根据《地规》第8.5.19条第2款第2）小款

$\lambda_{12} = \frac{a_{12}}{h_0} = \frac{0.626}{0.92} = 0.68$ ，满足 $0.25\sim 1.0$ 的要求。

$$ \alpha_ {1 2} = \frac {0 . 5 6}{\lambda_ {1 2} + 0 . 2} = \frac {0 . 5 6}{0 . 6 8 + 0 . 2} = 0. 6 3 6 $$

根据《地规》第8.2.8条

$$ \beta_ {\mathrm{hp}} = 1. 0 + \frac {0 . 9 - 1 . 0}{2 . 0 - 0 . 8} \times (1. 0 - 0. 8) = 0. 9 8 3 $$

$N_{l}=\beta_{12}\left(2c_{2}+a_{12}\right)\beta_{hp}\tan\frac{\theta_{2}}{2}f_{t}h_{0}=0.636\times\left(2\times1.039+0.626\right)\times0.983\times\tan30^{\circ}\times1430\times0.92=12\ 84kN$

因此选（C）