The drop of water table induced by excess drainage
after tunnel excavation in waterrich area would cause damage
to normal growth of vegetation and ecological balance. As a result, the methods
to determine the tunnel drainage volume based on ecological groundwater table are
proposed. By taking a highway tunnel under construction in Fuzhou for example,
a calculating method for the limit drainage volume of tunnel is proposed based
on hydrogeology and the concept of ecological equilibrium embedment depth of
groundwater. First, the groundwater seepage model of tunnel is established
based on areawell method in groundwater dynamics,
which reveals the relationship between the water inflow volume and groundwater
table drawdown. Second, according to the proposed groundwater seepage model,
the tunnel drainage time that meets the requirements of the ecological
equilibrium embedment depth of groundwater is obtained on the premise of the
survival of vegetation, and then the influence scope of the drainage funnel is
derived. Third, the rainfall supplement volume W within the influence range is obtained by using the method of
rainfall infiltration coefficient, and then the W is compared to the total groundwater discharge volume Qt. Finally, through adjusting unit
groundwater drainage q to
make W equal to Qt, q is the maximum allowable groundwater discharge in the tunnel site.
Some conclusions are drawn as follows: (1) When the ecological equilibrium
embedment depth of groundwater is constant, with the increase of q, the influence range of the tunnel
decreases, W also decreases,
and Qt increases gradually.
Therefore, there is a unit drainage that makes the total groundwater discharge
equal to rainfall supplement. (2) The limit tunnel drainage obtained without
considering the time effect of water stress is more conservative than that
obtained with water stress. The q of the tunnel under construction is 0.4 m3/(m·d).
XIAO Zerong
. Design and Calculation of Tunnel Drainage Based on
Ecological Equilibrium Embedment Depth of Groundwater[J]. Tunnel Construction, 2020
, 40(10)
: 1471
-1479
.
DOI: 10.3973/j.issn.2096-4498.2020.10.011
