Cave-ins pose the greatest risk and are much more likely than other excavationrelated accidents to result in worker fatalities. Other potential hazards include falls, falling loads, hazardous atmospheres, and incidents involving mobile equipment.

• The greatest risk in an excavation is a cave-in.
• Employees can be protected through sloping, shielding, and shoring the excavation.
• A competent person is responsible to inspect the excavation.
• Other excavation hazards include water accumulation, oxygen deficiency, toxic fumes, falls, and mobile equipment.

Soil failure is defined as the collapse of part or all of an excavation wall. The most common soil failure is typically described as an unexpected settlement, or cave-in, of an excavation. Soil sliding is the most common factor leading to soil failure.

The dangers of excavations come from the possibility of cave-ins, in addition to the possibility of the lack of oxygen (asphyxiation), fire, accidental break of underground utility lines (such as gas, electricity), collapse due to moving machinery near the edge of the excavations, inhalation of toxic materials, and …

Excavation Hazards:

• Damage to underground facilities.
• Personal, vehicle, equipment and materials falling inside excavation.
• Cave-in, Soil collapse due to loose soil and heavy equipment moment.
• Presence of toxic and flammable gases.
• Injuries due to employees working very close to each other.

Soils can be classified as Type A, Type B, or Type C. Type A soil is the most stable soil in which to excavate. Type C is the least stable soil. It’s important to remember that a trench can be cut through more than one type of soil.

Soil is classified into four types:

• Sandy soil.
• Silt Soil.
• Clay Soil.
• Loamy Soil.

Trenches 5 feet (1.5 meters) deep or greater require a protective system unless the excavation is made entirely in stable rock. If less than 5 feet deep, a competent person may determine that a protective system is not required.

There are three different types of soil—sand, silt, and clay. Each type of soil has different characteristics. The major difference is in the size of the particles that make up the soil. The soil types also have differences in color, amount of nutrients, and ability to hold water.

Here is a break down of the common traits for each soil type:

• Sandy soil. Sandy Soil is light, warm, dry and tend to be acidic and low in nutrients.
• Clay Soil. Clay Soil is a heavy soil type that benefits from high nutrients.
• Silt Soil.
• Peat Soil.
• Chalk Soil.
• Loam Soil.

The 5 Different Types Of Soil

• Sandy Soil. Sandy soil is light, warm, and dry with a low nutrient count.
• Clay Soil. Clay weighs more than sand, making it a heavy soil that benefits from high nutrients.
• Peat Soil. Peat soil is very rarely found in natural gardens.
• Silt Soil.
• Loamy Soil.

There are six main soil types:

• Clay.
• Sandy.
• Silty.
• Peaty.
• Chalky.
• Loamy.

Two materials commonly used for lowering the soil pH are aluminum sulfate and sulfur. These can be found at a garden supply center. Aluminum sulfate will change the soil pH instantly because the aluminum produces the acidity as soon as it dissolves in the soil.

There are six main types of soil: chalky, clay, loamy, peaty, sandy and silty. To test your soil, you need to take a look at it and feel it. Add water and try rolling it between your hands. Observe how your soil looks and feels, and whether it’s sticky, gritty, friable, or slimy.

The Twelve Soil Orders

• Alfisols.
• Andisols.
• Aridisols.
• Entisols.
• Gelisols.
• Histosols.
• Inceptisols.
• Mollisols.

Entisols are divided into six suborders: Wassents, Aquents, Arents, Psamments, Fluvents, and Orthents. Adapted from: The Twelve Soil Orders: Entisols.

This fertile surface horizon, known as a mollic epipedon, is the defining diagnostic feature of Mollisols….

Types. There are five major classes of structure seen in soils: platy, prismatic, columnar, granular, and blocky. There are also structureless conditions. Some soils have simple structure, each unit being an entity without component smaller units.

There are eight primary types of soil structure, including blocky, columnar, crumb, granu- lar, massive, platy, prismatic, and single grain.

Good soil structure is characterised by well-formed porous blocks with rounded edges, easily broken between the fingers when moist. Vertical fissures lead roots downwards. Soil with good structure is hard to damage. Poor soil structure has much harder, sharper blocks which are more difficult to break apart.

Through the interactions of these four soil processes, the soil constituents are reorganized into visibly, chemically, and/or physically distinct layers, referred to as horizons. There are five soil horizons: O, A, E, B, and C. (R is used to denote bedrock.)

C (parent material): The deposit at Earth’s surface from which the soil developed. R (bedrock): A mass of rock such as granite, basalt, quartzite, limestone or sandstone that forms the parent material for some soils – if the bedrock is close enough to the surface to weather.

clay particles

The A horizon is the top layer of the mineral soil horizons, often referred to as ‘topsoil’. This layer contains dark decomposed organic matter, which is called “humus”. The technical definition of an A horizon may vary between the systems, but it is most commonly described in terms relative to deeper layers.

In the A horizon, climate and topography had the greatest influence on soil pH. In the B and C horizons, the key factor that affected soil pH was parent material. Topography and climate also had great importance in the B horizon.

A and B are usually almost the same because they receive water and annually the deserts are filled with a quantity of water making the desert habitats have a broader horizon in comparison with others.

Soil Horizons (layers): Soil is made up of distinct horizontal layers; these layers are called horizons. They range from rich, organic upper layers (humus and topsoil) to underlying rocky layers ( subsoil, regolith and bedrock).

Two of the most important properties of soils are their texture and structure . By texture, we mean what soils are composed of and how this affects the way they feel and their cultivation. The main components of soil texture are: sand, silt and clay particles and organic matter.

Known as the “true soil,” the solum is where most of the biological activity in soil is confined. The C horizon is the lowest soil layer and lies directly above the bedrock. This layer is part soil and part decomposing bedrock fragments. It contains very little organic material.

FOUR LAYERS