The work area of a tunnel in northwest Sichuan is characterized by active tectonics,heavily fractured rock masses,and high water pressure,posing severe challenges for both construction and operation of the tunnel.To investigate the impacts of water inflow and water pressure on tunnel construction and operation,geological explorations were conducted in the tunnel site,followed by theoretical calculations and finite element simulations to analyze the water inflow volume and water pressure distribution during both construction and operational phases.The findings are summarized as follows:(1)The rocks within the hydrogeological units of the tunnel site are non-soluble rocks,with groundwater classified as fissure water in moderately water-bearing rock strata.Due to tectonic activities,the rock masses are extensively fractured,providing favorable conduits for groundwater seepage.The primary recharge source of groundwater in the tunnel site is precipitation,with an annual average rainfall of approximately 620 mm and a maximum recorded rainfall of around 1 034 mm.(2)The normal water inflow for the entire tunnel is estimated at about 6 940 m3/d,with a maximum potential inflow of up to 11 610 m3/d.(3)Following tunnel excavation,a precipitation funnel forms above the rock over the tunnel,leading to partial loss of groundwater,while heavy rainfall events significantly elevate the groundwater level.(4)As the water head height increases,a substantial surge in tunnel water pressure and inflow is observed,threatening the structural safety of the tunnel.The design of drainage and waterproofing structures,as well as tunnel lining,shall take into account the effects of heavy rainfall.
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