18-08-2012, 12:20 PM
Earthworks
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Earthworks are engineering works created through the moving of massive quantities of soil or unformed rock. Engineers need to concern themselves with issue of geotechnical engineering (such as soil fluidity and friction) and with quantity estimation to ensure that soil volumes in the cuts match those of the fills, while minimizing the distance of movement. In the past these calculations were done by hand using a slide rule and with methods such as Simpson’s rule. Now they can be performed using a computer and specialized software, including optimization on haul cost and haul distance (as haul cost is not proportional to haul distance).
Due to amounts of material to be moved-millions of cubic meters (or cubic yards) in the case of large dams-earthwork engineering was revolutionized by the development of the (Fresno) scraper and other earth-moving machines such as the loader, production trucks, the grader, the bulldozer, the backhoe, and the dragline excavator
Common errors in excavation
Common errors during excavation fall into two basic categories and one or the other is almost inevitable because excavation is a destructive process that removes the information it seeks to record in real time and mistakes cannot be rectified easily.
1. Under-cutting. Under cutting occurs where contexts are not excavated fully and some remainder of the context is left in situ masking the nature of the underlying contexts. This is especially common among inexperienced archaeologists who have a tendency to be timid. The consequences of undercutting are quite serious as the nature of the archaeological sequence is obscured and subsequent recording and excavation is based on a flawed reading of the deposits on site. Unchecked, what follows from under-cutting is the production of false data often from the failure to spot intrusive finds and in turn, serious ramifications for the ability to interpret the sequence post-excavation. Entire sites can be "thrown out of phase" where relationships recorded in the Harris matrix bear no genuine association with any understandable phase of occupation. If a regime of under-cutting is allowed to progress its effects multiply as the site is reduced.
2. Over-cutting. Over-cutting occurs when contexts are unintentionally removed along with material from other deposits and contexts. Heavy over-cutting represents reckless removal of the sequence. However some degree of over-cutting is almost impossible to avoid and is certainly preferable to unchecked under-cutting even though over-cutting represents a loss of information.
Why is compaction a problem?
Soil compaction is a vital part of the construction process. It is used for support of structural entities such as building foundations, roadways, walkways, and earth retaining structures to name a few. For a given soil type certain properties may deem it more or less desirable to perform adequately for a particular circumstance. In general, the preselected soil should have adequate strength, be relatively incompressible so that future settlement is not significant, be stable against volume change as water content or other factors vary, be durable and safe against deterioration, and possess proper permeability.
How long will compaction last?
The persistence of soil compaction is determined by the depth at which it occurs, the shrink-well potential of the soil, and the climate. As the depth increases, the more persistent the condition. The type and percentage of clay determine the shrink-well potential. The greater the shrink-well potential and number of wet/dry cycles, the lower is the duration of compaction at a particular depth. Freeze/thaw cycles also help decrease near surface compaction.
Site formation
Archaeological material would, to a very large extent, have been called rubbish when it was left on the site. It tends to accumulate in events. A gardener swept a pile of soil into a corner, laid a gravel path or planted a bush in a hole. A builder built a wall and back-filled the trench. Years later, someone built a pig sty onto it and drained the pig sty into the nettle patch. Later still, he original wall blew over and so on. Each event, which may have taken a short or long time to accomplish, leaves a context. This layer cake of events is often referred to as the archaeological sequence or record. It is by analysis of this sequence or record that excavation is intended to permit interpretation, which should lead to discussion and understanding.
CORE CUTTER
Core cutters are used for testing the compaction of cohesive/clay soils placed as fill.
The cylindrical cores of standard volume, 13cms long and 10cms diameter., they have a sharpened edge at one end to improve penetration of the soil surface.
These cores are driven fully into the surface to be tested, they are removed from the ground without disturbing the core contents.
In the laboratory they are cut flush top and bottom and weighed.
Bulk density can be quickly calculated, and by determining the moisture content of the soil the dry density of the fill can be calculated and hence the voids percentage.
A high percentage of voids indicating poor compaction
Trial excavations and evaluations in development led archaeology
There are two main types of trial excavation in professional archaeology both commonly associated with development-led excavation: the test pit or trench and the watching brief. The purpose of trial excavations is to determine the extent and characteristics of archaeological potential in a given area before extensive excavation work is undertaken. This is usually conducted in development-led excavations as part of Project management planning, the main difference between Trial trenching and watching briefs is that trial trenches are actively dug for the purpose of revealing archaeological potential whereas watching briefs are cursory examination of trenches where the primary function of the trench is something other than archaeology, for example a trench cut for a gas pipe in a road. In the USA a method of evaluation called a Shovel test pit is used which is a specified half meter square line of trial trenches dug by hand. Often archaeology provides the only means to learn of the existence and behaviors of people of the past. Across the millennia many thousands of cultures and societies and billions of people have come and gone of which there is little or no written record of existing records are misrepresentative or incomplete. Writing as it is known today did not exist in human civilization until the 4th millennium BC, in a relatively small number of technologically advanced civilizations. In contrast Homo sapiens has existed for at least 200,000 years, and other species of Homo for millions of years (se Human evolution). These civilizations are, not coincidentally, the best-known; they are open to the inquiry of historians for centuries, while the study of pre-historic cultures has arisen only recently. Even within a literate civilization many events and important human practices are not officially recorded.