In a soil specimen, the total stress, effective stress, hydraulic gradient and critical hydraulic gradient are $\sigma, \: \sigma’$, $i$ and $i_c$, respectively. For initiation of quicksand condition, which one of the following statements is TRUE?

1. $\sigma’ \neq 0$ and $i=i_c$
2. $\sigma’ = 0$ and $i=i_c$
3. $\sigma’ \neq 0$ and $i \neq i_c$
4. $\sigma = 0$ and $i=i_c$