No abstract

No abstract

No abstract

How to fill the empty annular space behind the segmental lining of tunnels is considered one of the most important questions in mechanized excavation, of which the main aim is to minimize settlement on the earth surface. In addition, the grout is the agent that creates a suitable bed for the segment lining of the tunnel and helps with its tightening. There are different methods of filling the empty space. One of them, using excavation by Earth Pressure Balance-Tunnel Boring Machine (EPB-TBM), is the injection of two-component grout at suitable pressure to the back of the segment as the shield of the excavator moves ahead. The grout utilized has suitable mechanical characteristics and efficiency. The main properties of grout refer to bleeding, fluidity and the results of the Marsh funnel test (ability to pump grout), setting time, gelling time (to avoid grout washing out) and compressive strength of grout (to minimize settlement on the earth level). The present study attempts to review the effect of any constituent materials of two-component grout on the parameters. Consequently, different tests with various constituent materials on the properties of grout were conducted.

No abstract

No abstract

An accurate determination of Hoek–Brown constant mi is of great significance in the estimation of the failure criteria of brittle rock materials. So far, different approaches such as rigidity index method (R-index), uniaxial compressive strength-based method, and tensile strength-based method, and the combination of these two methods (combination based method) have been proposed to calculate the value of mi. This paper aims to thoroughly review the previously existing methods to calculate the value of mi and make comparison between the obtain results to propose the new material constants that provide the best fit with the experimental data. In order to fulfill this goal, a large number of data for different quasi-isotropic intact rock types from the literature were collected and statistically analyzed. Additionally, based on rock types, new material constants are introduced for igneous, sedimentary, and metamorphic rocks. The obtained results proves that for different rock groups (igneous, sedimentary, and metamorphic rocks), R-index method provides the best fit with the experimental data among the others, and it is also independent of rock type. Interestingly enough, there is significant differences in the predicted mi values using different methods, which is more probably due to the quantity and quality of data used in the statistical analysis.

Earth pressure balance (EPB) tunnel boring machines have become increasingly common in the last decade for the construction of tunnels in soft soils. The performance of these machines is so different that they have a major effect on the outside conditions of drilling operations. They use the excavated soil in a pressurized head chamber to apply support pressure to the tunnel face during excavation. A machine may be designed to work in ideal ground conditions. However, natural soils rarely have these properties, and conditioning of the soil is usually necessary to alter its properties to suit the machine. Tunnel excavation is not impossible when the unconditioned soils around the tunnel are coarse and sticky. Effective soil conditioning significantly improves machine performance and control of the soil flow through the screw conveyor. This research presents experimental investigations of soil conditioning for soil/foam and foam/polymer/soil. Methods are also provided to establish a suitable conditioning procedure for determining the optimum foam injection ratio (FIR) for these soils and for studying the effective parameters in soil conditioning such as shear strength and plasticity paste of conditioned soils. Direct shear strength tests were conducted on a small scale, and the plasticity paste of soil was studied by slump tests. The slump tests show that the plasticity of sand/foam and sand/foam/polymer is dependent on the initial moisture content, type of soil, etc. Thus, these parameters are important for achieving optimum FIR and suitable conditioning. In addition, direct shear strength tests show that the injection of foam to sand Type C caused a reduction of 51 % in the internal friction angle. Thus, foams are suitable for modifying soil. Increasing the FIR by more than a special value (optimum FIR) did not change the shear strength significantly.