High Plasticity Index Research Articles

Earth pressure at rest of Søvind Marl — a highly overconsolidated Eocene clay

The present study evaluated the earth pressure at rest, K0, of Søvind Marl, a highly overconsolidated Eocene clay. This clay exhibits extremely high plasticity indices of up to 300%, a highly fissured structure, and preconsolidation stresses up to 6800kPa. Continuous Loading Oedometer (CLO) tests at a constant rate of strain were performed in the Danish CLO apparatus. This apparatus applies test water at 200kPa and measures total horizontal stresses via pressure gauges placed in a stiff oedometer ring. Horizontal and vertical stresses were measured from in situ stresses to various stress levels to estimate continuous K0 development in the clay. Normally consolidated earth pressures at rest were 0.42 and 0.68 for Søvind Marl at two different ages. Overconsolidated K0, K0(oc), reached values as high as 6 to 8 in the in situ stress range. The correlation between K0(oc) and the overconsolidation ratio, OCR, reported by Meyerhof in 1976 was inconsistent with the K0(oc) development of Søvind Marl. However, the development of OCR in the laboratory under the previously applied test stresses, OCRlab, as an alternative to preconsolidation stresses, showed congruent results regardless of sample age when an α-value of 1.05 was used.

High resource-capture and -use efficiency, and effective antioxidant protection contribute to the invasiveness of Alnus formosana plants

To investigate the traits contributing to the invasiveness of Alnus formosana and the mechanisms underlying its invasiveness, we compared A. formosana with its native congener (Alnus cremastogyne) under three light treatments (13%, 56%, and 100%). The consistently higher plant height, total leaf area, light-saturated photosynthetic rate (Amax), light saturation point (LSP), light compensation point (LCP), respiration efficiency (RE), and non-photochemical quenching coefficient (NPQ) but lower root mass fraction (RMF) and specific leaf area (SLA) of the invader than of its native congener contributed to the higher RGR and total biomass of A. formosana across light regimes. The total biomass and RGR of the invader increased markedly with increased RMF, Amax, LSP, LCP, RE, stomatal conductance (Gs) and total leaf area. Furthermore, compared with the native species, the higher plasticity index in plant height, RMF, leaf mass fraction (LMF), SMF, SLA, Amax and dark respiration rate (Rd) within the range of total light contributed to the higher performance of the invader. In addition, the activities of antioxidant enzymes were higher in the invader compared to the native, contributing to its invasion success under high/low light via photoprotection. With a decrease in light level, superoxide dismutase (SOD) and catalase (CAT) activities increased significantly, whereas total carotenoid (Car) and total chlorophyll (Chl) decreased; ascorbate peroxidase (APX) and glutathione reductase (GR) activities remained unchanged. These responses may help the invader to spread and invade a wide range of habitats and form dense monocultures, displacing native plant species. The results suggest that both resource capture-related traits (morphological and photosynthetic) and adaptation-related traits (antioxidant protection) contribute to the competitive advantage of the invader.

Integrating geotechnical and geophysical techniques in assessing frequent building collapse in Akpugo, Nkanu West L.G.A., Enugu State, Nigeria

Over the years, the people of Akpugo community in Nkanu West L.G.A., Enugu State, South-East Nigeria have suffered from frequent building collapse without knowing the cause. This study integrates geotechnical and geophysical techniques to evaluate possible factors responsible for this anomaly. Areas with cracked and non-cracked buildings were studied to assess the geotechnical properties of the soils. Samples were taken at different locations and subjected to x-ray diffraction analysis, grain size analysis, specific gravity, Atterberg limits, permeability, compaction, and triaxial tests. Electrical resistivity method was also used to delineate the geo-electrical layers and to image the lateral variations of the subsurface. Results revealed that problematic zone (areas with cracked buildings) has lower permeability (4.018–7.016 × 10−7 m/s), lower angle of shearing resistance (10–14°), and medium to high plasticity index (25.1–38.33), while the non-problematic zone (areas without cracked buildings) has higher permeability (1.55–1.925 × 10−6 m/s), higher angle of shearing resistance (15–18°), and low plasticity index (18.1–19.4). The x-ray diffraction results of the problematic zone revealed a significant amount of smectite which has a very high swelling and shrinkage potential. The presence of substantial quantity of smectite in the soils of the problematic zone may be a strong factor in the structural problems. The electrical resistivity profiling delineated the boundary between the problematic zone and non-problematic zone and showed that the problematic zone has lower resistivity values (2–25 Ωm) while the non-problematic zone has higher resistivity values (20–170 Ωm).

High phenotypic variation in Morus alba L. along an altitudinal gradient in the Indian trans-Himalaya

Ten quantitative morphological characters were studied in 56 Morus alba L. trees representing three natural populations from the trans-Himalayan Ladakh region. The altitude of collection sites ranged from 2815 to 3177 m above the sea level (asl). Coefficient of variation (CV) showed high phenotypic variation in M. alba. Linear regression analysis revealed that leaf and fruit size decreases with an increase in altitude. High CV was observed for leaf length, leaf width, petiole length, leaf area, inter-nodal distance, number of nodes, bud length, fruit length, fruit width and fruit weight. Similarly, a high phenotypic plasticity index was observed for bud length, leaf length, leaf width, petiole length, leaf area, inter-nodal distance, number of nodes, fruit length, fruit width and fruit weight. For every 100 m increase in altitude, leaf length, leaf width and leaf area decreased by 1 cm, 0.8 cm and 16.6 cm2, respectively. Analysis of covariance showed a predominant altitudinal effect on the morphological characters in comparison to the population effect. A small change in the altitude caused significant change in the plant morphological characteristics. The present investigation represents to our knowledge the first study addressing phenotypic variation in mulberry along an altitudinal gradient.

Connection of surface roughness to hysteresis loss in spine implants

To investigate roughness effect in spine implant, a contact model is offered in this paper. The contact surfaces are modeled macroscopically as semi-spherical containing micro-scale roughness. A minimum mean surface separation between two rough surfaces is defined and related to contact force. This is accomplished through a statistical account of elastic and plastic micro contact at the surface roughness scale and the subsequent integration of micron level events to obtain macro level expectation of force as a function of mean surface separation. Contact force - minimum separation relation facilitates the derivation of hysteretic energy loss during a load-unload event. It is found that the surface high plasticity index yields more energy per cycle. Using the force-minimum surface separation in a dynamic interaction of the implant, approximate leads to the prediction of contact natural frequencies and damping ratio of the implant. These characteristics along with energy loss in implant affect implant's performance and durability.

Moisture Content-Based Longitudinal Cracking Prediction and Evaluation Model for Low-Volume Roads over Expansive Soils

AbstractThis paper summarizes a methodology for using moisture content (MC) together with soil index properties to study and predict the progression of longitudinal shrinkage cracking (LSC) along low-volume roads through finite-element analysis. Extensive laboratory tests were performed on soil samples retrieved from six representative clayey sites in Texas, including five high plasticity index (PI greater than 25) sites and one low-PI site. Field measurements of moisture content, suction, and crack development were carried out at five representative farm-to-market roads constructed over the high-PI clayey materials in southern and eastern regions of Texas for verification. Compared to the prevailing suction-based approach, the MC-based approach offers more flexibility in terms of incorporating different drying/wetting paths into numerical modeling by laboratory-based material constitutive models. The estimated critical moisture content thresholds and locations of LSC showed good agreement with the field ...

GEOMECHANICKÉ VLASTNOSTI NEOGENNÍCH JÍLŮ NA ÚZEMÍ MĚSTA BRNA

Neogene clays in Brno area are formations belonging to the Carpathian Foredeep Basin. They form common foundation soil in this strongly urbanized area. Due to their specific mechanical characteristics and a large spreaded area in Brno a detailed study of the geomechanical properties of Neogene clays has practical importance for engineering geology and geotechnics. There are compared analyzed data of physical and mechanical properties from 81 engineering-geological reports at the Brno agglomeration (452 samples of Neogene clays from 180 bores). There are presented the anomalous, distant values, arithmetic average and mode of the Neogene clays. On the basis of assumed data from various geological-engineering reports are defined typical characteristics of these soils. Neogene clays are fine-grained cohesive soils. In terms of ČSN EN ISO 14688-1, 14688-2 and UCSC classification these are classified mainly as clay or silt with high, very high or extremely high plasticity. It is usually with high plasticity index, stiff and very stiff consistence and with medium and high undrained shear strength. Low values of cohesion could be related to soil damaged by landslide movements. Due to its unfavourable properties, Neogene clays refer to partly suitable environment for shallow strip-foundations mainly due to the possibilities of volume changes in the subground. For all projection of foundations, there should be paid special attention to good engineering-geological investigation at real site.

PENGARUH PENAMBAHAN SERBUK BATA MERAH TERHADAP STABILITAS TANAH LEMPUNG SEBAGAI TANAH DASAR JALAN

Moch. Sholeh1 & Dandung Novianto21 & 2Fakultas Teknik Jurusan Teknik Sipil Politeknik Negeri MalangABSTRACTClay consists of grains - grains are very small (<0002 mm) and shows the nature - the natureof plasticity and cohesion. Cohesion indicates the fact that part - the part that is attached to eachother, while the plasticity is a trait that allows the form of the material was changed - edit withoutchanging the content or without returning to its original form, and without any cracks or brokens.And clay with high plasticity index has strong support low when used as a basic foundation of thehighway, so the need for soil improvement.From the above problems then this study aims to engineer clay with red brick powder in fourcomparisons. The first native land. Both the original soil mixed with red brick powder 5%. The thirdnative soil mixed with red brick powder 7.5%. The four original soil mixed with red brick powder10%. Each of these sought specific gravity, liquid limit, plastic limit and plasticity index on theoriginal soil, mixing 5%, 7.5% and 10%. From the analysis of data obtained the following conclusion:the original soil, the value amounting to 60.9 Liquid limit, plastic limit values of 42.8 and plasticityindex value of 18.1. The most optimal additional percentage is 7.5%. And Plasticity Index value at7.5% is 20,31.Key words : Red brick powder, Soil Stability, Subgrade and the Road

Relationship of Plasticity Index of Soil with Laboratory and Field Electrical Resistivity Values

Borehole sampling and laboratory soil characterizations provide accurate engineering properties, yet it is time-consuming and expensive. Geo-electrical survey is an attractive tool for delineating subsurface properties without soil disturbance. The primary objective of the current research work is to investigate the relationship between electrical resistivity and plasticity index of soil. The results from electrical resistivity tests (field and laboratory) and Atterburg limit tests were analyzed to understand the relationship between electrical resistivity and plasticity index of soil. Plasticity index have a significant correlation with field and laboratory electrical resistivity values for all soil samples. It was found that silty sand soil samples are characterized by higher plasticity index and lower resistivity values whereas sandy soil samples have lower plasticity index and higher resistivity values.

Ring shear tests on slip zone soils of three giant landslides in the Three Gorges Project area

Reactivation of large-scale landslides along the reservoir banks of the Three Gorges Project (TGP) is recognized as the most likely form of geohazards threatening safety and operation of the dam and the navigation. This study presents an investigation into the naturally drained shear properties of slip zone soils of such landslides. Twenty-seven specimens of slip zone soils of three giant landslides are tested at three shearing rates (0.1, 1 and 10mm/s) by means of a large ring shear apparatus accommodating abundant coarse particles in the specimens. It is observed that a) soils with higher plasticity index or liquid limit tend to have lower residual shear strength; this influence of the Atterberg limits on the residual shear strength weakens as the shearing rate increases; b) even small variations in the particle size distribution (PSD) cause notable differences in shear properties. The PSD parameters, such as the coefficient of curvature, sand content, ratio of gravel content to the sum of remaining contents, and ratio of coarse fraction to fine fraction, have close correlations with the residual strength; and c) the residual strength is clearly affected positively by particle symmetry (quantified by elongation) and negatively by surface smoothness (quantified by convexity).

PENGARUH PENAMBAHAN SERBUK BATA MERAH TERHADAP STABILITAS TANAH LEMPUNG SEBAGAI TANAH DASAR JALAN

Dosen Teknik Sipil Politeknik Negeri Malang Clay consists of grains - grains are very small (<0002 mm) and shows the nature - the natureof plasticity and cohesion. Cohesion indicates the fact that part - the part that is attached to eachother, while the plasticity is a trait that allows the form of the material was changed - edit withoutchanging the content or without returning to its original form, and without any cracks or brokens.And clay with high plasticity index has strong support low when used as a basic foundation of thehighway, so the need for soil improvement.From the above problems then this study aims to engineer clay with red brick powder in fourcomparisons. The first native land. Both the original soil mixed with red brick powder 5%. Thethird native soil mixed with red brick powder 7.5%. The four original soil mixed with red brickpowder 10%. Each of these sought specific gravity, liquid limit, plastic limit and plasticity index onthe original soil, mixing 5%, 7.5% and 10%. From the analysis of data obtained the followingconclusion: the original soil, the value amounting to 60.9 Liquid limit, plastic limit values of 42.8and plasticity index value of 18.1. The most optimal additional percentage is 7.5%. And PlasticityIndex value at 7.5% is 20,31.Key words : Red brick powder, Soil Stability, Subgrade and the Road.

长白山林线树种岳桦幼树叶功能型性状随海拔梯度的变化

通过研究沿不同海拔岳桦幼树叶功能型性状,揭示其对环境的响应机制。结果表明:①随海拔升高,岳桦叶面积(LA)逐渐降低,比叶重(LMA)增加,但LMA较高的可塑性指数表明其适应更依赖叶片的薄厚变化;②岳桦叶绿素含量随海拔升高而显著下降,但类胡萝卜素Car和Car/Chl显著升高,Chlb和Car/Chl表现出较高的可塑性指数,更倾向于吸收蓝紫光和保护光合器官;③岳桦叶氮含量(N_area和N_mass)在海拔1800-1900m间最低,在低海拔和高海拔均表现较高,但Chl/N_mass却随海拔升高而显著增加,N_mass 比N_area具有较高的可塑性指数,对光能的吸收更依赖N_mass对Chl的贡献,高海拔主要将更多的氮投资于光合器官的保护(1900m以上),低海拔则更倾向于光合生产(1800m以下);④随海拔升高,MDA增加,但随之抗氧化物质DS、Pro和APX活性增加,负责对活性氧的抵御和清除,但APX活性最大的可塑性指数表明活性氧的清除更依赖于酶促系统,但在海拔1900m以上,APX活性差异不显著,生理抗性逐渐下降,限制岳桦继续向高海拔生长;⑤抗氧化物质可塑性指数最高,叶绿素和叶形态次之,叶氮最低,表明随海拔升高,岳桦林以保护自身的生存为最主要的适应策略机制,然后以增加吸收光能的Chlb及LMA指标为主要生长策略。;This study focuses on the leaf functional traits of <em>Betula ermanii</em> saplings along the altitude gradient of Changbai Mountain, a Natural Nature Reserve of China, and tries to reveal its environmental response mechanism. The main results are as follows: (1)As altitude increased, the leaf area (LA) of <em>B.ermanii</em> dropped significantly, while leaf dry mass per area (LMA) increased. But it also indicated that it more resorted to leaf thickness changing in the procedure of adaption due to a higher LMA plasticity index. (2)The content of Chlorophyll (Chla, Chlb andChla+b) of <em>B.ermanii</em> reduced as altitude climbing up, while carotenoids (Car) and the ratio of Car to Chla+b(Car/Chl) was just the opposite. A higher Chlb and Car/Chl plasticity index of <em>B.ermanii</em> suggested that it tended to assimilate ultraviolet-blue light and protect photosynthetic organs. (3)The content of Leaf nitrogen (N_area and N_mass) of <em>B.ermanii</em> was the least at altitude 1800-1900m, but was higher at the low and high altitude. However Chl/N_mass increased with height ascending. And absorption of light energy more relied on the contribution of nitrogen to Chl for a higher<em> N</em>_mass plasticity value in order to allocate more nitrogen into chemical defense in higher latitude(1900m above), and photosynthesis in lower latitude(1800m below). (4)With altitude increased, when the growth of<em> B.ermanii</em> was limited by the peroxide (such as MDA), antioxidant DS, Pro and APX activity adaptively increased, which was responsible for resisting and clearing reactive oxygen. The highest APX plasticity index of <em>B.ermanii</em> showed it more relied on enzymatic system to accomplish this process, But APX activity had no significant difference above 1900m, which meant that the physiological resistance decreased gradually, and a higher elevation may limit its distribution.(5)With elevation climbed up, <em>B. ermanii</em> took its own survival as the main policy mechanism due to the highest average plasticity index, and then took Chlb and LMA to absorb light energy as the main growth strategy with a higher plasticity index.

Physiological and morphological leaf trait variations in two Apennine plant species in response to different altitudes

Morphological and physiological traits of Crepis pygmaea L. subsp. pygmaea and Isatis apennina Ten. ex Grande growing at different altitudes in the Gran Sasso Massif (Abruzzo, Italy) were analyzed. The two populations of C. pygmaea and I. apennina growing at the highest altitude (C p2 and I p2 at 2,310 m a.s.l. and 2,350 m a.s.l., respectively) had a lower leaf mass area (LMA) than the two populations growing at the lowest altitude (C p1 and I p1 at 2,250 m a.s.l. and 2,310 m a.s.l., respectively). Leaf tissue density (LTD) had the same LMA trend, decreasing 23 and 10% in C. pygmaea and I. apennina, respectively, from the highest to the lowest altitude. C. pygmaea and I. apennina had the highest photosynthetic rates (P N) in July decreasing on an average 17 and 30%, respectively, in August and 50 and 38%, respectively, in September. Leaf respiration (R) in I p1 and I p2 had the same trend as C p1 and C p2, showing the highest rates in September. Global warming could drive C. pygmaea and I. apennina toward higher altitudes in the Gran Sasso Massif. Nevertheless, C. pygmaea with the higher plasticity index (PI) both at physiological and at morphological levels (0.50 and 0.35, respectively) might have a competitive advantage over I. apennina over the long term.

A Geotechnical Investigation on the Structural Failures of Building Projects in Parts of Awka, Southeastern Nigeria

Twelve samples of shale from different locations within the Imo Shale Formation in the Awka area (southeastern Nigeria) have been assessed to evaluate the impact of the shale formation on some geotechnical problems experienced by constructed projects in the area. Results indicate that shale samples from the formation have Atterberg limits that might be considered moderate to high; while liquid limit (LL) ranged from 32 - 78, the plasticity index (PI) ranged from 11 - 32. These relatively high LL and PI suggest presence of expansive clays, some swelling of the shale on moisture influx and high compressibility. Natural moisture content (with mean value of 17%) was also significantly high. Despite indicating fair stability as fills (Maximum dry density and soaked California bearing ratio have mean values of 1.85 mg/m 3 and 42%, respectively), the formation is likely to have low shear strength, as suggested by its low values of strength parameters (mean value of angle of internal friction is 22°, while mean cohesion is 21 kN/m 3 ). Geotechnical behaviours of the Imo Shale also give indications that the shale failed some relevant material specifications for general engineering purposes and, thus, was significantly responsible for structural failures and foundation problems of buildings that are prevalent in some parts of Awka area.

A characterisation of the physical properties of soil and the implications for landslide occurrence on the slopes of Mount Elgon, Eastern Uganda

Soil properties of major landslides that occurred recently on the mid-altitude slopes of Mount Elgon, eastern Uganda were analysed. A mudflow, located at the Kitati protected forest site, and two deep debris flows on the Nametsi and Buwabwala deforested steep slopes (36°–58°) were surveyed. In order to test the hypothesis that ‘soils at the landslide sites are particularly ‘problem soils’ and thus prone to landslides’, the following analyses were undertaken: particle size distribution, Atterberg limits, shear strength and factor of safety (Fs). Soils at the Kitati and Buwabwala sites exhibited expansive potential, owing to clay contents well above 20%. A clay content exceeding 32% was identified at the Nametsi debris flow site implying an extremely high expansive potential of the soil. High liquid limits (LLs) at Kitati (59%) and Buwabwala (53%) meant that the soils qualified as vertisols susceptible to landslides. High plasticity indices (PIs) (averaging 33%) also confirmed the vertic nature of soils at the Nametsi debris flow site. Whereas the value of Fs 1). Despite this finding, the stable sites could be described as only conditionally stable because of the interplay of various physical, pedological and anthropogenic factors. The results point to the fact that soils at the landslide sites are inherently ‘problem soils’ where slope failure can occur even without human intervention. Therefore, the hypothesis that soils at three landslide sites are inherently ‘problem soils’ and prone to landslides, is accepted.

Measurements of the Static Friction Coefficient Between Tin Surfaces and Comparison to a Theoretical Model

A new experimental apparatus is used to measure the static friction between tin surfaces under various loads. After the data is collected it is then compared to an existing theoretical model. The experiment uses the classical physics technique of increasing the incline of a plane and block until the block slides. The angle at the initiation of sliding is used to find the static friction coefficient. The experiment utilizes an automated apparatus to minimize human error. The finite element based statistical rough surface contact model for static friction under full stick by Li, Etsion, and Talke (2010, “Contact Area and Static Friction of Rough Surfaces with High Plasticity Index,” ASME Journal of Tribology, 132(3), p. 031401) is used to make predictions of the friction coefficient using surface profile data from the experiment. Comparison of the computational and experimental methods shows similar qualitative trends, and even some quantitative agreement. After adjusting the results for the possible effect of the native tin oxide film, the theoretical and experimental results can be brought into reasonable qualitative and quantitative agreement.

Characteristics of landslides induced by a debris flow at different geology with emphasis on clay mineralogy in South Korea

Landslides induced by debris flow have been discussed in relation to the geotechnical properties of soil developed on bedrock, together with an emphasis on the importance of mineralogy comprising precursor soils. Three areas composed of different types of geology were compared to relate landslide with soil compositions: Precambrian gneiss (Jangheung area), Jurassic granite (Sangju area), and Tertiary sedimentary rocks composed of shale and mudstone (Pohang area) in Korea. X-ray diffraction for mineral identification and quantitative analysis, Scanning Electron Microscope for observation of microtexture, and laser size analysis for very fine particles ranging from micrometer were performed, with conventional measurements of particle size, porosity, density, permeability, and consistency for the soils. Soils at landslide sites containing a large amount of finer particles have higher uniformity and gradation coefficients, but lower consistency than those at non-landslide sites. Landslide areas are characterized by higher porosity and lower density. Soil from the gneiss area shows a high plasticity index while that of mudstone has high water content. Main clay minerals contained in soils of the sites where landslides took place are illite, chlorite, kaolinite, and montmorillonite. Mineralogical information on the constituents and microtexture of soils aids in better understanding the causes and patterns of landslide, together with mechanical properties of soils.

Petrological, Physico-Chemical and Mechanical Characterization of the Topomorphic Vertisols from the Sudano-Sahelian Region of North Cameroon

In Cameroon, topomorphic vertisols are widespread in the Sudano-sahelian zone above latitude 9oN. With a depth of about 2 to 2.5 m above the water table, these soils show four main horizons from bottom to top: a dark grey horizon with hydromorphic patches (B3g), dark grey horizon (B21), dark grey horizon with slickensides (B1) and a surficial grey humiferous horizon (A1) with desiccation cracks. Also, they show a heavy clayey texture, very massive structure, high bulk density, very low porosity and a high compacity. The microfabric of the soils is marked by abundant plasmas, isotic at the surface but birefringent at depth, with numerous stress cutans. The microscopic analysis of heavy minerals reveals the presence of magmatic and metamorphic minerals from the upper part of the watershed. Quartz grains are mainly angular to sub-angular revealing short fluvial transport distance. The vertisols are thus formed from recent alluvial deposits from weathering, erosion and deposition of rocks from upper parts of the watershed. Physico-chemically, the studied soils are characterized by high cation exchange capacity (26-42 meq/100g), high sum of bases (74.30-94.23 meq/100g), high base saturation, low organic carbon and a very high C/N ratio. Geochemically, Si and Al are the dominant elements, characterised by a Si/Al ratio range of 2.27 and 2.94. According to this rate, 2/1 clay minerals, namely smectite, are predominant and their presence confirms the shrink-swell behaviour of the soils. Total base concentrations are high and could be related to the contrasted climate and the low landscape position. Mechanical analyses revealed very high liquid limits (36-46%), low plastic limits (10-17%), high plasticity indices and high shrinkage limits that permit to classify those soils as medium to high plasticity inorganic clays. Those soils could be potentially useful in many domains like the chemical industry, pharmaceutics, petroleum industry, agronomy or environmental protection.

Geotechnical and environmental problems related to shales in the Abakaliki area, Southeastern Nigeria

Six (6) samples of shale and five (5) water samples from hand-dug wells and boreholes, from different locations within the Abakaliki shale formation, have been assessed to evaluate the impact of the shale formation to the geotechnical and hydrogeo-environmental problems prevalent in the Abakaliki area (Southeastern Nigeria). Results indicated that the shale samples have Atterberg limits that might be considered moderate to high; while Liquid Limit (LL) ranged from 49 – 54, the Plasticity Index (PI) ranged from 34 – 38. These relatively high LL and PI suggested presence of expansive clays, some swelling of the shale on moisture influx and high compressibility. Natural moisture content (with mean value of 20%) was also significantly high. Hydrochemical analyses, on the other hand, revealed that the water samples had comparatively high content of ions and dissolved particles; Ca2+ ranged from 8.0 – 134.0 mg/l, Mg2+ ranged from 0.2 – 3.3 mg/l, HCO-3ranged from 21.8 – 1176.1 mg/l and total dissolved solids ranged 56.9 – 1415.0 mg/l. Dissolution of soluble minerals (predominantly calcite and other rock salts) contained in the shale might likely be responsible for the release of these particles. Geotechnical behaviours of the shale and hydrogeochemical characteristics of water samples from the shale formation, thus, provided insights into the probable causes of seasonal waterlogging, consistent poor groundwater quantity and quality, structural and foundation problems that are prevalent in the Abakaliki area. Key words: Abakaliki shale, dissolution, environmental problems, geotechnical analysis, groundwater quality, structural failure.

Development and Implementation of Ultrathin Concrete Road Technology for Suburban Streets in South Africa

There is a significant need in South Africa for the upgrading of suburban streets with a solution that performs well, is cost-effective, and requires minimal maintenance. There is also a need for job creation in road construction, using local labor when possible. The ultrathin reinforced concrete pavement (UTRCP) technology, one such solution, was developed by the Council for Scientific and Industrial Research in South Africa and has been implemented in a number of projects. The technology was developed for suburban streets and roads carrying fewer than 2,500 vehicles/day and is constructed with labor using light plant. UTRCP consists of a lightly reinforced, 50-mm-thick, 30-MPa concrete layer that is generally constructed on shaped and compacted in situ material; modification may be required if the in situ material has a high plasticity index. Experimental work was conducted by testing trial sections of UTRCP supported by various subbase layers. This included static testing, rolling wheel load testing with a heavy vehicle simulator, and evaluation of the performance of trial sections under normal traffic. The results of the experimental work and the subsequent proposed structural designs used in implementation projects are described. The technology has been implemented in various projects in suburban townships in South Africa in the Gauteng Province. The practical lessons learned from these projects are described. Lastly, criteria for the subbase design of pavement structures containing the UTRCP layer are proposed, and further work is suggested.