New Frontiers in Geotechnical Engineering

Microbial induced carbonate precipitation is a novel soil improvement method that has demonstrated potential to strengthen the ground in a sustainable and eco-friendly manner. Previous investigations have studied its mechanical behavior through conventional triaxial or soil column tests. However, there is limited information about the bio-cemented sand's properties under k₀ loading, which more closely resembles some in situ stress conditions. Using a modified consolidation cell with shear wave velocity monitoring via bender elements, the authors investigate the behavior of bio-treated sand under loading and unloading. The effects of cementation degree(shear wave velocity 350 m/s and 700 m/s after cementation) and initial densities(loose and dense) are explored through careful preparation of samples. The results of the bio-cemented specimens under an incremental loading and unloading sequence are compared to that of uncemented sand at similar densities.

Microbial Induced Calcite Precipitation (MICP) stands as a promising technique for modifying engineering characteristics of the soil including: strength, stiffness, and permeability. These modifications represent the requirements of several geotechnical and environmental applications. This paper studies the incremental changes in permeability correlated with the development in soil stiffness. Permeameter cells modified with s-wave bender elements were used to measure changes in permeability. The bender elements were used to continuously monitor the development in soil stiffness. A systematic study was performed to evaluate MICP product under different treatment conditions changing concentration of treatment solution, retention times and back pressure. Treatment concentrations from 0.25-1.0 M have been used, and the back pressure was applied at values between 0 and 100kPa while maintaining effective stress at 50 kPa for all experiments. Results have shown no notable changes in MICP changing pore water pressure. The major changes were ascribed to the concentration of chemicals used for treatment. At low calcite content, all treatment conditions lead to similar results for stiffness development and hydraulic conductivity reduction. Using high concentrations for treatment solutions resulted in earlier clogging that altered the manner by which soil acquires new characteristics. The outcomes presented by this paper provided a reference for evaluation of the proper use of MCIP.

This paper presents results of laboratory assessment of creating seepage barriers in a sandy soil using biopolymer additives (bio substance), which consist of polysaccharides and water. Polysaccharides strongly interact with water to produce a viscous suspension. The aim of the conducted work was to investigate the influence of a biosubstance employed in a highly permeable sandy soil. The amount of the biopolymer used in a sample fell between 0.1 and 1.5%, by dry weight. Tests were carried out on two different specimens, coarse sand (1.18 - 2.00 mm) and medium sand (0.075 - 1.00 mm). The test results indicate that the hydraulic conductivity values change significantly based on the amount of bio substance, gradation of the sand and curing time. It is concluded that such application, which is a relatively new soil improvement technique, could be used as a seepage barrier installation, required to protect some geotechnical works including foundation, underground structures and waste disposals.

This paper presents an extensive experimental investigation on the use of ground improvement techniques and biotechnological applications on earth science. In recent years, investigations in geomicrobiology have enabled significant advances in understanding the effect of microorganisms in the development of the soil behaviour. In this paper, a series of experimental study was conducted to investigate the applicability of biotechnologies in soil stabilization. Unconfined Compression and California Bearing Ratio (CBR) tests were employed during the experimental works for an assessment of two soil parameters of major importance - namely, compressive strength and bearing capacity. From the experimental results, it was observed that the unconfined compression strength and the CBR values of the sand increased with an increase of curing time.

A simplified nonlinear approach is proposed to study the behavior of the pile group with flexible cap. In this paper, the cap is modeled as a thin plate with the finite element method. By employing the load transfer method, a nonlinear finite differential formulation for the analysis of a single pile is created. Pile groups are analyzed by the superposition principle by assuming a linearly elastic behavior. Based on solutions for the stress and displacement in layered elastic half space, the interaction factor between two piles is determined by considering the shielding effect between a receiver pile and the surrounding soil. In order to verify the validity of the proposed nonlinear analysis method, calculated results are compared with the numerical and test results from the literature. Good agreement is achieved, thus showing that the proposed method can provide a simple and useful tool for engineering design.

Microbially induced calcite precipitation (MICP) using Sporosarcinapasteurii was employed to enhance the strength of weakly cemented soil and fill its voids. Weakly cemented sand with a cement ratio of 3% was prepared and cured for 3 days. The cemented sand was treated up to ten times with the Sporosarcinapasteurii microbe over a 20-day period. The resulting sand was then tested to evaluate its unconfined compressive strength (UCS) and the amount of calcite precipitation within the cemented sand particles. The level of calcite precipitation increased slightly with increasing number of microbe treatments. The UCS of the specimen treated once with the microbes showed a 5% increase compared to the untreated specimen. On the other hand, for the specimens treated more than twice, their strength decreased gradually by up to 50% compared to the untreated specimen. The precipitation of calcites within the cemented sand can adversely weaken the existing cementation caused by cement hydration.

This paper presents the effect of soil type on the contact stress under the footings. The soil type affects the distribution of contact stresses under footings. Several researches about the contact stresses were made with the linear elastic soil model. This model cannot take briefly the effect of soil type parameters, such as the c and φ. Therefore, the use of more realistic models is highly recommended. An elastic perfectly plastic, Mohr-Coulomb, model is considered to be a good, simplified, non-linear model. The Mohr-Coulomb model was adopted to simulate the soil model using PLAXIS2D V2012. Different footing rigidities on sand and clay were studied to investigate the distribution of contact stresses. Upon investigation, the resulting edge contact stress in sand is lower than that in clay for different footings rigidities. The use of flexible footings leads to increase of the contact stresses under footing center and decrease under footing edges for both soil types. The use of rigid footing results in high contact stresses near edges and low contact stress under footing center for both soil types. These results were compatible with some investigated measurements for the contact stresses presented in the literature. The significant result is that the resulting distributions of contact stress on sand and clay are not compatible with the probable stresses shown in references and standards. The cohesion of the clayey soil plays an important role for increasing the contact stress at footing edges more than that resulted in sand. It is worth mentioning that the resultantcontact stresses at edges have long arms during the calculation of the maximum bending moment at footing center. This increases the maximum moment on footings more than that calculated considering the uniform distribution of the contact stresses.

This paper presents the effect of soil model on the distribution of contact stresses under strip footing. Contact stress is related to the normal pressure at the contact surface between the foundation and the supporting soil. The soil model affects the distribution of the contact stress. Linear elastic soil models, sometimes referred to Boussinesq's model, result in concentration of stresses at footing edges. This concentration can be more than the ultimate stress of soil, which is not realistic. Therefore, a footing model that can consider the plasticity of soil is highly recommended in the calculation of contact stress. The elastic perfectly plastic model (Mohr-Coulomb model) is the simplified non-linear model that can be used to find a fair distribution shape for the contact stresses. In the measurements presented in the literature and in this soil model, the contact stresses near edges increased with the increase of the applied load. This increase limited to the ultimate stresses, and then plastic points are formed at edges that release the contact stresses toward footing center. The distribution is still high near footing edges and slightly low at footing center. With increase of the load, the plastic points are formed under footing in a distance beside the edge, and then the stress is released toward the footing center. This action is continued with increasing the applied load, and then the contact stresses distribution become nearly triangular. This distribution shape is the shape in the case of bearing capacity failure. Many standards and references suggested the shape of the contact stress of footing on sand. They suggested zero stress at edges and high under load. This shape can be done for the very flexible footing, which is not applicable, or at failure condition, which is not applicable by using the allowable bearing capacity. The authors suggested updating the distribution of the contact stress that presented in these famous references. Due to the resultant concentration at edges that has long arm during the maximum moment calculation, the maximum moment at footing section is more than that resulted using uniform contact stress and need to be further verified by several researches.

This paper investigates random wind loading, wind-induced fatigue loading, and the effect of wind-induced fatigue loading on the stability of wind power foundations. Wind climate statistical data were collected and analyzed based on the environmental meteorological conditions over past 50 years in the mid-west areas in the Inner Mongolia Autonomous Regions, China. The characteristics of random wind loading were analyzed in typical large MW wind power field construction. When the random wind loading was transferred from wind turbine tower to its foundation, the foundation is subject to repeated loading in a 360-degree direction, alternating change in the direction of bending moment, and large eccentric loading which indicate the obvious fatigue characteristics. This kind of wind-excited vibration of foundation leads to fluctuating stresses causing the accumulation of fatigue damage. Wind-induced fatigue loading acting on the foundation is simulated to the equivalent wind loading excitation on multiple particles of mass-spring-damper model, and its effect on the stability of wind power foundation is evaluated through finite element method. This paper develops a mathematical model aimed to obtain the characteristics of wind-induced fatigue loading and evaluate the anti-capsize stability of foundation.

This paper presents the results of a study of the effects of cyclic heating and cooling on the thermal and hydraulic conductivity properties of a geothermal well seal. In the US, bentonite is widely used in the annulus between the fluid circulating pipes and the formation for geothermal well systems and is subjected to many cycles of heating and cooling throughout the design life. In particular, the seal is expected to maintain contact with the circulating pipes and the formation in order to effect efficient transfer of heat into and out of the earth. Secondly, since many of these wells are 100 m deep and more, the seal must maintain a low hydraulic conductivity in order to isolate various aquifers over the well depth from cross-contamination. In the study, after 23 cycles of heating and cooling, the thermal conductivity remained constant but was different for cycles of heating and cooling; 0.173 W/m.K (0.1 Btu/hr ft °F) for cooling and 0.865 W/m.K (0.5 Btu/hr ft °F) for heating. A replicate trial yielded similar results. After 12 cycles of hydraulic conductivity testing, there appears to be some degradation in the hydraulic conductivity and intrinsic permeability.

Coal-based thermal power plants are the main source of power generation in many industrialized countries. Consequently, management of the considerable quantities of fly ash and other coal combustion residuals is of great importance with wet-storage impoundments being themost common storage option. Although the beneficial reuse of fly ash is increasing worldwide, the problems associated with diminishing impoundments capacities and possible negative impact of fly ash on environment is subsequently becoming a major concern. Legislation is proposed in the US to close or line all existing impoundments. Each of these progressions necessitates an increase in dewatering and transport of wet-disposal fly ash. Recently, geotextile tubes have been used to efficiently and economically dewater a number of low percent-solids sediments, by-products, and wastes. To investigate the effectiveness of geotextile tubes for dewatering hydraulically transported fly ash slurry a number of laboratory studies were conducted. The dewatering behavior of fly ash was evaluated with and without mixing with randomly dispersed waste fibers. The effect of anionic polyacrylamide flocculant on the dewatering performance was also evaluated. Results indicate that geotextile tubes can be effectively used for dewatering flocculated fly ash slurries, and that the strength of retained fly ash can be improved by adding fibers.

One of the popular offshore wind turbine foundations - monopile - has been largely used because of their cheapness and constructability. Monopile is subjected to large cyclic lateral loadings such as wind, wave and current. The P-y curve method - which represents a relationship between lateral pile displacement and passive soil resistance along the leading face of the pile - is known as a highly reasonable method to analyze lateral behaviors of pile. Performing reliability analysis of a monopile foundation using nonlinear p-y curves is difficult because the limit state functions (LSF) of pile head deformation and rotation angle of pile are in implicit forms. To solve such problems with implicit LSF, a response surface method (RSM) could be used. The basic concept of RSM is to approximate the limit state boundary using an explicit function of the random variables. In the case of using RSM, reliability analysis could be very simple; but, the accuracy of analysis due to approximation depends much on the linearity of the LSF and on the distance of the axial points in the failure space. This paper investigates the best combinations of the RSM techniques with a reliability analysis of monopile for an offshore wind foundation.

An assessment of hydro project-related geohazards (AHPRG) has, as its salient features, vast assessed project areas, timeliness, complex objects and contents, lack of large scale geologic maps and poor traffic conditions. Unfavorable factors often hinder engineering geologists arriving at geologic disaster sites successfully and in time. With the development of aerospace science and technology, more and more high-resolution terrain data are being used to assist geohazard assessments To some degree, with this type of assistance, the unfavorable factors inherent in conventional assessment procedures could be mitigated or even overcome. Moreover, some computer operation systems, such as Google Earth, have been developed to build visual terrain models directly on computers and allow users to manipulate the viewing parameters so that they may look at an object from different angles. The RIMS system is just one of these types of systems but, it is unique in that some functions were added to enable users to measure the orientations of engineering geologic features (virtual geologic compass (VGC)) and to directly map what they have observed, etc. After using RIMS and Google Earth in real AHPRG situations, the authors believe that these types of terrain image operation systems would be powerful tools for future AHPRG by combining basic geologic data, geohazard inventories and terrain images from different times.

There is an increasing interest in the use of Ground Source Heat Pumps (GSHPs) as a source of renewable energy in temperate countries. GSHPs coupled with buried heat collectors can harness the thermal energy from near-surface soils to provide the heating required for domestic properties. The performance of a GSHP system depends greatly on the thermal conductivity of the surrounding soils. Near-surface soils undergo cycles of drying and wetting due to, for example, the infiltration of rain water and/or fluctuations of the ground water table. Several parameters - including the properties of soil, suction head and saturation history - affect the thermal properties as well as the retention and flow of water. This paper presents results from a comprehensive laboratory investigation on sand samples with markedly different grain size distribution. Simultaneous measurements of thermal and hydraulic properties of the sands were taken under incremental increase/decrease in the suction head values to simulate cycles of drying and wetting. The results clearly suggest that the thermal conductivity is better expressed as a function of the matric suction head so as to reflect the saturation history. There has been almost five-fold increase in the measured value of thermal conductivity when the soil was wetted to a residual degree of saturation from being dry.

Synthetic lightweight aggregates (SLAs), composed of coal fly ash and recycled plastics, represent a resilient construction material that could be a key aspect to future sustainable development. This research focuses on a prediction of the elastic modulus of SLA, assumed as a homogenous and isotropic composite of particulates of fly ash and a matrix of polystyrene (PS). The elastic moduli of SLA with variable fly ash volume fractions are predicted based on finite element analyses (FEA) performed using the computer programs ABAQUS and PLAXIS. The effect of interface friction (roughness) between phases and other computation parameters - e.g., element type and boundary conditions - are included in these analyses. Analytical models provide a baseline for comparison. Overall, results indicate ABAQUS generates elastic moduli closer to those predicted by well-established analytical models than moduli predicted from PLAXIS, especially for SLAs with lower fly ash content. In addition, an increase in roughness between phases (from 10 to 90% roughness) produces up to 340% stiffer SLAs, especially as fly ash content increases. Future efforts will attempt to compare computational results to laboratory measurements of moduli.

The control of temperature crack has always been the key factor to ensure the quality of mass concrete construction. Taking the construction of a ship lock in Hai'an, China as an example, this paper combines distributed optical fiber temperature sensing (DTS) and Geological Statistics (GS) to implement an in-depth study on reconstructing the mass concrete temperature field. The results manifest that the distributed temperature field data based on DTS has laid a foundation for detailed description of the mass concrete temperature field. By adopting linear combination of nugget and spherical model, Kriging interpolation has been carried out to reconstruct the mass concrete temperature field. In this way, more precise results of field distribution are achieved. The average mean error of interpolation and the average relative error were 0.42° and 0.01°C, respectively, which verifies the effectiveness of the proposed method. Reconstruction and visualization of temperature field can be achieved using the DTS-GS method and significant evidence can be provided for the control of concrete temperature crack during the construction and maintenance of concrete structures.

The Support Vector Machine (SVM) has been widely used in displacement prediction of landslides, and value selection of three import parameters (penalty factor C, relaxation factor ζ, kernel function parameters δ) is the key point of affecting prediction accuracy. Six consecutive years of monitoring data of two typical reservoir landslides in Three Gorges reservoir area have been used to analyze the value selection of three parameters on the influence of displacement prediction accuracy by using the SVM model. Firstly, the moving average method is adopted to decompose the cumulative displacement into trend term and periodic term displacement, at the same time, the training and test datasets are built; then based on the analysis of landslide deformation mechanism and influential factors, the SVM prediction models of trend and periodic term displacement are established according to corresponding forecast variables; Next, the relationships between parameter C, ζ, δ value with prediction accuracy of the training and test data are analyzed. Finally, according to parameters influence law, three parameters value range are recommended, and which can be used as the initial search range of parameters optimization for SVM, results indicate the high accuracy can be obtained for landslides displacement prediction.

The virtual laboratory system played an important role in improving the traditional experimental education. The system for road engineering created virtual environment to simulate physical labs by using virtual reality and multimedia technology. Its design and implementation were described in the paper. The system design mainly focused on the framework structure, function division and results assessment method. It was shown that the framework took database as core and run over network. Besides, function management was divided into two, which were responsible for the experiment and system, respectively. Moreover, three methods were raised to assess experimental results. As for the implementation, after comparing the commonly used software, Flash was chosen for development. The system consists of virtual programs and websites are successfully established. It indicates that the system will increase the quality of test training.

With ArcGIS Engine and Visual Studio 2008 as a development platform, a system for risk assessment of sea-filling induced geological disaster in Beibu Gulf of Guangxi was established. VC++ object-oriented programming language and SQL Server database were used to establish the system. The geological disaster risk of sea-filling in Beibu Gulf was evaluated by the information model. The disaster information management, information query, information processing and spatial analysis of the sea-filling areas were carried out with this system. Comparing the prediction with monitoring value indicates that the risk assessment system of sea-filling induced geological disaster in Beibu Gulf of Guangxi is worthy to popularize.

Urban underground space (UUS) resources, as an important part of urban space, should be properly and rationally treated, and the urban geological conditions must be taken into account. In this paper, the geological suitability evaluation model was focused on in the light of four subjects: the topography and landform, the engineering geology, hydrogeology and the site stability which, respectively, have their indexes. By making use of the analytical hierarchy process (AHP) and ArcGIS software, the development suitability for the urban underground space can be obtained. The above method was applied in the Changzhou's plan of urban underground space exploitation and utilization as an example.

A semi-top-down excavation method is proposed for construction of an underground metro station in Shanghai, which is close to an elevated metro station and several high-rise buildings with shallow foundations. The semi-top-down method combined the construction sequence of temporary strut and middle floor slab of the substructure during excavation, which united advantages of the top-down method and the bottom-up method. The efficiency of the new method to reduce the environment deformation is analyzed based on the numerical analysis and field measurements. Both the settlement of buildings and the lateral displacement of retaining structure were obtained numerically and compared with those of the traditional excavation method. Predicted results shows that the increase of building settlements trend to be mild after the middle slab is constructed, which means that the semi-top-down method has a good effect on controlling the surrounding deformation. The monitoring results show that the proposed series of techniques is effective and the displacements of the adjacent structures are similar to that predicted by numerical method. The settlement observation of the high-rise building and elevated metro station show that both the settlements and the differential settlement are within control. Therefore, the new method can ensure the efficiency of deep excavation and reduce the environment deformation.

The land subsidence areas of Balizhuang and Dajiaoting, located in the eastern part of Beijing, are the earliest and most serious land subsidence areas of Beijing. The monitoring data indicate that the degree of land subsidence has become much more serious in recent years. Based on the historically monitored data and the new data from the high-resolution land subsidence monitoring system, a detailed analysis was performed on the evolutional characteristics of the land subsidence in these areas. The results indicate that the land subsidence is more serious in the north and east areas compared to the south and west areas. The excessive withdrawal of groundwater is the major cause of land subsidence. The land subsidence was found to be closely correlated to the groundwater level, groundwater withdrawal intensity and depth. Moreover, the position of the land subsidence funnels is closely related to the thickness distribution of the compressible soil. Specifically, the land subsidence center is commonly distributed in the area with the thickest compression layer. The results of this study provide some suggestions for reasonably utilizing groundwater and effectively controlling the land subsidence of Beijing.