Deadman Anchor Footing Design Guide
What a Deadman Anchor Does
A deadman anchor is a buried block or beam. It resists a pull through soil pressure. The soil in front of the anchor creates passive resistance. The footing size must match the design load. It must also fit the site geometry.
This calculator gives an early sizing check. It estimates the needed face length. It also checks the provided concrete block. The tool uses load, depth, soil weight, passive coefficient, and safety factor. It can add friction from concrete weight. Use that option with care. Friction may be reduced by wet soil, vibration, or poor contact.
Inputs That Control the Result
The main input is the service pull load. Enter the pull angle from horizontal. A level tie has a zero degree angle. A rising tie creates a vertical uplift part. The horizontal part pushes against the soil. The vertical part reduces useful weight. The calculator applies the safety factor to the horizontal demand. It also displays a provided safety factor.
Embedment depth is very important. Passive resistance changes with depth squared. A small depth increase can improve capacity. Soil quality still matters. Loose fill should not be treated like dense natural soil. Saturated soil can lose strength. Use conservative values for uncertain sites.
Soil and Resistance Factors
The passive pressure coefficient is called Kp. It depends on soil friction angle. Granular soil often has higher values. Clay needs a different engineering model. The reduction factor lowers the theoretical pressure. It helps account for excavation disturbance. It also covers rough construction tolerances. A lower value gives safer early sizing.
Concrete weight can help through base friction. The calculator multiplies net vertical weight by the friction coefficient. Uplift from the pull angle is subtracted first. If uplift is large, friction may become small. Passive resistance should normally be the main resisting action. Friction should not hide a poor embedment depth.
Dimensions and Bearing
The block dimensions also affect bearing pressure. Plan area equals face length times block width. Weight divided by plan area gives bearing pressure. The calculator compares it with allowable bearing. This is a simple gravity check. It does not replace settlement analysis. It also does not check sliding keys, tie rods, corrosion, or reinforcement.
Use the results as a planning guide. Increase depth first when space allows. Increase face length when trench length is available. Increase block width or height when weight and bearing help. Keep drainage in mind. Water behind or around the block can reduce resistance. Backfill should be compacted in controlled layers.
Safe Review Before Construction
A final design should include site soil data. It should also include local code requirements. Anchors near slopes need special review. Anchors near utilities need careful detailing. Temporary anchors may use different factors. Permanent anchors need durability checks. Ask a qualified engineer to review critical anchors before construction.
The example table below shows common trial cases. They are not recommended designs. They only show how inputs change capacity. A deep and narrow block can perform better than a shallow wide block. That happens because passive pressure grows fast with depth. However, construction access can limit depth. Frost depth can also matter in cold regions. The tie connection should pass through the block safely. Place steel so the pull spreads into concrete. Avoid sharp bends in rods or cables. Protect steel from corrosion. Record all assumptions before sharing the result. When uncertainty is high, choose a larger anchor and request field verification before backfilling the trench.