Tuesday, September 3, 2013



Earth Dams are usually constructed using the locally available soil. The soil properties used for construction of earth dam are important in design of slopes. Civil engineers involved in design and construction of earth dams know the difficulty of design of slopes for stability of earth dams. I worked as Assistant Engineer in Design Circle in 1999 in Tamilnadu Public Works Department. At that time I saw many engineers involved in design of earth dams working on A0-size graph sheets drawing the cross section and draw a slip circle. Then they will create many vertical slices of Earth dam portion and calculate the area of slices below MWL/FRL/DDL of SPZ/IPZ and take the moments of weight of slices and resisting forces and put them in tabular form in the graph sheet itself to find the factor of safety as per IS Code(Indian Standard code). The area is calculated by counting the number of squares manually from the graph sheet. The notations above are
MWL- Maximum water level
FRL  - Full Reservoir Level
DDL – Draw Down Level
SPZ  - Semi Permeable Zone( Outer Zone of earth dam)
IPZ   - ImPermeable Zone(Inner Zone of earth dam)
spzblk- Bulk Density of Semi Pervious Zone soil
ipzblk- Bulk Density of Im Pervious Zone soil
spzsub- Submerged Density of Semipervious zone
ipzsub- Submerged Density of Impervious zone
spzsat- Saturated Density of Semipervious zone
ipzsat- Saturated Density of Impervious zone

usually 6 trials for upstream and 6 trials for downstream are done for arriving at the minimum factor of safety against failure. Roughly one month will be taken to do the 12 no of trials and factor of safety for the worst condition is found out. After seeing the laborious work involved in that process, I develop a program in AutoLisp to work in Autocad with one input table in Visual Basic for AutoCAD. This program made the design of slope stability in one minute in Autocad.

You can download that STABILITY.RAR file from the following link.
The manual for this software is avalable in the following link