مجله زمین شناسی مهندسی
سال چهاردهم شماره 5 (زمستان 1399)

This paper investigates response of triangular shell strip footings situated on the sandy slope. A series of reduced-scale plate load tests were conducted to cover different parameters including three shell footing types with different apex angles in addition to a flat footing, four different distances for strip footings from the crest of the slope namely “edge distance” and reinforcement status (unreinforced and geotextile-reinforced statuses). Bearing capacity of shell footings adjacent to crest of the slope, bearing capacity ratio, shell efficiency factor, influence of apex angle on settlement of footings and the mechanism of slope failure are discussed and evaluated. Also, empirical equations for determination of the maximum bearing capacity of triangular shell strip footings are suggested. As a whole, it has been observed that decrease of shell’s apex angle as good as increase of edge distance could significantly improve the bearing capacity. However, as the edge distance increases, the effect of apex angle on the bearing capacity got decreased. Also, it was found out that the beneficial effect of reinforcement on the bearing capacity decreased with increase of the edge distance. Furthermore, the efficiency of shell footings on bearing capacity was attenuated in reinforced slopes compared to the unreinforced status.

The use of piles, helical anchors and, in general, helical foundations has considerably increased in the last 30 years. The adoption of this technology in the international and domestic codes of each country, as well as in research and studies, and, finally, the publication of numerous books and papers in this area, and the existence of manufacturers’ products, committees, and contractors of this technology has contributed to its expansion and development. However, such methods have progressed at a very slow pace in many countries, especially in developing countries. This paper attempts to assess the global advancement of the helical foundations by reviewing 292 papers from 1990 to 2020 and comparing the related research findings. This will help clarify the issue and determine the scope of technological progress. On the other hand, collecting valuable papers in this area will make it easier for researchers to make further research. Subsequently, the characteristics of this technology are highlighted and the reasons for its lack of progress in the developing countries are addressed. For this purpose, a questionnaire is sent to researchers, developers, designers, and contractors of the geotechnical projects. The purpose of this questionnaire is to specify the type of existing projects, the soil type of project site, the degree of familiarity with the helical foundation technology, the reasons for not using this method and the solutions available to expand and develop this method. Finally, there are suggestions to develop this approach and the issues that need further research.

Groundwater salinization in semiarid regions is a limiting factor of use with strategic importance. In this study, the sources of salinity, chemistry, and quality of groundwater in Robat (Khorramabad plain, Iran) were identified through the geochemical methods. Using data analysis, the concentration of cations and anions were recognized with the order of Ca2+>Na+ >Mg2+>K+ and HCO3-> Cl-> SO42+> NO3-> F-, respectively. The high concentration of Na+, Cl-, and EC in some places is attributed to the gypsum and salty formations. In the study area, the salinization processes are identified by natural and artificial activities. The salinization mechanisms are identified by the natural dissolution of gypsum and salt from Gachsaran formation and man-made sources including boreholes drilled through Gachsaran Formation, salt mining, and agricultural activity. Also, the high concentration of nitrate is related to agricultural fertilizers and karstification effects. It is seen that the atmospheric NO3-. HCO3-, Ca2+, and Mg2+ concentration exceeded the standard limit in a few samples probably due to the calcareous formation. Besides, hydrochemical facies of the groundwater are Ca- HCO3 and Na-K-HCO3. Due to the presence of calcareous and salt bearing formations, 46%, 26%, and 20% of all samples show a higher concentration of Ca2+, Na+, and Mg2+, respectively, which exceed the permissible limits. Sulfate and fluoride concentrations are less than the permissible limits. However, due to the presence of calcareous formation, salt bearing formation, and use of agricultural fertilizers, 100%, 26%, and 20% of all samples show a higher concentration of HCO3-, Cl-, and NO3- than the permissible limits.

The present work is conducted to investigate the effect of texture and carbonate content on internal friction angle of carbonate soils. Carbonate soils are majorly found in the bed of shallow waters and also offshores in tropical regions. Recently there is a huge construction projects including oil and gas extraction platform and facilities, harbors, refineries, huge bridges and other big construction projects in many offshore and onshore areas around the world. One of these area is located on southern part of Iran. We collected soil samples from different parts of northern coasts of Persian Gulf, then the following experiments were performed, carbonate content, three-dimensional grain size, angularity, relative density & direct shear. The results showed that the average of internal friction angle of carbonate soil is higher respect to known silicate sands. This angle is affected by effective grain size, grain angularity, and calcium carbonate content. Based on the experimental results of this study, one of the results was that the internal friction angle of carbonate soils decreases as their effective size of soil aggregates increases.

We collected soil samples at 23 sites from the petroleum contaminated soils (PC) in the west of Kermanshah province to investigate the sources and ecological risk of polycyclic aromatic hydrocarbons (PAHs). In this study, source apportionment has been carried out using Positive Matrix Factorization (PMF).The total PAHs concentration, have a mean value of 92.79 mg/kg, ranging from 7.37 to 609.67 mg/kg in PC soil samples. The average abundance order of different PAH ring compounds are 3 rings > 5+6 rings > 4 rings> 2 rings. The ecological risk assessment of PAHs revealed that all of the PAHs levels were higher contents than the effects range low (ERL) value and show higher concentrations than the ERM values, except for Pyr, Chr, BaA, BbF, BkF and BaP in the soil samples. The result of benzo (a) pyrene equation (BaPeq) values indicates that the carcinogenic potency of PAHs should be given more attention due to the impending environmental risk in the study areas. Based on the PMF analysis four sources of PAHs are identified including coal combustion (21.48%), vehicular source (13.74%), unburned petroleum (20.84%) and creosotes (43.92%).Therefore, it was concluded that petroleum activities were major sources of PAHs in west of Kermanshah province.

A jointed rock mass presents a more complex design problem than the other rock masses. The complexity arises from the number (greater than two) of joint sets which define the degree of discontinuity of medium.  The condition that arises in these types of rock masses is the generation of discrete rock blocks, of various geometries. They defined by the natural fracture surfaces and the excavation surface. Stability problems in blocky jointed rock are generally associated with gravity falls of blocks from the roof and sidewalls. Whereas for block defined in the crown of tunnel,the requirement is to examine the potential for displacement of each block under the influence of the surface tractions arising from the local stress field and the gravitational load, in this paper various types of wedge formation in the crown of tunnel due to intersection of joint sets with various dip were examined. The state of stability of the wedge was then assessed through the factor of safety against roof failure. Following that the formed wedges in New York city and Washington D.C tunnels crown were investigated with limiting equilibrium analytical method and by use of Hoek and Brown failure criterion. The obtained results from analytical method corresponded with field observation.