Amoussou Coffi Adoko

Mechanism of the Mudstone Tunnel Failures Induced by Expansive Clay Minerals

Expansive clay minerals can be a serious threat to underground rock structure because of their swelling behavior when absorbing water. Roof and wall collapse as well as large deformation were observed in Xiaotun Coal Mine, Guizhou Province, China. This paper studies the characteristics of expansive clays in order to understand the mechanism of the mudstone tunnel failures in the mine. The physical and mechanical properties of the tunnel surrounding rock samples, including mudstone, silty mudstone, argillaceous siltstone and fine sandstone were determined. X-ray diffraction analysis was conducted to determine the mineralogical composition while the scanning electron microscope was used to examine the internal structure of the different samples. The results indicate that the illite–smectite and the montmorillonite are the main minerals composing the rock samples. A series of micro-cracks and pores occur in the samples which suggest a good hydraulic conductivity. The results indicate that the mudstone has poorer mechanical properties in comparison to the fine sandstone. Also, the Flac3D numerical simulations were conducted and it was shown that the large deformations were consistent with the field observation due to weak mechanical properties of the surrounding rock under seepage action especially with the increase of water head and porosity. It is concluded that internal structure and mechanical strength of the mudstone is weakened by the illite–smectite and the montmorillonite mineral content as well as the combined action of underground water causing physical disintegration.

An Illustration of Determining Quantitatively the Rock Mass Quality Parameters of the Hoek–Brown Failure Criterion

In tunneling, determining quantitatively the rock mass strength parameters of the Hoek–Brown (HB) failure criterion is useful since it can improve the reliability of the design of tunnel support systems. In this study, a quantitative method is proposed to determine the rock mass quality parameters of the HB failure criterion, namely the Geological Strength Index (GSI) and the disturbance factor (D) based on the structure of drilling core and weathering condition of rock mass combined with acoustic wave test to calculate the strength of rock mass. The Rock Mass Structure Index and the Rock Mass Weathering Index are used to quantify the GSI while the longitudinal wave velocity (Vp) is employed to derive the value of D. The DK383+338 tunnel face of Yaojia tunnel of Shanghai–Kunming passenger dedicated line served as illustration of how the methodology is implemented. The values of the GSI and D are obtained using the HB criterion and then using the proposed method. The measured in situ stress is used to evaluate their accuracy. To this end, the major and minor principal stresses are calculated based on the GSI and D given by HB criterion and the proposed method. The results indicated that both methods were close to the field observation which suggests that the proposed method can be used for determining quantitatively the rock quality parameters, as well. However, these results remain valid only for rock mass quality and rock type similar to those of the DK383+338 tunnel face of Yaojia tunnel.

Fuzzy Inference System-Based for TBM Field Penetration Index Estimation in Rock Mass

Estimating the field penetration index (FPI) is an essential task in tunneling as the FPI is used to determine the tunnel boring machine (TBM) performance. In this study, fuzzy inference system (FIS) modelling is implemented to predict the FPI. Several models including fuzzy clustering and knowledge-based models were proposed. Data from the Queens Water Tunnel underneath Brooklyn and Queens were used to establish and validate the models. The input parameters include the rock type, uniaxial compressive strength, Brazilian tensile strength, rock brittleness (BI) of the intact rock, the angle between the plane of weakness and the TBM driven direction (Alpha), the distance between planes of weakness (FS), and the TBM cutter load. In order to evaluate the effect of the characteristics of the fractures on the FPI prediction, several models with different inputs and dataset structures were explored. The models were tested with independent datasets and performance indices used included the coefficient of determination R2, values account for (VAF), root-mean square error (RMSE) and mean absolute percentage error (MAPE). Overall, the model performance results were satisfactory with R2, VAF, RMSE and MAPE ranging between 0.79–0.92; 79.42–92.06%; 6.66–11.05; and 5.68–8.96%, respectively indicating good predictability capability. The models based on fuzzy clustering yielded higher accuracy. It was established that BI, Alpha and CL were the parameters controlling mostly the FPI. Based on that, the knowledge-based model was developed and satisfactory results were achieved as well. It was concluded that the FISs could be used to estimate the FPI values with a reliable accuracy.

Prediction of Rock Brittleness Using Genetic Algorithm and Particle Swarm Optimization Techniques

Determining the rock brittleness is often needed in a wide range of rock engineering projects; however, direct measurement of the brittleness are expensive, time consuming and also the test devices is not available in every laboratory. Due to that, assessing the brittleness of rock as a function of some rock properties such as uniaxial compressive strength, Brazilian tensile strength and density of rock is unavoidable. The aim of this paper is to develop predictive models for estimating the rock brittleness using two techniques, genetic algorithm (GA) and particle swarm optimization (PSO). For this aim, four different models including linear and non-linear were developed using GA and PSO techniques. Further, in order to validate the accuracy of proposed models, various statistical indices including the root mean square error (RMSE), the variance account for (VAF), the coefficient of determination (R2) and performance index (PI) were computed and utilized herein. The values RMSE, VAF, R2 and PI ranged between 2.64–5.25, 82.58–93.06%, 0.851–0.932 and 1.480–1.708, respectively; with the quadratic form of the GA approach indicating the best performance. It is concluded that both the GA and PSO techniques could be utilized for predicting the rock brittleness; however, GA-quadratic model is superior.

Generating Irregular Models for 3D Spherical-Particle-Based Numerical Methods

The realistic representation of an irregular geological body is essential to the construction of a particle simulation model. A three-dimensional (3D) sphere generator for an irregular model (SGIM), which is based on the platform of Microsoft Foundation Classes (MFC) in VC

Study on the Mechanical Behavior of Excavation and Support Construction of Shallow Tunnel

In this paper, the mechanical behavior of excavation and support construction of Weishe tunnel, which is a section of the Yangwu expressway, is studied quantitatively using 3D finite difference numerical simulation method. A sequential excavation method is used and the results show that the vault settlement occurs mainly on the phase of upper bench excavation. The convergences of upper and lower sidewalls occur mainly on the phase of lower bench excavation. During the construction, the surrounding rock pressure in the vault and sidewall of the tunnel decrease. Axial force of anchor reaches the maximum value after the finish of second lining. However, the surrounding rock pressure and internal force of steel arch reach the maximum value after completing the upper bench excavation, and then become as smaller as half of the peak value during the lower bench excavation.

Dam Phreatic Line Simulation on FLAC3D: A Case Study

Based on fundamental principle of saturated/unsaturated flow and characteristic of FLAC3Ds showing pore pressure nephogram, this paper was aimed at obtaining steady seepage within the dam, capturing the face on which pore pressure was equal to zero, and then identified the phreatic line of the dam. Using this method, phreatic line of a tailing dam in a mine was computed. The results were compared to field data. It was indicated that, the phreatic line calculated by this method was slightly higher in the mass, but was lower near the surface of the dam. This method has the merit of being faster and simpler to obtain approximate phreatic line of dams in comparison with site exploration.