Changes In Penetration Resistance Research Articles

Numerical and Physical Modeling of the Effect of the Cone Apex Angle on the Penetration Resistance in Coarse-Grained Soils

The tip shape of penetrometers and piles has an important influence on the soil resistance mobilized during penetration. Blunt or flat tips typically generate greater penetration resistances, which can lead to refusal during in-situ testing and pile driving in the field. Results are presented from numerical and experimental investigations on probes with conical tips of varying apex angles to quantify the effect of the apex angle on the mobilized penetration resistance and associated failure mechanisms. Discrete element modeling (DEM) simulations were performed in unconfined and confined (i.e., stress-controlled) specimens to model shallow and deep penetration conditions, respectively. Centrifuge penetration tests were performed by quasi-statically advancing an instrumented probe to a depth-to-probe-diameter ratio of 16.7. The numerical and experimental results indicate that at shallow depths, the sharper tips mobilize smaller penetration resistances. In deep penetration conditions, the changes in penetration resistance with tip apex angle are less pronounced. Based on the results of the two investigations and values reported in the literature, a relationship characterizing the functional form between tip apex angle and normalized penetration resistance is proposed. A mesoscale analysis of the DEM simulation shows differences in the failure mechanisms induced by sharp and blunt tips: the zone where large particle displacements and stress changes occur is large and located below the tip for penetration with blunt tips, whereas the zone is smaller and located both laterally and below the tip for sharp tips.

Centrifuge Shake Table Tests on the Liquefaction Resistance of Sand with Clayey Fines

A series of centrifuge shake table tests were carried out to investigate liquefaction resistance of sand deposits with different fines content. The effects of clayey fines on the generation and dissipation of excess pore water pressure, acceleration record, surface settlement, and stress-strain behavior were investigated. It was found that for the same initial relative density, liquefaction resistance increased as fines content increased from 0% to 10% and then decreased with a further increase in fines content from 10% to 20% in the centrifuge tests. For all tests, a reduced acceleration within the soil was observed after a certain number of cycles due to the onset of liquefaction. Dilative tendencies are different for all tests, but the sand with 10% clay test showed the most obvious dilative behavior during the cyclic mobility stage. The total ground surface settlement and the time for a complete dissipation of excess pore water pressure increased with increasing fines content. Shear strains in the sand deposits increased as the clay content increased from 0% to 20%. Moreover, cone penetration tests were performed before and after shaking to study the effect of fines on penetration resistance. At the same depth across all tests, the penetration resistance before shaking decreased with increasing clay content. However, the penetration resistance after shaking increased with increasing clay content from 0% to 10% and then decreased with increasing clay content from 10% to 20%. When compared with the before-shaking profile, the percentage change in penetration resistance after shaking increased with clay content at the same depth.

Liquefied strength ratio with stress densification and low stresses

This paper presents a comparison of four assumptions or approaches for using a liquefied shear strength ratio for sandy soils in cases where there has been a large increase in effective vertical stress, e.g., structure raising or remedial measure, that is outside the effective stresses of the case histories used to develop the empirical liquefied shear strength ratio and penetration resistance correlations. Changes in penetration resistance due to an increase in effective vertical stress are used in an example to illustrate the following four assumptions for determining a liquefied shear strength ratio in such a post-liquefaction stability analysis: (1) initial effective vertical stress and initial penetration resistance; (2) initial effective vertical stress and the expected increase in penetration resistance due to the increase in effective vertical stress; (3) final effective vertical stress and initial penetration resistance, which is suggested; and (4) final effective vertical stress and final penetration resistance. This paper also presents suggestions for using a liquefied strength ratio at low effective vertical stresses, e.g., approaching the toe of a dam or embankment, in a post-liquefaction stability analysis.

Impact of successive rainfall events on the dynamic relationship between vegetation canopies, infiltration, and recharge in engineered urban green infrastructure systems

AbstractSoil surface crusts have been extensively studied in arid and semi‐arid regions, but not in the context of engineered urban green infrastructure (GI) systems, especially in temperate environments. Raindrop impulses can break up larger soil aggregates into smaller particles, dispersing them from their original position, and contributing to the formation of a crust at the soil surface. Crusts, in turn, can reduce infiltration and increase both runoff and the soil's susceptibility to erosion. Vegetation canopies can help to mitigate crust formation by dissipating some of the drops' kinetic energy, though the extent of protection provided by the plants has not been studied in GI systems. This paper presents laboratory research conducted using a rainfall simulator to determine the ability of artificial vegetation canopies to minimize soil crust formation, in comparison with a bare soil control. The mechanical resistance of the soil surface to penetration was measured after each of the 22 different simulated rain events. Over the experiment, the percent change in penetration resistance increased by 83.5% and 148%, in vegetated and bare soil control boxes, respectively. The bare soil control box also displayed statistically significant (p < .001) increase in the duration of post‐storm ponding, compared with the control vegetated box, suggesting a reduced infiltration rate. These results suggest that vegetation canopies can play a key role in protecting the soils found in GI systems from raindrop impact.

An effective stress framework for estimating penetration resistance accounting for changes in soil strength from maintained load, remoulding and reconsolidation

Some offshore foundations are subjected to intermittent episodes of remoulding and reconsolidation during installation and operational processes. The maintained and cyclic loads, and subsequent reconsolidation processes, cause changes in the geotechnical capacity, particularly in soft clays. This changing capacity affects the in-service behaviour, including changes to the safety margin, the extraction resistance, the stiffness and structural fatigue rates and also the overall system reliability. This paper provides a new analysis framework to capture these effects, based on estimation of the changing soil strength. The framework is developed using critical state concepts in the effective stress domain, and by discretising the soil domain as a one-dimensional column of soil elements. This framework is designed as the simplest basis on which to capture spatially varying changes in strength due to maintained and cyclic loads, and the associated remoulding and reconsolidation processes. The framework can be used to interpret cyclic penetrometer tests, as well as foundation behaviour. This provides a basis for the approach to be used in design, by scaling directly from penetrometer tests to foundation behaviour. Centrifuge tests are used to illustrate the performance of this approach. The penetration resistance during cyclic T-bar penetrometer tests and spudcan footing installation with periods of maintained loading and consolidation is accurately captured. The framework therefore provides a basis to predict the significant changes in penetration resistance caused by changing soil strength, and can bridge between in situ penetrometer tests and design assessments of soil–structure interaction.

Evaluation of the dynamic cone penetrometer to detect compaction in ripped soils

Land degradation due to compaction is a critical issue facing 21st century agriculture. Deep ripping is a popular solution to remediate compacted Western Australian soils. However, these soils are particularly susceptible to recompaction under vehicle traffic: reliable methods to detect and monitor compaction are therefore needed to inform remediation strategies.Cone penetrometer testing (CPT) is a popular method to detect compaction under vehicle traffic in a range of soil conditions. However, traditional CPT equipment is unsuitable for large-scale use due to its expense and bulk. Dynamic penetrometers circumvent this issue by being inexpensive and man-portable. Such devices have seen recent success in determining properties of soft geotechnical materials but little is known of their performance in ripped soils. This study evaluated the ability of the “PANDA 2” dynamic penetrometer to detect compaction in ripped soils after the passage of aMassey Ferguson four-tonne tractor, which was typical of vehicles used at the test site. Two test sites of contrasting soil types were identified which had previously been ripped and left fallow and untrafficked for several years. Penetration resistance was measured along a high-resolution grid prior to trafficking and after one and five vehicle passes and compared to results from trial pits. Laboratory testing also examined the device's accuracy at shallow depths under controlled conditions. Results showed that the PANDA 2 was able to detect significant changes in penetration resistance after trafficking. However, several limitations on the device's use when interpreting field data were identified. Based on the findings of this study, dynamic penetrometers are not recommended to monitor compaction in ripped soilsfor the weight of vehicle used here. However, the devices may be of use when examining the passage of heavier vehicles.

Resistência à penetração em Latossolo sob floresta ripária e submetido ao pisoteio animal

O pisoteio animal em condições de umidade inadequada são alguns fatores que provocam deformações plásticas e não recuperáveis do solo. No presente trabalho avaliaram-se as possíveis alterações em alguns atributos físico-químicos e na resistência mecânica à penetração, provocadas pelo pisoteio do gado por aproximadamente 20 anos sobre o Latossolo Vermelho Amarelo de um fragmento florestal, localizado em Tremembé (SP). Foram coletadas amostras com estrutura preservada nas camadas de 0-20 cm e 20-40 cm em pontos da trilha de pisoteio e da floresta. O uso do solo não provocou alterações nos valores médios de densidade do solo (1,25 kg dm-3 na trilha e 1,22 kg dm-3 na floresta) e umidade do solo (293,15 g kg-1 na trilha e 301,5 g kg-1 na floresta) , mas provocou alteração na resistência à penetração na camada de 0-20 cm (8,15 MPa na trilha e 3,85 MPa na floresta). Quanto ao, pH, acidez potencial (H+Al), MO, soma de bases (SB) e a saturação de bases (V) não houve diferenças significativas entre as amostras da trilha de pisoteio e floresta. Conclui-se que o pisoteio do gado promoveu alterações na resistência à penetração na camada mais superficial do solo.

STRUCTURAL EVALUATION OF LOW VOLUME ROAD PAVEMENTS USING PAVEMENT DYNAMIC CONE PENETROMETER

Static and dynamic cone penetration tests are widel y used in Foundation engineering for measuring the penetration resistance of the ground and for relating it to the degree of compact ion and safe bearing capacity of soils. In Highway Engineering, Pavement Dynamic Cone Penetrometer (DCP) is used for rapid i n-situ strength evaluation of subgrade and other un bound pavement layers. In the present studies, an attempt has been made to id entify the strength and thickness of different pave ment layers of newly constructed low volume roads in the State of Karnataka, India u sing dynamic cone penetration studies and was compa red with actual measurements at the site. The evaluation of pavemen t test stretches was made for a period of two years , and changes in penetration resistance of different pavement layers were measur ed. A Software was used to analyze the DCP data an d to correlate with field observation. The results have favoured the possibil ity of using dynamic cone penetrometer as a quality control and pavement monitoring tool for low volume roads, eliminating t he need for a Benkelman beam or a falling weight de flectometer.

Experimental and numerical investigation of the sintering rate of snow

AbstractSintering rates in snow were investigated by measuring changes in penetration resistance with time and by using a numerical snow metamorphism model. Periodic Snow Micro Penetrometer (SMP) measurements were performed on uniform snow samples covering a wide range of densities. The mean penetration resistance of snow increased with time according to a power law with an average exponent of 0.18. Simulated changes in the bond-to-grain ratio for simplified spherical ice grains followed a power law with an average exponent of 0.18, showing that the mean penetration resistance, as measured with the SMP, closely relates to bond-to-grain ratio in snow. For lower-density snow samples, consisting mostly of dendritic snow morphologies, the measured increase in penetration resistance was lower. This is likely the result of two competing processes: (1) strengthening of the snow sample due to the creation and growth of bonds and (2) weakening of the snow sample due to the formation of unbonded small rounded particles at the expense of larger dendritic forms. On the other hand, the rate of increase in penetration resistance for snow samples consisting of closely packed depth hoar was similar to that of rounded grains.

Prediction of soil compaction under pneumatic tires a using fuzzy logic approach

Artificial intelligence systems are widely accepted as a technology offering an alternative way to tackle complex and ill-defined problems. They can learn from examples, are fault tolerant in the sense that they are able to handle noisy and incomplete data, are able to deal with non-linear problems, and once trained can perform prediction and generalization at high speed. Compared with traditional approaches, fuzzy logic is more efficient in linking the multiple inputs to a single output in a non-linear domain. The purpose of this study was to investigate the relationship between tire working parameters and soil compaction characteristics, and to illustrate how Fuzzy expert system might play an important role in prediction of soil. All experimental values were collected from soil bin. The trials were conducted in different tire types, vertical loads, inflation pressures and forvard velocities. In this paper, a sophisticated intelligent model, based on Mamdani approach fuzzy modeling principles, was developed to predict the changes in penetration resistance, final pressure and bulk density of soil due to wheel traffic. The verification of the proposed model is achieved via various numerical error criteria. For all parameters, the relative error of predicted values was found to be less than the acceptable limits (10%).

Effects of Slash, Machine Passes, and Soil Moisture on Penetration Resistance in a Cut-to-length Harvesting

Multiple entries into forest stands are often needed for fire hazard reduction and ecosystem restoration treatments in the Inland-Northwest U.S.A. region. However, soil compaction occurring from mechanized harvesting operations often remains for many years and may contribute to a decline in long-term site productivity. A controlled experiment on a silt loam soil was conducted to determine (a) the effectiveness of logging slash to buffer compaction, (b) the influence of the number of machine passes, and (c) the contribution of soil moisture to changes in penetration resistance during a cut-to-length harvest in northern Idaho. Penetration resistance was measured at three soil depths (10, 20, and 30 cm) for three different moisture contents (low, medium, and high) and slash amounts (none, light, and heavy) after each of 12 machine passes (one pass each with a harvester and an empty forwarder, and 10 passes with a fully-loaded forwarder). At all three soil depths the main effect of moisture content and machine passes on penetration resistance was significant, but slash amounts alone did not significantly affect penetration resistance. After 12 passes, we measured the greatest penetration resistance in the medium soil moisture treatment at 5 to15 cm of soil depth. When evaluated at similar moisture contents after harvesting, the soil that was driest during machine traffic (low moisture treatment) had the lowest penetration resistance. Slash was important for protecting the soil against compaction in the medium and high soil moisture treatments. Penetration resistance did not significantly increase after the second pass of a fully-loaded forwarder (31,752 kg) at any moisture content or slash level. Managing felling operations to take advantage of dry soil conditions or using slash when soils are moist may help reduce ruts and avoid long-term compaction impacts on this soil type.

PA—Precision Agiculture: Wheel Traffic Influence on Poplar Regeneration and Grass Yield

All transport in forest stands occurs on the ground that at the same time is used as a growth substrate, not only for timber production but for grass as well in several Argentine production systems. Heavy traffic will damage the ground vegetation, affect tree roots and compact the soil to a degree where the tree roots have difficulty in regenerating in the damaged zone. The main objective of this research was to evaluate changes in soil compaction, introduced by traffic, during harvesting operations in a timber forest where grass production is also used for cattle feeding. Four experimental variables were measured: changes in bulk density in the profile, changes in penetration resistance, grassland yield and forest plantation regeneration after harvesting traffic. The work was performed in the south of the Rolling Pampa region, Argentina. The soil was a fine clayey, illitic, thermic Typic Argiudoll. Treatments consisted of four different traffic intensities, due to different passes of a tractor pulling a trailer on the inter-row area of the plantation, during harvesting operations. Increasing the number of traffic passes, increased the depth at which differences in cone penetration resistance values began to be significantly higher.The increments in bulk density values after traffic were not so evident as those in penetration resistance values, but the same tendencies were shown. The least traffic intensity, corresponding to only one pass, resulted in a reduction of grass yield (40·3%) in comparison with the control (no traffic) treatment, although there was no effect on tree regeneration. Traffic within the plantation impacted principally on tree shoot mortality, with a maximum of 51·5%, measured 1 year after traffic, recorded in the ten pass treatment. Grassland production within the plantation, after harvesting operations, was directly associated with forest regrowth.

Soil compaction under timber harvesting machinery: a preliminary report on the role of brash mats in its prevention

Abstract. Forest soil sustainability and future crop productivity is at risk if mechanised harvesting operations cause soil damage. In UK upland forestry, soil protection is usually provided by placing harvesting residues (brash) over areas where machinery traffic is required. In this study, various thicknesses of brash mat were tested for their ability to reduce compaction of a surface water gley soil at Kielder Forest, Northumberland. Changes in penetration resistance and dry soil bulk density were studied after passes by forest harvesting and timber extraction machinery running on the brash. The study shows that normal harvesting operations caused some soil compaction. However, the brash mat system was shown as important in protecting the soil. Soil under brash mats experienced some compaction to at least 45 cm depth. The thickest brash mat, composed of residues from 10 rows of trees, was unable to prevent compaction completely. Nevertheless, the protective role of the brash mat system was clearly confirmed when compared to timber extraction over bare soil. The point at which compaction has a detrimental effect on the establishment and stability of future tree rotations remains uncertain.

Subsoil compaction caused by heavy sugarbeet harvesters in southern Sweden: I. Soil physical properties and crop yield in six field experiments

The introduction of six-row sugarbeet harvesters, with total loads of approximately 35 Mg on two axles, caused major concern among Swedish sugarbeet ( Beta vulgaris L.) growers regarding the risk for subsoil compaction. A project was started in 1995, which included six long-term field experiments in southern Sweden. The objective was to study effects of heavy axle load traffic during harvest of sugarbeets on penetration resistance, saturated hydraulic conductivity, bulk density and crop yield. Three of the field sites were loams (Eutric Cambisols), two were sandy loams (Eutric Cambisols) and one was sand (Haplic Arenosol). The treatments were: no traffic, four passes by a three-row harvester towed by a tractor (approximately 18 Mg total load on four axles, tyre inflation pressure of tractors 100–150, and 200–250 kPa for the harvester) and one and four passes by a self-propelled six-row harvester (approximately 35 Mg total load on two axles, tyre inflation pressure 200–240 kPa). Traffic was applied late in the autumn at a soil moisture content close to field capacity, but the treatment with four passes with a six-row harvester was also carried out under drier conditions earlier in the autumn. In the spring after traffic, no significant changes in penetration resistance were found. When measured 2–4 years after traffic, significant changes between treatments were found to 0.5 m depth on three sites. Differences between years are possibly an effect of age-hardening. Saturated hydraulic conductivity at 0.3 and 0.5 m depth, measured on cores sampled in the spring after traffic, was in several cases reduced by about 90% after four passes with a six-row harvester. As an average for all sites, this traffic significantly reduced saturated hydraulic conductivity and increased bulk density at 0.5 m depth. At two sites, measurements were repeated 4 years after traffic and differences in saturated hydraulic conductivity between treatments were approximately the same as on the first sampling occasion. Despite the great effects on soil physical properties, differences in yield between treatments were mainly small and insignificant. The data concerning saturated hydraulic conductivity may be useful for modelling the effects of subsoil compaction, for example on erosion and denitrification, since little such data is available in the literature. The results clearly demonstrate to farmers that heavy traffic during harvest of sugarbeet implies a major risk for compaction of the subsoil, which can be seen as a long-term threat to soil productivity.

Changes in penetration resistance of Ultisols from southern China as affected by shearing

Shear stresses and soil properties modified due to stress play an important role during formation of seals in a series of rainfall events and during tillage. The objectives of the study were to evaluate the effects of the penetrometer geometry on the penetration resistance as affected by shearing under different initial soil conditions and to use the information on soil strength to elucidate shearing process. Nine homogenous air-dried soils (<2 mm) were sprayed and stored so as to obtain equilibrium soil water contents. The moist soils were sheared by horizontal displacement of layers of soil particles/aggregates in between hands in one direction. The soil cores were prepared with comparable bulk density before the measurement of maximum penetration resistance ( P max) with a small flat tip and a cone tip penetrometers. At a wide range from 0.05 to 6.2 MPa, P max was linearly correlated between the small flat tip and the cone tip penetrometers. The conversion ratio was higher under the saturation condition irrespective of the shearing effect. The penetrometer with the small flat tip was more sensitive for the weak soils. Shearing generally increased P max in most cases, but it decreased P max for some sandy soils under both saturated and unsaturated conditions and for a clayey soil under the saturated condition. The soil consisting of swelling clay exerted a decrease in P max. Rearrangement and/or sliding of particles/aggregates and increase in soil suction during shearing were attributed to the increase in P max. Increase in porosity due to the aggregation during shearing was ascribed to the decrease in P max. In addition, it was shown that agricultural cultivation resulted in a reduction in soil strength.

Soil penetration resistance, root growth and yield of maize as influenced by tillage system on ridges in Malawi

Ridge-tillage is a traditional method of seedbed preparation in Malawi and is performed annually by manual operation with a hand hoe. A 3-year field experiment was conducted to evaluate the effects of minimum (MT) and conventional (CT) ridge-tillage systems on soil strength and maize ( Zea mays L.) growth. Minimum tillage consisted of planting maize on ridges made in the previous year(s) while in CT it was grown on new ridges constructed at the beginning of each season. The soil was an Oxic Rhodustalf. Results indicated that a distinct hard and compact layer had developed below the ridges (about 25 cm depth) in both CT and MT. Soil on ridges of CT had consistently lower penetration resistance than did MT. Bulk density and penetration resistance of soil on the ridges were less under CT than under MT. Penetration resistance in both tillage treatments was strongly related to soil water content, which depended on the amount of rainfall. Consequently, the pattern in changes of penetration resistance in the soil during the season generally mirrored that of rainfall. The presence of compacted subsurface soil layers in both treatments and the significantly higher ( P ≤ 0.05) penetration resistance in the MT affected root penetration and distribution. The MT had significantly lower root length density in the 0–20 cm depth and roots were concentrated near the surface compared with those of CT. Maize grain yields, however, were not affected by the tillage system in the first two seasons of the study but were significantly reduced by MT in the third season. The average grain yields over the three seasons were 4812 and 4644 kg ha −1 for CT and MT, respectively. Use of MT resulted in remarkable reductions of working time and energy requirement for maize production compared with CT. This study has shown that maize yields of around 4000 kg ha −1 can be achieved by using previous years' ridges under smallholder farmers circumstances of low resource input.

Biophysics of the growth responses of pea roots to changes in penetration resistance

Biophysics of the growth responses of pea roots to changes in penetration resistance

Slow Rate Penetration of Packaging Films

A detailed evaluation of the slow rate penetration resistance measure ment was conducted on twenty-two different monolithic, coextruded, or laminated flexible barrier packaging films using five different probe geometries. No universal change in penetration resistance with penetration rate was found. Decreasing probe sharpness or severity increased the observed penetration resis tance and improved the signal-to-noise ratio. However, similar rankings of film per formance were possible regardless of probe geometry. After considering these and many other factors, it is recommended that measurement of slow rate penetration re sistance should be made using a 20 mm/min penetration rate and a 3 2 mm dia hemispherical probe with a probe:clamp diameter ratio of 10.

Off-road Motorcycle Effects on a Desert Soil

The effects of controlled motorcycle traffic on a Mojave Desert soil in California were studied in order to describe soil compaction quantitatively. Four experimental trails, representing 1, 10, 100, and 200, passes each with an off-road motorcycle were established in a loamy sand at 6.2% by weight moisture content. Penetration resistance, density, infiltration rate, and response to rainfall, were measured for the undisturbed soil and for the experimental trails immediately after the conclusion of the impact, and soil cores were measured in the laboratory to determine pore-size distributions. The soil density was remeasured again one year after the impact, to determine the amount of recovery.Immediately after motorcycle use, the average density of the soil in the 0 to 60 mm depth increased from an average of 1.53 metric tons/cubic metre in the undisturbed soil to 1.77 t/m3in the 200 pass trail, and the average density in all the trails could be expressed empirically as a logarithmic function of the number of motorcycle passes. The soil penetration resistance profile for the 200-passes-trail showed that the maximum compaction occurred between 30 and 60 mm depth, and that changes in penetration resistance could be measured to a depth of 0.21 to 0.25 m. The infiltration rate after 2 hours decreased from an average of 98 mm/hr in the undisturbed soil to 29 mm/hr in the 200 pass trail.The undisturbed soil infiltrated artificial rainfall up to an intensity of 46 mm/hr before surface ponding occurred in the 100- and 200-passes-trails at intensities greater than 25 mm/hr. Decreases in the soil-pore volume were greatest in pores with effective radii greater than 150 μm, with incremental decreases occurring in pores with radii between 150 and 4.5 μm; the total volumes of smaller pores were similar in the compacted and undisturbed soils. One year after the impact, the density of the soil at a depth of 0–30 mm had decreased significantly in the 10-, 100-, and 200-passes-trails but the densities at 30–60 mm depth remained unchanged.

Tidal variations in the compaction of beach sediments

Measurements of the penetration resistance of beach sands on a gently sloping (1:50) high tidal range (9.5 m) beach are described. It has been found that at any one position the penetration resistance reaches a maximum value about 1 hour before that section of the beach is submerged by the incoming tide, and that this maximum value is largest at the mid-tide level. This behaviour cannot be explained by a tidally induced change in the beach water table alone and it is suggested that spatial changes in penetration resistance may be related to the varying amounts of exposure of the beach face to wave activity in the surf zone as the latter is swept in and out over the beach face by the tide. In particular a “cut and fill” mechanism would lead to the observed variations in compaction of the beach sediment and additionally a momentary failure of the beach face under breaking waves might give similar results.