Porous Limestone Research Articles

Influence of self-healing induced by polylactic-acid and alkanoates-derivates precursors on transport properties and chloride penetration resistance of sound and cracked mortar specimens

The possible beneficial impact of self-healing on chloride transport through cracks has been assessed for two bacteria-based self-healing mortar mixtures in comparison with Ordinary Portland cement mortar. Intact self-healing specimens featured lower chloride transport coefficients thanks to a denser microstructure and to the formation of a layer of calcium carbonate on their surface. However, self-healing of cracks of cracked mortar specimens did not significantly reduce chloride penetration during 28 days of chloride exposure compared to cracked and non-healed specimens. On the other hand, this study demonstrated that self-healing of 150–200 µm wide cracks reduced chloride ingress during shorter term (14 days) chloride exposure in comparison to cracked but non-healed specimens. The results of this study suggest that self-healing of cracks through calcium carbonate formation results in water blockage (sealing) of cracks but that the limited amount of limestone formed creates an imperfect barrier against diffusion of chloride ions through the apparent porous limestone. The short-term positive effect of self-healing with respect to reduced chloride ingress could be beneficial in applications where chloride exposure is limited or non-permanent such as concrete structures irregularly exposed to deicing salts or located in the splash zone in marine environments.

Comparison of Petrophysical Properties of Porous Rocks Using NMR, Micro-CT, and Fluid Flow Simulations

Micro-computed tomography (micro-CT) is increasingly utilized to image the pore network and to derive petrophysical properties in combination with modelling software. The effect of micro-CT image resolution and size on the accuracy of the derived petrophysical properties is addressed in this study using a relatively homogenous sandstone and a heterogenous, highly porous bioclastic limestone. Standard laboratory procedures including NMR (nuclear magnetic resonance) analysis, micro-CT analysis at different image resolutions and sizes and pore-scale flow simulations were used to determine and compare petrophysical properties. NMR-derived pore-size distribution (PSD) was comparable to the micro-CT-derived PSD at a resolution of 7 µm for both the rock types. Porosity was higher using the water saturation method as compared to the NMR method in both rocks. The resolution did not show a significant effect on the porosity of the homogeneous sandstone, but porosity in the heterogeneous limestone varies depending on the location of the sub-sample. The transport regime in the sandstone was derived by simulations and changed with the resolution of the micro-CT image. The transport regime in the sandstone was advection-dominated at higher image resolution and diffusion-dominated when using a lower image resolution. In contrast, advection was the dominant transport regime for the limestone based on simulations using higher and lower image resolutions. Simulation-derived permeability for a 400 Voxel3 image at 7 µm resolution in the Berea sandstone matched laboratory results, although local heterogeneity within the rock plays an integral role in the permeability estimation within the sub-sampled images. The simulation-derived permeability was highly variable in the Mount Gambier limestone depending on the image size and resolution with the closest value to a laboratory result simulated with an image resolution of 2.5 µm and a size of 300 Voxel3. Overall, the study demonstrates the need to decide on micro-CT parameters depending on the type of petrophysical property of interest and the degree of heterogeneity within the rock types.

Reservoir characterization of the upper Turonian – lower Coniacian Khasib formation, South Iraq: Implications from electrofacies analysis and a sequence stratigraphic framework

The Upper Turonian – Lower Coniacian Khasib Formation is a significant hydrocarbon reservoir in southern Iraq. The present study integrates multiple data sets of 33 wireline wells, available core, and thin sections from two important oilfields: Amara and Noor to interpret the lateral and vertical facies changes and petrophysical reservoir variability within a sequence stratigraphic framework. Cluster analysis based on well log data including gamma ray, sonic, neutron, bulk density data were used to classify the Khasib Formation into five carbonate electrofacies and determine the petrophysical properties. These electrofacies consists of compacted marly, argillaceous, chalky, porous, and vuggy limestones which are interpreted to have been deposited in a ramp setting. Sequence stratigraphic analysis shows that the Khasib Formation consists of two third-order sequences with three sequence boundaries refer to global sea-level changes: the Mishrif-Khasib regional unconformity, the intra-Khasib unconformity, and the Khasib-Tanuma formational boundary. Each sequence consists of a transgressive system tract (TST) and a highstand systems tract (HST) which are separated by a maximum flooding surface (MFS). Reservoir correlation and mapping of the Khasib Formation in both the Amara and the Noor oilfields show the best important oil-bearing zones are located dominantly in transgressive system tracts (TSTs).

Correlation between various mechanical properties of porous limestones from Hungary

This study focuses on the mechanical parameters of Miocene limestones from Hungary. Four different lithotypes of porous limestone from two localities were analysed in laboratory conditions. These lithologies have been widely used for centuries as construction material in Central Europe. One type of the Badenian Leithakalk limestone, which is a bioclastic grainstone containing molluscs, foraminifera and Lithothamnium and three types of Sarmatian porous limestone; a fine-grained, medium-grained and a coarse-grained bioclastic lithotype were compared in laboratory conditions. Bulk density, water absorption, apparent porosity, uniaxial compressive and tensile strength tests were performed to obtain data set for correlation analysis. With water saturation under atmospheric pressure, the uniaxial compressive strength and tensile strength of all studied lithotypes were reduced significantly. A good correlation between dry bulk density and apparent porosity was found for two lithotypes; meanwhile, for the two other lithotypes a less significant relationship was found. Bulk density correlates with uniaxial compressive strength and with tensile strength for all lithologies. However, a significant difference was found in the coefficients of determination of the different lithotypes. The coefficients in air-dry conditions were over 70%, but they became smaller after water saturation. According to these results, microstructure, porosity, and water saturation influence porous limestones’ damage mechanism.

3D Geological Model Creates Potential for Increased Production in Libyan Field

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 201417, “Reservoir Characterization and Geostatistical Model of the Cretaceous and Cambrian-Ordovician Reservoir Intervals, Meghil Field, Sirte Basin, Libya,” by Mohamed Masoud, Sirte Oil Company; W. Scott Meddaugh, SPE, Midwestern State University; and Masud Eljaroshi Masud, Sirte Oil Company, prepared for the 2020 SPE Annual Technical Conference and Exhibition, originally scheduled to be held in Denver, Colorado, 5–7 October. The paper has not been peer reviewed. The study outlined in the complete paper focuses on developing models of the Upper Cretaceous Waha carbonate and Bahi sandstone reservoirs and the Cambrian-Ordovician Gargaf sandstone reservoir in the Meghil field, Sirte Basin, Libya. The objective of this study is to develop a representative geostatistically based 3D model that preserves geological elements and eliminates uncertainty of reservoir properties and volumetric estimates. This study demonstrates the potential for significant additional hydrocarbon production from the Meghil field and the effect of heterogeneity on well placement and spacing. Introduction The reservoir of interest consists of three stratigraphic layers of different ages: the Waha and Bahi Formations and the Gargaf Group intersecting the Meghil field. The Waha reservoir is a porous limestone that forms a single reservoir with underlying Upper Cretaceous Bahi sandstone and Cambro-Ordovician Gargaf Group quartzitic sandstone. The Waha provides excel-lent reservoir characteristics. The Bahi has fair to good reservoir characteristics, while the Gargaf Group has very poor reservoir quality. The Waha and Bahi contain significant amounts of hydrocarbons. The Bahi is composed of erratically distributed detritus from the eroded Gargaf Group. The characteristic of the Gargaf sediments is quartzitic sandstones indurate to a quartzite with low reservoir quality.

Construction works above cavities, investigation of an undermined area

Construction work above previous mining area is always a great challenge from the engineering point of view. In the southern part of Budapest, the previous mining activities resulted more than a hundred thousands of square meters of cavities. These cellars cut into porous limestone with different depth, but mostly close to the surface; nowadays, these cellars are located inside a residential area, and some part of the undermined area is planned to build because this is an empty and valuable area. For the construction of these improvements, it is necessary to perform detailed investigations and stability calculations. This paper is introducing the detailed investigation process of a significant cellar which will be involved by construction activities. Three buildings are planned to build above it. The studied cellar located in the 22nd district of Budapest, Hungary, with a depth between 4.3 – 7.7 m, with a wide range of pillars’ width between 0.73 – 7.7 m according to the studied cross-sections. The investigation starts with geometrical measurements and core drillings to map the rock mechanical properties of the host rock. Several laboratory tests were done for obtaining rock mechanical parameters for modelling. After creating the geotechnical model, it was used for FEM calculations using RS2 software. Four cross-sections were chosen across the cellar system in different locations and various directions modelling the surface load of the planned building. The stability of the cellar was studied from two different viewpoints: firstly, the factor of safety was determined, and secondly, the settlement was calculated as an effect of the surface load. A displacement measurement system was set up in several cross-sections of the cellar to compare the calculated and real displacements in the future.

Salt weathering and ultrasonic pulse velocity: condition assessment of salt damaged porous limestone

Salt weathering is one of the crucial causes of building stone decay. For assessing the durability of stones against salt weathering, a standardised test procedure (EN 12370:2020 Determination of resistance to salt crystallisation) is used: the mass loss of the stone is measured during sodium sulphate crystallisation cycles. Porous, Miocene limestone test specimens collected from the Sóskút quarry (Hungary) were subjected to salt crystallisation cycles in laboratory conditions. The limestone with open porosities of up to 32 V% is composed of ooids, various types of bioclasts and other carbonate grains. Besides the classical measurements of mass changes, the ultrasonic pulse velocity was also recorded after each crystallisation cycle. The ultrasonic pulse velocity values of quarry stones and salt-laden porous limestone specimens were compared. The results indicate that when salt crystal clogs the pores, an increase in ultrasonic pulse velocity is observed. Additional salt crystallisation cycles reduce the pulse velocity. This negative shift in pulse velocities is linked to the opening of micro-cracks, indicating the damage of the studied limestone. Our tests have proved that ultrasonic pulse velocity testing device can detect salt crystallisation damage in a non-destructive way. Its application is recommended in the condition assessment of salt damaged stone heritage structures.

Freeze–Thaw and Salt Crystallization Durability of Silica Acid Ester Consolidated Porous Limestone from Hungary

The durability of consolidated highly porous limestones was tested after salt and freeze–thaw cycles. Three porous limestone lithotypes that were commonly used in construction in the Central-European region during previous centuries were selected for the tests. Specimens of Miocene limestone were consolidated with four different types of ethyl silica-based consolidants (KSE 100, KSE 300, KSE 300 E, KSE 300 HV). After consolidation, the samples were exposed to freeze thaw cycles and salt crystallization tests. Water saturation under atmospherically pressure, capillary water absorption and splitting tensile strength were measured on treated and untreated samples to assess change attributed to consolidation in the open porosity and mechanical parameters. The increase in the tensile strength of the medium-grained samples was higher than that of the consolidated fine-grained lithotypes. The effect of consolidation treatment was very different in terms of pore-size distribution as obtained by Mercury intrusion porosimetry (MIP). Untreated and consolidated samples were subjected to 10 cycles of sodium sulphate crystallization (EN 12370) and 10 freeze–thaw cycles (EN 12371) tests. Experiments concluded that in addition to the initial strength increase after the conservation, the modified pore structure is the crucial factor to evaluate the long-term efficiency of stone conservation.

Stress sensitivity of porosity and permeability under varying hydrostatic stress conditions for different carbonate rock types of the geothermal Malm reservoir in Southern Germany

In geothermal reservoir systems, changes in pore pressure due to production (depletion), injection or temperature changes result in a displacement of the effective stresses acting on the rock matrix of the aquifer. To compensate for these intrinsic stress changes, the rock matrix is subjected to poroelastic deformation through changes in rock and pore volume. This in turn may induce changes in the effective pore network and thus in the hydraulic properties of the aquifer. Therefore, for the conception of precise reservoir models and for long-term simulations, stress sensitivity of porosity and permeability is required for parametrization. Stress sensitivity was measured in hydrostatic compression tests on 14 samples of rock cores stemming from two boreholes of the Upper Jurassic Malm aquifer of the Bavarian Molasse Basin. To account for the heterogeneity of this carbonate sequence, typical rock and facies types representing the productive zones within the thermal reservoir were used. Prior to hydrostatic investigations, the hydraulic (effective porosity, permeability) and geomechanical (rock strength, dynamic, and static moduli) parameters as well as the microstructure (pore and pore throat size) of each rock sample were studied for thorough sample characterization. Subsequently, the samples were tested in a triaxial test setup with effective stresses of up to 28 MPa (hydrostatic) to simulate in-situ stress conditions for depths up to 2000 m. It was shown that stress sensitivity of the porosity was comparably low, resulting in a relative reduction of 0.7–2.1% at maximum effective stress. In contrast, relative permeability losses were observed in the range of 17.3–56.7% compared to the initial permeability at low effective stresses. Stress sensitivity coefficients for porosity and permeability were derived for characterization of each sample and the different rock types. For the stress sensitivity of porosity, a negative correlation with rock strength and a positive correlation with initial porosity was observed. The stress sensitivity of permeability is probably controlled by more complex processes than that of porosity, where the latter is mainly controlled by the compressibility of the pore space. It may depend more on the compaction of precedented flow paths and the geometry of pores and pore throats controlling the connectivity within the rock matrix. In general, limestone samples showed a higher stress sensitivity than dolomitic limestone or dolostones, because dolomitization of the rock matrix may lead to an increasing stiffness of the rock. Furthermore, the stress sensitivity is related to the history of burial diagenesis, during which changes in the pore network (dissolution, precipitation, and replacement of minerals and cements) as well as compaction and microcrack formation may occur. This study, in addition to improving the quality of input parameters for hydraulic–mechanical modeling, shows that hydraulic properties in flow zones largely characterized by less stiff, porous limestones can deteriorate significantly with increasing effective stress.

Evolution of calcite surfaces upon thermal decomposition, characterized by electrokinetics, in-situ XRD, and SEM

The present study analyses transformation pathways of pristine and thermally treated porous limestone and dense marble surfaces by means of time-resolved streaming current and potential measurements coupled with scanning electron microscopy and in-situ X-ray diffraction. The results reveal that under nonequilibrium conditions the zeta potential (ζ) of natural carbonates may exhibit positive and negative signs and ζ drifts in opposite directions. Sample surface roughness influences ζ because it contributes to dissolution, as observed particularly in the initial period of time-resolved measurements. Thermal treatment causes a temporary charge reversal from negative to positive. The reactivity of calcium hydroxide on calcite surfaces governs the net electrokinetic potential and isoelectric point (IEPpH), even at low surface coverage, as cross-validated by in-situ XRD. It was also found that pore conductivity may lead to ~90% underestimation of ζ when assessed by streaming potential. SEM studies revealed micro cracks inducement on marble after thermal treatment, which can result in underestimation of ζ up to the same extent as for the porous limestone. When an asymmetric cell configuration involving calcite and polypropylene surfaces is used, the fractional contribution of polypropylene to the IEPpH is 0.3 and to the overall determined ζ up to 0.5. Our findings contribute to the understanding of nonequilibrium and time-dependent electrokinetic potential modifications associated with the reactivity of porous surfaces. This study highlights the effectiveness of the streaming potential technique for monitoring such changes further supported by the use of ancillary techniques to analyze the extend of chemo-mineralogical and physical alterations.

The Brittle‐Ductile Transition in Porous Limestone: Failure Mode, Constitutive Modeling of Inelastic Deformation and Strain Localization

AbstractUnderstanding of the mechanics of the brittle‐ductile transition (BDT) in porous limestone is significantly more challenging than for sandstone because of the lack of consistent acoustic emission activity in limestone, meaning that one must rely on alternative techniques. In this paper, we investigate systematically the failure modes in Indiana limestone using X‐ray microComputed Tomography imaging (μCT) and Digital Volume Correlation (DVC). Our new mechanical data show that the envelope for the onset of shear‐enhanced compaction can be well approximated by an elliptical cap. The DVC analysis revealed the development of shear bands through the BDT, but no evidence of compaction bands. The shear band angles were between 29° and 46° with respect to the maximum principal stress. Compiling these new results with published data on Purbeck and Leitha limestones, we showed that inelastic compaction in each of these dual porosity allochemical limestones was in a good agreement with the normality condition, as defined in plasticity theory. Comparison of the observed failure modes with predictions based on bifurcation analysis showed that the shear band angles are consistently smaller than the theoretical predictions.

A contribution to understand the Portuguese emblematic Ançã limestone bioreceptivity to fungal colonization and biodeterioration

• Portuguese Ançã limestone bioreceptivity to fungal colonization analysis. • Penicillia growth is favored in copiotrophic environments. • Aspergilli and Aeminium ludgeri growth is only slightly superior in oligotrophic environments. • After one-year incubation period all fungal species produced alterations. • Aspergillus westerdijkiae induced calcium carbonate mineralization. Fungal deteriorative action on historical stone objects often leads to important and incalculable cultural heritage losses. The Ançã stone is a unique limestone type widely used in some of the most important and emblematic Portuguese monuments. Being a soft and porous calcium carbonate limestone, this substrate is known to have a significant bioreceptivity to microbial colonization often resulting in notorious biodeterioration. Nonetheless, fungal bioreceptivity and biodeterioration of this lithotype remains scarcely characterized. With this in mind, the main aims of this work were to evaluate these aspects in a controlled laboratory environment. Inoculation of several fungal species in stone replicas revealed that Penicillia growth occupied larger areas under rich micro-nutrient environments, while Aspergilli and the black fungal species Aeminium ludgeri only denoted a slightly more accentuated growth under depleted nutrient conditions. Moreover, all species produced noticeable aesthetic alterations. In addition, we were able to verify A. ludgeri endolithic growth, Aspergillus glaucus putative hyphae penetration into calcite layers and mineralization phenomena occurring around A. westerdijkiae hyphae. By itself, this study provides a key update regarding fungal biodeterioration of this ancient, emblematic and remarkable limestone.

Analysis of physicochemical factors regulating transport behaviors of sulfonamide antibiotics in saturated porous media

Sulfonamide antibiotics (SAs) are commonly used antibiotic classes in livestock worldwide. SAs are discharged to the environment and then may accumulate in rivers and aquifers, thereby diminishing water quality and the overall health of the ecosystem. While the occurrence and distribution of SAs in water environments have been the subject of numerous investigations, the fate and transport of SAs in aquifers have been less understood. In the present work, four of the most used SAs, including sulfadiazine (SDZ), sulfathiazole (STZ), sulfamethazine (SM2), and sulfamethoxazole (SMX), were selected for laboratory experiments and modeling analysis. The experiments were conducted in saturated columns filled with two common porous media, quartz sands and limestone grains. Results showed that the SAs had mobility changing on the order (from high to low) of SMX > SM2 > SDZ > STZ in the column, with SMX being the least absorbed SA by quartz sand or limestone grains. Moreover, calcium ionsinhibited the transport of SAs more strongly than that of sodium ions, while the inhibitory effect was slightly enhanced with an increasing Na+ concentration from 0 to 10 mM. In contrast, the presence of humic acid facilitated the transport of SAs. Although the four SAs have similar molecular structures, their adsorption and transport characteristics were shown to be quite different. The dynamics of the adsorption and transport of SAs in groundwater can be effectively described by a two-site adsorption model coupled with advection and dispersion. This study sheds new light on the transport of SAs, contributing to a better understanding of how to control the presence and migration of antibiotics as new emerging contaminants in groundwater.

Experimental Study on an Innovative Biopolymeric Treatment Against Salt Deterioration of Materials in Cultural Heritage

Salt crystallization is one of the harshest deterioration mechanisms affecting heritage materials, causing impressive decay patterns and the loss of a high thickness of original materials. Although salt damage has been widely investigated in the literature from the theoretical and experimental points of view, the solutions to mitigate this problem are still extremely limited. In the present paper, a new biopolymeric treatment based on chitosan was tested on two kinds of porous limestones widely used in historic architecture, aiming at inhibiting the crystallization of sodium sulphate inside the stone and promoting the formation of salt efflorescence over the surface, rather than harmful subflorescence inside the pore network. The treatment was applied to the bare stone and also after an inorganic pre-treatment based on the formation of hydroxyapatite in the stone. Hydroxyapatite was recently proposed for the consolidation and protection of carbonate stones and here it is expected to provide an effective anchoring layer for the chitosan coating on the pores surface, and also to prevent the calcite washout from the stone and hence the removal of chitosan. The effect of hydroxyapatite alone was also tested, for comparison’s sake. Treated and untreated stone specimens were subjected to two different accelerated salt crystallization tests, one based on crystallization cycles (wetting-drying cycles) and the other one based on continuous capillary absorption of a saline solution (“wick effect”), evaluating the results in terms of weight loss, efflorescence formation, and changes in porosity and mechanical properties. The results showed that all the treatments are compatible with the stones, and the combined treatment (hydroxyapatite + chitosan) is extremely promising for the prevention of salt damage.

In Situ Investigation of Fluid‐Rock Interactions at Ångstrom Resolution

AbstractThe flow of aqueous phases through porous media shapes the world. It changes the courses of rivers, erodes mountainsides, dissolves historical monuments, builds caves, regulates the carbon cycle, and changes porosity in aquifers and hydrocarbon reservoirs. Despite the significance of this process both to natural phenomena and human endeavors, fundamental insight into the mechanisms that drive it at the Ångstrom scale is scarce. Here, we employ environmental transmission electron microscopy (ETEM) to visualize interactions between water and various types of porous media, including sandstone, limestone, and dolostone samples, at Ångstrom resolution in real time. Unlike other techniques presented in the literature, ETEM allows for direct visualization of both the aqueous phase and the porous media. As expected, dissolution and recrystallization were observed to significantly impact the shapes, sizes, and interconnectivities of the pores in the rocks. However, for the first time, we provide direct in situ experimental evidence that adsorption‐induced strain can also significantly impact the above‐mentioned parameters, especially in micropores. In some cases, adsorption was observed to reduce effective pore size by more than 60%. The magnitude of the change in pore size was found to vary with pore wall mineralogy and pore geometry. This work presents the first direct Ångstrom‐resolution observations of liquid adsorption films and adsorption‐induced strain.

Petrophysical rock typing (PRT) and evaluation of Cenomanian–Santonian lithostratigraphic units in southwest of Iran

Southern Iran is one of the most significant parts of the world in terms of economic aggregation of hydrocarbons. In this paper, reservoir quality of the Cenomanian–Santonian deposits has been evaluated in southwestern Iran. According to the reservoir qualification, five particular rock types have been classified based on log responses through K-nearest neighbors (KNN) method. 1–5 are representing poor, weak, moderate, superior and non-reservoir types of rock, respectively. Rock types 3 and 4 are determined as the best types which can play a suitable reservoir role in hydrocarbon accumulation. The mentioned groups generally consist of porous limestones with low level of clay content. Rock types number 1 and 2 indicate the low porosity tight limestones and rock type 5 belongs to clays and shaly layers with high gamma radiations. Lithology of these intervals is specified using Rhomaa–Umaa and NPHI–RHOB crossplots which displayed calcite mineral is the main mineral formed both formations. SEM analysis and Th–K crossplot confirmed that Illite, Montmorillonite and Kaolinite are major clay minerals settled in these intervals that may have impact on reservoir characteristics. Interparticle and micro-porosities are considered as dominant kinds of porosities based on velocity deviation log (VDL) and it is proved by SEM results. Rock types 3 and 4 have been considered as the most productive zones which can be the best target for future perforating operation. According to petrophysical evaluation results, Ilam (Santonian) reservoir quality is enhanced toward northeast and southwest (Maximum abundance of rock type 4) of the studied area in comparison to central part. The Sarvak (Cenomanian–Turonian) Formation is in the highest level of reservoir quality in the southwest of the studied area (abundance of rock types 4 and 3).

Impact of no-tillage on water purification and retention functions of soil

There are still uncertainties regarding the long-term impact of no-tillage farming practices on separate soil functions in the United Kingdom. This paper aimed to evaluate the chemical and physical processes in two different agricultural soils under no-tillage and conventional management practices to determine their impact on water related soil functions at field scale in the United Kingdom. The field-scale monitoring compares two neighboring farms with similar soil and topographic characteristics—one of the farms implemented no-tillage practices in 2013, while the second farm is under conventional soil management with moldboard plowing. Two soil types were evaluated under each farming practice: (1) a free-draining porous limestone, and (2) a lime-rich loamy soil with high silt and clay content. Field monitoring was undertaken over a two-year period and included nutrient analysis of surface and subsurface soil samples, bulk density, soil moisture, infiltration capacity, surface runoff, and analysis of phosphorus (P) and suspended solids in watercourses in close proximity to the test fields. The conversion to no-tillage changed the soil structure, leading to a higher bulk density and soil organic matter content and thereby increasing the soil moisture levels. These changes impacted the denitrification rates, reducing the soil nitrate (NO₃) levels. The increased plant material cover under no-tillage increased the levels of soil phosphate (PO₄^3–) and PO₄^3– leaching. The extent to which soil functions were altered by farming practice was influenced by the soil type, with the free-draining porous limestone providing greater benefits under no-tillage in this study. The importance of including soils of different characteristics, texture, and mineralogy in the assessment and monitoring of farming practice is emphasized, and additionally the between field and in-field spatial variability (both across the field and with depth) highlighted the importance of a robust sampling strategy that encompasses a large enough sample to effectively reveal the impact of the farming practice.

Weathering Processes and Mechanisms Caused by Capillary Waters and Pigeon Droppings on Porous Limestones

This investigation studies the physical and chemical effect of salt weathering on biocalcarenites and biocalcrudites in the Basilica of Our Lady of Succour (Aspe, Spain). Weathering patterns are the result of salty rising capillary water and water lixiviated from pigeon droppings. Surface modifications and features induced by material loss are observable in the monument. Formation of gypsum, hexahydrite, halite, aphthitalite and arcanite is associated with rising capillary water, and niter, hydroxyapatite, brushite, struvite, weddellite, oxammite and halite with pigeon droppings. Humberstonite is related to the interaction of both types of waters. Analysis of crystal shapes reveals different saturation degree conditions. Single salts show non-equilibrium shapes, implying higher crystallisation pressures. Single salts have undergone dissolution and/or dehydration processes enhancing the deterioration process, particularly in the presence of magnesium sulphate. Double salts (humberstonite) have crystals corresponding to near-equilibrium form, implying lower crystallisation pressures. This geochemical study suggests salts precipitate via incongruent reactions rather than congruent precipitation, where hexahydrite is the precursor and limiting reactant of humberstonite. Chemical dissolution of limestone is driven mainly by the presence of acidic water lixiviated from pigeon droppings and is a critical weathering process affecting the most valuable architectural elements present in the façades.

Post-peak behaviour of rocks under cyclic loading using a double-criteria damage-controlled test method

Cyclic loading–induced hazards are severe instability problems concerning surface and underground geotechnical projects. Therefore, it is crucial to understand the rock failure mechanism under cyclic loading. An innovative double-criteria damage-controlled testing method was proposed in this study to capture the complete stress–strain response of porous limestone, especially the post-peak behaviour, under systematic cyclic loading. The proposed test method was successful in applying the pre-peak cyclic loading and then in controlling the self-sustaining failure of rock during the post-peak cyclic loading. The results showed that the strength of the rock specimens slightly increased with an increase in the fatigue life in the pre-peak region due to cyclic loading–induced hardening. Additionally, a combination of class I and class II behaviours was observed in the post-peak region during the cyclic loading tests; the class II behaviour was more dominant by the increase in fatigue life in the pre-peak region. Damage evolution was assessed based on several parameters, such as the elastic modulus, energy dissipation ratio, damage variable and crack damage threshold stress, both in the pre-peak and post-peak regions. It was found that when the cyclic loading stress is not close to the peak strength, due to a coupled mechanism of dilatant microcracking and grain crushing and pore filling, quasi-elastic behaviour dominates the cyclic loading history, causing more elastic strain energy to accumulate in the specimens.

The Effect of the changing cover thickness on the stability of cellars

The stability of natural and man-made cavities is a very important topic nowadays especially if it is located under new construction areas. There are a lot of residential areas in Budapest and other cities of Europe such as Rome, Paris, and Cracow with stability problems because of cavities. For stability calculations, the geometry of the cavity, strength properties of the rock mass and joints are needed as input parameters, which can be obtained by field and laboratory tests. The FEM software is effective for stability calculations and with them; it is not so difficult to perform parametric analysis. This paper is focusing on the effect of the thickness of the cellar cover on their stability. The investigation site is in Budapest, Hungary, where there are several cellars cut into porous limestone. These cellars are more than 100 years old and nowadays cause difficulties for the building improvements. The geometrical parameters of the cellars and strength properties were measured. The cover of the studied cellar is around 6.0 m, but other cellars in the area have various cover thicknesses from 2.0 to 9.0 m. Therefore, the paper studied the effect of the cover on the stability to find the relation between the depth and the cellar stability. The modelling has been done by Rocscience software (RS2), using a real cross-section that crosses six branches of the cellar system.