B$1.$ A $5$m by $3$m raft foundation, shown in Figure B$1,$ supports a permanent vertical load of $1000$kN and a variable vertical load of $500$kN spread uniformly over the area of the foundation. There is also a horizontal load of $20$kN acting at $5$m above the formation level. It is known to be stable with the current ground water level at $5$m below ground level. A ground investigation shows that the underlying soil profile consists of medium dense sand with a cohesion of $3$kPa, and an angle of friction of $35\backslash$deg $.$

The current ground water level is $5$m below the ground level and this was used when the original design was undertaken. It is now anticipated that the ground water level will rise to $1$m below the ground level because of changes to drainage conditions.

Check whether the foundation will still be stable when the ground water level rises to $1$m below ground level. Use Eurocode Design Approach $1$ Combination $1$ to check the stabilityFigure B$1$ Cross section of the foundation and ground profile