Volumen 38 (2016): Edición 3 (September 2016)

In the present paper, a three-dimensional problem of bearing capacity of square footing on random soil medium is analyzed. The random fields of strength parameters c and φ are generated using LAS procedure (Local Average Subdivision, Fenton and Vanmarcke 1990). The procedure used is re-implemented by the authors in Mathematica environment in order to combine it with commercial program. Since the procedure is still tested the random filed has been assumed as one-dimensional: the strength properties of soil are random in vertical direction only.

Individual realizations of bearing capacity boundary-problem with strength parameters of medium defined the above procedure are solved using FLAC3D Software. The analysis is performed for two qualitatively different cases, namely for the purely cohesive and cohesive-frictional soils. For the latter case the friction angle and cohesion have been assumed as independent random variables. For these two cases the random square footing bearing capacity results have been obtained for the range of fluctuation scales from 0.5 m to 10 m. Each time 1000 Monte Carlo realizations have been performed. The obtained results allow not only the mean and variance but also the probability density function to be estimated. An example of application of this function for reliability calculation has been presented in the final part of the paper.

This paper presents selected results of research connected with the development of a (3D) geostatistical hydrogeochemical model of the Kłodzko Drainage Basin, dedicated to the spatial variation in the different quality parameters of underground water in the water intake area (SW part of Poland). The research covers the period 2011-2012. Spatial analyses of the variation in various quality parameters, i.e., contents of: iron, manganese, ammonium ion, nitrate ion, phosphate ion, total organic carbon, pH redox potential and temperature, were carried out on the basis of the chemical determinations of the quality parameters of underground water samples taken from the wells in the water intake area. Spatial variation in the parameters was analyzed on the basis of data obtained (November 2011) from tests of water taken from 14 existing wells with a depth ranging from 9.5 to 38.0 m b.g.l. The latest data (January 2012) were obtained (gained) from 3 new piezometers, made in other locations in the relevant area. A depth of these piezometers amounts to 9-10 m.

Data derived from 14 wells (2011) and 14 wells + 3 piezometers (2012) were subjected to spatial analyses using geostatistical methods. The evaluation of basic statistics of the quality parameters, including their histograms of distributions, scatter diagrams and correlation coefficient values r were presented. The directional semivariogram function γ(h) and the ordinary (block) kriging procedure were used to build the 3D geostatistical model. The geostatistical parameters of the theoretical models of directional semivariograms of the water quality parameters under study, calculated along the wells depth (taking into account the terrain elevation), were used in the ordinary (block) kriging estimation.

The obtained results of estimation, i.e., block diagrams allowed us to determine the levels of increased values of estimated averages Z* of underground water quality parameters.

The primary objective of the present paper is an attempt at evaluating the influence of sub-level caving operations on the slope stability of a still-functioning open pit coal mine in Vietnam. Initially, various methods of predicting the impact of underground mining on surface stability are discussed. Those theoretical considerations were later utilized in the process of constructing a Flac-2D-software-based numerical model for calculating the influence of underground operation on the deformation and possible loss of stability of an open pit slope. The numerical analysis proved that the values of open pit slope displacements were affected mainly by underground exploitation depth, direction of operation (i.e., from one slope to the other) and the distance from the slope plane. Real geomechanical strata parameters from the Vietnamese coal basin of Cam Pha were used in the modeling process. The paper is, therefore, a critical review of the hitherto proposed methods of predicting the impact of underground operation (UG) on open pit mining (OP), illustrated with selected examples of case studies on OP-UG interaction, followed by an original experiment based on numerical modeling method. This is first such study for the genuine conditions of the coal mining in Vietnam. The obtained results, however, should not be generalized due to a highly specific character of the analyzed phenomenon of mining-induced surface deformation. The practical implications of the study may occur extremely useful in the case of an UG-OP transition. Such a transition is often necessary for both technical and economical reasons, as in some coal basins open pit operations at greater depths occur unfeasible, which calls for a proper selection of parameters for a planned underground operation.

This paper analyzes two approaches to serviceability limit state (SLS) verification for the deep excavation boundary value problem. The verification is carried out by means of the finite element (FE) method with the aid of the commercial program ZSoil v2014. In numerical simulations, deep excavation in non-cohesive soil is supported with a diaphragm wall. In the first approach, the diaphragm wall is modeled with the Hookean material assuming reduced average stiffness and possible concrete cracking. The second approach is divided into two stages. In the first stage, the wall is modeled by defining its stiffness with the highest nominal Young’s modulus. The modulus makes it possible to find design bending moments which are used to compute the minimal design cross-section reinforcement for the retaining structure. The computed reinforcement is then used in a non-linear structural analysis which is viewed as the “actual” SLS verification.

In the second part, the paper examines the same boundary value problem assuming that the excavation takes place in quasi-impermeable cohesive soils, which are modeled with the Hardening Soil model. This example demonstrates the consequences of applying the steady-state type analysis for an intrinsically time-dependent problem. The results of this analysis are compared to the results from the consolidation-type analysis, which are considered as a reference. For both analysis types, the two-phase formulation for partially- saturated medium, after Aubry and Ozanam, is used to describe the interaction between the soil skeleton and pore water pressure.

The paper presents the results of a triaxial test conducted on stiff, consolidated clays. The standard TXCIU procedure (isotropic consolidation and undrained shearing) was applied in the laboratory soil tests. The undrained elastic modulus E_u50 was determined from each test.

The E_u50 values were determined for soil samples cut out from different depths and tested under different confining pressures. There was a significant scatter of values with depth, and no relationships between E_u50 modules or other geotechnical parameters (e.g., c_u) were observed.

This work presents the concept of normalization of E_u50 modulus values using modified normalization SHANSEP (Stress History And Normalized Soil Engineering Properties). This method was first proposed for estimating the value of the undrained shear strength c_u normalizing the parameter relative to the in situ effective vertical stress σ′_vo and loading history (overconsolidation stress σ′_p and overconsolidation ratio OCR) of the soil.

The study demonstrated that the concept of normalization of soil properties can also be used for testing elastic modulus E_u50 of consolidated natural clays and normalized values of geotechnical parameters taking into account the state of stress and load history can be correlated with the value of the overburden pressure.