China
Africa
Explore chapters and articles related to this topic
Control strategies for acid mine drainage in Arctic regions
Published in Hans Kristian Olsen, Lida Lorentzen, Ole Rendal, Mining in the Arctic, 2020
Frost heaving occurs as a result of the formation of segregated ice, e.g., lenses and needles, as well as the volumetric expansion of water during freezing. Models are available to simulate and predict the mechanisms responsible for frost heaving (e.g., Chamberlain 1981, Black 8c Hardenberg 1991). Marion (1995) summarized the most important factors for the degree of frost heaving, including soil texture, pore size, freezing rate, temperature gradients, moisture and overburden stress. Frost heaving in tailings is considered a disadvantage as it produces cracks and preferential pathways that allow the infiltration of oxygen gas and oxygenated water. However, frost heaving is seldom observed in tailing areas, probably due to high ion concentrations that tend to reduce frost heaving. As pointed out by Sheeran & Yong (1975), this is to be expected because high ion concentrations increase the unfrozen water content and reduce the water available for forming segregated ice in tailings. Frost heaving may be important in cover materials provided as protection on top of tailings, and grain size and porosity should be considered in order to minimize frost heaving.
Optimization of Water-Permeable Concrete
Published in A.M. Brandt, Optimization Methods for Material Design of Cement-Based Composites, 1998
Frost resistance is an important characteristic defining the durability of porous concrete, because freezing and thawing cycles may cause considerable destruction to a drainage system composed of multiple elements. The process of the structural destruction of concrete due to cyclic freezing and thawing of water is quite complicated, and the crucial problem here is to define the degree of frost resistance. Considering the requirements of ENV 206 17.81 and the well-known properties of concrete (e.g. Neville 17.91), it is possible to assume that the required degree of frost resistance equals 75 cycles of freezing and thawing. That kind of frost resistance should be tested using an ordinary method, i.e. air freezing at -18 ± 2 :C for at least 4 hours and defrosting in a water bath at +18 ± 2 °C for not less than 2 hours. The result of the test is mass loss or drop in the strength of the frozen specimens.
Network construction
Published in Nemanja Trifunović, Introduction to Urban Water Distribution, 2020
Extreme temperatures can have an impact on the operation of water distribution systems, not only by affecting the water consumption but also causing pipe damage either by freezing or very high temperatures. While deciding on the optimal trench depth, care should be taken to minimize the temperature impact on pipes and joints. On the other hand, increasing the depth beyond what is really essential is more costly, not only during installation but also in the maintenance phase. Some degree of pipe burst under extreme weather conditions is always acceptable if the repair can be conducted quickly and without disturbance to a large number of consumers. In general, the minimum cover over the pipe crown in moderate climates are: 1.0 m, for transmission lines,0.8 m, for distribution pipes, and0.6 m, for service pipes. For frost prevention, pipes are laid deeper in areas with a cold climate, sometimes up to 2.5-3 m, which depends on the degree of frost penetration in the ground. An example of trenches as deep as 5 meters can be met in Mongolia (Figure 5.14, left-hand side). The reason is that this country suffers from extremely low winter temperatures running up to minus 50°C and resulting in the soil freezing down to a depth of over 4 meters. Alternatively, pipes in shallow trenches can be laid with thermal insulation; an example in Figure 5.14 (right-hand side) shows additionally insulated DI pipes. In extremely hot climates, the pipes will also be buried deeper, mainly to preserve the water temperature. Examples of typical depths of soil covers from European practice are shown in Table 5.1.
Investigation of mechanical performance and voids structure of cement-stabilised macadam under freeze-thaw actions
Published in International Journal of Pavement Engineering, 2023
Haiyang Liu, Jinsong Qian, Chen Jin, Xin Qian
Besides, the mechanical performance of cement stabilised material subjected to F-T actions can be affected by many factors including aggregate, admixture, temperature and so on. On the one hand, the characteristics of the material itself, such as aggregate composition and cement content, play a significant role on mechanical properties (Kevern et al.2010, Zhang et al.2016). For example, removing small particles weakened the degree of frost heave, and adding cement effectively compensated for the loss of compressive strength (CS) in F-T process (Arulrajah et al.2015, Wang et al.2018). Different supplementary cementitious materials, such as ternary concrete with silica fume or adding rubber particles, can improve frost resistance (Farhan et al.2015, Shon et al.2018). On the other hand, the deterioration of mechanical properties due to F-T actions is related to the environmental conditions, such as freezing rate, minimum freezing temperature, and initial moisture content. The investigation of concrete at the waterline indicated that the damage of frost action increased as the surrounding moisture content increased (Rosenqvist et al.2015). Some studies compared the F-T resistance of concrete at standard freezing temperature (−18) and extreme temperature (−52.5) and found that lowering the freezing temperature or slowing the freezing rate resulted in a more significant loss of strength (Bumanis et al.2018, Şahin et al.2021). However, for CSM, it is essential to further consider the effect of these factors because of the lack of existing research.
Performance of the UAS-LiDAR sensing approach in detecting and measuring pavement frost heaves
Published in Road Materials and Pavement Design, 2023
Farah Zaremotekhases, Adam Hunsaker, Eshan V. Dave, Jo E. Sias
To better understand and quantify the differences between the measured values in different seasons, statistical analyses have been conducted on the collected LiDAR data. Figure 13 plots the residuals distribution histogram for the measured values of Rt26a and Rt26b in July and January. In Rt 26a, the measured values in July are scattered around the zero line and are not concentrated on positive or negative areas, which means residuals are normally distributed around the fitted line. Moreover, distribution histogram shows that point data are more frequent near the mean in July as compared to January. In Rt 26b (Figure 13c), the scattering of data around the fitted line and distribution of data around the mean is close in two different seasons, which shows that the road pavement condition has not changed significantly due to emerging frost heaves between these two seasons. It should be noted that based on initial visual inspection, this section was considered as a test section with a low degree of frost susceptibility. In addition, Figure 14a,b depict the normal quantile plots for Rt 26a. The slope line is the cumulative value of standard normal distribution, and if the plot of residuals are completely within the two curves of 95% confidence, the data set can be considered to be following a normal distribution. According to the graph, the residual values of the collected data in July are better placed within those two limits, and there is the most deviation from the normality for the collected data in January. The same analysis has been conducted on the collected data from two other sections. Figure 14e–g compare the normal quantile plots of Rt 17a in July, January, and March. The residual values of the collected data in July are better placed within those two limits and shows less deviation from the fitted line. Comparing the results from different seasons shows the ability of LiDAR sensors and applied protocols to capture the presence of heaves and vertical deviations on the road surface.