GEOGRAPHIC TEST - DETERMINATION OF SOIL WATER RESISTANCE

1. Concepts:

Soil moisture (W): The amount of water contained in the soil, expressed as a percentage of the dry mass of the soil. Soil moisture must be determined in its natural state.

Soils in their natural condition almost always contain water as part of their structure. The moisture content of a soil sample is defined as the amount of water in the void space between soil particles that can be removed when dried at 105 – 110 ⁰ C, and expressed as a percentage of dry soil mass. . Dry soil here means that the soil is dried at that temperature (105 – 110 ⁰ C) to constant weight, usually for a period of 12 – 24 hours.

For non-stick soil particles, the above process will remove all existing water.

There are several ways in which water is retained in cohesive soils, the shape and size of clay mineral particles (< 2µm), along with their chemical composition allowing them to combine to hold water. A simple illustration of the waters surrounding a clay grain is shown below:

1) Adsorbed water (strongly bound water) is held on the surface of solid particles by electric gravity and is mostly in the solid state. This layer has a very small thickness, about 0.005 µm. This water cannot be removed at the drying temperature of 110 ⁰ C, so is considered part of the solid particle.

         2) Water is weakly bound, water is not tightly bound and can be removed with an oven, but not by air drying.

         3) Capillary water, held by surface tension, is removed by means of air drying

         4) Gravity water, water can move in voids and can be removed by drainage channels.

         5) Chemical water, water in the form of hydration in a crystalline structure. With the exception of gypsum and some tropical clays, this water usually cannot be removed

2. Calculation formula:

Inside:

                                        - W Soil moisture (%);

                                        - m _w  Mass of water contained in the soil (g);

                                        - m _d   Weight of dry soil (g).

3. Applicable standards:

TCVN 4196 : 2012 Construction soil - Determination method - Humidity and hygroscopicity in the laboratory.

ASTM D2216 - 10 Standard Test Methods for Laboratory Determination of Water (Moisture) Content of Soil and Rock.

4. Experimental equipment:

- Drying oven adjustable to 300 °C;

- Technical balance with accuracy to 0.01 g;

- Desiccator;

- Aluminum cup;

- Tray, earth cutter;

VIDEO EXPERIENCE FOR DETERMINATION OF SOIL moisture