No description available.

No description available.

Remedial ground densification is commonly used to reduce the liquefaction susceptibility of loose, saturated sand deposits, wherein controlled liquefaction is typically induced as the first step in the densification process. Assuming that the extent of induced liquefaction is approximately equal to the extent of ground densification, the purpose of this research is to assess the feasibility of using earthquake liquefaction data in remedial ground densification design via energy-based concepts. The energy dissipated by frictional mechanisms during the relative movement of sand grains is hypothesized to be directly related to the ability of a soil to resist liquefaction (i.e., Capacity). This hypothesis is supported by energy-based pore pressure generation models, which functionally relate dissipated energy to residual excess pore pressures. Assuming a linearized hysteretic model, a "simplified" expression is derived for computing the energy dissipated in the soil during an earthquake (i.e., Demand). Using this expression, the cumulative energy dissipated per unit volume of soil and normalized by the initial mean effective confining stress (i.e., normalized energy demand: NED) is calculated for 126 earthquake case histories for which the occurrence or non-occurrence of liquefaction is known. By plotting the computed NED values as a function of their corresponding SPT penetration resistance, a correlation between the normalized energy capacity of the soil (NEC) and SPT penetration resistance is established by the boundary giving a reasonable separation of the liquefaction / no liquefaction data points. NEC is the cumulative energy dissipated per unit volume of soil up to initial liquefaction, normalized by the initial mean effective confining stress, and the NEC correlation with SPT penetration resistance is referred to as the Capacity curve. Because the motions induced during earthquake shaking and remedial ground densification significantly differ in amplitude, duration, and frequency content, the dependency of the derived Capacity curve on the nature of the loading needs to be established. Towards this end, the calibration parameters for energy-based pore pressure generation models are examined for their dependence on the amplitude of the applied loading. The premise being that if the relationship between dissipated energy and pore pressure generation is independent of the amplitude of loading, then the energy required to generate excess pore pressures equal to the initial effective confining stress should also be independent of the load amplitude. However, no conclusive statement could be made from results of this review. Next, first order numerical models are developed for computing the spatial distribution of the energy dissipated in the soil during treatment using the vibratory probe method, deep dynamic compaction, and explosive compaction. In conjunction with the earthquake-derived Capacity curves, the models are used to predict the spatial extent of induced liquefaction during soil treatment and compared with the predicted spatial extent of improvement using empirical expressions and guidelines. Although the proposed numerical models require further validation, the predicted extent of liquefaction and improvement are in very good agreement, thus giving credence to the feasibility of using the Capacity curve for remedial ground densification design. Although further work is required to develop energy-based remedial densification design procedures, the potential benefits of such procedures are as follows. By using the Capacity curve, the minimum dissipated energy required for successful treatment of the soil can be determined. Because there are physical limits on the magnitude of the energy that can be imparted by a given technique, such an approach may lead to improved feasibility assessments and initial designs of the densification programs. / Ph. D.

Lime stabilisation is a ground improvement technique used to improve the engineering properties of cohesive fill materials. During earthworks operations, specialist plant is used to rotovate the clay fill material and intermix lime binder around clay clods. After completion of the lime treatment, the layer is compacted in the usual way. Immediately after mixing, the lime instigate a series of physico-chemical reactions within the clay soil. Where the chemical reactions are favourable and with time after compaction (curing) the material becomes progressively stronger and durable to environmental influences, e.g. inundation by surface or ground water. However, where sulphate is present within the soil, the reactions may change and the ingress of water into the layer can result in the expansive growth of deleterious minerals e.g. ettringite. While sulphate swell issues are relatively rare, when they do occur the degree of expansion can be very high. A high profile sulphate swell failure developed during the construction of the M40, Oxford, UK in 1989. Over the winter period after the lime stabilisation works, a 250mm deep lime treated layer heaved by up to 150mm - destroying the overlying road construction. Since the M40 failure, a substantial amount of effort has been undertaken to better understand the sulphate swell reactions and in this regard the state of scientific knowledge is relatively strong. A fundamental issue for field applications of lime stabilisation is that the vast majority of research has been undertaken on laboratory specimens prepared using methods which do not reflect site practice. Laboratory studies often use oven dried and finely crushed clay, whereas site operations will treat much larger clay clods to result in a more heterogeneous distribution of lime through the compacted soil body. With large clay clods, the chemical reactants must migrate through clods and this may cause the sequence of chemical reactions to change. A further challenge is that laboratory studies are typically undertaken with cure temperatures of 20°C, whereas a typical near surface temperature in the UK is <10°C. This is of particular relevance to sulphate swell failures which are reported to coincide with a reduction in ambient temperature over winter periods. Thus, the direct relevance of laboratory studies to site application was unclear. A series of laboratory experiments using a preparation method which reflects field applications of lime stabilisation was used to investigate the influence of large clay clods on the durability of lime stabilised clay soil. This method was applied to both low and high sulphate clay soils. A fundamental discovery from work on low sulphate clay is that the addition of lime binder to the surface of the clay clods causes a physico-chemical boundary to form. This boundary develops due to the rapid increase to the plastic limit of the clay preventing adjacent clods from joining together during compaction. This causes the engineering properties of each individual clod to develop independent to its neighbours and for each clay clod to be separated by an inter-clod pore space. The strength of each individual clay clod will increase with curing as the added lime dissociates into Ca2+ and OH- and migrates to form C-S-H deep within the clods. Where the material is compacted wet of the optimum water content, this condition improves ion migration and enables development of diffuse cementation deep within clods. The inter-clod porosity remains as a weakness throughout curing especially during specimen soaking, where the pore channels comprise a pathway, accelerating the ingress of soaking water. With low sulphate soil, the soaking water softens the treated material, however, with high TPS soil substantial sulphate swelling may develop. Thus, efforts to minimise this porosity during preparation is important and the use of quicklime with longer mellowing periods can cause the clay clods to develop high strength before compaction. The high strength clods resist compaction and the degree of inter-clod porosity in the compacted mass increases, worsening specimen durability to water ingress. The investigations into high sulphate clays included the development of a Novel Swell Test (NST) to assess volume change. A unique aspect of the NST was that the sulphate swell response of the lime treated material was investigated at site realistic temperatures of 8°C. It was identified that, when compared with standard laboratory test temperatures of 20°C the rate of sulphate swell is substantially higher at the low temperature. The mineralogical testing has permitted the hypothesis that, at 8°C the growth of crystalline ettringite becomes slower and the ettringite precursor, which has a high affinity to imbibe water, remains in this state for much longer. Thus, laboratory swell tests at 20°C may substantially underestimate the degree of swell that may develop in the field. As a pressing need, it is recommended that the industry adapt sulphate swell test methods to appraise the degree of swell at field realistic temperatures i.e. < 10°C. The work also identifies that the primary defence against sulphate swell is to condition the fill so that the risk of post compaction water ingress, via inter-clod porosity, is minimised. The use of GGBS and water addition during extended mellowing periods also reduces the degree of sulphate swell in natural clay soils. This work concludes that working methods for lime stabilisation of medium high plasticity soils of a potentially high sulphate content, should be adapted to encourage diffuse cementation and minimise the degree of (post compaction) inter-clod porosity. Practically this involves the use of hydrated lime and the addition of mixing water throughout extended mellowing periods. Fundamentally, the study recommends that where construction programmes allow, the long term durability of a fill material should be the priority over immediate strength.

Construction of pavements requires the subgrades - which are the foundation of the structure, to be capable of supporting traffic loads that would be applied onto them. In the case that the subgrades are unable to support the structure, failure would occur. The subgrade being in-situ soil can be of poor quality if not properly constructed or improved if necessary. In Canada, the eastern region precisely Ontario and Quebec, is dominated by sensitive marine clays which when disturbed lose their strength drastically making them a geotechnical hazard. The soil's high sensitivity causes this behavior it poses. Therefore, to construct pavements in this type of soil, improvement techniques are required. One such is lime stabilization which improves the engineering properties of the soil. Research on the stabilization of sensitive marine clay in Canada has been conducted to a certain extent showing the effectiveness of the process in improving the soil's poor engineering properties. However, during the process of stabilization, the thermal (T), hydraulic (H), mechanical (M) and chemical (C) processes and interactions that occur influence the behavior of the stabilized clay. Environmental stresses such as moisture and temperature are also known to affect the coupled processes that occur. However, these coupled processes and their impact on the stabilized clay are not well known and understood. The goal of the research was to therefore, conduct various column experiments and monitoring to determine the evolution of the coupled THMC processes under normal curing and when daily thermal cycles were applied to the treated and untreated clay. Various columns were prepared in the laboratory to accommodate the compacted treated and untreated sensitive marine clay for monitoring over 28 days. In addition, columns from which samples for extensive geotechnical testing were collected, were prepared. The soils' strength and hydraulic conductivity were determined through testing while the suction, electrical conductivity and temperature evolution were determined by use of sensors placed within the columns. The developed mechanical properties of the soil were significantly improved by use of lime. This development of mechanical properties was further enhanced when the daily thermal cycles were applied to the soil due to increased curing temperature stimulated. In addition, to temperature and chemical reactions, it was observed that the hydraulic properties also contributed to the developed soil strength. The strongly coupled THMC processes were thus, observed during the treatment of the clay with lime. The results obtained will therefore, contribute to a better understanding of the coupled THMC processes that occur when sensitive marine clay is treated with lime. It will further contribute to cost effectively designing pavements in regions with sensitive marine clays or similar.

Polyurethane resin injection is a treatment being considered as a replacement for traditional methods of ground improvement. It has been used to re-level foundations and concrete slabs that have settled over time. Additional claimed benefits of the treatment have been noted recently, including improved factors of safety against soil liquefaction and reduced earthquake-induced settlements. To investigate the capability of the polyurethane resin injection treatment to mitigate liquefaction, two full-scale blast liquefaction tests were performed; one test was conducted in an improved panel (IP), an 8 m circular area treated with the polyurethane resin in a 1.2 m triangular grid from a depth of 1 to 6 m, and another test in an untreated 8 m circular area, the natural panel (NP). Each blast test was severe enough to produce liquefaction (ru ≈1.0) in the respective panel, with blast-induced settlements in the range of 70 to 80 mm. Despite similar levels of ground-surface settlement in the IP and NP, settlement within the top 6 m of the IP was about half that of the NP. A CPT-based predicted settlement for each panel was employed using the Zhang et al. (2002) methodology. Good correlation was found between the observed settlements and predicted settlements in both panels. Differential settlements across the panels were calculated based on ground-based lidar surveys, with a reduction of 42 to 49% between the IP and NP. The measured total and differential settlements following resin injection were at the bottom of the range observed in blast tests on a variety of shallow ground improvement methods conducted by the New Zealand Earthquake Commission in 2013. The persistence of the polyurethane resin injection ground improvement three years following its installation was indicated by the lasting increase of fundamental in situ test parameters. The results of the study indicate that resin injection is a viable method of ground improvement to reduce liquefaction-induced settlements by creating a stiffer surficial crust.

Passive site remediation is a new concept proposed for non-disruptive mitigation of liquefaction risk at developed sites susceptible to liquefaction. It is based on the concept of slow injection of stabilizing materials at the edge of a site and delivery of the stabilizer to the target location using the natural groundwater flow. The purpose of this research was to establish the feasibility of passive site remediation through identification of stabilizing materials, a study of how to design or adapt groundwater flow patterns to deliver the stabilizers to the right place at the right time, and an evaluation of potential time requirements and costs. Stabilizer candidates need to have long, controllable gel times and low viscosities so they can flow into a liquefiable formation slowly over a long period of time. Colloidal silica is a potential stabilizer for passive site remediation because at low concentrations it has a low viscosity and a wide range of controllable gel times of up to about 100 days. Loose Monterey No. 0/30 sand samples (Dr = 22%) treated with colloidal silica grout were tested under cyclic triaxial loading to investigate the influence of colloidal silica grout on the deformation properties. Distinctly different deformation properties were observed between grouted and ungrouted samples. Untreated samples developed very little axial strain after only a few cycles and prior to the onset of liquefaction. Once liquefaction was triggered, large strains occurred rapidly and the samples collapsed within a few additional cycles. In contrast, grouted sand samples experienced very little strain during cyclic loading. What strain accumulated did so uniformly throughout loading and the samples remained intact after cyclic loading. In general, samples stabilized with 20 weight percent colloidal silica experienced very little (less than two percent) strain during cyclic loading. Sands stabilized with 10 weight percent colloidal silica tolerated cyclic loading well, but experienced slightly more (up to eight percent) strain. Treatment with colloidal silica grout significantly increased the deformation resistance of loose sand to cyclic loading. Groundwater and solute transport modeling were done using the codes MODFLOW, MODPATH, and MT3DMS. A "numerical experiment" was done to determine the ranges of hydraulic conductivity and hydraulic gradient where passive site remediation might be feasible. For a treatment are of 200 feet by 200 feet, a stabilizer travel time of 100 days, and a single line of low-head (less than three feet) injection wells, it was found that passive site remediation could be feasible in formations with hydraulic conductivity values of 0.05 cm/s or more and hydraulic gradients of 0.005 and above. Extraction wells will increase the speed of delivery and help control the down gradient extent of stabilizer movement. The results of solute transport modeling indicate that dispersion will play a large role in determining the concentration of stabilizer that will be required to deliver an adequate concentration at the down gradient edge. Consequently, thorough characterization of the hydraulic conductivity throughout the formation will be necessary for successful design and implementation of passive site remediation. The cost of passive site remediation is expected to be competitive with other methods of chemical grouting, i.e. in the range of $60 to $180 per cubic meter of treated soil, depending on the concentration of colloidal silica used. / Ph. D.

Foundations constructed by the deep mixing method have been used to successfully support embankments, structures, and excavations in Japan, Scandinavia, the U.S., and other countries. The current state of practice is that design is based on deterministic analyses of settlement and stability, even though deep mixed materials are highly variable. Conservative deterministic design procedures have evolved to limit failures. Disadvantages of this approach include (1) designs with an unknown degree of conservatism and (2) contract administration problems resulting from unrealistic specifications for deep mixed materials. This dissertation describes research conducted to develop reliability-based design procedures for foundations constructed using the deep mixing method. The emphasis of the research and the included examples are for embankment support applications, but the principles are applicable to foundations constructed for other purposes. Reliability analyses for foundations created by the deep mixing method are described and illustrated using an example embankment. The deterministic stability analyses for the example embankment were performed using two methods: limit equilibrium analyses and numerical stress-strain analyses. An important finding from the research is that both numerical analyses and reliability analyses are needed to properly design embankments supported on deep mixed columns. Numerical analyses are necessary to address failure modes, such as column bending and tilting, that are not addressed by limit equilibrium analyses, which only cover composite shearing. Reliability analyses are necessary to address the impacts of variability of the deep mixed materials and other system components. Reliability analyses also provide a rational basis for establishing statistical specifications for deep mixed materials. Such specifications will simplify administration of construction contracts and reduce claims while still providing assurance that the design intent is satisfied. It is recommended that reliability-based design and statistically-based specifications be implemented in practice now. / Ph. D.

The feasibility of using ground improvement at existing highway bridges to mitigate the risk of earthquake-induced liquefaction damage has been studied. The factors and phenomena governing the performance of the improved ground were identified and clarified. Potential analytical methods for predicting the treated ground performance were investigated and tested. Key factors affecting improved ground performance are the type, size, and location of the treated ground. The improved ground behavior is influenced by excess pore water pressure migration, ground motion amplification, inertial force phasing, dynamic component of liquefied soil pressure, presence of a supported structure, and lateral spreading forces. Simplified, uncoupled analytical methods were unable to predict the final performance of an improved ground zone and supported structure, but provided useful insights. Pseudostatic stability and deformation analyses can not successfully predict the final performance because of their inability to adequately account for the transient response. Equivalent-linear dynamic response analyses indicate that significant shear strains, pore water pressures and accelerations will develop in the improved ground when the treated-untreated soil system approaches resonance during shaking. Transient seepage analyses indicate that evaluating pore pressure migration into a three-dimensional improved zone using two-dimensional analyses can underestimate the pore pressures in the zone. More comprehensive, partially-coupled analyses performed using the finite difference computer program FLAC provided better predictions of treated ground performance. These two-dimensional, dynamic analyses based on effective stresses incorporated pore pressure generation, non-linear stress-strain behavior, strength reduction, and groundwater flow. Permanent movements of structures and improved soil zones were predicted within a factor of approximately two. Predictions of ground accelerations and pore water pressures were less accurate. Dynamic analyses were performed with FLAC for an example bridge pier and stub abutment on an approach embankment supported on shallow foundations and underlain by thick, liquefiable soils with and without improved ground zones. Ground improvement that restricted movements of the pier and stub abutment to tolerable levels included improved zones of limited size extending completely through the underlying liquefiable soils and formed through densification by compaction grouting or cementation by chemical grouting or jet grouting. A buttress fill at the abutment was unsuccessful. / Ph. D.

The response of an aggregate pier foundation system during seismic loading was investigated. The factors and phenomena governing the performance of the aggregate pier and the improved ground were identified and clarified. The key factors affecting the performance of the aggregate pier include soil density, stiffness modulus, and drainage capacity. The improved ground is influenced by soil stratification, soil properties, pore pressure dissipation, and earthquake time history. Comprehensive numerical modeling using FLAC were performed. The focus of the study in this research was divided into three parts: the studies of the ground acceleration, the excess pore water pressure ratio and the shear stress in soil matrix generated during seismic loading. Two earthquake time histories scaled to different peak acceleration were used in the numerical modeling: the 1989 Loma Prieta earthquake (pga = 0.45g) and the 1988 Saguenay earthquake (pga = 0.05g). The main results of the simulation showed the following effects of aggregate pier on liquefiable soil deposits: 1) The aggregate pier amplifies the peak horizontal acceleration on the ground surface (amax), 2) The aggregate pier reduces the liquefaction potential up to depth where it is installed, 3) Pore pressures are generally lower for soils reinforced with aggregate pier than unreinforced soils except for very strong earthquake, 4) The maximum shear stresses in soil are much smaller for reinforced soils than unreinforced soils. The excess pore water pressure ratio and the shear stress in the soil matrix calculated by FLAC were generally lower than those predicted by available procedures. / Master of Science