Model experiments on seepage through the steel sheet pile walls were performed. The volume of water leaking out through interlocking joints of sheet piles, and the water head at the front and rear parts of the sheet pile wall were measured under the various conditions of the water pressure applied by changing the head of water tank located behind the sheet pile wall.
　The results are as follows:
　The volume of water flowing out per unit length of interlocking joint, in unit time period, q, is expressed by the formula, q=K・hn, where h is the head loss between the front and rear point of interlocking joint; K and n are coefficients.
　The value of n is practically 0.5 for sheet pile walls without saturated soils at the both sides. On the other hand, the value of n is practically 1.0 for sheet pile walls with saturated soils at the one side or both sides.
　Based on these results, the practical calculation method of seepage for structures with sheet pile walls was examined.