Excavation

Composting by the addition of readily degradable hulking agents is also a useful option for relatively small volumes of excavated contaminated soil. 

In the past, removing metal and metalloid contaminants from soil has been impossible, and site clean-up has meant excavation and disposal in a secure landfill. An exciting new approach to this problem is phytoextraction, where plants are used to extract contaminants from the soil and harvested. Immobilization and Toxicity-Minimization. 

Explosive Detonation pressure, GPa Bulk specific gravity Detonation velocity, km/s Contains high explosives Heat of detonation kj /g Excavated vol relative to equal wt of TNT... 

Trace-element analysis, using emission spectroscopy (107) and, especially, activation analysis (108) has been appHed in provenance studies on archaeological ceramics with revolutionary results. The attribution of a certain geographic origin for the clay of an object excavated elsewhere has a direct implication on past trade and exchange relationships. 

Bronze disease necessitates immediate action to halt the process and remove the cause. For a long time, stabilization was sought by removal of the cuprous chloride by immersing the object in a solution of sodium sesquicarbonate. This process was, however, extremely time-consuming, frequentiy unsuccesshil, and often the cause of unpleasant discolorations of the patina. Objects affected by bronze disease are mostiy treated by immersion in, or surface appHcation of, 1 H-henzotriazole [95-14-7] C H N, a corrosion inhibitor for copper. A localized treatment is the excavation of cuprous chloride from the affected area until bare metal is obtained, followed by appHcation of moist, freshly precipitated silver oxide which serves to stabilize the chloride by formation of silver chloride. Subsequent storage in very dry conditions is generally recommended to prevent recurrence. 

Materials that have been buried underwater cause a special problem. Waterlogged woods and leathers (139), although quite stable under such burial conditions, are ia danger of irreversible damage through drying out upon recovery. Indeed, after excavations from bogs or upon recovery from underwater sites, these items need to be stored underwater until laboratory treatment. 

A smooth coal pile surface, coupled with the gradual slope, minimi2es the differential wind pressures and consequent oxygen penetration. A 4-6 X 10 t lignite stockpile from the excavation for the Garrison Dam in North Dakota has been stable for many years as a result of this storage method. 

Quarries that excavate soft stone, notably mad or chalk, do not dtiU or blast, but extract the stone usiag heavy-duty rippers and scrapers. In the Middle West and Florida, lake mads and soft coralline limestone are dredged ia a process much like stripmining. 

Fig. 3. The four basic methods of mining (a) scraping, (b) excavating, (c) fluidizing, and (d) tunneling (46).

Sludge-blanket clarifiers are difficult to start up because the first blanket must be estabUshed, and large-scale units require extensive excavation. Sizes range from 600 x 600 mm to 50 x 50 m. Precipitation and crystallization can be carried out in similar hopper-designed units, having overflow rates of 80 m/h or higher. 

Soil Stabilization/Grouting. Sodium sihcates have been used in soil stabih2ation for most of the twentieth century. This usage represents the largest market in Japan in the mid-1990s. Sodium sihcates can be used for water control and soil stabih2ation in tunneling and excavation projects. 

Fig. 7. Mining with a bucket-wheel excavator, where (-) represents the ultimate si2e of the dyke.

Draglines are equipped with a 71-m bucket at the end of a 111-m boom and can be employed to dig both a portion of the overburden, which is free-cast into the mining pit, and the tar sand, which is piled in windrows behind the machine. Bucket-wheel reclaimers, similar to bucket-wheel excavators, load the tar sand from the windrows onto conveyor belts which transfer it to the plant. 

Cemented carbides play a cmcial role in the recovery of metallic ores and nonmetals by underground or open-pit mining practices, recovery of minerals such as coal (qv), potash, and trona, and drilling for oh and gas. The methods of excavation can be broadly classified into three types rotary... 

---