一、按水量平衡方法推导 如图1所示,采用浮动座标系,x轴位于堤坝底部,纵座标h_1轴则是浮动的,在任何时刻,使它通过库水位(或河水位)与虚拟坝坡m＇_1的交点上.m＇_1=m_1~2/(m_1+0.5). 库水位下降期间,浸润线将出现峰点(分水岭),并且峰点位置也将随时间变化.当初始状态时,库水位h_0尚未下降,故h_0=H_1,此时峰点位于B点,渗流全部泄向下游,由于B点位于浮动纵轴上,故峰点离纵座标之距l=0,当库水位下降到与下游水位齐平时,即h~0=H_2,堤坝内部渗流场呈对称状态,峰点位于浸润线中点,由于纵座标此时通过A点,故峰点离纵轴之距l=L/2,L是AC之距,是一已知数.当库水位h_0自H_1下降到H_2过程中,峰点轨迹可近似地以直线代替如图2所示 First, according to the water balance method derived as shown in Figure 1, the use of floating coordinate system, the x-axis is located at the bottom of the dam, the vertical axis h_1 axis is floating, at any time, make it through the reservoir water level (or river level) M’_1 = m_1 ~ 2 / (m_1 + 0.5) at the intersection of imaginary dam slope m’_1.The peak point (watershed) of the infiltration line will appear during the fall of the reservoir water level, and the position of the peak point will also change with time Initial state, the reservoir water level h_0 has not yet dropped, so h_0 = H_1, then the peak point at point B, the flow bleeds downstream, because B is located on the floating vertical axis, so the peak point from the vertical coordinate l = 0 , When the reservoir water level drops to the same level as the downstream water level, ie, h ~ 0 = H_2, the seepage field inside the dam is symmetrical, and the peak point is located at the midpoint of the saturation line. Since the ordinate passes through point A at this time, Axis distance l = L / 2, L is AC distance, is a known number.When the reservoir water level h_0 from H_1 down to H_2 process, the peak point trajectory can be replaced by a straight line as shown in Figure 2