Terzaghi provided a rational approach to design of filters. The following filter criteria should be satisfied-
D₁₅ of filter / D₈₅ of base materials < 4 to 5 < D₁₅ of filter/ D₁₅ of base materials
The filters should be such that neir embankment nor foundation material can penetrate and clog filters.

Earn dams are suitable for any type of foundation but re has to be a separate provision for spillway location. The mode of failure is sudden and requires high maintenance and overall life is not so long. It requires low to moderately skilled labors and moderate capital cost.

Swedish circle method is also called as method of slices and Fellenius method is a modified version of it. Swedish circle method assumes condition of plain strain with failure along a cylindrical arc. The location of center of possible failure arc is assumed and earth mass is divided into slices.

The outer zone is made of fairly pervious material like grit, gravel, and murrum. The innermost zone is done with fairly impervious material. The central core is covered by comparatively pervious transition zone which prevents piping through cracks which may develop in core.

There is a possibility that water may boil up near toe of dam when large scale seepage takes place through pervious foundation overlain by a thin less pervious layer. Relief wells or drain trenches and d/s berms beyond toe of dam are all provided to control sand boiling.

In case of large scale stratification a vertical filter is also provided along with horizontal filter so as to effectively intercept seeping water. This arrangement is nothing but is termed as chimney drain. It helps in keeping phreatic line well within dam body and also helps in rapid consolidation.

In this method, an embankment is created by water and earth slurry which is discharged inwards to form a central pool at site. When water is pumped to site it spreads coarser material drops out first and finest at last. Thus core material settles within central pool forming a zoned embankment and high pore pressures develop in core.

Equipotential lines are lines of equal energy. Every point on upstream face of an earth dam will be under equal total energy, this line acts as an equipotential line. Similarly, upstream floor of a weir acts as an equipotential line.

The entire dam may slide or just one face slides over foundation when foundation of earth dams is made of soft soils. Then foundation bulges out on side of movement. The top of embankment gets cracked and lower slope moves outward forming large mud waves near heel.

The toe filter consists of three layers of fine sand, coarse sand, and gravel with stone size or rock chips varying from 15 to 20 mm. It acts as a transition zone and prevents choking of toe and height of rock toe is kept between 1/3 to 1/4 of dam height to achieve good results.