Geo-China 2016: New Frontiers in Civil Infrastructure

This paper presents an advanced analysis of shallow foundations using both strip and isolated footings. Taylor (1948) assumed uniform distributions for the contact stresses under the concentrically loaded footings, and most references and standards have followed this assumption. They have also used this distribution in the calculation of the bending moment acting on footings that are resting on sand and clay. In the literature, many researchers have presented distributions that depart from the Taylor assumption. Approximately equal distributions of contact stress in sand and clay are presented here. The distribution is of higher stress near the edges and lower stress under the column. This paper also examines the problem of contact stress distribution under strip and isolated footings using PLAXIS 2D-AE and 3D-AE, respectively. Linear elastic and Mohr-Coulomb models are adopted to simulate the soils. The results showed that the Mohr-Coulomb soil model is more appropriate in the study of the contact stress distribution than the linear elastic model. The resulting contact stress distributions under the concentrically loaded strip and isolated footings are in good agreement with the previous research results. The contact stresses is highly concentrated near edges and lower under the column. These concentrations of stresses near edges have long arms in the calculation of the maximum bending moment under the footings. Therefore, the maximum bending moment estimated by this modern analysis is higher than the one calculated using the Taylor (1948) assumption. Accordingly, references and standards should be updated to include the real distributions of contact stress. Large scale models should be established to determine the real distributions of the contact stress under footings.

This paper presents the effect of the soil structure interaction on the modulus of subgrade reaction. Many of structural designers represent the footings as hinged support in the structural models, while the other de-signers represent the footings as a group of springs with spring coefficient K (kN/m). Designers assumed this modulus by different equations that are not considering the soil structure interaction. This paper showed that, the soil structure interaction has a significant effect on the modulus of subgrade reaction. k_s is not uniformly distributed under the footings. Using of soil structure interaction in the calculation of the normal forces in columns is resulting a relatively change. Plane two-bay frames and two-bay by two-bay frames were studied using geotechnical and structural 2D and 3D finite element programs, respectively. It is investigated for the plane frames that, the normal force in the inner wall decreased and it is increased for the outer walls. For the three dimensional frames, the inner column’s normal force is decreased and the edge column’s normal force is increased with the same normal force in the corner walls. For the complex structural systems, the distribution cannot be estimated, so the use of geotechnical finite element programs that can consider the soil, foundation, and superstructure effect is highly recommended for the practical and researcher engineers.

High rockfill dams with impervious core or concrete face located in areas of high seismicity in Mexico, require rigorous analysis of seismic stability, which have to observe the standards for dams design. The analyses are clearly dependent on the seismic coefficient for maximum credible and operation earthquakes, which could be deeply increased in order to have a safety factor. Consequently, these coefficients involve the necessity of more conservative geometries for dams, highest quality materials and strict compaction processes, which directly affects the cost and performance during construction. For these reasons the local rules suggest a particular risk study for each dam. In order to have coefficients that may be more realistic, achieving a better cost-benefit-time ratio. This paper describes the study of some existing curtains in Mexico, with seismic coefficients in accordance with those considered during the design and construction stages and using the results of the studies conducted for each site available in the code by the Mexican Electricity Federal Commission. Finally, the implications and consequences related with the constructive activities for each of the analyzed cases are commented, as well as some lessons learned and suggestions for future analyses in order to contribute for sustainable projects.

Dams have been built more than 90% are earth and rockfill dams in china, a large number of survey data about high earth and rockfill dams show that, in the long working process, the reservoir level fluctuation, temperature changes, the saturation line promotion and demotion, rainfall infiltration, evaporation and other factors, will lead to the mechanical properties of rockfill obviously deterioration, and cause additional deformation in the dam. The article summarizes the current research status and problems from the flowing and wetting deformation, environmental change, and particle breakage. It is urgent assignment that research and development the weathering test instrument about rockfill materials under the severe environment, and the study on the rule of rockfill materials particle breakage, mechanics property weakened, volume deformation, flow rate under the change of the environment factors must to be done. The research conclusion will predicate reasonable the long-term deformation of high earth and rockfill dam under the severe environment, and provide important theoretical and technical support for protecting the security and stability of the whole life cycle of the dam.

In this study, a customized spherical bearing combined with a set of sliding-control cables was developed. To verify the characteristics of the developed bearing, an experimental study on both longitudinal and transverse direction was conducted. Test results confirmed the effectiveness of the proposed design. To simulate this system, a 2-link-element simulation method was presented. Comparison showed that the numerical simulation method can match the test results of the bearing properly. Furthermore, a numerical case study featuring an extradosed bridge was presented in which the results implied that the proposed design can control the relative displacement between the girder and pier effectively.

Several bored pile field-testing observations showed the arching phenomena and its effect on side shear resistance. Finite elements numerical model is developed in this paper to study the arching phenomena of bored pile and the effect on the overall compression capacity of single board piles. The numerical models developed apply a hardening/softening model (multi-surface) constitutive model to account for sandy soil non-linear behavior. 2D-axisymmetric finite elements full pile model has been developed and calibrated using several field-testing available in the literature. The numerical study has been conducted to investigate the effect of arching close to the single pile shaft on pile bearing capacity considering three major influence factors: pile length, pile diameter, and sand relative density. The numerical analyses conducted show the important of the arching phenomenon on the overall behavior of piles and on the prediction of bored piles bearing capacity.

This paper is dedicated to the study of elastic shortening of the pile body under applied vertical static load. It considers cast-in-place RC piles, executed by using casing pipe. Very often, the importance of the elastic shortening is overlooked in practice. In the cases when designed piles are standing, the elastic shortening can reach the impressive 71% of total vertical deformation. It is impossible to be ignored. The study is based on thirteen in-situ and one laboratory experiments and their comparison with the Theory of elasticity. The in-situ experiments are executed near different major cities in Bulgaria and the laboratory test is hold in “Todor Kableshkov”, University of Transport, Sofia, Bulgaria.

The dams with the greatest capacity in Mexico, as most of the large dams in the country, were built during the 20th century. Many of them have been in operation for over 50 years, and their environmental and basin conditions have changed mainly due to deforestation and urbanization. Some dams show signs of geotechnical, structural, or hydrological behavior that differs from the one expected. Therefore, they have received a special follow-up as to their behavior, which includes stability analysis, hydraulic–hydrologic functioning, revision of spillway and outlet structures, and channel conditions downstream of the dam. The paper describes general revision works performed to several dams in order to verify that their current operation conditions are acceptable, with emphasis on the geotechnical aspects of earthen dams, concrete-face rock-fill dams, and some masonry dams. The results obtained in the studies and the proposals for risk mitigation, as well as the solutions that have been implemented to improve their safety, are commented on.

The bearing capacity of foundations on rock masses is complex because it is mostly a function of both the intact rock material and the rock discontinuities. The allowable bearing capacity of foundations of structures resting on jointed rock masses with one and two sets of discontinuities is of prime interest to rock mechanics engineers. Jointed rock mass properties are generally spatially variable. The uncertainties may exist due to the laboratory estimation of in situ rock properties. The factor of safety concept in rock mechanics in the estimation of allowable bearing capacity is inadequate to account variability. Reliability based design optimization (RBDO) is accomplished using statistical parameters and probability density functions for each discontinuity parameter. Deterministic bearing capacity is estimated using a lower bound bearing capacity model which is known as the Bell model coupled with a simple discontinuity strength model. Allowable bearing capacity of strip foundations resting on jointed rock masses is computed by considering the variability associated with the jointed rock mass properties, namely discontinuity orientation (θ₁), rock material cohesion (c_r), rock material frictional angle (ϕ_r), discontinuity cohesion (c_i) and discontinuity frictional angle (ϕ_i) and uniaxial compressive strength of intact rock (σ_ci). The design charts for the estimation of allowable bearing capacity factor are presented for the discontinuity orientation of joints in rock mass for the target reliability indices ranging from 1 to 6.

Robust design of continuous compaction measurement value aims at selecting the best combination of control factors in order to reduce the sensitivity to noise factors, so that the accuracy of the continuous compaction control can be improved. Based on the dual response surface methodology, mean and variance of the compaction meter value (CMV) are used as the optimization objective to develop a second-order polynomial model. Using the Box-Behnken design, continuous compaction control tests are carried out for three factors and three elevation levels at Zhijiang construction site of Shang Hai-Kun Ming High-Speed Railway. The three factors are vibration amplitude, excitation frequency and roller speed. The results show that the degree of stability on the CMV is given by: excitation frequency > amplitude > roller speed. Due to the “smaller-the-better” characteristic of the CMV, the best combination of technical parameters for the vibratory roller is: excitation frequency=28.0 Hz, roller speed=4.0 km/h, and vibration amplitude=1.10 mm. Finally, the field test verifies the applicability and the accuracy of this combination of technical parameters.

Rural road connectivity, and its sustained availability, is a key component of rural development. Rural roads are connecting areas of production with markets and connecting these with each other or to the state and national highways. The unavailability of database is major constrain to the access of rural roads. This paper envisages consolidation of the existing rural road network to improve its overall efficiency as a provider of transportation services for people, goods and services. This study has undertaken an extended attempt to develop geographic information system (GIS) based rural road database so that planners, decision makers, researchers and other different level authorities in the rural road sector will be benefited from the final output. The study area is located in Warangal District, Telangana, India. Network analysis has been conducted to select shortest path, service area accessibility, and closest facility, location allocation of a facility and shows the vehicle routing in terms of travel time, between two locations in the study area and towards rural hubs. The average travel times were observed from the field surveys. Rural hubs has been selected, from 46 habitations found in the study area, based on the cumulative weightage of rural infrastructures and the number of trough-routes they have. Furthermore, an evaluation of road network has done based on the connectivity measures before and after identification of critical links of the network and also identifies the centroid point of the network by measuring the connectivity values of the nodes. The paper also focused on development of planning model for upgradation of rural roads based on the link weightage and pavement condition index (PCI) of the road.

Plastic concrete is a suitable material for building earth dam cut off due to low permeability, high deformability and enough strength to withstand applied stresses. Due to the lack of a specified standard for plastic concrete materials, evaluation of the effect of the amount and quality of materials such as concrete aggregates (fine and coarse gravel and sand), cement, water and bentonite on the mechanical properties of plastic concrete is considered to be a serious need. In this study, we have investigated the effect of the ratio of mixing materials (mixture proportions) and cement as well as the materials’ quality such as the type of bentonite on compressive strength and modulus of plastic concrete elasticity. The results of this study showed that by decreasing the ratio of term activity, compressive strength will be reduced due to increasing free water in case of the stability of other parameters. However, the effect of aggregates unlike cement has no direct effect on mechanical properties of plastic concrete.

This paper studies the seismic response of buildings located on slopes, taking into account the coupled behavior of building, foundation and slope. Two representative building-foundation systems on two different slopes are considered and response under gravity and seismic actions is compared with ‘flat ground’ and ‘fixed at base’ conditions. Nonlinear 2D finite element analysis using ABAQUS is performed. The effects of interaction between building, foundation and slope on the position of the sliding surface, foundation settlement, vertical and lateral displacement of the building, and bending moments and shear forces in superstructure columns and beams are explored. It is observed that the interaction has significant effect not only on the slope stability but also on the building response. The effect of foundation-soil is much larger in case of buildings on slopes, than the buildings on flat terrain.

In order to predict the exact amount of maximum surface settlement value, this paper presents a method to predict ground movement above tunnels with random forests (RF). Surface settlement above a tunnel due to a tunnel construction is predicted with the help of input variables that have direct physical significance. The RF-based model is developed by free R programs, trained and tested with parameters obtained from the detailed investigation of different tunnel projects published in literature. The maximum settlement is taken as a function of tunnel diameter, depth to the tunnel axis, cohesion, internal friction angle, compressibility modulus of soil, grouting pressure, percent tail voild grout filling, thrust force and advance rate for shield tunneling. A repeated 5-fold cross-validation procedure (10 repeats) is implemented to determine the optimal parameter values during modeling and an external testing set is employed to validate the prediction performance of models. Two performance measures namely R² and RMSE have been employed. The RF demonstrated a promising result and predicted the desired goal fairly successfully.

Two-dimensional dynamic distribution models of voidage in each longwall mining-disturbed stratum were proposed to investigate the heterogeneous distribution and periodical responses of voids with the extraction of coal. It indicated that the developed zone of voids periodically extends forward with the advance of the longwall mining face. Along coalbed strike and dip, the voidage in the caved zone has a "basin-type" distribution, and the transverse and longitudinal voidage distribution in the fractured zone are "saddle-type" and from "arch-type" to "saddle-type", respectively. Additionally, the voidage gradually decreases from the deep to the shallow around the perimeters of mining-disturbed stratum, but the change is inverse near the center. Further research illustrated that the distribution shape of transverse voidage along the strike alters from the "∩-type" to the "M-type" as time goes on. However, the distribution shape of longitudinal voidage keeps in the "M-type". The distribution models of voidage can be hopefully applied to guide coalbed methane extraction, water influx prevention, coal fire prevention and control, and so on.

Instability of pile foundations due to liquefaction of surrounding soil is considered as one of the vital cause of its failure. Many case studies are available, where pile foundations are subjected to severe damage due to liquefaction even though designed with good factor of safety. Assuming incorrect failure mechanism in design is probable reason for these failures. Earlier studies idealize pile as a column, and a buckling mode of failure is postulated as a failure mechanism. Lateral spreading during liquefaction can cause large lateral loads on the pile and induce a different failure mode. This is the focus of the present study. Here pile is idealized as a beam-column and failure analysis is performed against buckling as well as flexural instabilities. By considering flexural as well as buckling instabilities, a simplified approach to quantify the critical axial load on pile is formulated in the present paper. A case study is also presented to demonstrate the calculation of critical axial load. Results from the case study infer that, at certain level of lateral spreading piles fail in yielding rather than buckling, which needs to be given due consideration in the design of pile foundations in liquefiable soils.

Any effort that each engineer may offer toward rational designs for construction dams is linked to a rational use of natural resources. After years of experience using roller compacted concrete (RCC) in dam construction, a rational method for mixtures design based on a mechanistic reasoning has not been developed yet. Experts, depending on their particular experiences, aim according to his/her personal approach. However, despite these methods are quite different among them, and some very successful, none are based on a mechanistic reasoning but empirical. This shortcoming turns the design in a long trial-error process, which leaves the production-placement stage subject to decisions out of the track of the desired goals. Therefore, it can be said that a design method which relies on a mechanistic reasoning, trends to short the trial-error cycle that entails any geomaterial’s design. On the other hand, once the final mixture design is achieved, dispose such designing tool, might lead to improve the quality control stage due to the rationality that supports all the process. This paper proposes an approach similar to that used for design of asphalt mixtures, based on a standardized process and standardized input elements.

Seismic event and quarry blast classification is one of key issues in seismic data processing. However, automatic microseism classification is still a challenging work in practice. In this paper, based on discrete wavelet transform (DWT), a novel approach combining singular value decomposition (SVD) and support vector machine (SVM) techniques was proposed to categorize seismic signals. Firstly, the DWT was used to obtain wavelet coefficients, then correlation coefficient and variance contribution ratio were proposed to choose main wavelet coefficients. After that, the SVD was employed to compress data and extract features of the selected main wavelet coefficients. Finally, the BP neural network, Bayes and SVM classifiers were implemented to identify seismic events and quarry blasts of Yongshaba Mine, China. The results show that SVD can effectively reflect signal features and classification results of SVM is better than BP neural network and Bayes in accuracy, specificity and sensitivity, being the value of 95.5%, 97.0% and 94.0%, respectively. Thus DWT-based SVD and SVM techniques provide a useful method for seismic event and quarry blast classification.

Analysing the rock slope stability is a classical problem for geotechnical engineers. Recently, Hoek-Brown failure criterion has drawn more and more attention for rock slope stability assessments. It would be due to the fact that the nonlinearity is more pronounced at the low confining stresses that are operational in slope stability problems. However, it is still not popular yet. Therefore, in this study, slope stability analyses will be performed based on the generalised Hoek-Brown failure criterion using a commercial software, Phase 2. The Hoek-Brown strength parameters will be used as direct inputs in numerical simulations. In addition, two rock slope cases will be investigated. It is expected that better understandings of rock slope mechanisms can be obtained.

This paper established a computing model of surface roughness coefficient (JRC). To begin with, fractional Brownian functions were adopted to generate random fractal curve, which compared with standard Barton’s curve. Slope root mean square and curvature root mean square were calculated for test samples. Based on neural network algorithm and particle swarm algorithm, BP-PSO calculation program were constructed. Test samples were used to train the neural network and JRC value under two-dimensional condition were calculated. Since random error and systematic error are considered, the method in this paper is easier to acquire accurate result compared with traditional explicit quantitative relationship between geometrical statistical parameters and JRC value. By scanning three-dimensional joint surface, point cloud data were acquired. Spatial distribution of effective contacting area of joint surface was analyzed according to different shearing direction, and the roughness coefficient computing method was reformed according to three-dimensional condition. The calculating model in this paper offers a new way to evaluate JRC value.

The symplectic method was applied in the orthotropic beams under the thermal mechanical coupling in the present paper. With Hamiltonian variational principle and Legendre’s transformation, Hamiltonian canonical equations are obtained, together with side boundary conditions. So the analytic solution with different boundary conditions can be converted into determination of eigensolution with separation of variables and symplectic expansion. The results showed that the present solution have better convergence and precision, which provides a basic theory for studying the plane beam under thermal-mechanical coupling.

In present paper, the symplectic method was introduced for the two dimensional transient heat conduction problems. Based on the fundamental equations, the symplectic space constituted by original variable temperature and dual variable heat flux density has been built, which was reduced to finding the eigen solutions and eigen values, so the analytic solutions of temperature field in Hamilton system are obtained. Finally, the distribution of temperature was analyzed with different thickness ratio, time steps. The results showed that symplectic method is effective to study two dimensional transient heat conduction.

Valiasr Metro Station located at Valiasr Intersection where two subways crossed and the Valiasr Underpass that is a pedestrian underpass is recently constructed there. This paper presents the design and construction process of the access tunnel that connects the ticket hall of the metro station to the underpass. The shallow depth of the access tunnel and existence of the numerous underground construction and installations are parts of the limitation of the design and construction process. The metro station and the under pass were under operation during the construction time. NATM was considered to construct the access tunnel and 2D and 3D numerical models were applied to simulate the staged construction process and to design of the tunnel’s initial lining.