Bulletin of Engineering Geology and the Environment

The tunnel crossing active fault is severely damaged under the action of fault dislocation. Considering the “economic and safety” principle in engineering design, the tunnel damage should be effectively reduced. In this work, a two-level design method for fault dislocation was proposed and the Urumqi subway tunnel in China was chosen as a typical model to deeply investigate its application feasibility. Based on the definition of the design events of different levels and corresponding design goals, three-dimensional finite element soil-tunnel models were established to estimate the response of tunnel. Meanwhile, the rationality of soil-tunnel model was judged by tunnel deformation and internal forces distribution characteristics analysis, and the two-level design goals were evaluated by comparing tunnel damage degree and volumes. The results suggest that under the condition of fault dislocation, the tunnel without disaster mitigation method suffers severely shear, tensile-crack, and compressive damage, which may eventually induce the tunnel collapse. The tunnel damage is reduced significantly by adopting the method of flexible joint. For Urumqi subway tunnel with flexible joints, both of the two-level design goals are effectively realized.

Limestone powder produced by mechanical crushing of quarried rocks to usable sizes is a by-product, which has been studied as an alternative additive material for stabilising mechanical behaviour of a low plastic silt. Use of such application can reduce the amount of waste limestone powder, thereby reducing the environmental impact from disposal into landfills. The low plastic silt mixed by adding 0%, 5%, 10%, 20%, 30%, 40%, and 50% of dry limestone powder has been characterized by means of various laboratory tests, including fall cone, unconfined compressive strength (UCS), California Bearing Ratio, and one-dimensional consolidation test. The testing results indicated a substantial decrease in Atterberg’s limits, increment in strength, and a decrease of its deformability with limestone powder addition in the silt. The specimens tested in UCS were cured for 0, 7, 14, and 28 days. This results in a reduction of about 25% in thickness of flexible pavement with limestone powder treated subbase layers. Evidently, the optimum content of limestone powder used appears to be about 30% of the total powder content in mixtures tested.

It is well known that the mechanical and physical properties of subsoil layers as well as poor construction practices play an important role in determining the level of structural damage sustained from earthquakes. Thus, sufficient knowledge of these properties is essential for estimating the weak points of a region. The ground vulnerability index (Kg), an indicator of the weak points of a region, also has a substantial importance role in mitigating earthquake hazards in multidisciplinary studies. In this context, we have used engineering basement shear wave velocity (vs30), fundamental frequencies and peak amplitude values of the horizontal-to-vertical ratio (H/V) to calculate Kg values for the study area (Kocaeli Province, Turkey). Structural damage was investigated after the August 17, 1999 Kocaeli (Mw = 7.4) Earthquake and compared with the calculated Kg values. The results indicate that the Kg values decrease towards the southern part of the study area, which is in good agreement with damage distribution from this earthquake. Kg values of >10 appear to be indicative of the most vulnerable areas in the study area. Structures built along the coastlines in Değirmendere area were the mostly severely damaged or collapsed entirely; we found that the subsoil beneath them have high Kg values of between 10 and 25 In contrast, Kg values in the southern districts, which sustained little or no damage, are relatively low (Kg < 10). In our study, the Kg values and soil types showed good agreement. Potential vulnerable areas also have poor subsoil conditions. Therefore, it could be important to consider these results for the future planning and designing of urban areas. These results could also be used as a rapid way to detect potential vulnerable areas before the occurrence of a destructive earthquake.

Most of the geological formations in the Northern Apennines are made up of flysch and tectonic mélanges. A general characterization of the most common rock masses cropping out in the Val Parma is presented in this paper, using the Marinos–Hoek classification based on the Hoek–Brown criterion. Three groups were identified: heterogeneous rock masses essentially controlled by single discontinuities with strengths much lower than the main rock mass (HH); truly heterogeneous rock masses with approximately equal alternations of hard and weak horizons which fail through the weaker materials (TH) and a rock mass in which the majority of the material is weak, tending to soil-like behaviour (WH). A general engineering geological map of the study area is presented, highlighting the spatial distribution of the three different groups.

Wave velocity is closely related to the transverse propagation direction of rock fracture surfaces. In this study, the directions of the principal stress and principal strain in different height planes of the samples were determined by circumferential ultrasonic measurements. Considering the relationship among the directions of the principal strain, transverse propagation, and in situ stress release, the mechanism of transverse fracture propagation driven by micro-cracks caused by in situ stress is explained. The effects of the confining pressure, initial rock damage, and circumferential wave velocity anisotropy on the incline angle were analysed. The results indicate that the directions of the principal stress and principal strain were approximately perpendicular to the central position of the samples. Significant deflection occurred in the principal stress direction at the top and bottom. The fracture surface transverse propagation direction was close to the principal strain direction at the central position, and the incline angle decreased with increasing confining pressure. The influence of the micro-crack volume proportion on the angle decreased with an increase in the initial damage. In addition, the incline angle and initial damage first decreased and then increased with the fractal dimension. Under different fractal dimensions, the change trend of the lower envelope incline angle exhibited a negative exponential relationship with the confining pressure. The fractal dimension decreased exponentially related to the chlorite content. This study provides a theoretical guidance for predicting failure locations in rock engineering.

Beachrock is among the important features of tropical coastlines. It appears to have an anchoring effect on dynamic islands that provides protection from erosion. However, the origin of cement micritic peloidal remains uncertain. Petrographic analysis is a method used by many geologists to accurately identify specific aggregated minerals present in an area. It also helps to understand historical petrogenesis interpretations of a sedimentary rock formation and cementation process inside rock particles. In this study, petrographic analysis was used to identify the structure, texture, composition, and presence of minerals from beachrock samples collected from Okinawa, Japan and Sadranan beach, Yogyakarta, Indonesia. Field investigations and laboratory analysis (petrographic and geochemical measurements) were aimed at understanding the formation mechanism of natural fresh beachrock. Subsequently, laboratory-scale experiments on artificial beachrock were based on solidification tests and were conducted to use microbial-induced calcium carbonate precipitation (MICP) with Pararodhobacter and Ocenisphaera bacterium species to draw comparisons between natural beachrock and artificial beachrock. The cementation process based on petrographic analysis of thin sections has an assumption that the cement type and other added materials determine the strength of the material, and that the cement mineral occurring represents the sedimentary environment. The cement mechanism behavior of natural beachrock has potential in manufacturing artificial beachrock using the MICP method, an eco-friendly development method for coastal areas.

The Birrimian rocks are structurally complex and extensively weathered in most places. The transition from rock to soil in the formation is often rather imperceptible. With just the basic site investigation equipment available in the country, site investigation in the residuals of the Birrimian rocks could be challenging. The only way to avoid over-designing is patient and systematic analysis of investigation data based on full understanding of the geology of the material at every site. This paper analyzes the problems associated with the Birrimian residuals encountered during site investigation at over sixty sites within the Birrimian, highlights solutions prescribed, and shows how a judicious combination of rock and soil mechanics principles could lead to reasonable solution of site investigation problems in soils with predominant structural features.

Reservoir sediments create a range of severe problems for hydropower dams. Although reservoir sediments can be excavated, nonetheless, sizeable dumping lands for such excavated sediments are unavailable at this time. This paper presents an experimental investigation of the destructive and nondestructive properties and microstructural characteristics of reservoir sediments solidified with fly ash–cement blend for reuse as construction materials. The obtained natural sediment was classified as well-graded sand with silt. The destructive experiments comprised unconfined compression, indirect tension, California bearing ratio, resilient modulus, and durability against wet–dry cycle tests, while the nondestructive experiments included a free–free resonance test. Microstructural investigations consisting of X-ray diffraction, thermogravimetric analysis, scanning electron microscopy, and energy-dispersive X-ray spectrometry were performed to verify the macroscale test results. The results showed that fly ash–cement blend exhibited increased strength values on the order of 2 to 9 times that of unsolidified sediments. Using fly ash-blended cement was more effective than using sole cement or sole fly ash, and mixtures with 10% fly ash delivered the best strength and modulus values. Various functional empirical correlations were proposed. Utilizing six wet–dry cycles is acceptable because the strength of the samples subjected to the six wet–dry cycles was lower than the given value. The results of the peak intensities of calcium silicate hydrate, mass losses, calcium contents, and scanning electron microscopy images derived from the microstructural investigations confirmed the macroscale test results.

The Serra do Mar mountain range is a fault scarp with steep slopes that are often affected by shallow landslides triggered by extreme rainfall. Most of these events result in casualties and economic and environmental damage, especially in areas close to urban centers, major roadways and agricultural areas. The goal of this study was to evaluate the susceptibility to shallow landslides in the Serra do Mar, specifically within a drainage basin affected by such an event in January of 1985. For this purpose, the mathematical modeling technique of SINMAP was used by introducing the topographic values from a digital terrain model as well as geotechnical and hydrological values from previous studies performed in the Serra do Mar. In all, 32 susceptibility scenarios were generated, and three were analyzed for this study. These scenarios were validated using landslide scar maps produced using orthophotography; this technique was also used to analyze the functions of morphological parameters (e.g., slope angle, curvature and hypsometric features). The basin was classified as unstable, with landscape rates above 70 % for all three of the scenarios chosen. A higher landscape frequency was expected on straight slopes with angles between 30° and 50° under unsaturated soil conditions, as evidenced by low moisture rates, especially for N–S-facing slopes. The susceptibility maps generated using this model should prove useful for other critical parts of the Serra do Mar to understand better and, above all, predict these landslides, which annually cause significant damage in Brazil.