反覆衝擊載重下鑽孔對岩石損傷影響

Abstract

岩石隧道工程常見的工法為新奧工法以及TBM工法，相較於適於長隧道、地質變異小的TBM工法，新奧工法因開挖、支撐作業彈性大，而有較大的適用性。新奧工法主要以鑽炸或是機械進行岩盤開挖，前者開炸效率較高，但開炸擾動較大，且伴隨振動與噪音，使用上會有所限制；後者遂成為應用新奧工法在環境限制條件下的最後選項。然而對於節理稀疏、靭度較高岩盤，岩石破碎難度大，現地常利用鑽堡在開挖面鑽孔，再利用液壓錘反覆衝擊岩盤表面，增加開挖效率。儘管實務上常見預鑽孔提高反覆衝擊開挖岩盤的作業方式，然而鑽孔的效益為何? 是否存在對反覆衝擊開挖岩盤的碎岩機制有何差異? 目前相關研究付之闕如，以致鑽孔與反覆衝擊錘擊位置的配合，儘能憑藉作業人員經驗及運氣。 本研究應用離散元素法建立一套數值模式，探討鑽孔存在與否情況下，反覆衝擊生成應力波在岩盤中的傳遞差異。數值模型透過應力波振幅隨傳遞距離增加而衰減驗證其正確性，並試圖透過物理模型試驗結果比較其應用性後，繼而應用於探討反覆衝擊下鑽孔對岩盤損傷的影響。 研究結果顯示，根據數值模擬結果能與應力波相關理論進行驗證，得以確定數值模擬符合理論。當應力波傳遞過孔洞時對周遭的速度振幅會有影響，在不同孔洞大小及位置還有擊打時所產生的波長都會對此造成有不同結果。擊打時孔洞周遭會有破壞的產生也能利用波傳特行進行解釋，得以確認鑽孔可對開挖效率提升。

The common construction methods for rock tunnel engineering are the New Austrian Tunnelling Method (NATM) and Tunnel Boring Machine (TBM) method. Compared to the TBM method, which is suitable for long tunnels with less geological variability, the NATM offers greater flexibility in excavation and support operations, making it more versatile. The NATM primarily involves rock excavation using drilling and blasting or mechanical methods. The former has higher excavation efficiency but causes greater disturbance, vibration, and noise, limiting its usage. Therefore, the latter becomes the final option when applying the NATM under environmental restrictions. However, for rock formations with sparse joints and higher strength, rock fragmentation becomes more challenging. In such cases, boreholes are drilled on the excavation face, and hydraulic hammers are used to repeatedly impact the rock surface, thereby increasing excavation efficiency. Although pre-drilling is commonly employed to improve the effectiveness of repeated impact excavation, the benefits of drilling are often unclear. Furthermore, the existence of differences in rock fragmentation mechanisms during repeated impact excavation remains largely unexplored. As a result, the coordination between borehole placement and the impact locations of the hammer mainly relies on the experience and luck of the operators.

This study applies the Discrete Element Method (DEM) to establish a numerical model to investigate the differences in the propagation of stress waves in rock formations under repeated impacts, considering the presence or absence of boreholes. The numerical model verifies its accuracy by examining the attenuation of stress wave amplitudes with increasing propagation distance. Furthermore, the applicability of the model is evaluated by comparing it with physical model test results. Subsequently, the model is employed to examine the influence of boreholes on rock damage under repeated impacts. The research findings indicate that the numerical simulation results are consistent with the theoretical principles of stress wave propagation, confirming the validity of the numerical model. When stress waves pass through boreholes, they affect the velocity amplitudes in the surrounding area. The size and location of the boreholes, as well as the wavelength generated during impacts, produce different outcomes. The presence of boreholes can enhance excavation efficiency, as the damage around the boreholes during impacts can be explained by the propagation characteristics of waves.