Permanent Rotation Research Articles

Geotechnical fragility analysis of monopile foundations for offshore wind turbines in extreme storms

Offshore wind turbines (OWTs) must withstand harsh environmental loads over their 20- to 30-year design life. Fragility analysis investigates the probability of damage over a range of hazard intensities and is integral to a performance-based engineering approach. The focus of this paper is on monopiles, which are widely used to support OWTs in water depths up to around 40m. The paper presents a fragility analysis of monopiles in extreme storms in terms of geotechnical performance, measured by permanent rotation of the foundation. Geotechnical fragility has so far not been comprehensively addressed due to the challenge of predicting soil behaviour under cyclic loading and estimating the probability of extreme responses. On the latter, the paper develops efficient Karhunen-Loeve representations of wind and wave loading that can be combined with inexpensive probabilistic methods to compute fragility. The framework was demonstrated using a representative scenario of a 5 MW OWT installed in clay. Non-linear foundation response was captured by a dynamic 3D finite element model. Fragility curves were generated using subset simulation for storms with return periods (RPs) from 1 to 100 years. Fragility during extreme storms (with 50- and 100-year RPs) was significantly higher than storms with RPs of 10 years or less.

Smart Education 4.0: Balancing Dual-Distance and Reskilling Revolution

On January 22, 2020, in Davos, the World Economic Forum launched Reskilling Revolution, a multistakeholder initiative aimed at providing better education, new skills, and better jobs for a billion people worldwide by 2030, so questions about improving the quality of education by introducing dual distance education and retraining of personnel at enterprises are becoming more and more relevant. In the course of the study, the authors analyzed the current problems of universities and enterprises, which allowed them to propose the creation of a smart cluster. The authors demonstrated the interaction of cluster participants using the example of education. The study showed that it is with such a tool that it is possible to solve the current problems of the participants, and in general, to improve the quality of education, the well-being of the region and, as a result, when scaling up, the well-being of the country and its image and culture on the world stage. The study showed that only through joint efforts and cooperation between universities, employers, research institutes and the state, it is possible not only to improve the quality of education but also to provide enterprises with a qualified workforce on a permanent rotation basis than to increase the competitiveness of business. This will allow research institutes and universities to raise funding, which can be directed not only to maintaining the current state but also to the development and introduction of resource-saving technologies, which we see as further research methods.

Strong anisotropy in aqueous salt solutions revealed by terahertz-induced Kerr effect

Terahertz Kerr effect technology, as a novel tool, is expected to study the low-frequency molecular dynamics of liquids since it can directly distinguish the time-resolved anisotropy information on the sub-picosecond scale. Here, this technology is used to measure a variety of aqueous salt solutions and observe the effects of different anions and cations on the structure and dynamics of water network. The obtained bipolar anisotropic response increases under the influence of multiple ions, which is mainly due to the energy transfer between the permanent dipole moment rotation of water molecules and the restricted translational motion of adjacent water molecules with THz electric field excitation. The classic viscosity-related coefficient B is used to analyze the amplitude and characteristics of the obtained anisotropic response, which implies the relationship between the intermolecular hydrogen bond dynamics and the macroscopic thermodynamic properties in the ionic aqueous solution. This work provides a new perspective for observing the low-frequency molecular motion in aqueous salt solutions.

Centrifuge Modeling for the Evaluation of the Cyclic Behavior of Offshore Wind Turbine with Tripod Foundation

In this study, the cyclic responses of an offshore wind turbine with a tripod foundation installed on an actual site were evaluated in a centrifuge. To understand the behavior of the turbine at the site, the site soil conditions, environmental loads, and real offshore wind turbine structure installed at the actual site were modeled by considering the centrifuge scaling law. From a series of cyclic loading tests, the cyclic responses of the tripod foundation were evaluated in terms of temporary/permanent displacements and cyclic stiffness. Moreover, the long-term behavior of the tripod foundation was predicted from the experimental results. The test results showed that the initial stiffness of the soil–foundation system decreased as the loading amplitude increased and that the stiffness increased with the number of cycles due to soil densification. The findings revealed that the cyclic behaviors of the tripod were more affected by the load amplitude than the number of cycles. In addition, the permanent rotation increased logarithmically with the number of cycles. A simple method to predict the displacement and change in the foundation stiffness of the actual wind turbine is proposed based on the results of the model tests. The results of this study also provide key insights into the long-term cyclic behavior of tripod foundations for offshore wind turbines.

ЭФФЕКТИВНОСТЬ ВОЗДЕЛЫВАНИЯ ЛЬНА МАСЛИЧНОГО, ОЗИМОЙ ПШЕНИЦЫ, МОГАРА В ПОЖНИВНОМ ПОСЕВЕ И ГОРОХА ПРИ АДАПТИВНОЙ СИСТЕМЕ ОСНОВНОЙ ОБРАБОТКИ ЧЕРНОЗЕМА ОБЫКНОВЕННОГО

The development of resource-saving tillage and direct seeding technologies (no-till) of field crops end up making a profit when it is based on the results of research and practice but this is not the case in all regions. Taking this into account, in the central zone of the Krasnodar Region in the permanent crop rotation from 2013 through 2018, we studied the integrated effect of plowing (22-24 cm -the control), surface tillage (6-8 cm) and zero tillage (herbicide treatment) and the crop in the rotation on the economic efficiency of production and elements of soil fertility. The average annual air temperature in the area is +12.1°C; the precipitation amount is 614 mm. The soil is represented by ordinary chernozem; humus amount in the arable layer makes 3.8%; P2O5-22-28 mg kg of soil; K2O -350-380 mg kg of soil (according to B.P. Machigin). The accounting area of the plots amounted to 5000 m2; fourfold plot replica-tion; threefold temporal replication. The crops were sown with the Rapid600 seeder with fertilizer application. Pesti-cides and growth promoters were used. The crops were harvested with a Claas Tucano combine harvester. It was found that the tillage variants affected the yields of crown flax, winter wheat,foxtail millet in stubble field, and field pea; and also changed the production costs and the condi-tional net income for crops and the course of the crop rota-tion. Under direct seeding technology, the conditional net income for the course of the crop rotation made 58.6 thou-sand rubles per ha; fuel consumption -127 kg ha and labor costs -16.98 man-hours per ha which was by 5%, 43% and 11%, respectively, less than those in the control. Sur-face tillage also had an advantage in terms of these indica-tors. Moldboard plowing reduced the intensity of organic matter accumulation 1.5-1.2 times as compared to direct seeding (no-till) and surface tillage. The cultivation of 4 crops in a course of the crop rotation for 3 agricultural years stabilizes economic indicators and soil fertility. The developed technologies for crop optimization in a rotation (the crops in constant demand by the market); adaptive methods of basic tillage; preservation of soil fertility may be used by land users with similar soil and climatic conditions.

Effects of rocking coefficient and critical contact area ratio on the performance of rocking foundations from centrifuge and shake table experimental results

The major objective of this study is to correlate rocking foundation performance parameters with their capacity parameters and earthquake demand parameters using results obtained from 142 centrifuge and shaking table experiments, which include a variety of soil conditions, foundation geometries, structural models, and types of ground motions. The analysis presented in this paper considers all experimental results together, collectively as big data, through nondimensional parameters to identify hidden relationships among different parameters in a capacity-demand-performance framework. Rocking system performance parameters such as seismic energy dissipation in soil, permanent settlement, peak and permanent rotation, tipping-over stability ratio, self-centering ratio, rocking moment capacity, and acceleration amplification ratio are correlated with rocking system capacity parameters such as critical contact area ratio, rocking coefficient, and slenderness ratio of rocking systems and the earthquake demand parameters such as Arias intensity and peak ground acceleration of earthquake. It is found that energy dissipation and settlement correlate reasonably well with rocking coefficient and Arias intensity of earthquake, while peak rotation and acceleration amplification ratio correlate reasonably well with slenderness ratio, rocking coefficient, and peak ground acceleration of earthquake. Rocking foundations in clayey soils show superior performance in terms of seismic energy dissipation and permanent settlement compared to those in sandy soils, especially for relatively small to medium intensity shakings, and the ability of rocking foundations to de-amplify the earthquake motion increases as the magnitude of shaking increases.

A procedure for predicting the permanent rotation of monopiles in sand supporting offshore wind turbines

Foundations for Offshore Wind Turbines (OWTs) are designed following the limit state philosophy. One of the considered states is the Serviceability Limit State (SLS), which verifies that the permanent rotation of the foundation generated from accumulated strains in the soil is below a project specific criterion. Despite design codes requiring an estimation of the permanent rotation, there is not clear guidance on how to implement this. This paper describes a methodology to estimate the monopile permanent rotation for SLS and discusses its advantages and limitations. The methodology combines an accumulation method with results from 3D Finite Element Analyses (FEA) and a soil model that accounts for strain accumulation as a function of the number of cycles, relative density and load characteristics. The performance of the proposed methodology is compared against experimental centrifuge tests and results from advanced 3D FEA, indicating that it can predict the permanent rotation with satisfactory accuracy, and with a considerable reduction in computational effort. This is important for the design of OWTs, where different load histories might be required to be checked – often under tight time constraints – to find which load history leads to the largest permanent rotation, and therefore is more critical to SLS design.

Characterization of ballast particle’s movement associated with loading cycle, magnitude and frequency using SmartRock sensors

SmartRock has recently been adopted in obtaining the particle-scale characteristics of ballast track and gives microscopic explanation of track performance under cyclic loads, such as degradation and reinforcement. We notice that the contact state of individual ballast particles changes with loading cycles, which in reverse gives rise to different particle movements. The changes of contact state and particle movements may accumulate as loading cycle increases and could be considerable. This makes the response of individual particles uncertain and thus brings practical difficulties in evaluating the performance of ballast track via particle-scale characteristics, especially for long-term loading. In order to learn more about the response uncertainty of individual particles, this study conducts a full size model test to investigate the variation of particle movement and inter-particle normal contact force with loading cycle, amplitude as well as frequency by using SmartRocks. The equivalent axle load ranges from 14 to 36 t, the frequency of the cyclic loading varies from 1 to 18 Hz. Two smart rocks were placed below the sleeper end and the shoulder region respectively. It is found that the long-term variation of particle’s movements and contact force with loading cycle show obvious fluctuation due to the continuous accumulated changes of particle’s contact state. While particle’s movements are generally stable during short-term loading. The movements of SmartRock beneath sleeper end are positively correlated with loading magnitude and frequency, nevertheless also shows a characteristic independent on loading cycles, magnitude as well as frequency: particles’ rotation in horizontal plane is mainly permanent rotation (accumulated rotation), while particle’s rotation in planes perpendicular to the lateral and longitudinal directions is mainly recoverable rotation. The influences of loading magnitude and frequency on ballast particle movements are found different. The results provide effective particle-scale indicators for investigations related to ballast track.

Impact of Social and Institutional Factors on the Uptake of Conservation Agriculture: A Case of Zambia and Zimbabwe

Conservation agriculture (CA) involves the practice of three interlinked principles of minimum soil disturbance, a permanent soil cover and crop rotation. Despite the many stated benefits of the technology, its uptake in Africa has been slow. This study applies the theory of planned behaviour to investigate the attitudes, the role of the social system (social influence, by-laws and customs) and the institutional environment in the decision to practice CA principles and on the area under CA in Choma, Zambia and Nkayi, Zimbabwe. The study finds differing attitudes between districts towards CA outcomes. Local by-laws have a positive correlation with the practice of minimum soil disturbance but negative correlations with the practice of soil cover and crop rotation. Social influence and customs have significant relationships with the area under CA. Institutional support is perceived to be necessary for the practice of minimum soil disturbance but not so for the practice of crop rotation or on the area under CA. We conclude that the attitudes towards CA depend on the performance of the CA options promoted to farmers while the effects of the social system components and institutional factors on the uptake of CA depends on how the particular CA principle fits into the social and institutional environment in which it is promoted. We recommend agriculture extension services and policymakers to pay more attention to these issues in the promotion of CA.

Determination of the virucidal properties of the new biocide “DezSan”

The high concentration of farm birds in a limited area creates favorable conditions for the spread of viral diseases. In this regard, the veterinary service is faced with the task of preventing the outbreak of infectious diseases of the poultry and the further spread of the disease. For this purpose a complex of antiepizootic measures is carried out, the key point of which is the disinfection of poultry buildings, equipment, containers, inventory, etc. Industrial poultry is constantly in need of the latest modern disinfectants, which will have the following properties: high biocidal capacity, prolonged action, reduced aggressiveness to treated surfaces, safety for personnel and the environment, ease of use, moderate price. Over time, microorganisms can create resistance to disinfectants. In order to prevent this phenomenon, a permanent rotation of disinfestations at a poultry enterprise, which will be created on the basis of various active substances, is necessary. The goal of the work. Investigate the virilidine action of the new disinfectant “DezSan” for RNA and DNA-containing viruses. Materials and methods of research. To verify the virilidic effect, two series of experiments were carried out using the ducts of hepatitis RNA and the DNA-virus of smallpox of the pox. To determine the effectiveness of the virilidic concentration of “DezSan” in relation to the bird pox virus – DNA-content was cultured on chorionic-alantium shell in the 10–12 day chick embryos and to the hepatitis virus duckling virus-RNA-purposive, a suspension of the virulent material that was obtained after propagation virus in primary cultures of dactylon embryo cells. For the experiment, 10 mattresses were used. The virus content of the liquid was mixed with equal volume of disinfectant solution “DezSan”, withstand 15, 30 and 60 minutes. In this case, used 0.1%, 0.25%, 0.5% and 1% solution of disinfectant “DezSan”. The effectiveness of decontamination of test object surfaces from the pox virus and the hepatitis virus ducts disinfectant was checked in the following order: on a sterilized surface of test objects, a sterile pipette was applied to a suspension of 1 to 2 cm3 of the virus. Contaminated test objects were left in the cuvettes horizontally and vertically, dried for 1–2 hours and with the help of the sprayer, the wetted surface was treated with an experimental disinfectant solution, taking into account the concentration, exposure and amount of disinfectant used. Results of research and discussion. “DezSan” in a concentration of 0.1% after 15 minutes. Inactivated hepatitis virus ducts by 46.3%; after 30 minutes – by 91.1%, and in an hour – by 94.1%. At 0.25% concentration of the solution at exposure for 15 minutes. the death of the virus was observed at 99.5%. 30 minutes later and 1 hour – the virus of hepatitis ducklings has been neutralized by 100%. Complete inactivation of the virus in 15 minutes was carried out in the treatment of test surfaces of 0.5% and 1% solution “DezSan”. In the washings taken after 30 and 60 minutes from surfaces treated with 0.5% and 1.0% solution of disinfectant, changes in test systems were not detected. 0.1% solution of disinfectant “DezSan” after 15 minutes. inactivated viral particles by only 45.7%. 30 minutes later the virus was already eradicated by 93.0%, and after 1 hour – by 96.0%. A solution of “DezSan” at a concentration of 0.25% after 15 min. destroying 99.6% of viral particles. And after 30 minutes and 1 year completely inactivated the virus. Thus, the experimental means “DezSan” in the concentration of 0.5% and 1.0% showed a pronounced virilidine activity and is capable of within 30 and 60 minutes. completely destroy the virus of hepatitis Ducklings. At 0.25% of the solution “DezSan” after 15 minutes. 99.7% of the viral parasites of the pox had been disposed of. And after 30 minutes and for 1 hour, the vehicle at the same concentration completely inactivated the virus. It should be noted that in the concentration of 0.5% and 1.0%, “DezSan” had a pronounced virilidine activity and could completely inactivate the pox virus pox during all controlled periods. Conclusions and prospects for further research. It has been proved that the “DezSan” biocide has expressed virilidic properties in relation to the RNA-containing virus of infectious hepatitis ducts during exposure for 15 minutes at concentrations of 0.25% and above. It was found that 0.25% solution of disinfectant “Dezsan” at exposures of 30 and more minutes completely kills the DNA – containing pox virus of smallpox. The drug “DezSan” can be used for disinfection measures in poultry farms with viral diseases, as it is effective against RNA and DNA-containing viruses. In future, the sporocidal properties of the biocide “DezSan” will be studied.

Influence of prefabricated vertical drains on the seismic performance of similar neighbouring structures founded on liquefiable deposits

Increasing the resilience of structures to seismically induced soil liquefaction is a major objective for the earthquake engineering community. Increasingly, soil drains are being used to mitigate the liquefaction hazard. By facilitating drainage, excess pore pressures can be limited to acceptable levels, thus reducing settlement and rotation of structures founded on liquefiable soils. However, drain design is currently based on procedures developed for the free-field. Structures change the stress distribution and flow patterns in the soil, altering the occurrence of liquefaction. At present, none of the available engineering procedures considers soil–structure interaction (SSI) in the design of drains. In dense urban environments, further complications arise from interaction between neighbouring structures. To investigate the influence of pre-fabricated vertical drains (PVDs) on structure–soil–structure interaction (SSSI), a series of geotechnical centrifuge tests was conducted to compare the performance of an isolated structure, a pair of similar structures without mitigation and a pair of structures where PVDs were present around just one building. Results show that, without improved drainage, SSSI can reduce permanent rotation of structures. However, where PVDs were placed around one of a pair of structures, the consequences for permanent rotation of and inertial demand on the adjacent unmitigated superstructure were detrimental.

Do lunar rover wheels sink equally on Earth and Moon?

There has been a long discussion on how the low-gravity effects that LRUs (Lightweight Rover Units) on the Moon will experience, can affect mission planning and surface operations. In particular, the sinkage observed when regolith soil layers collapse under a normal wheel load has been an important source of contradiction in the field of Terramechanics in the last years. In this short report we review the different authors opinions on this topic, examining in detail their definition, methods, and results.The sinkage of static wheels under lunar gravity could be less than on Earth (fixing body dimensions and soil), given the decreased normal load experienced by loose regolith. This is known as static sinkage. On the other hand, if the wheels are in permanent rotation, the effect of poor soil’s bearing capacity in lower gravities can lead to a deeper intrusion of the wheels as compared to the case on Earth (dynamic sinkage). The dynamic and static sinkage are low in lunar gravity and have more or less similar values in case the wheel surface is plane (smooth). However, if the wheel under test incorporates grousers, the lugs motion and soil’s bearing capacity would make the separate effect of dynamic sinkage to be much larger than in plane wheels. Finally, we evaluated a method that (at difference from previous models), can express more accurately the effect of static and dynamic sinkage in different gravity environments. The novel semi-empirical approach to estimate wheel penetration into soils assumes a dependency from wheel parameters, slip and terrain mechanical properties, demonstrating an improved goodness-of-fit (R2) from 91 to 99%, distinctly in a gravity interval of 16 up to 2 times the gravity on Earth.

Permanent accumulated rotation of an offshore monopile wind turbine in sand during a storm

Offshore wind turbines exposed to storm situations are subjected to static and dynamic loads from the same direction over a considerable period of time. Such cyclic loading can potentially result in soil degradation, leading to an undesired permanent rotation of the wind turbine. This paper presents a workflow to predict the permanent accumulated rotation of an offshore monopile wind turbine in sand during an extreme storm event incorporating the use of fully nonlinear irregular waves versus linear waves in current practice. The fully nonlinear irregular waves are realized from a potential flow solver OceanWave3D previously validated at up to near-breaking wave conditions. Given the wave kinematics, the aero-hydro-elastic code HAWC2 is used to calculate horizontal loading and bending moment acting on the embedded pile head. The irregular load series is then decomposed into a set of constant-amplitude load parcels using rainflow counting. Eventually, the permanent accumulated rotation is predicated using the method proposed by LeBlanc et al. (2010b) with Miner’s rule-based superposition. In this paper, a case study of the DTU 10MW wind turbine supported by a monopile at 33 m water depth in sand is presented, where the pile is primarily laterally loaded. The simulation results suggest the importance of taking accumulated rotation into design. The permanent accumulated rotation is primarily decided by soil capacity, loading characteristics and pre-loading history. Furthermore, the results show that wave nonlinearity has only limited influence on the permanent accumulated rotation.

Improved bracing systems to prevent exterior girder rotation during bridge construction

Concrete placement and temporary formwork of bridge deck overhangs result in unbalanced eccentric loads that cause exterior girders to rotate during construction. These construction loads affect the global and local stability of the girders and produce permanent girder rotation after construction. In addition to construction loads, the skew angle of the bridge also contributes to girder rotation. To prevent rotation (in both skewed and non-skewed bridges), a number of techniques have been suggested to temporarily brace the girders using transverse tie bars connecting the top flanges and embedded in the deck, temporary horizontal and diagonal steel pipes placed between the webs of the exterior and first interior girders, and permanent cross frames. This study includes a rigorous three-dimensional finite element analysis to evaluate the effectiveness of several bracing systems for non-skewed and several skewed bridges. In this paper, skew angles of 0°, 20°, 30°, and 45° were considered for single- and three-span bridges. The results showed that permanent cross frames worked well for all bridges, whereas temporary measures have limited application depending on the skew angle of the bridge.

IMPLEMENTATION OF THE MERITOCRATIC PRINCIPLE IN EUROPEAN PUBLIC ADMINISTRATION SYSTEMS

The article analyzed the experience of forming the personnel of the public administration system in France, Germany, Great Britain, Poland, Latvia. The author defined the procedures for selection and formation of a management elite in these countries. The article noted that the main stages of selection and formation of managerial personnel is the passage of the system of examinations on language proficiency and knowledge of legislation. The author stated that in France, Germany, Great Britain, Poland, Latvia there is no legislative regulation of the meritocratic principle as a principle of selection of talented specialists. In addition, the personal qualities of the managerial elite remain to be neglected. Separately, the question of creating a reserve of talented youth is needed, which will allow permanent rotation of staff in the system of public administration, and also create conditions for the development of personnel, depending on their talents and abilities. The author proposes ways to improve the system of examinations and procedures for recruiting.

On the Regular Precessions of an Asymmetric Liquid-Filled Rigid Body

The conditions for the existence of a linear invariant system of Poincare–Zhukovsky equations have been found. In a linear invariant system, three configuration conditions have been obtained that are sufficient to allow a mechanical system without dynamic symmetry to undergo regular precession. The explicit expression of the moments of inertia of a system consisting of a rigid body with an ellipsoidal cavity filled an ideal vorticity fluid is given in terms of the cavity dimensions; the velocities of precession and self-rotation are found. The particular case of the permanent rotation of an asymmetric rigid shell around the angular momentum vector is considered; in this case, any axis rigidly bound to the shell can be used as the axis of permanent rotation.

Carbon and nitrogen contents and aggregation index of soil cultivated with onion for seven years using crop successions and rotations

Onion is usually cultivated using conventional tillage system (CTS), with excessive soil turning, leaving it with low or no vegetation cover. This favors erosive processes and impacts negatively diverse edaphic attributes. Adopting soil management systems with conservationist bases that use permanent soil coverage and crop rotation can maintain or improve these attributes (for example, soil aggregation and soil organic matter). The objective of this work was to evaluate the total organic carbon (TOC) and total nitrogen (TN) contents, aggregation index, and aggregate mass distribution of a Humic Cambisol cultivated with onions in succession or rotation with other species in no-tillage system (NTS) and CTS. The treatments were: maize/onion (NTS-T1); cover plants (winter)/onion (NTS-T2); maize/winter grasses/onion (NTS-T3); velvet bean/onion (NTS-T4); millet/cover plants (winter)/onion (NTS-T5); velvet bean/rye/onion (NTS-T6); maize/onion (CTS-T7); intercrops cover plants (summer)/onion (NTS-T8). Seven years after the implementation of the experiment, the weighted mean diameter (WMD) of the aggregates, distribution of macroaggregates, mesoaggregates, and microaggregates, and TOC, and TN contents of the soil (0–0.05, 0.05–0.10 and 0.10–0.20 m layers) were evaluated. Periodic soil turning (CTS) in the succession of maize, and onion (T7) reduces TOC and TN contents in the soil surface layer, compared to succession and rotation systems with onion crops in NTS. This negative effect on soil quality is connected to the reduction of aggregate stability, especially the decrease in the amount of macroaggregates. The use of grasses, especially winter grasses in rotation with maize (T3), preceding onion crops in NTS increases TOC content in the soil surface layer. Higher TN accumulation in the surface layer is found in areas with more soil cover plant species in rotation or succession with onion in NTS (T2, T3, T5, T6 and T8). The use of NTS for onion crops generates high soil aggregate stability, with predominance of macroaggregates, regardless of the crop succession or rotation system used. Treatments with no winter soil cover plants (T1, T4 and T7) reduce soil TOC contents and the mass of water-stable macroaggregates and increase the amount of microaggregates in the soil surface layer when compared to the other treatments.

A Centrifuge Study of Seismic Structure-Soil-Structure Interaction on Liquefiable Ground and Implications for Design in Dense Urban Areas

Current practice in seismic design often assumes free-field conditions for the estimation of liquefaction-induced building settlement. This is inaccurate, as a structure places additional stresses on the soil, resulting in changes to the spatial and temporal occurrence of liquefaction, accelerations, and deformations. Further complications arise in dense urban environments where closely spaced structures may interact through structure-soil-structure interaction (SSSI). Previous studies have shown that SSSI may have positive or negative effects on the response of adjacent structures in terms of permanent settlement, rotation, and flexural deformations. However, little is known regarding how to maximize the benefits of SSSI with minimal risk of adverse consequence. In this study, centrifuge tests were conducted on both isolated and closely spaced structures to identify how the building separation and ground motion characteristics affect the response of adjacent structures founded on a layered, liquefiable soil profile. Results indicate that properly planned configurations and interactions may be employed in combination with traditional mitigation strategies to improve the settlement-rotation response of adjacent structures, while also reducing the demand imposed on the superstructure.

Effects of drainage control on densification as a liquefaction mitigation technique

Ground densification is among the most popular techniques for liquefaction mitigation employed in practice. Yet, the effects of densification, especially in combination with strategies that enhance or inhibit drainage to or from the densified area, on the performance of the soil-foundation-structure system are not well understood. This paper describes dynamic centrifuge experiments to evaluate these effects, considering 3- and 9-story, moment-resisting frame structures with different embedment depths, founded on layered liquefiable soil deposits. The experiments compared structures mitigated with densification alone, and mitigated with a combination of densification and either prefabricated vertical drains (enhancing drainage) or a flexible impermeable latex barrier (inhibiting drainage) around the densified area. Ground densification tended to reduce the foundation settlement, although not to acceptable levels (based on limiting values typically considered in design and performance assessment), but amplified the drift and acceleration demands on the superstructure. The addition of a flexible impermeable barrier around the densified area did not have a notable influence on foundation settlement. However, it increased the excess pore pressures under the edges of the 3-story structure by inhibiting outward flow, amplifying its foundation rotation compared to the case with densification alone. In the case of the heavier and deeper, 9-story structure, adding a barrier around the densified zone restricted the locally inward flow from the adjacent loose soil. This helped reduce net pore pressures under the edges of the structure after strong shaking, foundation rotation, and seismic demand on the superstructure. Enhancing drainage around the densified zone, on the other hand, notably reduced permanent foundation settlement and rotation during all motions nearly to acceptable limits, but amplified accelerations, imposing additional seismic demands on the structure, which could lead to damage if not considered in design. These results demonstrate the importance of considering the structure's dynamic properties and force-deformation behavior, foundation and ground motion properties, and soil-structure interaction when planning the geometry of ground densification and drainage.

Pushover and shaking table tests on a rocking-governed column-footing model on dry dense sand

Footings are normally used on firm ground. Previous studies have indicated that footings with large vertical bearing capacity have small settlement and recentering characteristics during excitation. The rocking foundation design is, therefore, considered quite suitable for a firm ground condition; however, some 1 g shaking table tests have shown that rocking structures still might have stability problems leading to toppling. In this study, we conducted pushover and shaking table tests on a rocking-governed column-footing model on dry dense sand to investigate the performance of a rocking structure on sturdy ground. Even in a dense soil condition, the structure had a longer period response than in the fixed-base condition, but this did not necessarily reduce the seismic demand on the structure. The major source of rocking isolation is that the maximum acceleration response of the structure is limited by the ultimate moment capacity of the footing; however, it is important to note that extensive rocking may induce a larger permanent rotation, which may influence the functionality of structures, and also may lead to structure instability, such as foundation twisting observed in this study.