Soil Engineering

In rainstorm, the runoff from rainfall infiltrate into the top layer of fill slopes. It may result in saturation of this layer of fills leading to the decrease in soil suction. Consequently shallow slope failure may occur.

If the fill slope is in a loose state, the soils would tend to decrease in volume during deformation. As a result this induces a rise in pore-water pressure which triggers slope failure in form of mud-avalanche.

If the fill slope is in a dense state, the soils would tend in increase in volume during deformation and it only fails like a mud slump.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

Janbu’s method and Morgenstern-Price method are non-circular analytical method and they are frequently used for soil slopes while Bishop’s method is circular analytical method. Bishop’s Simplified method and Janbu’s Simplified method assume that the inter-slice forces are horizontal and inter-slice shear forces are neglected.

Equilibrium Method	Moment Equilibrium	Force Equilibrium
		Horizontal	Vertical
Janbu’s Simplified	No	Yes	Yes
Bishop’s Simplified	Yes	No	Yes
Morgenstern-Price	Yes	Yes	Yes

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

When ever explosive substances are used to blast, a large amount of vibration occurs. This vibration is not only dangerous for people working their but also to the neighboring structures. Therefore proper care must be taken to keep vibration in check.

The vibrations caused by blasting are related to velocity (V), wavelength (L) and frequency (f) as
L= V/f

Now Velocity V depends on the amplitude of the vibrations A and is given by
v=2pfA
Where p – pie = 3.14

Case – When we know velocity velocity v₁ at a distance D₁ from the explosion and wish to find velocity v₂ at a distance D₂ from the explosion
v₂=(approx) v₁(D₁/D₂)^1.5

The scaled-distance formula is used for vibration control
V=H[D/(W)^1/2]^-b

Where
b and H are constants and depend on site.

Many people wonder that why the soil looks bulkier after excavation. The answer is that with increase in voids, the volume of soil increases and thus the soil pile looks bulkier. Here is a mathematical formula for this change in soil volume

V_b = V_bL = (100/(100 + % swell))V_L
where
V_b = original volume, yd³ (m³),
V_L = loaded volume, yd³ (m³),
L = load factor

Similarly when we compact the soil, its volume decrease as voids are now filled.
V_c = V_bS
where
V_c = compacted volume, yd³ (m³)
S = shrinkage factor.

Whenever their is a movement, friction comes into action. The same is the case with earth moving equipments. We term this as rolling resistance and this has to be overcomed by vehicle engine so that it can move on that surface. This is the formula to calculate rolling resistance

R=R_fW + R_pPW
where
R = rolling resistance, lb (N)
p = tire penetration, in (mm)
R_f = rolling-resistance factor, lb/ton (N/tonne)
W = weight on wheels, ton (tonne)
R_p = tire-penetration factor, lb/ton in (N/tonne mm) penetration
R_f usually is taken as 40 lb/ton (or 2 percent lb/lb) (173 N/t) and R_p as 30 lb/ton in (1.5% lb/lb in) (3288 N/t mm).

So the above equation becomes
R=(2%+1.5 % p) W’=R’W’

where
W’ = weight on wheels, lb(N)
R’ = 2% + 1.5%p.

Case – When we have a slope
G = R_gsW
where
G = grade resistance, lb(N)
R_g­ = grade-resistance factor = 20 lb/ton (86.3 N/t) = 1%
s = percent grade which is positive for uphill motion and negative for downhill motion.

The total road resistance is calculated by adding the rolling and grade resistances and is given by:
T = (R’+R_g s )W’ =(2%b + 1.5%p + 1%s)W’

Loss due to Altitude
Generally we take 3 percent pull loss for each 1000 ft (305 m) above 2500 ft (762 m).