The expansive soil is one of the most important problems faced by the engineer in the field of soil mechanics and foundation engineering because of the damage caused by engineering facilities such as light buildings, roads and other light engineering facilities.
The objective of the study is to study the volumetric variation of the soil as a result of the leakage of water from the pipes and septic tanks using the uncoupled solution with finite elements method based on the Seep / W and Sigma / W packages of the Geo-studio 2012 program. We chose (Siddiq district) from the left side of Mosul city Because of it swelling properties and effect on the buildings sited on it. The effect of the change of the base width, the load, distance the source of the leakage from the base edge, was studied on the swelling and the type of relationship that the inflation associated with these variables. The results showed that there is a critical distance to the drainage tank from the edge of the base where the swelling is at its greatest value, and the swelling decreases as we move away from this distance. A study of the effect of water leakage from sewage pipes revealed that there is a critical depth of these pipes on the base edge, which has a swelling at its highest value and also decreases as we move away from this depth. Therefore, when designing the buildings built on the soils, the sites of the pipes and reservoirs of sewage and then from both the critical and critical depth, which leads to reduce the rate of swelling and achieve the integrity of engineering origin. It is noted that the highest swelling rate (0.96%) was at a width of 3m and carried a 50kN load when the sewage pipe was 2m horizontally and vertically from the edge of the foundation and the soil surface, respectively. (-0.98%) for the basis of width (0.5m) and under the influence of a load of 150kN when the coordinates of the tube (1m) from the surface of the earth and (6m) from the edge of the base.