Developments in triaxial testing technique

Summary A simple triaxial cell is described together with details of the technique employed for triaxial testing. Triaxial strength results for 254 specimens of eight rock types are tabulated.

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Zusammenfassung Ein einfaches Triaxial-Prüfgerät wird, zusammen mit Einzelheiten des experimentellen Verfahrens, beschrieben. Ergebnisse dreiachsiger Festigkeitsprüfung sind für 254 Proben aus acht verschiedenen Gesteinsarten in Tabellen wiedergegeben.

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Résumé Un appareil triaxial simple est décrit avec des détails sur la technique expérimentale. Des résultats de résistance triaxiale pour 254 échantillons pris parmi huit types de roche sont donnés.

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With 2 Figures     

Longitudinal characterization of a tidal marsh creek separating two hydrographically distinct estuaries

Jones Creek, South Carolina, connects two hydrographically distinct estuarine systems: North Inlet and Winyah Bay. One hundred fifty-two sets of hydrographic measurements from February 1978 indicate the existence of a Jones Creek nodal point, an effective barrier limiting flow exchange between the end regions of the creek. Morphologic and vegetation observations and water quality ratings suggest that this nodal point is a permanent feature of Jones Creek and may be present in other similar systems.     

The stability of transition metal dolomites in carbonate systems: a discussion

The instability of transition metal dolomites [CaR²⁺(CO₃)₂ where R²⁺ is Fe, Co, Ni, Cu, or Zn] and the limited substitution of transition metal cations for Mg in the dolomite structure can be accounted for by the effect of octahedral distortion. For example, trigonal elongation of the Fe octahedron, due to the Jahn-Teller effect, observed in siderite and ankerite, results in elongation of the Ca octahedron which is sensitive to distortion because the radius of Ca²⁺ is close to the upper limit for octahedral coordination. Co, Ni, Cu, Zn octahedra are also thought to be deformed, relative to Mg octahedra, in carbonates.The free energy of formation (ΔG^o_f) of R²⁺CO₃ becomes more positive with increasing octahedral distortion. Estimated ΔG^o_f(dolomite) as well as stabilities and solubility limits of R²⁺ in natural and synthetic dolomites suggest a series in order of decreasing stability: Mg >Mn >Zn >Fe >Co >Ni >Cu.ΔG^o_f(est.) for the terminal Fe-dolomite solid solution [72 mol% CaFe(CO₃)₂] in the system CaCO₃-MgCO₃-FeCO₃ may represent an empirical threshold value for dolomite stability which lies between ΔG^o_f for Mn- and Zn-dolomites. While Zn-dolomite is probably not a stable phase, very extensive solid solution toward CaZn(CO₃)₂ is to be expected in the system CaCO₃-MgCO₃-ZnCO₃. The tendency for transition metal dolomites to contain excess CaCO₃ can also be accounted for in terms of octahedral distortion and AG^o_f.     

On the influence of urbanization on the water budget in Nairobi city: A numerical study

The impact of the growth and development of the City of Nairobi on the water budget is simulated using a high-resolution limited-area numerical model. The water substance fields are modelled with full physics in a control experiment. Five sensitivity experiments are then performed by altering the land-use/cover over the domain of study to assess the influence of the city, forests and terrain undulations on the water substance fields. Results showed that the highest evaporation occurred in areas of the study domain with open grasslands/scattered bush-land's vegetation types and the least at the city centre. Deforestation would lead to a substantial increase in the loss of water effected through evaporation despite a reduction in transpiration. The observed rainfall amount and frequency were highest in the high ground portions to the northwest of the study domain. Numerical analyses showed that the urban heat island had a destabilizing effect on the flow, which enhanced convection that resulted in increased rainfall downwind of the urban area. Further growth and expansion of the city of Nairobi would increase the area and amount of rainfall received. Deforestation would decrease rainfall amounts. Massive reforestation would increase the observed rainfall. There has been a decrease in soil moisture at the current location of the city centre; the decrease is bound to increase with the expansion of the city. The City of Nairobi has resulted in a large decrease in the soil moisture through converting the natural fabric to concrete/asphalt material. Deforestation would result in a marginal decrease in the soil moisture. Further growth and development of Nairobi City would modify the water substance budget appreciably. This revised version was published online in July 2006 with corrections to the Cover Date.     

Rock mass characterization using photoanalysis

Summary Rock formations are distinguished from each other by measuring first the properties of the intact rock, and second those of the jointing. Whereas simple methods are available for measuring intact rock properties, those available for measuring jointing remain slow, expensive, and sometimes dangerous. Digitized photographs (photoanalysis) may provide a solution. In this paper, the new techniques of photoanalysis are reviewed together with applications, promising areas for research, and also some obstacles that remain to be overcome. Aspects of the rock mass that lend themselves to photoanalytical measurement include those of individual joints, such as persistence, orientation and roughness, and those relating to the mass as a whole, such as block size and the spacing or intensity of jointing. Photoanalysis can also be applied to measurement of blasting. It allows characterization of the rock about to be blasted, helping the engineer to predict fragmentation and to design an appropriate blasting pattern. Afterwards, the same methods can be used to measure fragmentation, overbreak and backbreak, for quality control and for diagnosis of problems.Presented at the 28th US ROck Mechanics Symposium, Tucson, Arizon, 29 June–1 July 1987.     

Pedogenetic and diagenetic fabrics in the Upper Proterozoic Sarnyëré formation (Gourma, Mali)

Several diagenetic fabrics are described in the uppermost member of the Sarnyéré formation, an Upper Proterozoic dolomite (700-600 Ma). Micronodular micrite, microsparite showing nodulisation processes, orbicular crusts and oncoids are thought to be due to the pedogenetic alteration of an algal (Porostromata) boundstone. Further evolution in a vadose zone creates a network of cavities which are later filled by “cave stromatolites”, micropopcorn micrite and multilayered cements. A rhythmical repetition of facies evidences a polyphased pedogenetic history, leading to a 30 m thick highly complex section. Such numerous and diversified structures are rarely preserved, especially in Proterozoic rocks, but each of them have equivalents in recent examples of caliche soil profiles.