Lateritic Gravel Research Articles

Geomorphology and land development in the Maraca area of northern Roraima, Brazil.

The geomorphological materials and forms of the Maraca area of Roraima, Brazil are described, an their sgnificance for land development examined. Significant contrasts are noted in areas presently under rainforest and savanna vegetation. Lateritic gravels and extensive shetwash accumulations in savanna areas constrast with incipient or absent plinthite development, few gravels and limited evidence of colluvium under rainforest. Terrain is in general relatively highly-dissected. Slope profiles are characterised, particularly within the savanna zone, by a relatively steep lower concavity. These contrasts are sharply-demarcated by the present savanna/rainforest bondary, unexpectedly in view of the generally accepted hypothesis of repeated contraction an expansion of Amazonian rainforest throughout the Pleistocene. It is concluded that geomorphological conditions in the Maraca area are not favorable for land develoment.

Towards understanding the behaviour of naturally-occurring road construction materials

Naturally-occurring road construction materials generally contain a greater amount of fines, and the fines have a higher plasticity than traditional materials such as a crushed rock aggregates. This makes their behaviour more difficult to understand and predict since soil suction and fabric become important controlling factors. The concepts of suction and fabric are outlined, and their role in controlling the behaviour of road construction materials is illustrated by a fundamental laboratory study of a lateritic gravel and two calcrete gravels. These materials have successfully been used as road base construction materials in low-volume bituminous-surfaced roads in Kenya and Botswana. It is concluded that the presence of fines can be an advantage, since they allow significant suctions to develop and also reduce the permeability.

Studies on potassium-magnesium interaction in coconut (Cocos nucifera)

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

Mechanical properties of Thailand lateritic gravels : Ruenkrairergsa, T; Waiwudthikeart, W Proc Ninth Southeast Asian Geotechnical Conference, Bangkok, 7-11 December 1987V2, P9.11–9.22. Publ Bangkok: Southeast Asian Geotechnical Society, 1987

Mechanical properties of Thailand lateritic gravels : Ruenkrairergsa, T; Waiwudthikeart, W Proc Ninth Southeast Asian Geotechnical Conference, Bangkok, 7-11 December 1987V2, P9.11–9.22. Publ Bangkok: Southeast Asian Geotechnical Society, 1987

Road construction using lateritic gravel in Western Australia : Proc 2nd International Conference on Geomechanics in Tropical Soils, Singapore, 12–14 December 1988 V1, P369–384. Publ Rotterdam: A A Balkema, 1988

Western Australia has an extensive network of bitumen surfaced roads carrying low and medium volumes of traffic. Lateritic gravels have been widely used in the pavement of these roads. The performance of these gravels has generally been better than might be predicted on the basis of particle size distribution and plasticity tests alone. In this paper the characteristics of some lateritic materials which have been used are presented. Evidence of the increase of the strength (self stabilisation) of lateritic gravels in road pavements is also presented (A).

Geotechnical properties of a compacted lateritic gravel from Cachoeira Porteira Dam : Costa Filho, L M; de Campos, T M P; Ritter, E; Ribeiro, A C O Proc 2nd International Conference on Geomechanics in Tropical Soils, Singapore, 12–14 December 1988V1, P127–1134. Publ Rotterdam: A A Balkema, 1988

Geotechnical properties of a compacted lateritic gravel from Cachoeira Porteira Dam : Costa Filho, L M; de Campos, T M P; Ritter, E; Ribeiro, A C O Proc 2nd International Conference on Geomechanics in Tropical Soils, Singapore, 12–14 December 1988V1, P127–1134. Publ Rotterdam: A A Balkema, 1988

In-situ direct shear tests for lateritic gravels in Taiwan : Chu, B L; Hsu, T W; Lai, T C Proc 2nd International Conference on Geomechanics in Tropical Soils, Singapore, 12–14 December 1988V1, P119–125. Publ Rotterdam: A A Balkema, 1988

In-situ direct shear tests for lateritic gravels in Taiwan : Chu, B L; Hsu, T W; Lai, T C Proc 2nd International Conference on Geomechanics in Tropical Soils, Singapore, 12–14 December 1988V1, P119–125. Publ Rotterdam: A A Balkema, 1988

Use of geostatistical methods for the survey of lateritic gravels (In French)

Use of geostatistical methods for the survey of lateritic gravels (In French)

Stabilization of lateritic soils by extensible fibre reinforcement

Direct shear tests were run on samples of dry laterite sand and dry laterite gravel reinforced with different types of fibres. Both natural and synthetic fibres plus copper wires were tested. Test results showed that fibre reinforcement increases the peak strength and modifies the stress-deformation behaviour of laterites in a significant manner. It increases the peak shear strength and limits the amount of post peak reduction in shear resistance. Fibres increase significantly the angle of internal friction of the composite laterite. These shear strength increases were greatest for initial fibre orientations of 0° and 60° with respect to the shear surface while 120° orientation indicates the least for a laterite. Of all the various types of fibres used, inextensible earth reinforcements (high modulus metals) give the lower shear strengths relative to the extensible ones (i.e. low modulus geotextiles). The shear strength increases from coarse sand laterite through fine gravel laterite to medium gravel laterite and the shear strength is highest when the reinforcement is installed at 50% of the depth (mid point) of the sample (shear mould).

High phosphorus concentration in Trifolium balansae and Medicago polymorpha seed increases in herbage and seed yields in the field

Seed of Trifolium balansae and Medicago polymorpha, of the same size (mean ± s.d., T. balansae 0.8 ± 0.01 mglseed, M. polymorpha 3.6 ± 0.05 mg/seed) but with increasing phosphorus (P) concentration in the seed (T. balansae 0.34 to 0.63% P, M. polymorpha 0.40 to 0.64% P), were sown in field experiments as singlestrain, dense, ungrazed swards on 2 different soil types (a sand and a lateritic gravel sand) in south-western Australia. Different amounts of superphosphate were drilled with the seed (5-40 kg P/ha for the sand, and 15-100 kg P/ha for the lateritic gravel sand). Increasing P concentration in seed increased yields of dried herbage measured at each harvest, and also increased seed yields (measured for M. polymorpha only). Increasing P concentration in the seed increased the effectiveness of superphosphate drilled with the seed, so that less fertiliser was required to produce the same yield as P concentration in the seed increased.

Lateritised gravel bed: A new guide horizon for lateritic gold?

Geological studies made in the area of Mara Rosa in Goias State, Brazil, where small occurrences of gold are known in river placers, have revealed an interesting and extensive “lateritised gravel bed” overlying an inexpressive nodular lateritic crust horizon. The gravel has pebbles of vein quartz, quartzites and gneisses, which are interlocked and compacted by intense lateritisation with brown hydrous Fe-oxide (goethite). The underlying nodular crusts grade from deep brown to mottled, and occasionally have cavities. They possibly represent an interface between the bed rock and the gravel bed. The intensity of lateritisation is attributed to the existence of volcanogenic mafic sequences in the rock. The presence of pebbles of the same nature in the small placers with Au, suggest that Au has been dissolved and precipitated during the lateritisation process. Its abundance is mainly restricted to the lateritic gravel bed, which in turn has contributed Au to the stream placers. Thus, it is considered as a new guide horizon for lateritic Au.

A study on engineering properties of compacted lateritic gravels

Abstract This study aims to apply modified and parallel models to the study of the engineering properties of lateritic gravels. These two models; using the reduction in the maximum grain sizes, are based on the investigation of the in situ grain size distribution of lateritic gravels. The elastic moduli are also estimated by the differential scheme of composite materials in different proportions of laterite to gravels. The experimental results show that the modified model has a better prediction on both one‐dimensional compressibility and shear strength properties, whereas the parallel one is an effective model for the permeability characteristics. The elastic moduli predicted by the differential scheme are in good agreement with the experimental observations.

Construction control of low cost pavements on residual lateritic gravels over phyllite : Gidigasu, M D Proc 1st International Conference on Geomechanics in Tropical Lateritic and Saprolitic Soils, Brasilia, 11–14 February 1985V4, P261–278. Publ Sao Paulo: Brasilian Society for Soil Mechanics, 1985

Construction control of low cost pavements on residual lateritic gravels over phyllite : Gidigasu, M D Proc 1st International Conference on Geomechanics in Tropical Lateritic and Saprolitic Soils, Brasilia, 11–14 February 1985V4, P261–278. Publ Sao Paulo: Brasilian Society for Soil Mechanics, 1985

The geotechnical properties of lateritic and non-lateritic soils of southeastern Nigeria and their evaluation for road construction

The soils within the entire length of the Port Harcourt—Enugu expressway consist of (1) concretionary laterite gravels (2) non-lateritic tropical sandy/clayey soils which are gravelly in some places and (3) silty to fat clays formed from shales. The particle size distribution and the plasticity of the majority of the soils indicate that by standard acceptance specifications they are unsuitable for base materials. Field compaction results revealed that the relative compaction of 95–100% can be easily achieved in the field using 10–12 ton vibratory rollers. Although the pavement materials used for the expressway are inferior under conventional standards, mostly isolated rather than widespread pavement failures have so far occurred. Such failures are presumed to be more related to poor field compaction rather than the inferior quality of the construction materials. Where the troublesome weathered shale forms the subgrade, severe pavement failure usually occurs.

The physical and mechanical properties of laterite gravels from southeastern Nigeria relative to their engineering performance

Laterite gravels are used extensively as aggregates for highway construction, concrete making and fills in SE Nigeria. This paper presents results of laboratory investigations carried out to evaluate the physical and mechanical properties of these gravels. High mechanical strength, as measured by aggregate crushing (AC), and Los Angeles abrasion (LAA) values were found to be significant factors controlling the performance. Results indicate that significant correlations exist between these and specific gravity, water absorption and angularity of the gravels. No clear distinction in physical and mechanical properties could be found between the laterite gravels formed over sandstones and shales, indicating perhaps that effects of parent rock on the physical and mechanical nature of laterite gravels is of secondary importance. It is proposed that laterite gravels with AC and LAA values in the range of 30–40% and 34–45%, respectively and 10% fines value of between 8 and 4 tonnes be used only for medium and light trafficked roads. Those with AC and LAA values of less than 30% and 34%, respectively and 10% fines value of greater than 8 tonnes can be used for heavily trafficked roads, provided that acceptable gradation, plasticity limits (on the fines) and other construction specifications are met.

Survival of Phytophthora cinnamomi in Buried Eucalyptus Roots

AbstractColonization and survival of Phytophthora cinnamomi in roots was tested in 3 months old, axenically grown seedlings of Eucalyptus maculata (field resistant) and E. sieberi (susceptible). The roots were inoculated, then one week later were excised and buried in three non‐sterile, conducive soils; a lateritic gravel, an infertile duplex soil, a loamy sand as well as in a fertile, suppressive krasnozem. Pathogen viability, percentage root colonization and chlamydospore numbers were examined at matric potentials of −1/3, −5 and −10 bar after periods of 10, 100 and 200 days at 21°C.At 10 days, survival was 100% in the form of mycelium and the only significant difference was between the two Eucalyptus species. At 100 days survival was solely due to chlamydospores, but the pathogen was viable in all inoculated roots and at each matric potential. At 200 days soils had dried to less than −10 bars and the pathogen failed to survive. No significant differences were found between the two pathogen isolates but significant differences were obtained between the susceptible and field resistant Eucalyptus species.Pathogen viability, percentage root colonization and chlamydospore number were highly correlated with soil types and matric potential. These components declined with decreasing soil matric potential. The Krasnozem was only suppressive at relatively high soil matric potentials (−1/3 bar). At lower values (−5, −10 bar) survival of the pathogen, chlamydospore numbers and percentage colonization of the roots in the Krasnozem were comparable with that of the 3 conducive soils tested.Chlamydospores were present, but in low numbers in roots buried in the suppressive soil at −1/3 bar.

Geotechnical evaluation of residual gravels in pavement construction

The paper discusses the laboratory and pavement constructional evaluation of residual lateritic gravels over phyllite. Laboratory classification, compaction and bearing test results indicate that the natural materials are unsuitable by standard gravel acceptance specifications for road base construction. However, the bearing properties can be improved to meet base-material specifications through treatment with about 5% cement. Results of construction control studies also revealed that the laboratory compaction properties of both the raw and cement-stabilised gravels are easily reproduced in the field using fairly light, smooth-wheel rollers. This means that the complaints by contractors of difficulty in achieving design specifications using similar plants during construction is not justified. Notwithstanding the results of the studies reported herein, it is not possible at the moment to suggest any construction control specifications for these gravels until more data on their in-service performance in the roadway has been collected and analysed over a number of years.

The Acheulian industry of rock shelter IIIF-23 at Bhimbetka, central India - a preliminary study

It is over a century and a decade ago that the first Acheulian implement - a cleaver - was found by Robert Bruce Foote in a lateritic gravel pit at Pallavaram near Madras During the following three decades Acheulian finds were made from many sites in peninsular India, mainly by Foote himself but also by some other amateur archaeologists.

The Acheulian Industry of Rock Shelter IIIF-23 at Bhimbetka, Central India - A Preliminary Study1

It is over a century and a decade ago that the first Acheulian implement - a cleaver - was found by Robert Bruce Foote in a lateritic gravel pit at Pallavaram near Madras During the following three decades Acheulian finds were made from many sites in peninsular India, mainly by Foote himself but also by some other amateur archaeologists.

Throughflow as a mechanism responsible for excessive soil salinisation in non-irrigated, previously arable lands in the Western Australian wheatbelt: A field study

Summary A throughflow model of salt accumulation in the Western Australian wheatbelt is introduced and tested by field observations and data from several locations. Areas of excessive soil salinity (salt scalds) in the York-Mawson area are associated with specific soil/geomorphic conditions. Thirty-eight scalds and their catchments were examined: of these ten were mapped in detail and 100 soil profiles in 15 catenary sequences were examined and described. Valley-side slopes of the gently rolling landscape are low-angled, with the modal slopes of the 15 catenas ranging between 1.2 and 3.5 degrees. Interfluves are characterised by sand-textured soils that overlie lateritic duricrust or gravels at varying depths. Valley-sides above the salt scalds are predominantly erosional/transportational landsurface units with a sharp decrease of soil permeability at about plough depth. Further marked reductions in permeability and hence water infiltration occur at greater depth. The salt scalds vary considerably in size (0.02 to 64.4 ha) and nearly all are located in valley bottoms. The latter are usually occupied by well defined stream channels with ephemeral streamflow regimes, and all salt scalds occur on predominantly colluvial and/or alluvial aggradational soil materials. The layering of these materials produces one or more perched soil-water tables at relatively shallow depths below the scald surfaces, and impermeable hardpans occur below the aggradational soil materials. Four areas were examined in detail in the Dalwallinu area, where salt scalding is virtually continuous along the floors of the wide, flat valley bottoms. The results demonstrate that soluble salts move from the catchments to the valley bottoms by a combination of the following processes: (1) occasional overland flow; (2) throughflow, at varying depths below the surface, generally concentrated in percolines; and (3) streamflow down minor tributaries, this streamflow being fed by a combination of (1) and (2). The water supplied to the valley bottoms by these cascades is prevented from percolating to deeper levels by a thick impermeable hardpan which, in turn, also comprises the upper, confining material of the deeper-seated aquifer system in which groundwater is under pressure. Surface or near-surface waterlogging of the valley bottoms is essentially a shallow, perched water phenomenon. Evaporation during summer concentrates the salts in the valley bottom soil materials, leading to very high salinity levels. The water inputs responsible for the increased extent and duration of saturation of scalded soils since clearing appear to be derived primarily from an increase in throughflow and less from overland flow. A successful attempt at salt scald rehabilitation and recent drilling in other parts of the wheatbelt provide further evidence in support of the throughflow model of salt accumulation. An implication of these findings is that valley-side interception of throughflow should result in substantial rehabilitation of many salt scalds in the Western Australian wheatbelt.