Earthworks Are an Important Part of Most Civil Engineering Works
Types of earthworks can include modification of natural slopes to suit the requirements for transport systems like roads or railways. Earthwork descriptions can also include the forming of canals for drainage or irrigation systems and can by themselves be massive engineering undertakings like the Chicago River diversion and the Panama Canal. The formation of dikes along the sides of rivers prone to floods or to reclaim land like in the Netherlands is earthwork that involves a lot of engineering and design. Earthen dams have been built to create artificial reservoirs for irrigation, and while the heights of these are generally restricted because of the strength required, they have been known to form large bunds for long lengths to supplement a masonry or concrete dam which would be formed across the main spillway portion of the river or water source being dammed up.
Earthwork is also involved in the construction of most buildings and would involve the removal of overburden to reach structurally capable earth or soil, excavation for basements and other underground structures, and to make structural fills to support floors. Various types of earthworks have been use for centuries for building structures, fortifications, roads and canals and the earliest on customs prevalent for such construction has been documented in a book called the Dschou-Li, a book written about 5,000 years ago in China.
Earthwork for military purposes has been in use for centuries and the use of moats, and even earthen forts, are matters well documented. Military engineers still use trenches, foxholes, and other earthwork to help them in defensive positions. Earthen embankments suitably covered are also used for gun emplacements, storage of munitions, and creating command centers.
Image Source: Wikimedia : Earthen Dam
Investigations Prior to Any Earthworks
Prior to doing any earthwork for a structure, whether it be a road, building, embankment, dam or other structure, a thorough investigation is necessary to assess local conditions. A roadwork or embankment would require a detailed topographical survey which would enable the engineer to estimate the total earthwork involved. If local available material is to be used, the soil will need to be analyzed to see whether it can achieve the strength needed for the structure. Quite often soil conditions vary from area to area. An engineer may also have to mark out the areas that can provide the required material and limit quarrying to these areas only. It is also necessary to pay attention to drainage as heavy precipitation can damage earthworks and proper drainage of the completed work is necessary to minimize this damage.
Specifications for Earthworks
While the basic material used in earthwork is soil obtained locally, analysis of this material allows engineers to design the earthwork to perform all the functions that they require of it. The main considerations in this design are the compaction of the soil and the moisture content that allows it to gain the maximum compaction.
Geotechnical engineers would consider three fundamental types of earthwork specifications before they give their recommendations for the scientific control necessary while doing any earthwork.
The first is the method specification which will specify the thickness of the layer to be used while filling material. It will also specify the type of compaction to be used and the number of passes of this equipment over the layer of material. This specification is meant for the engineers executing the earthworks.
The end product specification will advise of the compaction that has to be achieved. This will depend on the laboratory analysis of the soil which would determine the percentage of various grain sizes in the soil and the possibility of the soil to be compacted. Its existing water content and the water content that will achieve maximum compaction is also determined under laboratory condition. Quality control engineers would determine whether the specified compaction and moisture content has been achieved before allowing further work to proceed.
The performance specification is more of a long range attempt to determine the longevity of the earthwork in contention, and is more in use where such earthworks are meant to serve over long periods of time. Here the settlement of the earth, ground water level, drainage and other factors that can affect the strength of the earthwork in the long run have to be considered. Engineers have designed instrumentation that can be embedded in earthwork that will give them constant readings on all these parameters even at remote locations.
Image Source: Wikimedia : Embankment
Earthworks: A Guide by N. A. Trenter