As the weight (load) from the foundation of a building is transferred to the soil it spreads downwards outside the footprint of the foundation at a typical angle of 45 degrees.
Wrth i bwysau (llwyth) sylfaen adeilad gael ei drosglwyddo i'r pridd, bydd yn ymledu tuag i lawr y tu allan i ôl troed y sylfaen, ar ongl nodweddiadol o 45 gradd.