Site Soil Conditions Research Articles

Toward optimisation of water use efficiency in dryland pastures using carbon isotope discrimination as a tool to select plant species mixtures

Pastoral agriculture is important for supplying global demand for animal products but pasture productivity is often water limited. Increased plant diversity has been shown to increase water use efficiency (ω) and productivity under water limitation but the optimal mix of species varies spatially, dependent on climate, soil type, and plant water requirements. Consequently, a cost-effective method to screen for high ω plant species and mixes in situ at farm scale is needed. Using carbon isotope discrimination (∆13C) to examine ω is attractive because the method integrates over useful time scales, does not modify the measurement environment, and is cost-effective. Field scale ω was measured using eddy covariance (EC) at two sites with contrasting plant diversity (2 species, 7 species) and compared to the seasonal progression of ω calculated from foliage ∆13C (ω∆). Soil water evaporation (ES) was removed from EC measured total ecosystem evaporation using a modelling approach and canopy ω (ωC) was calculated as gross primary production (GPP) divided by canopy evaporation. Mixed species foliage samples were harvested pre-grazing, dried, sub-sampled, ground, and the ratio of 13C to 12C was measured. A strong positive correlation was found between ω∆ and ωC at both study sites (r2 > 0.83, p < 0.01). In addition to bulk biomass samples, individual species were also harvested seasonally. Relative increases in both ω∆ and production for some species showed that manipulation of pasture species mixtures may lead to increased ω. Combined with production monitoring, ∆13C could be developed as a tool to optimise species selection for site specific climate and soil conditions to maximise ω and farm production and profit.

Bayesian probabilistic seismic hazard analysis with respect to near-fault effects

Uniform hazard spectrum (UHS) provides a set of spectral accelerations at various periods which have the same probability of exceedance. In this research, UHS for Bojnord region was determined based on the Bayesian concept as a powerful approach in considering and combining randomness and uncertainties. Source-to-site geometry parameters were included in the seismic hazard analysis to consider the near-fault directivity effects. Results show that near-fault hazard spectra for rock and soil site conditions are 20% larger than ordinary ones at periods longer than 1 s, on average. It was shown that near-fault pulse effects can be approximately included by systemically multiplying ordinary UHS by a near-fault amplification factor. Two-point method modified with the near-fault amplification factor was used to construct design response spectra having the highest similarity with the calculated uniform hazard spectra on different soil site conditions. The parameters of the two-point spectrum found here are close to those of ASCE7, except that the long-period site coefficient for soft soil is 1.21 and 1.10 times those of ASCE7-10 and ASCE7-16, respectively.

Influence of multi-component ground motions on seismic responses of long-span transmission tower-line system: An experimental study

Seismic performance is particularly important for life-line structures, especially for long-span transmission tower line system subjected to multi-component ground motions. However, the influence of multi-component seismic loads and the coupling effect between supporting towers and transmission lines are not taken into consideration in the current seismic design specifications. In this research, shake table tests are conducted to investigate the performance of long-span transmission towerline system under multi-component seismic excitations. For reproducing the genuine structural responses, the reduced-scale experimental model of the prototype is designed and constructed based on the Buckingham\'s theorem. And three commonly used seismic records are selected as the input ground motions according to the site soil condition of supporting towers. In order to compare the experimental results, the dynamic responses of transmission tower-line system subjected to single-component and two-component ground motions are also studied using shake table tests. Furthermore, an empirical model is proposed to evaluate the acceleration and member stress responses of transmission tower-line system subjected to multi-component ground motions. The results demonstrate that the ground motions with multi-components can amplify the dynamic response of transmission tower-line system, and transmission lines have a significant influence on the structural response and should not be neglected in seismic analysis. The experimental results can provide a reference for the seismic design and analysis of long-span transmission tower-line system subjected to multi-component ground motions.

Effects of deep tillage and municipal green waste compost amendments on soil properties and tree growth in compacted urban soils

Large trees are often seen as a means of offsetting negative consequences of growing urban densification. To increase the tree canopy cover of dense urban landscapes, developers, planners and urban tree managers are often forced to plant into damaged and compacted sites. Compacted urban soils can hinder the establishment and growth of deep rooted, woody plants by: 1) impeding root exploration and development which is critical for water and nutrient acquisition; 2) reducing infiltration of water into the soil and the availability of water to plants; and 3) reducing gas exchange and the balance between anaerobic and aerobic conditions.At three sites in Melbourne, Australia with compacted and damaged soils, we established four soil remediation treatments: 1 & 2) tillage to 0.25 m with and without 50% (v/v) municipal green waste compost (MGWC) additions, and 3 & 4) tillage to 0.5 m with and without 50% MGWC addition, plus a non-remediated control. Each treatment was replicated (n = 3), and one Corymbia maculata (spotted gum) tree was planted into the centre of each 2 × 2 m treatment plot (n = 15), at all three sites (n = 45).Bulk density and field-saturated hydraulic conductivity were improved by tillage, at least in the short-term. The use of MGWC may maintain these changes for longer. Depending on site soil conditions tree growth may be improved by tillage alone. At one site, we found that additions of MGWC lead to nitrogen immobilisation due to site soil conditions. At another site, deep tillage (with or without MGWC) led to significantly improved tree growth.Compacted and degraded urban soils may be improved through simple tillage and/or organic amendment strategies for the successful establishment of deep rooted woody plants. However, site soil conditions will dictate whether the addition of MGWC is beneficial or not, as one site showed no positive response to any tillage or MGWC. This research has examined a technique that can be used by landscape managers to improve soil physical characteristics and, in certain circumstances, can improve deep-rooted woody plant establishment and growth in challenging compacted urban soil conditions.

Pedotransfer functions for predicting available water capacity in French soils, their applicability domain and associated uncertainty

Soil available water capacity is an important soil property for land use planning, drought risk assessment, and modelling crop production or carbon cycling. Measurements of soil moisture at several soil water potentials are expensive and time-consuming, hence it is common to estimate available water capacity with pedotransfer functions (PTFs). Available PTFs for France rarely provide uncertainty estimates for the model coefficients and predictions, which are often required for error propagation analysis and modelling ecological processes. The objectives of this study were: 1) to develop class-PTFs and 2) continuous-PTFs with associated uncertainties, and 3) to assess the domain of applicability of the PTFs across metropolitan France. We used the SOLHYDRO database for calibrating continuous and class PTFs. For continuous PTFs we used linear regression models using sand, clay, organic carbon (SOC), and bulk density (BD) as predictor variables, whereas class-PTFs were defined by texture class, bulk density, and horizon type (all horizons, topsoils, subsoils). The models were validated with an independent validation dataset. The domain of applicability of the PTFs was evaluated calculating the Mahalanobis distance between the calibration dataset and horizon data from the French soil monitoring network (RMQS). At independent validation, texture class-PTFs had a RMSE between 0.047 cm3 cm–3 and 0.058 cm3 cm–3 and continuous-PTFs had a RMSE between 0.040 cm3 cm–3 and 0.053 cm3 cm–3. Texture class-PTFs had similar or better predictive performance than texture-structural class-PTFs. The prediction performance of continuous-PTFs improved slightly when including SOC and BD in the models. The variance of the predictions of continuous-PTFs associated to error in the model coefficients was rather small, and increased as the values of the predictor variables were more distant to the centroid of the calibration data. We provide the PTF users with tools for classifying new samples as within or outside the applicability domain of the PTFs. When applied to the RMQS dataset, >50% of the horizons outside the domain of applicability were located in forests and natural areas or managed pastures. The spatial distribution of RMQS horizons outside the domain of applicability of the PTF can inform future sampling locations for increasing the diversity of the soil properties and site conditions represented by the SOLHYDRO dataset.

Incorporating the local faults effects in development of seismic ground-motion hazard mapping for the Peninsular Malaysia region

The probabilistic seismic ground-motion hazard maps for the Peninsular Malaysia region have been developed by the present study. Despite the earlier seismic hazard maps for this region, which were proposed only based on far-field Sumatran seismic sources, this study has attempted to present the new maps using the combination of the local faults within the region, Sumatran fault, and Sumatran subduction source zones. The composite earthquake catalogue of the study region has been extended to cover an area limited by 10°S–10°N Latitude and 90°–110°E Longitude with the period from 1900 to 2014. The seismic source zones were categorized into subduction and fault sources. Line, area, and background source models were used to model the seismic sources with variable characteristics along them. In order to consider the epistemic uncertainty, logic-tree framework was used to incorporate basic quantities such as different source modelling, maximum magnitudes, and ground-motion prediction equations (GMPEs). The hazard maps are presented over a 12.5 km grid in terms of peak ground acceleration (PGA) for 10 and 2% probabilities of exceedance in 50 years corresponding to 475 and 2475 years return periods (RP), respectively. The proposed new hazard maps give the expected ground motions based on the extended earthquake catalogue, upgraded seismic source parameters, and more compatible GMPEs than applied in the development of previous hazard maps. The estimated PGAs on rock site condition across the Peninsular Malaysia region for RP475 and 2475 years are in the range of 1.0–10.0%g and 2.0–20.0%g, respectively. The horizontal elastic acceleration response spectra on different soil site conditions have been also presented for the region of interest following the principles of Eurocode 8 through the calculated uniform hazard spectra.

Empirical scaling relations for pseudo relative velocity spectra in western Himalaya and northeastern India

In this paper, frequency-dependent empirical scaling equations are developed for pseudo relative velocity (PSV) spectrum amplitudes of strong earthquake ground accelerations in western Himalaya and northeastern India for five ratios of critical damping ζ = 0.00, 0.02, 0.05, 0.10, and 0.20. These are based on the frequency-dependent attenuation functions developed in our recent work (Gupta and Trifunac [38]) for these two regions. The proposed scaling relations are shown to have physically realistic dependence on earthquake magnitude, source-to-site distance, and local site geological and soil conditions. The extension of the empirical PSV amplitudes to short and long periods, beyond the empirical period range, is also illustrated using available techniques (Trifunac [89,90]). To demonstrate the validity of a long-period extension, independent estimates of peak ground displacement from recorded accelerograms and estimates of the seismic moment from distant recordings of earthquakes are shown to be in good agreement with the extended spectral amplitudes. The validity of a short-period extension has been also tested by comparing the values of pseudo acceleration spectral amplitudes at short periods with the recorded peak ground accelerations. The realistic nature of short- and long-period extensions provides additional tests for the accuracy of the present scaling relationships. Such relationships can thus be considered to provide a sound basis for macro- and micro-zoning specific to the highly seismic regions of western Himalaya and northeastern India.

Basic characteristic parameters and influencing factors of long-period ground motion records

199 earthquake records with reliable information are selected from the PEER and NIED firstly, and the Seismo Signal software is applied to correct the baseline of original earthquake records. Then the basic characteristics and strength parameters under near-fault/far-field long-period ground motions and common ground motions are compared. Moreover, the influence on basic strength parameters affected by earthquake magnitude, rupture distance (or epicenter distance) and site condition under near-fault/far-field long-period ground motions is analyzed one by one. Study results are obtained as follows: Near-fault earthquake has high amplitude intensity and short strong-shock duration, and its energy release process is concentrated in a short time. A Far-field earthquake has a small peak of acceleration, velocity, displacement and long strong-shock duration, and its energy release process is mild. The strength parameter index PGV/PGA under long-period ground motions is beyond 0.2, and its frequency distribution is concentrated within the low-frequency band (0.1-1.0 Hz) while the frequency distribution of common ground motions is concentrated within a relatively high-frequency band (1.0-2.3 Hz); The strength parameter indexes IA, Eρ, P, IC and CAV under near-fault earthquake are greater than those under far-field earthquake. For a near-fault earthquake, the parameter index PGA decreases, and the strong-shock duration increases with the earthquake magnitude from Mw 6.6 to Mw 7.3, while the parameter index PGA, PGV decreases and PGV/PGA, strong-shock duration increase with the increases of rupture distance. Site-soil condition is the key factor affecting the basic strength parameter index under far-field earthquake, and the PGA, PGV parameter indexes increase under far-field earthquake with the site soil condition from class C to D and E. It is suggested to be related to the effect of filtering out high-frequency components and amplifying low-frequency components in soft site-soil.

Analysis of rotation sensor data from the SINAPS@ Kefalonia (Greece) post-seismic experiment\u2014link to surface geology and wavefield characteristics

Although rotational seismology has progressed in recent decades, the links between rotational ground motion and site soil conditions are poorly documented. New experiments were performed on Kefalonia Island (Greece) following two large earthquakes (MW = 6.0, MW = 5.9) in early 2014 on two well-characterized sites (soft soil, VS30 ~ 250 m/s; rock, VS30 ~ 830 m/s, VS30 being harmonic average shear-wave velocity between 0 and 30 m depth). These earthquakes led to large six-component (three translations and three rotations) datasets of hundreds of well-recorded events. The relationship between peak translational acceleration versus peak rotational velocity is found sensitive to the site conditions mainly for the rotation around the vertical axis (torsion; dominated by Love waves): the stiffer the soil, the lower the torsion, for a given level of translational acceleration. For rotation around the horizontal axes (rocking; dominated by Rayleigh waves), this acceleration/rotation relationship exhibits much weaker differences between soft and rock sites. Using only the rotation sensor, an estimate of the Love-to-Rayleigh energy ratios could be carried out and provided the same results as previous studies that have analyzed the Love- and Rayleigh-wave energy proportions using data from translational arrays deployed at the same two sites. The coupling of translational and rotational measurements appears to be useful, not only for direct applications of engineering seismology, but also to investigate the composition of the wavefield, while avoiding deployment of dense arrays. The availability of new, low-noise rotation sensors that are easy to deploy in the field is of great interest and should extend the use of rotation sensors and expand their possible applications.Graphical abstract.

Scaling of Fourier Spectra of strong earthquake ground motion in western Himalaya and northeastern India

It is necessary to develop scaling models of various functionals of ground motions for different seismic regions to obtain region-specific motion characterizations for the design of structures and for seismic hazard studies. Until recently, a paucity of strong-motion data has limited such work in seismic regions in India. In this study, scaling of Fourier spectrum amplitudes is attempted for the western Himalayan and northeast regions of India in terms of magnitude, source-to-station distance, component orientation, and geological and soil site conditions. The scaling model considered is similar to that of Trifunac and co-workers for the California region in the 1980s and 1990s. A database of 1236 recorded accelerograms for both regions of India is used with the assumption that dependence on earthquake magnitude, site geology, site soil and component direction is the same. Separate attenuation models are then developed for the western Himalayan and northeast Indian regions in the period range of 0.03–3.0s. The assumption of identical dependence of Fourier amplitudes on earthquake magnitude in the western Himalaya and northeast India region is found to be consistent with the actual data. These amplitudes grow with magnitude, reaching a maximum for magnitude around 7.0 for periods below 0.1s and for magnitude exceeding 8.0 for longer periods. The Fourier amplitudes are amplified on sediments (with respect to basement rocks) at periods longer than 0.24s, which are also amplified on “stiff soil” (with respect to the “rock” soil sites) at periods longer than 0.2s. Extension of the proposed models to shorter and longer periods is also presented using the available techniques and validated by establishing their consistency with the independent estimates of seismic moment, stress drop, and radiated wave energy in both western Himalaya and northeast India.

MAXIMIZING RESTORATION SUCCESS WHEN THE GOOD GROUND IS GONE

INTRODUCTION “The good ground is gone” often refers to the challenging nature of construction sites these days. Building on steeper slopes and within tighter boundaries while accelerating construction schedules is adding to the challenge of construction managers. Often the revegetation and restoration is unfortunately not planned or timed for successful long-term vegetation success. Site soil conditions are frequently overlooked and the timing necessary for seed germination, expression, and establishment are rarely factors in determining the schedule of seeding applications for optimum results. All too often less than desired results or failure is the accepted outcome. This will increase the future maintenance costs and encourage the repeated “finger pointing” while seeking to blame one cause or another. Typically, this often-repeated process fails to address the fundamental causes and thereby rarely fixes the problems moving forward. In an effort to break out of this all too often repeated cycle, let's break down the principle challenges and explore options for successful restoration of challenging sites. Successful, long-term revegetation starts with the soil. Without quality soil that takes years to accumulate naturally, revegetation efforts regularly fail or the outcomes are less than ideal. During construction, mining, and general land disturbing activities the soil will be degraded even while practicing the best topsoil harvesting and stock-piling management practices. Many areas where vegetation is desired are essentially mineral without any organic matter or biological activity. When available, stockpiled topsoil will also degrade; the environment within the pile will create conditions that microbes, essential for plant health, will be negatively affected. The longer the stripped soils are stockpiled, the more living organisms are lost. Recommendations and even requirements for limiting the depth of the pile to reduce the loss of beneficial microbes is rarely possible given the tight boundaries of project limits facing site operators. When the stockpile depth is able to be minimized, the pile must also be turned regularly to reduce the loss of the essential nutrient cycling microbiome present in healthy soils.

Monitoring the behavior of segment joints in a shield tunnel using distributed fiber optic sensors

Summary Shield tunneling is a popular tunnel construction technique for its efficiency and speed. However, uncertainties associated with site soil conditions, past loading histories and analytical modeling, can result in performance issues. To monitor shield tunnels and ensure performance and safety, fiber optic sensing technique is proposed. Based on Brillouin optical frequency domain analysis, the technique can monitor the opening and closing of segmental joints in shield tunnels with high sensitivity. To determine tunnel lining segment displacement, different fixed-point spacings have been tested in the lab. The test results show that the difference in fixed-point distances had no impact on the test accuracy and the sensing cable with 0.9-mm polyurethane sheath coater has the best performance. For demonstration, the Brillouin optical frequency domain analysis-based monitoring technique is applied to the Suzhou Metro Line 1 tunnel for tunnel lining segment joint monitoring. The technique detected minor deformation of the segment joints in tunnels in operation and located leakages within the tunnel. The technique further identified that the minor deformations of the segment joints and track bed expansion were closely associated with temperature variations.

Influence of soil-structure interaction on seismic responses of offshore wind turbine considering earthquake incident angle

Displacement response and corresponding maximum response energy of structures are key parameters to assess the dynamic effect or even more destructive structural damage of the structures. By employing them, this research has compared the structural responses of jacket supported offshore wind turbine (OWT) subjected to seismic excitations apprehending earthquake incidence, when (a) soil-structure interaction (SSI) has been ignored and (b) SSI has been considered. The effect of earthquakes under arbitrary angle of excitation on the OWT has been investigated by means of the energy based wavelet transformation method. Displacement based fragility analysis is then utilized to convey the probability of exceedance of the OWT at different soil site conditions. The results show that the uncertainty arises due to multi-component seismic excitations along with the diminution trend of shear wave velocity of soil and it tends to reduce the efficiency of the OWT to stand against the ground motions.

Influence of Gap Size on the Dynamic Behavior of Perforated Tube under Seismic Excitation

Perforated tubes form a part of the reactor regulating and protection system in Indian Pressurized Heavy Water Reactors (IPHWRs). These tubes are being analyzed for design basis and beyond design basis seismic loading conditions. Experimental studies have been carried out on full scale shutdown system sub-assembly to evaluate the responses of the perforated tube under multi support seismic excitation. Dynamic characterization of the tube subjected to seismic excitation, simulating rock site and alluvium soil condition, has been carried out. In order to study the interaction of these tubes with the nearby structure/assemblies under beyond design basis seismic excitation, experimental studies have also been carried out to quantify the variation of impact forces with gap sizes, and their influence on the dynamic behavior of these tubes. Non-linear analytical calculations have been carried out simulating the above test conditions. Responses from experimental and analytical studies have been compared, and are found to be in good agreement.

Mid-rotation response to fertilizer by Pinus radiata D. Don at three contrasting sites

Mid-rotation responses to fertilization of Pinus radiata D. Don plantations after the first or second thinning have been observed in research experiments in many regions where the species is grown. The practice is not however common in commercial plantations. This is probably because the effects of soil-site conditions on the magnitude and duration of tree and stand growth responses are not well understood. The effects of nitrogen (150 and 300 kg N · ha -1 ) and phosphorus (0, 20 and 40 kg P· ha -1 ) including common base fertilization of boron (8 kg B· ha -1 ) and potassium (65 kg K · ha -1 ) were evaluated in three mid-rotation P. radiata plantations after thin- ning. The plantations were located on sites with contrasting nutrient and water availability, sandy, granitic and red- clay sites, in south-central Chile. The magnitude and duration of growth response was site specific. After 8 years, the growth response to the highest dose of fertilization relative to the control was 57 m 3 · ha -1 (16%) at the granitic and 24 m 3 · ha -1 (14%) at the sandy site. No response to either nitrogen or phosphorus fertilizer was observed at the red-clay site. Nitrogen and phosphorus were limiting at both granitic and sandy sites, and high fertilization doses considering 300 kg N · ha -1 plus 40 kg P · ha -1 would ameliorate nutrient resource limitations and yield a cost-effective increment in stand volume.

Micropropagation of Leuce-poplar clones and its role in selection breeding

Leuce-poplars (mostly white poplar and its natural hybrid grey poplar) are native tree species trough Hungary. They are covering more than 4.0 per cent of the Hungarian forested area (77 000 ha). The white (grey) poplars play a significant role in the forestation under sandy soil site conditions as well as they are of importance from nature conservation point of view as well.&#x0D; Long-term selection breeding work is going on at the National Agricultural Research and Innovation Centre Forest Research Institute (NARIC FRI), involving selection of fast-growing Leuce-poplar clones under dry site conditions.&#x0D; Micropropagation technology is relatively quickly spreading in forestry. In vitro multiplication of trees is applied mainly in fruit growing in Hungary, in case of forestry it is used mainly for selection breeding.&#x0D; This paper presents a short overview on the micropropagation trials with different Leuce-poplar clones and the early evaluation of the seedlings growing of the micropropagated clones/varieties.

RESPONSE SPECTRA ANALYSIS OF SYMMETRIC AND ASYMMETRIC BUILDINGS WITH VARIATION IN NATURAL PERIOD AND SOIL STRATA

Abstract Seismic analysis and design of any structure requires time history data. Unavailability of records at all the locations makes response spectra as a powerful analysis tool. As a scope of this paper, a set of 10 buildings with their period varying from 0.1 to 1.18 sec were considered and response spectra analysis was carried out for the soil site conditions as per IS code. The variation of acceleration, velocity and displacement responses with respect to change in period of the structure and the soil type were compared. This study is extended to buildings with asymmetry as well. Another set of asymmetric buildings whose time periods were varied from 0.1 to 1.19 sec are also analyzed for the same above mentioned soil conditions. It was observed that all buildings with fundamental mode period between 0.1 to 0.4 sec in the chosen direction have same response irrespective of the soil type. The maximum variations in the responses for building resting on stiff medium and soft strata are presented for both the buildings with symmetry and asymmetry. The results obtained shows need to carefully study responses of buildings with smaller frequencies and that resting on less stiffer soils.

Constant-Damage Yield Strength Spectra for RC Structures Using Modified Park-Ang Damage Model

In this study, constant-damage yield strength spectrum (CDYSS), which is defined as the yield strength demand of a single-degree-of-freedom (SDOF) system of varying natural vibration period with the target constant damage index and specified ductility capacity, is derived by averaging the nonlinear time-history analysis results of a SDOF system under different earthquake ground motions. A modified Park-Ang damage model proposed by the authors, eliminating its non-convergence problem both at upper and lower limits with higher precision and smaller scatter, is adopted to calculate the damage index of the SDOF system. In the construction of CDYSS, 641 sets of earthquake ground motion records are adopted and classified into 12 groups in line with Chinese code for seismic design of buildings. The yield strength demands of SDOF systems with given ductility capacity are obtained through trial and error method. Then, the mean CDYSS and the corresponding coefficient of variation for different group of site soil conditions are calculated. The effects of ductility capacity and local site soil conditions on CDYSS are discussed. Lastly, the empirical formulas of CDYSS are developed by multivariable nonlinear regression analysis and compared with actual CDYSS.

Plant and soil effects on bacterial communities associated with Miscanthus × giganteus rhizosphere and rhizomes

AbstractBacterial assemblages, especially diazotroph assemblages residing in the rhizomes and the rhizosphere soil of Miscanthus × giganteus, contribute to plant growth and nitrogen use efficiency. However, the composition of these microbial communities has not been adequately explored nor have the potential ecological drivers for these communities been sufficiently studied. This knowledge is needed for understanding and potentially improving M. × giganteus – microbe interactions, and further enhancing sustainability of M. × giganteus production. In this study, cultivated M. × giganteus from four sites in Illinois, Kentucky, Nebraska, and New Jersey were collected to examine the relative influences of soil conditions and plant compartments on assembly of the M. × giganteus‐associated microbiome. Automated ribosomal intergenic spacer (ARISA) and terminal restriction fragment length polymorphism (T‐RFLP) targeting the nifH gene were applied to examine the total bacterial communities and diazotroph assemblages that reside in the rhizomes and the rhizosphere. Distinct microbial assemblages were detected in the endophytic and rhizosphere compartments. Site soil conditions had strong correlation with both total bacterial and diazotroph assemblages, but in different ways. Nitrogen treatments showed no significant effect on the composition of diazotroph assemblages in most sites. Endophytic compartments of different M. × giganteus plants tended to harbor similar microbial communities across all sites, whereas the rhizosphere soil of different plant tended to harbor diverse microbial assemblages that were distinct among sites. These observations offer insight into better understanding of the associative interactions between M. × giganteus and diazotrophs, and how this relationship is influenced by agronomic and edaphic factors.

Development of Socketed Foundatio for Cable Guardrail Posts

This study developed socketed foundations for two cable guardrail posts, the S3×5.7 and the Midwest weak post (MWP). The design efforts focused on developing cylindrical, reinforced concrete foundations with a steel tube embedded in the top center to create a socket. Foundations were designed to minimize damage and limit foundation displacements to less than 1 in. Satisfying these criteria ensured that damaged barrier posts could be replaced without the need for repairing or resetting the foundation. The foundations were evaluated for three soil types (weak soil, strong soil, and an asphalt mow strip) to gain an understanding of the link between soil conditions and foundation performance. Fourteen dynamic component tests were conducted on socketed foundation designs. Three socketed foundation options were developed for use with S3×5.7 posts: a 12-in.-diameter foundation in soil, a 15-in.-diameter foundation in soil, and a 12-in.-diameter foundation in asphalt. The S3×5.7 post foundations in soil with 12-in.-diameter sockets were found to be susceptible to concrete shear cracking and fracture, but they remain an option for those who can accept the risks of minor damage during severe impacts. The 15-in.-diameter foundations and those placed in asphalt had no indication of damage. Further, the reduced strength of MWPs resulted in no visible damage to 12-in.-diameter foundations. Guidelines based on site soil conditions and frost line depth were developed for the embedment depth of each foundation–post combination required for resistance to excessive displacements.