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Purpose This paper aims to focus on three-dimensional (3D) numerical simulation of a monitored urban underground road consisting of diaphragm walls supported by one row of temporary steel struts and a cover slab in the central area. In addition to the lateral wall displacements, the analysis focuses on the load development in the struts and the evolution of the total stresses at the soil–wall interface, and highlights the 3D effect on the behavior of the structure. Design/methodology/approach Computation by back-analysis has become an important contribution to the understanding of observed phenomena. In this context, this paper investigates a full 3D numerical back-analysis of diaphragm wall deformation using the finite difference code FLAC3D. Findings The instrumentation allows a deep understanding of the ground response and the soil-structure interaction phenomena. It also provides an opportunity to validate numerical models. Using a soil model with simple failure criteria, the wall displacements are strongly influenced by the soil deformation modulus. The strut stiffness considerably influences the wall behavior. The geometrical effects have a significant impact on the induced wall displacements. Originality/value In the present study, the main soil geotechnical characteristics were deduced from laboratory and in situ tests. However, Young’s modulus of the soil has been adjusted to take account of the unloading effect. In the same context, the non-linearity of the elastic characteristics of the steel struts has been taken into account by modeling the struts using their experimental stiffness instead of their theoretical rigidity.

In this research, three- dimension finite difference method was applied to simulate the tunnel excavation by earth pressure balance (EPB) boring machine of Tehran Metro Line 7 tunnel in Iran. Sensi...

Rock mechanical parameters and their uncertainties are critical to rock stability analysis, engineering design, and safe construction in rock mechanics and engineering. The back analysis is widely adopted in rock engineering to determine the mechanical parameters of the surrounding rock mass, but this does not consider the uncertainty. This problem is addressed here by the proposed approach by developing a system of Bayesian inferences for updating mechanical parameters and their statistical properties using monitored field data, then integrating the monitored data, prior knowledge of geotechnical parameters, and a mechanical model of a rock tunnel using Markov chain Monte Carlo (MCMC) simulation. The proposed approach is illustrated by a circular tunnel with an analytical solution, which was then applied to an experimental tunnel in Goupitan Hydropower Station, China. The mechanical properties and strength parameters of the surrounding rock mass were modeled as random variables. The displacement was predicted with the aid of the parameters updated by Bayesian inferences and agreed closely with monitored displacements. It indicates that Bayesian inferences combined the monitored data into the tunnel model to update its parameters dynamically. Further study indicated that the performance of Bayesian inferences is improved greatly by regularly supplementing field monitoring data. Bayesian inference is a significant and new approach for determining the mechanical parameters of the surrounding rock mass in a tunnel model and contributes to safe construction in rock engineering.

In this chapter, we present an efficient Bayesian back-analysis procedure for braced excavations using wall deflection data at multiple points. A response surface method is adopted to efficiently evaluate the wall response. Deflection data for 49 wall sections from 11 case histories are collected to characterize the model error of the finite element method for evaluating the deflections at various points. A braced excavation project in Hangzhou, China is chosen to illustrate the effectiveness of the proposed procedure. The results indicate that the soil parameters could be updated more significantly for the updating that uses the deflection data at multiple points than that only uses the maximum deflection data. The predicted deflections from the updated parameters agree fairly well with the field observations. The main significance of the proposed procedure is that it improves the updating efficiency of the soil parameters without adding monitoring effort compared with the traditional method that uses the maximum deflection data.

A back analysis method based on multioutput least-squares support vector regression machine (MLSSVR) and improved differential evolution algorithm (IDE) is proposed to estimate multiple mec...

At present, with the rapid development of society, concrete has been widely used in various construction. For example, building construction, bridge construction and so on, almost all construction can not be separated from concrete. Therefore, the use of concrete is also profoundly related to the quality and safety of the building. In the process of using concrete, the temperature field of concrete has a great influence on concrete. In the process of concrete construction, cracks are likely to appear due to excessive temperature difference between inside and outside, which has a serious impact on building quality and safety. Therefore, it is particularly important to study the temperature field of concrete and effectively control its temperature. Thermodynamic parameters and boundary conditions have the greatest influence on the accuracy of concrete temperature control experimental calculation. However, obtaining these relevant parameters by means of traditional experiments requires high experimental cost, and is often inconsistent with the actual situation of concrete. Therefore, on the basis of simulated annealing algorithm, this paper makes relevant improvements. Through implementation, it can be found that the improved simulated annealing algorithm can be applied in the back analysis of concrete temperature field, and relevant Suggestions and measures can be put forward for the temperature control of concrete.

A method based on the least-squares method was proposed for the back analysis of water and earth loads using in situ monitoring data of a limited amount of structural strain values for a shallow shield tunnel buried in the soil stratum. Theoretical formulas were used to calculate the internal forces, conduct an assessment of the ultimate limit state, and determine the safety factors of compression and shear. Based upon all of the above, an assessment system was established, and its procedures were illustrated. The highlights of this assessment system are that only a few strain monitoring points are required for the back analysis of the external loads, the internal forces in every position of the segment are calculated by the uniform rigidity ring model, and the safety assessment is conducted by the proposed ultimate limit state formulas. According to the in situ monitoring project in Nanjing subway line 1, the monitoring data of internal forces were close to the back analysis data, which proves the reliability of this method.

Results of laboratory tests on geocell-reinforced soils indicate negligible change in the internal friction angle and development of an apparent cohesion. If sufficient apparent cohesion to withstand applied loads on foundations can be determined, then a suitable kind of soil-geocell composite may be selected among pretested ones by laboratory means. In the present study, using numerical methods of lower bound limit analysis, the required apparent cohesion in the geocell layer to bear the applied load on strip foundations has been determined by back analysis. Effects of contributing factors were evaluated on the results for single and double layer reinforcements.

The paper summarises key results of a class A prediction obtained from 2D and 3D finite element analyses performed for the Embankment Prediction Symposium 2016. In addition class C predictions are included and the changes in input parameters for the finite element model are discussed. Although different constitutive models have been employed in the class A prediction where short term displacements, i.e. after embankment construction, have been considered in addition to long term consolidation and creep settlements only long term displacements are dealt with in this paper. Thus, only results obtained with the Soft Soil Creep model implemented in the finite element code Plaxis are presented. Input parameters have been chosen based on laboratory and in situ experiments and verified by back calculation of undrained triaxial tests and CRS tests. 3D FEA have been carried out confirming that a 2D representation is sufficient for this problem.

Due to the development of joints, wedge failure has become the main failure type of rock slopes. Obtaining accurate parameters is an important prerequisite in studying slope stability. However, these are difficult to obtain due to the restrictions of field conditions. Based on a real and simple wedge, the method of stability analysis and parameter acquisition of a wedge with the nonlinear Barton-Bandis failure criterion is discussed, and then this method is extended to the conventional form of a wedge. With minimal available data, a simple field test and the reliability back analysis method are combined to propose a specific method for determining the most likely combination of nonlinear strength parameters when wedge failure occurs. This approach can provide a simple and practical method for determining the nonlinear strength parameters for engineering applications. Thus, the small frequent collapse incidences in jointed rock slopes can be effectively utilized to provide a reference for the prevention and control of large-scale failure.

For its complicated depositing environment of surrounding rock mass for underground roadways, it is a very important work to back-calculate the mechanical parameters of surrounding rock mass by measurement displacements. To overcome the shortcomings of the traditional neural networks, a new neural network based on black hole algorithm has been proposed. Then, a new back analysis method based on new neural network has been studied. Using this new back analysis method, the mechanical parameters of surrounding rock mass for two deep roadways in Huainan coal mine of China have been back-calculated based on the measurement convergence displacements. Moreover, the good performance of the new back analysis method has been compared with those by back propagation network, neural networks based on genetic algorithm and immunized evolutionary programming proposed in previous studies. The results show that, using the back-calculated parameters, the computed displacements agree with the measured ones. And, considering the computing effect and efficiency comprehensively, the new back analysis method is the good method to determine the suitable mechanical parameters of surrounding rock mass for underground roadways.

In this paper, a new approach for back analysis of a geogrid reinforced soil (GRS) wall failure is presented. A new zero-thickness cohesive fracture element is utilized to simulate the slip surface behind the GRS wall. This element can simulate displacement discontinuity as well as tractions across the shear band effectively. The numerical results are compared with the measured values from the physical test as well as the obtained values from the typical finite element method. This paper demonstrates that the proposed finite element algorithm via discrete modeling of the shear band can effectively improve the quality of numerical back analysis of the soil failure which explains its necessity.

In 1984 an embankment instability occured in a dike recently heightened in stages. After the instability, an extensive research program has been set up to back-analyse the settlements and the pore pressures measured during construction, focussing especially on the effects of shear stress and plastic yielding. Back-calculations have been performed using two uncoupled FEM codes in sequence : one to estimate initial stresses and the total stress increments at the undrained loading phases and another to simulate the intermittent consolidation. A simplified cap model has been introduced for undrained loading. The present paper presents the results of back-calculations using the Soft Soil and the Soft Soil with Creep models. Comparing them with those of the first back-calculations allow to overlook the progress made in soil modelling, to indicate the remaining vital input of engineers judgement and to propose some directions for further development.

The back analysis method is widely used in geotechnical and geological engineering to guide construction and assure safety through feedback analysis and dynamic design. In this study, a back analysis framework was developed by combining a reduced-order model (ROM), simplicial homology global optimization (SHGO), and a numerical model. The ROM was used to approximate the response of the geotechnical structure. Moreover, SHGO was regarded as an optimization method for investigating the mechanical and strength properties of geomaterials based on the ROM using the developed framework. The developed framework was then verified and illustrated by application to a circular rock tunnel. The determined parameters of the rock mass were in excellent agreement with the actual values, and the deformation law predicted by the developed method was consistent with the analytical solution in the tunnel. These results demonstrate that the developed method is feasible for geotechnical and geological engineering. Further, the new framework was applied to a practical slope project. The results indicate that the proposed method is practical, accurate, and convenient when used to determine the geomaterials mechanical properties based on monitored information. Thus, our method is a promising tool for back analysis in practical geotechnical and geological engineering applications.

High core rockfill dams exhibit complex deformation mechanisms because of complicated geological conditions, many material partitions and severe weather conditions. When realistic parameters cannot be obtained through laboratory tests or engineering analogies because of effects of size or time, back analysis is necessary to predict deformation characteristics. This paper proposes a method of deformation back analysis based on the response surface method and genetic optimization theory. The parameters of the creep and Duncan–Chang models for the Pubugou gravelly soil core rockfill dam are sequentially calculated. Back analysis performed using this method efficiently yields more precise results than those obtained from laboratory-determined parameters.

Estimation of the stability of an operating tunnel through a back analysis is a difficult concept to analyze. Specially, when a relatively thick lining is constructed as in case of a subsea tunnel, there will be a limit to the use of displacement-based tunnel back analysis because the corresponding displacement is too small. In this study, DEA is adopted for tunnel back analysis and the feasibility of DEA for back analysis is evaluated. It is implemented in the finite difference code FLAC3D using its built-in FISH language. In addition, the stability of a tunnel lining will be evaluated from the development of displacement-based algorithm and its expanded algorithm with conformity of several parameters such as stress measurements.Keywords: Differential Evolution Algorithm(DEA) Optimization, Back Analysis, FLAC3D, Operating Tunnel 초 록: 운영 중 터널의 역해석을 통한 안정성 평가는 다루기 어려운 개념이다. 특히, 해저터널처럼 라이닝이 상대적으로 두껍게 시공된 경우에 발생하는 내공변위가 작기 때문에, 일반적으로 터널 역해석에 사용되는 변위 기반의 터널 역해석에는 한계가 있을 것으로 판단된다. 여기서는 FLAC3D 프로그램에 내장된 FISH 언어를 사용해서, 다양한 역해석 알고리즘 중에 차분진화 알고리즘의 구축을 통한 터널 역해석에 대한 적용성을 확인하였다. 또한, 변위 기반의 알고리즘 구축과 더불어 응력 계측값 등 다양한 인자의 적합성을 확인하여 터널 라이닝의 안정성을 평가하고자 한다.주요어: 차분진화 알고리즘(DEA) 최적화, 역해석, FLAC3D, 운영 중 터널Copyright ⓒ2016, Korean Tunnelling and Underground Space Association

The Longtan tunnel is one key tunnel along the Hurong (Shanghai---Chengdu) national roadway in the Hubei province of China. This tunnel is a typical long and deep tunnel, with a length of approximately 8700 m and a depth of approximately 500 m. Because of the complicated geological conditions and high initial stress, to compute the stability of the surrounding rock, it is very important to back analyze the material parameters and initial stress from the measured displacements. Based on a novel evolutionary neural network proposed by the author, a new back analysis method is proposed that can be used to simultaneously determine the material parameters and the initial stress. Using this new back analysis method, some typical monitoring sections of the Longtan tunnel are computed. From numerical computations using the back analysis results, it is found that the stability of the tunnel is consistent with engineering practice and that the initial stresses determined from the back analysis coincide very well with the measured values. Therefore, using the proposed back analysis method, the relevant parameters for the entire tunnel can be conveniently obtained.

In views of the limitations of the existing methods for calculating the pile foundation capacity, a back analysis approach of the m-value is introduced. In order to consider the sensitivity of pile behavior to the m-value, the relationships between the applied horizontal loads at pile head and the corresponding m-value along with the pile stiffness changes are studied. Based on statistics data from the extensive in-situ tests, the back analysis results suggest an exponential expression for the m-value in various soil conditions and horizontal displacements at pile head. This method is capable of providing an accurate m-value in calculating the pile responses under lateral loads.

Engineering behaviour of jointed rocks is substantially incompetent as compared to intact rocks due to the presence of joints. Rock bolts are routinely used to reinforce jointed rocks at project sites. The assessment of the strength behaviour of bolt-reinforced jointed rock is a challenging task due to the complex interaction between the joints and the bolts. The present paper attempts to resolve this issue through an experimental study. Natural rock cores with a natural joint, and synthetic rock cores with smooth joint have been tested under uniaxial compression. The tests have been performed on specimens without and with bolt. Grouted steel bolt was used to reinforce the rock. Results from the tests indicate that the provision of the bolt alters the failure mode of jointed rock, and enhances the strength and modulus values. Strength and modulus of the reinforced rock were found to be correlated with each other. It is proposed that the strength of reinforced rock can be obtained from strength and modulus of the intact rock and the modulus of the reinforced rock. The intact rock strength and modulus may be obtained from laboratory tests and the modulus of the reinforced rock may be obtained by back analysing the deformations observed in the field. Sakurai's critical strain concept has been analysed and it is observed that the correlations suggested through proposed empirical approach closely commensurate with critical strain approach and hence give scale free results.

An instrumented section of a 10-m-diameter circular shaft located at a depth of 1.2 km in an average quality rock mass was back analyzed to establish the rock mass behavior. Extensometers were installed radially at four locations and provided the primary data for the back analyses. Three- and two-dimensional continuum models were analyzed using the numerical codes FLAC3Dand Phase2 to assess the rock mass behavior. An initial set of mechanical parameters obtained from empirical relationships were found to give a reasonable match to the measured response of extensometers 2 and 4, when using a Mohr–Coulomb strain softening model. A different set of parameters were needed for FLAC3D when trying to match the significantly higher displacements recorded by only one of the extensometer. It was noted that regardless of the material model and corresponding parameters, the three-dimensional models were not able to give reasonable match to the results of all extensometers. It was shown that for the given problem, there is a theoretical limit for ratio of displacements predicted for different extensometers using a continuum isotropic material model. The two-dimensional models in Phase2, however, gave an apparently better overall match to all the extensometers. Comparison of the results of three-dimensional models with the assumed longitudinal displacement profile for the two-dimensional model indicated that the three-dimensional effects were not adequately captured in the two-dimensional model.

A back analysis procedure implemented in a spreadsheet environment that uses construction monitoring data for supported excavation systems to continuously recalibrate the soil parameters and thus enable updating of the lateral wall deflection predictions is presented. With this framework, the observed maximum wall deflections are used to update the soil parameters through a recently developed semi-empirical polynomial regression model. This paper demonstrates that the updated soil parameters recalibrated from the current stage of excavation can be used to predict the maximum wall deflection in the subsequent stages of excavation. The proposed framework is computationally efficient and can easily be implemented in a spreadsheet. The feasibility and effectiveness of the proposed methodology is illustrated through seven well-documented excavation case histories. The results of the case histories show that the updated soil parameters improve the accuracy of estimations of the wall deflections in braced excavations.

With the development of civil engineering, the box shaped beam has been widely applied in practical engineering. In general, it is composed of concrete and steel and compared with mechanical analysis, little research has been carried on the back analysis of elastic modulus of box shaped beam. With degraded solid element theory, the shell element is deduced and the displacement function is obtained. The necessary observation revision equation and Kalman regenerative matrix are derived. The stochastic filtering back analysis steps of elastic modulus of the box shaped beam are presented and the analytical procedure is compiled. Through analysis of a classic example, some important conclusions about stochastic filtering back analysis of elastic modulus of box shaped beam are obtained.

A ground load prediction method is suggested herein based on the deterioration of the primary support during its durable life. This study includes two contents; firstly, the real behavior of primary support was evaluated and secondly, it was used to propose back analysis procedure based on measurement data. To predict the ground load acting on the primary support, it is important to estimate the real behavior of shotcrete and steel sets by performing experiments. Thus, large-scale experiments were performed on archshaped specimens, combining the application of axial forces and bending moments. The results show that shotcrete can resist only axial forces but steel sets can withstand both axial and flexural loads. Based on these results, back analysis was performed to predict ground load, using the measurement data from a domestic construction site. Compared to other widely used methods, the proposed method predicts 21% to 51% smaller ground load values in different zones. Because the proposed method predicted different ground loads in the same ground conditions, it was deduced that these ground load values were more realistic than the previously predicted results.

For a save design and construction and the technical and economic optimisation of deep foundation systems a realistic modelling of the soil-structure interaction is necessary. Especially for the hybrid deep foundation system Combined Pile-Raft Foundation (CPRF) this has to be considered. Based on an adequate soil investigation, in-situ pile load tests and a high-level design using the Finite-Element-Method (FEM) it is possible to design complex foundation systems for high-rise buildings even in soft soil conditions. For guarantee of the ultimate limit state (ULS) and the serviceability limit state (SLS) an independent peer review and the application of the observational method is necessary. The paper explains some special aspects of the optimisation process of the design and presents several projects from engineering practice, where the CPRF has been successfully applied.

Site geotechnical engineers are often reliant on elastic numerical modelling to assist with mine design and the selection of appropriate stoping sequences. Although plastic numerical models are often preferred, site engineers do not have access, or the ability, to use these codes. Hence, three-dimensional elasto-plastic analyses are not viable at most sites. The challenge for the site engineers is to use the available tools most effectively, and present the results in a way that most clearly communicates the mine design requirements. A first step is to establish a mine design criteria, which should not be confused with failure criteria. Mine design criteria correlate observed conditions with modelled stress states at a specific location. An effective mine design criterion then enables the assessment of probable future ground conditions on modelled stress states. Many design criteria could be used concurrently on a single mine site, as different failure mechanisms cannot be assessed with the same criterion. Comparing actual conditions or measurements with modelled stress states is the only way to establish a correlation that could be generalised into a design criterion. During the back analysis process, the actual response of the rock mass is recorded and categorised with a damage classification system and compared to different modelling result parameters. Different correlations are evaluated, and the criterion with the most consistent performance selected to make predictions of future ground conditions. This paper shares case studies where design criteria were successfully used at the Callie underground mine, and discusses the potential application areas for future evaluations. Keywords: back analysis of elastic numerical modelling

Laboratory experiment and back analysis are common methods for selecting shear strength parameters. However, every way has its shortcomings. A way combining two methods is used to determine shear strength parameters for Hutoumao landslide. The result can meet the need of project according to comparison experience value.

The paper deals with the back analysis method in geotechnical engineering, that goal is evaluation the more objective and reliable parameters of the rock mass on the basis of in-situ measurements. Stress, deformational, strength and rheological parameters of the rock mass are usually determined by some inaccuracies and errors arising from the complexity and variability of the rock mass. This higher or lower degree of imprecision is reflected in the reliability of the mathematical modelling results. The paper presents the utilization of direct optimization back analysis method, based on the theory of analytical functions of complex variable and Kolosov-Muschelischvili relations, to the evaluation of initial stress state inside the rock massif.

Accurate prediction of soil parameters is a challenge to braced excavation systems design, especially when the wall retains “Fill” containing artificial materials. This paper presents a case study of a braced diaphragm in situ wall supporting 14 m of Fill in Egypt with the objective of estimating representative parameters for the Fill. The wall, designed based on conservative strength and deformation parameters, was monitored using inclinometers. Back analysis is conducted to determine representative Fill parameters using the beams on elastic foundation (BEF) and finite element (FE) methods. The FE analysis is conducted using the hardening soil constitutive model, and a comparison is made with Mohr–Coulomb (MC) model. The results show that the hardening soil model can reproduce the wall movement better than MC model and the BEF method. Hence, representative parameters are estimated for the retained Fill. It is illustrated that adopting the deduced values could result in considerable savings.

Through the analysis of ‘gap parameter’ and ground movement pattern in shield tunnel, this paper researched and corrected the model of ‘equivalent circle zone’ proposed by predecessors. The ‘equivalent circle zone’, which is a comprehensive reflection of shield gap, grouting filling and stratum perturbation, is considered to be unequal thickness in this paper. With the measured data of practical shield tunneling, the unknown parameters of corrected ‘equivalent circle model’ can be obtained by back analysis through numbering analysis. The back analysis of Shen Zhen line-5 is carried out to validate the rationality of the method proposed in this paper. Research shows that: the corrected model can reflect the feature and values of ground settlement more factually than the previous model and can offer a reference to predict ground deformation during shield tunneling.

Long time monitoring is acquired to obtain the displacement data for displacement-based geotechnical material back analysis, and these data are hard to be measured under some special condition, such as earthquake. For a simple homogeneous slope, the position of a critical failure surface is determined by value of c/tan ϕ. Utilizing upper bound theorem of limit analysis, the external work rate and internal energy for normal slope under earthquake forces are given, and the formula for minimum safety factor is derived. On this basis, the equation of slip surface and the surface depth of a given position are solved. In this way, the strength parameter can be analyzed by known slip surface depth. For practical use, the surface depth for a given slope under varying strength parameter is presented. Finally, two examples are given to show its simplicity and effectiveness.

The surrounding rock strain field monitoring have been done during a highway tunnel excavation. The rock rheological parameters was inversed by neural network based the field monitoring data. The predicted value and the field monitoring data have been compared, the result shows that the difference is 12%, the predicted value is credible.

A new method of displacement back analysis, named SVM-CTS, was proposed based on support vector machine (SVM) and continuous tabu search (CTS). On the one hand, SVM-CTS used SVM to build the nonlinear mapping relationship between the measuring point displacements and rock and soil mechanics parameters of positive analysis based on the study samples. On the other hand, SVM-CTS used the global optimization performance of CTS to catch the optimal rock and soil mechanics parameters in the global space. The nonlinear mapping relationship built by SVM can fit and forecast the measuring point displacements under different parameters with high accuracy. CTS can prevent object function from trapping in local optimum and improve precision of back analysis. Case study shows that SVM-CTS can be well applied to the displacement back analysis in geotechnical engineering.

In this paper, the authors present a probabilistic back-analysis of a recent slope failure at a site on Freeway No. 3 in northern Taiwan. Post-event investigations of this failure found uncertain strength parameters and deteriorating anchor systems as the most likely causes for failure. Field measurement after the event indicated an average slip surface of inclination 15°. To account for the uncertainties in input parameters, the probabilistic back analysis approach was adopted. First, the Markov Chain Monte Carlo (MCMC) simulation was used to back-calculate the geotechnical strength parameters and the anchor force. These inverse analysis results, which agreed closely with the findings of the post-event investigations, were then used to validate the maximum likelihood (ML) method, a computationally more efficient back-analysis approach. The improved knowledge of the geotechnical strength parameters and the anchor force gained through the probabilistic inverse analysis better elucidated the slope failure mechanism, which provides a basis for a more rational selection of remedial measures.

A rigorous back analysis of shear strength parameters of landslide slip was presented. Kinematical element method was adopted to determine factor of safety and critical failure surface, which overcomes the disadvantage of limit equilibrium method. The theoretical relationship between the combination of shear strength parameters and stability state was studied. The results show that the location of critical slip surface, F/tan ϕ and F/c depend only on the value of c/tan ϕ. The failure surface moves towards the inside of slope as c/tan ϕ increases. According to the information involving factor of safety and critical failure surface in a specific cross-section, strength parameters can be back calculated based on the above findings. Three examples were given for demonstrating the validity of the present method. The shear strength parameters obtained by back analysis are almost consistent with their correct solutions or test results.

The selection of material parameters relates to the excavation stability of the underground caverns. However, back analysis is an efficient method to evaluate mechanical parameters. Given the defects of BP neural network, such as low capability of generalization and long training time, by using GA, which have global optimization ability to optimize the BP neural network weights. The parameter of surrounding rock was designed by uniform and orthogonal method, not only reduced the iterative time also improved the accuracy of the prediction. The proposed method is further illustrated with its application to the underground cavern of Lvchunba railway tunnel. Based on the surrounding rock’s parameters obtained by back analysis, the displacement of the surrounding rock was predicted. The results showed that the error between numerical calculation value and actual monitoring value was 13.2%,-8.3%,-8.9%,9.4% respectively.

ZHANG Xiedong Ph.D Professor Wuhan University of Technology,Hubei, ChinaZhangxd@189.cnZhang Xiedong, born 1964, received his civil engineering doctor degree from the Wuhan University of Technology.The main 2D back analysis model is established considering actual situations of the way the arch ring is set and the composition of its section. After introducing the stress release rate and the load bias parameter to composing the integral equation of the influence value, the data of arch crown settlement and horizontal convergence can be used to back analyse the load status of the supporting structure. By changing the modeling parameters, the optimizing construction scheme can be simulated and the most unfavorable stress value is analyzed, which can provide references to similar engineering.