Collapsible soils have considerable strength and stiffness in their dry natural state but settle dramatically when they become wet. This paper documents a low-cost, qualitative evaluation scheme using fuzzy set analysis to determine regional collapsibility based on subjective knowledge of the geological and geotechnical conditions and their uncertainty. The geological and geotechnical factors and their category were defined based on relevant literature. Each factor and category was then weighted or rated using linguistic terms developed from expert assessment. The linguistic data or information obtained from the assessments was represented and processed using fuzzy sets. To assess the criteria, 87 collapse potential tests were performed on undisturbed soil samples gathered from 27 different locations throughout Iran. It is shown that the geotechnical criteria predict soil collapsibility much better than the geological criteria.

Collapse, defined as the additional deformation of compacted soils when wetted, is believed to be responsible for damage to buildings resting on compacted fills, as well as failure in embankments and earth dams. In this paper, three different types of neural networks, namely, conventional Back-Propagation Neural Network (BPNN), Recurrent Neural Network (RNN) and Generalized Regression Neural Network (GRNN) are employed as computational tools to predict the amount of collapse and to investigate the influence of various parameters on the collapse potential. To arrive at this goal, 192 series of a single oedometer test were carried out on three soils with different initial conditions and inundated at different applied pressures. The test results were used to prepare the necessary database for training the neural network. Similar test results available in literature were also included in the database to arrive at a total of 330 sets of data. A comparison of the network prediction for collapse potential with some available models shows the superiority of the network in terms of the accuracy of prediction. Moreover, by analyzing the network connection weights, the relative importance of different parameters on collapse potential was assessed. Based on this analysis, for a given soil type, the initial dry unit weight, γd, is the most important factor influencing collapse potential.

Collapsible soils are one of the problematic soils, as they exhibit good stability in dry conditions but undergo sudden and significant settle-ments upon water entry. The surrounding layers of collapsible soil can be either permeable or impermeable, but the existing devices for determining the collapse potential lack the ability to model the drain-age conditions around the collapsible soil layer. In this study, an ap-paratus capable of modeling drainage conditions was constructed. A collapsible soil was made in laboratory, and its collapse potential was determined using single and double oedometer tests as well as the constructed apparatus. The results show that drainage conditions are an influential factor on the behavior of collapsible soils. The col-lapse potential obtained from this apparatus is lower than the col-lapse potential obtained from the oedometer test. The comparison of the two conditions with drainage and without drainage in two point and wide water distributions shows that in both water distributions, the collapse potential is higher in the condition with drainage than in the condition without drainage. For example, in the point distribution, the collapse potential with drainage is 27.7% higher than the without drainage, while in the wide distribution, it is 19.5%higher.

Abnormal load due to natural events, implementation error and some other issues can lead to the occurrence of progressive collapse in structures. In the research undertaken so far, most have involved 2-D models and are based on bare steel frames without consideration of the contribution of the floor systems, which reduces the accuracy of the model. Consideration of the effects of three dimensional and concrete floor slabs can play a crucial role in the progressive collapse response. For this purpose, in this research, a 3-dimensional finite element model of a five story steel building was simulated by Abaqus/CAE 6.11 software; First, with consideration of the slabs, and next, without their consideration. Then, the potential for progressive collapse was simulated. The results of the analysis indicate that the lack of consideration of the slabs during computation can lead to errors in assessing the potential for progressive failure of structures. The following results can be concluded from this study: when a structure is subjected to unusual external loads, such as a motor vehicle collision, explosion of a bomb in a vehicle, etc., the most critical columns are located in the nearest frame to the outer frame of the structure. So, engineers should focus more on resistant design against progressive collapse, as it could be a key factor that has a significant role in reducing the progressive collapse potential. In progressive collapse evaluation, when external columns are removed and the structure is damaged, the closest columns to the external frame are critical. Also, after removing the columns in different modes, the loads are split between the adjacent members; hence, these members must have sufficient ability to withstand the additional forces. Therefore, the distribution of forces in these members, before and after column removal, can be seen by monitoring the axial force values for adjacent members of the removed column. Because all the members are designed to withstand earthquake loads and non-interference of related loads (i.e., earthquake ground motion) with progressive collapse, even by removal of the main load bearing members, other columns still have enough capacity to carry the existing loads.

Collapsible soils are one of the moisture sensitive soils that experience sudden and significant settlements due to wetting. These soils are widely distributed and constitute about 10% of the total land area of the world, which are typically located in arid and semi-arid areas. In foundation engineering, the most important issue in dealing with these soils is to measure their collapse potential with different water infiltration patterns. The effect of parameters such as initial soil conditions, loading conditions and gradation quality on the behavior of these soils has been investigated. The amount of clay in the soil is considered as an important factor in the behavior of the collapsible soils. Water enters the soil from different sources, but the existing devices and tests to measure the collapse potential are not capable of modeling water infiltration patterns. In this study, an apparatus was used that simulates different water infiltration patterns based on the direction of water movement (from top or bottom) and type of water distribution (point or wide). The results show that in oedometer tests and tests with the ability to simulate the water infiltration patterns, with the increase in the amount of clay in the sample, the collapse potential increases, but the amount of increase is not the same in different tests. The amount of increase in collapse potential due to the increase of clay in the sample is greater in single and double oedometer tests than in tests with the ability to simulate the water infiltration patterns, and for a more accurate prediction of the collapse potential, tests with the ability to simulate the water infiltration patterns should be used. Among the different water infiltration patterns in the soil, for the sample with clay compared to the sample without clay, the highest increase in collapse potential is related to the top-point water infiltration pattern ) and the lowest increase is related to the bottom-wide water infiltration pattern( ). But for the sample with 23% clay compared to the sample without clay, the highest increase in collapse potential is related to the top-wide water infiltration pattern( ) and the lowest increase is related to the bottom-wide water infiltration pattern.

Collapse soils have a stable loose honeycomb-type structure in a low degree of saturation which is susceptible to a large reduction in total volume or collapse upon wetting. The aim of this study is to evaluate the collapse potential and shear strength parameters due to saturation of soil caused by the infiltration of contaminants including leachate wastewater and chemicals into the soil. Since the separation of leachate components is difficult, especially with change of ingredients and pH in long time, the two factors sulfuric acid and sodium hydroxide were used as representatives of the leachate in the pH of 1 to 14. Furthermore, collapse tests and direct shear tests were performed on soil samples which were saturated by leachate. Experimental results show that leachate with a low pH or acidic solutions increase the soil collapse potential; on the other hand, leachate with a high pH or alkaline solutions cause less soil collapse. Variation range of soil collapse in acidic solution was much more than alkaline solution. Direct shear test results demonstrate that acidic leachate increase the soil cohesion and reduce the internal friction angle of soils; however, alkaline leachate reduce the soil cohesion and increase the friction angle of soils.

Iran is a country with unstable soil. If soil classes, characteristics and structures are not identified properly, railroads or roads that are to be built can face significant problems, as the soil becomes saturated. Some soils in our environment cannot undergo the normal tension they encounter, and by the slightest increase in the ratio of humidity, will encounter high settlement. These kinds of soil, mainly found in hot and dry regions, like deserts, are called collapsible soils. In this article, to correct the soil of these regions, some items, like the behavior of lime injected materials in the presence of clay in cementitous soil, for creating suitable adhesion among grains and micro-silica as porosity filling materials, are studied separately.In this study, to investigate and stabilize soil, reduce collapse potential and increase its strength properties, the use of limestone injection technology has been considered. Then, the collapse potential of the soil under injection has been compared with that of natural state soil. The results indicate the good performance of the injection method compared with existing methods. These results show that the injection of lime will reduce the potential for soil collapse. The soil shear strength parameters improved after injection, and the value of fu after injection reached an amount of approximately 2.15 times the initial internal friction angle. Parameter f’ increased up to 1.62, which, considering the fixed amount of tension in both tests on soil in normal state, and the injected soil, was associated with an increase in internal friction and a reduction in the adhesion of soil grains. The results of field and laboratory tests reveal that according to clay cementation among soil grains on site, the injection of lime would result in a considerable reduction in the collapsibility potential of soil in a saturated condition. Therefore, it can be suggested as a suitable solution.

Collapsible soil is defined as loose deposit with a metastable and porous structure and mostly is found in arid and deserted regions. The particles of soil in the unsaturated state are connected together by capillary tension and in the dry state by cementation such as clay and silt bond or by other cohesive material like calcium silicate. The cementation agent makes a relatively high apparent strength in this type of soils but it will collapse in wet condition due to weakening effect of moisture. As city of Semnan is located in a dry area with collapsible soil in some parts of its urban district. It is highly endangered by this natural phenomenon. Therefore further studies on recognition and developing method of dealing with this phenomenon is really important. This study investigated the effect of bentonite, microsilica and rice husk ash on soil volume change has been studied. Based on test results on stabilized samples, by adding microsilica up to 4% of total weight of soil sample will reduce collapse potential, but increasing percentage of microsilica will have opposite effect. In addition by adding a mixture of additives consists of fixed portion of 3% of microsilica and variation portion of bentonite as well as by adding rice husk ash the results show that collapse potential had been reduced continuously.

Progressive collapse is a particular phenomenon in structures in which all or a part of the structure is collapsed due to a local damage or fracture in a limited part of the structure. This phenomenon is often triggered by an accident such as an explosion in the structure and then progresses for reasons other than the proper redistribution of forces between other members of the structure. In this phenomenon, failure is often triggered by an accident such as an explosion in the structure and then progressed to other parts of the structure due to some reasons such as inappropriate redistribution of forces between the other structural members. In recent years, study on progressive collapse in structures has been increasingly taken into account and a number of different researches have been conducted on this topic. One of the issues discussed in this regard is the impact of structural systems on the potential for progressive collapse in buildings. One of the most common types of building structures is reinforced concrete buildings that are also widely used in Iran. In these buildings, various types of structural systems such as “ moment-resisting frames systems” , “ bearing wall systems” , “ dual systems include moment-resisting frames and shear wall” , etc. are used. Choosing an appropriate system to have more safety against a premature failure requires knowledge of the behavior of these systems against this phenomenon. Proposing and choosing an appropriate structural system to have more safety against the progressive collapse, taking account economic considerations, requires having sufficient knowledge of the behavior of these systems against this phenomenon. In this paper, an attempt has been made to compare the behavior of various structural systems of reinforced concrete structures against the progressive collapse. In this regard, after literature review on the researches and existing standards/codes provisions related to this issue, nine reinforced concrete frames different in structural systems or number of stories have been modeled and the behavior of these frames has been investigated. These frames consist of 3, 7, and 10-story frames, as well as three structural systems: “ Intermediate reinforced concrete moment frame” , “ special reinforced concrete moment frame” and “ Intermediate reinforced concrete moment frame + Intermediate reinforced concrete shear walls” . The loading and design of these frames is done in two ways: taking into account the criteria for progressive collapse, without taking into account these criteria. In the design of the structures with the aim of preventing a progressive collapse, the UFC-4-023-03 regulations have been used and these structures have been evaluated under different column removal scenarios. Finally, the provisions for linear and nonlinear analysis presented in this code are also compared. The results show that in terms of the ability to withstand the loads on the structure after column removal and also economic considerations, “ Intermediate reinforced concrete moment frame” have better behavior than other structural systems studied in this paper. Moreover, in the studied structures, it is determined that the UFC-4-023-03 regulations, in the nonlinear analysis method, has been provided more conservative criteria compared with linear analysis.

Progressive collapse is defined as a local failure that may occur due to various factors in structural members; then, it can spread to adjacent members and ultimately result in the total collapse of the structure or a large portion of it. Though the abnormal loads could cause progressive collapse, many structures have experienced progressive collapse due to seismic actions in our modern history. Recently, some code specifications and guideline requirements such as Unified Facilities Criteria (UFC) have introduced different analysis methods for the assessment of progressive collapse in buildings based on increasing strength, ductility, and continuity. Many research works have been conducted in relation to the phenomenon of progressive collapse almost considering the gravity loads and, in recent years, seismic progressive collapse has attracted much attention and is an open research area for researchers. Lead Rubber Bearing (LRB) is considered as one of the most conventional isolation systems that has been studied and examined theoretically and developed widely in practice. This study investigates the potential of LRB base isolation under progressive collapse. For this purpose, the behavior of intermediate steel moment frames in the two cases of fixed and with the LRB seismic isolator with 4, 8, and 12 number of stories under progressive collapse is compared using nonlinear static and dynamic analysis in different situations of the column removal. At first, two fixed and isolated 3D structures were designed by SAP2000 software according to Iranian codes; then, analysis was performed under gravity load (consist of nonlinear static and dynamic analysis) according to UFC guild-lines and seismic loading (by nonlinear time history analysis) using Perform-3D software. The base isolation is modeled with an isolator element in the Perform-3D software, and these separators provide hysteresis damping through the sink of lead core. The addition of seismic base isolation system to structures averagely reduces the response of the frames under earthquakes by 61%. The progressive collapse potential of fixed and base isolated structures in the middle and corner column removal conditions is the same as the results of nonlinear static and dynamic analysis according to loading UFC instructions. Furthermore, the results of the progressive collapse analysis show that increasing the number of structural members leads to a reduction in progressive failure potential. It is observed that the use of base isolation system has a significant impact on the localization of the failures under seismic loads and prevention of their expansion in the structure.