Excavation is an essential component of construction operations – particularly for foundations and drainage (sewage) – and on construction sites in general. When carrying out excavation work – the condition of the soil varies greatly and often over short distances – and there is no soil, whatever its nature, that can be relied upon to support its own weight or weight for any period of time, long or short.
It is possible to make a reverse slope for the excavation so that it is with a safe slope, and the sides need supports to prevent the possibility of their collapse. Therefore, they are:
Provide safe conditions for personnel working in or near excavations.
It helps to perform the work without any interruption.
Protecting nearby property – and public services close to the pits.
Safety and health require a safe workplace and safe means of entry and exit to and from the excavations, and the property of third parties must be protected.
In the case of the need to carry out excavation work, it must be taken into account to give importance to the nature of the soil, the method of excavation that will be used, and the way in which the necessary and required supports for the sides of the excavation will be made.
Wooden blocks are traditionally used as props for excavation work. However, modern methods use steel as props.
All excavation work within or near equipment areas – requires a work permit in addition to the usual hot and cold work permits.
This required permit is for excavation work – and in cases where the excavation depth exceeds a certain limit, this also requires the issuance of an entry permit to a closed space.
(Confined Space Entry Permit) Although the pits remain open, a closed space entry permit is required before anyone is allowed to enter the pits.
♦ Benching included terraces
It is a way to protect workers from collapses by digging the sides so that part of it is flat – or several flat parts in sequence – or in the form of steps – with vertical or near-vertical surfaces between these steps.
It is the separation of a mass of soil – or rocky materials from the sides of the excavations or the loss of soil under the sides or supports – and its sudden fall into the excavations – either by collapsing or sliding and in large quantities sufficient to confinement of people – or burying them – or injuring them and their inability to move them – or the possibility of moving them .
♦ Competent Person
It is the skilled person who has the ability to know the dangers present – or expected in the surrounding areas – or in the nature and conditions of work – that are incorrect or dangerous to workers, and he is the one who has the authority to take prompt measures to correct or remove these dangers.
♦ Angle of Repose
It is the largest angle with respect to the horizontal position at which the materials stay in place without slipping.
They are pieces of wood that connect the cross pieces to the main horizontal parts.
♦ Excavation drilling
Any void or depression from the surface of the earth by human action, including the sides, side walls, or faces that are formed as a result of removing dust, thus forming soil that is not supported or supported by excavation.
If there are forms of installations or the like, they are placed to reduce the depth-to-width ratio of the excavation.
They are the materials that are placed so that they are connected with each other to form a wall (such as wood, iron or concrete) in order to resist the lateral pressures of water – or neighboring dust – or any other materials.
It is the materials resulting from excavation work.
♦ Struts / Braces
They are the horizontal parts of the prop system for excavation – whose end or limbs bear the existing vertical parts – or the longitudinal ribs.
♦ Tight Sheeting
It is the lamination that is superimposed with each other to form a continuous solid wall in order to resist the lateral pressures of dust – or water or any other materials.
It is a narrow excavation below ground level – in general, the depth is greater than the width, but the trench width does not exceed 15 feet.
♦ Trench Shield
It is a system of supports consisting of iron plates and supports (Bracing) that support and are fixed to each other by welding or rivets – and it supports and supports the walls of the trench from the surface of the ground to the bottom of the trench – which can be moved forward as the work progresses.
♦ Horizontal strapping panels – or horizontal supports (Wales / Stringers)
They are the main horizontal parts of the lamination system whose sides support against vertical loads – or dust.
♦ Protective System
It is a way to protect workers from collapses – and from materials that can fall or roll over due to excavation work – or the collapse of nearby structures.
The protection systems include the support systems – and the inclination of the sides – or the graduated terraces system, the shield systems – and other systems that provide the necessary protection.
It is a way to protect workers from collapses due to excavation work – by making the sides of the excavations inclined outward from the excavations to prevent collapse.
The angle of inclination required to prevent collapse varies with soil type, exposure length and additional loads.
3- General Requirements
The following conditions of the nature of the site must be taken into account in order to conduct drilling safely:
2- Surface and groundwater
3- The proximity of the constructions and their nature to the excavation site
4- Surface and ground services
6- Weather conditions
Prior to the commencement of excavation operations – the standard regulations require the employer to specify the location of the utilities – such as sewers – telephones – gas and electricity lines – water lines or any other underground facilities that may be encountered in excavation operations.
No person is allowed to operate any piece of equipment – prior to obtaining appropriate training to use this equipment – and that he p
I am aware and aware of the potential dangers.
The standard systems require that there be a skilled person (Competent) who inspects the excavation work on a daily basis – as well as the neighboring areas for fear of any collapses that may occur or are possible – or the failure of the protection systems for the excavation or equipment or the presence of a dangerous atmosphere – or any other circumstances dangerous.
The provision of protection systems for workers must be used – through inclinations for the sides of the excavation, or lamination of the sides – or shields prevailing for the sides.
Protective gear must be provided to workers and worn wherever necessary in order to ensure their protection.
• All excavation waste and dirt piles must be placed at least 2 feet from the sides of the excavation – and waste piles must not block the safe exit points for individuals.
• If the trench or excavation is 4 feet in depth or more – steps, ladders or terraces must be used as a safe means of ascent and descent. For trenches, workers should not have to walk more than 25 feet to reach exit ladders or stairs from excavations.
• No worker is allowed to work inside the excavations if there is water accumulating in the excavations unless there are special measures to protect the workers.
The skilled person must inspect all excavation works – and trenches daily, prior to the exposure of workers to enter the excavations – and after any rain – or a change in the nature of the soil or any other time during the work shift – and he must take immediate and rapid measures to remove any dangers.
Excavations – or trenches with a depth of 4 feet or more – in which there are potential risks of toxic materials – or dangerous atmospheres – must be detected and examined at least daily, and if the weather is not suitable or unfit – protective systems must be used for workers .
If the work is in the field of traffic – workers must be provided with a reflective orange vest – signs and barriers must also be used to ensure the safety of workers – and passing cars – and pedestrians.
4- Ground Conditions
4/1- General Introduction
Before starting any excavation operations – it is very important to determine the type of land in which the excavation work will begin. The table attached to the excavation works is very useful as a guide in determining the different cases that we might find.
When examining holes or ground holes – or a pilot hole for information, special importance should be given to the location or location of the groundwater level.
If the level of the groundwater surface will be exposed when excavating, then this requires giving special care about the duration of the impact of this water on the stability of the sides of the excavation, as groundwater can have a significant impact on the stability of any soil, especially non-cohesive soil – just as water Groundwater can enter the excavation sites as a drain for running water.
• Whatever the source of this water – effective action must be taken – either to stop the water from surface sources entering the excavations – or in the case of groundwater, the need to reduce its impact to the maximum degree.
4/2- Surface Water
Potholes and basins – waterways and so on – may be disrupted by excavation work – and may need to be diverted. If the digging is across a mile in the ground, a cut-off course of water must be made. Whether the excavation work in the rainy season. And in places where the sewers are visible or exposed. It must be cut and turned before starting the main excavation.
4/3- Ground Water
The presence of ground water is more difficult to deal with than surface water, as it can affect the sides of the excavation to the extent that leads to the removal of water for the materials behind the lamination of the sides of the excavation – despite the presence of supports and in some types of soil – the bottom of the excavation becomes unstable and boils ( Boil), which is the effervescence of the floors, which may lead to the collapse of the trenches or pits.
The relationship between groundwater and soil quality needs to be analyzed carefully enough before making a decision about the type and nature of the supports that will be used.
• If the land is suitable, one of the appropriate means can be used to withdraw this water. Such methods include either pumping water from a shallow hole – or directing the water to a pumping well from it.
Any of these methods, the pumping of water will have a significant impact in reducing the groundwater level to the extent that the drilling works will reach.
5- Soil Classification & Identification
• The standard system of (OSHA) defines the classification of soil through a simplified classification system, which consists of four groups, namely:
1. Stable rock soil
2. Soil type (A)
3. Soil type (B)
4. Soil of type (C
• The degrees of stability in the fixed rocky soil is the highest degree of stability for the soil, and the degree of stability decreases as we move towards quality (A) and even quality (C), which is the least stable.
Fixed rock: (Stable Rock) can be defined as a solid natural mineral in which drilling can be performed with vertical sides – and it remains coherent throughout its existence exposed (for example, granite and sandstone).
Type (A) soil: it is a sticky and cohesive soil – indicated by an unconfined compressive strength of up to 1.5 tons / square foot or more (for example, clay – or loamy silt – or sandy clay or loamy sand).
Soil type (B): It is cohesive and adherent soil and has an unconfined compressive strength greater than 0.5 ton/sqft but less than 1.5 ton/sqft (for example – clay and loamy silt).
Soil type (C): It is a cohesive and cohesive soil – and it has an unconfined compressive strength of 0.5 tons / square foot or less (eg gravel – sand – loamy sand and soil immersed in water – or soil from which water flows easily and freely).
6- Soil Test & Identification
There are many types of equipment and methods that are used to determine the type of soil a
prevalent in a region and as shown as follows:
1/6- Pocket Penetrometer
The penetrometer gives a direct reading – a machine that operates with a spring system – and is used to determine the free or open compressive strength – of the saturated adhesion soil – and once it is stitched into the soil, the indicator gives the reading directly.
6/2- Visual Test
If the excavated soil is in the form of blocks – it is considered cohesive and sticky, but if it is easily broken – and does not remain in the form of blocks, then it is granular soil.
6/3- Thumb Penetration Test
The thumb penetration method is to try to press your thumb firmly into the soil under test. If a deep hole is formed with difficulty, then the soil is likely to be of type (A), but if the finger penetrates the thumb within the limits of the finger nail, then the soil may be of type (B), but if the penetration of the soil is along the length of the thumb, then the soil may be of type (C).
6/4- Dry Strength Test
Try to break up the sample in your hands with your fingers – if it breaks up into granules, then it is granular soil – either silt or clay does not break into granules but breaks into small chunks.
6/5- Wet Manual Test
Wet the fingers of the hand and knead the sample between the fingers – with regard to silt, it becomes a slippery wonder when it is wet – meaning that it is sticky soil – but if the fragmentation falls in the form of granules, then the soil is granular.
7- Excavation Protection Systems
There are three basic systems for protection for excavation or trench work, namely:
7/1 Sloping and Benching systems.
7/2- Side support systems (Shoring System).
7/3- Shields System for the sides.
Protective systems must be able to withstand without fail all that will or is likely to fall upon them – or pass on to the bones.
7/1 Sloping and Benching systems
7/1/1 Sloping Systems
The maximum slope allowed for excavations less than 20 feet (6 meters) deep, depending on the type of soil and the angle of inclination relative to the horizontal, is as follows:
Soil type, aspect ratio, slope angle
* Fixed rock soil vertical 90 degrees
* Soil type – (A) ¾: 1 53 degrees
* Soil type – (B) 1: 1 45 degrees
* Soil type – (C) 1 : 1 ½ 34 degrees
7/1/2- Benching System
There are two types of terraces system – simple type and multiple type – the type of soil determines the ratio of the horizontal length to the vertical length of the excavated side in the form of terraces and as a general rule – the bottom of the pits should not exceed the vertical height of 4 feet for the first terrace while the following terraces may reach a height of 5 1.5 feet (1.5m) in type A soils, up to 4 feet (1.2m) in type B soils, and up to 20 feet in trench.
7/2- Shoring Systems
A shoring system is a support system for excavation faces – used to prevent movement of soil or underground facilities – or foundations. The shoring method is used when the site – or the depth of the excavation where the slope or inclination to the maximum permissible extent is impractical. The shoring system consists of columns, horizontal tie-down plates, reinforcing beams, and bore wall cladding plates.
There are two main types of supports – either wooden blocks – or aluminum.
7/2/1- Hydraulic Shorting
It is a prefabricated truss or horizontal bonding panels made of aluminum or iron. The hydraulic shoring system gives a safety advantage over the block shoring system as operators do not need to go down to the pits to install or remove the hydraulic shoring.
All types of supports are top-to-bottom and bottom-up removal.
7/2/2- Pneumatic Shorting
It works in a similar way to hydraulic shoring – the only difference is that air pressure is used instead of hydraulic.
One of the drawbacks of this system is the necessity of having an air compressor on site.
7/3- Shielding Systems
7/3/1- Trench Boxes
It differs from the shoring system – or the buttresses, in that instead of making full height shoring for the sides – or the shoring up of the trench sides, the box system is basically to protect the workers from any collapses of the sides of the excavations and other similar accidents. In this system the space between the boxes and the excavation side should be as small as possible. Also, the space between the boxes and the side of the excavation is backfilled to prevent lateral movement of the box.
7/3/2- Combined Use
Trench boxes are used in open areas – but can also be used with sloped sides or terraced sides.
The box should extend at least 18 inches higher than the surrounding area if there is a slope towards the excavation. This can be achieved by providing an area in the form of terraces adjacent to the box.
8- Drill files:
Temporary excavation waste shall be placed no less than 2 feet (0.61 m) from the edge of the excavation.