Analysis of soil nail walls performance - Case study

This study surveys the performance of temporary soil nail walls with a maximum height of 29.3 m in the Yas project, located in Tehran. Some numerical models, with various modelling approaches, were developed using finite element software and the proper modelling approaches were specified and verified.The modelling results were analysed and compared with the in situ monitored data. The results demonstrate the model’s horizontal deformations are generally greater than the in situ monitored values. To decrease the differences between models and monitored results, the effect of variations of the soil parameters had been surveyed and the limits of needed variations were specified.     

Damage Estimation in Masonry Buildings Based on Excavation-Induced Ground Movements

Excavation-induced ground movements and the resulting damages to adjacent structures and facilities is a source of concern for excavation projects in urban areas. The concern will be even higher if the adjacent structure is old or has low strength parameters like masonry building. Frame distortion and crack generation are predictors of building damage resulted from excavation-induced ground movements, which pose challenges to projects involving excavations. This study is aimed to investigate the relation between excavation-induced ground movements and damage probability of buildings in excavation affected distance. The main focus of this paper is on masonry buildings and excavations stabilized using soil nail wall method. To achieve this purpose, 21 masonry buildings adjacent to 12 excavation projects were studied. Parametric studies were performed by developing 3D FE models of brick walls and excavations stabilized using soil nail wall. Finally, probability evaluations were conducted to analyze the outputs obtained from case studies. Based on the obtained results, simple charts were established to estimate the damage of masonry structures in excavation affected distance with two key parameters including “Displacement Ratio” and “Normalized Distance”. The results also highlight the effects of building distance from excavation wall on its damage probability.

     

Modeling and Interpretation of Pressuremeter Test Results with Artificial Neural Networks

In this paper, three types of artificial neural network (ANN) are employed to prediction and interpretation of pressuremeter test results. First, multi layer perceptron neural network is used. Then, neuro-fuzzy network is employed and finally radial basis function is applied. All applied networks have shown favorable performance. Finally, different models have been compared and network with the most outstanding performance in two stages is determined. Contrary to conventional behavioral models, models based neural network do not demonstrate the effect of input parameters on output parameters. This research is response to this need through conducting sensitivity analysis on the optimal structure of proposed models.     

RETRACTED ARTICLE: Study of Factors Affecting the Compressive Strength of Sandy Soil Stabilized with Polymer

Material engineers are continually confronted by depletion of quality construction materials for road and airfield construction. Even if good quality construction materials for road and airfield are available, the haul costs may preclude their use. Stabilization of soils in order to improve strength and durability properties often relies on cement, lime, fly ash, and asphalt emulsion. These materials are inexpensive, relatively easy to apply, and provide benefits to many different soil types. In addition, there are a variety of nontraditional soil stabilization/modification additives available from the commercial sector such as polymer emulsions, acids, lignin derivatives, enzymes, tree resin emulsions, and silicates. These additives may be in liquid or solid state and are often touted to be applicable for most soils. Polymers may be easy to apply in permeable materials such as sand and may achieve good stabilization in relatively shorter periods of time. These polymer materials can be used for stabilizing, soil in road shoulders, slopes, and pads of military and emergency airports. In addition, these types of materials can be used to prevent the movement of the dune sands on the sides of railroads and stabilizing the dust on the surface of access roads. Within the present research, two different polymers of wide range of dosages have been applied. Following results have been achieved: (1) These polymers improve the compressive strength from 0.03 N/mm2 for control sample to 5.2 N/mm2 for improved sample. (2) The optimum curing time of dune sands with different polymers is 7 days. (3) The UC strength of stabilized samples soars with an increase in the temperature, in the first 24 h of the curing process. (4) When the concentration of salt increased from 1 to 10 percent, UC strength of stabilized samples decreased.     

Stabilization of Dune Sand with Poly(Methyl Methacrylate) and Polyvinyl Acetate Using Dry and Wet Processing

Dune sands were stabilized using poly(methyl methacrylate) and polyvinyl acetate and examined using physical and mechanical tests. The California Bearing Ratio test was used to measure the engineering properties of the stabilized materials under dry and the wet environmental conditions, revealing the bearing ratio of the improved dune sands. Our results indicate that both polymers have good potential for increasing the strength of dune sands in the dry state and that there is little decrease in the CBR strength in the saturated state in comparison with the dry state, indicating the stiffness and stability of the compounds against moisture. This is an important point to consider for longevity of roads and road repair and maintenance, because good strength of stabilized sand in saturated sand can prevent early destruction of the road caused by demolition or erosion of the road bed during saturation. The results also demonstrate that the optimum added quantity of polymer for maximum effect was 3% by weight and that the curing time for maximum effect was 28 days. The amount of polymer added was very more important factor for improved dune sand California Bearing Ratio strength in comparison with curing time of the stabilized specimens.     

Seismic active pressure distribution history behind rigid retaining walls

Evaluating the seismic active earth pressure on retaining walls is currently based on pseudo-static method in practices. In this method, however, it is not simple, choosing an appropriate value for earthquake coefficient, which should fully reflect the dynamic characteristics of both soil and loading is an important problem. On the other hand, by using only two extra dynamic parameters that are shear wave velocity of soil and predominant frequency of probable earthquake, one can benefit from another more accurate tool called pseudo-dynamic method to solve the problem of earth pressure.In this study in the framework of limit equilibrium analysis, pseudo-dynamic method has been applied into horizontal slice method of analysis to account for the effect of earthquake on lateral earth pressure history behind rigid retaining walls. The pressure history resulted from a number of analyses shows that before and after reaching the peak resultant force, different pressure distributions occur behind a wall that put more local pressure than the same at peak. This method would be a tool to control this phenomenon in wall design.     

Effects of plastic fines on the instability of sand

The effects of plastic fines on the instability of sand were studied in this article. For this purpose, the results of undrained monotonic triaxial compression tests conducted on specimens of sand with variation in fines content from 0% to 30% are presented. The specimens were prepared in two different initial dry unit densities and were subjected to two different confining pressures. The results of the tests are shown in four groups. They demonstrate that an increase in plastic fines leads to an increase in the instability, followed by a decrease with a further increase in fines content. It is also seen that the slope of the steady-state lines in p’-q space increases with increase in fines content, but after certain fines content, it begins to decrease. A reverse trend is observed for the slope of instability lines; it decreases at lower fines content, followed by an increase with a further increase in fines content.