真空降水與動力夯實合併用於軟弱土壤改良的效果研究

Innovative Soft Soil Stabilization using Simultaneous High-Vacuum Dewatering and Dynamic Compaction

王仁志(Jen-Chin Wang)

指導教授 ： 張達德

中原大學/工學院/土木工程研究所/碩士(2010年)

https://doi.org/10.6840/cycu201000883

摘要

動力夯實工法適用於顆粒性、鬆軟砂土，而當細粒料含量高時，孔隙水壓消散速度慢，則不適合使用；強制性真空降水，則又需進行預壓，機具設備流動困難度高，用於大面積的改良效果有限。”高真空擊密法”是結合了動力夯實與真空降水的ㄧ種工法，用於加固飽和的軟地基。經由多次真空降水與夯實，有效達到加固軟地基的功效。
本研究介紹此種創新的工法(動力夯實+真空降水)，應用於改良飽和軟黏土時的成效，在經由多次的夯擊與真空降水循環作用下得以達到預期的地盤改良效果。本文亦針對大陸寧波港煤炭試驗區，其對高真空擊密法的技術要求、施工流程與加固機理方面進行深入的探討，確認和優化相關排水參數，得以用來為大面積施工提供夯擊能量、夯點間距、夯擊次數等施工參數。並且於試驗過程中，進行各項自主檢測與監測，試驗過程中和試驗後的監測與檢測結果顯示，於粉煤灰層圓錐灌入試驗qt值提高2.5倍以上；淤泥質粘土層圓錐灌入試驗qt值提高到1.5倍以上；地基承載力達到135kPa。並由於在數遍的高真空作用下可節省工期時間約50%，若一般土壤水泥混合方法比較下可節省40%以上的造價。

關鍵字

動力夯實 ； 垂直排水帶 ； 真空降水 ； 高真空擊密法

並列摘要

Dynamic compaction is applicable for granular and loose sandy soil. With the fines content at a high level, it become difficult for the pore water pressure to dissipate and for the energy to transfer. In such situation stage, vertical drainage method such as wick drains, somehow be useful to solve the problem. But, it requires pre-loading, process to build up excess pore water pressure. For the pre-loading stage, large amount of soil mass to used and may encounter difficulties in move in and out. One of the old traditional technique, the vacuum method, which requires no pre-loading soil mass, but its subsequent drainage effectiveness gradually decreases. Therefore, a combination of the dynamic compaction and vacuum method is applied for the improvement of saturated soft foundation. Repeated vacuum dewatering and compaction cycles, can achieve rapid effectiveness enhancing of soft deposit .
In this study, a combination of the high vacuum and dynamic compaction method (hereafter called the “HV+DC” method) is simultaneously employed for the improvement of saturated soft foundation. HV and DC are applied alternately and repeatedly to achieve the required level of ground improvement. The current study presents an in-depth investigation of the technical requirements, processes and mechanisms involved in the “HV+DC” method at the Ningbo Harbor Coal test site near Shanghai, China. Relevant drainage control parameters are identified and optimized so as to provide the construction parameters, such as compaction energy, spacing, drop number, vacuum dewatering number and location, wellpoint depth and number, for large area construction. The monitoring during the field trial case study presented here indicates that the method is not only based on sound concepts, has rapid stabilization effects, and low construction cost, but also holds significant promise as an innovative ground improvement method whenever soft soils are encountered. The application of the “HV+DC” method increased the cone penetration tip resistance, qt of the pond fly ash layer at the Ningbo site to over 2.5 times, and that of the clay mud layer to over 1.5 times (compared to unmodified ground), and improved the characteristic value of the bearing capacity of the foundation up to 135 KPa, all of which adequately met the design requirements. For the total area of 400,000 m2 of the main project, this innovative method has saved over 40% of total cost, and about 50% of construction time from the original design of soil cement mixing method.

並列關鍵字

Vacuum Dewatering ； Dynamic Compaction ； High Vacuum Densification Method (HVDM) ； Wick Drain

參考文獻

【7】余明山、何泰源、林英堂，「台灣地區地盤改良技術發展之回顧與展望」，地工技術雜誌，第100期，第41~62頁，2004。

【52】林本騏、莫若楫，「曼谷第二國際機場之機場空側區地盤改良工程案例探討」，地工技術，第93期，第81~96頁，2002。

【47】闕河淵、張修碩、于中原、方仲秋，「台北捷運北投機廠填土沉陷案例」，

【41】王正吉、沈文忠，「地質改良-垂直排水帶工法及實例介紹」，地工技術，第63期，第47~56頁，1997。

【28】鍾毓東、葉嘉鎮、吳偉康、余名山，「深層夯實改良應用於新生地之案例」，地工技術，第五十一期，第67 ~78頁，1995。