Construction and Geotechnics

The problem of improving soil physical and mechanical properties always appears when constructing and operating buildings and structures on soft ground to increase their bearing capacity and reduce deformability. On the one hand this is a problem, but on the other it is an opportunity for innovation and modernization of the existing methods of soil strengthening. Artificial soil strengthening is the impact on the soil through a variety of structural and technological measures, which increases soil bearing capacity and reduces strain. Currently, there are many methods of soil strengthening. Each method has advantages and disadvantages. Application area of the method often depends on the type of soil. This article presents the most popular methods of soil strengthening such as thermal grouting by hot air and burning fuel, freezing, thawing naturally and artificially, electro-osmosis, water depression by light ejector well points and vacuum, preloading using fill, vibrocompaction, dynamic and explosive compaction, the use of different fibrous materials and stone columns, silicatization, the use of enzymes, tarring of soil, jet grouting, bituminous grouting. Also, recommended soil conditions are described in tables for the use of a particular method considering its advantages and disadvantages. Each method is briefly described the work technique and the mechanisms used. The choice of each method must be unique. With this classification and tables the selection of a suitable method of soil strengthening can be greatly simplified.

In work questions of dependence of physicomechanical characteristics of soil on the factors that determine their stress state. As transition from the strength and deformation characteristics received the laboratory for soil samples to the similar characteristics corresponding to the undisturbed soil massif is insufficiently reasonable now, it is necessary to conduct the researches directed to establishment of analytical dependences between the strength properties of soil and parameters defining their stress state. For establishment of interrelation between strength characteristics of the composing soil and geometry of homogeneous unloaded slope in ultimate states are analysed earlier executed researches. For example, homogeneous, isotropic and linear of the soil slope shows that the strength properties composing the soil are, to a certain mutual dependence, if the stress level is such that priodonta region was in the ultimate state. More detail the dependence of the angle of internal friction from the angle of laying the slope for different values of lateral pressure coefficient. The calculations are made and composed of streamlined table ultimate strength characteristics of soils. Graphical and analytical dependences, allowing to illustrate the regularities.

The major environment problem is the case of preserving and increasing green spaces in cities and towns. The next serious and actual problem is indifferent attitud of citizens to environment. The authors of the article rises the question of the civic engagement of urban dwellers to conserved of the green frame in the cities. The Pittsburgh Greenspace Alliance is an affiliation of non-profit organizations working on greenspace issues in and around the Pittsburgh area. The article describes the successful experience of one of them - “Tree Pittsburgh” (PA, USA). The information is based at the meeting between the leadership and activists of the organization “Tree Pittsburgh” with the staff and students of the Civil Engineering Faculty, PERU in September 2014. The article describes green spaces protection on the example work of the administration and public organizations of the city of Perm. It is analyzed directions and methods of the structures responsible for urban landscaping in Pittsburgh and Perm. Recommendations are given to use of experience “Tree Pittsburgh” for the city of Perm. The authors are proposed a complex of organizational and educational activities to an awakening of public environmental consciousness.

The article describes one of the main problems of pile foundation on the basis of precast concrete piles - they cannot be defect-free dive-related, primarily, with complex ground conditions. This problem leads to the need to produce felling heads piles with non-project immersion ("aspiring pile") or a pile hammer understudy. An alternative to the use of driven piles are bored piles. The article presents a detailed classification of bored piles, the analysis and comparison of the characteristics of steel and fiberglass, which suggests the expansion of the scope of the latter in the field of construction and, in particular, when the pile foundation. The uniqueness of fiberglass in comparison with any other material used as a casing, is the possible combination of properties which will create bored piles with increased strength characteristics. Technology device bored piles in the casing made of fiberglass, proposed by the authors, corrosion resistance and frost resistance are not inferior designs, which are made entirely of polymer materials, and strength, rigidity and stability are superior to polymeric materials and are not inferior to steel. The main physical meaning of the method of creation of bored piles in the casing made of fiberglass is as follows: sealed fiberglass shell (fiberglass pipes) protects concrete pile from the external environment that determines its durability, acts as a reinforcement, perceiving mechanical loads and simultaneously performs the function formwork, which keeps the heat inside the concrete mix design, thanks to the low thermal conductivity, which improves the quality of work performed in accordance with the schemes of operational quality control.

According to code SP 24.13330, combined foundation is reinforced concrete slab and piles, which transmit a load on ground base together. That foundations transmit a load by means of “pile - soil”, “pile - pile”, “slab - soil”, “slab - pile” interaction. And it’s a very important to take care of design concept during site preparation and excavation works. The paper describes winter season construction mode of combined foundation in Tyumen. Construction period was from December 2013 to March 2014. The construction site is within the city limits. And there are high water table and strongly swollen soil on the construction site. For the time of zero cycle work air temperature changed from -39 ºС in the end of January to +7 ºС in the middle of March. The temperature gradient for the time of zero cycle work was ∆ Т = 46 °С. For the time of zero cycle excavation and pile-driving works the ground base was freezed in water-inundated condition and the ground base contact layer was mechanically damaged. The authors proposed contact layer “foundation - ground base” recovery operation. The operation consists of cement mortar injection to bugholes under slab and in gravel and concrete layer. This method could be use in construction mode of combined slab-pile foundation and deep-grid pile foundation. This method effectively liquidates sagging consequences of swollen soil and recovery soil structure after different damage, such as meteorically influence, ground base water influence, dynamic influence of the machinery and builder mistakes during zero cycle works.

It is noted that the fundamentals of Geotechnics are load-bearing capacity of soil and the quality of the concrete. Offered analogue-discrete model of soil and concrete based on a fragile body KR (Kulachkin-Radkevich). Quality concrete are investigated using acoustic methods. The critical analysis of methods of testing piles is done. Dynamic methods, Dynamic Load Test, Statnamic and Gersevanov method - are effective. Osterberg method (static method) has significant limitations. Plate test after drilling wells to piles are effective for assessing the bearing capacity of piles with consideration of lateral friction when applying the casing. Combination of Ultrasonic and Load Strain Test (Seismoacoustics) increases the information content of acoustic research and can be used for piles, diaphragm walls, walling, and others. The dependence of the acoustic wave velocity (SPL) on the strength of concrete has linear character, used for Low Strain Test as part of a one-dimensional wave theory. Visual inspection and analysis of geotechnical engineering research within the Observation Method (observation method) is of practical importance, particularly for linear structures, allowing make necessary changes to the project during cobstruction.

In the Kuban State Agrarian University are conducted a study on assessment of works of separating barriers in weak clay soils, arranged to protect the existing buildings on the impact of the new building. To reduce the development of additional settlement strip foundations of the existing building on the influence of pressure, transmitted to the ground situated close to the new slab foundation, considered two options for separating barriers. In first variant separating barrier made of a metal sheet pile Larsen. Under the terms of the task are believed that the metal sheet piling dipped into the ground indentation (or vibro) to excavation opening a new building. Sheet piling length is assigned by calculation or constructively, often under the assumption that the entire thickness cutting through weak clay soils. It was found that the best results are achieved in the metal sheet pile when it based in the lower end of the ground low compressibility. In a second embodiment of separating barrier made of geotechnical (grouting) barriers. Under the terms of the task is believed that prior to the start of major construction works originally produced by cementation of soil injectors (soil preparation), in which filled all the cavities, cracks, zones of low density at the bottom. Thus, there is a compaction and reinforcement of soil lenses cement grout and create a more rigid structure that can respond to a further injection of an injectable solution. According to the results of the calculations and modeling determined that the greatest positive effect on the separating wall foundations is achieved when it is arranged as a geotechnical barrier. Additional settlement strip foundation of an existing building has decreased to 60-65 % (about 4,2 cm) as compared with 8,5 cm additional settlement, which will be in the absence of separating barrier. If the separating barriers between the foundation of the building is used a metal sheet piling Larsen, an additional strip foundation settlement will also be reduced, but only by 20-25 % and will amount to about 6,8 cm.