{"id":241,"date":"2022-01-13T23:17:25","date_gmt":"2022-01-13T23:17:25","guid":{"rendered":"https:\/\/books.gw-project.org\/land-subsidence-and-its-mitigation\/chapter\/spirit-leveling\/"},"modified":"2022-01-16T17:06:46","modified_gmt":"2022-01-16T17:06:46","slug":"spirit-leveling","status":"publish","type":"chapter","link":"https:\/\/books.gw-project.org\/land-subsidence-and-its-mitigation\/chapter\/spirit-leveling\/","title":{"raw":"3.1 Spirit Leveling","rendered":"3.1 Spirit Leveling"},"content":{"raw":"
\r\n

Spirit (differential) leveling is the traditional method of determining ground elevation changes and, despite its simplicity, can be very accurate. Equipment and procedures are described in detail in several manuals, for example, in Rappleye (1948) and Floyd (1978). The technique was developed in the nineteenth century and continues to be applied. The method allows surveyors to carry an elevation from a known reference point to other geodetic marks using a precisely leveled telescope and a pair of graduated vertical rods. For each survey, the elevation difference, e<\/em>d<\/em><\/sub>,<\/em> between two benchmarks is recorded twice by accumulating the elevation differences between a series of temporary turning points. The method assumes the stability of the reference benchmark, thus special care must be taken in tectonically active zones. The discrepancy between e<\/em>d<\/em><\/sub> measured in the forward and backward directions (relative to the direction of the traverse) must not exceed [latex]1.5\\sqrt{D}[\/latex] mm for a \u201cvery high (first order)\u201d precision survey, and [latex]3\\sqrt{D}[\/latex] mm for a \u201chigh (second order)\u201d precision survey, D<\/em> being the length of the benchmark line in kilometers. Typically, benchmarks are spaced 1\u00a0km apart and turning points are 20 to 100\u00a0m apart. Once a network of benchmarks has been established and surveyed by precise leveling, a further survey at some later date shows whether vertical movements have occurred (Figure\u00a019).<\/p>\r\n\"Sketch\r\n

Figure\u00a0<\/strong>19<\/strong>\u00a0<\/strong>\u2011\u00a0<\/strong>Sketch of a leveling survey.<\/p>\r\n

Digital levels and invar rods (invar is an alloy of iron and nickel with a negligible coefficient of expansion) help fulfill the selected accuracy, eliminating the human errors and increasing the measurement speed. To ensure long\u2011term time series, the benchmarks, a brass cup or headed bolt, are grouted into massive structures, such as bridge abutments, bedrock outcrops, or attached at the top of a 5 to 10\u00a0m long bar driven into the ground and protected by an outer sleeve. Examples of leveling networks established to control land subsidence due to fluid withdrawal are published by Ikehara and others (1997) and Tosi and others (2007).<\/p>\r\n\r\n<\/div>","rendered":"

\n

Spirit (differential) leveling is the traditional method of determining ground elevation changes and, despite its simplicity, can be very accurate. Equipment and procedures are described in detail in several manuals, for example, in Rappleye (1948) and Floyd (1978). The technique was developed in the nineteenth century and continues to be applied. The method allows surveyors to carry an elevation from a known reference point to other geodetic marks using a precisely leveled telescope and a pair of graduated vertical rods. For each survey, the elevation difference, e<\/em>d<\/em><\/sub>,<\/em> between two benchmarks is recorded twice by accumulating the elevation differences between a series of temporary turning points. The method assumes the stability of the reference benchmark, thus special care must be taken in tectonically active zones. The discrepancy between e<\/em>d<\/em><\/sub> measured in the forward and backward directions (relative to the direction of the traverse) must not exceed \"1.5\sqrt{D}\" mm for a \u201cvery high (first order)\u201d precision survey, and \"3\sqrt{D}\" mm for a \u201chigh (second order)\u201d precision survey, D<\/em> being the length of the benchmark line in kilometers. Typically, benchmarks are spaced 1\u00a0km apart and turning points are 20 to 100\u00a0m apart. Once a network of benchmarks has been established and surveyed by precise leveling, a further survey at some later date shows whether vertical movements have occurred (Figure\u00a019).<\/p>\n

\"Sketch<\/p>\n

Figure\u00a0<\/strong>19<\/strong>\u00a0<\/strong>\u2011\u00a0<\/strong>Sketch of a leveling survey.<\/p>\n

Digital levels and invar rods (invar is an alloy of iron and nickel with a negligible coefficient of expansion) help fulfill the selected accuracy, eliminating the human errors and increasing the measurement speed. To ensure long\u2011term time series, the benchmarks, a brass cup or headed bolt, are grouted into massive structures, such as bridge abutments, bedrock outcrops, or attached at the top of a 5 to 10\u00a0m long bar driven into the ground and protected by an outer sleeve. Examples of leveling networks established to control land subsidence due to fluid withdrawal are published by Ikehara and others (1997) and Tosi and others (2007).<\/p>\n<\/div>\n","protected":false},"author":1,"menu_order":14,"template":"","meta":{"pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-241","chapter","type-chapter","status-publish","hentry"],"part":132,"_links":{"self":[{"href":"https:\/\/books.gw-project.org\/land-subsidence-and-its-mitigation\/wp-json\/pressbooks\/v2\/chapters\/241","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/books.gw-project.org\/land-subsidence-and-its-mitigation\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/books.gw-project.org\/land-subsidence-and-its-mitigation\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/books.gw-project.org\/land-subsidence-and-its-mitigation\/wp-json\/wp\/v2\/users\/1"}],"version-history":[{"count":3,"href":"https:\/\/books.gw-project.org\/land-subsidence-and-its-mitigation\/wp-json\/pressbooks\/v2\/chapters\/241\/revisions"}],"predecessor-version":[{"id":390,"href":"https:\/\/books.gw-project.org\/land-subsidence-and-its-mitigation\/wp-json\/pressbooks\/v2\/chapters\/241\/revisions\/390"}],"part":[{"href":"https:\/\/books.gw-project.org\/land-subsidence-and-its-mitigation\/wp-json\/pressbooks\/v2\/parts\/132"}],"metadata":[{"href":"https:\/\/books.gw-project.org\/land-subsidence-and-its-mitigation\/wp-json\/pressbooks\/v2\/chapters\/241\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/books.gw-project.org\/land-subsidence-and-its-mitigation\/wp-json\/wp\/v2\/media?parent=241"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/books.gw-project.org\/land-subsidence-and-its-mitigation\/wp-json\/pressbooks\/v2\/chapter-type?post=241"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/books.gw-project.org\/land-subsidence-and-its-mitigation\/wp-json\/wp\/v2\/contributor?post=241"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/books.gw-project.org\/land-subsidence-and-its-mitigation\/wp-json\/wp\/v2\/license?post=241"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}