Test Borings Research Articles

Structure due to volume shrinkage in the bedding-replacement fluorspar deposits of southern Illinois

Flat-lying, elongate bedding-replacement fluorspar deposits in southern Illinois commonly exhibit structural features best explained as the results of net loss of rock volume during the ore forming process.Synclines found over many deposits are regarded as the results of a thinning of limestone strata localized in the ore-bearing areas. A statistical study of test borings shows that such localized thinning is a characteristic feature of the district. Also many evidences of subsidence are apparent within the deposits, such as measurable thinning and removal of part or all of certain limestone beds, spalling and collapse of slabs of roof-rock and other layers of rock into the body of the deposits, presence of V-structures, and cavities and tabular openings at the sides and tops of deposits.The mechanism responsible for the indicated volume shrinkage is considered to be in part the stoichimetric replacement of calcite in limestone by denser fluorite, and in part the actual removal of limestone by the action of solvent mineralizing fluids.

Recovery of ground‐water supplies by pumping from watertable ponds

This paper summarizes a study made to determine whether ground‐water storage in the glacial deposits in the vicinity of Fresh Pond, a water‐table pond used as part of the public supply of the City of Cambridge, Massachusetts, is available to augment the supply from surface‐water reservoirs.Test wells were drilled; water level, well and test boring, and quality of water data, and data on Inflow and outflow from Fresh Pond were collected, and seismic profiles were run, to determine whether the glacial deposits in the vicinity of the pond contribute appreciable quantities of water to the pond. The data show that water levels in certain wells fluctuate with the level of Fresh Pond and that certain other water levels do not, indicating ground‐water contributions to the pond when it is at low stages and increases in ground‐water storage when pond stages are high. The largest changes in ground‐water storage occur in the glacial deposits underlying the banks to the west and northwest of the pond. Mineral characteristics of the well and pond waters offer no evidence as to the direction of ground‐water flow.

Effect of Sedimentation on Floods in the Kickapoo Valley, Wisconsin

The Kickapoo River, a tributary of the Wisconsin River, is the largest stream entirely within the rugged Driftless Area of the Upper Mississippi Valley. The drainage area is submaturely dissected, with an average relief of about 400 feet. Deforestation, cultivation, and grazing of the sloping ridge crests and valley sides have resulted in greatly accelerated soil erosion, and consequently fluvial sedimentation has also been accelerated. Nearly all the dark-gray or black first-bottom soils have been covered by stratified brownish modern sandy silt since about 1850. Numerous test borings indicate that the flood plains of the main Kickapoo River and the lower parts of two main tributaries have been aggraded an average of about 2.5 feet. Re-surveys of river cross sections beneath railroad bridges indicate an average rate of river-channel aggradation of about 1 foot in twenty years, and it is concluded that the river and flood plain are being aggraded at about the same rate. Excessive sedimentation from floo...

The Cuscatlan Bridge in El Salvador

THIS bridge is the largest in Central America, and has been erected across the Lempa River, to complete another link in the Pan-American Highway (Earthquake Notes, 14, Nos. 3 and 4 ; June 1943). The main suspension span of 820 ft. is carried by cables of open construction chosen to fit the unusual erection conditions. The bridge is near the base of an extinct volcano, and test borings indicated that the foundations and anchorages would be in volcanic materials consisting of cemented ash and loose boulders or stones. These materials lie in very irregular strata and pockets. Since the bridge may be subjected to earthquake shocks, special care was necessary to support the assumed earthquake forces in the design of the concrete approaches. A study of this feature indicated that multiple-span rigid -frame structures were required. A factor in the design of structures built to resist earthquakes is the natural period of vibration. Resonance must be avoided by making this different from the supposed destructive earthquake frequencies likely to arise in the district. In this case periods of from 0.5 sec. to 1.5 sec. were avoided. The natural periods of the transverse bents of the Lempa River Bridge concrete approaches is less than 0.5 sec. and that of the longitudinal frames is of the order of 0.25 sec. A factor contributing to the safety of the longitudinal frames against resonance is the varying heights of the columns, each of which has a natural period of its own different from the others. Tunnel anchorages have been used. The principal mass of the bridge is contained in the main-span trusses and the floor, and this mass would produce the greatest transverse earthquake force on the towers at the level of the trusses. The cables have a small mass but transmit heavy loads to the towers. The earthquake forces on the towers from the cables would be small, and the conservative design of the bridge was not affected by the assumed earthquake forces.

The Peat Deposits of Bermuda and Evidences of Postglacial Changes in Sea-Level

The evidences of recent submergence of Bermuda are from four sources: (1) topog-raphy, (2) submerged limestone caverns, (3) buried cedars and peat bogs, and (4) existing marshes. The most convincing proof of postglacial submergence is found in the marshes on the island. The Hamilton marsh, 97.7 feet deep, gives evidence of a postglacial rise in sea-level of at least this amount. A test boring was made in this marsh to a depth of 42 feet. Five layers of woody peat were encountered, which are best interpreted as representing periods of relative stability of sea-level. They therefore show that the change was periodic and not gradual. They also offer an unusual means of determining the rate of peat accumulation and the length of postglacial time. It may be possible to correlate with their aid recent changes in level in other parts of the world.

The Artesian Water Supply for the Latham Water District, New York

The artesian wells furnishing water to the Latham Water District, Colonie, New York, are among the largest in the State. They are also somewhat unique because of their location between the Hudson and Mohawk rivers which are respectively 300 feet and 125 feet lower than the well sites. The presence of artesian water was discovered about 3J miles west of Watervilet in the late nineties by engineers engaged in making test borings over a proposed canal route from the Hudson to the Mohawk river. The City of Cohoes interested in securing anew water supply then did considerable prospecting in the vicinity of the present Albany Airport, which lies at an elevation of 270 feet above sea level, and developed several wells. Some of them are still flowing and are being used by the Airport, Albany County Welfare Buildings, and Hospital. They have a static head of about 25 feet and a free flow of about 250,000 gallons per day. For many years they furnished water to the Shaker settlement which stood where the Airport now is and maintained service on the second floors of the community buildings without pumping. My interest in this field was first aroused in 1906. In 1912 an opportunity was afforded to have the wells cleaned and placed in order for a test. They were found to be about 100 feet deep and seated without strainers into a shallow bed of gravel varying in thickness from 18 to 24 inches. The overlying stratum was mostly clay. The wells were pumped in rotation over a period of about three months and the effect noted on the other wells in the field. From