The modelling pressure on concrete dam walls project

Concrete walls dam are made up of concrete and steel reinforcements. Concrete wall dams’ faces pressure and stresses of different types on its walls and bed due to water pressure, weight of dam, waves and ice pressure and many other factors. This creates stability issues in dam. This report examine all those stresses and pressure that concrete dam wall faces and devise an algorithm using which safety factor can be calculated in order to deal with pressures.

There are various kinds of pressure that a concrete wall dam faces. 

1. Water stresses and pressure:

The water in the dam acts perpendicularly on the upstream dam’s face. Now there can be two conditions when the upstream face of dam is vertical and downstream side of the dam is empty. Now the water pressure is in horizontal direction as well as it acts on the upstream wall or the face at a certain height of H/3 from the bottom of dam. The water pressure can be computed by using the equation below: (Joel Anderson)

 

 

 

Forces acting on dam

 

 

Pressure1=wH²/2

Where ‘w’ is specific weight of water 

‘H’ is height in meters

Now as if there is a presence of slope at the upstream side of dam another pressure acts vertically downwards due to presence of water column that rests on the slope on upstream side wall. Now this pressure can be calculated as:

 

Pressure 2 = (bh₂w) + (0.5bh₁w)

Where ‘b’ represents the portion of b beneath the column.  Another condition is when the water is present at both sides i.e. upstream and downstream side. In this condition this pressure can be neglected as the water pressure at the downstream side would balance the pressure or reduce the pressure at the upstream side and overall it will stabilize the same concrete walls.

 

2.                          Stability issue due to water pressure:

 

Stability issue arises when there is water pressure at only one side of the concrete wall i.e. upstream side. The concrete wall has to be strong enough to bear the water pressure to ensure stability of wall.

1. Weight of dam:

The weight of dam includes the weight of concrete walls, mass of all the construction material  used and all additional shapes or structures given to it. This weight can be calculated using formula as follows: (Joel Anderson)

 

W= P_c * V * g +Σ F_ex

Where ‘P_c’ represents density in Kg/m³

‘V’ represents Volume in m³

‘Σ F_ex’ represents the sum of all installations in the dam

     

     2.                          Ice pressure on dam concrete walls:

As the climatic variations occur so a snow or ice sheets over the surface of dam can add to the dam weight. If the thickness of ice sheets is greater than 0.4 m then it cannot be neglected. (Joel Anderson)

     

      3.                          Pressure due to waves:

There are some loads that are dynamic such as the variations in the water flow. The waves generated when are moving at faster rate and hits the dams wall with pressure, it has the potential to crack the concrete walls. Small magnitudes can be neglected but larger magnitude imparts great pressure. (Joel Anderson)

 

      4.                          Silt and rocks sediments pressure:

Rock sediments and silt often get deposited over the dam beds. This will create additional pressure on the dam’s walls and it depends on the dimensions of the rocks. The pressure due to sediments can be calculated using formula:

Ps = (Ka * r * Z₃²)/2

Here r represents the saturated unit weight of the sediments

Z₃ represents the depth of sediment

Ka equals to:  Ka= 1-sin θ / 1+ sin θ

Where θ is the angle of the shearing resistance of the sediment

      

     5.                          Earth quakes and erosions:

Whenever any seismic activity occurs, it releases sudden energy and results in sudden breaking of dam. This results in tsunamis. In addition to that sudden erosions or volcanic eruption can also results in the earth quakes.

 

     6.                          Uplift pressure and seepage loads pressure:

At the base of concrete dams, there is pressure due to creation of cracks and fissures as water penetrates into them. This pressure can be controlled by using relief drains in the lower part of dam.

 

     3.                          Stability issues:

There are three kinds of stability issues or failure modes that can occur in the dam. Those are: (Joel Anderson)

                    Rotation and overturning:

 

As many types of pressures are exerting on the dam, so if the resultant of these forces at any section of dam passes through the toe of dam the dam will rotate and overturn about the toe and create instability in dam.

                    Translation and sliding:

This type of instability occurs when the sum of horizontal forces acting on a dam at its base exceeds the sum of frictional forces, it generates a sliding failure.

                                    Overstress and material failure:

Sometimes the material used in construction fails such as cracks in the concrete walls and water seepage in these cracks can create instability in walls.