Month: November 2019

## Moorum Ballast

The moorum is a soft aggregate, it is a form of laterite after decomposition. It has red and sometimes a yellow colour. It is used for unimportant lines and sidings. It can prevent water from percolating into the formation.

It is used as an initial ballast for new construction and also as a sub-ballast. The most reliable moorum for ballast is that which contains a large amount of small laterite stone.

The following are the advantages of moorum ballast:

1. The moorum ballast can be safely used as a blanket for the new embankment.
2. It has good drainage properties.
3. It is easily available in India.

The following are the disadvantages of moorum ballast:

1. The moorum ballast is very soft and it turns into dust under heavy loads.
2. The maintenance of the track laid on moorum ballast is very difficult.

Requirements of the good ballast

# Floating gradient – Highway engineering

The gradient on which a motor vehicle moving with a constant speed continues to descend with the same speed without any application of power brakes is called floating gradient.

# 5 Empirical Formula for Determination of the Coefficient of Permeability of Soil(K)

## 5 Empirical Formula for Determination of the Coefficient of Permeability

The coefficient of permeability of soil(K) can also be computed from several empirical formulae, which are given below:

### 1. Jaky’s Formula

Jakey in 1944 found an empirical formula of ‘K’ for all soils; $K = 100 D_{m}^{2}$ , Where $D_{m}$ is grain size (in cm) that occurs with the greatest frequency.

### 2. Allen Hazen’s Formula

$K = C D_{10}^{2}$ , where C is a constant. The value of C is taken approximately equal to 100, when $D_{10}$ is expressed in cm.

### 3. Terzaghi’s Formula

Terzaghi (1955) developed the following formula for fairly uniform sands, which reflects the effects of grain size and void ratio.

$K = 200 D_{e}^{2} . e^2$ , Where $D_{e}$ = Effective grain size.

### 4. Kozney’s Formula

$K = \frac{1}{K_{k} \eta S_{s}^{2}} \times \frac{n^3}{1-n^3}$ , where $S_{s}$ = Specific surface of particles, $\eta$ = Viscosity, and $K_{k}$ = Constant( that is equal to 5 for spherical particles).

### 5. Louden’s Formula

$\Rightarrow log_{10} (KS_{s}^{2}) = a + bn$

Where a and b are constants, the value of which are 1.365 and 5.15 respectively for permeability at 10°C.

# Capillarity Permeability Test – To Determine the Coefficient of Permeability(K) of Soil

## Capillarity Permeability Test

In the previous articles, We have discussed and for the determination of the coefficient of permeability of the soil. In this article, we are going to discuss the capillarity permeability test or the horizontal capillarity test, which is another method used for determining the coefficient of permeability as well as the value of the capillarity height of the soil sample.

In this test, a sample of dry soil, at the desired density is placed in a transparent glass or lucite tube, about 4cm in diameter and 35 cm long. Water is allowed to flow through the soil sample from one end, under a constant head $h_0$ and the other end is kept open to the atmosphere through an air vent tube.

At any time interval ‘t’ after the beginning of the test, let the capillary water travels through a distance x from point A to B. At the point A, there is a pressure head $h_0$, while at the point B, there is a pressure deficiency $h_c$ ( i.e., a negative pressure head ).

Head lost in causing flow from A to B (x distance apart)

 $= h_{0} - (-h_{c}) = h_{0} + h_{c}$

$i = \frac{h_{0} + h_{c}}{x}$

From Darcy's law

$v = K.i$   [Where    $v_{s} = \frac{v}{n}$ ]

Or, $n.v _{s} = K.i$
Where $v$ = Discharge velocity,
$v_{s}$  = Seepage velocity
and  $n$  = Porosity

But seepage velocity = $\frac{dx}{dt}$

If the coefficient of permeability is designated as $K_u$ at a partial saturation $S$, then the above expression may be rewritten as:

$S.n.v_{s} = K_{u}.i$

$S.n. \frac{dx}{dt} = K_{u}. \frac{h_{0} + h_{c}}{x}$

Or, $x.dx = \frac{K_{u}}{S.n} (h_{0} +h_{c}) . dt$ 

Integrating between the limit $x_1$ and $x_2$ for $x$, and corresponding values of time $t_1$ and $t_2$, we get

$\int_{x_{1}}^{x_{2}} x.dx = \frac{K_{u}}{S.n}(h_{0}+h_{c})\int_{t_{1}}^{t_{2}} dt$

$\left |\frac{x^2}{2} \right |_{x_1}^{x_2} = \frac{K_{u}}{S.n} (h_{0}+h_{c})\left |t \right |_{t_1}^{t_2}$

$\frac{(x_{2}^{2} - x_{1}^{2})}{(t_{2} - t_{1})} = \frac{2K_{u}}{S.n} (h_{0}+h_{c})$  

If $S$= 100% ( that means S= 1). Now, the above expression becomes

  $\frac{(x_{2}^{2} - x_{1}^{2})}{(t_{2} - t_{1})} = \frac{2K_{u}}{n} (h_{0}+h_{c})$


In the above equation, there are two unknowns: $k$ and $h_c$. In order to overcome this difficulty, the test is performed in two stages, with two different heads of water $h_0$. The first set of observations is taken under a head $h_{(0)1}$ up to capillary saturation penetrating about half the length of the test tube.

As the capillarity saturation proceeds, the value of $x$ is recorded at various time intervals. A graph between $x^2$ and $t$ will give a straight line, and its slope is given as:

  $\frac{(x_{2}^{2} - x_{1}^{2})}{(t_{2} - t_{1})} = m_1$


In the second stage, for the next half of the tube, is performed with head $h_{(0)2}$, and the recorded values of x and t are again used to plot a graph between $x^2$ and $t$. The slope of this line, say $m_2$, is now determined.

   $\frac{(x_{2}^{2} - x_{1}^{2})}{(t_{2} - t_{1})} = m_2$

Knowing the two slopes, the values of $h_0$ and $k$can be computed by the following two-equation.

$\frac{(x_{2}^{2} – x_{1}^{2})}{(t_{2} – t_{1})} = m_1 = \frac{2K_{u}}{S.n} (h_{0(1)}+h_{c})$

$\frac{(x_{2}^{2} – x_{1}^{2})}{(t_{2} – t_{1})} = m_2 = \frac{2K_{u}}{S.n} (h_{0(2)}+h_{c})$

The degree of saturation S can also be found by measuring the wet mass of the soil sample at the end of the experiment. The porosity is computed from the known dry mass, volume and specific gravity.

Factors Affecting The Permeability

Permeability of Soil – Darcy’s law

# Installation Process of Ground Anchors

## Installation Process of Ground Anchors

The entire procedure which is adopted for the installation of a ground anchor is described below in steps.

### Step: 1

First of all, Holes of the required size are drilled with the help of a drill rig, etc., at the locations selected for the installation of anchors. The depth of the holes will be the desired depth as the design depth. Holes will be drilled with or without casing pipes, either vertically or at an inclination as required.

### Step: 2

The anchor tendon is inserted centrally into the hole.

### Step: 3

A grout, usually cement, is pumped into the space left between the tendon and the hole at predetermined grouting pressure. The pressures vary for the primary grouting and the secondary grouting.

Usually, a sheath is provided around the tendon in the secondary grout area to protect it from corrosion. If a casing pipe is used in drilling the hole, it will be withdrawn during grouting. The grout is finally allowed to cure.

### Step: 4

A reaction and locking mechanism are connected on the ground surface or on a structural surface, which is called an anchor head.

### Step: 5

Extended tensile stress is applied to the anchor by a hydraulic jack, which is greater than the design load. The value of this tensile stress usually varies from 1.25 to 2 times the design load of the anchor. They may sometimes be pre-stressed to control the longitudinal movement.

### Step: 6

When the load is applied to the anchor, the lock-off system is engaged, and the applied tension from the jack is released.