8. A school is holding a basketball shooting contest, with a total of 64 participants. It is known that each participant has a shooting accuracy of $\frac{3}{4}$ per shot. The rules are: only those who hit two consecutive shots will be admitted, and once admitted, they stop shooting; otherwise, they continue shooting until they have taken 4 shots. Let $\xi$ represent the number of admitted participants. Then $E \xi=$ $\qquad$
8. $\frac{189}{4}$.

The probability of each participant being admitted is
$$
\begin{aligned}
p & =\frac{3}{4} \times \frac{3}{4}+\frac{1}{4} \times \frac{3}{4} \times \frac{3}{4}+\frac{1}{4} \times \frac{1}{4} \times \frac{3}{4} \times \frac{3}{4} \\
& =\frac{189}{256} .
\end{aligned}
$$

Therefore, the number of admitted participants $\xi$ follows a binomial distribution, i.e.,
$$
\xi \sim B\left(64, \frac{189}{256}\right) \text {. }
$$

Thus, $E \xi=64 \times \frac{189}{256}=\frac{189}{4}$.