The purpose of this report is to illustrate the types of plant required in order to excavate an area 150m x 50m x 15m trench for the storage of the reactor cores of decommissioned nuclear submarines. The area identified for the trench is located in an area owned by the MOD – coastal site in Coulport (Argyll & Bute). This site was looked upon as a potentially suitable location. For the purpose of this report, it is assumed that the location of the trench will be at the coastal site in Coulport. The storage site will hold a maximum of 37 de-fuelled reactor compartments twenty-seven (27) existing plus an assumed number of a ten(10) astute class.
“Project ISOLUS is committed to the timely development and implementation of a solution for the dismantling of the UK’s de-fuelled nuclear powered submarines which inspires public confidence, is safe, environmentally responsible, secure and cost-effective.”
Project ISOLUS involves identifying the most suitable land storage solution and location(s) for the cut up of the decommissioned submarines and for the subsequent storage of radioactive material contained within the Reactor Compartment.
Afloat storage has proved to be a safe arrangement for over twenty years. However, it is estimated that current afloat storage capacity will be reached before 2020. Project ISOLUS was established to find an interim land-based storage solution for radioactive material from the twenty-seven (27) nuclear powered submarines, of which eleven (11) have left naval service and are currently stored safely afloat – seven (7) at Rosyth and four (4) at Devonport.
A total of 118 MOD owned coastal sites were considered. Coastal sites were considered on the basis that moving intact Reactor Compartments inland was ruled out due to their size (750 tonnes and the size of two double-decker buses). One MOD owned coastal site, Coulport (Argyll & Bute), was found potentially suitable as mentioned above.
The plant chosen for this task is based on the following assumptions:
> The ground is clay therefore the swell factor is 1:20 – 1:40
> The dig is taking place during the summer months
> Access to the site and site working conditions are good
> There is a sufficient amount of skilled labour available as well as experienced supervision.
In order for earthworks to be carried out effectively and efficiently it is necessary to determine what types of plant are required. As well as plant we need to know the availability, maintenance and repair facilities within the vicinity of the dig.
Selection of plant
To undertake the dig in the most efficient and effective manner, information has been gathered from CECA01 and CECA07 as well as the Liebherr website.
The dig will be undertaken utilizing the following plant:
> 2 x Backhoes
> 1 x Bull Dozer
> 1 x Loading Shovel
> 4 x Dump Trucks
> 1Sheepsfoot Roller
Backhoes R 954c (see www.liebherr.com)
It is recommended that we have 2 backhoes for the dig.
The Backhoe will be used for the excavation of the trench in this project. This is operate by the boom digging towards the machine in an arc starting at ground level to a position vertically below the rear edge of the machine. Loading is carried out by swinging the boom away from the excavation and depositing the material either on a stockpile or in to haulage vehicles. The maximum depth of excavation depends on the length boom and size of the base unit. (CECA07-4) The size of the bucket depends on the type of the material to be excavated. In this project we will use 2m3 bucket (based on the Chart in CECA07 -8).
Visibilities from machine can be poor. In addition, the noise made by the machine will make it unlikely that the operator would hear verbal warnings or instructions so other personnel and plants must be kept well clear at all times. When this is not possible a banksman should be present to provide visual signals to the operator.
Bull dozer PR 724(see www.liebher.com)
This is the type of bull dozer we will use for this project to move forwards pushing material in front. It can be used to excavate level surfaces, grade and spread materials, maintain haul roads and haul material up to 100m. We can use it to grade and spread the material from the trench. The steel blade is adjusted by hydraulic rams which control the depth of dig and apply a downward force. The rams can also be used to angle the blade to deposit the material at one side (useful for grading haul roads) -see(ceca01-2)
Loading shovel type-LR634 see ( www.liebher.com)
This is the type of loading shovel we are planning to use for this dig. It is used for top loading of haulage vehicles. It can handle most material. The loader moves forward into the soil and the bucket is filled. The loader then reverses while raising the bucket and then moves forward to deposit the material either into a haulage vehicle or on to stockpile. The normal bucket is formed from steel plate. Teeth can be added at the front edge to assist penetration of stiff soils. Multi-purpose buckets are also available for alternative modes of operation: dozer, shovel, clamshell, scraper.(CECE01-3). It can also be used for striping the topsoil before the excavation of the trench begins. We envisage this working alongside the bull dozer and loading dump trucks.
Dump trucks are designed specifically for earthmoving on large scale construction projects. The truck has a large area on to which material can be loaded. The loading height is also low. A heavily reinforced section is placed over the drivers cab for protection. The truck has a wedge shaped load carrying section which facilitates a quick discharge when dumping. The commonest type has rear dumping but side and bottom dumping trucks are also available. Dump trucks should have four(4) wheel drive to overcome difficult ground condition. In our project we will use a large dump truck with an articulated cab to allow easier manoeuvring.
Provide a kneading action as the Roller moves forwards, most effective on silts and clays.
Describe appropriate methods and resources to ensure safe and productive operations particularly in deep excavations and trenching
The excavation will include major movement of materials such as the construction of embankments, haulage roads and the formation of cuttings we have to make sure that earth work is carried out in a safe manner.
The embankments and the haulage roads are a volume of filled material the top of which is higher than the surrounding area. They are usually constructed from compacted ayers of material placed in a uniform thickness. Compaction is a vital process in the construction of haulage roads and embankments. The purpose of compaction is to decrease the permeability and the settlement of the soil. It also increases the shear strength and the density of the soil. See Ceca 02 and 05.
All the plant that works on the embankment construction will provide some form of compaction. It must be noted however, that this cannot be relied upon to provide the necessary degree of compaction required by the specification. This must be provided by plant designed for this purpose. See Ceca 05. In this project we will utilise a sheepsfoot roller.
Cuttings are formed by removing a volume of material. The bottom of the cutting is lower than the surrounding area. The cutting can be formed using an excavating machine. In this project we will utilise a backhoe.
Both embankments and cuttings have slopes, hence the importance of ensuring their stability. The stability of embankments and cuttings are affected by the type of soil, ground water condition, slope angle, slope height, surcharge, level of water table and soil density (moisture content). See Ceca 05
For this project we will utilise several methods to increase the slopes stability as mentioned below:
Reducing the Slope Angle
This involves the acquisition of a wider strip of land on both cuttings and embankments. See ceca05
Removing Material from the Top of the Cuttings and Embankments
This removes the loading due to the volume of soil which has been removed. The effective slope angle is then reduced. See ceca05
This involves the banning of both building and road construction near to the top of the slope. See ceca05.
Define types of temporary works particularly those required to deal with stability and groundwater problems
In order to carry out work safely during temporary excavations, several important factors must be taken into consideration. The type of soil, the ground water conditions, as well as the depth and width of the excavation. In this project the soil we are excavating is clay. The depth being excavated will not exceed 6m and the trenches are narrow. We will support the excavation with double sided support. The short length will be excavated and the sides will be supported with boards and struts.
The boards support the soil pressure, exerted by the excavated faces. The walings support the loads carried by the boards and transfer the force into the struts. The struts have an equal and opposite force at each end therefore providing the stability required. See Ceca 03-2.
The following should also be taken into consideration when performing the temporary work during the excavation:
All safety legislations should be complied with.
All operatives who work on the installation and/or removal of temporary earthwork supports must have had adequate training. See Ceca 03-7.
Controlling the ground water is an important part of the temporary works in the excavation. To prevent flooding of the trenches we will utilize a simple sump pump.
The sump, will be placed in the corner of the trench as this is where most of the water puddles. Sump pumping is suitable for excavation, where small volumes of water are involved.
In the event that there are large amounts of water collating, it is feasible to utilize a jetted sump. This requires for formation of a disposable wellpoint, which consists of a disposable pipe and a perforated metal or plastic intake strainer which is connected to the suction pipe of a pump and is lowered into the bottom of the hole. The space between the suction pipe and the metal tube is filled with a sand or gravel filter medium, as this is placed the metal tube is pulled out of the ground. By carrying out the excavation sump first before construction works start, the groundwater can be kept below the excavation level at all times. See Btech08-6 .