How to fix the crack,please find the image.some one explain the reason and solut

Cracks can occur due to chemical reactions in construction materials, changes in temperature and climate, foundation movements and settling of buildings, environmental stresses like nearby trains, earth quakes etc. Faulty design, bad quality materials, wrong method of construction, weather effects and lots of wear and tear can create cracks in walls, floors and ceilings.

In my opinion

1 It is due to settlement of earth filling i.e the earth filled under floor is not compacted well and voids remain which is settle letter on.

2. Settlement of foundation.

3. There is possibility of water leakage from any water supply pipes or sewer pipe or from rainy water enter in the earth under floor which damages the floor and wall.

For crack fixing you can take help from any good mason who will open the crack and fill it with cement and coarse sand mortar.This is temporary method but look ugly for the beauty of house.

The second method is first find the cause than remove the floor and compact the earth under floor and lay the new floor.