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The risk of cave-in increases from surcharge load, which is any weight placed outside the trench near its edge. These loads include the spoil pile (soil excavated from the trench) or heavy equipment. These add extra stress to the walls of the trench. Inability to escape the trench because of steep and unstable walls, which may be difficult to ...
Issues such as the effectiveness of certain trench layouts or the percentage of the site to be dug (normally around 5% at present) are widely discussed. Whether an effective picture of past human activity on a site can be truly estimated through this methods is widely debated.
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.
The method requires considering soil characteristics and the loads applied to the surface. In cases where the soil is sandy, the water table is at shallow depth, or heavy loads like that of urban traffic are expected, the depth of excavation has to be such that the pressure of the load on the surface does not affect the bore, otherwise there is ...
While a trench is being excavated to create a form for a wall, it is simultaneously filled with slurry (usually a mixture of bentonite and water). The dense but liquid slurry prevents the trench from collapsing by providing outward pressure, which balances the inward hydraulic forces and also retards water flow into the trench.
A similar method that uses wood planks is called soldier boarding. Hydraulics tend to be faster and easier; the other methods tend to be used for longer term applications or larger excavations. Shoring should not be confused with shielding by means of trench shields. Shoring is designed to prevent collapse, whilst shielding is only designed to ...
Tunnel Construction. Tunnels are dug in types of materials varying from soft clay to hard rock. The method of tunnel construction depends on such factors as the ground conditions, the ground water conditions, the length and diameter of the tunnel drive, the depth of the tunnel, the logistics of supporting the tunnel excavation, the final use and shape of the tunnel and appropriate risk management.
Selection of a trench excavation method must take into account a range of rock and machine properties. It is suggested that the advantages of using chain trenchers in suitable rock outweigh the limitations and may have cost benefits and fewer adverse environmental effects compared with alternative methods. [1]