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Geological Maps
Published in F.G.H. Blyth, M. H. de Freitas, A Geology for Engineers, 2017
F.G.H. Blyth, M. H. de Freitas
Normal equipment for mapping includes a topographical map of the area, a map case, soft pencils, compass, clinometer, pocket binoculars and hammer. A hammer head weighing about 0.5 kg is usually sufficient and is made from forged steel so as not to splinter when breaking hard rock (suitable geological hammers can be purchased). The clinometer is used for measuring the dip of surfaces such as bedding and cleavage; it may be a separate instrument, as shown in Fig. 12.8, or incorporated in the compass (as in a Brunton compass). In its simplest form it consists of a plummet which hangs vertically against a scale, and can be made by mounting a protractor on to a thin plate of material such as plywood or perspex sheeting, with a plum-bob hung from the centre of the protractor circle. The compass is needed for measuring directions of dip or strike; many geologists use a prismatic compass because it also allows the accurate sighting of distant objects, as needed for orienting the map. Other useful equipment includes a surveyor’s notebook (although some notes can be written on the map), a straight edge or scale, a pocket lens or magnifier (× 5 is a useful magnification for field work) and a haversack. If air photographs are available, especially when the area to be covered is large, they give a comprehensive view of the ground and are a valuable adjunct. But the geology has to be inspected and mapped on the ground itself.
Evolution of a karstic groundwater system, Cave Hill, Augusta County, Virginia: A multi-disciplinary study
Published in Barry F. Beck, Felicity M. Pearson, Karst Geohazards, 2018
Sedimentary rock strata are steeply inclined at Cave Hill and are nearly vertical in Grand Caverns, Madisons Saltpetre Cave, and Stegers Fissure. Attitudes of bedding were measured using a Brunton compass (Kastning, 1991b). To date, over fifty strike-and-dip readings have been taken on Cave Hill and within the caves, and most are indicated on the geologic map (Figure 1).
Effects of discontinuities on the rock block geometry of dimension stone quarries: a case study
Published in Geomechanics and Geoengineering, 2023
Hamid Ranjkesh Adarmanabadi, Arezou Rasti, Navid Mojtabai, Morteza Tabaei, Mehrdad Razavi
Sixty-three exposed bench faces with a total of 2258 m of scanline were mapped. In addition, cores from several boreholes were used to define the structure of the rock mass better. The applied scanlines on each bench faces were straight with having approximately 90-degree inclination. Figure 2 shows a generalised schematic of scanline mapping used for this investigation. The number of discontinuities, discontinuities’ orientation, and discontinuities spacing were recorded. The orientations of the discontinuities were measured using a Brunton compass during the survey. The discontinuity spacing, which has a crucial effect on the block size, was measured during the scanline survey. The frequency of discontinuities is measured to be able to find the mean value for the discontinuities spacing. Accordingly, the volumetric joint count index was estimated for different bench faces using the mean spacing of each joint set. The weighted joint density index was estimated using the discontinuities frequency and angle between the discontinuities and survey area. In addition, the rock mass block quality designation of quarries is estimated using the total length of scanline survey and spacing of discontinuities equal or greater than 1 m. The results of RQD, volumetric joint count index, weight joint density index, and rock mass block quality designation of quarries are compared, and a correlation is evaluated. An empirical index was proposed by authors to evaluate the block’s volume based on the discontinuities network. It was tried to consider and apply all discontinuities’ features in the proposed index to increase its accuracy. Finally, the predicted volumes of in situ rock blocks using the empirical equations are compared with the mean volume of rock blocks excavated from the site.
Site-specific geological and geotechnical investigation of a debris landslide along unstable road cut slopes in the Himalayan region, India
Published in Geomatics, Natural Hazards and Risk, 2020
C. Prakasam, Aravinth. R, B. Nagarajan, Varinder S. Kanwar
The landslide studied is located along the road cut section of National Highway-05 near Jhakri Town of Himachal Pradesh. The rod cut section trends along NNW by SSE (Figure 5(a)). Satellite imageries and field investigations equipment such as Brunton compass were used to study the geometry of the slopes. The direction of the trending of the landslides and the angle of the slope post landslides failure were noted down during field investigations and the height of the slopes is estimated with the help of data obtained from the total station.
Towards a glacial subdivision of the Ediacaran Period, with an example of the Boston Bay Group, Massachusetts
Published in Australian Journal of Earth Sciences, 2022
Stratigraphic sections were measured using tape and the level of a Brunton compass, with degree of development and of dilute acid reaction estimated in the field using the scales of Retallack (1997), and colour from a Munsell chart (Munsell Color, 1975) with additional tropical and gley pages (Figure 6). Samples of paleosols were collected in the field for preparation of sawn slabs and petrographic thin-sections, and also analysed for major oxides using X-ray fluorescence by ALS Chemex of Vancouver, British Columbia, who also determined ferrous iron using the Pratt titration, and weight percent organic carbon using a LECO carbon analyser (Table 1). Bulk density was determined by weighing paraffin-coated clods some 2 cm2 in size both in and out of water at 6°C (Table 1). Errors were calculated from 10 replicates for bulk density, and from 89 laboratory trials for other analyses. Thin-sections were point-counted using a Swift Automated stage and collator and an eyepiece micrometre to determine proportions of sand–silt–clay components of the paleosols (Figure 7; Table 2). Past trials have shown that the error associated with such 500-point counts is 2% (Murphy, 1983). Molar ratios were also calculated from bulk chemical analyses to give products over reactants of common soil-forming chemical processes (Retallack, 1997), such as salinisation, calcification, clayeyness, base loss and gleisation (Figure 7). A more detailed accounting of geochemical change following Brimhall et al. (1992) is mass transfer of elements in a soil at a given horizon (τw,j in moles) calculated from the bulk density of the soil (ρw in g.cm−3) and parent material (ρp in g.cm−3) and from the chemical concentration of the element in soils (Cj,w in weight %) and parent material (Cp,w in weight %). Changes in volume of soil during weathering are called strain by Brimhall et al. (1992), and estimated from an immobile element in soil (such as Ti used here) compared with parent material (εi,w as a fraction). The relevant Equations 1 and 2 are the basis for calculating divergence from parent material composition (origin in various panels of Figure 8).