Digging for data can put projects on the fastrack.The design, construction and cost of a building foundation in the New York City New York City: see New York, city. New York City City (pop., 2000: 8,008,278), southeastern New York, at the mouth of the Hudson River. The largest city in the U.S. area are usually dictated by the widely varying geologic conditions encountered in the five boroughs. Rock extends well above sea level at the northern reaches of Manhattan Island and the Bronx falls to depths of more than 800 feet at the barrier islands at the southern extremities of Brooklyn. These highly variable geologic conditions, significantly affected by past glacial activity, dictate different design and construction approaches throughout the five boroughs. At some locations extensive rock removal is required, while long piling is necessary elsewhere. Similar changes can occur within a limited project site on Manhattan Island. A thorough understanding of the local geology, as well as very detailed site specific geotechnical data, are essential to the proper design and construction of foundations. New York City lies at the junction of three major geologic provinces: the New England New England, name applied to the region comprising six states of the NE United States—Maine, New Hampshire, Vermont, Massachusetts, Rhode Island, and Connecticut. The region is thought to have been so named by Capt. Upland to the northwest, the Triassic Lowland to the southwest and the Coastal Plain to the southeast. These provinces contain several different foundation rock types and numerous soil deposits, recording a geologic history spanning over a billion years. The Bronx, Manhattan and parts of Brooklyn, Queens and Staten Island Staten Island (1990 pop. 378,977), 59 sq mi (160 sq km), SE N.Y., in New York Bay, SW of Manhattan, forming Richmond co. of New York state and the borough of Staten Island of New York City. lie in a region of the New England Uplands locally known as the Manhattan Prong, a northeast trending deeply-eroded sequence of metamorphic rock metamorphic rock Any of a class of rocks that result from the alteration of preexisting rocks in response to changing geological conditions, including variations in temperature, pressure, and mechanical stress. . Eastern Queens and Brooklyn are in the low-lying Coastal Plain province. The boundary between the Manhattan Prong and the Coastal Plain is called the fall line. Site conditions are significantly different on either side of the line. The soil deposits in the New York New York, state, United States New York, Middle Atlantic state of the United States. It is bordered by Vermont, Massachusetts, Connecticut, and the Atlantic Ocean (E), New Jersey and Pennsylvania (S), Lakes Erie and Ontario and the Canadian province of area are derived largely from two geologic periods. The broad Coastal Plain along the Atlantic seacoast was formed during the Cretaceous period Cretaceous period (krĭtā`shəs), third and last period of the Mesozoic era of geologic time (see Geologic Timescale, table), lasting from approximately 144 to 65 million years ago. . In the Pleistocene period, most of the earlier soil in the northern part was obliterated o·blit·er·ate tr.v. o·blit·er·at·ed, o·blit·er·at·ing, o·blit·er·ates 1. To do away with completely so as to leave no trace. See Synonyms at abolish. 2. by advancing and retrenching glaciers, leaving a complex stratigraphy stratigraphy, branch of geology specifically concerned with the arrangement of layered rocks (see stratification). Stratigraphy is based on the law of superposition, which states that in a normal sequence of rock layers the youngest is on top and the oldest on the . An understanding of the multiple advances and withdrawals of the glaciers and the formation of outwash outwash Deposit of sand and gravel carried by running water from the melting ice of a glacier and laid down in stratified deposits. An outwash may be as much as 330 ft (100 m) thick at the edge of a glacier, and it may extend for many miles. deposits is a useful introduction to a site and permits the foundation engineer to understand the general geologic characteristics of the area. Engineering firms with extensive records of prior exploration experience in the New York area, like Mueser Rutledge Consulting Engineers, are able to provide developers with early estimates of likely subsurface sub·sur·face adj. Of, relating to, or situated in an area beneath a surface, especially the surface of the earth or of a body of water. Adj. 1. conditions to aid in preliminary planning of the height of the building, economical depth of basements and likely type of foundation, thus permitting preliminary comparative cost evaluations. This information is also useful in planning a comprehensive subsurface investigation for the site. The extent of exploration and testing is dictated by site variations. Borings are needed to identify changes in general strata, top of rock elevations and quality of rock, especially if there were extreme variations in the rock profile across the site. The quality of the rock and the variations in elevation of the rock surface can have a significant effect on the design of foundations. Testing of the soil can provide specific properties Specific properties of a substance are derived from other intrinsic and extrinsic properties (or intensive and extensive properties) of that substance. For example, the density of steel (a specific and intrinsic property) can be derived from measurements of the mass of a steel bar for analysis of bearing, stability and settlement. An understanding of the general New York area geology permits the geotechnical engineer to properly address these questions in the exploratory program. The New York City Building Code specifies the numbers of borings required for various types of foundations. These numbers may or may not be adequate, depending upon variations in geology discovered throughout a site. When unanticipated variations in profile occur within site additional exploratory holes might be necessary to further define conditions. In general, the Code requirement should be considered as a minimum, except where sufficient information is available from adjacent sites, where the rock surface is exposed or where the geologic conditions are sufficiently uniform to not warrant further exploratory work. GEORGE J. TAMARO, P.E. SENIOR PARTNER MUESER RUTLEDGE CONSULTING ENGINEERS |
|
||||||||||||||||||
Printer friendly
Cite/link
Email
Feedback
Reader Opinion