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The cultivation of innovative talents is an important development strategy in China. Especially in the stage of basic education, there is an urgent need for specific instructional strategies for cultivating innovative capability. Based on the theories of "Hands-On Inquiry learning" and Constructionism and teaching practice, this study put forward an innovation capability cultivation oriented design-based learning model in junior high school information technology curriculum. The model has three characteristics: simple teaching links, reverse teaching design and equal teacher-student relationship. It is hoped to provide guidance on teaching operation level for frontline information technology classroom teaching, or for other disciplines’, and to provide a reference for international scholars to do the research about constructing instructional models for skill cultivation in the 21st century.

The facing is a key component for the design of soil nail walls. However, current design specifications of soil nail walls in China do not specify methods for estimation of facing tensile forces, which has posed challenges for engineers to produce consistent, safe, and cost-effective facing designs. This study first constructs the facing tensile force as the product of the maximum nail load and a facing factor. Then a database containing 91 measured facing tensile force data collected from the literature is developed and used to calibrate the facing factor matching six maximum nail load models that are commonly adopted in China, namely, the simplified incremental calculation models based on the Rankine and Coulomb earth pressure theories, the China Academy of Building Research model, and the China Association for Engineering Construction Standardization model. Based on the developed database, the accuracies of the six proposed models for facing tensile forces are demonstrated to be unbiased on average and the dispersions in the prediction accuracy are ranked from low to medium. Furthermore, the influences of three wall working conditions on prediction accuracy of the developed models are investigated and shown to be practically insignificant. Last, the model biases are characterised as lognormal random variables.

Machine learning (ML) approaches have stormed nearly all engineering fields since recent years. However, the situation is somehow subtle in civil engineering practice, especially in the sub-field of geotechnical engineering where data from real-life projects are usually scarce, which in turn prevents development of meaningful mapping tools based on ML techniques. This study first shares a database containing a total of 376 measured horizontal displacements from instrumented soil nail walls reported in the literature. Then, these data are utilized to develop three types of ML models for mapping the wall horizontal displacement along depth, including artificial neural network (ANN), random forest (RF), and support vector machine (SVM). The uncertainties of the ANN, RF, and SVM models are then quantitatively evaluated using bias statistics where bias is defined as the ratio of measured to predicted horizontal displacement. The three ML models are proved to be accurate on average with medium dispersions in prediction, which outperform the existing simple empirical regression models. Probability distribution functions for those biases are also characterized. This study demonstrates that introduction of machine learning approaches into the reliability-based design framework for soil nail walls and other geotechnical structures is promising.

The shearing mechanical properties of an interface are of great significance to the stability analysis of soil–structure interaction in practice. Based on the theory of damage mechanics, an interface subjected to shearing conditions can be divided into two parts: damaged and undamaged, together bearing the entire shear load. Under the action of shear load, the damaged part gradually increases and the area of the undamaged part simultaneously decreases. Eventually, the interface is completely damaged. The damage variable modelled as a Weibull distribution is introduced to describe the damage evolution of the interface. According to the principle of force equilibrium on the interface, the shear damage softening model is established, which can describe the shear softening behaviours as well as estimate the residual strength of the interface. The physical meaning of each parameter in the model is elaborated and the relationship with normal stress is established. A method to determine each parameter is proposed. Based on the Abaqus software platform, the model is coded into the friction subroutine, and numerical simulation is carried out with reference data. The shear damage model is validated using experimental data and numerical simulation results.

This study first develops a database containing 56 measured facing tensile forces from instrumented soil nail walls during or at completion of construction. Based on the compiled database, the accuracies of both default and modified federal highway administration (FHWA) simplified models for estimation of short-term facing tensile forces are evaluated. Here, accuracy is defined by the model bias computed as the ratio of measured to predicted facing tensile force. The analysis results show that predictions are highly conservative and highly dispersive using the default model, and moderately conservative and medium dispersive using the modified model. Moreover, the prediction accuracy is statistically correlated with magnitudes of the computed facing tensile forces and several model input parameters. An out-of-sample approach is used to develop and validate a recalibrated FHWA model which is then demonstrated to have least empirical constants but best accuracy compared to the default and modified models. The biases for the three models are characterized as lognormal random variables. An example of reliability-based analysis for facing flexure limit state is illustrated to both elaborate the application and highlight the benefit of using the recalibrated model for design practice from the perspective of cost-effectiveness.

This study compiles a broad database containing 312 measured maximum soil nail loads under operational conditions. The database is used to re-assess the prediction accuracies of the default Federal Highway Administration (FHWA) nail load model and its modified version previously reported in the literature. Predictions using the default and modified FHWA models are found to be highly dispersive. Moreover, the prediction accuracy is statistically dependent on the magnitudes of the predicted nail load and several model input parameters. The modified FHWA model is then recalibrated by introducing extra empirical terms to account for the influences of wall geometry, nail design configuration, and soil shear strength parameters on the evolvement of nail loads. The recalibrated FHWA model is demonstrated to have much better prediction accuracy compared to the default and modified models. Next, an artificial neural network (ANN) model is developed for mapping soil nail loads, which is shown to be the most advantageous one as it is accurate on average and the dispersion in prediction is low. The abovementioned dependency issue is also not present in the ANN model. The practical value of the ANN model is highlighted by applying it to reliability-based designs of soil nails against internal limit states.

This study first presents accuracy assessments of two default models proposed in two popular soil nail wall design specifications and their calibrated versions for estimation of maximum soil nail loads under operational conditions. The assessments are based on a general nail load database reported in the literature. Evaluation results showed that predictions using the default and calibrated models are unsatisfactory as the dispersions are high to extremely high. Simple calibration terms are introduced to the calibrated models for performance enhancement. The recalibrated models are shown to be accurate on average, and the prediction dispersions are significantly reduced. The model biases for the above six models are demonstrated to be lognormal random variables. Individual reliability-based designs for the nail pullout and nail-in-tension limit states using the six models are carried out. System reliability of nails against internal failures is also explored. The correlation between the two limit states is investigated, and its influences on system reliability evaluation are discussed. The practical value of model calibration is demonstrated as using the recalibrated models for nail designs leads to the most cost-effective design outcomes. This study represents a solid step toward development of reliability-based design framework for soil nail walls.

Statistical evaluation of the accuracy of effective stress method (ESM) equations for prediction of the ultimate bond strength of soil nails was performed using the maximum likelihood method. Over 500 pullout tests were examined for soil nails installed in two different Hong Kong soils. The data were parsed into tests that reached pullout failure before reaching 90% of the nail tendon yield strength (uncensored data) and tests terminated at the 90% yield strength criterion (censored data). A log-likelihood function was constructed to include both types of bias data, where bias is the ratio of measured to predicted ultimate nail bond strength. The accuracy of two ESM equations previously reported in the literature was evaluated using both uncensored data alone and then combined censored and uncensored data. A revised ESM equation with two empirical coefficients is calibrated using the larger combined data sets, and its accuracy is compared to the two earlier formulations using the same expanded database. The revised formulation has the advantage that mean of bias values is 1 for both soil types and there are no bias dependencies with magnitude of predicted pullout capacity or overburden pressure. However, for one soil type the COV of bias values is less using the larger database and for the other soil type the value is greater. A practical lesson for calibration of equations of the type investigated here is that including censored data for calibration is of great importance to reach a better and more thorough understanding of the performance of the model.

Soil nails are extensively used to stabilize existing slopes and new cuts in Hong Kong. The current method adopted for estimation of nail bond strength is the effective stress method (ESM), which h...

The facing design of soil nail walls against flexure, punching shear, and headed-stud tensile limit states has been rarely studied within the reliability-based design framework. This study...

This paper demonstrates reliability-based design for tensile rupture and pullout limit states for mechanically stabilized earth (MSE) walls constructed with geosynthetic (geogrid) reinforcement. The general approach considers the accuracy of the load and resistance models that appear in each limit state equation plus uncertainty due to the confidence (level of understanding) of the designer at the time of design. The reliability index is computed using a closed-form solution that is easily implemented in a spreadsheet. The general approach provides a quantitative link between nominal factor of safety, which is familiar in allowable stress design practice, and reliability index used in modern civil engineering reliability-based design practice. A well-documented MSE wall case study is used to demonstrate the general approach and to compare margins of safety using different load and resistance model combinations. A practical outcome from the case study example is the observation that the pullout limit state is much less likely to control design than the ultimate tensile rupture state for walls with continuous reinforcement coverage. The more accurate “simplified stiffness method” that is used to compute tensile loads in the reinforcement under operational conditions is shown to generate a more cost-effective reinforcement option than the less accurate American Association of State Highway and Transportation Officials (AASHTO) simplified method.

The design of soil nail walls in China is dictated by two national technical specifications, namely, Technical Specification for Retaining and Protection of Building Foundation Excavations by China Academy of Building Research (CABR) and Specifications for Soil Nailing in Foundation Excavations by China Association for Engineering Construction Standardization (CECS). Each specification proposes a method for computation of maximum nail loads while the prediction accuracy of the method is still not yet fully assessed. To fill the gap, this study evaluates the accuracies of the two methods using 144 measured nail loads collected from fully instrumented soil nail walls in China. The influences of three wall working conditions on the prediction accuracy of the methods are also examined. The results show that the two default methods overestimate the maximum nail loads by about 40% on-average and the spread in prediction generally ranges from 70% to 100%. However, the prediction accuracy is not significantly influenced by wall working conditions. Simple calibrations with two or three empirical constants are introduced to the two methods to achieve great improvements in prediction accuracy. The calibrated CABR and CECS methods are demonstrated to be unbiased on average and the prediction dispersions are reduced to about 50%.

Deterioration modelling has been a bottlenecking step towards risk-informed asset management of municipal water distribution networks. To close the gap, we proposed a two-time-scale (TTS) point process model on a pipe level for modelling and prediction of water main breaks. This paper presents the characterization, statistical parameter estimation, probabilistic features, and application of the model. Combining Poisson and renewal models into one, the proposed TTS process is characterized by a conditional intensity function of two time variables-one in a pipe clock for overall pipe aging and the other in a repair clock for local renewal. As a result, different aging patterns including the complicated bathtub-type behaviour can be modelled. A novel statistical method that combines data augmentation and Markov Chain Monte Carlo was developed for model estimation to deal with partially missing event histories. A case study using real-life data collected from a regional municipality in Canada was presented to illustrate the application of the proposed model. The modelling process ranging from model estimation, verification, validation, and updating to application in asset management was thoroughly demonstrated. This study also demonstrated that one must use the full distributions of the parameters to obtain an unbiased prediction of mean number of water main breaks. The proposed model was also compared with the Poisson process model in terms of break intensity, survival probability, mean cumulative number of breaks, and mean annual number of breaks. The implications of the different results to asset management were carefully discussed as well. Last, the ability of the proposed model to capture the maintenance effectiveness of pipe repair was proven. This work represents a solid advancement towards holistic assessment of the aging risk of a municipal water distribution network.

Resistance factors for load and resistance factor design (LRFD) of pullout limit state of both permanent and temporary soil nails are calibrated against a wide design space using the current Federa...

The technique of pit-in-pit excavations is increasingly used in China to provide an efficient solution of maximizing the utilization of underground space while minimizing the amount of solid waste due to excavations. One of the critical steps toward the successful implementation of the pit-in-pit excavation technique is to rationally estimate the passive earth pressure, which is typically done using approaches such as numerical modeling, field monitoring, or traditional Coulomb or Rankine earth pressure theories. This paper presents a simplified approach for computing passive earth pressures for pit-in-pit excavations. A trapezoidal-shaped failure wedge is formed between two levels of retaining walls. A complete symmetric soil arch is used to describe the stress field of soils in the rectangular zone, whereas a half arch with one base acting on the wall and another base acting on the inclined shear surface is proposed for soils in the triangular zone. The soil arching effect is explicitly considered to derive the earth pressure for both cohesionless and cohesive soils at any intermediate passive state. A parametric study is conducted to demonstrate that the mobilized passive earth pressure increases nonlinearly with the magnitude of wall movement and soil shear strength parameters. The allowable spacing between two walls is also defined to produce a design chart. In the end, the proposed model is assessed against experimental measurements from model-scale tests.

This paper presents a generalized plastic mechanics–based constitutive model for the estimation of dynamic stresses in unsaturated subgrade soils under repeated vehicle loading conditions....

Reliability analyses of nail pullout, nail-in-tension, and system reliability of internal limit states are presented for both permanent and temporary soil nails that are designed using defa...

The accuracy of the default Federal Highway Administration (FHWA) simplified model for estimation of facing tensile forces for soil nail walls under in-service conditions was evaluated using a large quantity of measured long-term and short-term facing tensile force data collected from the literature. The estimation accuracy was quantified by the mean and coefficient of variation (COV) of the bias where bias is defined as the ratio of measured to calculated facing tensile force. Based on the available data, the default FHWA simplified model equation was found to overestimate long- and short-term facing tensile forces by about 15% and 23% on average, respectively. The corresponding spreads in estimation accuracy expressed as the bias COV were about 43% and 67%. Undesirable correlations between bias values and calculated facing tensile forces using the default FHWA simplified model equation were detected. A modified FHWA simplified model was proposed to improve the on average accuracy, reduce the spread in estimation accuracy, and remove the hidden correlations noted above. In addition, the modified equation has fewer empirical coefficients than the current formulation (i.e., four versus five). The facing tensile force equations developed in this study are a contribution to the design of facing of soil nail walls within the current FHWA soil nail wall design framework.

A rigorous probabilistic-based approach for load and resistance factor design (LRFD) calibration of internal stability tensile rupture and pullout limit states for geogrid reinforced mechan...

Cross correlations between nominal load and resistance terms in limit state functions for geotechnical soil–structure interaction problems can be expected. A closed-form solution for the reliability index for a simple linear limit state function is used to examine the influence of nominal load and resistance correlations on computed margins of safety. The formulation also includes the contribution of the underlying accuracy of the load and resistance equations (method bias) and bias dependencies with the magnitude of nominal load and resistance values assumed in the limit state design function. Sensitivity analyses and example problems for the external sliding limit state for a cantilever wall and the pullout limit state for internal stability of reinforced soil walls with different soil reinforcement types are presented. Ignoring nominal correlations where they exist is shown to underestimate the reliability index in some cases and to overestimate the reliability index in other cases. In the example problems, these differences are shown to exceed one order of magnitude in terms of probability of failure, but in the sensitivity analyses using a wider range of input parameter values, the differences can be several orders of magnitude.

Estimating runoff and infiltration in slopes is essential to predict flooding and landslide triggering. An approach jointly using a dual-permeability model and a kinematic wave model was proposed for integrative analyses of infiltration and surface runoff of rainwater for slopes with macropores in soils subjected to rainfalls. Laboratory tests were conducted to evaluate the performance of the proposed approach. Analyses showed that the presence of macropores greatly facilitates rainwater movement in the slope and the maximum depth of wetting front could be one order of magnitude larger than in cases without macropores. The influence of rainfall intensity, initial pore water pressure, coefficient of permeability of soil matrix, and slope angle was also examined.

A general approach for calibration of resistance factors for load and resistance factor design (LRFD) of pullout and tensile failure internal limit states of soil nail walls is presented. T...

The model uncertainty in prediction of facing tensile forces using the default Federal Highway Administration (FHWA) simplified equation is assessed in this study based on the Bayesian inference method and a large number of measured lower and upper bound facing tensile force data collected from the literature. Model uncertainty was quantified by model bias which is the ratio of measured to nominal facing tensile force. The Bayesian assessment was carried out assuming normal and lognormal distributions of model bias. Based on the collected facing tensile force data, it is shown that both the on-average accuracy and the spread in prediction accuracy of the default FHWA simplified facing tensile force equation depend largely upon the distribution assumptions. Two regression approaches were used to calibrate the default FHWA simplified facing tensile force equation for accuracy improvement. The Bayesian Information Criterion was adopted to quantitatively compare the rationality between the competing normal and lognormal statistical models that were intended for description of model bias. A case study is provided in the end to demonstrate both the importance of model uncertainty and the influence of distribution assumptions on model bias in reliability-based design of soil nail walls against facing flexural limit state.

Subgrade soils experience repeated traffic loads, such that dynamic stress and displacement are accumulated to jeopardize the stability of pavement foundations. Laboratory element testing is often conducted to apply cyclic loads to the soil. In fact, the stress state of subgrade soil is complex due to the constant rotation of principal stress induced by moving vehicles. It is hard to select constitutive relations for unsaturated subgrade soils in numerical or analytical calculation, since most models are developed without proper consideration of principal stress rotation. Furthermore, most available earth pressure sensors cannot provide stress measurements in three orthogonal directions for a soil element at the same time. A novel orthogonal earth pressure transducer is developed to measure dynamic stresses of subgrade soils in three directions under a roadway at Chencun, China. The cumulative effect of dynamic stress with load cycles is observed explicitly. Results indicate that the dynamic stress becomes negligible at 2 m from the roadway, and stabilization is suggested to be limited within this width. A series of constitutive relations is proposed to correlate the dynamic stress with the resulted displacement in different directions, which can be used to guide the design of unsaturated subgrade soils in South China.

Uncertainty in the predicted ultimate pullout strength of soil nails can be significant due to the complexity of nail–soil interactions, inherent variability in soil properties and the effects of nail installation. The paper first presents a statistical evaluation of the accuracy of ultimate bond strength of soil nails using the effective stress method (ESM) equation that has been adopted in Hong Kong. A total of 113 ultimate nail capacity data points from field pullout tests were collected from the literature and used to estimate the accuracy of the current ESM. Based on the available data, the current ESM default pullout model is found to be excessively conservative (on average) by at least a factor of three. The spread in prediction accuracy measured by the coefficient of variation (COV) of bias is in the range of 36–43 % after removing anomalous test data. Here, bias is the ratio of measured to predicted pullout load capacity. In addition, the accuracy of the current ESM equation for prediction of nail bond strength is shown to be dependent on the magnitude of predicted ultimate bond strength and magnitude of nominal vertical effective stress which is undesirable. The paper examines four candidate-modified bond strength equations with empirical coefficients that have been back-fitted to measured bond strengths to improve the overall accuracy of the equation and to reduce or remove the undesirable dependencies noted above. One equation with an empirically corrected stress-dependent term is judged to be the best candidate model based on the mean of bias values, spread (COV) of bias values, lack of dependencies and simplicity. Finally, the relative contributions of random variability in soil shear strength to measurement bias in bond strength (prediction accuracy) for each soil type are computed for the best bond strength model. Analysis of the contribution of soil shear strength to prediction accuracy showed that the combination of variability due to factors other than soil shear strength was greater than the variability in soil shear strength alone, where the latter is defined by the soil secant friction coefficient.

This paper presents reliability analyses of soil nail walls against two external ultimate limit states, global and sliding stabilities, which are related to the external stability failures of soil nail walls. Reliability analyses are conducted using Monte Carlo simulation technique. Soil nailing is a popular retaining system in highway construction and slope stabilization, and its current design practice is still based on the working stress design. There remains a need to establish a more rational design framework—load and resistance factor design—based on the concept of limit state design and reliability analysis for soil nail walls. The development of load and resistance factor design approach must consider multiple ultimate limit states, associated with external, internal, and facing failures. The analyses of resistance factors against two external failures are conducted in this study considering various influencing factors, including statistical parameters of soil friction angle, ultimate bond strength between soil and nails, soil type, wall geometry (wall height, back slope angle, and face batter angle), and nail configurations (nail inclination angle, drillhole diameter, and nail spacing). In the end, a series of resistance factors are proposed for potential application of load and resistance factor design approach against external failures for soil nail walls according to different design codes.

Endogenous metabolites of amino acids and their derivatives in biosamples are frequently highlighted as the most differential metabolites in recent metabolomics studies. The method for the detection of amino acid derivatives such as N-acetyl amino acids and oligopeptides is rarely reported. We developed a rapid, high-throughput, sensitive and reliable quantitative method to simultaneously profile 40 underivatized amino acids and their derivatives including N-acetyl amino acids and oligopeptides in cell lines, based on ultra-high-performance liquid chromatography-electrospray tandem mass spectrometry (UHPLC- MS/MS) by using a hydrophilic interaction liquid chromatography (HILIC) column. The optimized method was successfully validated with satisfactory linearity, sensitivity, accuracy, precision, matrix effects, recovery and stability for all analytes. Only one compound (cysteine-glutathione disulfide) showed relatively low recoveries at three concentration levels (60.8–74.3%). The limit of quantification (LOQ) for most compounds was in the range of 0.6–10 ng/mL (6–100 pg on column). This method was successfully applied to the analysis of amino acids and their derivatives in breast cancer cell samples. Principal component analysis (PCA) and the orthogonal projections to latent structures (OPLS) showed a clear discrimination of the non-tumorigenic breast epithelial cell line MCF-10A from the breast cancer cell line HCC 1806. Characteristic metabolic changes in amino acid metabolism were observed in the breast cancer cell line. This quantified analytical method of 40 endogenous amino acids and their derivatives in cell lines meets the requirement of quantification in specific expanded metabolomics studies with good sensitivity.

Statistical characterization of model uncertainty has been exclusively focused on reliability-based design of soil nail walls against ultimate limit states; little has been accomplished for predictions of horizontal and vertical displacements at the top of the wall for analysis of serviceability limit states. To fill the gap, this study first develops a database containing 461 measured wall horizontal and vertical displacements from 75 fully instrumented soil nail walls under working conditions reported in the literature. Then, the database is used to evaluate the accuracies of simplified wall displacement models currently adopted in four national soil nail wall design manuals. The results show that on average the current models tend to over-predict displacements for walls in sandy soils, but under-predict displacements for walls in clayey soils. Predictions using the current models are moderately to highly dispersive. Simple models are developed and calibrated for prediction of displacements based on the established database. Predictions using the developed models are demonstrated to be accurate on average and significantly less dispersive. In addition, a simple model for prediction of horizontal wall displacement along depth is developed and optimized. The present work is practically valuable for reliability-based design of soil nail walls against serviceability limit states.

A general approach for reliability-based analysis and design for pullout and tensile failure internal limit states of soil nail walls is presented. Reliability index values are computed usi...

A total of 123 measured maximum nail-load data were collected from instrumented soil nail walls reported in the literature. Filtered data sets corresponding to short-term and long-term measurements were used to evaluate the accuracy of the current Federal Highway Administration (FHWA) simplified method to calculate maximum nail loads under operational conditions. The accuracy of load predictions was quantified by the mean and coefficient of variation (COV) of the ratio (bias) of measured load to predicted load. Data in short-term and long-term categories were also investigated according to frictional-cohesive and frictional soil types. Based on the available data, the current FHWA simplified method was found to overestimate both long-term and short-term maximum nail loads on average. The spreads in prediction accuracy measured by the COV of bias were 38 and 52% for long-term and short-term data, respectively. Large spreads in prediction accuracy were also found using data for walls with cohesive-f...

Due to the characteristics of dispersion of guided waves, the waveforms recorded in ultrasonic nondestructive testing (NDT) of rock bolts are complicated to interpret. With a goal to increase the inspection sensitivity and accuracy in NDT of rock bolts, an approach of waveform interpretation based on wave modes identification is developed. The numerical simulation of full rock bolt and rock bolts with grout defect by Finite Element Method (FEM) is applied to illustrate the approach; it is found that the sensitive and low attenuation wave modes exist. Laboratory tests on full rock bolt and rock bolt with grout loss using NDT are conducted to evaluate the efficacy of the approach of waveform interpretation. In addition to that, a parametric study was conducted on rock bolt models with different sectional defect size. Based on the waveform interpretation, the mode-based reflection coefficientRis proposed to evaluate the sensitivity of wave modes to the defect size of sectional area. It is found that the sensitivity of the wave mode does not change with the defect sectional area, and the amplitude depends on the size of the defect.

This study presents reliability analyses of soil nail walls (SNWs) against global and sliding stability failures in layered ground. The load and resistance factor design (LRFD) has been studied and advocated for SNW design over the past few years. However, the majority of those studies were exclusively focused on SNWs in single-layer ground and few have investigated the case of layered ground. In this paper, the reliability is evaluated using the first-order reliability method (FORM) for SNWs that are designed based on traditional working stress design (WSD) methods. Based on analyses of a great variety of combinations of two soils, a stiff clay layer and a dense sand layer, reliability indices calibrated from traditional WSD exceed 3.0 for global stability designs but may be lower than 3.0 for sliding stability designs. This study also reveals that the sequence and the thickness ratio of layers are two important factors for the reliability of both global and sliding stability modes. SNWs in layer...