Showing papers in "Geotechnical and Geological Engineering in 2020"
TL;DR: The comparison reveals that the optimised machine learning methods have great potential to estimate bearing capacity of piles and the particle swarm optimisation algorithm is efficient in the hyper-parameter tuning.
Abstract: Accurate estimation of the bearing capacity of piles requires complex modelling techniques which are not justified by timeframe, budget, or scope of the projects. In this study, six advanced machine learning algorithms including decision tree, k-nearest neighbour, multilayer perceptron artificial neural network, random forest, support vector regressor and extremely gradient boosting are employed to model the bearing capacity of piles in cohesionless soil, and the particle swarm optimisation algorithm is used to optimate the hyper-parameters of machine learning algorithms. A dataset comprising of 59 cases is employed and the R-squared value, root mean square error and variance accounted for are used as performance metrics to compare the performance of optimised machine learning methods. The comparison reveals that the optimised machine learning methods have great potential to estimate bearing capacity of piles and the particle swarm optimisation algorithm is efficient in the hyper-parameter tuning. The results show that R-squared values of six optimised machine learning approaches on the testing set vary from 0.731 to 0.9615. Also, the optimised extremely gradient boosting (R-squared value = 0.9615) shows the best performance compared with other algorithms. Furthermore, the relative importance of influential variable is investigated, which shows that effective stress is the most influential variable for bearing capacity of piles with an importance score of 30.9%. In addition, the results by the optimised machine learning method are compared to the β-method which is a popular empirical method. It is revealed the prominent performance of optimised machine learning approaches.
63 citations
TL;DR: In this paper, the authors investigated the stability of unlined square tunnels in anisotropic and non-homogeneous clays by the lower bound finite element limit analysis using second-order cone programming.
Abstract: In general, the undrained strength anisotropy of clays is found in nature. Its effect on a stability problem during undrained loading should be considered in order to get a more accurate and realistic safety assessment. In this paper, the undrained stability of unlined square tunnels in anisotropic and non-homogeneous clays is investigated by the lower bound finite element limit analysis using second-order cone programming. The anisotropic undrained strength of clays is modelled by using an elliptical strength envelope under plane strain conditions. The stability analyses of the problem are performed by the comprehensive investigations of the effects of the cover-depth ratio, the normalized overburden pressure, the normalized strength gradient, and the anisotropic strength ratio on the stability load factor and associated failure mechanisms. The computed lower bound solutions are validated with the existing results of square tunnels in isotropic clays. The new approximate equations of the stability load factor and factor of safety for square tunnels in anisotropic and non-homogeneous clays are first time presented by using a nonlinear regression, hence providing a reliable, accurate and convenient tool for stability analyses of the problem in practice. The numerical results reveal that the strength anisotropy has a significant impact on the stability load factor, especially when anisotropic clays have much difference in undrained strengths between compression and extension.
60 citations
TL;DR: The comparison of performance indicators of the models obtained from both methods showed that the ANN-PSO hybrid algorithm with proper performance indicators for the model had higher precision in predicting the utilization factor compared to ANN.
Abstract: Performance prediction of the tunnel boring machine (TBM) in the construction of urban tunnels is under the consideration of tunnel experts due to its ability in minimizing the time and cost of the tunneling project implementation. The utilization factor of TBM is one of the most important factors, indicating the TBM performance. The present study provides an advanced intelligent model for predicting the utilization factor in order to evaluate the performance of TBM, hence, the aims of this study are to compare three prediction models including the multiple linear regression (MLR), artificial neural network (ANN) and hybrid algorithm of the neural network-particle swarm optimization (ANN-PSO) to determine the best prediction model. In the present research, data of the east–west section of the tunnel on line 7 of Tehran Subway were used as the case study and its utilization factor was calculated in 44 working days, and the influential factors include geological condition’s factors, technical properties of the TBM and technical measuring factors which were taken and used during this study. Finally, the comparison of performance indicators of the models obtained from both methods showed that the ANN-PSO hybrid algorithm with proper performance indicators for the model including R2 = 0.998, RMSE = 0.023 and VAF = 99.634 had higher precision in predicting the utilization factor compared to ANN.
43 citations
TL;DR: A simple literature review on cemented composites, common non-conventional stabilizers, reinforcing fibrous inclusions and the simultaneous use of a stabilizer and a reinforcing agent is provided.
Abstract: Strength and compressibility characteristics of problematic soils such as loose sands and extra-sensitive clays need to be enhanced for the construction purposes which is due in part to the population growth and society’s ever-expanding requirements. Accordingly, cemented soils are being used as a world-renowned soil stabilization practice in all geotechnical engineering applications, yet the high energy consumption and cost of cement is to blame. Therefore, various types of binders have been proposed to partially or even totally supplant the cement, whilst fibers have emerged to be used as composite reinforcement. The current study provides a simple literature review on cemented composites, common non-conventional stabilizers, reinforcing fibrous inclusions and the simultaneous use of a stabilizer and a reinforcing agent. It encapsulates highlighted studies which are stated in a logical sequence to introduce the most practical mixtures used for the stabilization purposes. Moreover, microstructural analysis and measurements regarding variable properties of mortar-like and cemented granules composites will be discussed. Eventually, future works such as an appropriate use of weight–volume relationships as well as adopting an objective qualitative assessment for the selection of the additives will be recommended.
33 citations
TL;DR: In this article, the peak strength of salt rock was calculated based on the axial strain value (6%) or the initial point of dilatancy, which was then calculated to verify the feasibility of this method.
Abstract: The deformation and strength characteristics of rock salt is significant for the safety of hydrocarbon energy (oil, gas) storage in salt caverns. To overcome the problem of determining the peak strength by simultaneously considering the dilatancy characteristics of salt rock, compression experiments were carried out on Pingdingshan salt rock under different confining pressures. The results shew that the uniaxial experiment of salt rock presented a brittle failure, but the presence of impurities improved the strength of samples. After the confining stress reached a "Transition confining pressure"—6.55 MPa, which was determined by using a chart method, the strength of salt rock increased greatly and behaved a strong strain hardening phenomenon. An empirical method to determine the "transition confining pressure" was put forward, and it was also suggested that the minimum operating pressure in a gas storage salt cavern should be higher than this value. The experiments under different confining pressures indicated that the higher the confining pressure was, the more hysteretic the dilatancy occurred. Based on this result, a method to determine the peak strength of salt rock based on a certain axial strain value (6%) or the initial point of dilatancy was proposed. Then the peak strength of the salt rock samples in this study was calculated to verify the feasibility of this method. This study provided the determination methods for the "transition confining pressure" and the peak strength for salt rock, which was a reference for the evaluation and operation of the gas storage salt caverns.
28 citations
TL;DR: In this paper, the Vipulanandan p-q model was modified and used to represent the particle size distribution of soils and the results of prediction were compared with the Fredlund and Logistic Growth models used in the literature.
Abstract: In this study, permeability, particle size distribution of the sandy soils and collected data from several research studies were analyzed and modeled using Vipulanandan p–q model and the results of prediction were compared with the Fredlund and Logistic Growth models used in the literature. The Vipulanandan p–q model was modified and used to represent the particle size distribution of soils. The Vipulanandan p–q model parameters were correlated very well to various soil properties such as the diameter in the particle size distribution curve corresponding to 10%, 30%, 60%, and 90% of finer (d10, d30, d60, and d90 respectively), mean particle size the diameter in the particle size distribution curve corresponding to 50% finer (d50), and fines content (F%). The range of particle sizes investigated in this study was 0.14–0.94 mm, 0.075–1.76 mm, and 0.15–3.59 mm for the d10, d30, and d60, respectively. Also, from the Vipulanandan p–q model parameter, the permeability of the soils have been predicted successfully. A current study also had quantified the lower groutability limit based on the d50 and the Vipulanandan p–q model parameters. The relationship between fines content and d50 were also generalized using the Vipulanandan p–q model to quantify the upper and lower groutability limits for sandy-soils.
28 citations
TL;DR: The most commonly used stabilizer is cement, which reinforces earth by enhancing its strength and water resistance with chemical bonds, while at the same time significantly increasing its embodied energy and reducing its sorption capacity as discussed by the authors.
Abstract: It has become general practice to stabilize earthen materials with chemical binders, since one of their main weaknesses is their lack of durability. The most commonly used stabilizer is cement, which reinforces earth by enhancing its strength and water resistance with chemical bonds, while at the same time significantly increases its embodied energy and reduces its sorption capacity. These side-effects greatly reduce the sustainability appeal of earthen materials, leading to a contradiction in this application of cement. Since the researcher community has been aware of this more and more results are published of experiments with alternative stabilizers. This review provides an overview of research about the durability of stabilized earthen walls, the methods used to assess it and parameters that have been shown to affect it. The review features a brief history of this field, but focuses more on recently published data about the water erosion performance of stabilized earthen construction materials. Conclusions about the existing test methods are drawn, with directions for further development suggested.
27 citations
TL;DR: In this paper, the authors investigated the 3D heading stability of two circular tunnels horizontally aligned in cohesive undrained clayey soil and obtained rigorous upper bound and lower bound critical stability numbers at collapse and blowout.
Abstract: This paper investigates the three-dimensional (3D) heading stability of twin circular tunnels horizontally aligned in cohesive undrained clayey soil. The stability is described by Broms and Bennermarks’ undrained stability number, which combine all stresses into a single dimensionless number. A recently developed 3D finite element limit analysis technique is used to obtain rigorous upper bound and lower bound critical stability numbers at collapse and blowout. The interaction effects of the distance between the tunnels on the stability are determined for a series of tunnel cover-to diameter ratios. As an additional verification of the rigorous bounding solutions, the obtained stability results are compared with other published solutions available in the literature. Results from this study are summarized in stability charts and tables for use by designers and practising engineers.
25 citations
TL;DR: In this paper, a road cut slope stability analysis of five locations were carried out along NH-7, between Shivpuri to Kaudiyala in Uttarakhand, India.
Abstract: The rocks of the Himalayan terrain are highly deformed and distorted due to complex geological and tectonics setup. Failures of slopes are always reported along National Highway (NH)-7, in the Uttarakhand Himalayan region, which causes loss of lives, traffic blockage, and destruction of property and also deterioration of the environment gradually. The road cut slope stability analysis of five locations were carried out along NH-7, between Shivpuri to Kaudiyala in Uttarakhand, India. For that a rigorous field investigation was done to collect the geotechnical parameters of slopes and also the potential instability condition of cut slopes were monitored with real time. To know the characteristic of rock mass, the geotechnical data's were studied based on rock mass rating (RMR) and geological strength index (GSI). The kinematics of the blocky (good and fair) rock-mass shows in general wedge, toppling and planar type of failures for different rock slopes. The petrography of representative rock samples was also carried out to see the mineralogical variation in quartzite and phyllitic quartzite. The comparative analysis of different empirical methods for slope stability as slope mass rating (SMR), continuous slope mass rating (Co-SMR), and Chinese slope mass rating (CSMR) shows a decent correlation and revealed that slopes are mostly partially stable. Qslope stability has also been applied to reveal the stability problems and to find out stable slope angle for different slopes. Further to clarify the stability of these slopes, numerical models (LEM and FEM) were applied. The numerical result, (FoS) of different slopes revealed that slopes are stable, critically stable and unstable, with a good agreement between LEM and FEM models. The collective effort of slope stability analysis through analytical and numerical methods will give the better perception to find out the potential remedial measures and optimum slope design.
24 citations
TL;DR: The application of the recently proposed multiverse optimisation (MVO) algorithm in determining the lowest FS along the critical slip surface with a considerably low uncertainty is presented.
Abstract: In professional practice, slope stability assessment of natural or man-made slopes is performed using traditional limit-equilibrium-based methods. These methods often fail to identify the critical slip surface corresponding to the minimum factor of safety (FS). Optimisation methods based on stochastic search techniques can more easily locate the global optima solution than traditional methods can. The paper presents the application of the recently proposed multiverse optimisation (MVO) algorithm in determining the lowest FS along the critical slip surface. Four benchmark examples are analysed to test the performance of the multiverse optimiser for slope stability assessment. The results demonstrate that the MVO algorithm can capture the critical slip surface and compute its corresponding FS with a considerably low uncertainty.
23 citations
TL;DR: In this paper, a study of deterministic seismic hazard for Bengkulu City is presented, where three parameters including peak ground acceleration, spectral acceleration at 0.2 ǫ s (SA at 0ǫ 2 s), and spectral acceleration of 1ǫ n (SA 0.1 s) are analyzed to generate seismic hazard maps.
Abstract: Bengkulu City is one of cities in Indonesia, which is located on the west coastline of Sumatra. Within last two decades, Bengkulu City had undergone at least two large earthquakes with magnitudes ≥ Mw 7.0. This paper presents a study of deterministic seismic hazard for Bengkulu City. The hazard analysis is initiated by determining the controlling earthquake. Site investigation results are also studied for seismic ground response analysis. Analysis is performed by propagating seismic wave to investigate seismic behaviour during earthquake. Three parameters including peak ground acceleration, spectral acceleration at 0.2 s (SA at 0.2 s), and spectral acceleration at 1 s (SA at 1 s) are analysed to generate seismic hazard maps. In general, this study could help people to understand seismic hazard in Bengkulu City. The results also could recommend local engineers to consider earthquake in structural design and spatial plan in Bengkulu City.
TL;DR: In this article, a probabilistic approach based on Monte Carlo simulation (MCS) is proposed to evaluate the failure probability of a rock slope system and to determine a safe maximum slope height for rock slope design.
Abstract: A probabilistic approach that is based on Monte Carlo simulation (MCS) was developed in this study to design and perform sensitivity analysis of rock slope. The probabilistic approach uses MCS to perform a series of single objective optimizations for design of rock slope and to perform sensitivity analysis of rock slope stability. The MCS-based approach was used to evaluate the failure probability of a rock slope system and to determine a safe maximum slope height for rock slope design. To achieve this, the performance of different rock properties and rock slope conditions were explicitly considered towards achieving the target reliability index of the rock slope. The approach can achieve multiple rock slope design specifications using different target reliability indexes from a single run of MCS. The proposed probabilistic approach was illustrated through an example of rock slope design to determine feasible designs under different rock slope conditions. Also, sensitivity studies were performed to explore the effects of uncertainties in tension crack depth and water depth in tension crack, and variability in rock unit weight. The results show that the effects of uncertainties and variability on rock slope stability can be significant and should be incorporated during design analysis. Incorporating such uncertainties and variability in rock slope design is achieved with relative ease using the proposed approach.
TL;DR: In this article, the effect of adding recycled polyester fiber and nano-SiO2 on engineering properties of the soil, especially the maximum dry density and shear strength using silty loess with low liquid limit, was investigated.
Abstract: The present study investigated the effect of recycled polyester fiber in combination with nano-SiO2 as a new stabilizer for improving the geotechnical properties of the loess soil. In addition, it intended to evaluate the effect of adding recycled polyester fiber and nano-SiO2 on engineering properties of the soil, especially the maximum dry density and shear strength using silty loess with low liquid limit. To this end, three different combinations of fiber and nano-SiO2 ratios were used ranging between 2 and 6% in proportions of 33% and 50% for the total dry weight of the soil. Furthermore, three different combinations of fiber-soil ratios were employed which ranged between 0.5 and 1.5% for the total dry weight of the soil, as well as three different combinations of nano-SiO2 ratios ranging between 2 and 6% for the total dry weight of the soil. The results from the compaction test indicated that the maximum dry density of the stabilized loess decreased while the optimum water content increased by adding recycled polyester and nano-SiO2. Based on the results of the direct shear test, the shear strength improved by increasing the contents of the recycled polyester fiber and nano-SiO2 in the soil mixture. Thus, the addition of recycled polyester and nano-SiO2 improved the strength properties of the loess soil. In order to obtain the maximum increase in shear strength, the optimum content of the recycled polyester fiber and nano-SiO2 was 4% of loess soil dry weight in proportions of 33% and 50% in the mixture.
TL;DR: In this paper, a brief review of analytical, experimental and numerical studies carried out on conventional and innovative piles subjected to monotonic and cyclic lateral loads was discussed, which revealed the use of finned and helical piles in improving the lateral resistance and reducing the pile head deflections.
Abstract: This paper includes a brief review of analytical, experimental and numerical studies carried out on conventional and innovative piles subjected to monotonic and cyclic lateral loads. State-of-the-art developments and the important approaches relevant to the field of laterally loaded pile was discussed. The observations from small-scale experiments confirmed that monopiles embedded in cohesionless soil undergoes progressive accumulation of displacement and the rate of accumulation does not approach zero even after 10,000 cycles. The accumulated rotation of the foundations under the offshore loading conditions mainly depends on the characteristics of cyclic loading such as the magnitude of maximum and minimum load during a cycle. The review of existing works showed that there are hardly any studies addressing the effect of gentle seabed slope and also the effect of multi-directional loading on the magnitude of accumulated rotation of rigid monopiles. It is critically suggested to consider the influence of strong vertical loads and moments on stiff monopiles installed on gentle seabed slopes. The current study reveals the use of finned and helical piles in improving the lateral resistance and reducing the pile head deflections. However, further investigations are required to validate their performance in varying soil conditions and also to optimize and ease the design through the development of cyclic p–y curves.
TL;DR: In this article, a model was proposed to quantify the relationship between water retention and internal stress for fine-grained and coarsegrained soils at saturations over the full range.
Abstract: Quantifying the relationship between water retention and internal stress state of unsaturated soils has long been a challenge. Current effective stress formulations can effectively capture the relationship for coarse-grained soils, where capillary mechanisms dominate internal stress state over a wide range of saturation, but fail for fine-grained soils, particularly at low to intermediate saturation, where surface adsorption mechanisms dominate water retention and corresponding stress state. Internal stress state of compacted kaolinite specimens spanning saturation (S) from 0 to 0.73 is measured through Brazilian tensile strength tests. Changes observed in strength, strain, and stiffness are analyzed to calculate evolution of internal stress with saturation. A model is proposed to quantify the relationship between water retention and internal stress for fine-grained and coarse-grained soils at saturations over the full range (0 ≤ S ≤ 1). Performance of the model is evaluated by comparison with experimental results from the literature.
TL;DR: In this article, a laboratory investigation on the use of construction demolition waste in poor clayey soil to improve its strength and drainage characteristics was presented, which revealed that the addition of CDW in poor soil reduced both maximum dry density and optimum moisture content.
Abstract: This paper presents a laboratory investigation on the use of construction demolition waste in poor clayey soil to improve its strength and drainage characteristics. Various laboratory tests such as differential free swell, Atterberg’s limits, compaction, unconfined compressive strength (UCS), California bearing ratio (CBR), and permeability have been conducted on un-stabilized and Construction Demolition Waste (CDW) stabilized clayey soil. The outcomes revealed that the addition of CDW in poor soil reduced both maximum dry density and optimum moisture content. The UCS, CBR, and permeability got improved on adding optimum content of CDW in poor clayey soil. The secant modulus also increased on addition of the CDW in virgin soil. The regression analysis performed for different tests showed good agreement of laboratory results with predicted values. Thus, it can be revealed that using CDW in stabilization of poor clayey soil will not only solve the problem of its disposal but will also be cost effective and protect the environment.
TL;DR: In all cases, many essential studies should be carried out before deciding the location of a dam as discussed by the authors, in order to decide the best location for a dam construction in all cases.
Abstract: Dams are engineering structures constructed for different purposes. They are of differentsizes, shapes and types. In all cases, many essentialstudies should be carried out before deciding thelocati ...
TL;DR: In this paper, the stabilization of black cotton soil (BCS) using envirosafe alkali-activated binders (AAB) instead of traditional cement-based binders is discussed.
Abstract: Expansive soil is predominantly impervious and exhibits dual nature (swelling/shrinkage) when exposed to moisture fluctuation. It is difficult to control the heave action which renders the loss of mechanical strength of such soils. The present study emphasizes on the stabilization of black cotton soil (BCS) using envirosafe alkali-activated binders (AAB) instead of traditional cement-based binders. Mineralogical and microstructural characterization for both untreated BCS and AAB-treated BCS are performed through X-ray diffraction (XRD), scanning electron microscope (SEM), Fourier-transform infrared (FTIR) spectroscopy, and energy dispersive X-ray spectroscopy (EDS). The influences of varying percentages of AAB at different curing periods are investigated through index and shear strength properties of treated BCS. The binder treatment shows a significant improvement in geoengineering properties and aids in enhancing the CBR and unconfined compressive strength (UCS) values of BCS. The reduction in swelling and plasticity index is attributed to mineral alteration due to treatment of BCS with AAB. This study may prove to be very effective in devising an economic technique to address the problems associated with BCS.
TL;DR: In this article, the effects of EPS incorporation into different sorts of mixtures through reviewing the most prominent studies over EPS beads and blocks subjected to static and cyclic loadings are investigated.
Abstract: Expanded polystyrene (EPS) is a polymeric material whose low density and high strength/density ratio has made it renowned to be used as a lightweight geosynthetic in the embankments and retaining structures to enhance the slope stability and reduce the lateral earth pressure. Besides, due to its low heat transfer coefficient and flexibility, it is geared to being used as a sound heat insulator in the building construction. So far, particular attention has been paid to the use of EPS as a lightweight material in different types of soils to both make the composite cost-effective and modify its mechanical properties, which ultimately provides the target strength. The present paper investigates the effects of EPS incorporation into different sorts of mixtures through reviewing the most prominent studies over EPS beads and blocks subjected to static and cyclic loadings. Having a comprehensive review throughout the literature, the study proposes some practical essential topics to be pursued for further research which the current literature lacks. Correlation of some useful mechanical parameters of EPS-soil mixtures, simultaneous use of EPS beads with petroleum derivatives and performance of some complementary static and cyclic tests are amongst them.
TL;DR: In this paper, the authors employed the discrete element method (DEM) to simulate the tunneling procedure of the line-7 of Tehran underground urban train tunnel utilizing the micro mechanical parameters calculated from back analysis on direct shear tests.
Abstract: Cutterhead torque and thrust are the two main designing parameters of the shield TBM, which have to be evaluated and optimized, based on the interaction between the TBM and excavated material. This study employs the discrete element method (DEM) to simulate the tunneling procedure of the line-7 of Tehran underground urban train tunnel utilizing the micro mechanical parameters calculated from back analysis on direct shear tests. The resultant torque and thrust are then compared against the actual parameters and then with those estimated from the numerical analyses. This result shows that DEM is able to estimate the TBM torque and thrust applying actual boundary conditions and material properties for the model. Furthermore, the impact of ground properties, overburden height, linear and radial velocity on cutterhead torque and thrust and its performance are evaluated and optimized.
TL;DR: In this article, the authors investigated the TBM tunnelling-landslide relationship by employing 3D numerical analyses and showed that the last 600m of the tunnel has a potential landslide hazard and some additional measures should be considered along this part to ensure tunnel safety.
Abstract: Owing to the increase in population, transportation has become one of the major research topics. Among existing transportation systems, railway is one of the most economic and fast systems, and therefore, there has been an increase in new railway constructions in recent years. In Turkey, the longest railway tunnels, the Bahce–Nurdag high-speed rail tunnels, are under construction in the southern part of the country. This twin tubes tunnels are approximately 10 km in length, and they are excavated using tunnel boring machines (TBM). The tunnel route locates in the East Anatolian Fault Zone and the portal region is composed of debris and old landslide deposits. For this reason, mitigating the potential landslide hazard is critical for the tunnel. Therefore, the present study investigates the TBM tunnelling–landslide relationship by employing 3D numerical analyses. The analyses show that the last 600 m of the tunnel has a potential landslide hazard and some additional measures should be considered along this part to ensure tunnel safety. The tunnel conditions are highly complex, and thus it is an interesting case for tunnel engineers.
TL;DR: In this paper, a correct way for numerical simulation related to underground excavation is described according to gradually eliminating (incremental) stress around tunnels based on the numerical modeling in the finite-difference code called FLAC.
Abstract: Tunnels are structures which have vital roles in the development of societies. In the numerical models of underground cavities, such as tunnels, loading due to zone elimination is induced instantaneously in the soil mass, and it might cause a disturbance in the stress state especially around the excavation area. However, this is not compatible with the principles of elastoplastic constitutive models used in soil behavior simulations. Besides, the predicted load on the tunnel liner will be larger than the actual value in this kind of modeling. In other words, it causes the so-called overestimated design. Using an appropriate constitutive model could lead the numerical analyses to accurate results. In this research, loading increment in the simulation of soil behavior is evaluated according to experimental data. Next, a correct way for numerical simulation related to underground excavation is described according to gradually eliminating (incremental) stress around tunnels based on the numerical modeling in the finite-difference code called FLAC. Hence, the effect of releasing the stress on the results is illustrated by the stress paths and deformations around a tunnel. Finally, the installation time of the tunnel liner and its impact on the numerical results are considered based on some experimental and field data. It is concluded that the use of software default in modeling the tunnel issues might lead to extreme oscillations in the stress paths, and it could affect the numerical results. Therefore, it is reasonable to utilize a proper way to release the stress around the excavation area gradually.
TL;DR: In this article, the Back Propagation-Artificial Neural Network (BP-ANN) approach was used to predict the Unconfined Compressive Strength (UCS) of Basalt Rock.
Abstract: Basalt rocks as building stones were used in many historical buildings in Jordan, and maintenance of these buildings is usually required with time. As part of the effort to collect the necessary information that is needed for future works in repair/strengthen the basaltic structures against any possible future damage. The dry density, Ultrasonic Pulse Velocity, Schmidt Hammer Rebound test, Brazilian Tensile Strength Test, Slake durability, and Point Load test were recorded for specimens tested in the lab to develop indirect methods of estimating the rocks Unconfined Compressive Strength (UCS). Simple regression (SR) analyses were performed to establish correlations between UCS and the results of each above-mentioned rock indices. The SR results showed that a regression model with multiple inputs is needed. In this study, the Back Propagation-Artificial Neural Network (BP-ANN) approach was utilized to predict the USC of Basalt Rock. Two ANN models were developed; one using the physical properties of rocks and the other one using the mechanical properties of rocks. Part of the data collected was used to train the ANN, and a set of independent data was used to validate the developed model. The performance of the ANN model in predicting UCS was compared to that of Multivariate Regression (MVR). The obtained results showed that the ANN model gave higher prediction performance compared to other models. A sensitivity analysis for the developed ANN model was performed to verify the importance of each input. The prediction of UCS can be used to design the proper conservation and repair/strengthen strategies that will allow dealing with the current conditions and the future natural hazards to which these structures are exposed.
TL;DR: In this paper, the shear strength of saturated fiber reinforced soil is studied through a series of unconsolidated undrained shear tests, and the test results show that the stress-strain relationship of the fiber-reinforced soil is strain hardening and the failure mode of the samples is bulging failure.
Abstract: To research the unconsolidated undrained shear strength and deformation properties of saturated cotton fiber reinforced soil, the shear strength of saturated fiber reinforced soil is studied through a series of unconsolidated undrained shear tests. The test results show that the stress–strain relationship of the fiber reinforced soil is strain hardening, and the failure mode of the samples is bulging failure. Tensile properties of fibers require a certain strain to be “mobilized”. When the strain is less, the fiber content and the fiber length have less influence on the principal stress difference, and the reinforcement effect is weak. The reinforcement effect enhances with the increasing of axial strain. The unconsolidated undrained shear strength of saturated fiber reinforced soil increases first and then decreases with the increasing of fiber content and fiber length. The strength is the best under the condition of 1.0% fiber content and 3.09 cm fiber length, and the strength of fiber reinforced soil increases by 63.5% compared with that of unreinforced soil. Fiber reinforcement can weaken the end effect of the samples, and effectively constrain the radial deformation of the soil. By analyzing the interaction modes between the fibers and the soil particles, it is found that the interaction modes are contact, bending and interweaving. These three actions provide the interfacial shear stress between the fibers and the soil particles, and the tensile stress of fibers to restrict the movement of soil particles, and the interactions improve the shear strength of soil.
TL;DR: In this paper, the authors compared the performance of inclined and vertical cores with numerical models to simulate the seepage and hydraulic gradients and used the Limit of Equilibrium Method to calculate slope stability.
Abstract: Water seepage affects dam stability and loss of water from reservoirs. Consequently, seepage is an important problem in the design, implementation, and operation of embankment dams. One type of embankment dam is a non-homogeneous (zoned) dam with a clay core. Water passes through the core of the dam and loses much of its energy due to friction. Zoned embankment dams can be designed and implemented with inclined or vertical cores. In this study, the performance of inclined and vertical cores are compared using numerical models to simulate the seepage and hydraulic gradients. Also, the Limit of Equilibrium Method is used to calculate slope stability. The permeability ratio of the dam shell to the clay core is a variable. The result of this study shows that seepage with a vertical core is less than that with an inclined core. Meanwhile, the factor of safety for upstream slope failure is higher (about 55.5%) for the embankment with an inclined core compared to the vertical core case. Also, comparisons were made using different methods to calculate the stability of the slope. The Bishop’s method showed the highest safety factor and the Fellenius’ method predicts the lowest safety factor.
TL;DR: In this article, a geodatabase for soil properties for An-Najaf was created by using the ArcGIS 10.5 software to interpolate the spatial data to produce 33 geotechnical maps for fine soil, coarse soil and USCS for 13 depth levels.
Abstract: The unified soil classification system (USCS) first proposed by Casagrande and subsequently developed by the Army Corps of Engineers. It widely used in many building codes and books. An-Najaf city is the most important city in Iraq due to its religious and spiritual value in the Muslim world, so it is fast expanding and continuous developing city in Iraq. The data from 464 boreholes in the study area for depths of 0–26 m have been used. 13 Soil samples were collected from each borehole with 13 depths level (0–26) m with 2 m intervals. The USCS was applied to the soil samples from 13 depth levels borehole. This research aims to create a geodatabase for soil properties for An-Najaf. The ArcGIS 10.5 software was used to interpolate the spatial data to produce 33 geotechnical maps for fine soil, coarse soil and USCS for 13 depth levels. For numerical soil data, Ordinary Kriging has been used for interpolation mapping of Fine and Coarse percentage data for each depth. For non-numerical (nominal) soil data (USCS class), the Indicator Kriging method is used. The results show that the coarse soil occupied 85–95% for depth 0–16 m and consist of (SP, SP-SM, SM) while fine soil occupied 5–15% consisting of (OL, CH, ML) subsequently, this soil when compacted has a permeability of pervious to semi impervious, good shearing strength, low to very low compressibility and acceptable workability as a construction material. The results also show that after 16 m depths until 26 m, the fine soil percentage increased to 40% with a coarse soil percentage of 60%, indicating changes in soil characteristics as the permeability became semi-pervious to impervious, fair shearing strength, medium compressibility and fair workability as a construction material. The study results will provide help and saving time, efforts and money in preliminary engineering designs.
TL;DR: In this article, the effect of Rice Husk Ash (RHA) on swelling, shrinkage, and compaction characteristics of the expansive soil was investigated and it was concluded that adding RHA in appropriate proportions not only reduces the swelling and shrinkage behavior of expansive soil significantly but also makes it more stable.
Abstract: Black cotton soils are expansive soils which exhibit high swelling and shrinking when exposed to changes in moisture content. Durability of structure resting on expansive clays is always in question due to swelling/shrinkage of such clays. The performance of paved and unpaved road pavements constructed over such expansive soil subgrades is often poor and in most cases show cracking, potholes, wheel path rutting, serious differential settlements and heaving in various locations. In addition to problems related to expansive soils another problem arising in all developing and developed countries is due to the wastes generated from various activities which not only cause severe environmental problems, but also occupy a huge area of land for its disposal. Rice husk ash (RHA) is one such wastes produced from the burning of rice husk and if used as an additive to expansive soil shall not only significantly reduce the swelling/shrinkage characteristics of such soils but also solve the environmental and disposal problems being created by the ash. The paper presents the results of an experimental investigation conducted to study the effect of RHA on swelling, shrinkage and compaction characteristics of the expansive soil. The RHA was mixed with expansive soil in varying proportions. Free swell index, Atterberg limits, light compaction tests, unconsolidated undrained triaxial compression tests, California bearing ratio tests were carried out with specimens containing varying percentages of RHA. It is concluded that addition of RHA in appropriate proportions not only reduces the swelling and shrinkage behavior of expansive soil significantly but also makes it more stable.
TL;DR: In this article, a 3D numerical model of a horseshoe-shaped pipeline was established with ALE algorithm using ANSYS/LS-DYNA, and the propagation law of a blasting seismic wave was analyzed, and transverse and longitudinal vibration response characteristics of pipelines under tunnel blasting vibration were studied.
Abstract: In order to ensure the safety of horseshoe-shaped pipeline during tunnel blasting excavation, the vibration test and dynamic response of horseshoe-shaped pipeline were investigated. The velocity and frequency of tunnel blasting vibration were analyzed. Sodev's empirical formula was used for regression analysis of the velocity of blasting vibration. 3D numerical model of a horseshoe-shaped pipelines was established with ALE algorithm using ANSYS/LS-DYNA. The propagation law of a blasting seismic wave was analyzed, and the transverse and longitudinal vibration response characteristics of pipelines under tunnel blasting vibration were studied. The velocity of the pipeline increases gradually and the frequency tends to decrease with the decrease of the distance away from the explosion source center under the same charge. The principal frequency of vibration in the Z direction is mainly distributed from 50 to 80 Hz, which is difficult to generate resonance with the pipelines. The maximum relative error between the simulated and measured velocity of X, Y and Z directions was 8.2%. It was reliable to study the dynamic response of pipelines under blasting vibration based on this numerical model. The blasting seismic wave first reached the bottom of the pipeline right above the explosive. Subsequently, seismic waves propagated along the transverse and the longitudinal axes of the pipeline, and the pressure on the pipeline increased gradually. And when it attenuated completely in the soil, the pipeline stopped its response. The peak value of tensile stress of each element of the vault is the largest. However, the velocity of the bottom plate and the arch roof of pipeline are the largest. The peak values of velocity and tensile stress exist in 0 to 4 m away from the explosion source, and gradually decrease as the distance away from the explosion source increases.
TL;DR: In this article, the authors investigated the effect of overburden stress factors on the undrained capacity of laterally loaded piles under combined horizontal load and moment by employing the three-dimensional finite element analysis.
Abstract: A large number of studies on various aspects of laterally loaded piles in clay have been conducted in the literature based on experimental and numerical analyses; however, the lack of studies on the influence of the soil unit weight on the undrained capacity of the problem is obvious. In this paper, the effects of the overburden stress factors on the undrained capacity of laterally loaded piles under combined horizontal load and moment are comprehensively investigated by employing the three-dimensional (3D) finite element analysis. In the present study, soil–pile interfaces are modelled as the no-tension condition while the influences of the pile length ratios are also examined in the numerical analyses. The failure envelopes of laterally loaded piles under combined horizontal load and moment incorporating overburden stress factors, pile length ratios are presented. Employing the normality rule to the derived failure envelopes, the failure mechanisms corresponding to the ratio between applied moment and horizontal load are postulated in this paper. An approximate solution of the failure envelope of laterally loaded piles is also proposed by using a nonlinear regression analysis, and provides a convenient tool for predicting the undrained lateral capacity of piles considering overburden stress factors in practice.
TL;DR: In this article, the authors investigated the effect of soil suction and moisture content on gas permeability for different biochar application percentages at high degree of compaction and developed an artificial neural network (ANN) based model to predict the air permeability and obtain optimized value of soil SUction and water content for extreme gas passage.
Abstract: Passage of municipal waste induced greenhouse gases such as carbon di oxide (CO2) and methane in landfill covers, majorly depends on the state of unsaturation and compaction of soil biochar composite (SBC). The unsaturated state of SBC can be identified by measuring soil suction and volumetric water content (VWC) that can affect the air permeability of landfill covers. To design the landfill covers, it is required to propose a model which can forecast the air permeability up to a certain degree of accuracy. The aim of this study is to investigate the effect of soil suction and moisture content on gas permeability for different biochar application percentages at high degree of compaction and develop an artificial neural network (ANN) based model to predict the gas permeability and obtain optimized value of soil suction and moisture content for extreme gas passage. In this study, results represent that presence of biochar can decrease the gas permeability significantly. For 5% and 10% biochar application percentages decrement in gas permeability is around 50% and 65% with respect to bare soil. Developed ANN model shows that in the presence of biochar, gas permeability of SBC is more sensitive to VWC than soil suction i.e. a small change in VWC can change the gas permeability, significantly. Optimization analysis also shows that addition of biochar can increase the optimized VWC for biochar amended soils which can help to design most effective soil cover to provide required nutrients and water for vegetation growth.