Theory of tachometry

S (Staff intercept)

I (Stadia Interval)

F (Focal Length)

D (Distance of vertical axis from optical center)

u (Distance of object from optical center)  

Tachometry

A special theodolite with three horizontal in cross hair through which staff reading taken which are used to calculated the distance between two points.

Anallatic Constant

Instrument for which multiplying constant ‘K’ is kept 100

                                          Additive constant ‘C’ kept 0

Counter fort retaining wall 

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Points to be remember:

1.       It is provided in height of retained earth goes beyond 7 to 8 m.

2.       Cantilever action of stem and heel slab of cantilever retaining wall converted into continuous slab.

3.       Design positive and negative bending moment calculated using bending moment coefficient.

4.       Clear spacing b/w counter forts lies b/w H/3 to H/2)

5.       Counter fort is designed on T-beam and main R/F provided on inclined face.

Cantilever retaining wall

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Points to be remember:-

1. It becomes uneconomical if height of retained earth goes beyond 8mtr.

2. Stem, heel and toe slab bend like cantilever.

3. Thickness of any slab should not be less than 150mm.

4. Stem is generally tapered with maximum thickness of bottom.

5. Main R/F of stem is provided on bank face.

6. Main R/F of heel and toe slab is on top and bottom respectively.

7. Critical section for bending of heel and toe slab are at back and front respectively.

8. Critical section for bending of stem is at the junction of base slab and stem.

9. Active earth pressure produces disturbing force and disturbing moment for sliding and overturning.

10. Disturbing Force =Pa=

11. Disturbing Moment=PaxH/3

12. Restoring moment is obtained by self weight of retaining wall and soil above heel slab.

                (Restoring moment=09w x Perpendicular distance between W and toe point.)

13. Restoring force for sliding is obtain from friction between base slab and soil below it. If friction is not sufficient than shear key is provided and placed in such a way that main R/F of stem can be extended inside the shear key for anchorage.

                             (Restoring force=Friction +Pp)