Civil Engineering - Surveying - Discussion

@All , Here is the explanation.


If we keep the instrument at downside on slope surface (1/10), then staff distance should not be more than 15m, otherwise, we can not see the reading on staff, as per this equation.

The Horizontal distance = height of staff/ slope ratio, d= 1.5/(1/10) = 15m.

Then the instrument will be moved to forward (upward direction) for BACK SIGHT reading, then we need to keep the instrument at this distance = (4-1.5) / (1/10) = 25m, more than 25m we can not see the staff or staff readings.

So, the total horizontal distance is 15+25 = 45m.

Solution;

Note: Here in Q it is not 1 1/2 actually it is only 1/2 so,
if upward slope asked then i.e +ve.
Sight= (Staff ht + instrument ht.)/(Slope)
Sight=(4+1/2)(1/10)
Sight=(4.5)*(10)
Sight=45 m.

And It will be 55 m in case if 1 1/2 only.

@Anshul & @Abhay.

You are making mistake the formula is,

h = (height of instrument + height of staff) / gradient.

How can you change the rule of solving round bracket first and then division?

h = height of the instrument+height of staff/gradient.

Slope = h square (2x staff length).

h = 3/2+4/10
= 1.5 + 0.4 = 1.9.

Slope = 1.9 square (2*4) = 0.45 m.

For 100 m slope = 45 m.

Sight on the up slope=(Instrument height +length of the staff)÷gradient.
=(4+1.5)÷1/10,
=55m.

The answer will be 20 because the slope is 1 in 10 it means in every 10 mtr slope height increasing 1 mtr then in 20 mtr it will be 2 mtr where HI is 1.5 mtr ( Slope is UPWARD).

h = height of the instrument+height of staff/gradient.

Slope = h^2/(2x staff length).

h = 3/2+4/10 = 1.5 + 0.4 = 1.9.

Slope = 1.9^2/(2*4) = 0.45 m.

For 100 m slope = 45 m.

Grading is 1:10 which is upwards and instrument height is 1.5m so 1.5*10=15m, ie only horizontal 15m is possible for zero staff reading.

And the Answer must be 15m.

I think height should be 15 m because here is up gradient, not down gradient so here 1.5 m height should be read by instrument, so

L =height/slope =1.5/(1/10)=15m.

Slope = 1/10.

H.I = 3/2 = 1.5 m.

Height of staff = 4.0 m.

Sight = (4 + 1.5)/(1/10) = 55 m.

According to the question much nearer value is 45 m.