Оценка прочности стальной винтовой однолопастной сваи при действии осевых нагрузок

The purpose of this work is resolving the problem of evaluating the structural strength of the steel screw single-bladed pile under the pressure of axial loads in various soil conditions. Calculations in this area constitute the necessary condition for assessing the possibility and feasibility of using pile-screw technology in specific construction conditions, inter alia, at main pipeline facilities. The dependence of the pressure curve on the blade on the soil stiffness modulus was revealed in the course of numerical simulation performed by the finite element method in the ANSYS software. The maximum pressures are observed at the junction of the blade and the pile shaft with a large soil stiffness modulus, if the soil stiffness modulus is small, then the maximum pressures are observed at the edge of the blade. An analytical method for assessing the strength of a single-blade screw pile is proposed based on the theory of bending of circular and annular plates, as well as the results of numerical modeling. Comparison of the analytical method for calculating the strength of a screw pile with the results of numerical modeling to assess the accuracy. The comparison results showed an accuracy sufficient for engineering calculation methods. Цель настоящей работы – решение задачи оценки прочности конструкции стальной винтовой однолопастной сваи при воздействии осевых нагрузок в различных грунтовых условиях. Расчеты в этой области – необходимое условие для оценки возможности и целесообразности применения свайно-винтовой технологии в конкретных условиях строительства, в том числе на объектах магистральных трубопроводов. По результатам численного моделирования, выполненного методом конечных элементов в ПК ANSYS, выявлена зависимость изменения эпюры давления на лопасть винтовой сваи от модуля деформации грунта: с увеличением значения модуля деформации грунта максимальные давления наблюдаются в узле сопряжения лопасти и ствола сваи, при малых значениях модуля деформации максимальные давления отмечаются у края лопасти. На основании теории изгиба круглых и кольцевых пластин, а также результатов численного моделирования предложен расчетный метод оценки несущей способности однолопастной винтовой сваи по материалу. Для оценки точности разработанного подхода к расчету прочности винтовой сваи проведено сравнение предложенного аналитического метода с результатами численного моделирования, которое показало достаточную для инженерных методов расчета точность. Общий принцип, заложенный в рассмотренном методе расчета, может быть использован для создания различных эпюр давления на лопасть в зависимости от модуля деформации грунта и характеристик винтовой сваи.

Comparative Study on Complex Modulus and Dynamic Modulus of High-Modulus Asphalt Mixture

In the French high-modulus asphalt mixture design system, the complex modulus of the mixture under the conditions of 15 °C and 10 Hz is taken as the design index. However, in China, the dynamic modulus under the conditions of 15 °C, 10 Hz, 20 °C, 10 Hz and 45 °C, 10 Hz was taken as the stiffness modulus index of high-modulus asphalt mixture. The difference in modulus values between the two systems caused the pavement structure layer to be thicker and the construction cost to be higher in China. In order to find out the appropriate modulus value of high-modulus asphalt mixture suitable for China’s modulus parameter conditions to better carry out the reasonable design and evaluation of high-modulus asphalt mixture in China, the modulus of four types of high-modulus asphalt mixtures under the two systems through the two-point bending complex modulus test of the CRT-2PT trapezoidal beam and the SPT uniaxial compression dynamic modulus test were analyzed in this paper. Under the premise of meeting the stiffness modulus index of the French high-modulus asphalt mixture, the relationship conversion models between the dynamic modulus and complex modulus of high-modulus asphalt mixture under different temperatures were established. According to the conversion models, the design evaluation value range of dynamic modulus suitable for China’s condition was recommended. It is recommended that the dynamic modulus of China’s high-modulus asphalt mixture at 15 °C and 10 Hz is not less than 16,000 MPa, the dynamic modulus at 20 °C and 10 Hz is not less than 14,000 MPa, and the dynamic modulus at 45 °C and 10 Hz is not less than 2500 MPa. Five kinds of high-modulus asphalt mixtures used in actual road engineering were tested to verify the reliability of the recommended dynamic modulus values based on the modulus conversion model, and the results are consistent with the recommended value range of the model.

Influence of Aramid-Polyolefin Fibers on the Properties of Bituminous Mixtures

The use of additives in bituminous mixtures such as fibers has been the subject of various studies. Different fibres including cellulose fibres, steel fibres, basalt fibres, glass fibres and aramid fibres can be used to improve the properties of bituminous mixtures. Depending on the type of fibres used, different characteristics can be changed. The paper contains results of comparative tests of bituminous mixtures with aramid-polyolefin fibres. Asphalt concrete used for wearing course with maximum aggregate size of 11 mm was evaluated in the study. Reference mix with an average penetration grade of 50/70 was chosen as a base for modifications. Due to difficulty in preparing mixtures with fibers in a laboratory mixer, test specimens were obtained from a stationary plant. The fibers and aggregate mix was prepared before adding the asphalt. The fibers were added at a rate of 0.5 kg per 1000 kg of finished bituminous mixture. This allowed to obtain an even distribution of fibers in the mixture resulting in a homogeneity necessary for planned tests. This allowed to omit the scale effect, that could occur due to differences between laboratory and stationary mixing. Stiffness modulus tests were performed using the IT-CY (Indirect Tension to Cylindrical Specimens) method for a wide temperature range of 0-30°C. The specimen resistance to permanent deformation was evaluated. Obtained results has shown a clear increase in the resistance to permanent deformation of mixtures with aramid- polyolefin fibers, which is especially important for mixtures used for wearing course. The results has also shown a significant increase in the stiffness modulus regardless of temperature range. Results of conducted experiments has shown that it is possible to reduce the thickness of bituminous overlay in case of reinforcement of the existing pavement structure. The analysis of results has shown that the application of aramid-polyolefin fibres in bituminous mixtures can improve the functional features of the pavement and be beneficial to the investors.

Recycling of Waste Materials Using Bitumen Emulsion for Road Pavement Stabilized Base Courses: a Laboratory Investigation

The valorisation and reuse of waste materials can enhance the environmental sustainability of road constructions, especially by means of cold recycling techniques, which, moreover, allow to reduce polluting emissions in atmosphere. Among the various technological approaches, the use of bitumen emulsion to stabilize waste materials is very common, especially in case of reclaimed asphalt pavement (RAP) aggregates. However, even other types of waste materials could be considered using a Cold Central Plant Recycling (CCPR) approach. The paper discusses the main results of a laboratory investigation aimed to evaluate the mechanical performance of bitumen emulsion stabilized mixtures for road pavements base courses, prepared with RAP, steel slag, coal ash and glass wastes, used with various percentages. In a first step of the laboratory study, both physical and toxicological properties of each waste material have been investigated, in order to assess their environmental compatibility. Subsequently, an extensive mechanical analysis of the bitumen emulsion stabilized mixtures has been carried out in the laboratory, in terms of indirect tensile strength, indirect tensile stiffness modulus at three temperatures (10°C, 25°C, 40°C) and repeated load axial tests at 30°C. The moisture resistance of the mixes has been also investigated by means of indirect tensile strength tests carried out on soaked specimens. Very good results have been observed, depending on the mix composition: indirect tensile strength at 25 °C on dry specimens up to 0.52 MPa and stiffness modulus up to 4,056 MPa (at 25 °C, for a rise time equal to 124 ms). Therefore, it has been verified that the waste materials considered in the study can be successfully reused to completely substitute conventional aggregates in bitumen emulsion stabilized mixtures for road pavements base courses.

Asphalt Concrete for Binder Courses with Different Jute Fibre Content

Since the beginning of modern road construction, there have been effort to make durable, long life pavements. But no one pavement can fulfil designed purpose forever. On the other hand, some natural resources are limited, so it is important to maximize use of renewable resources. In recent years, there is a visible pursuit of this trend, in road construction represented mostly by use of waste materials, such as industrial by-products or recycled asphalt pavement itself. Within the effort, fibrous additives were established on the market to prolong life of pavement layers. Some commercial ones are synthetic polymer based, so it does not go well with the renewable part of pavement life cycle if we want to secure sustainable future. This paper describes use of fibres from natural renewable resource, specifically jute plant (Corchorus). Three asphalt mix variants with jute fibres were designed and further compared. Fibre content was 0.1 %, 0.2 % and 0.3 % by weight. Several tests were conducted to examine the effect of fibres on mixture properties, with aim on stiffness modulus (IT-CY) and crack propagation (SCB). Furthermore, indirect tensile strength ratio was calculated as a parameter showing performance of the mixture under the wet conditions. Control mixtures with paving grade and polymer modified bitumen were tested for better comparison and evaluation of the results.

Investigation on Fatigue Performance of Asphalt Mixture Reinforced by Basalt Fiber

Basalt fiber has been widely used in asphalt mixture due to its excellent mechanical properties and good combination with asphalt. In order to systematically evaluate the enhancement effect of basalt fiber on the fatigue performance of the mixtures, gradations of Stone Mastic Asphalt and Superpave with different nominal maximum aggregate sizes, namely SMA-13, SUP-20 and SUP-25, were prepared, and a four-point bending beam fatigue test was adopted under the strain control mode. The fatigue damage mode was assessed based on the phenomenology theory, energy dissipation theory and change rate of dissipated energy. The results showed that basalt fiber could well increase the fatigue life of the mixtures. Basalt fiber could also increase the cumulative dissipated energy of the mixtures, and it was linearly correlated with the fatigue life in double logarithmic coordinates. In the meantime, adding basalt fiber could increase the change rate of dissipated energy of the mixtures. Furthermore, it is not appropriate to take the stiffness modulus declined to 50% of the original as the fatigue failure criterion of the mixture; this paper suggested that it is reasonable when the stiffness modulus was 15–25% that of the initial. These findings provide a theoretical basis for exploring the fatigue failure of asphalt pavements.

A Machine Learning Approach to Determine Airport Asphalt Concrete Layer Moduli Using Heavy Weight Deflectometer Data

An integrated approach based on machine learning and data augmentation techniques has been developed in order to predict the stiffness modulus of the asphalt concrete layer of an airport runway, from data acquired with a heavy weight deflectometer (HWD). The predictive model relies on a shallow neural network (SNN) trained with the results of a backcalculation, by means of a data augmentation method and can produce estimations of the stiffness modulus even at runway points not yet sampled. The Bayesian regularization algorithm was used for training of the feedforward backpropagation SNN, and a k-fold cross-validation procedure was implemented for a fair performance evaluation. The testing phase result concerning the stiffness modulus prediction was characterized by a coefficient of correlation equal to 0.9864 demonstrating that the proposed neural approach is fully reliable for performance evaluation of airfield pavements or any other paved area. Such a performance prediction model can play a crucial role in airport pavement management systems (APMS), allowing the maintenance budget to be optimized.