Geotechnical Engineering Lab Report

Abstract

This lab report presents the findings from a series of experiments conducted to determine the geotechnical properties of soil samples. The primary objectives included the determination of soil texture, Atterberg limits, compaction characteristics, and shear strength. Standard procedures were utilized to ensure the accuracy and reliability of the results. The findings are critical for construction purposes, providing insights into the suitability of the soil for various engineering applications.

Introduction

The purpose of geotechnical engineering is to evaluate soil properties and their behavior under different conditions. Understanding soil characteristics is essential in designing foundations, retaining structures, and other constructions. This report encompasses various tests performed on soil samples to determine properties that are crucial for engineering analysis and design.

Materials and Methods

Materials

• Soil samples

• Apparatus for sieve analysis

• Atterberg limits devices (liquid limit device, plastic limit roller)

• Proctor compaction apparatus

• Direct shear test apparatus

• Moisture cans

• Balance and weighing scale

• Drying oven

Methods

Sieve Analysis

The sieve analysis was performed to determine the grain size distribution of the soil samples. The procedure involved the following steps:

1. Weighing the dry soil sample

2. Passing the soil through a stack of sieves of decreasing mesh size

3. Weighing the amount of soil retained on each sieve

4. Calculating the percentage of soil retained on each sieve

5. Plotting the grain size distribution curve

Atterberg Limits

The Atterberg limits tests included the determination of liquid limit (LL) and plastic limit (PL). The steps were as follows:

Liquid Limit

1. Preparing a soil paste

2. Placing the paste in a liquid limit device

3. Grooving the soil and counting the number of blows to close the groove

4. Repeating the process to obtain multiple readings

5. Plotting a flow curve and determining the LL from the curve

Plastic Limit

1. Rolling a soil thread until it crumbles at a 3mm diameter

2. Repeating to obtain an average plastic limit

Compaction Test

The compaction characteristics of the soil were evaluated using the Standard Proctor test. The procedure included:

1. Placing the soil in three layers into a mold

2. Compacting each layer with 25 blows of a standard hammer

3. Measuring the weight and volume of the compacted soil

4. Repeating the test for different moisture contents

5. Plotting the dry density versus moisture content curve

Shear Strength Test

The shear strength of the soil was determined using the direct shear test apparatus. The procedure included:

1. Placing a soil sample in the shear box

2. Applying a normal load and shearing the sample at a constant rate

3. Recording the shear force at failure

4. Repeating the test for different normal loads

5. Plotting the Mohr-Coulomb failure envelope

Results

Sieve Analysis

Sieve Size (mm)	Weight Retained (g)	Percent Retained (%)	Cumulative Percent Retained (%)	Percent Finer (%)
4.75	50	10	10	90
2.00	70	14	24	76
0.425	130	26	50	50
0.075	150	30	80	20
Pan	100	20	100	0

Atterberg Limits

Test	Value
Liquid Limit	42%
Plastic Limit	22%
Plasticity Index	20%

Compaction Test

Moisture Content (%)	Dry Density (g/cm3)
10	1.65
12	1.75
14	1.85
16	1.90
18	1.88

Shear Strength Test

Normal Load (kPa)	Shear Strength (kPa)
50	30
100	60
150	90

Discussion

The results from the sieve analysis indicate that the soil sample predominantly comprises medium to fine sand, with a significant percentage of fines. The Atterberg limits suggest a medium plasticity soil, with a plasticity index of 20%. The compaction test results show that the optimum moisture content is approximately 16% with a maximum dry density of 1.90 g/cm3. The direct shear test results indicate a linear relationship between the normal load and shear strength, confirming the soil's shear parameters.

The data suggests that the soil has good compaction characteristics and moderate shear strength, making it suitable for subgrade and foundation purposes in construction. However, further tests such as consolidation and permeability tests might be required for a more comprehensive assessment depending on specific project needs.

Conclusion

Various geotechnic tests were performed to evaluate the properties of the soil sample. The findings from sieve analysis, Atterberg limits, compaction tests, and shear strength tests point towards a soil type that is suitable for use in construction, especially for subgrade and foundation applications. Future work may include additional testing for a more detailed understanding of the soil's behavior under different environmental conditions.

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