The purpose of the study is to establish accuracy of determining the load-bearing capacity of bored piles according to the method specified in Regulations 24.13330.2011 "Pile foundations". Relevance of the topic is determined by the following: the load-bearing capacity of a pile is a fundamental indicator affecting all subsequent activities related to foundation design, and accuracy of analytical solutions for complex engineering and geological conditions is highly questionable. Field tests of bored piles were carried out in engineering and geological conditions of Saint Petersburg with deformation modulus from 10 to 40 MPa at a load in the range from 1,000 to 6,300 kN, at achievement of absolute settlement of 40 mm. Piles with a diameter from 0.15 to 0.88 m and a length from 10 to 47 m were made using various technologies: using casing, using slurry, using a flight auger. Following the results of field tests, diagrams of load-bearing capacity of piles according to the material, depending on geometrical parameters and manufacturing techniques, diagrams of actual and designed load-bearing capacity of piles were plotted. Approximating functions to describe the dependences were obtained. According to the analysis of the results, it is possible to conclude that the load-bearing capacity of the bored pile during field tests is 1.4–1.7 times higher than the load-bearing capacity of the pile designed according to Regulations 24.13330.2011; the average share of the load-bearing capacity along the side surface of the pile was 65% and under the pile toe — 35%.
АннотацияВведение. Системы водоотведения на железнодорожном транспорте должны обеспечивать осушение верхнего слоя грунтов под путями. Подкюветный дренаж эффективен в грунтах с хорошим коэффициентом фильтрации. В слабоводопроницаемых грунтах его устройство нерационально, так как дальность его действия не позволяет снизить влажность на всем участке от кювета до рельсов. Рассмотрена новая система бесполостного дренажа, устраиваемая непосредственно под рельсами, на основной площадке земляного полотна. Система в поперечном разрезе выполнена в виде двух бесполостных дрен прямоугольного поперечного сечения, расстояние между осями которых равно ширине рельсовой колеи. Методы. Для анализа эффективности водоотведения применен аналитический метод. Использованы апробированные формулы, на основе которых получены оригинальные решения для расчета времени формирования и стабилизации кривой депрессии. Оценка изменения прочности грунтов проведена по закрепленной в строительных нормах методике. Результаты. Определено для конкретных размеров дренажной системы время осушения до уровней 0,6 и 1 м от дна дрены. Доказано, что время осушения до заданных значений от ввода дрен в строй до достижения стабильного положения кривой депрессии не превышает 12 суток в самых неблагоприятных условиях, при постоянной инфильтрации 15 мм/сут. Показано, каким образом можно прогнозировать изменение несущей способности земляного полотна, используя данные об изменении его влажности. Заключение. Системы бесполостного дренажа в слабоводопроницаемых грунтах значительно увеличивают несущую способность земляного полотна при использовании их в подрельсовой зоне. Ключевые слова: бесполостной дренаж, гидрологический расчет, деформация грунтов, слабоводопроницаемые грунты, земляное полотно, расчетное сопротивление грунтов. AbstractIntroduction. Railway drainage systems should provide the drainage of the topsoil under the tracks. Subdrainage is efficient in soils with a good filtration coefficient. In poorly permeable soils, it is not so efficient since its range is not enough to reduce the moisture content in the entire area from the drain to the trackway. The paper addresses a new system of noncavity drainage constructed directly under the rails at the main site of the roadbed. In cross-section, it is represented by two rectangular non-cavity drains. The distance between their axes is equal to the width of the rail track. Methods. To analyze drainage efficiency, the authors applied an analytical method. They used accepted equations, based on which original solutions to calculate the time of depression curve formation and stabilization were obtained. Changes in the soil strength were evaluated using the method established in building regulations. Results. The authors determined the time of drainage to levels of 0.6 and 1 m from the bottom of the drain for a drainage system of specific dimensions. It was proved that the time of drainage to the set levels (from putting drains into operation until depression curve stabilization) does not exceed 12 days even under the...
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