فهرست مطالب مهدی مخبری

Due to the fast growth of urban and industrial facilities, the necessity of construction in new land becomes inevitable. Most of these lands were left as a result of the existence of weak layers that make them unsuitable for construction. One the methods in treatment of such lands that have weak clay layers is the application of surcharge with or without prefabricated vertical drains or vacuum. In this literature first a brief description of the vacuum and surcharge preloading is presented and then a case history was investigated by finite element method that consists of only vacuum and prefabricated vertical drains without embankment. Based on the results the application of vacuum preloading alone even in the absence of surcharge, would give satisfactory results, especially where the application of surcharge preloading is not possible due to the unavailability of suitable loading material or the existence of sensitive buildings or infrastructures. The results of this literature can be used by consulting companies or personals who are active in land reclamation, especially in offshore regions.

Collapsibility is the sudden volume change of the soil due to the increase degree of saturation. This phenomenon occurs in sands due to the grains sliding on each other and in clays due to the loss of electron bonds between particles. The percentage of soil collapsibility depends on various conditions such as soil type, mineral composition, moisture percentage, dry weight, stress applied during wetting, and the amount of initial soil moisture increase. This paper has been conducted to investigate the effect of nanomaterials on soil collapsibility potential. The soil was selected from the Allahabad region of Kerman in south east of Iran with a high loamy index. For this purpose, Nano-silica, Nano-clay, aluminum Nano-oxide, and Calcium-Nano-Carbonated additives with percentages of 0.5, 1, 1.5, and 2% were used to improve the soil. Double consolidation and direct shear tests were the two main criteria for evaluating the performance of nanomaterials. The results showed that the collapsibility index of the desired soil due to the addition of Nan- clay compared to the addition of calcium Nano-Carbonate, Nano silica, and aluminum oxide causes a greater decrease in the collapsibility index. Furthermore, the results obtained from the SEM images indicate that the collapsible soil has microscopic and macroscopic holes, which the addition of an additive destroys larger holes and creates a correlation between soil particles. This problem reduces the amount of collapsibility index.

In this literature a case study that includes surcharge and prefabricated vertical drains (PVDs) was introduced and verified using finite element program Geostudio 2018R2. Based on the verified model, the lateral displacement and horizontal strains were calculated. It was shown that the safe zone for this special case study is 40 m that is approximately equal to the length of the constructed embankment. In urban areas as a result of the existence of water and wastewater pipes, optical fibers, oil and gas transition lines or trenches and excavations, these infrastructures are in serious danger due to the lateral displacements and horizontal strains. The same case is true for constructions in industrial areas. Since the mentioned infrastructures do have special importance in passive defense doctrine, exclusive attention should be considered by the owners, consultants and contractors in such projects all phases including preliminary investigation, during the construction and after the compilation of the treatment process in the case of permanent embankment. It was shown that due to the obstacles related to surcharge and PVDs treatment, this method is not suitable in urban areas.

Marls are one of the problematic soils that undergo more erosion due to their deformability and sensitivity to humidity and weather conditions. The effects of these soils have been observed on subgrades of pavements, abutment of dams, foundation of high-rise structures, the interaction of soil-structure and etc. The strength and deformation of marls are more effective to moisture content. In addition, the dynamic parameters of theses soil are considerable as well as static geotechnical specifications. Soil dynamic parameters can be obtained from both laboratory experiments and field experiments. With the aim of understanding the dynamic behavior of marl soils, this study was carried out to evaluate the marls of northwest region of Shiraz City which is mixture of marls containing the expansive anhydride gypsum. For this purpose, the laboratory cyclic triaxial test and in situ downhole test has been performed. The results showed that for normal consolidated marls, with increasing the confined pressure from 400 to 600 kPa (increasing soil depth), the shear modulus increases from 50 to 200 kPa. In addition, the behavior of the damping ratio is relatively different for strains less than and greater than 1%, but in general, for strains higher than 1%, the damping ratio decreases from 0.21 to 0.18 with the increase confined pressure from 100 to 600 kPa.

Preloading is a well-known and classic way for soil treatment in engineering practice. For south part of Iran, this method is an economic and also effective way for soil treatment. In this method, the preloading is done using vertical drains to accelerate the consolidation and also a surcharge that is embankment. The preloading induces the required settlement to weak and compressible layers and hence the settlement would be reduced considerably after the compilation of the main structure and also the risk of differential settlement in the future would be decreased considerably. In this article the Mahshahr clarifying unit has been modeled and then the results were compared with instrumentation on site.

The problematic expansive soils are spread in all parts of the world. The water content variations cause large soil volume changes and consequently, great losses on the infrastructure. The expansive clayey soils show swelling - shrinkage behaviour respectively in wetting and drying cycles. In this study, the swelling-shrinkage behaviour of a natural severely expansive bentonite was verified in its natural state and after being improved by nanosilica, polypropylene fibres, and the EAF slag. Firstly, the swelling potential of the natural soil was determined and then, different combinations of the stabilizerschr('39') effects on the swelling potential were assessed by means of oedometer tests under 1 kPa loading. The swelling potential of the untreated expansive clay sample was measured as 75.26%, thus the soil sample provided for the study was considered in the very high expansion category. The results indicated that the swelling potential of one-day cured samples by the addition of 0.5% of nanosilica decreased by 22.8%. The improvement by means of 0.5% of nanosilica and 0.6% of polypropylene fiber, and the optimum composition of 0.5% of nanosilica, 0.6% of polypropylene fibers, and 10% of EAF slag decreased the swelling potential by 70 and 85%, respectively. Afterwards, the wetting and drying cycleschr('39') effects on the swelling and shrinkage of the natural soil and that of the best identified combination of additives were verified by means of modified oedometer. The measurement of the axial deformation of soil, void ratio, and the saturation ratio during the swelling-shrinkage cycles indicated that the wetting and drying cycles caused the reduction of swelling potential of both untreated/natural and improved expansive soil samples. Additionally, the variation of void ratio versus soil water content during the wetting and drying cycles showed that the variation was an S-shape curve, which was almost a horizontal S shape for the improved soil. It was observed that the equilibrium occurred in lower number of wetting and drying cycles for the improved sample, compared to that of the natural soil. In addition, for the untreated samples, the highest void ratio variations occurred at saturation degree between 50 and 90%. However, for improved soil sample, the highest void ratio variations were recorded at saturation degree between 70 and 90%, reflecting the reduction of negative effects of water content variations on volume changes when the expansive soil samples were improved. Consequently, it was concluded that the additives used in the study not only decreased the swelling potential of expansive soil samples with very high expansion degree, but also decreased the swelling-shrinkage behaviour of the soil and increased the durability of the samples during wetting and drying cycles.

Asphalt construction is one of the most important parameters of asphalt pavement quality that should always be carefully considered in any asphalt pavement project. The purpose of this study was to evaluate the performance of the decision tree algorithm and artificial neural network in predicting mixture and field design parameters affecting pavement compaction in order to identify and control these parameters to control the compaction parameter value. In this study, we used data collected from relative asphalt compaction determination report, grain curve report and results of hot asphalt experiments and asphalt mix design report recovered from soil mechanics laboratory and using decision tree and artificial neural network algorithm have been proposed to predict the parameters affecting compaction. The results show that data with a distribution temperature between 126 and 155°C, fracture rates in two sides greater than 95.5%, strength (Marshall Resistance) less than 1417.5 kg-force, and Asphalt Void less than 5.45 had a good compaction rate (more than 97%). Also, three parameters of thickness, distribution temperature, and void were introduced as influence variables affecting compaction in the software.

Many factors or parameters influence the field density of asphalt mixes. Since the number of variables affecting a large and somewhat different compacts affects each other, it is almost impossible to determine a constant interpolation relationship. Data mining and its techniques are a way of discovering hidden knowledge between dependent and independent variables, as well as indirect and nonlinear relationships can be identified by dividing the data into groups or leaves in the decision tree method. In this study, commonly used data mining techniques in civil engineering, including the neural network, logistic regression and decision tree. By emphasizing the application of decision tree method, with the aim of exploring knowledge models and providing predictions, other data mining tools are used to assist in constructing and evaluating the developed satistical model. The explanatory variables used in the three models of this study are the percentage of void, asphalt mix strength, aggregate size, bitumen percentage, asphalt mix flow. The results show that the percentage of void content of stone materials, the percentage of passage of sieve 200 and 4, and the bitumen percentage had a greater effect on the density and compaction of asphalt mixture. Also, a multiple linear regression model with a correlation coefficient of nearly one between the density of asphalt mixture and variables were presented.

Dynamic soil characteristics such as natural frequency, damping ratio, and shear wave velocity have important effects on seismological structures response. Earthquake codes have been used to determine frequency or damping ratio that are suggested by analytical methods and empirical amount, while due to the influence of several factors such as designing style, type of structure, construction materials and site conditions, the existing structures have different response to earthquake. Therefore, the proposed dynamic properties are not sufficiently reliable yet. In order to recognise the natural frequency and damping ratio, experimental approach can be used to evaluate the natural frequency of buildings by using the seismic records of existing buildings. The soil layer specifications are recognized by different methods, including geotechnical and geophysical as well as spectral ratio. A method that can be used to determine the structural response, and estimate the natural frequency from ambient records, is the horizontal-to-vertical spectral ratio of microtremor (H/V). This technic has been revealed by Nakamura (1989), a practical method in site characterization studies due to its low cost and its functionality. This paper has presented a method to estimate the variation of structure’s natural frequency with stories that changes, using the spectral ratio of microtremor H/V. The study was carried out to investigate the influence of building’s age and performance on frequency changes. Accordingly, the natural frequency values obtained from the two methods of numerical analysis of structures and microtremor analysis have been compared. As a matter of fact, 12 buildings including 6 new constructed and 6 old ones in Shiraz were selected. The buildings included from 1- and 2-story masonry buildings up to 12-story framed structures. The new buildings are designed or retrofitted by new standards such as 3rd or 4th edition of Iranian Code of Practice for Resistant Design of Buildings (Standard No 2800). The old buildings have been designed and constructed by oldest earthquake codes and have more than 30 years of age. In order to evaluate the dynamic characteristics of the buildings, two methods were used. First, the analytical results obtained from ETABS software analysis, to find the dynamic properties of structures. Therefore, the architectural and structural map of these buildings was prepared and the structures were numerically analyzed again. Secondly, the empirical data resulted from H/V spectral ratio of microtremor records. Microtremor measurement were performed on the floors and roofs of the building. Microtremor H/V spectral ratios were obtained according to the SESAME H/V user guidelines. Finally, the relationship formula resulting from these two techniques were compared in terms of fundamental frequency, amplitude, exhibiting agreements and disagreements. In both methods, the correlation formula between the resonant frequency and the number of stories of buildings were compared and the effect of age, construction methods, materials and standards codes on natural frequency were evaluated. The results show that the spectral ratio method of microtremor H/V can be a useful approach for real analysis of seismic response of buildings. In addition, the numerical analysis is conservative compared to the field measurement methods. Also, the frequency variation of the building follows the power functions as the stories increased. The age of structure and changes in the earthquake standards code cause about 10% difference in the frequencies value. In addition, comparison of the formula correlation obtained from numerical analyzes with the values resulted from microtremor H/V spectral ratio show that the proposed relationships of the analytic methods are more unreliable from the values of ambient vibrations data. Finally, the results show that the properties of the soil layers, the material of the building, the regular and irregular effect of the building and the site effect have a significant influence on the frequency variations.

Catchments consist of a series of sloping pervious overland whose surface and subsurface runoffs are transmitted to their outlet through stream networks. In the catchments with high perviousness and good vegetation cover, the amount of subsurface gains more significance and it might have a considerable share in the direct runoff. In this study, a hydrologic rainfall simulator model with the length of 1.92 meter and width of one meter and depth of 0.35 meter has been used which its surface and subsurface amount of flow have been measured by means of two different weirs. The texture of soil in Estahban Watershed was loamy sand. The experiments were conducted under three slope angles of 0.1, 3, 6 and 9 degrees and under rainfall intensity of 31.73, 47.6 and 63.46 millimeter per hours. Based on the results, the slope changes from 0.1 to 3 degrees resulted in 50 percent decrease in the subsurface flow and 10 to 15 percent increase in the surface flow in different rainfalls, but, from the slope of 3 to 9 degrees, no significant change was observed in the two flows and in the slope change from 6 to 9 percent of subsurface flow and 2 percent of surface flow, there was surface flow observed. The increase in rainfall intensity causes rise in hydrograph amount of surface and subsurface flow. The proportion of surface to subsurface flow changed on average between 7.5 and 14.5 times the subsurface flow under three rainfalls for the loamy sand. With the increase in slope, the surface flow amount increases and infiltration decreases. In this study, two non-linear regression equations were presented for measuring surface and subsurface peaks which is a function of length, slope and rainfall intensity of the slope.