Site Investigation

1.  One borehole

It was a small urban site, which had been cleared to ground level.  One borehole was sunk, in the middle of the Site.  Below "Made Ground" it was sand all the way.

Foundations were designed on that basis.

When digging started, there was NO sand.

Further investigation showed that the borehole had been sunk down an abandoned well back-filled with sand..

2. Inland tides

When they were driving a long Tunnel in the middle of South Africa . . .

It is located some 250 miles from the sea, and is over 4000 feet above sea level.
As part of the ground investigation, they checked the water levels in local farm boreholes.
They discovered that the water levels rose and fell - with the passage of the moon - i.e. the water table was subject to tides.

They also noticed that the water level in one borehole rose when a train went past on the railway line - three miles away.

The tunnel happened to intersect a fault, through which water poured into the tunnel, which was then about a mile long; it was flooded within 24 hours.  They found that farm borehole water levels fell - up to sixty miles away.