Numerical simulation of karst environments to study subsidence

Abstract

Karstic zones, due to dissolution of limestone rocks, are a problem in several areas of the world, being associated with damage sustained by facilities, among other issues. A numerical study is presented using Plaxis 2D to analyse terrain subsidence on the surface, considering a transversal section to apply a road load, while cavities in the ground increase due to karsticity. Results allow perception of the surface subsidence, associated with the number of cavities, before and up to collapse of the first voids created. Stress paths developed in the cavities’ opening process are built from the interpretation of results provided by the numerical analyses. These stress paths make it possible to obtain the way in which stress values change between initial and final states, defining an in situ stress variation for the void's presence. Furthermore, it is concluded that there is a tendency towards stability for the superficial displacement and a maximal affected horizontal length associated with a specific number of cavities, despite the fact that more of these are developed in the zone. The rocks and the soil were simulated by Hoek–Brown and Mohr–Coulomb constitutive models, considering the specific characteristics of rocks and soil endemic to Yucatan, Mexico.

Numerical Evaluation for Roads Considering the Addition of Geogrids in Karst Geohazards Zones

“…Rock layer 45 Granular soil layer Furthermore, the cavities modelisation, follow the criterion proposed by Conrado-Palafox [3], since it demonstrated the numerical stability of the cavities with a FEM modeling and the change of the stresses developed in the rock layer. The cavities are subject to an internal pressure to avoid collapse (See Figure 5) [38] in the phases denominated Cavities (Table 1), and thus this pressure (Pi) leads a simplified model of the cavities before the collapse, therefore internal pressure values were obtained iteratively in the model, until to find a minimal internal pressure.…”

“…Once the road reinforcement structure was completed, the static truck load was applied over the asphalt layer. The methodology of opening and creating the cavities in the finite element model was obtained from Conrado-Palafox [3]. In the following section each step of the flow chart is explained more in detail.…”

“…Geotechnical properties considered correspond to the stratigraphy near the coast of Yucatan [40] and were taken from [3]. The material parameters and the constitutive models for the road structure and the geogrids are listed in Table 3.…”

“…The τ mob − p' stress paths in the rock layer are presented in Figure 13 in three different depths y = 0.0 m, −1.9 m and −5.0 m and considering these when there are geogrids (long dashed lines) and without geogrids (grey lines). This last stress paths were collected from the article [3]. It is important to point out, that the magnitude of the static load, is the same in both papers.…”

“…Karst geomorphology in the world is produced by dissolution of carbonate rocks, developing surface characteristics as poljes, sinkholes (dolines), shallow holes and it is through these voids or conduits that groundwater can flow [1]. The karst landscape is part of the 20% of the area in the earth [2] and according to Conrado-Palafox [3], the karst activity has a high influence on the stresses in the ground that produces settlements on the terrain. The settlement represents a handicap in the road design and in its structural performance as well as in other constructions.…”