The sand miners monuments is off of West Shore Rd in a parking lot just south of the light for Harbor Links golf course entrance. I'm assuming that's also the location of the conveyor tunnel which is said to have been incorporated into the monument. I remember as a kid the old sand mine long after it was abandoned. There was a massive structure that I guess was the elevator and conveyor.
The "tunnel" under Sands Point Rd is really more of an underpass ever since the mining operation. You'll notice how Sands Point Rd slopes uphill gently from Manorhaven into Sands Point, but if you're on any street from Boxwood and up til about Kirkwood, you'll notice that its all flat but dead ends at a steap hill with Sands Point up top. This is the neighborhood that was mined. The underpass, as was said before can be viewed from Ashwood (between Ford and Cambridge) or on the other side at the back of the Sousa parking lot. This underpass, according to a website that had been referred to on this website years ago, was for a turn around loop used by a rail service that carried the sand closer to the water for loading on to barges.As far as I know, It was NOT ever connected to LIRR.