根据《桩规》5.9.7条，$b=0.8d=0.8\times400=320\mathrm{mm}$。$h=700\mathrm{mm}0.25$。$\beta_{1x}=\beta_{1y}=\frac{0.84}{\lambda_{1x}+0.2}=\frac{0.84}{1+0.2}=0.7$。冲切承载力=$2[\beta_{1x}(b_1+a_{1y})+\beta_{1y}(h_1+a_{1x})]\beta_{hp} f_t h_0=2\times[0.7\times(0.65\times2+0.8+0.59)+0.7\times(0.65\times2+0.8+0.59)]\times1.0\times1570\times(0.7-0.11)=6976.9\mathrm{kN}$。选A。