Reliability-based robust geotechnical design of braced excavations considering multiple failure modes

Reliability design of braced excavation is still a challenge for geotechnical community.Optimization design is a normal method to control the safety and cost of braced excavations.This study presents an advanced reliability-based robust geotechnical design method,which can consider multiple failures and uncertainty of statistical information.A universal design sample was conducted to verify the necessity of considering the uncertainty of statistical information.Ultimate limit state and serviceability limit state of braced excavations were defined,and point estimating method was used to evaluate the standard deviation of failure probabilities.Two-objective and three-objective optimization models were developed to illustrate the application of proposed methods in detail.In addition,the performance of optimization algorithms and further application of multiple-objective models were discussed.The results from this study indicate that the proposed method has a good performance in determining the optimal design with reasonable robustness and cost.New algorithms have higher efficiency in solving nonlinear and multiple-objective optimization problems than the 2nd Non-dominated sorting genetic algo-rithm.This study can guide the design of retaining systems of braced excavations in clay.

Constitutive modeling for mechanical behaviors of geomaterials, newdesigns and techniques in geotechnical engineering

This Special Issue of the Journal of Rock Mechanics and GeotechnicalEngineering （JRMGE） contains 13 papers prepared by internationalexperts on various general topics in geomechanics, rockmechanics and geotechnical engineering. It represents a usefulmix of theoretical developments, testing and practical applications.We present in the following brief details in the papers, alphabeticallyin accordance with the last name of the first author.Barla presents a review of tunneling techniques with emphasison the full-face method combining full-face excavation and facereinforcement by means of fiber-glass elements with a yieldcontrolsupport. This method has been used successfully in difficultgeologic conditions, and for a wide spectrum of ground situations.The validation of the method with respect to the Saint Martin LaPorte access adit along the LyoneTurin Base tunnel experiencingseverely squeezing conditions during excavation is also includedin the paper. The numerical modeling with consideration of therock mass time-dependent behavior showed a satisfactory agreementwith monitoring results.

Robust design of self-starting drains using Random Forest

Groundwater lowering is one of the most important countermeasures to avoid the risk of rainfall-triggered landslides.However,the long-term reliability of many drainage methods is often a matter of concern since the drains may easily get clogged.A new hydraulic-driven self-starting drainage method is presented in this paper.In the proposed Random Forest(RF)based robust design approach for the selfstarting drains,the datasets are generated using an automatically controlled numerical modeling technology.The deterministic analysis is carried out based on uncertain soil parameters and the specific designs selected using Uniform Design(UD).The ensemble of RF models is applied in the design process to improve computing efficiency.Safety requirements,design robustness,and cost efficiency are simultaneously considered utilizing multiobjective optimization.A straightforward and efficient framework that focuses on difficulties caused by an enormous design space is established for the robust design of the self-starting drains,and improved computation efficiency is achieved.The effectiveness of the proposed approach is illustrated with a case study,the Qili landslide in Zhejiang Province,China.

Performance of reliability-based design formats in geotechnical applications

Geotechnical design codes and guidelines are all switching from traditional factor of safety design to modern load and resistance factor design(LRFD)or partial factor design(PFD),in the belief that the latter two bring more flexibility and reliability consistency across various design scenarios,thus produce safe and cost-effective design outcomes.This paper first reviews the LRFD and PFD developed for geotechnical applications.A total of seven methods to calibrate the load and resistance factors are also introduced.The ability of the LRFD and PFD to produce designs with consistent reliability is examined and compared to that of a traditional factor of safety method using two examples of the bearing capacity of strip footings and the global stability of soil nail walls.Results showed that the framework of LRFD offers no apparent advantages over working stress design(WSD)in achieving more consistent reliability for geotechnical structures;the dispersion in design probabilities of failure could be five to seven orders of magnitude difference.The variation will be reduced to three orders if using the PFD.Neither reducing the variability in soil shear strength parameters nor allocating partial resistance factors with respect to soil types would efficiently harmonize the reliability levels when dealing with multiple soil layer conditions.In addition,the uniformity of reliability levels is insensitive to calibrations with or without presetting the load factors.This study provides insights into the LRFD and PFD frameworks currently developed for geotechnical applications.

Assessing the influence of jet-grouting underpinning on the nearby buildings

This paper focuses on the underpinning-induced ground movement due to jet-grouting. Jet-grouting technique can cause distortions as a result of an inaccurate processing sequence and/or errors made at different stages of work execution. The aim of this paper is to determine the minimum value of such movement on the basis of the findings obtained at two similar construction sites located in the Historical Center of Moscow, considering that the maximum value is usually unpredictable. Numerical simulation of the process of soil eroding agrees well with the observational data at the current stage. It was found that the minimum value of deformations （only settlement was considered in this study） due to jetgrouting is no less than 2-3 mm. By contrast, the negative scenario of deformation due to foundation underpinning is clearly demonstrated. Also, this paper provides some general solutions for excavation supporting system as well as for underpinning design.

Energy tunnels:concept and design aspects

Geotechnical structures are increasingly employed as energy geostructures in Europe and worldwide.Besides being constructed for their primary structural role,they are equipped to exchange heat with the ground and supply thermal energy for heating and cooling of buildings and de-icing of infrastructures.This technology can play a fundamental role in the current challenge of addressing the increasing need for clean and renewable sources of energy.This study investigates the possibility of thermal activation of tunnel linings.Particularly,attention will be paid on a new energy segment,which can be used together with tunnel boring machine tunneling to create so-called energy tunnels.Thermal and mechanical designs need to be developed by making effective use of computational methods to quantify the exploitable heat and assess the possible consequences on the surrounding ground and the structure itself.Guidance on how to proceed in this direction will be provided in this study,showing how thermo-hydro and thermo-mechanical numerical analyses can be used to achieve a proper and effective design of energy tunnels.Two examples of possible applications will also be presented.