Numerical simulation of uneven settlement of municipal solid waste landfill by FLAC 3D

After the landfill site is sealed, the uneven settlement is related to the safety of reutilisation of the site, and it is critical to calculate the uneven settlement of the site without error. In this article, the soil parameter of garbage body was changed with biodegradation. Fast Lagrangian Analysis of Continua in three dimensions (FLAC 3D) numerical simulation was applied to the settlement of the landfill site closure. In calculating the settlement of landfill, the soil parameters of landfill with age were obtained by field drilling experiments. The parameters can reflect the characteristics of soil organic matter in different biodegradation stages. Finally, the uneven settlement within 20 years of the closure period was obtained by the numerical simulation taking Jinzhou Nanshan landfill as an example. The results show that the settlement with the age increases gradually, but the rate will be more and more moderate, and the maximum subsidence value in the sealing field after 20 years will be 9.11 m, 15.71% of the maximum elevation. Around the landfill slope position of uneven settlement rate is bigger, and the maximum angle of uneven settlement is up to 45°. But the middle position is small, which is close to 0°.

Analysis of Stability Factors of Roadway Roof and Determination of Unsupported Roof Distance

To determine the impact of influencing factors on unsupported roof stability in coal mine roadway, a mechanical model of the unsupported roof was built. FLAC 3D numerical simulation was utilized to study the stability of the unsupported roof under the influence of the depth of the roadway, the thickness of the roof, and the unsupported-support distance. In view of the key influencing factors, the geological conditions of the site, and the relationship between the tensile stress and tensile strength of the unsupported roof, the maximum unsupported roof distance during roadway excavation was determined. Considering the surplus safety factor of the unsupported roof, the reasonable unsupported roof distance during the excavation of roadway 150802 was finally determined to be 2.08 m. The comprehensive roadway excavation speed increased by 62.7%, achieving a monthly progress over 500 m.

Expanded Longitudinal Deformation Profile in Tunnel Excavations Considering Rock Mass Conditions via 3D Numerical Analyses

In the convergence–confinement method, the longitudinal deformation profile (LDP) serves as a graphical representation of the actual tunnel convergence (both ahead of and behind the face); therefore, it is considered important for determining the distance of support installation from the face or the timing after excavation in this method. The LDP is a function of the rock mass quality, excavation size, and state of in situ stresses; thus, obtaining the LDP according to the rock mass conditions is essential for analyzing the complete behavior of convergence during tunnel excavation. The famous LDP shows that the best fit for the measured values of tunnel internal displacement reported simply expresses the ratio of the preceding displacement as approximately 0.3. This can lead to an error when predicting the ratio of the preceding displacement while neglecting the rock conditions; consequently, a complete tunnel behavior analysis cannot be realized. To avoid such error, the finite difference method software FLAC 3D is used to develop an expanded longitudinal deformation profile (ELDP) according to the rock mass conditions. The ELDP is represented by graphs featuring different shapes according to the rock mass rating (RMR), and the empirical formula of the LDP best fitted for the tunnel convergence measurement values is expanded. This expanded LDP formula is proposed in a generalized form, including the parameters α and β from the empirical equation. These parameters α and β are expressed as functions of the RMR and initial stress. Statistical analysis results of the 3D numerical analysis of 35 cases were analyzed in the ranges of α = 0.898–2.416 and β = 1.361–2.851; this result is based on the empirical formula of Hoek (1999) (α = 1.1, β = 1.7), which was expanded in the current study according to the rock quality and initial stress conditions.

TEORÍA DE CONSOLIDACIÓN, UNA REVISIÓN DE LA LITERATURA

El objetivo de esta presente investigación, es una revisión literaria de 60 referencias bibliográficas de las cuales 46 son artículo de revistas indexadas en la base de datos Scopus y Scielo, 13 libros y 01 tesis que sustentan la evolución de la teoría de la consolidación unidimensional propuesta por Terzaghi en 1925 para predecir los asentamientos producto de la disminución de los vacíos debido a la expulsión parcial y total del agua, A través del tiempo está teoría tomó mayor soporte teórico y es usada en muchos proyectos geotécnicos y civiles para el cálculo de asentamientos a través de programas de elementos finitos como PLAXIS y FLAC 3D. Se concluye que se ha logrado grandes avances de modelar el comportamiento hidromecánico de suelo en programas de elementos finitos para poder explicar la heterogeneidad del suelo y explicar la interacción que debe de tener con la superestructura.

Heave analysis of shallow foundations founded in swelling clayey soil at N’Gaous city in Algeria

The design of shallow foundations on swelling soils needs a thorough study to evaluate the effect of swelling potential soil on the final foundation heave. For this reason, a simple analytical approach based on the soil stress state under the foundation can be used to calculate the foundation heave. This paper reports a set of analytical and numerical analysis using the finite-difference code (FLAC 3D), performed on an isolated shallow foundation founded on a swelling soil mass at N’Gaous city in Batna Province, Algeria, subjected to distributed vertical loads. Further, the influence of some parameters on total heave was analyzed, such as the embedded foundation and soil stiffness. The analysis results from the proposed 3D modelling was compared and discussed with analytical results. The numerical results obtained show a good agreement with the analytical solutions based on oedometer tests proposed in the literature, and deliver a satisfactory prediction of the heave of the shallow foundations.

Static and dynamic analyses of the heightening of concrete face gravel dam Limon (Peru)

Aims of research. Expert validation of all proposed design solutions, development of necessary design solutions for the heightening of the Limon dam according to the ICOLD recommendations. Methods. The detailed static and seismic (dynamic) analyses of stressstrain state and seepage of concrete face rockfill dam Limon (Peru) were performed using the advanced software FLAC-3D (USA) and PLAXIS 2D (Holland), respectively. The elasto-plastic model with Mohr - Coulomb criterion with variable shear angles of gravel and pebble zones of dam materials and its foundation soils was used in the static and seismic (dynamic) analyses of the dam. The dynamic nonlinear analyses of stress-strain state of two variants of Limon dam with full reservoir under Maximum Credible Earthquake (MCE) action of the Mar-Chile Earthquake accelerogram. Results. On the base of these analyses the recommendations were developed for the project of the dam heightening from 43 up to 82 m before the initial filling of the reservoir. Expert validation of all proposed design solutions, necessary design solutions for the heightening of the Limon dam were developed according to the ICOLD recommendations.

Comparison of the Results of Analytical and Numerical Models of Pre-Reinforcement in Shallow Tunnels

The steel pipe umbrella is a widely used technology when tunnelling in weak soils in order to create pre-support ahead of the tunnel face. The design of steel pipes is frequently done through simplified analytical approaches which are easy to apply but require proper assessment of the loads acting on the pipe. To provide information on this key design aspect, the results of the comparison between a three-dimensional numerical model developed with the code FLAC 3D and an analytical model based on the approach of a beam on yielding supports is presented and discussed. The comparison refers to a shallow tunnel with an overburden of three times its diameter for two different types of weak rock masses. The obtained results provide suggestions about the load that has to be applied in the analytical model for the design phase.