Weathering of the Oporto granite: geotechnical and physical properties

Begonha, Arlindo; Braga, M. A. Sequeira

doi:10.1016/s0341-8162(02)00016-4

Cited by 113 publications

(67 citation statements)

References 9 publications

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“…This granitic bedrock displays thin crushed quartz veins and is evansite enriched, especially in interlocking rock joints and faults fillings [36,37] and is, generally, weathered to different grades, from fresh-rock to residual soil over short distances. These variable weathering fronts result in arenisation and kaolinisation, which may reach depths of more than 30 m [38]. The granitic vertical profile involves different hydrogeological compartments, the weathered surface (alterites), the weathered-fissured zone and the unweathered fracture zone.…”

Section: Porto Urban Area: Paranhos and Salgueiros Spring Watersmentioning

confidence: 99%

Environmental Groundwater Vulnerability Assessment in Urban Water Mines (Porto, NW Portugal)

Afonso

Freitas

Pereira

et al. 2016

Water

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A multidisciplinary approach was developed to estimate urban groundwater vulnerability to contamination combining hydrogeology, hydrogeochemistry, subterranean hydrogeotechnics, groundwater ecotoxicology and isotope tracers. Paranhos and Salgueiros spring waters in Porto City were used as a case study. Historical and current vulnerability scenarios were compared using hydrogeological GIS-based modelling. Potential contamination sources were mapped around the spring galleries. Most of these were point sources and their potential contamination load was moderate. The ecotoxicological assessment indicated a low acute toxicity potential. Groundwater radionuclides appeared to be mainly controlled by geological factors and biomineralisation. Vulnerability maps suggest that most of the area has a moderate to low vulnerability to contamination. However, some surface sources such as sewage systems cause contamination and contribute to increased vulnerability. This integrated approach was demonstrated to be adequate for a better knowledge of urban hydrogeological processes and their dynamics, and highlighted the importance of a vulnerability assessment in urban areas.

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Section: Porto Urban Area: Paranhos and Salgueiros Spring Watersmentioning

confidence: 99%

Environmental Groundwater Vulnerability Assessment in Urban Water Mines (Porto, NW Portugal)

Afonso

Freitas

Pereira

et al. 2016

Water

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“…We found that gaps in the data made the decision between power, log or linear trends between the porosity and UCS in our data difficult. We selected an inverse power relationship because many authors have reported an inverse power correlation for a variety of rock types (Lama and Vutukuri, 1978;Palchik, 1999;Begonha and Sequeira Braga, 2002;Li and Aubertin, 2003;Sousa et al, 2005;Chang et al, 2006;Heap et al, 2014b). We have used the resulting inverse power correlation (Fig.…”

Section: Porosity (φ)mentioning

confidence: 99%

The development and application of the alteration strength index equation

Wyering

Villeneuve

Wallis

et al. 2015

Engineering Geology

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We have developed an alteration strength index (ASI) equation to address the effect of hydrothermal alteration on mechanical rock properties. This equation can be used to estimate a range of rock strengths, comparable to uniaxial compressive strength (UCS), based on rapid analysis of mineralogy and microstructure. We used rock samples from three geothermal fields in the Taupo Volcanic Zone (TVZ) to represent a range of alteration types. These are sedimentary, intrusive and extrusive rocks, typical of geothermal systems, from shallow and deep boreholes (72 measured Depth (mD) to 3280 mD). The parameters used in ASI were selected based on literature relating these aspects of mineralogy and microstructure to rock strength. The parameters in ASI define the geological characteristics of the rock, such as proportions of primary and secondary mineralogy, individual mineral hardness, porosity and fracture number. We calibrated the ASI against measured UCS for our samples from the TVZ to produce a strong correlation (R 2 of 0.86), and from this correlation we were able to derive an equation to convert ASI to UCS. Because the ASI-UCS relationship is based on an empirical fit, the UCS value that is obtained from conversion of the ASI includes an error of 7 MPa for the 50th percentile and 25 MPa for the 90th percentile with a mean error of 11 MPa. A sensitivity analysis showed that the mineralogy parameter is the dominant characteristic in this equation, and the ASI equation using only mineralogy can be used to provide an estimated UCS range, although the error (or uncertainty) becomes greater. This provides the ability to estimate strength even when either fracture or porosity information are not available, for example in the case of logging drill cuttings. This research has also allowed us to provide ranges of rock strengths based solely on the alteration zones, mineralogy, and depth of lithol-ogies found in a typical geothermal field that can be used to update conceptual models of geothermal fields.

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“…Coarse materials such as sandy loam or saprolite generally have low aggregation due to low content of cementing agent like clay (Hillel, 1983). Moreover, saprolite is not close to rigid material but still is on weathering process, which means its components such as quartz and mica can fragment into small pieces over time (Zhang et al, 2014;Begonha and Braga, 2002). Zhang et al (2014) also reported that saturated hydraulic conductivity of piled saprolite decreased over time, probably due to macropore clogging of fine particles formed by weathering of mica and feldspar in saprolite.…”

Section: Influences Of Accumulate Types and Elaped Time On Physico-chmentioning

confidence: 99%

Physico-chemical Properties of Disturbed Plastic Film House Soils under Cucumber and Grape Cultivation as Affected by Artificial Accumulation History

Han¹,

Muhammad²,

Zhang³

et al. 2015

Korean Journal of Soil Science and Fertilizer

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This study was carried out to investigate the effects of profile disturbance with different artificial accumulation history on physico-chemical properties of soil under plastic film house. The investigations included soil profile description using soil column cylinder auger F10cm x h110cm, in situ and laboratory measurements of soil properties at five sites each at the cucumber (Site Ic ~ Vc) and grape (Site Ig ~ Vg) plastic film houses with artificial soil accumulation. The sites except sites Ic, IVc, IVg and Vg, belong to ex-paddy area. The types of accumulates around root zone included sandy loam soil for 3 sites, loam soil for 1 site, saprolite for 2 sites, and multi-layer with different accumulates for 3 sites. Especially, Site IIg has mixed plow zone (Ap horizon) with original soil and saprolite, whereas disturbed soil layers of the other sites are composed of only external accumulates. The soil depth disturbed by artificial accumulation ranged from 20 cm, for Site IIg, to whole measured depth of 110 cm, for Site IVc, Vc, and Site IVg. Elapsed time from artificially accumulation to investigation time ranged from 3 months, Site IIc, to more than 20 years, Site Vg, paddy-soil covering over well-drained upland soil during land leveling in 1980s. Disturbed top layer in all sites except Site Vg had no structure, indicating low structural stability. In situ infiltration rate had no correlation with texture or organic matter content, but highest value with highest variability in Site IIIc, the shortest elapsed time since sandy loam soil accumulation. Relatively low infiltration rate was observed in sites accumulated by saprolite with coarse texture, presumably because its low structural stability in the way of weathering process could result in relatively high compaction in agro-machine work or irrigation. In all cucumber sites, there were water-transport limited zone with very low permeable or impermeability within 50 cm under soil surface, but Site IIg, IIIg, and Vg, with relatively weak disturbance or structured soil, were the reverse. We observed the big change in texture and re-increase of organic matter content, available phosphate, and exchangeable cations between disturbed layer and original soil layer. This study, therefore, suggest that the accumulation of coarse material such as saprolite for cultivating cash crop under plastic film house might not improve soil drainage and structural stability, inversely showing weaker disturbance of original soil profile with higher drainage.

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Weathering of the Oporto granite: geotechnical and physical properties

Cited by 113 publications

References 9 publications

Environmental Groundwater Vulnerability Assessment in Urban Water Mines (Porto, NW Portugal)

Environmental Groundwater Vulnerability Assessment in Urban Water Mines (Porto, NW Portugal)

The development and application of the alteration strength index equation

Physico-chemical Properties of Disturbed Plastic Film House Soils under Cucumber and Grape Cultivation as Affected by Artificial Accumulation History

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