In Situ Tests in Geotechnical Engineering

Jacques Monnet

• Publisher: Wiley-ISTE
• Year: 2015
• Print ISBN: 9781848218499
• eBook ISBN: 9781119145615
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Civil Engineering
• Index: Technology & Engineering

This book deals with in-situ tests that are performed in geotechnics to identify and characterize the soil. These measurements are then used to size the Civil Engineering works

This book is intended for engineers, students and geotechnical researchers. It provides useful information for use and optimal use of in-situ tests to achieve a better book adaptation of civil engineering on the ground

1
Measuring Water Content and Density

1.1. Sample collection method

1.1.1. Measuring water content using the frying pan method

This method of measuring water content is carried out on site. It is subject to a standard [AFN 96c]. The procedure is as follows:

• – weigh an empty and dry container: tare T;
• – yake the soil sample to be studied;
• – weigh the container filled with the soil to be tested: the total wet mass m_th;
• – heat the soil enough to dry it out completely but without breaking it down (for clay). A Bunsen burner, camping gas or methylated spirits can be used…;
• – weigh the container with the dry soil: the total dry mass m_td.

The water content of the soil w is then given by the formula:

[1.1]

1.1.2. Measuring water content using the oven-dry method

This method is carried out in a laboratory and is subject to a standard [AFN 95c]. The approach is the same as before, but the soil is heated using an electric oven at 105°C for a minimum of 4 and 24 h if possible. This method enables:

• – the prevention of clay decomposition;
• – the evaporation of all the free water contained within the soil.

It is also possible to use a microwave oven. This process is subject to a standard [AFN 96b].

1.3.1. Measuring dry density using a membrane densitometer

This measurement is carried out in situ with a membrane densitometer or a sample of soil on a core taken from the soil. In both cases, a wet density is measured and then converted into a dry density as follows:

• – the water content of the soil taken is measured using one of the previous methods, with w as the water content;
• – a sample of soil of mass m_h is taken, which then breaks down into a grain mass m_s and a mass of water m_w [1.2]. If the water content w is known, the water mass of the sample can be determined [1.3]. If the volume of the sample V is known, the wet density can be determined [1.4] and the dry density deduced [1.6]. Measuring the volume is done following the membrane densitometer method or using the external volume of the core.

[1.2]

[1.3]

[1.4]

[1.5]

[1.6]

The densitometer is a device that measures cavity volume (Figure 1.1). To use it, a hole is dug in the soil whose volume is to be determined. The device is first filled with water and a membrane is placed at its base. The procedure is as follows:

• – the densitometer is positioned at the surface of the ground to be tested after some surface stripping;
• – the piston is pressed so that the flexible membrane is applied onto the ground surface and an initial volume reading is taken;
• – the superior part of the device is removed, leaving the perforated disk (on the left in Figure 1.1);
• – a hole is made in the ground to match the diameter of the densitometer;
• – the extracted soil is weighed and its water content determined;
• – the densitometer is repositioned back onto the perforated disk;
• – the membrane is pushed into the hole by pushing on the densitometer’s piston, and a final volume reading is taken;
• – the volume of the hole is determined by the difference between the two volumes;
• – the wet density is determined following the formula [1.4] and the dry density fol...

Table of contents

• Cover
• Table of Contents
• Title
• Copyright
• Foreword
• Symbols and Notations
• Introduction
• Chapter 1: Measuring Water Content and Density
• Chapter 2: Soil and Rock Sampling Methods
• Chapter 3: Measuring the Total Pressuring, the Interstitial Pressure and the Groundwater Table Rating
• Chapter 4: Measuring Movement, Settling and Force
• Chapter 5: Static Loading Tests
• Chapter 6: Tests by Flat Dilatometer (DMT)
• Chapter 7: Penetrometer Test (CPT, CPTU, SPT, DCPT) and Variants
• Chapter 8: Direct Shear Tests In Situ
• Chapter 9: Pressuremeter Tests (PMT, SBP) and Variants
• Chapter 10: Water Tests in Soils
• Chapter 11: Characterization of Sites and Soils by In Situ Tests
• Bibliography
• Index
• End User License Agreement