Bulletin of Engineering Geology and the Environment

The engineering activities of deep stratigraphic resources development and space utilization are often subjected to complex stress conditions. In terms of gas-bearing coal resource mining, the dynamic mechanical properties of coal at complex loaded stress and gas environment were researched in this paper. Through the split Hopkinson pressure bar (SHPB), the dynamics experiments were performed, in which the factors of axial static load, circumferential confining pressure, internal gas pressure, and outside impact load were considered. Based on the stress and strain results of gas-bearing coal, the dynamic compressive strength and peak failure strain characteristics with strain rates were obtained. Under different loaded conditions, both dynamic compressive strength and peak failure strain added linearly along with strain rates increasing. In fact, high strain rates were the results of comprehensive loading conditions, so the effects of them to coal mechanical properties were discussed. And the improved dynamic material model of gas-bearing coal at high strain rates was proposed, which considered pre-damage of static load, hardening effects of strain rate, and weakening role of gas. Through using this model in numerical simulation, the plastic deformation and stress distribution of coal specimens subjected to impact failure were researched, which verified the results of dynamics experiments. Dynamics achievements of gas-bearing coal at complex loaded environment will provide guides for disaster prevention and promote green mining.

Remotely sensed fracture patterns from southwestern Saudi Arabia are quantified so as to provide some basic data for engineering and water resources structures in the area. For this purpose, fracture lengths, orientations, frequencies, regional fracture intesities and connected fracture patterns for groundwater movement from two perpendicular directions are either mapped or qualitatively explained. The area has significant permeability anisotropy. Various regional fracture pattern maps help to identify safe sites for engineering activities and potential groundwater recharge and movement. Necessary qualitative rock descriptions are proposed for any infrastructure construction in this area. It is observed that Landsat image processing provides a rather rapid and extremely economical preliminary solution compared to conventional fracture pattern assesment techniques.

The paper describes the failure of harbour walls which occurred at Malaga on 4th July 2004 and at Barcelona on 1st January 2007, associated with an inadequate consideration of the ground conditions in the light of the marine environment. At Malaga, there was an existing breakwater hence the new harbour was protected from the effect of the waves while at Barcelona, the construction of the quay wall proceeded at a faster rate than the breakwater. In both cases the wharf backfill was placed rapidly on the soft muds, progressing from the inland side. The paper discusses the importance of an overview including the ground investigation, engineering design, construction method and speed of construction.

Concrete cracking is prone to occur in secondary linings during tunnel operation. In this article, the Zhegu mountain tunnel, which is mainly situated in weak phyllite stratum, was taken as an example to study this issue. Firstly, a field investigation was conducted to reveal the cracking status of the tunnel lining. Then, similarity model tests were adopted to analyze the mechanical responses of linings in layered rock strata with different inclination angles. Finally, the damage Mohr-Coulomb criterion with a statistical distribution feature is put forward to investigate the damage patterns of linings. The results show that: (1) the anisotropic behavior of phyllite is the main factor that causes the asymmetric cracking in secondary lining. (2) The distribution of inner force and displacement along tunnel perimeter has distinct asymmetric features, and their increasing trends with loading steps contain three stages, e.g., elastically, plastically, and unsteadily deformed stage. (3) The failure processes of linings situated in layered strata with different inclination angles are similar with three pronounced period, that is, initial damage period, damage period, and instability period.(4) For layered stratum, the serious damage sections of lining are distributed in certain range with the tangent of tunnel contour being parallel to the direction of bedding planes, and the line connecting the central points of serious damage sections on both sides deflects toward the direction of minor principal stress to a certain extent.(5) The existence of void leads to a more concentrated distribution of serious damage area in lining than that of lining with no void behind it.

L'objectif de cette étude est la recherche, en laboratoire, d'une relation entre la teneur en eau volumique (θ) d'un sol et la constante diélectrique (ε) et l'impédance (RL) du même sol. Cette relation est établie en utilisant la méthode TDR, une technique qui permet de suivre en même temps la teneur en eau et la conductivitéélectrique (et l'impédance) d'un sol d'une manière continue. Par la suite, on vérifie la possibilité de calculer la succion du sol en utilisant la constante diélectrique et l'impédance du sol. Nous suivons aussi la variation de la teneur en eau au cours d'un essai de retrait. Les résultats des essais montrent une dépendance de la mesure de la teneur en eau avec le type de sol et la conductivitéélectrique du liquide, lorsque le paramètre TDR utilisé est l'impédance du sol. La constante diélectrique est donc le paramètre à utiliser pour caractériser la teneur en eau d'un sol. Les résultats obtenus lors des essais de retrait faits sur trois bentonites ont montré la possibilité d'utiliser la méthode pour les fortes teneurs en eau et pour le contrôle de l'humidité des barrières étanches.

To better understand the influence of edge flaws on the fracture behaviors of central-flawed specimens, a series of uniaxial compression tests were carried out on the central-flawed rock-like specimens with two edge flaws using a servo-controlled testing apparatus. Two edge flaws were divided into coplanar and non-coplanar distribution (F-L1 and F-L2). The acoustic emission, digital image correlation and high precision video were applied simultaneously to monitor the internal AE signals, surface strain, and crack propagation of rock-like materials, respectively. The results show that the degradation effect of non-coplanar edge flaws on the peak strength, elastic modulus, and crack initiation angle are more significant than that of coplanar edge flaws. When the inclination angle of the central flaw increases from 15° to 60°, the peak strength, elastic modulus, and crack initiation angle decrease. In contrast, the complete initiation angle, total energy density, and accumulated acoustic emission energy first decrease and then increase. The acoustic emission counts and acoustic emission accumulated energy occur a sudden increase when the rock-like specimen deforms into the next stage. Moreover, central flaw controls the initiation of new cracks, whereas edge flaws influence the propagation trajectories of new cracks. Furthermore, the coalescence between the central and edge flaws in the F-L2 specimen is easier to happen than that in the F-L1 specimen.

Petrographic, mineralogical (X-ray diffraction), and chemical analyses performed on granite-derived lateritic gravels of the Ngankè–Bonis road section show that those materials consist of quartz (26–41 wt%), kaolinite (30–41 wt%), goethite (10–14 wt%), hematite (9–11 wt%), and gibbsite (7–8 wt%). The values of the relative rock virtual weathering degree (30.03–43.12%), potential importance of free aluminum (18.85–19.57%), and potential importance of free ferric iron (18.65–23.08%) indicate that these materials are poorly to moderately altered, plastic, and clearly rupture under loading. The values of the silica/sesquioxide ratio (2.65–3.68 > 2) indicate that these lateritic gravels are suitable for use as sub-base layer materials. The geological data are corroborated by the results of geotechnical and mechanical tests on those materials: fine particles 18–30%, liquid limit 53–64%, plasticity index 22–32%, California bearing ratio 47–69%, uniaxial compressive strength 1.22–1.28 MPa, and tensile strength 0.80–0.84 MPa. A combination of 25–30 wt% of grain-fraction 5/20 granite aggregates (Los Angeles abrasion <30%) with 70–75 wt% of lateritic gravels provides concrete with California bearing ratio values of between 82 and 87, thus making the studied materials of Ngankè–Bonis area suitable for use as base layers on roads ranging from Cameroon to the Central African Republic.