木質生態工程擋土牆結構分析與測試

Abstract

木材因加工能源消耗較水泥為低，且可涵存二氧化碳，具備節能減碳的特性，也是一種生物性的可分解材料，並且施工簡便，因此常在生態工程中使用；尤其在國內的邊坡整治，經常以「木格框擋土牆」的形式構築。木格框擋土牆施工法是相當古老的一種工法，因此已有不少的改良形態出現，如近年由日本研發的「O&D工法」。然因缺乏可靠的強度資訊，使得許多使用者對其安全性產生疑慮，限制其於小型的崩塌地整治所採用。本研究便模擬真實情形的O&D工法擋土牆試驗，以及使用STAAD PRO 2005軟體分析擋土牆的載重和位移量。 常見的木格框擋土牆設計，一般以長1m，寬1m為構築單位，高度182cm。構築時需先以2,000PSI的水泥灌注基礎至少15cm厚。測試樣本至少為一個構築單位，待現場組裝完成後，回填合格的石材至框中，將100噸油壓缸一端安裝於反力牆，一端安裝夾具與木格框連結，施以5kN/sec和40mm/sec的載重，以模擬擋土牆使用時的受力情形，並以NDI 3D Investigator Motion Capture System紀錄其資料。 經過測試發現，實際的測試值並未和電腦模擬有完全的一致性，其原因除了木材本身為非完全均勻的異方性材料，變異性也較大，再加上施工品質的關係，因木材本身材質特殊，必須在現地施工的時候隨機應變，因此經驗法則大於設計圖上的規劃，種種因素造成電腦模擬和實作的誤差。 在試驗之後可以發現，木格框擋土牆的最大載重可達5.6噸，而最小者有2.6噸，在沒有放置岩石的情況下最大載重亦可達2.4噸。測試結果可以發現，7座木格框擋土牆試驗的安全係數以及電腦模擬的結果皆在標準值(擋土牆抵抗滑動之安全係數，於長期載重狀況應大於1.5，於地震時應大於1.2。擋土牆抵抗傾覆之安全係數，於長期載重狀況時應大於2.0，於地震時應大於1.5。)之上。

Wood has the characteristics of energy saving and carbon dioxide reduction because it consumed less energy than cement did during process and sequestrated carbon dioxide. Due to the biodegradable and convenient constructive, Wood is often used in eco-technology engineering work in Taiwan. Wood was often applied in cellular retaining wall in slope remediation. Since wood cellular retaining wall was a very old construction method, it was improved in many types. The O&D (outdoor) method from Japan was one of the examples. However, the reliable strength information is insufficient; there are many safety concerns on it. Hence, the utilization area was limited and it was only constructed in small site in small scale. In this study, we simulate the real situation of the wood cellular retaining wall by method O&D test, and analyzing STAAD PRO 2005 software load and displacement of wood cellular retaining walls. The common frame of wood cellular retaining wall is generally long 1m, 1m to build a unit width, height 182cm. Before constructing, it’s required to build the 2,000 PSI of cement for base at least 15cm thick. The test sample must be one building unit at least, after assembly, such as on-site the qualified stone backfill to the wood cellular retaining wall. One end of the 100 tons of hydraulic cylinders is mounted on the reaction wall and another end of it is mounted on the lag screw block. The load imposed is set to 5kN/sec and 40mm/sec. At the same time, we use NDI - 3D Investigator Motion Capture System recording the data. In testing, the actual test values and computer simulations have not been entirely consistent, due to the reason for the wood itself is not completely homogeneous anisotropic materials, variation is also larger. With the relationship between construction quality and construction must be adaptable in the site. Therefore, the rule of thumb is more important than the planning on the design. All these factors cause the computer simulation and implementation errors. According to tests, the maximum load of wood cellular retaining wall is 5.6 tons, while the smallest is 2.6 tons. When the wood cellular retaining wall is not placing any rock inside, the maximum load could be 2.4. However, the safety factor of seven wood cellular retaining walls and computer simulation results are above the standard value.