Geotechnical Engineering (CEP)

Here, we will analyze a real-time Geotechnical Engineering problem and solve it by using different techniques.

Complex Geotechnical Engineering Problem

An embankment for a highway 30 m wide and 1.5 m thick is to be constructed from sandy soil, trucked in the form of a borrow pit. The water content and void ratio of the sandy soil in the borrow pit are described in table 1 below. Specifications require the embankment to compact to a dry weight of 18 KN/m³.

Determine the following for the required length of the embankment (see table 1)

1. The dry unit weight of sandy soil from borrow pit to construct the embankment, assuming that G_s = 2.7
2. The number of 10 m³ truckload of sandy soil required to construct in the embankment
3. The weight of water per truck load of sandy soil
4. The degree of saturation of the in-situ sandy soil

Objective

To apply technical knowledge gained throughout the course in real-world applications.

Problem statement

An embankment for a highway 30 m wide and 1.5 m thick is to be constructed from sandy soil, trucked in the form of a borrow pit. The water content and void ratio of the sandy soil in the borrow pit are described in table 1 below. Specifications require the embankment to compact to a dry weight of 18 KN/m³. Determine the following for the required length of embankment (see table 1)

1. The dry unit weight of sandy soil from borrow pit to construct the embankment, assuming that G_s = 2.7
2. The number of 10 m³ truckload of sandy soil required to construct in the embankment
3. The weight of water per truck load of sandy soil
4. The degree of saturation of the in-situ sandy soil

Available data

Embankment width: 30 m

Embankment thickness: 1.5 m

Specific gravity: 2.70

Dry weight (): 18 KN/m³

Group assigned data

In-situ moisture content (%): 15.00

Void ratio: 0.69

Embankment length: 1 km = 1000 m

Solution

• Determination of dry unit weight of sandy soil from borrow pit for embankment construction.

Simply apply the formula for dry unit weight as shown below

1. The number of 10 m³ truckloads of sandy soil required to construct in the embankment.

First, determine the required volume of sandy soil for embankment construction by applying the formula given below:

V = L x W x H

Calculation:

V = 1,000 * 30 * 1.5

V = 45,000 m³

Now, to determine the total number of truckloads of sandy soil required, divide the total volume of soil required by the capacity (volume) of one truckload. The procedure is shown below.

Truckloads required = 45,000 / 10 = 4,500

• The weight of water per truckload of sandy soil.

To calculate the weight of water per truckload of sandy soil, first, use the equation shown below to calculate the weight of solids.

This value is, however, the total weight and not the weight of water for one truckload. Hence, to calculate the weight of water for one truckload, divide the total weight of water by the number of truckloads, as shown below.

• The degree of saturation of the in-situ sandy soil.

The degree of saturation is a percentage value, to calculate which, simply use the formula given below.

Also, check Tunneling and Excavation Engineering CEP.