洞室开挖稳定分析、如何建设隧洞外文文献翻译（四篇）.docxVIP

TunnelStability Analysis of Tunnel ExcavationAspillway tunnel for an embankment dam is to be constructed in a poor qualitysandstone. The excavated diameter of the tunnel is about13m and the cover over the roof is 8m. The tunnel is to have a 1.3 m thick un-reinforced concrete liningand,after placement ofthis lifting, a 28 to high portion of the rockfill dam will he over the constructed tunnel.The questions to be addressed are:(1)What support is required in order to excavate the tunnel safely under the very shallowcover? (2)Is the proposed top heading and bench excavation sequence, using drill and blastmethods, appropriate for this tunnel?(3)How will the concrete lining respond to the loading imposed by the placement of 28m of rockfill over the tunnel?In order to answer these questions a series of two-dimensional finite element analyseswere carried using the program PHASE`. The first of these analyses examined the stabilityand support requirements for the top heading excavation. The final analysis included theentire excavation and support sequence and the placement of the rockfill over the tunnel.The rock mass is a poor quality sandstone that, being close to surface, is heavily jointed. The mechanical properties assumed for this rock mass are a cohesive strength C=0.04Mpa,afriction angle of 40 and a modulus of deformation E =1334 MPa. No in situ stressmeasurements are available but, because of the location of thetunnel in the valley side, it hasbeen assumed that the horizontal stress normal to the tunnel axis has been reduced by stress relief.The model is loaded by gravity and a ratio of horizontal to vertical stress or 0.5 is assumed. A simplifiedversionofthe model was used toanalyse the stability and supportrequirements for the top heading. This model did exclude the concrete liningand the benchexcavations.The first model was used to examine the conditions for a full-face excavation of the top heading without anysupport. This is always a useful starting point in