Subgrade Materials Research Articles

Effect of static pore water pressure on shear behavior of saturated kaolin clay

To study the mechanical properties of sedimentary marine clays in deep seabed, static pore water pressure (SPWP) is often prescribed in triaxial shear tests by applying different back pressure levels (B.P.) corresponding to in-situ position of the water table. In this paper, several undrained and drained triaxial tests have been conducted to study the effect of SPWP on the mechanical behaviors of kaolin clay, which is often used to create artificial marine clay or as a subgrade material in the centrifuge tests of offshore geotechnical engineering. The magnitude of SPWP is found to impact undrained shear strength, initial growth rate of excess pore pressure, friction angle, while has little effect on initial undrained shear stiffness and ultimate excess pore pressure. A new unique line can be determined which is parallel to total stress path by fitting all the critical failure points during undrained shearing. The influence mechanism is considered to be related to a nonuniform distribution of SPWP in different kinds of pores, which makes the clay microstructure changeable under different SPWP. There may exist a "pseudo-suction" when certain SPWP is applied, resulting in a higher friction angle of kaolin clay.

Use of an Eletrokinetic Remediated Soil as a Road Subgrade Material

The soil investigated for suitability checks, as a subgrade material in this study, was a crude oil contaminated (COC) soil treated using an electrokinetic technique. The index properties and compaction characteristics of the electrokinetic remediated (EKR) soil are natural moisture content was 10.97%; The Atterberg limit test showed liquid limit, plastic limit, plasticity index and linear shrinkage of 36.50%, 22.05%,14.45 %, and 4.30%, respectively. The percentage of 62.80% passes 0.075mm sieve with a maximum dry density (MDD) of 1.77 Mg/m3, and the moisture content decreased from 13.2% to 11.81%. The soil is classified as A-6 according to AASHTO classification system and belong to clay of low plasticity CL or OL group according to the Unified Soil Classification System. The unconfined compression strength, (UCS), durability, and California bearing ratio (CBR) of the electrokinetic remediated soil improved marginally from 46.63kN/m2 to 92.64kN/m2; from 18% to 23%; and from 2.55% to 4.05% respectively. However, these results obtained, do not meet the minimum requirement of the Nigerian General Specification. As a result, it is advised for further research, that an EKR soil be stabilized using cement stabilization to achieve the desired subgrade strength.

Water characteristic curve and permeability function of recycled concrete aggregate

Construction and demolition waste are one of the major waste streams in the world. Aggregates must be used in significant quantities during road construction and maintenance as base and sub-base materials. Government and local businesses are promoting the use of recycled material in old pavement andconstruction material due to the high cost of virgin aggregates. Concrete, road subgrade, and railroad ballast materials can all be made from recycled concrete aggregate (RCA), a type of recycled material. The engineers must properly comprehend the material's qualities, including its unsaturated properties, in order to use RCA in these projects. The goal of this project is to investigate the unsaturated permeability and thewater characteristic curve of RCA. These unsaturated qualities were discovered through sophisticated laboratory experimentation. The study's findings showed that the RCA has the same qualities as gravel or natural aggregate.

Toward an Improved Surface Roughness Parameterization Model for Soil Moisture Retrieval in Road Construction

In passive microwave remote sensing, the estimation of the surface roughness parameter is a significant obstacle for soil moisture (SM) retrieval. For a given SM content, the geometric soil surface roughness has been shown to have a large impact on the surface emission at L-band frequency, which affects the SM retrieval success when using the information observed from the radiometer and is represented through the so-called the surface roughness parameter ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$H_{R}$ </tex-math></inline-formula> ). Moreover, no previous study has examined the effect of this factor in the context of road construction, where the geometric soil surface roughness is affected by the compaction process, resulting in a substantial change in roughness before and after compaction. Accordingly, a series of experiments at various compaction levels and SM contents was performed for a sand subgrade material in order to identify their effects on <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$H_{R}$ </tex-math></inline-formula> . The soil brightness temperature (TB) was measured using an L-band radiometer at different incidence angles and a laser profiler was used to measure the surface roughness standard deviation ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sigma$ </tex-math></inline-formula> ) before and after compaction. The results of this article have demonstrated that the incidence angle ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\theta$ </tex-math></inline-formula> ) and SM both affect <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$H_{R}$ </tex-math></inline-formula> and its relation to the geometric soil surface roughness. Importantly, these factors are not accounted for by existing models. Consequently, a modified surface roughness parameter ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$H_{R}$ </tex-math></inline-formula> ) model, based on the traditional Choudhury model, was developed to include the contribution of these two factors, and its impact on the accuracy of SM retrieval results tested. Specifically, it was shown that it is possible to obtain SM retrieval results with an accuracy of 0.04 cm3/cm3 at almost all incidence angles using either dual-polarization [both horizontal (H) and vertical polarization (V)] or only vertical polarization observations. The modified surface roughness parameter ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$H_{R}$ </tex-math></inline-formula> ) model has improved the performance of the SM retrieval model to achieve an accuracy of 0.04 cm3/cm3, whereas the traditional Choudhury model achieved an accuracy of only 0.05 cm3/cm3.

Influence of cohesion on California bearing ratio of clay–gravel mixtures

An understanding of the behavior of cohesive sediment is required to solve various engineering problems such as scour around bridge elements, mitigation of soil erosion, pavement design, river bed degradation, stable channel design. Pavement foundation designers principally use the California bearing ratio (CBR) to describe the subgrade and subbase materials and their strength. Several laboratory experiments were done to study the variation in the CBR of cohesive mixtures comprised of clay–gravel mixtures. Nine different clay–gravel mixtures were used in which the clay content varies from 10% to 50% by weight. The variation of the CBR with clay percentage, moisture content, and undrained shear strength parameters was studied. The CBR value reduces with the increase in the moisture content and clay fraction in the mixtures and increases with an increase in the dry density of the mixture under unsoaked conditions. The CBR also increases with the increase of the angle of internal friction of clay–gravel mixtures. A functional relation has been identified to estimate the CBR of clay–gravel mixtures. Using multiple linear regression analysis (MLRA), a relation is proposed to estimate the CBR of clay–gravel mixtures under unsoaked conditions. A statistical analysis was done to judge the behavior of the pertinent variables on the CBR. The proposed relation predicts the CBR of clay–gravel mixtures very well. Artificial neural network (ANN) analysis using R programming was also done to determine the effects of the pertinent variables on the CBR. ANN methodology was applied to predict the contribution of each variable. Three different methods: Garson algorithm, Olden algorithm, and Lek's profile model are used to assess the influence of variable parameters. The Olden algorithm and Lek's profile both show positive association of cohesion with CBR in an unsoaked condition. The role of moisture content was found to be marginally negative in the Olden algorithm and Lek's profile results. It is found that both the ANN and MLRA models are accurate in predicting the CBR of clay–gravel mixtures. It was further found that the MLRA and ANN models are reliable and rapid tools for correct assessment of the CBR of cohesive soil mixtures using the basic soil properties.

Characterisation and modelling of subgrade resilient modulus for pavement structural design in Egypt

In Egypt, estimation of subgrade resilient modulus (MR) for the structural pavement design is based on empirical correlation with California Bearing Ratio (CBR) adopted from literature. Thus, this study aims at verifying if this correlation is still valid for different Egyptian subgrade soils, otherwise calibration is warranted. A comprehensive experimental program is conducted on local sixteen subgrade materials. The testing program includes MR, CBR, and index soil properties such as gradation, Atterberg limits, Proctor compaction characteristics, and shear strength parameters. Four simple regression models correlating MR and CBR values are developed for local subgrade materials based on the anticipated field stresses under two different traffic loading conditions pertinent to Egypt. The proposed correlations yield more accurate MR values for the local materials and traffic loading conditions. Consequently, this is expected to contribute to a realistic pavement structural design, and hence better pavement performance over the service life.

An Investigation on the Potential of Cellulose for Soil Stabilization

The construction industry remains a significant contributor to global carbon emissions. Several sustainable alternatives have emerged to overcome this issue in geotechnical engineering. In this study, cellulose, an abundant biopolymer, is investigated for its potential to modify geotechnical properties favourably. Sodium carboxymethyl cellulose (NaCMC) is an anionic ether derivative of natural cellulose with good binding and moisture-retaining capacity. Experimental investigations were conducted on organic silt stabilized with 0.25% to 1.00% NaCMC, and the results indicate that unconfined compression strength (UCS) increased by 76.7% with 0.5% NaCMC treated soil after 28 days. Hydraulic conductivity (HC) of the 0.5% NaCMC treated soil decreased by 91.7% after 28 days, and the additives suppressed the compression index of the soil by 50%. The California bearing ratio (CBR) test indicated that the additive improved the subgrade strength by 33.2%, improving it from very poor to a fair sub-grade material. Microstructural analysis using a scanning electron microscope (SEM) and chemical investigation using x-ray diffraction (XRD) indicates that NaCMC’s interaction with soil did not form any new chemical compounds. However, the viscous nature of the material formed fibrous threads that bind the soil to enhance the geotechnical properties, establishing itself as a prominent stabilizer for ground improvement applications.

Mixed-mode fracture of compacted tailing soils. I: Fracture toughness

Mine tailings are man-made soils and leftovers from the mineral processing that share the similar geotechnical properties with natural soils. In areas with abundant mineral reserves and developed mining industries, tailings could be utilized as an alternative of natural soils for subgrade materials of pavement and adobes for building and construction constructions. The tailing soils are also the based materials for tailing dams. The compacted tailing soils might thus be subject to combined opening or shearing deformations that were unexplored in the current academic society. In this paper, a test configuration called asymmetric semi-circular bending (ASCB) was adopted to investigate the mixed I/II mode fracture properties of the compacted tailing soils. First, the load–displacement relationships of the SCB specimens for different notch depths and span ratios were presented. The mode I and II fracture toughness components were then calculated by referring to the theoretical solutions derived from classical fracture mechanics. The fracture envelope from mode I and II fracture toughness components were presented. Meanwhile, the mixity parameter was introduced to evaluate the mode mixity of the ASCB specimens. Finally, the crack initiation angles of the SCB specimens were measured through experimental tests and compared to the theoretical results obtained from generalized maximum tangential stress criterion (GMTS). Results show that the mode I fracture toughness component of the compacted tailing soils increased with the span ratio, while the mode II fracture toughness component increased with the decrease of span ratio. The mode mixity and crack initiation angles of the SCB specimens under mixed mode loading conditions increased with the decrease of span ratio.

Engineering Properties Investigation of Soft Clay as Potential Subgrade Material

Highway pavement design using soft clay soil as a subgrade is always a great challenge and can cause problems such as roadbed instability and soil settlement. To overcome this problem, the knowledge of the subgrade soil characteristic should be studied first because it needs to be considered during the design phase of pavement. This study was conducted to investigate the engineering properties of soft clay that can be used as potential subgrade material. Some soil laboratory tests were performed to establish the engineering properties of the soft clay. From the standard proctor compaction test, the results revealed that the maximum dry density and optimum moisture content are 1.58 Mg/m³ and 20.15 %, respectively. The finding from the soil-water characteristic curve (SWCC) test indicates that the SWCC did not present a residual suction. The compression modulus and pre-consolidation pressure obtained from the compacted soil sample for the consolidation test are higher than the undisturbed soil sample. Based on triaxial test results, the effective cohesion acquired from the compacted soil sample is greater than the undisturbed sample. This research provides a reference for the study of soft clay engineering characteristics.

Sustainable utilization of sugarcane bagasse ash in highway subgrade- a critical review

Pavement subgrade stabilization is one of the major problems in the transportation industry due to the diversity in the type of soil. Sometimes, weak soils are encountered, which are inadequate for carrying the self-weight of the pavement layers and traffic load, compromising the stability of highways. In this instance, either they are replaced with more suitable material or modified to increase their load capacity. Former is a costlier affair if the material is not locally available. Various modification techniques, such as chemical modification, can be done using traditional or non– traditional additives. The cement and lime are commonly used to provide sufficient strength of the subgrade soil, but due to their high cost of production and a negative impact on the environment in the form of greenhouse gas emissions, these must be replaced by a more sustainable and eco-friendlier substitute. This study reviews the suitability of by-products of sugarcane industry, i.e., sugarcane bagasse ash (SCBA) for subgrade stabilization, focussing on its sustainable use and analysing engineering properties of different types of weak subgrade and its mechanism involved in stabilisation. It can be concluded from the literature that the use of bagasse ash is a less expensive and sustainable solution compared to traditional one. So, SCBA needs to be promoted to improve and enhance engineering properties of subgrade material.

Effects of Particle Size and Soil Bed on the Shear Strength of Materials in the Direct Shear Test

Generally, direct shear apparatus is used to determine the shear strength parameters of soil and rock for designing a geotechnical engineering structure. However, the size of the shearing box and the soil sample is key for evaluating the shear strength parameters of test materials, and also testing conditions in the laboratory are different from site conditions. This research aimed to focus experimentally on the effect of particle size and the property of subgrade materials that were necessary keys for installing apparatuses for the direct shear test. According to the experimental results based on a 5 x 5 cm shear box, an increase in average particle size and coefficient of curvature could provide higher shear strength in terms of internal friction angle of the sample, but not for the case of higher value of the uniformity coefficient. Using both 5 x 5 cm and 30 x 30 cm shear boxes, a large B/Dmax ratio is not the key for determining appropriate parameters when testing with samples that have a nearly uniform size. Samples varied in thickness of both the ballast and subgrade layers, were investigated and observed by a large shear box. It was found that good properties of subgrade materials affected the shear strength of ballast materials, and they provided underestimates of strength when the bottom of the shearing box was rigid. The modified parameter of ballast materials on the subgrade layer is suggested for obtaining strength parameters reflecting the ballasted track system.

Effect of Saturation Degree on Mechanical Behaviors of Shallow Unsaturated Expansive Soils

In the southwest of China, there are widely distributed expansive soils. However, to save costs and manage the speed of construction, these shallow expansive soils are often filled with subgrade materials. Therefore, it is necessary to clearly understand the mechanical behaviors of unmodified shallow expansive soils. Current research on the mechanical behaviors of shallow expansive soils is mainly focused on shear and compressive strengths but rarely on the tensile strength since general tests are costly, time consuming, and difficult to conduct. Therefore, uniaxial tensile, unconfined compression and direct shear tests were carried out to study the mechanical behavior of shallow unsaturated expansive soils under different saturation degrees, and the tests analyzed the change mechanism of its mechanical behavior. The following were found: (1) with an increase in saturation degree, the uniaxial tensile strength, unconfined compressive strength, shear strength, cohesive force, and internal friction angle first increased and then decreased; (2) when the saturation degree increased from 18.7% to the saturation degree corresponding to the peak, the uniaxial tensile strength, unconfined compressive strength, cohesive force, and internal friction angle increased by about 11 times, 3.24 times, 2.34 times, and 0.52 times, respectively; (3) when the saturation degree increased from the saturation degree corresponding to the peak to 80.3%, they decreases by about 42%, 51.4%, 36%, and 50%, respectively; (4) with the increase in dry density, the saturation degree corresponding to the peak of uniaxial tensile strength gradually increased, while the saturation degree corresponding to the peak of unconfined compressive and shear strength did not significantly change.

Investigation on the pollution release characteristics of subgrade base materials prepared by oil-based cutting thermal desorption residues.

The preparation of oil-based cutting thermal desorption residues into subgrade materials is one of the methods of their resource utilization. While the environmental safety for subgrade materials is lack of discussions. In this study, through the semi-dynamic leaching tests, the leaching characteristics of pollutants from residues subgrade materials under extremely acidic conditions were simulated. According to Fick's second law, combined with the effective diffusion coefficient (De), the risk of pollutant leaching and release in residue subgrade materials were evaluated. The concentrations of naphthalene, anthracene, benzo(a)anthracene, dibenzo(a,h)anthracene, Cd, and Zn met the requirements of class III water quality in the Chinese standard GB/T14848-2017. The release of naphthalene, anthracene, benzo(a)anthracene, dibenzo(a,h)anthracene, and Cd of leaching was dominated by diffusion. The release of benzo(a)pyrene and Zn of leaching was mainly dissolution. Hence, based on the investigation, the release law and characteristics of pollutants were explored when thermal desorption residues were applied as subgrade materials, which provided an important reference basis for the resource and utilization of oil-based cutting thermal desorption residues.

Komparativna analiza učinkovitosti otpada od orezivanja palmi i geotekstila na stabilizaciju posteljice

This paper proposes a novel and environmentally friendly solution for subgrade stabilization that not only contributes towards waste material recycling but also enhances the bearing capacity of subgrade soil. Laboratory plate load tests were conducted under static loads to evaluate the potential use of palm tree pruning waste (PTPW) as a soil reinforcement material instead of commercially manufactured geotextiles, as well as to analyse the impact of the reinforcement depth, number of reinforcement layers, and the relative density of the subgrade material. The results revealed that as the number of reinforcements increased, the load-bearing pressure behaviour of the reinforced subgrades improved. Furthermore, when the reinforcement depth decreased, the load-bearing pressure behaviour improved significantly. All PTPW-reinforced subgrades performed better than geotextile-reinforced subgrades under the same conditions. Additionally, the bearing capacity improvement in the reinforced subgrades was evaluated based on the bearing capacity improvement factor (BCIF). The highest BCIF was obtained when the PTPW was used as a reinforcement with two layers at a sand subgrade relative density of 80 %.

Utilizing Tunnel Boring Machine (TBM)-Crushed Limestone as a Construction Material.

Tunnel boring machine (TBM) materials are usually crushed powder obtained during tunnel excavations for subways and transportation networks. Huge quantities of crushed rock powder are generally treated as waste. This study is aimed at assessing proposed mixtures of TBM and granular material for use in construction. This approach will help in a greener environment and reduce the need for crushed aggregates used in sub-base and subgrade layers of pavements. Assessment is executed using dynamic and static strength tests, including the modulus of resilience and the California bearing ratio (CBR). The TBM-crushed material can be sorted and screened on site to optimize its use as a construction material. The blending ratios for the 3/8-inch aggregate (G1) to the material-passing sieve number 4 (P4) were found to influence the pavement design parameters. This study recommends sorting the TBM-crushed limestone by an on-site sieving operation. A guide to optimizing the quality of the material is suggested by blending 3/8-inch aggregate with the crushed limestone fine-powder material at a specified percentage ranging from 5 to 10% by weight. The stability and durability tests conducted on the TBM-crushed powder material confirmed its suitability as a pavement construction material for subgrade and sub-base layers. Modulus of resilience, CBR values and compressive strength tests were carried out for different suggested mixtures.

Deformation and critical dynamic stress for compacted volcanic ash subjected to monotonic and dynamic loads

Volcanic ash is widespread in volcanic areas and is considered as a potential construction material. Therefore, volcanic ash can be used as subgrade material when building highways and railways in volcanic areas. However, there is limited research on the critical dynamic stress as well as deformation characteristics of volcanic ash under dynamic load. The Global Digital System (GDS) monotonic triaxial tests and dynamic triaxial tests are presented in this paper to quantify the critical dynamic stress as well as deformation characteristics of volcanic ash subjected to monotonic and dynamic loads. The critical dynamic stress and deformation of volcanic ash are affected by stress level, water content and dynamic stress amplitude. Under monotonic loads, the strength of volcanic ash decreases with increasing water content and increases with increasing confining pressure. The deformation of volcanic ash exhibits strain softening behavior which is enhanced with increasing water content and weakened with increasing confining pressure. According to the shakedown theory, the patterns of accumulative plastic strain for the volcanic ash under different dynamic stress amplitudes are classified into three categories, named plastic shakedown, plastic creep, and incremental collapse. This study redefines the shakedown limits for volcanic ash based on the shakedown theory. The adoption of new shakedown limits provides more accurate descriptions of deformation characteristics at different stress levels, water contents and dynamic stress amplitudes. Based on the new shakedown limits, this paper presents empirical models for the calculation of critical dynamic stress for volcanic ash shakedown limits using regression analysis. As a contribution to the literature and potential engineering applications, the proposed models may provide theoretical significance for the subgrade state evaluation.

Geotechnical investigation and statistical relationship of subsoil properties derived from two parent rock types in Southwestern Nigeria

This study is aimed at using geotechnical properties and statistical relationship between geotechnical parameters to evaluate the performance of subsoil derived two different rock types for pre- and post-engineering construction planning and design of roads. Twelve soil samples underlain by two rock types (granite gneiss & grey gneiss) were taken at the depth of 1 m for analysis. The geotechnical properties of these soils were tested. The atterberg limit, grain size analysis, California bearing ratio (CBR) and compaction tests of both soils types met the Nigeria specifications of good subgrade material. Soil derived from grey gneiss has better ratings in linear shrinkage, grain size analysis, specific gravity, compaction and CBR tests. Twelve parameters of the soil samples were correlated against each other and sixty-six values of correlation coefficient were recorded for each rock type. Soil derived from grey gneiss has more positive pairwise Pearson’s (r) correlation (37) than the soil derived from granite gneiss (34). Granite gneiss derived soil has better ratings in thirty-three (33) out of sixty-six (66) Pearson’s correlation (r) values to thirty-two (32) of grey gneiss with one of the variables correlation having the same value. There exist five strong positive and five strong negative correlation variables that are common to the two rock types’ derived soils. The Pearson’s correlation coefficient (r) values that are within the critical (r) value are negligible. For regression analysis, granite gneiss derived soil has better ratings than the grey gneiss derived soil with both rock types derived soils having these two pairwise correlation variables (GRV-SAND and OMC-MDD) for excellent prediction.

Experimental study on potential suitability of natural lime and waste ceramic dust in modifying properties of highly plastic clay

Working with expansive soil as pavement subgrade is not technically easy due its poor workability and insufficient capacity to support the imposed cyclic traffic loading. For satisfactory performance of the pavement structure constructed in such foundation hence the properties of the weak subgrade have to be modified. One of the ideal solutions to these problems might be looking towards naturally abundant and industrial waste materials that are produced in large quantities as stabilizing agent for clay subgrades so that the instability concerns can be alleviated. This study hence primarily aimed at experimentally scrutinizing the stabilizing potential of waste ceramic dust and natural lime in modifying geotechnical properties of the highly plastic subgrade material. Both the separate and combined effects of the two stabilizing agents were investigated with respect to mitigating the key parameters required for stable road construction. The degree of improvement for various mix ratios were compared with the design and requirements of Ethiopian roads authority specifications for road construction. Accordingly, the optimum dosage for natural lime was 6% whereas that of the waste ceramic is 20% for safe road subgrades. It was also indicated that natural lime is more powerful than the waste ceramic dust from effectiveness point of view. The conducted experimental test revealed that the response of soil parameters to variation in amount of stabilizers in the separate application method is more sensitive for natural lime than the waste ceramic dust. The improvement rate in magnitude of the required geotechnical parameters in the combined case is by far greater than the separate application of the additives.

Use of Red Mud as An Inferior Building Material

Aluminum's usage as a steel and wood alternative has resulted in rapid growth for the aluminium sector. Aluminum manufacturing leaves behind red mud as a byproduct. Red mud leftovers amount to 1 to 2 tonnes of dry weight each tonne of aluminium produced. The main aim of the study is Use of Red Mud as an Inferior Building Material. A computational approach and an experimental investigation of red mud are both included in the current work. Investigation of morphology, chemical composition, and mineralogy and geotechnical properties of red mud as a subgrade material is the experimental approach. It is concluded that red mud as a subgrade building material is investigated in this research using laboratory geotechnical testing, model footing tests, and FE modelling.

Performance Characteristics of Black Vertosol as a Subgrade Material in Unpaved Granular Pavements

Performance Characteristics of Black Vertosol as a Subgrade Material in Unpaved Granular Pavements