30.24=(2.4+2*0.45)*(3.6+2*0.45)*2+1/3*0.45*0.45*2*2*2=（a+2c+kh)(b+2c+kh)h+1/3*k*k*h*h*ha~长边b~短边c~工作面宽度k~放坡系数h~深度
