Awareness from geomechanics properties where underground structures were built is main and basic option in design, support and stability analysis for such structures. knowledge from geomechanics properties, stability control and optimization available support system, monitoring results and back analysis method as a tools for reassessment input data in execution time and after generate underground structure were used. So that to access geomechanics properties of TBM launch cavern Asgaran, direct back analysis method using optimization technique can be used. To appraisal main geomechanics parameter for tunnel design, elastic modulus (E) and ratio of horizontal to vertical stress (K), in this cavern was performed by univariate Optimization Technique and FLAC3D software. To effecturate between monitoring result and to exhibit stability analysis of ceiling and walls, Direct Strain Control Technique (DSCT) suggested. So results showed that the ceiling and walls of cavern stable and didn't require essential support.


For design and construction of an underground structure, it is important to predict the in situ stress state and mechanical properties of surrounding rock masses. Some field tests are usually conducted for such purpose. For example, plate-bearing tests are used to determine the deformation modulus of rock masses. Hydraulic fracturing tests and borehole stress-relief tests are applied to measure in situ stresses. Due to the influences of joints or fissures, these field tests are often costly and time-consuming with dispersive data covering small test domain. Sometimes, large-scale field tests are necessary for major excavation projects in rocks. Alternative indirect methods can be very helpful for cost-effective determination and validation of the field test results[1]. Because displacements of rock masses induced by excavation can be measured easily and reliably. the displacement-based backanalysis techniques have been always used in many monitoring projects. For stability support assessment of TBM launch cavern Asgaran are used from monitoring of displacement results. Then with assist a three dimensional (3-D) back analysis method main design parameters control, deformability module (E) and ratio horizontal stress to vertical stress (K) are determined. Upshot with using of direct strain control technique (DSCT) stability of this cavern is perused.

Back analysis

Back analysis is generally defined as a technique which can provide the controlling system parameters by analyzing its output behavior. This technique has been constantly studied in rock engineering during the last decade. In back analysis of rock engineering problems, the main objective is to determine the initial stresses and material constants, etc., from the field measurement data. Back analysis problems may be solved in two different ways, defined as inverse and direct approaches[2]. In the inverse approach, the mathematical formulation is just the reverse of ordinary stress analysis. It numerically solves some of the material parameters or loading conditions based on 876 measured displacements. Rapid numerical solution is one of the advantages of the inverse method. However, the number of the measured values should be greater than the number of unknown parameters, so that optimization techniques can be used to determine the unknowns.

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