應用改良式動力貫入法判釋土壤垂直結構

Applying a Modified Dynamic Cone Penetration Test to Detect Vertical Soil Structures

鄭名宏(Ming-Hung Cheng)

指導教授 ： 梁偉立

國立臺灣大學/生物資源暨農學院/森林環境暨資源學研究所/碩士(2018年)

https://doi.org/10.6342/NTU201802187

摘要

土壤厚度與土壤岩層交界面位置不僅為土地利用、經營管理中相當重要的指標，除此之外，土壤岩層交界面也是影響邊坡穩定、水文動態的重要邊界，若能取得完整的地下土壤結構資訊，將有助於評估崩塌潛勢及土地利用分級等議題。一般認為土壤岩層交界面為淺層崩塌的潛在破壞位置，但現地的檢證案例仍為少數，崩塌破壞面的地中位置特性仍無定論，如何於坡地環境直接調查淺層崩塌潛在破壞位置的方法也有改進的空間。
本研究首先藉由一事前已掌握土壤地層資訊的崩塌事件，檢視崩塌破壞面的地中位置及特性，透過崩塌前地中土壤阻抗分佈、崩塌前後地表地形變化等資料，發現整個集水區有向下陷落的現象，而土壤岩層交界面的地形、坡度對於崩塌位置及土體的移動有著相當大的影響。
簡易貫入為適合坡地的調查方式，能探測土壤厚度，且能得知土壤阻抗N_h的分佈，但若要調查坡地土壤厚度的空間變異，就需要大量的樣本及調查時間。故本研究改良簡易貫入試驗之打擊方式，將簡易貫入的重錘落下改以撞擊馬達替代，發展調查速率較快的動力貫入試驗，縮短調查時間的同時也能得到土壤阻抗N_pd的分佈。透過不同硬度材料堆疊的試驗槽實驗，發現動力與簡易貫入均可良好描述阻抗分佈，兩者阻抗對應關係可以線性模型表示，關係式為Npd=0.0197×Nh，決定係數為0.84。應用動力貫入於野外測線，發現所得貫入阻抗能夠反應不同土層結構的特性，在環境單純、土壤岩層分明的地區，能與簡易貫入探得相同的土壤厚度與阻抗特性；而在環境較複雜之區域，動力貫入與簡易貫入相比，同樣能夠獲得一致的土壤阻抗特性、辨識土壤岩層的交界面，且能排除掉小型石塊的阻礙，探測到更深層的結構，其保有可攜帶性的同時能順利減少調查所耗費時間，在短時間內蒐集大量資料，為一項能實際應用且效率較高的調查方式。

關鍵字

土壤厚度 ； 土壤岩層交界面 ； 簡易貫入試驗 ； 動力貫入試驗 ； 貫入阻抗

並列摘要

Soil depth and soil–bedrock interface locations are critical indexes for land utilization and management. The soil–bedrock interface is also a crucial boundary affecting slope stability and hydrological dynamics. Therefore, obtaining complete information on underground soil structures would improve the grading of land utilization and the evaluation of potential landslides. Generally, the soil–bedrock interface is believed to be the potential destruction location in shallow landslides; however, few empirical studies validated this hypothesis. Furthermore, properties of this interface remain unclear. In other words, potential destruction locations of shallow landslides warrant further investigation.
This study analyzed the location and characteristics of a landslide destruction interface in a landslide event by using pre-existing data of soil structure before the landslide event. By investigating distributions of soil resistance and variations in surface topography, we found that the entire area was falling down and that the topography and slope of the soil–bedrock interface strongly influenced soil movement.
A core penetration test (CPT) is a direct measurement technique for detecting soil depth and obtaining soil resistance (N_h) on a hillslope. However, detecting spatial distributions of soil depth using a CPT requires a large sample size and much time. In this study, we developed a dynamic cone penetration test (DCPT), a form of CPT, to reduce the investigation time in the field. The DCPT can obtain the soil resistance (N_pd) through penetration. The DCPT features a knocking engine instead of the knocking weight of the CPT. We used an experimental device containing layers of varying hardness to evaluate the DCPT and CPT; the vertical distribution of penetration resistance as measured using the two tests corresponded well to each other. The relationship of the penetration resistance measured using the DCPT and CPT can be expressed through a linear regression—N_pd = 0.0197 N_h—with an R2 value of 0.84. On applying the DCPT in a field and digging a trench close to the penetration cone, we obtained the following results. In a simple environment, the DCPT and CPT successfully yielded the same soil depth, soil–bedrock interface, and characteristics of soil resistance. Similarly, in a complex environment, the DCPT and CPT yielded the same characteristics of soil resistance and identified the soil–bedrock interface; however, the DCPT overcame more obstructions caused by small rocks to detect deeper structures in shorter time. These results demonstrate that the DCPT greatly reduces survey duration without compromising on portability. Thus, the DCPT is an efficient method for obtaining underground information in the field.

並列關鍵字

Cone penetration test ； dynamic cone penetration test ； penetration resistance ； soil depth ； soil–bedrock interface

參考文獻

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