以UDEC探討處置坑道開挖引致圍岩損傷之研究

將以 UDEC 離散體分析軟體建立處置場坑道開挖之二維數值模型，據此分析處置母岩在不同的岩覆深度與可能的既存裂隙(或弱面)條件下，因坑道開挖引致的岩體損傷。首先，根據已蒐集之單壓強度、彈性模數、柏松比、應力應變曲線及試體破壞型態，作為力學參數訓練與率定之依據。處置坑道 UDEC 模型建模與開挖模擬分析考量深度(Z)與現地應力比(K)條件下之處置坑道及既存裂隙(45度角)之位態等條件下進行 UDEC 數值模型開挖分析。本文主要獲致結論如下： 1.使用UDEC分析開挖處置坑道對周圍岩體與節理行為之影響，獲知其關鍵因子為現地應力比K與深度Z兩者，其中，K值主要控制發生破壞之區域，而深度Z則主控破壞之嚴重程度， (i)先開挖處置坑道後，在隧道周圍會呈現低壓力區或受張力區，因此當周圍岩體在承受較大壓力時(深度Z越深)，愈容易在此處形成損傷破壞；(ii)再開挖處置孔後，會因應力重新分配的轉移過程，會釋放原來在處置隧道轉角處之應力集中現象，此點亦與FLAC之分析類似(胡乃壬，2021)。 2.開挖處置坑道對位於處置孔旁的節理面之影響，獲知: (i)先挖處置隧道後，應力傳遞過程會在節理兩端形成壓應力集中；(ii)再開挖處置孔後應力釋放，因節理造成周圍應力傳遞上的阻隔，致使節理面上方近孔端節理面上之正向應力會被釋放至0，亦表示張力破壞多先發生於近孔端，滑動破壞則接續在張力破壞之後，遠端則仍承受少許正向應力作用保持穩定狀態。節理面下方則主要受現地應力條件的影響。節理破壞型態主要有:張力破壞與滑動破壞；節理破壞型態主要受K值影響，K>1時節理只發生張力破壞，而K≦1則產生張力破壞與滑動破壞之混合破裂型態。 3.處置孔壁之側向位移量、隧道地面的隆起量、節理面近孔端之開口量主要受深度Z的影響，當深度Z越深時會產生較大的位移量。當處置孔周圍存在節理面時也會造成較大之位移量，且最大開口量發生在節理與孔壁交會處。 4.開挖處置孔後，張力區受節理傾角之影響，傾斜節理皆會使張力區範圍增加，而水平節理則使張力區範圍縮減。 5.從UDEC單獨採用連續體模式(zone)及結合voronoi之非連續體模式之模擬結果發現: (i)兩類模型皆可顯示開挖處置隧道與處置孔後，在幾何轉角處的應力集中現象；但對顯示低壓應力帶，非連續體模型(w/ block)則可呈現出較細部的應力分布。(ii)節理尖端之破裂延伸軌跡，在連續體模型是由破壞網格(zone)來表現；而非連續體模型則可知道塊體間發生張力破壞與其軌跡。 6.經UDEC與FLAC比較可得知(i) 由於UDEC可設置voronoi非連續體的塊體( Block)，故應力呈現更詳細，FLAC則是比較巨觀顯示； (ii)UDEC結合voronoi塊體可將顆粒間接觸面發生張力/滑動破壞分辨顯示出來，而FLAC則是將破壞模式依照整個區域(zone)大小來顯示。

關鍵字

花崗岩； UDEC ；處置坑道；裂隙；張力破壞/滑動破壞

並列摘要

The UDEC discrete volume analysis software will be used to establish a two-dimensional numerical model of the excavation of the disposal site. Based on this analysis, the disposal of the parent rock will be caused by the excavation of the excavation under the conditions of different rock cover depths and possible existing cracks (or weak surfaces). Rock damage. First, according to the collected single compressive strength, elastic modulus, Poisson's ratio, stress-strain curve and the failure type of the specimen, it is used as the basis for mechanical parameter training and calibration. Disposal tunnel UDEC model modeling and excavation simulation analysis considers the depth (Z) and the existing stress ratio (K) of the disposal tunnel and the existing cracks (45 degree angle) under the conditions of UDEC numerical model excavation analysis. The main conclusions obtained in this paper are as follows: 1. Use UDEC to analyze the impact of excavation and disposal of tunnels on the surrounding rock mass and joint behavior, and it is known that the key factors are the in-situ stress ratio K and the depth Z. Among them, the K value mainly controls the area where damage occurs, and the depth Z is the main factor. Control the severity of damage, (i) After excavation and disposal of the tunnel first, there will be a low pressure zone or a tension zone around the tunnel. Therefore, when the surrounding rock mass is under greater pressure, the easier it is Damage and destruction are formed here; (ii) After the disposal hole is excavated, the original stress concentration phenomenon at the corner of the disposal tunnel will be released due to the transfer process of stress redistribution. This point is also similar to the FLAC analysis. 2. The impact of excavation of the disposal tunnel on the joint surface next to the disposal hole is known: (i) After the disposal of the tunnel is first excavated, the stress transfer process will form a compressive stress concentration at both ends of the joint; (ii) the stress after the excavation of the disposal hole Release, due to the resistance of the surrounding stress transmission caused by the joint, the normal stress on the joint surface above the joint surface near the hole end will be released to 0, which also means that the tension failure mostly occurs at the near hole end first, and the sliding failure continues in the tension After the failure, the distal end still bears a little normal stress to maintain a stable state. The bottom of the joint plane is mainly affected by the existing ground stress conditions. The joint failure types mainly include tension failure and sliding failure; the joint failure type is mainly affected by the K value. When K>1, only tension failure occurs in the joint, and K≦1 produces a mixed failure type of tension failure and sliding failure. 3. The lateral displacement of the hole wall, the uplift of the tunnel ground, and the opening of the joint surface near the hole end are mainly affected by the depth Z. The deeper the depth Z, the greater the displacement will be. When there is a joint surface around the disposal hole, it will also cause a larger displacement, and the maximum opening occurs at the intersection of the joint and the hole wall. 4. After excavation and disposal of holes, the tension zone is affected by the inclination of the joint. Inclined joints will increase the scope of the tension zone, while horizontal joints will reduce the scope of the tension zone. 5. From the simulation results of UDEC using the continuum model alone and the discontinuity model combined with voronoi, it is found that: (i) Both types of models can show the stress concentration phenomenon at the geometric corner after the excavation and disposal of the tunnel and the disposal hole; but For displaying low-pressure stress zones, the discontinuous model can show a finer stress distribution. (ii) The fracture extension trajectory of the joint tip is represented by the broken mesh in the continuum model; the non-continuum model can know the tension failure and its trajectory between the blocks. 6. The comparison between UDEC and FLAC shows that (i) Since UDEC can set the voronoi discontinuity block, the stress is more detailed, while FLAC is a more macroscopic display; (ii) UDEC combined with the voronoi block can combine the particles The tension/sliding failure of the contact surface is distinguished and displayed, while FLAC displays the failure mode according to the size of the entire area.