Resilient Design and Construction of Geostructures Against Natural Hazards

The marine clay is generally regarded as poor materials for urban applications because of its high settlement and instability. In this study, the soft marine clay is mixing with cementitious material such as cement and lime in different ratios, so that the geotechnical characteristics of blends improved. A series of laboratory experiments are conducted to verify the enhanced performance of treated marine clay. The optimum moisture content (OMC) along with maximum dry unit weight obtained from Standard Proctor compaction test and Harvard miniature test. Unconsolidated undrained test (UUT) and unconfined compression test (UCT) are implemented to find out the compressive strength of samples. Blends selected from the dry side of the compaction curve own larger compressive strength than the others, which means an appropriate amount of water is enough for blends mixing. The results of laboratory tests are utilized to establish neural network models to predict engineering properties such as, compressive strength, optimum moisture content, and maximum dry density of treated marine clay. The correlation between the additive contents as well as curing days and compressive strength has been approved according to the test results. The properties such as maximum dry density, water contents, and additive contents are used as inputs to predict the compressive strengths. The predicted consequences of neural networks are well fitted with laboratory test results.

About 25% of bridges in Craighead County, a part of Northeast Arkansas (NEA) in the United States of America, are in a poor condition. The NEA region is situated within a major seismic zine called the New Madrid Seismic Zone (NMSZ). In recent years, several new bridges have been proposed for new highways or improvement of existing highways within this zone. With the existing vulnerability due to the presence of the nearby active fault and higher seismic design force requirements, future investment in the repairment of bridges and new construction are critical issues. The main objectives of this study are to estimate seismic site coefficients for this zone by ground response analysis and compare them with coefficients recommended by researchers and agencies such as the American Association of State Highway Official (AASHTO). The shear wave velocity profiles (SWVP) of this zone have been collected from historical construction projects in the NEA and Mississippi Embayment (ME) areas. The seismic hazard analysis (SHA) has been carried out for different locations within this zone. Using a unified 1-D (one-dimension) equivalent linear (EQL) and nonlinear (NL) site response analyses platform called DEEPSOIL (Version 7.0), a series of ground response analyses has been carried out to evaluate possible variabilities of SWVPs, dynamic soil properties, and SHA results. Finally, seismic acceleration site coefficients have been estimated for selected locations within this zone. The findings of this study are expected to help the city and state highway design engineers to calculate design forces for existing and new bridges that will lead to the avoidance of expensive field investigations.

Soil conditioning is an available auxiliary measure to improve the efficiency and safety of earth pressure balance (EPB) shield tunneling. In order to optimize soil conditioning strategy during tunneling in gravelly sand stratum, it is essential to understand rheological and compressive behavior of conditioned muck and its flow characteristics inside chamber. This paper establishes a constitutive model of compressible modified Bingham fluid for characterizing macroscopically rheological and compressive behavior of foam-conditioned gravelly sand and determines the model parameters by vane shear tests with variable shear rate and lateral confining compression tests. Based on the above theory and computational fluid dynamics (CFD), crucial spatial distribution characteristics of conditioned muck static pressure and flow speed inside chamber are captured by numerical simulations, which is verified the reliability in simulating muck movement during tunnelling. Overall, investigation of macro-hydrodynamics behavior of foam-conditioned gravelly sand and numerical simulation of muck movement in excavation chamber and screw conveyor will inspire soil conditioning assessment while EPB shield tunneling in gravelly sand stratum.

By its specific geographical and climate conditions, Iran benefits from high environmental and climate variability. Besides abundant relative advantages, this variety has increased the potential of different natural risks. Earthquake, as one of the most significant geotechnical risks, threatens most regions throughout Iranian Plateau. The importance of earthquake risk in Iran has been increased by the increased development of cities and the concentration of population. Tehran, as the most important city based on its population, economic and social infrastructures, and because it has been surrounded by several active faults as well as located on some active ones, exposed to high risk against earthquake risk. In this case, one of the requirements of urban management in Tehran is studying the seismic risks of this town as well as estimating its probable damages. For this reason, region 3 of district 1 of Tehran municipality having many old textures than other districts have been chosen as a region of study. The methodology of this study, data collection, and analysis are conducted by methods based on database benefiting from RADIUS Program, and there have been considered two scenarios based on both faults in the North Tehran as an origin for estimating the risks from the probable earthquake in the region. Results indicate that maximum risk might be considered in the scenario of fault located in North Tehran.

Expansive soil has the characters of swell-shrink, fissured and over-consolidated, which can affect the safety of construction projects in expansive soil areas. Deep soil mixing (DSM) is a widely used ground improvement method. It can improve the mechanical properties and reduce the permeability of expansive soil effectively. In this study, a series of direct shear tests and unconfined compressive tests were conducted to study the effect of cement content and curing time on the mechanical properties of cemented soil. Relationship among the mechanical properties and cement content and curing time were analyzed qualitatively and quantitatively by the test results. Recommendations for design and construction of the DSM in expansive soil areas were also proposed in this study.

Microbially-induced calcium carbonate precipitation (MICP) is an emerging technique that can improve the engineering properties of geomaterials. A microfluidic chip is designed to capture the MICP process in pore throats and large voids under flow conditions. Results show that the growth of crystals presents similar accumulative behaviors in those two areas, while the shapes of crystals are different. The precipitates formed in the pore throats exist as crystalline aggregates, whereas those in large voids present in the form of single crystals. The preferential growth at the upstream face is observed for the single crystal. The distinctions between the single crystal and the crystalline aggregates might result from different flow fields of the growth environment. Those preliminary results could advance the understanding of the growth behaviors of calcium carbonate and have implications for a wide range of applications.

Clogging is often observed in the improvement of dredged fills using the vacuum pressure combined prefabricated vertical drains. Due to the clogging at the drain, vacuum pressure needs some time to achieve the target value, and the magnitude of the pressure reduces along the drainage path in the spreading process. In this study, a large strain consolidation model is built under boundary conditions varying with time and distance to the vacuum connector. The model is solved by a numerical method to compare the total consolidation and the radial distribution of excess pore water pressure under different boundary conditions. The large strain consolidation model is also compared with results of small strain consolidation and measurements in field tests with the variation of vacuum pressure considered. Based on the comparisons, it is found that time-dependent variation makes impacts on the rate of consolidation, and the distance-dependent variation affects the ultimate consolidation results.

Many geomaterials are mixed composites and the permeability coefficient of each phase differs widely. Determining the overall permeability coefficient of mixed materials is still a challenging task due to the heterogeneity. Few studies have focused on the physical mechanism of the hydraulic property of mixed geomaterial. To address this lack of knowledge, a constant head permeability test and numerical simulation based on CFD (computational fluid dynamics)-DEM (discrete element method) are conducted to investigate seepage performance of mixture specimens. To explore the effects of content of each phase on the overall permeability coefficient, glass beads as inclusion phase are distributed uniformly and randomly in quartz sand, and different contents of inclusions ranging from 0% to 60% are considered. The experimental and numerical results show that the overall permeability coefficient increases with the content of the glass beads and porosity. It can be seen that the overall permeability coefficient is not only related to the content and property of each component, but also more determined by the interconnected paths. This work provides new sights for the future research of hydraulic property of mixed materials.

In geotechnical engineering, strain localization and the formation of shear bands is regarded as initiator of failure as a result of non-uniform deformations within soil, making clear understanding of strain localization very important to geotechnical engineers dealing with slope stability. In this paper strain localization in natural clay is studied numerically using finite element method (FEM). A new elasto-viscoplastic constitutive model that is implemented into ABAQUS with the ability to accurately describe the time-dependent, over-consolidated and structural characteristics of natural soft clay is used to perform 2D plane strain compression test under undrained conditions on undisturbed Kyuhoji marine clay. The influence of confining pressure and strain rate on strain localization is studied by numerically analyzing their effects on the formation and evolution of shear bands, thickness as well as the orientation of shear bands in natural clay. The results show that four crossing shear bands are observed in which higher confining pressure results in thinner shear band and a slightly smaller shear band angle as compared to lower confining pressure. An increase in strain rate increases the shear band angle and shear band thickness. Mesh dependency is not very apparent on the mechanical response of the specimen but affects the shear band features.

This paper established the analysis of the results of calculated subgrade settlement in the loess area, due to traffic load and partial saturation of the loess. Loess has high strength and low compressibility in a dry state, which is known as structure of loess. However, it is easy to absorb water due to the high porosity, which induced loess lose structure and strength reduction. During the construction of the subgrade, due to inadequate protection during the intense rainfall, partial saturation of the loess layers occurred, which will destroy the initial structure of the loess and cause significant settlement after construction. Besides, traffic moving loading produces dynamic stress in subgrade which may lead to additional plasticity and then produce an excessive settlement. To assess the development of settlements under traffic load and partial saturation, the settlement calculations were performed based on the collapse potential and increase of moisture content. The calculated subgrade settlement was compared with the observed settlement for validation. Further, some measures were proposed in order to ensure the safe operation of the subgrade based on the settlements.

The loess tends to behave in an instable manner when subjected to external loads since it is characterised by metastable structure, high porosity, and water sensitivity. Therefore, the Chinese Loess Plateau has been deemed as a landslide-prone area in northwest China. This study explores the potential use of the loess-waste straw mixture as an alternative backfill material to improve the stability of loess against shallow slope failure and functionalise the agricultural solid waste. The displacement-controlled direct shear tests aim to document the baseline shear strength parameters of the loess specimen with and without waste straw inclusion, whereas the stress-controlled direct shear tests reveal the temporal relations of horizontal and vertical displacement under given shear stresses. The increase in cohesion, induced by the effect of waste straw inclusions, contributes the most to the increase in shear strength, and it is predicted using the perpendicular model. The measured results are generally in line with the prediction. Further, the stress state at failure in a displacement-controlled direct shear test and a stress-controlled direct shear test for same specimen under equal testing conditions shows good correspondence to each other irrespective of testing method, and their results approximate a single failure envelope.

Expansive soils possess swelling behavior on the absorption of water, causing heaving on the ground surface. Two artificial highly-plastic soils are tested for the enhancement in engineering properties after treatment with a hydrophobic chemical. The water-proofing nature of the chemical resulted in the reduction of swelling and shrinking behavior. This study involves the evaluation of swell pressure, compressibility, strength on the dry and wet side of optimum moisture content. Shrinkage behavior is evaluated based on linear shrinkage test done at 2% higher than the liquid limit of the soil. The optimum dosage of lignosulfonate is decided based on the swell-shrinkage characteristics with different variation of the chemical. Crack intensity factor obtained from linear shrinkage tests is decreased by 50% after the addition of optimum chemical content. For soil A with a liquid limit of 140.94%, the optimum chemical mix is at 3% of the mass of soil while for soil B with a liquid limit of 105%, it is at 2% chemical.