A site located on the island of Brač is known in history for world-famous architectural stone and stone mining, dating all the way back to ancient Greek and Roman times. The most famous building constructed from the stone from Brač is the Diocletian Cesar Palace in the town Split. Prospective new locations for quarries are still required because the demand for the stone from the island is still high. This paper presents a review of undertaken geophysical investigations, as well as engineering geologic site prospection, with the purpose of determining if the rock mass quality is suitable for the mining of massive blocks needed for an architectural purpose—dimension stones. Several surface noninvasive geophysical methods were applied on the site, comprising of two seismic methods, multichannel analysis of surface waves (MASW) and shallow refraction seismic (SRS) electrical methods of electrical resistivity tomography (ERT), as well as electromagnetic exploration with ground penetrating radar (GPR). Results of geophysical investigations were compared to the engineering geologic prospection results, as well to the visible rock mass structure and observed discontinuities on the neighboring existing open mine quarry. Rock mass was classified into three categories according to its suitability for dimension stone exploitation. Each category is defined by compressional and shear seismic velocities as well as electrical resistivity. It has been found that even small changes in moisture content within the large monolithic rock mass can influence measured values of electrical resistivity. In the investigated area, dimension stone quarrying is advisable if the rock mass has values of resistivity higher than 3000 Ωm, as well as compressional seismic velocities higher than 3000 m/s and shear wave velocities higher than 1500 m/s. Georadar was found to be a good tool for the visual determination of fissured systems, and was used to confirm findings from other geophysical methods.
This paper was prepared based on in situ measurements carried out by the authors using the CPTu and DMT static penetration probes. The list of study sites includes seven specific locations in the northern parts of Croatia and one study site on the southern border of the country. The sites were selected based on the criterion of soil type, which falls into the category of soft to firm, slightly over-consolidated silty clays and silty sands. Intermediate soils are prevalent in the wider region, and most engineers deal with them in their everyday practice. For this reason, local characterization is of most importance for engineering purposes. In this investigation, results of in-situ tests are compared in order to validate the quality of the constrained modulus obtained from a CPT test to the one obtained by a DMT flat dilatometer. A comparison was made between the CPT test cone resistance and two DMT parameters—normalized modulus and horizontal stress index . Dependencies were analyzed for the main soil groups and intermediate data groups. Clay soils were divided into two subgroups based on the identification parameter , while silty soils were analyzed in three subgroups. The results for each subgroup differed significantly, and the analyses showed deviations from published values, especially for the intermediate soil groups. The usefulness of the application is demonstrated with examples at two sites, showing improvements over the most commonly used formula for the constrained modulus from the CPT test.
Design in accordance with Eurocode 7 applies the partial factors of geotechnical parameters to take into account uncertainties of various sources. The prescribed values of partial factors are unique, even though the degree of uncertainty can vary significantly. This can lead to an unequal reliability level of structures designed using the same procedures and methods. This paper analyses the influence of undrained shear strength variability on the reliability index (β), using reliability theory and statistical methods. Analyses were performed in the case of a shallow footing designed in accordance with Eurocode 7, design approach 3. It is shown that reliability indexes of a shallow footing could be lower than the target values prescribed in Eurocode. To meet these values, additional elaboration and calibration of undrained shear strength partial factor (γcu) was proposed.
Groundwater can be considered a non-polluting, renewable energy source. It can be used as a fluid in industrial, commercial, and residential building heating and airconditioning systems. Usually the water table is deep enough, so atmospheric conditions have a negligible influence on water temperature. Consequently, annual temperature variation is minor, and groundwater can therefore also be considered a reliable energy source. This paper presents some aspects of the groundwater heat pump (GWHP) wells design and addresses problems that can occur during their exploitation. The heat pump system consists of two types of wells: extraction wells and recharge wells. This paper shows that the distance between the two is a crucial parameter that affects the efficiency of the whole system. An example of wells design for a production hall groundwater heat pump is given. The wells are constructed is in the northern part of Croatia. Geological and hydrogeological conditions at the site, regarding water temperature and soil hydraulic conductivity, are highly favorable. Due to insufficient distance between wells thermal breakthrough occurred, i.e. water temperature in the extraction well rose, which resulted in a lower efficiency of the GWHP system.
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