Lateritic Gravel Research Articles

Mechanical Behavior of Materials Used for Paving in the Southwest of the Brazilian Amazon

This study presents geological aspects of the southwestern Brazilian Amazon and analyzes the geotechnical characteristics and mechanical behavior of lateritic gravel soils of this region in the country. The soils in this paper were divided into two groups: soils selected for the BR-429/RO project and a laterite deposit located in the Porto Velho city. Resilient modulus was determined by repeated load triaxial test for determination and evaluation of the total permanent deformation considering various stress states. In results of the tests was observed high resilient modulus values and low values of permanent deformation for all materials analyzed, a fact which corroborates the good mechanical behavior of materials used as road paving materials.

Microstructure, geotechnical and mechanical characteristics of quicklime-lateritic gravels mixtures used in road construction

Microstructure of quicklime-lateritic gravels mixes, containing up to 8 wt.% quicklime, was investigated by using X-ray diffraction, infrared spectrometry, differential thermal analysis, scanning electron microscopy and energy dispersive spectrometry. Geotechnical and mechanical properties of the mixtures were also measured. Quicklime additions resulted of reduction of clayey fraction, plasticity index, methylene blue value and maximum dry density and the increasing of optimum moisture content. The results showed also that quicklime admixtures resulted in the formation of calcium silicate hydrate type I (C–S–H (I)), portlandite and calcite. This CSH (I) was formed through the pozzolanic reaction between a part of the kaolinite and hydrated lime in the basic medium. Moreover, C–S–H (I) marked crystallization with curing time and observed for the quicklime amounts (⩽3 wt.%), contributed to the improvement of mechanical properties. These lime modified lateritic gravels are convenient for base course in road geotechnical applications.

ECONOMICS OF SOIL MOISTURE CONSERVATION IN COCONUT LANDS USING COCONUT HUSKS AND COIR DUST

Economic feasibility of soil moisture conservation in coconut production usingcoconut husks and coir dust was examined in this study. The preliminary data for thestudy were collected from two trials conducted by the CRI along with several othersecondary information. The results of the analysis' revealed that calculated Benefit-Costratios and Net Present Values are financially and economically acceptable under all thescenarios addressed in this study. Three different interest rates, such as 10%, 15%, 18%and two.effective time periods (viz. six and nine years) were used for the analysis.Based on the estimated economic parameters, it is concluded that the efforts on moistureconservation using coconut husks and coir dust in lateritic gravel and sandy soils areeconomically viable propositions. As the initial cost of investment is substantial, othermeans to overcome the problems of financial constraints in investment may be lookedinto.

Studies On Potassium Magnesium Interaction In Coconut (Cocos nucifera)

The widespread deficiency of magnesium in coconut acts as a limiting factor to increasedproduction. Two ongoing experiments on potassium-magnesium (K-Mg) interaction incoconut conducted in lateritic gravels (ultisols), in the wet and intermediate agroclimatic zonesof Sri Lanka showed significant yield responses (P=0.01) to differential K treatments, in thewet zone, but not in the intermediate zone. Differential Mg treatments, however, did not giverise to yield responses. Leaf and nut water analysis showed significant changes in theconcentrations of Na, K and CI (P=0.001), with a distinct inverse relationship between Na andK when K was applied. Differential Mg applications showed a significant effect only for leafMg (P=0.001), in the fourth year of the experiment, in the wet zone. Results indicate theusefulness of nut water analysis as an additional diagnostic tool, for Na, K and CI

Construction of unpaved rural road using jute–synthetic blended woven geotextile – A case study

Jute–high density polyethylene (HDPE) blended geotextile samples produced using HDPE slit-film in the machine direction and jute yarn in the cross direction for use in the construction of unpaved rural roads. Use of HDPE slit-film resulted in high productivity of jute-based geotextiles in modern high-speed machines, while jute (≈85%) in cross direction resulted in notable increase in modulus, breaking strength, CBR puncture resistance of the blended geotextile as compared to 100% HDPE geotextile. The optimized geotextile (plain-weave fabric with 111 tex HDPE in machine direction, 2 × 360 tex jute yarn in cross direction having area density, 316 g/m 2) was used in a field trial. During road construction, the geotextile was covered with a layer of 10 cm thick laterite gravels as the sub-grade, compacted by rolling, and then finally covered with 10 cm small granular lateritic stones, and rolled again. The field trial showed that the monitored section where geotextile was used showed an even surface without any notable subsidence or rutting after 18 months. However in sections of the road constructed without the geotextile, 5–35 mm deep ruts were observed. CBR tests (carried out 11 months and 18 months after construction) showed a 67–73% improvement in the road due to the use of jute–HDPE blended geotextile than that obtained for the part of the road where geotextiles were not used.

Water relations and mineral nutrition of closely related woody plant species on desert dunes and interdunes

Vegetation on dunes and interdunes in hot, subtropical deserts is profoundly influenced by the temporal and spatial variation in availability of water and nutrients in the landscape. We hypothesised that water is more available to plants on the dunes but that nutrients are in greater concentrations on the interdunes in the Great Sandy Desert, Western Australia. During the course of 2 years, we examined water relations and photosynthesis of six dominant woody species throughout each season, in addition to foliar δ13C, δ15N and nutrient composition. In general, stomatal conductance (gs) was greater and leaf water potential (ΨL) less negative for dune species than for closely related species on the interdunes. The largest tree species in the landscape, Corymbia chippendalei ((D.J.Carr & S.G.M.Carr) K.D.Hill & L.A.S.Johnson), occurred only on the dunes, and maintained moderate gs values year round, ranging between 240 mmol H2O m–2 s–1 in the wet season and 160 mmol H2O m–2 s–1 in the middle of the dry season. It also displayed a relatively stable ΨL, between –0.3 and –0.5 MPa at predawn, and between –1.3 and –1.6 MPa at midday throughout the year, unlike the closely related species on the interdunes, Eucalyptus victrix (L.A.S.Johnson & K.D.Hill), which always displayed significantly lower ΨL values (0.2–1.1 MPa more negative). The two Grevillea species displayed ΨL values within a similar range as for C. chippendalei, while the Acacia species exhibited consistently more negative values, especially late in the dry season. Considerable reductions in gs occurred at this time for all species, except C. chippendalei. Rates of photosynthesis (A) followed the trends in gs, yet δ13C values varied little between related species in the dune and interdune habitats. Mineral nutrient concentrations in soil and foliage tended to be greater in the interdunes. Average N : P ratio in foliage was 28 : 1, indicating P was more limiting than N. Soil depth and texture, in conjunction with their effects on water availability and root growth, were considered to be the most influential factors affecting plant distribution in the Great Sandy Desert. It is concluded that dunes hold relatively more water than adjacent interdunes, sustaining more favourable water status in deep-rooted species from this habitat, further into the dry season. Conversely, species on the interdunes must be more desiccation tolerant and develop root systems with greater ability to penetrate conglomerated lateritic gravel layers in order to access water where and when it is available.

Cement-lateritic gravels mixtures: Microstructure and strength characteristics

Microstructure of cement-lateritic gravels mixes, containing up to 8 wt% cement, was investigated by means of X-ray diffraction, infrared spectrometry, differential thermal analysis, scanning electron microscopy and energy dispersive spectrometry. Also, strength characteristics of the mixtures were measured. The results show that cement admixtures resulted in the formation of 1.4 nm-tobermorite, ettringite, iron oxyhydroxide, portlandite and calcite. The increasing amount of tobermorite, due to the increase of the cement content, was attended with a noticeable reduction of particles segregation. In addition, its marked crystallization, observed for the high curing time (28 days), contributed to the improvement of the mechanical strength. As regards the application aspect, the results show that cement amended lateritic gravels are convenient for base course construction.

Recognizing, in lateritic cover, detritus shed from the Archaean Gossan Hill Cu–Zn–Au volcanic-hosted massive sulphide deposit,Western Australia

Cenozoic cover about the Golden Grove Gossan Hill volcanic-hosted massive sulphide (VHMS) deposit consists of lateritic colluvium, remnants of lateritic duricrust, associated lateritic soils and lateritic gravels. Clasts in these materials were investigated for features diagnostic of the mineralized system. The pebble-sized clasts showed: (a) preservation of tuffaceous and other volcanic textures with relict cassiterite (an associate of the ore zone sulphides); (b) relict micrometre-scale Cu, Zn, As or Pb sulphide inclusions in quartz; (c) micrometre-scale gold grains; (d) interpreted ferruginous pseudomorphs after base metal sulphides; and (e) elevated trace amounts of Cu, As, Zn or, more rarely, Sb or Bi in the core matrix of clasts, and in cutans on some of the clasts. All samples studied from an area extending laterally c. 600 m from the central strike of the VHMS ore system are positive, despite intensive weathering, to one or more of these diagnostic criteria. The background samples (2 km to 5 km from the ore system) are negative to all the criteria. A qualitative indication of proximity to the ore system can be derived by listing the occurrence of each of the diagnostic criteria within mineralized clasts in individual samples. A more specialized case of general models for interface sampling is proposed for exploring areas of thick transported cover in deeply weathered terrain. The model focuses on recognizing the described diagnostic criteria in basal cover from samples provided by drill core or cuttings.

Selection and Use of Locally Available Pavement Materials for Low-Volume Roads in Western Australia

In many countries locally available granular materials are an important source for the base course and subbase in the construction of flexible pavements. On low-volume roads, these include fine-grained materials such as well-graded silty and clayey sands (sand–clay), coarse and medium-grained materials such as natural gravels, and materials produced by ripping and rolling rock. Many materials have been used that do not meet conventional selection criteria but still give satisfactory performance. Their choice is based on locally developed selection criteria, non-standard testing, and attention to construction technique. Selection criteria are presented here for lateritic base course gravels (covering a wide range of climates), crushed lateritic caprock, limestone, and sand–clay. The criteria have been adapted from research in several countries and refined through experience and field research in Western Australia. Some techniques are suggested for low-volume roads to cope with large truck combinations on the basis of the experience of Western Australia, where some road trains have more than 20 axles. Nonstandard test methods include the Western Australia confined compression test accelerated triaxial test and chemical composition tests. Suggestions are made concerning the bitumen surfacing of some materials to improve seal adhesion. Adequate strength by itself is insufficient for the successful use of locally available materials, and attention to construction technique and workability is needed. Guidelines are given on issues such as winning (mining), curing, mixing, oversize and compaction, dry-back, and surface preparation before sealing.

Geotechnical, mechanical, chemical and mineralogical characterization of a lateritic gravels of Sapouy (Burkina Faso) used in road construction

Geotechnical and mechanical tests conducted on lateritic gravels of Burkina Faso showed that this material presents: fines (10.5 wt.%), plasticity index (10.5%), Californian Bearing Ratio (43%), compressive strength (1.26 MPa) and tensile strength (Brazilian test) of 0.09 MPa. The X-ray diffraction (XRD) and the chemical analysis revealed a quartz amount of 42 wt.%, 26 wt.% of kaolinite, 15 wt.% of goethite, 6 wt.% of rankinite and 3 wt.% of hematite. The results of geotechnical and mechanical tests combined to those of the XRD and the chemical analysis particularly the silica/sesquioxides ratio showed that the lateritic gravels is suitable for the sub-base course in road construction.

Deformability characteristics of brazilian laterites

This paper summarizes the resilient and permanent deformation characteristics of laterite gravels, determined by cyclic loading in triaxial tests of compacted specimens. A study of laterite pavements was carried out on eight paved road sections in the state of Mato Grosso. Also reported is the influence of fine sand admixture, specimen size and soaking in two laterite samples from Roraima and Rondonia in the North of Brazil. The experimental relationships of resilient moduli against applied stresses are interpreted empirically for models what may be incorporated in a structural analysis of full depth of laterite pavement.

Properties of Ironstone Lateritic Gravels in Relation to Gravel Road Pavement Construction

A laboratory investigation was conducted to determine properties of five samples of ‘oolitic ironstone’ lateritic gravel aggregates which are relevant to their use as road construction materials. Measured values of physico-chemical, physico-mechanical as well as index properties and compaction characteristics are similar to those of other lateritic, gravels occurring in West Africa which are used in road pavement applications. These lateritic clayey gravels have good workability as engineering construction materials and are rated fair to good as road aggregates in terms of probable in-situ behaviour based on water absorption values. Relationships between maximum dry unit weight and optimum moisture content as well as those between California bearing ratio and some derived soil parameters such as grading modulus, plasticity product or plasticity modulus can be described using a third-order polynomial function. The maximum dry unit weight has a bimodal frequency distribution and can be predicted from logarithm to base 10 of compaction energy with fairly good accuracy.

The Dynamic Cone Penetrometer in Compaction Verification on a Model Road Pavement

Abstract Compaction verification studies were conducted on a model site during a road construction project. Three compaction plants of different capacities were used on model pavements constructed using loose lifts of lateritic gravel measuring 120, 170, and 220-mm thick. After every two passes of the roller the dynamic cone penetrometer (DCP) test was conducted on the compacted layer alongside the sand replacement test to determine the level of compaction. A correlation was made between the sand replacement and the DCP tests resulting in a calibration equation of the general form log(LC) = κ - λ log(DPI) between the DCP penetration rate, DPI, and the level of compaction (LC) achieved as measured by the sand replacement method. κ and λ were found to be 2.184 and 0.337, respectively. The level of compaction values was back-calculated across the depth of the pavement using the DPIs. These values indicated that the sand replacement method gives the average degree of compaction over the depth tested whereas the DCP test allows the detection of low-level compaction pockets deeper within the layer.

Critical-state parameters for an unsaturated residual sandy clay

This paper presents experimental data from constant water content triaxial tests on a residual soil from Singapore, tested under unsaturated conditions with measurements of matric suctions. The data for critical-state conditions from these tests are presented within a framework previously proposed by the first author. The unsaturated critical state requires five parameters: Ma, Mb, Γab, λa and λb. At high degrees of saturation (in a non-aggregated condition) Ma = Mb = Ms (the saturated critical-state stress ratio). At lower degrees of saturation, the value of Mb drops considerably and reaches values near to zero at degrees of saturation below 60%. Conversely, the value of Ma appears to increase as the degree of saturation reduces. A similar pattern is observed for λa and λb. The functions relating the critical-state parameters to degree of saturation (or volumetric water content) can be expressed in normalised form by referencing them to the saturated state. The same normalised functions for Ma/Ms, Mb/Ms, λa/λs and λb/λs fit the experimental data for the residual sandy clay from Singapore and a lateritic gravel from Kenya previously tested. This suggests that the form of these functions may be common to a range of soil types.

Critical-state parameters for an unsaturated residual sandy clay

This paper presents experimental data from constant water content triaxial tests on a residual soil from Singapore, tested under unsaturated conditions with measurements of matric suctions. The data for critical-state conditions from these tests are presented within a framework previously proposed by the first author. The unsaturated critical state requires five parameters: Ma, Mb, Γab, λa and λb. At high degrees of saturation (in a non-aggregated condition) Ma = Mb = Ms (the saturated critical-state stress ratio). At lower degrees of saturation, the value of Mb drops considerably and reaches values near to zero at degrees of saturation below 60%. Conversely, the value of Ma appears to increase as the degree of saturation reduces. A similar pattern is observed for λa and λb. The functions relating the critical-state parameters to degree of saturation (or volumetric water content) can be expressed in normalised form by referencing them to the saturated state. The same normalised functions for Ma/Ms, Mb/Ms, λa/λs and λb/λs fit the experimental data for the residual sandy clay from Singapore and a lateritic gravel from Kenya previously tested. This suggests that the form of these functions may be common to a range of soil types.

Increased P application to lateritic soil in 1976 increased Colwell soil test P for P applied in 2000

In a field experiment, 6 amounts of superphosphate [0–800 kg phosphorus (P)/ha] were applied in July 2000 to an acidic lateritic ironstone gravel sandy soil treated 24 years previously (May 1976) with 6 amounts of superphosphate (0–599 kg P/ha). In October 2001, samples of the top 10 cm of soil were collected to measure the capacity of the soil to sorb P by the phosphate retention index (PRI) and P buffer capacity (PBC) methods, and to measure soil test P by the Colwell (sodium bicarbonate) procedure. The capacity of the soil to sorb P, as measured by both PRI and PBC, decreased with increased P application in 1976. For all amounts of P applied in 2000, Colwell soil test P increased with increased P application in 1976. We conclude that increasing amounts of P applied in 1976 decreased the capacity of the soil to sorb the subsequent application of P, thereby increasing soil test P values of soil treated with the subsequent P.

An equation of state for unsaturated soils

The enthalpy within a soil system under equilibrium conditions is investigated theoretically. Terzaghi's effective stress equation for a saturated soil is first examined and the approach extended to determine the enthalpy associated with the air, water, and solid phases, and the interactions between the phases, in an unsaturated soil. An equation of state is developed which links the stress state variables (p – ua) and (ua– uw) to the specific volume (v) and specific water volume (vw) and thus to the volumes of the phases. The equation is shown to provide a logical interpretation of the average volumetric "coupling" stress p'cwithin unsaturated soils which highlights the significance of the dual stress regime and bimodal structure. The new equation is compared with previously reported experimental data on kaolin and a lateritic gravel. The agreement is good and it provides insight into unsaturated soil strength and deformation behaviour and clarifies various previously identified anomalies.Key words: partial saturation, unsaturated soils, thermodynamics, effective stress, equation of state, critical state.

Geochemical behavior under tropical weathering of the Barama–Mazaruni greenstone belt at Omai gold mine, Guiana Shield

Mineralogical, petrographical, and geochemical studies of the weathering profile have been carried out at Omai Au mine, Guyana. The area is underlain by felsic to mafic volcanic and sedimentary rocks of the Barama-Mazaruni Supergroup, part of the Paleoproterozoic greenstone belts of the Guiana Shield. Tropical rainy climate has favoured extensive lateritization processes and formation of a deeply weathered regolith. The top of the weathering profile consists of lateritic gravel or is masked by the Pleistocene continental-deltaic Berbice Formation. Mineralogical composition of regolith consists mainly of kaolinite, goethite and quartz, and subordinately sericite, feldspar, hematite, pyrite, smectite, heavy minerals, and uncommon mineral phases (nacrite, ephesite, corrensite, guyanaite). A specific feature of the weathering profile at Omai is the preservation of fresh hydrothermal pyrite in the saprolith horizon. Chemical changes during the weathering processes depend on various physicochemical and structural parameters. Consequently, the depth should not be the principal criterion for comparison purposes of the geochemical behavior within the weathering profile, but rather an index that measures the degree of supergene alteration that has affected each analyzed sample, independently of the depth of sampling. Thus, the mineralogical index of alteration (MIA) can provide more accurate information about the behavior of major and trace elements in regolith as opposed to unweathered bedrock. It can also aid in establishing a quantitative relationship between intensity of weathering and mobility (leaching or accumulation) of each element in each analyzed sample. At Omai, some major and trace elements that are commonly considered as immobile (ex: TiO 2, Zr, etc.) during weathering could become mobile in several rock types and cannot be used to calculate the mass and volume balance. In addition, due to higher “immobile element” ratios, the weathered felsic volcanic rocks plotted in identification diagrams are shifted towards more mafic rock types and a negative adjustment of ∼20 units is necessary for correct classification. In contrast, these elements could aid in defining the material source in sedimentary rocks affected by weathering. Generally, the rare-earth element (REE) patterns of the bedrock are preserved in the saprolith horizon. This can represent a potentially useful tool for geochemical exploration in tropical terrains. Strong negative Ce and Tb anomalies are displayed by weathered pillowed andesites, which are explained by the influence of the water/rock ratio.

Engineering properties of common subgrade soils below pavement structures in Kenya

This paper reports findings of laboratory testing of common sub-grade soils in pavement structures in Kenya. The materials were collected from different parts of the country. The results are intended to form a database for use by practicing engineers and researchers in the field of pavement engineering. The investigated materials include the expansive black soils, silty clayey soils, sandy loamy clayey soils and lateritic gravels. In addition the properties of lime improved gravels are reported. For the fine-grained soils the plasticity index was found to be linearly proportional to the liquid limit. In all the investigated soils the optimum moisture content was found to be inversely proportional to the maximum dry density. The increase in the strength of lime improved materials was found to increase with lime content at a diminishing effect. (Journal of Civil Engineering, JKUAT: 2002 7: 1-12)

Laterite geochemistry for regional exploration surveys – a review, and sampling strategies

Numerous orientation studies and regional sampling campaigns by CSIRO and, more recently, the Cooperative Research Centre for Landscape Evolution and Mineral Exploration (CRC LEME), over the past 20 years, have demonstrated that residual lateritic gravels and duricrust are useful sampling media for regional, district and detailed exploration for gold, base metals and rare metals in the Yilgarn Craton. This paper focuses on regional exploration. A regional approach to geochemical sampling, using lateritic duricrust and lateritic gravels, based on regolith–landform models, is advocated. Sampling of areas of 10 000 km 2 or more, or integrating several data sets, is intended to identify geochemical trends and detect large geochemical haloes several hundred square kilometres in size, arising from concealed ore deposits or mineralized districts. In unexplored or underexplored regions, sampling at 3 km spacing on a triangular grid is appropriate at the reconnaissance stage. Results of this study show that, even if the sampling pattern is opened up to 9 km spacing, major trends can still be identified. In relict landform regimes, follow-up sampling should progressively close the spacing through 3 km, 1 km, 300 m, and less, in areas of interest. The effectiveness of a broad scale approach to laterite sampling is demonstrated by using As and Ni data for the southwestern part of Western Australia, where regional geochemical trends are apparent even at a 9 km sample spacing. For regional sampling in semi-arid terrains, use of a helicopter is effective because it provides the geologist with the optimum view of the landscape for regolith–landform control, as well as flexibility to choose an appropriate site for sampling. Whereas lateritic residuum (ferruginous gravels and duricrust) represents the preferred sample medium for regional surveys, other ferruginous materials are also suitable, particularly at the follow-up stage. Assigning regolith codes to all sample media and categorizing each sample are essential. The codes become part of the geochemical database and allow valid statistical evaluation of data for specific regolith materials. In all cases, analysis of a multi-element suite, including target and pathfinder elements, is recommended. Multi-element analysis allows interpretation that can take into account variable characteristics due to sample matrix, landform position, weathering environment and gross bedrock lithology. Multi-element geochemistry also provides the opportunity for multi-commodity exploration.