3 dimension array

how do i create a 3 dimension array using a looping? e.g [ [[1, 2], [3, 7] ], [ [9, 7], [7, 5] ] ]

here is the code i’m using, but it doesn’t work

_global.QU4 = new Array();
for (i=0; i<40; i++) {
for (b=0; b<40; b++) {
QU4*** = [i,i];
}
}

thanks