Latest Advancements in Underground Structures and Geological Engineering

A new approach to the interpretation of wave fields has been developed to determine the contours or surfaces of composite local hierarchical objects. An iterative process has been developed to solve a theoretical inverse problem for the case of determining the configurations of 2D hierarchical inclusions of the l-th, m-th, and s-th ranks located one above the other in different layers of the N-layer medium and various physical and mechanical properties for active acoustic monitoring with sources of longitudinal and transversal waves. When interpreting the results of monitoring, it is necessary to use data from such observation systems that can be configured to study the hierarchical structure of the environment. Such systems include acoustic (in the dynamic version) and electromagnetic monitoring systems. The hierarchical structure of the geological environment is clearly visible when analyzing rock samples taken from ore mines. On the other hand, the more complex the environment, the each wave field introduces its information about its internal structure, therefore, the interpretation of the seismic and electromagnetic fields must be conducted separately, without mixing these databases. This result is contained in the explicit form of the equations of the theoretical inverse problem for a 2D electromagnetic field (E and H polarization), as well as for the propagation of a linearly polarized elastic wave when excited by an N-layer conducting or elastic medium with a hierarchical conducting or elastic inclusion located in the ν-th layer. In the present work, the inverse problem for a complicated hierarchical model of inclusions is considered. It can be used when conducting monitoring seismic and acoustic borehole studies to monitor the fluid return of oil fields, to analyze the dynamic state of a mountain range of deep-seated deposits which are under various mechanical effects.

An imminent challenge currently being faced in Dubai is the occurrence of soft rock underlying the quaternary aeolian sand deposits. One such offender encountered, is the thinly laminated calcareous sandstone of the Ghayathi Formation, which may occur as alternating beds of very dense sand and extremely weak sandstone. The current accepted method for differentiating between soil and rock is dependent on a UCS strength occurring below 0.6 MPa. Laboratory experiments performed on samples retrieved from the Ghayathi Formation exhibit an average UCS, Point Load Index and E-modulus of 0.71 MPa, 0.11 MPa and 1128 MPa respectively. However, strength and deformation is controlled by inherent physical properties of the material such as mineral composition, density, structure, fabric and porosity. Petrographic analysis of representative samples from the Ghayathi Formation shows the sandstone comprises of highly porous fine-grains with sporadic bands of coarser material cemented together by a thin uniform crust around depositional grains with some degree of compaction. Overall the mineralogical composition by volume comprises of: calcite (80%) as a cementing agent and bioclasts, quartz (16%), rare feldspars (2%), trace amounts of pyrite (1%) and igneous rock fragments (<1%). Primary pore spaces remain unfilled and result in a high inter-particle porosity of 27.69%, which is inversely proportional to the bulk and dry densities exhibiting average values of 1968 kg/m³ and 1660 kg/m³ respectively. The high inter-particle porosity resulted in the degree of saturation predominantly ranging between 40–80% but the inherent water content had minimal influence on the strength of the samples. This petrographic analysis comparison to laboratory results highlights some of the complexities currently being faced in soft rocks research and further supports that improved sampling techniques, laboratory testing methods and understanding of soft rock characteristics is required for improved classification.

The vulnerability of GIFT city from seismic hazards due to geological fault lines present in that region was assessed, and potential seismic sources were identified. GIFT city lies in Zone 3 according to seismic zonation maps of India and is nearby to the Zone 4. The past earthquake catalogue of GIFT city region is prepared. All earthquakes in the radius of 500 km from the GIFT city were taken (from United States Geological Survey), and the datasheet was prepared according to the latitude, longitude, magnitude, time and date. Spatial and temporal distribution of the foreshocks and aftershocks within 30 days from the main earthquake were analysed and declustering was done. Magnitudes of all earthquakes were homogenized and taken in terms of Moment magnitude (M_W). Seismic tectonic map of GIFT city region was taken and superimposed with these past earthquakes, and the effect of each fault line nearby was studied. Previous earthquakes were assessed, and their sources were identified. The Peak Ground Acceleration (PGA) and Ground motion attenuation were calculated using these data. The fault lines that can cause tremors or earthquakes in the GIFT city were assessed and studied.

Rock characterisation is important to the feasibility of the Handlebar Hill open cut mine at Mt Isa, Queensland-Australia, because of the complex structural geology and the diversity of slope formations. The different rocks are affected by complete and moderate oxidisations coupled with mining works, giving rise to potential slope instability. Through the characterisation of these rocks, there is more confidence in the prediction of their behaviors in terms of failure mechanisms and slope stability. The objective of this research was to evaluate the properties of the pit rock masses. The geotechnical engineering practice approach was based on defining the parameters of the Hoek-Brown, Barton-Bandis and Mohr-Coulomb failure criteria. A program involving investigation that included field measurements, laboratory tests, hydrogeological settings, empirical indices and findings using the RocLab program was applied. The inputs help to analysis of pit slope stability and to understand the effects of different pit configurations on slope performance to allow safe and economic mining operations.

Slopes in open pits exhibit fracturing around excavations, often initiated by extension strain which results from a combination of principal stresses adjacent to the slope boundaries. This extension strain is commonly described using minimum principal strain or minimum principal stress equations. These equations show that the extension strain can expand and fracturing occurs if the extension strain exceeds a critical value. Anisotropic rock masses with multiple and complex structures increase the potential of the development and coalesce of cracks with pre-existing discontinuities for further potential failure.

This paper presents finite element analysis to model the extensions strain implementing the criterion of Stacey (1981). The distributions of extension strain are predicted around slope of Handlebar Hill open pit mine at Mt Isa, Queensland, Australia. Around the pit wall, fracturing near the excavation boundary is often the result of extension strain of the rock. Through the mining activities, fractures in the slope face can manifest into slabbing and spalling. Extension strain may develop circumferential fractures close to the slope surface, the closer to the excavation perimeter, the more open the cracks. The result of the extension strain distribution simulated in this paper is in accord with failure events observed on site. The numerical modelling and the discussion of this study focused on the prediction of potential fracturing zones within the critical values of the extension strain around the slope.

In rock slopes prone to topple, mechanical, physical or chemical weathering might degrade the rock mass properties and compromise the stability of that rock slopes. However, the nature of the joints distribution and the degree of continuity is extremely important in determining the stresses magnitude and sign inside the rock masses. This is mainly due to the stress concentration and distribution near the joint tips inside the rock slope if rock bridges exist. In this paper, a man-made rock slope is numerically modeled and investigated under two types of joint sceneries; out-dipping persistent joint and non-persistent joint models. One point, near the crest, inside the rock slope were used to monitor and measure the major and minor principal stresses as the excavation at the toe of the slope progressed step by step. To generate the two models, the discrete element method with the Voronoi tessellation joint pattern was utilized. One of the advantages of this modeling approach is that it al-lows for generating non-persistent joint as well as persistent joint patterns inside the rock slope. The results of this numerical study show that in large rock slopes such as the one examined in this study, the stress concentration in the non-persistent model is three to four times larger than the stresses at the same point in the persistent joints model. The minor principal stresses in both modeling cases were negative tensile stresses and up to several MPa in magnitude.

In recent years, using helical piles as deep foundations for different types of structures has been increased considerably. In this paper, by using finite element software (ABAQUS), the compressive and tensile load capacities of helical piles screwed in sandy and clayey soils have been studied numerically and corresponding load-displacement curves are presented. For this purpose, different geometrical aspects of the helical pile element (including the pile length, the main shaft diameter, the helix diameter and the internal helix spacing) have been taken into account for different soil properties conditions. In modeling efforts, a disturbed zone around the pile element is also considered for better catching the effect of the soil disturbance during pile installation procedure.

Based on the obtained results, it is observed that for both types of the studied soils, increasing the helix diameter leads to an increase in load capacities. In addition, it is observed that by increasing the internal helix spacing up to three times of the helix diameter, the ultimate load capacities were increased and then remained almost unchanged. Similar trend was obtained from parametric study on the main shaft diameter. However, increasing the pile length was shown to have consistent increasing effect on the ultimate load capacities.

In this paper, to verify the obtained results, some experimental records are also considered and compared statistically with corresponding load capacities from numerical simulations. Comparisons show very good agreement between the numerical results, the experimental records and analytical solutions.

Strength and deformation behavior of jointed rock is essential in the viewpoint of design of slopes, construction of tunneling and mining projects due to the presence of natural hair cracks, fissures, bedding planes, faults, etc. In order to avoid problems like loss of strength due to cracks during construction, strength and deformation characteristics of various rock matrices is helpful to simulate such cracks and to give a reliable solution. For this purpose, experimental based study was conducted on laterite rock procured from Kutch, Gujarat to evaluate the shear parameters of the proposed rock mass matrix having two horizontal cuts (at H/4 and H/2 height of the specimen) with 0°, 10° and 30° inclination with horizontal. Stress-strain characteristics and strength behavior was studied using Mohr-Coulomb strength theory and results were compared with intact rock and various jointed rock matrix specimens. Results derived from Mohr-Coulomb strength theory were also compared with the Hoek-Brown strength theory. Results demonstrated that the orientation of the rock matrix shows little increase in cohesion value and decrease in angle of internal friction with increasing inclination of cut from zero to 30° with respect to horizontal. Failure pattern was observed in jointed rock matrix specimens comprises of axial failure, block rotation, splitting of blocks through joints and shear failure.

Iglas and Beswan are the towns in Aligarh district in of Uttar Pradesh, India. These are located along Aligarh- Mathura high way at 24 km from Aligarh. These are located at 27°43′ N 77°56′ E. It has an average elevation of 178 m. The town area extends from Karban River (towards Mathura) to old Canal (towards Aligarh). In the present study Groundwater samples were collected from Iglas and Beswan town. The samples were collected without any air bubbles. These bottles were rinsed before collection of water samples which are sealed labelled and transported for Laboratory analysis. The dissolved oxygen was measured in situ.

Results showed that pH level in the study area was 7.10 in Iglas and 7.79 in Beswan. The total alkalinity 476 mg/L in Iglas and 350 mg/L in Beswan. Similarly total hardness was 570 mg/L in Iglas, and 210 mg/L in Beswan. The concentration of calcium was 82.50 mg/L in Iglas, and 120 mg/L in Beswan, Magnesium concentration was 145.50 mg/L in Iglas and 90 mg/L in Beswan. Conversely turbidity 0.31 mg/L in Iglas and 0.84 mg/L in Beswan. The concentration of chloride was 52 mg/L in Iglas and 368 mg/L in Beswan are respectively. Overall, the results showed that groundwater sources in Iglas and Beswan are suitable for drinking, except for high Cl in Iglas. Although, no health based guideline value is suggested for Cl in drinking water. Cl concentrations above 250 mg/L can give rise to detectable taste in water. This study has shown that Groundwater is comparatively suitable for drinking. However, broader studies evaluating Groundwater over wider spatial and temporal scales are recommended, since this analysis was based on few parameters and limited spatial scale.

The carbonated reservoirs, concentrated mainly in the Middle East, contain about 50% of the world’s hydrocarbon resources, where the considerable challenge they represent for the sustainable development of oil resources and the challenges posed by their production are commensurate with this potential. The characterization of these reservoirs through the control of their heterogeneities makes it possible to reduce the uncertainties on the quantification of their reserves inorder to improve their productivity as well as their recovery rate.

The recovery rates obtained today on the main carbonated fields are mainly related to their sedimentary deposits and the very varied climatic conditions, resulting in a very heterogeneous geology and represent difficult challenges to overcome where the permeability is not the same, only condition for better production. This can vary from less than 10% to more than 40% on medium permeability deposits (10 to 100 md). To these parameters is added the diversity of recovery mechanisms and development patterns, on which the dynamic behavior of the deposit depends, which are far from being conditioned by the single permeability factor.

Currently, in Algeria, the valorization of carbonated reservoirs, mainly located at the level of South Eastern Constantinois reservoirs where most of these reserves remain unexploited, are among the strategic and priority objectives, because of their complexity.

Indeed, the study of stratigraphic heterogeneities, obtained from logging data and core studies, applied to South-Eastern Constantinois reservoirs (Algeria), shows that the results play an important role in the development of carbonate reservoirs production in this area.