Intelligent Stability Design of Large Underground Hydraulic Caverns: Chinese Method and Practice

The global energy shortage has revived the interest in hydroelectric power, but extreme geological condition always pose challenges to the construction of hydroelectric power stations with large underground caverns. To solve the problem of safe design of large underground caverns, a Chinese-style intelligent stability design, representing recent developments in Chinese techniques for the construction of underground hydropower systems is presented. The basic aim of this method is to help designers improve the stability and design efficiency of large underground hydropower cavern groups. Its flowchart consists of two parts, one is initial design with an ordinal structure, and the other is dynamic design with a closed loop structure. In each part of the flowchart, analysis techniques, analysis content and design parameters for caverns’ stability are defined, respectively. Thus, the method provides designers with a bridge from the basic information of objective engineering to reasonable design parameters for managing the stability of hydraulic cavern groups. Application to two large underground caverns shows that it is a scientific and economical method for safely constructing underground hydraulic caverns

chenxiating/urban_green_gray_model: Initial release v1.0

This release contains the simulation scripts used for manuscript "Integrating the spatial configurations of green and gray infrastructure in urban stormwater networks" in Water Resources Research

A simple shear strength model for interlayer shear weakness zone

International audienceInterlayer shear weakness zone (ISWZ) is a widespread zonal weak geotechnical system with variable thickness in rock masses, representing a potential threat to the overall stability of structure constructed on or within the rock mass due to their relatively poor mechanical properties. Its shear behaviour depends on both the interlayer soil and the interlayer soil/host rock interface (soil/rock interface). In this study a dynamic approach is adopted by treating ISWZ as an unfilled joint (rock/rock interface) that is increasingly filled with interlayer soil of variable thickness. Based on the available experimental data, a simple shear strength model is developed, capable of describing both the shear behaviours of interlayer soil and soil/rock interface. Because the geometric factors (i.e., the thickness of interlayer soil and the morphology of interface) and the mechanical conditions (i.e., normal stress, uniaxial compressive strength of rock and shear strength of interlayer soil) are all taken into account, the combining mechanical effect of interlayer soil and soil/rock interface on the ISWZ is totally included in the model. This is partly confirmed by the good agreement between the model prediction and the experimental results from laboratory and field tests

Use of the equivalent continuum approach to model the behavior of a rock mass containing an interlayer shear weakness zone in an underground cavern excavation

International audienceAn interlayer shear weakness zone (ISWZ) is a weak zonal geotechnical system of variable thickness that occurs between different rock strata (e.g., tuff and basalt). At the site of the future Baihetan hydropower station, Sichuan Province, China, because of the relatively poor ISWZ mechanical properties, the overall stability of the underground powerhouse is potentially at risk. In this study, to evaluate the effects of ISWZs on the stability of the future underground powerhouse by means of three-dimensional continuum modeling (3-D continuum modeling), the concept of a virtual rock mass composed of ISWZ and host rock is proposed. An equivalent continuum approach, including a rock soil composite material (RSCM) model, is elaborated, with corresponding expressions for the input parameters. Comparisons were made between the predictions from the RSCM model, the results obtained by an analytic method, and existing data from physical model tests. The comparison showed that all three types of information showed good consistency in terms of failure mode and strength. This indicates the suitability of the RSCM model for describing the behavior of a rock mass containing discontinuities. Furthermore, comparison between the predictions of the proposed equivalent continuum approach, the joint element approach, and the solid element approach for a deformation of a test tunnel section containing an ISWZ show that the results produced by the first two approaches are similar, but much smaller than that using the third approach. Further comparison of the actual state of the ISWZ-containing rock mass in the test tunnel section confirmed the applicability of the proposed equivalent continuum approach to prediction of deformation of the rock masses containing ISWZs at the future Baihetan underground powerhouse site

Effects of water content and particle crushing on the shear behaviour of an infilled-joint soil

International audienceRing shear tests were carried out on a compacted low plasticity infilled joint soil from Beihetan site. Different initial water contents (5.0, 9.0 and 13.5%) were considered. It was observed that the failure envelope is linear for the peak deviator stress but highly non-linear for the residual deviator stress in the range of high normal stresses (higher than 400 kPa), evidencing the particle crushing effect on the residual strength. Furthermore, this particle crushing effect was water content dependent: the residual friction angle is larger at higher water content. Further grain size analysis on the portion taken in the zone of shear band after each test was performed, and changes of the fractions of 75 µm and 2 µm were compared for different water contents. The results indicate clearly that the effect of water content on particle crushing depends on the particles size. For large particles (>75 µm), water content increase enhances the particle crushing by the fracture mechanism. On the contrary, for smaller particles (< 2 µm), water content increase reduces the particle crushing by the mechanism of attrition or abrasion. Deeper analysis of the effect of the ratio of the final to initial fraction of the particle size less than 2 µm, S2, on the shear strength suggests that the effect of particle crushing on the residual shear strength is mainly through the production of extra clay size particles (< 2 µm)

Back Analysis of Rock Hydraulic Fracturing by Coupling Numerical Model and Computational Intelligent Technology

Hydraulic fracturing is widely used to determine in situ stress of rock engineering. In this paper we propose a new method for simultaneously determining the in situ stress and elastic parameters of rock. The method utilizing the hydraulic fracturing numerical model and a computational intelligent method is proposed and verified. The hydraulic fracturing numerical model provides the samples which include borehole pressure, in situ stress, and elastic parameters. A computational intelligent method is applied in back analysis. A multioutput support vector machine is used to map the complex, nonlinear relationship between the in situ stress, elastic parameters, and borehole pressure. The artificial bee colony algorithm is applied in back analysis to find the optimal in situ stress and elastic parameters. The in situ stress is determined using the proposed method and the results are compared with those of the classic breakdown formula. The proposed method provides a good estimate of the relationship between the in situ stress and borehole pressure and predicts the maximum horizontal in situ stress with high precision while considering the influence of pore pressure without the need to estimate Biot’s coefficient and other parameters