting a accelerometer on the hammer and connected the data logger(TEAM490) system to the personal computer, the variation of acceleration during the impact of hammer can be measured. The peak values of acceleration in the acceleration-time curves are defined as (Impace acceleration or retardation). This research discussed the influences of hammer mass, droping height of hammer, relative density and mold size on the experimental results. From these experimental results, it is understood that a larger hammer mass will cause a smaller acceleration for the specimens with the same density. If the dorping height of hammer was increased, the impact acceleration would be increased also. Under the same condition of droping height of hammer, if the penetration depth is larger, the impact acceleration would become smaller. The boundary condition influences the experimental results obviously. For the same relative density of soil specimens, the values of will be greater than that of . In order to verify the large scale mold has no influence of boundary conditions on the results of experiments, we used the indoor test pit to perform tests and found a formula which can be used to predict the unit weight and relative density of soil in field.

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