根据《桩规》第 5.9.10 条第 1 款
$$
\beta_ {\mathrm{hs}} = \left(\frac {8 0 0}{h _ {0}}\right) ^ {1 / 4} = \left[ \frac {8 0 0}{9 2 0} \right] ^ {\frac {1}{4}} = 0. 9 6 6
$$
$$
\lambda = a _ {\mathrm{x}} / h _ {0} = \frac {4 0 0}{9 2 0} = 0. 4 3 5 \in [ 0. 2 5, 3 ]
$$
$$
\alpha = \frac {1 . 7 5}{\lambda + 1} = \frac {1 . 7 5}{1 . 4 3 5} = 1. 2 2
$$
$$
V \leqslant \beta_ {\mathrm{hs}} \alpha f _ {\mathrm{t}} b _ {0} h _ {0} = 0. 9 6 6 \times 1. 4 3 \times 3 0 0 0 \times 9 2 0 \times 1 0 ^ {- 3} = 4 6 5 1 \mathrm{kN}
$$
因此选（B）
根据《桩规》第 5.9.7 条第 2 款
$$
a _ {0 \mathrm{x}} = a _ {0 \mathrm{y}} = 4 0 0 \mathrm{mm}
$$
$$
\lambda = a _ {0} / h _ {0} = \frac {4 0 0}{9 2 0} = 0. 4 3 5 \in [ 0. 2 5, 1. 0 ]
$$
$$
\beta_ {\mathrm{hp}} = 1. 0 - \frac {0 . 1 \times (1 0 0 0 - 8 0 0)}{2 0 0 0 - 8 0 0} = 0. 9 8 3
$$
$$
\beta_ {0} = \frac {0 . 8 4}{\lambda + 0 . 2} = \frac {0 . 8 4}{0 . 4 3 5 + 0 . 2} = 1. 3 2
$$
$$
F _ {l} \leqslant \beta_ {\mathrm{hp}} \beta_ {0} u _ {\mathrm{m}} f _ {\mathrm{t}} h _ {0} = 0. 9 8 3 \times 1. 3 2 \times (0. 7 + 0. 4) \times 4 \times 1. 4 3 \times 9 2 0 = 7 5 1 1 \mathrm{kN}
$$
因此选（D）
