ALBERT

Description: Swelling soils cause serious damage to engineering structures, and they pose a problem worldwide. The fluctuation of water content is known as one of the most important factors that cause the swelling pressure of soils, especially for soils found in arid and semi-arid regions. The swelling soils found in these regions are exposed to cycles of volume increase and decrease in the rainy and dry periods. Thus, low-rise buildings and infrastructure constructed on/in these soils are exposed to potential damage. Although the relationship between swelling parameters and the physical-index properties of soils have been investigated in detail in previous research, the effect of variations in the initial water content on the swelling pressure of soils has not yet been sufficiently studied. For this reason, samples were prepared at the same dry unit weight and with different initial water contents to examine the effect of water content on the swelling behaviour of soils. According to swelling test results reported here, there is a statistically significant linear relationship between initial water content and swelling pressure. Some predictive empirical models with high correlation coefficients are obtained. In addition, a new approach called “Swelling Pressure Designation (SPD)” is recommended to be used for predicting the swelling pressure of soils of any water content.

Description: Most analytical and semi-analytical models for pumping-induced land subsidence invoke the simplifying assumptions regarding characteristics of geomaterials, as well as the pattern of drawdown response to pumping. This paper presents an analytical solution for one-dimensional consolidation of the multilayered soil due to groundwater drawdown, in which viscoelastic property and time-dependent drawdown are taken into account. The presented solution is developed by using the boundary transformation techniques. The validity of the proposed solution is verified by comparing with a degenerated case for a single layer, as well as with the numerical solutions and experimental results for a two-layer system. The difference between the average consolidation degree Up, defined by hydraulic head, and Us, defined by total settlement, is discussed. Detailed parametric studies are conducted to reveal the effects of viscoelastic properties and drawdown patterns on the consolidation process. It is revealed that while the effect of different drawdown response patterns is significant during the early–intermediate stages of consolidation, the viscoelastic properties may have a more dominant influence on long-term consolidation behaviour, depending on the values of the material parameters, which are reflected in both the deformation process of soil layers and the dissipation of excess pore-water pressure.

Description: An investigation of seepage was conducted at the Golfaraj Reservoir Dam with a particular emphasis on determining the seepage areas based on regional and site-specific hydrogeological studies. The primary goal of the investigation was to develop strategies intended to minimize dam and reservoir seepage. Leakage from the reservoir is a serious problem and of considerable concern to the local populace. Substantial reduction of seepage from the Golfaraj Reservoir Dam is the ultimate goal of the investigations conducted. The Golfaraj Reservoir Dam, located in the East Azerbaijan province, NW Iran, was built to provide water for agricultural and industrial needs in the Golfaraj plain and neighbouring lands. The Golfaraj Reservoir was constructed through the Miocene Upper Red Formation, which consists of sequences of sandstone, mudstone, conglomerate and gypsiferous marl. Following reservoir filling, seepage of water into adjacent formations was found to occur at an estimated rate of 70 l s−1. After reservoir impoundment, groundwater levels in Shahmar village, 2 km downstream and just north of the dam axis, rose and land surfaces became abnormally wet. Lugeon values in some boreholes drilled around the Golfaraj Dam before and after dam construction were high enough to indicate that the dam base had sufficient permeability to allow water to escape by underflow. Twenty-four Casagrande piezometers installed around the dam axis at four sectors provided additional information on seepage pathways through the dam body and underneath or through the cutoff wall. Water-level variations in the Casagrande piezometers confirmed the seepage routes. Study results showed that reservoir water is likely to seep through the reservoir bottom, and beneath and through the cutoff wall. The west side of the dam and near the reservoir reflected water-level rises in accordance with the rise in reservoir-water level. Seepage in this area is probably due to its proximity to the Golfaraj Reservoir. Hydrogeochemical analyses further suggest that the water source at the Shahmar Drain, c. 1800 m north of the Golfaraj Dam, cannot be from the east or west embankments of the dam because the electrical conductivity in the Shahmar Drain water approximates to the electrical conductivity of the Golfaraj Reservoir water and is lower than the electrical conductivity of groundwater in some of boreholes. Potential future seepage mitigation measures will focus on methods to seal the reservoir floor and cutoff wall sections I2–I2 and I3–I3, although some efforts may be directed at the west side of the dam. Such measures could take the form of the installation of a geomembrane barrier over the west side of the dam, concrete cutoff walls downstream of the dam and pumping wells to intercept seepage.Thematic collection: This article is part of the Sustainability in engineering geology and hydrogeology collection available at: https://www.lyellcollection.org/cc/sustainability-in-engineering-geology-and-hydrogeology

Description: In view of the clay slope instability caused by environmental temperature and rainfall infiltration in summer and autumn, the mechanism of the effect of temperature and saturation on unsaturated clay slope stability was discussed. To achieve this objective, this study uses the theoretical and numerical methods. Based on the theory of unsaturated clay and the law of heat conduction, the relationship between cohesion and matrix suction of unsaturated clay was derived considering the influences of temperature and saturation. Considering the effect of temperature and saturation, the coupling equation of shear strength of unsaturated clay was constructed under conditions of rainfall infiltration. The coupling equation of temperature and saturation was used in the strength reduction method, and the slope stability was analysed by FLAC software. The results show that the cohesion of unsaturated clay slope increases with the increase of depth, and the safety factor considering the coupled effect of temperature and saturation is smaller than that without considering the temperature effect; the clay slope is unstable considering the coupled effect of temperature and saturation, but stable without considering the coupled effect when the saturation of soil reaching 80%.Thematic collection: This article is part of the Role of water in destabilizing slopes collection available at: https://www.lyellcollection.org/cc/Role-of-water-in-destabilizing-slopes

Description: This case study presents a levee breach induced by piping erosion under cyclonic conditions in 2019. The levee is a 2.5 m high, 500 m long, mass earth fill embankment; with no cut-off trench, core, or ancillary structures. Located near Port Hedland on the north coast of Western Australia; its purpose is diversionary, to redirect cyclonic surface water away from the nearby Great Northern Highway. The levee was founded directly on Alluvium in 1987; and formed of locally sourced clayey sandy gravel. In 2003, the levee was partially excavated to enable the placement of a buried pipeline through the levee.Following a cyclonic event in 2019, a 27 m length of the levee breached, resulting in significant scour of the foundation and downstream soil. A site visit and investigation were conducted shortly thereafter, where in situ testing and laboratory soil tests on the levee and foundation materials were conducted.Analysis of the site observations and laboratory testing data led to the probable failure mechanism being theorised as having been initiated within the foundation by piping erosion within sand-rich beds of Alluvium. The large quantity of water ponding upstream of the levee then caused a progressive washout and breach of the levee.Thematic collection: This article is part of the Role of water in destabilizing slopes collection available at: https://www.lyellcollection.org/cc/Role-of-water-in-destabilizing-slopes

Description: Experimental tests were conducted to study the influence of natural cooling and water cooling on the physical and mechanical properties of quartz sandstone. This study aims to understand the effect of different cooling methods on the physical and mechanical properties of quartz sandstone (such as mass, volume, density, P-wave velocity, elastic modulus (E), uniaxial compressive strength (UCS), etc.). The results show that the UCS and E of the specimens cooled by natural cooling and water cooling decrease with heating temperature. At 800°C, after natural cooling and water cooling, the average value of UCS decreased by 34.65 and 57.90%, and the average value of E decreased by 87.66 and 89.05%, respectively. Meanwhile, scanning electron microscope (SEM) images were used to capture the development of microcracks and pores within the specimens after natural cooling and water cooling. It was found that, at the same temperature, water-cooling treatment was more likely to cause microcracks and pores, which can cause more serious damage to the quartz sandstone. These results confirm that different cooling methods have different effects on the physical and mechanical properties of quartz sandstone, and provide a basis for the stability prediction of rock mass engineering in cases such as a tunnel suffering from exposure to fire.

Description: Pyrite-bearing unbound fills, widely used in eastern Ireland have heaved, causing serious structural damage to thousands of buildings. This study compares calcareous mudstones that degenerated rapidly, causing severe structural damage, with argillaceous limestones that did not. Framboidal pyrite in the mudstones is widely dispersed – every aggregate particle contains abundant framboidal pyrite. Oxidation of this produced sulfuric acid that reacted with calcite producing supersaturated solutions of CaSO4 and CO2 gas. It is suggested that the latter exerted pressures approaching 5 MPa within rock particles, creating micro-fractures into which gypsum crystallized. Antitaxial growth of gypsum continued expansion, a process analogous to the formation of mineral veins in rocks. Heave of the fill took place since all the load-bearing particles expanded. The limestones have a lower pyrite content, which occurs mainly in the shaly seams and is concentrated in the fines; limestones suffered similar oxidation, but the coarser aggregate remains unaltered, and gypsum is mainly pore-filling; little expansive force was generated. It is concluded that the actual amount of pyrite present is a less important factor controlling expansion of unbound fills than its crystal size, and its distribution throughout the aggregate.

Description: At present, many levees contain a large number of loose bodies as a result of poor-quality construction, biological damage and other factors. In this context, loose bodies refer to soil with a relative density less than a specified value. Taking the Huaishu River levee in China as an example, this paper studies the distribution characteristics of loose bodies in the levee using statistical methods. First, ground-penetrating radar and other geophysical exploration methods are used to investigate loose bodies in the levee. The frequency distribution and Shapiro–Wilk method are then employed to study the distribution characteristics of the area and depth of loose bodies. The influence of loose bodies on the seepage field of the levee is then examined considering the spatial distribution of the loose bodies. It was found that the areas of loose bodies in the western and eastern upstream slope obey a logarithmic normal distribution. In the shallow layer (depth 0–1 m), loose bodies appear relatively frequently, and the frequency initially increases with depth before decreasing. The maximum hydraulic gradient of the levee initially increases and then decreases as the depth of the loose body increases.

Description: The Lower Greensand (LGS) forms the second most important aquifer in the London Basin but, being largely absent beneath the city itself, has received much less attention than the ubiquitous overlying Chalk aquifer. While the general directions of groundwater flow in the Chalk are well established, there has been much less certainty about flow in the LGS owing to regionally sparse borehole information. This study focuses on two hitherto uncertain aspects of the confined aquifer: the sources of recharge to the west-central London Basin around Slough, and the fate of LGS water where the aquifer thins out on the flank of the London Platform in the Gravesend–Medway–Sheppey area on the southern side of the basin. The application of hydrogeochemical techniques including environmental isotopes indicates that recharge to the Slough area is derived from the northern LGS outcrop, probably supplemented by downward leakage from the Chalk, while upward leakage from the LGS in North Kent is mixing with Chalk water to the extent that some Chalk boreholes on the Isle of Sheppey are abstracting high proportions of water with an LGS fingerprint. In doing so, this study demonstrates the value of re-examining previously published data from a fresh perspective.Thematic collection: This article is part of the Hydrogeology of Sandstone collection available at: https://www.lyellcollection.org/cc/hydrogeology-of-sandstone

Description: The objectives of this paper are to provide a regional description of the shrinkage parameters of Neogene clays and glacial tills from central Poland; and to present the effects of hydrocarbon contamination on the shrinkage behaviour of soils. Forty samples containing from 19 to 90% clay-size particles were tested. The comparison of the three methods applied has indicated that the shrinkage limit values obtained by the BS 1377-2 method provide a greater margin of safety when used in the classification of expansive soils and yield the best matching in the analysis of the variability of the shrinkage limit in relation to other soil index parameters. A good correlation was found between the shrinkability index and the consistency index, which leads to a new classification of soils. The shrinkage tests of clean and diesel oil-contaminated samples revealed that contamination has a significant and irregular effect on the values of shrinkage parameters. For low degree of contamination the shrinkage limit of both soils had the lowest values and the volumetric shrinkage was maximum, and then with increasing ON content the shrinkage limit values tend to increase, while the volumetric shrinkage decreased.