Soil compaction by wheeling may cause considerable damage to the structure of the tilled soil and the subsoil and consequently to crop production, workability and the environment. Soil compaction models are reviewed and their evaluation under laboratory or field conditions is discussed. The development of a compaction model includes: (i) modelling the propagation of the loading forces within the soil resulting from forces applied at the soil surface from farm vehicles; (ii) modelling soil stress–strain behaviour. Models predict stress distribution in the soil induced by farm vehicle and change in soil structure: increase in dry bulk density and rut depth formation. We conclude that models based on Boussinesq equations for stress propagation are useful since they use a small number of parameters. They have been successfully evaluated in field conditions for homogeneous soil under a wide range of soil and water conditions. The difference between simulations and observations becomes more apparent when dealing with heterogeneous structures (clods, firm subsoil). The models based on the finite element method (FEM) have been shown to be more adequate for modelling the 3D distribution of stress within the soil induced by wheeling and the complex stress–strain behaviour of soil. Nevertheless, these models require more mechanical parameters and have been evaluated under limited conditions in laboratory bins or in the field with low compaction intensities. This review stresses the need to test FEM soil compaction models, so as to extend the range of conditions where these models can be applied.

Models of soil compaction due to traffic and their evaluation

Using the compressibility test, the effect of soil management and moisture content on the preconsolidation pressure (σp) of three soils, a Red-Yellow Latosol (LV), a Dusk Red Latosol (LR) and a Dark-Red Latosol (LE) under annual crop, natural forest and pasture, was studied in the area of Lavras (MG) at two depths (0-0.03 and 0.27-0.30 m). For each condition, five undisturbed soil samples and a disturbed one were collected, with three replications. The undisturbed soil samples with different soil moisture content were used in the uniaxial compression test, with compression curves being obtained, from which preconsolidation pressures were extracted. The plasticity and shrinkage limits, texture and organic matter were determined using the disturbed soil samples. The models of compaction tested were based on the preconsolidation pressure and on soil moisture. For the same soil management system and depth, significant difference was observed among the clay and sand content of the three soils. The values of the initial soil bulk density (Dsi) were statistically different for all soil management systems in the same soil depth, except the 0-0.03 m for the annual crop. Increased soil moisture content caused a exponential decrease in the preconsolidation pressure, indicating a reduction in the load support capacity of the soil. The LR had in general higher load support capacity than LE and LV. This higher load support capacity may be associated with its higher clay content and lower sand content. The load support capacity of the friable zone varied from 154 to 167 kPa for LV, 77 to 183 kPa for LR and from 77 to 132 kPa for LE. The soil moisture contents 0.33 to 0.30 kg kg-1, 0.42 to 0.27 kg kg-1, and 0.35 to 0.33 kg kg-1 correspond to the friable zone (LP - LC) of the LV, LR and LE, respectively. The model based on the stress history of the soil evidenced the effect of the compaction caused by the machines in the 0.27-0.30 m layer, for the annual crop, while for the pasture the cattle trampling effect was evidenced in the 0-0.03 m layer.

https://www.scielo.br/pdf/rbcs/v23n2/04.pdf

Compressibilidade de três Latossolos em função da umidade e uso

Nature induces man to live preferentially in certain climatic zones that also happen to be those best suited for agriculture. In Canada, 60% of the best agricultural land is situated within 80 km of major urban centers (Duman-ski, 1980). Urban and industrial expansion place further demands on the total land resource, such that agricultural land is affected directly through conversion to other uses, or indirectly by serving as a sink for sometimes hazardous by-products of industry (Coote, 1980). The changing face of human endeavor has created urban opportunities at the expense of the farm labor force. The diminishing land and labor resource, coupled with the increasing demand for food and higher input costs, have put pressure on science and technology to increase the productivity of existing agricultural soil and the efficiency of agricultural production.

Soil Compaction in Agriculture: A View Toward Managing the Problem

Subsoil compaction has become a problem of world-wide concern, especially under highly mechanised agricultural practices. Severe structural degradation impedes plant growth. Therefore, compaction must be limited to layers which can be structurally reclaimed with reasonable effort by tillage. The purpose of this study was to investigate the impact of a single pass with a sugar beet harvester on the soil properties of an unploughed Eutric Cambisol. In autumn 1998 and 1999 field measurements and laboratory testing were carried out in Frauenfeld, Switzerland. The wheel loads were 107 kN in 1998 and 108 kN in 1999. Changes of bulk density, total porosity, macroporosity and pre-consolidation pressure show that compaction effects were restricted to the topsoil (0–0.25 m depth). Below 0.25 m depth no changes were measured. The compaction beneath the tyre was modelled with a two phase finite element model in the framework of critical state soil mechanics. The model predicts the degree and depth of compaction of an Eutric Cambisol caused by a single pass in Switzerland. Modelled data and field results agree quite well.

Compaction of a Eutric Cambisol under heavy wheel traffic in Switzerland:: Field data and a critical state soil mechanics model approach

Summary

A critical-state finite element model was used to simulate compaction under single and dual tyres and tracks. The compaction involved deformations at three different scales, from small tyres with a contact area of about 70 cm2 (single tyre) supporting a load of about 50 kg, to large tyres of about 1.2 m2 (dual tyres) supporting a load of about 4500 kg. The predictions were compared with measured values for several different quantities. These included: rut depths; vertical displacement and shear strain: vertical stresses; and, void ratios and precompression stress measured on sampled soil cores. In general, the predictions and measurements agreed reasonably well. However, the agreement between prediction and measurement depended on the precision of measurements, soil disturbance, and the volume of soil involved in a measurement relative to the volume of soil influenced by the tyre or track. This study shows that the critical-state finite element model is useful, offering insight into the compaction process, the dependence of compaction on soil strength and compressibility, and practical implications for soil management.

Simulating soil deformation using a critical‐state model: II. Soil compaction beneath tyres and tracks

FINITE element procedure was used to simulate multiple wheel loading and to predict its effect on soil compaction. Results of nonlinear analysis, conducted using an incremental loading procedure, show effects of tire size, soil type, and number of passes on soil compaction . The results of the study also demonstrate the potential use of the procedure in compaction related studies. However, experimental verification of the model is necessary before the procedure can be recommended for wider use. INTRODUCTION Effects of soil compaction on soil structure, texture and strength , and on plant development and crop yields have received considerable attention from researchers in the past (Klingbiel and O' Neal , 1952; Ingles, 1974; Fountaine, 1958; Negi et al. , 1980; Chancellor, 1971; Camp and Gill, 1969; Eavis and Payne, 1968; Rosenburg and Willits, 1962; Voorhees, 1977). In recent years , there has been a growing interest in machine-induced soil compaction, perhaps because of the steady increase in the size of field machines as well as increased use of conservation or no-tillage practices. During most agricultural and forestry operations, a significant portion of the site will be exposed to single or, at times, multiple passes of vehicles. The compaction which can result from this single or multiple loading will depend on factors such as soil and vehicle type, soil moisture level, number of passes, vehicle weight, contact pressure, etc. Most studies dealing with vehicle loading and soil compaction have been experimental. One disadvantage with the experimental procedure is that it is laborious, time consuming, and expensive. An alternative is to develop a mathematical model capable of describing the soil-tractive device interaction . Combined use of such a model and experimental procedure should be helpful to better understand the effects of various soil and vehicle parameters on soil compaction as well as the machanics of soil compaction . Therefore, the overall objective of this study was ·to develop a numerical procedure to predict the soil compaction from multiple wheel loadings. The specific objectives of the study were: 1. To develop a finite-element model to predict the The authors are: D. POLLOCK, JR. , Mechanical Engineer, Belvoir Research and Development Center, Fort Belvoir, VA; J. V. PERUMPRAL, Professor, Agricultural Engineering Dept., and T. KUPPUSAMY, Associate Professor, Civil Engineering Dept., Virginia Polytechnic Institute and State University, Blacksburg, VA . \"[ _.,_ lli so1 sur ace ...-::; ::r-

/pdf/finite-element-analysis-of-multipass-effects-of-vehicles-on-2c71ajw599.pdf

Finite Element Analysis of Multipass Effects of Vehicles on Soil Compaction

Ring-shank nails are used extensively in post-frame construction due to their superior performance, yet
surprisingly little testing has been done on nail sizes above 12d. Experience in the post-frame industry suggests that
published allowable design values for ring-shank nails may be overly conservative and need revision. The goal of the
research reported herein was to characterize the withdrawal strength of ring-shank nails embedded in Southern Pine
lumber. Three sizes of galvanized and ungalvanized (bright) ring-shank nails from two manufacturers were studied. Ringshank
nails had approximately twice the withdrawal resistance of smooth-shank nails of the same diameter. Galvanizing
slightly reduced withdrawal strength (approximately 8%) due to partial filling of the threads. Nail head pull-through was
studied as a possible failure mode. Even allowing for galvanizing and head pull-through, strong evidence is presented for
increasing withdrawal design values for ring-shank nails.

/pdf/withdrawal-strength-of-ring-shank-nails-embedded-in-southern-8a7h3sfv3q.pdf

Withdrawal strength of ring-shank nails embedded in southern pine lumber

Ring-shank nails are used in engineered structures with lateral connection design values based on theoretically derived equations which were validated only for common nails. The goal of this study was to quantify the input parameters and lateral connection strength of several types of ring-shank nails in Southern Pine lumber and critically evaluate the applicability of the theoretical equations for ring-shank nails. Two sizes of galvanized and ungalvanized, hardened steel ring-shank nails from two manufacturers were studied. The hardened, ring-shank nails carried significantly higher loads than the common wire nails studied. Because the current method of determining yield load does not give adequate credit to hardened, ring-shank nails, an alternate method is proposed.

/pdf/lateral-resistance-of-ring-shank-nail-connections-in-5amle8pi2h.pdf

Lateral Resistance of Ring-shank Nail Connections in Southern Pine Lumber

Threaded nail fasteners are commonly used in agricultural and commercial post-frame structures, yet there has been insufficient research to fully understand the effect of threads on withdrawal and lateral load resistance. The objective of this article is to review technical information on threaded nail fasteners and to identify problems facing manufacturers, designers, and users of threaded nail fasteners for engineering applications. Recommendations are given concerning research and standardization needs.

/pdf/threaded-nail-fasteners-research-and-standardization-needs-3fovsbu6zw.pdf

Threaded-nail Fasteners — Research and Standardization Needs

Recently published test data for bolted and nailed connections was evaluated to assess the structural reliability inherent in current allowable stress design procedures for connections in wood structures. Reliability indices were determined for timber connections using standard firstorder, second moment (FOSM) procedures. For the connections considered in this study, reliability indices range from 2.6 to5.1, generally providing higher levels of safety than the structural members in timber structures.

/pdf/reliability-indices-for-bolted-and-nailed-connections-in-qsy81d430u.pdf

Reliability Indices for Bolted and Nailed Connections in Wood Structures

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