Soil Fatigue Due To Cyclically Loaded Foundations

Cyclic loading on civil structures can lead to a reduction of strength of the used materials. A literature study showed that, in contrast to steel structures and material engineering, there are no design codes or standards for fatigue of foundations and the surrounding ground masses in terms of shear strength reduction. Scientific efforts to study the fatigue behaviour of geomaterials are mainly focused on strain accumulation, while the reduction of shear strength of geomaterials has not been fully investigated. It has to be mentioned that a number of laboratory investigation have been done and some models have been already proposed for strain accumulation and pore pressure increase which can lead to liquefaction. Laboratory triaxial tests have been performed in order to evaluate the fatigue of soils and rocks by comparing the shear strength parameters obtained in cyclic triaxial tests with the static one. Correlations of fatigue with both, the number of cycles and cyclic stress ratio have been given. In order to apply cyclic movements in a triaxial apparatus, a machine setup and configuration was made. A special program was written in LabVIEW to control the applied stresses and the speed of loading, which allowed simulating the natural loading frequencies. Matlab scripts were also written to reduce the time required for the data processing. Both cohesive and cohesionless geomaterials were tested: artificial gypsum and mortar as cohesive geomaterials, and sedimentary limestone, and different sands, as cohesionless and low-cohesive natural materials. The artificial gypsum, mortar and natural limestone exhibit mostly brittle behaviour, where the crumbled limestone and other sand typical ductile one. All the sands as well as the crumbled limestone were slightly densified before testing therefore; they can be treated as dense sands. The UCS for the crumbled limestone is 0.17 MPa and standard error of estimate σest = 0.021 MPa, where for mortar UCS = 9.11 MPa with σest = 0.18 MPa and for gypsum UCS = 6.02 MPa with standard deviation = 0.53. All triaxial tests were conducted on dry samples in the natural state, without presence of water (no pore pressure). The range of the confining pressure was between 0 MPa and 0.5 MPa. The cyclic tests carried out were typical multiple loading tests with constant displacement ratio up to a certain stress level. The frequency was kept low to allow for precise application of cyclic load and accurate readings. What is more, the frequency of the cyclic loading corresponds to the natural loading of waves and winds. The number of applied cycles was from few cycles up to few hundred thousand (max number of applied cycles was 370 000). Due to the complex behaviour of materials and high scatter of the results, many tests were required. Two different strategies were used to investigate fatigue of geomaterials: 1) the remaining shear strength curve; after a given number of cycles, a final single load test was done until failure in order to measure the remaining shear strength of the sample. 2) the typical S-N curve (Wöhler curves); there is simply a constant loading until failure. The remaining shear strength (or strength reduction) curve has been compared with the standard S-N curve, and is found to be very similar because the cyclic stress ratio has little influence. The cyclic loading on geomaterials, being an assemblage of different sizes and shapes of grains with voids etc., showed different types of effects. Cohesionless materials show a shear strength increase during the cyclic loading, while cohesive ones show a shear strength decrease. For the cohesive materials the assumption was made that the friction angle remains constant; so, the fatigue of geomaterials can be seen as a reduction of the cohesion. In this way, the fatigue of a cohesive geomaterial can be described by a remaining cohesion. The imperfections in the artificial gypsum have a significant impact on the results of the (especially cyclic) strength tests. Therefore another man made materials was used – a mixture of sand and cement (mortar). As the first static test results were very promising, mortar was used in further tests. The cyclic tests, however, presented similar, high scatter of results as for artificial gypsum. An unexpected observation for both materials was a lack of dependency of the remaining shear strength on the cyclic stress ratio. The strain-stress relationship in cyclic loading shows that the fatigue life of the geomaterials can be divided into three stages, just as for creep. The last phase with a fast increase in plastic strains could be an indicator of an incoming failure. The accumulation of strains and increase of internal energy could be good indicators too, but no strong correlation, has been found. Similar to the shear strength, the stiffness changes during cyclic loading; for cohesive materials the stiffness increase, while for cohesionless it decreases. This could help to predict the remaining shear strength of a geomaterial by using a non-destructive method

Shear strength and stiffness degradation of geomaterials in cyclic loading

Cyclic loading on civil structures can lead to a reduction of strength and stiffness in the loaded materials. The life span of many cyclically loaded structures such as wind turbines, high-speed train tracks and bridges strongly depends on the foundation. The soils and rocks in the foundation can be subjected to cyclic loads from natural and human sources. In order to evaluate the fatigue behaviour of geomaterials, this paper presents static and cyclic triaxial test results for several geomaterials. It was concluded that cyclic loading on different geomaterials can cause different types of effects. The shear strength of cohesionless crumbled limestone increases during cyclic loading; while for cohesive materials, such as gypsum and mortar, the strength decreases. The strength decrease can be seen as a degradation of the cohesion. The most significant factor in the cohesion reduction was found to be the number of applied cycles. It was also noticed that the friction angle for sands does not reduce under cyclic loading. A fatigue limit was not found for cohesive geomaterials; neither a dependence of the strength reduction on the cyclic loading ratios

Fatigue of rocks

Cyclic loading on civil structures can lead to a reduction of strength of the used materials. For the materials concrete and especially steel, there are clear design codes about how to account for the reduction of the material shear strength due to this cyclic loading, which is called fatigue. For the material rock, however, there are no design codes or standards for fatigue, in terms of shear strength reduction. For this reason, a large number of laboratory triaxial tests have been performed, in order to evaluate the fatigue of rocks by comparing the shear strength parameters obtained in cyclic triaxial tests with the static shear strength. Tests have been performed on artificial gypsum, a mixture of sand and cement (mortar) and soft sedimentary limestone. Correlations of the fatigue, for both the number of cycles and the cyclic stress ratio, have been obtained. All triaxial tests were conducted on dry samples (no pore pressure) in the natural state. The range of the confining pressure was between 0 MPa and 0.5 MPa. The frequency was kept low to allow for a precise application of the cyclic load and also accurate readings. The number of applied cycles was from a few cycles up to a few hundred thousand. The imperfections in the artificial gypsum have a significant impact on the results of the (especially cyclic) strength tests. Therefore another man made material was used – a mixture of sand and cement (mortar). As the first static test results were very promising, mortar was used in further tests. The cyclic tests, however, presented a similar, high scatter of results as for artificial gypsum. Due to the complex behaviour of the cohesive materials and high scatter of the results, many tests were required. Two different strategies were used to investigate the fatigue of the cohesive geomaterials: 1. the remaining shear strength curve: after a given number of cycles, a final single load test until failure, measures the remaining shear strength of the sample. 2. the typical S-N curve (Wöhler curves): one counts the number of constant loading cycles until failure. The fatigue of rocks can be seen as a reduction of the cohesion. In this way, the fatigue of a cohesive geomaterial can be described by (a reduction of) the remaining cohesion. An unexpected observation for both artificial gypsum and mortar was that unlike the number of cycles, the size of the cyclic stress ratio has little influence on the remaining shear strength, and therefore on fatigue. The remaining shear strength (or strength reduction) curve has been compared with the standard S-N curve, and is found to be rather similar for both artificial gypsum and mortar. The reason for this is this unexpected observation. Because of this, the S-N curve and the remaining shear strength curve should be theoretically identical. The results of the triaxial tests show however that, the S-N curve gives a bit steeper slope than the remaining shear strength curve, which would imply a shorter life and a faster reduction in comparison to the remaining shear strength curve, but this is only because, the prematurely failed samples are not included in the remaining shear strength curve, while a significant number of the S-N samples are prematurely failed samples from the remaining shear strength tests

Triaxial tests on Maastricht marlstone

De civiele werken van de A2-tunnel in Maastricht zijn onlangs voltooid. Tijdens de bouw werd de Limburgse mergel in de bouwput als een stijve, stevige grondlaag beoordeeld, terwijl het na het verwijderen als een cohesieloos zand werd aangezien. Om het sterktegedrag van deze mergel beter te begrijpen is door de Universiteit van Luxemburg aanvullend onderzoek gedaan. Uit triaxiaalproeven blijkt verrassenderwijze dat de sterkteparameters van verkruimelde mergel weinig afwijken van intacte mergel. De toplaag van de mergel heeft een zeer kleine cohesie en een grote hoek van inwendige wrijving. Alhoewel hierdoor de mergel onder druk zeer sterk is, is de mergel vrijwel niet in staat om trek op te nemen

Laboratory tests on Dutch limestone (Mergel)

In this note, results of triaxial laboratory tests on very weak sedimentary limestone from the construction of the “Geusselt A2” tunnel in Maastricht in the Netherlands are presented. The main purpose of the triaxial tests was to evaluate the strength of this rock. Particularly interesting was that the strength parameters obtained in the laboratory, were much lower than what was expected after preliminary visual inspections. The two most popular models in soil and rock mechanics, the Mohr-Coulomb and Hoek-Brown failure criteria, were used to estimate the strength parameters and both did not give satisfying results. Still the Mohr-Coulomb model is the best model to use

The Impact of Various Culture Conditions on Human Mesenchymal Stromal Cells Metabolism

In vitro and in vivo analyses are closely connected, and the reciprocal relationship between the two comprises a key assumption with concern to the conducting of meaningful research. The primary purpose of in vitro analysis is to provide a solid background for in vivo and clinical study purposes. The fields of cell therapy, tissue engineering, and regenerative medicine depend upon the high quality and appropriate degree of the expansion of mesenchymal stromal cells (MSCs) under low-risk and well-defined conditions. Hence, it is necessary to determine suitable alternatives to fetal bovine serum (FBS—the laboratory gold standard) that comply with all the relevant clinical requirements and that provide the appropriate quantity of high-quality cells while preserving the required properties. Human serum (autologous and allogeneic) and blood platelet lysates and releasates are currently considered to offer promising and relatively well-accessible MSC cultivation alternatives. Our study compared the effect of heat-inactivated FBS on MSC metabolism as compared to its native form (both are used as the standard in laboratory practice) and to potential alternatives with concern to clinical application—human serum (allogeneic and autologous) or platelet releasate (PR-SRGF). The influence of the origin of the serum (fetal versus adult) was also determined. The results revealed the key impact of the heat inactivation of FBS on MSCs and the effectiveness of human sera and platelet releasates with respect to MSC behaviour (metabolic activity, proliferation, morphology, and cytokine production)

Blasthole performance by means of explosive techniques using PG-7M shaped charged warhead

Głównym sposobem urabiania skał w górnictwie podziemnym i odkrywkowym jest wykorzystanie materiałów wybuchowych. Najbardziej optymalnym sposobem urobienia skały jest w tym przypadku wprowadzenie ładunku do otworu strzałowego. Proces wiercenia otworów w porównaniu do załadunku i detonacji materiału wybuchowego jest najbardziej czasochłonną operacją. Dodatkowo względy techniczne mogą utrudniać lub uniemożliwiać wykonanie otworów strzałowych. Głowice kumulacyjne są głównie stosowane do celów wojskowych, jednak wykorzystuje się je również w górnictwie naftowym i gazowym. Wyeliminowanie procesu wiercenia poprzez zastosowanie ładunków kumulacyjnych może znacząco wpływać na zwiększenie postępów drążenia. Niniejsza praca ma na celu określenie możliwości wykonywania otworów strzałowych, wykorzystując głowicę kumulacyjnego pocisku przeciwpancernego PG-7M do granatnika RPG-7. Wyniki przeprowadzonych badań będą służyły do opracowania, wykonania i wprowadzenia do górnictwa nowego typu ładunków kumulacyjnych, które w przyszłości umożliwią zwiększenie efektywności górnictwa przy utrzymaniu lub obniżeniu kosztów.The use of explosives constitutes the primary method of rock extraction in underground and surface mining. The most optimal method of rock extraction in this case is the insertion of a charge into a blasthole. Compared to the loading and detonation of explosives, the blasthole drilling process is the most time-consuming operation. Additionally, technical factors may render the drilling of blastholes difficult or impossible. Shaped charges are primarily used for military purposes, but they also find application in oil and gas mining. Elimination of the drilling process based on the application of shaped charges could significantly increase the progress of tunnelling. The purpose of this article is to determine the possibility to produce blastholes through the application of the warheads PG-7M anti-tank projectiles used in RPG-7 rocket-propelled grenade launchers. The results of the conducted tests will serve to develop, produce and implement a new type of shaped charge for mining purposes, which in the future will increase the efficiency of mining while retaining or lowering its costs

Whether they return:Modeling outdoor recreation behaviors, decision-making, and intention-to-return in congressionally designated wilderness

Visitation to parks and protected areas (PPAs) has become increasingly widespread in the United States. This increased visitation is especially concerning within congressionally designated wilderness areas where federal agencies are tasked with the dual mandate of preserving wilderness character while simultaneously providing high-quality outdoor recreation experiences. This study investigated the influence of social, situational, and ecological factors on outdoor recreation visitor behaviors and decision making within the Lye Brook Congressionally Designated Wilderness (LBW) area in Vermont, USA. An on-site intercept survey (n = 576) was employed to collect data from LBW visitors in the summer of 2021. Descriptive and multi-variate statistics (e.g., binary logistic regression, structural equation modeling) indicated that visitor behaviors (e.g., coping, substitution) and decision-making (e.g., intention-to-return) were significantly influenced by social (e.g., conflict), situational (e.g., litter, access), and ecological (e.g., trail conditions, weather) impacts. Moreover, the presence of various weather conditions was found to significantly influence the severity of perceived social, situational, and ecological impacts. Study results indicated that outdoor recreation experiences are multifaceted, necessitating a suite of social, situational, and ecological considerations, especially when examining the relationship between visitor coping behaviors and intention-to-return. This research advances the coping framework, provides empirical support for future examination of social–ecological system (SES) theory, and emphasizes the utility of employing an adaptive systems approach for sustainable PPA management