Highway Engineer 

Abstract: Artificially prepared, lime-treated mixtures of sand-clay were studied in the laboratory. The experimental programme was arranged with two types of clay mineral (kaolinite and montmorillonite), three levels of clay content (10,30 and 50 per cent), four levels of lime content for the kaolinite soils (0,2,4,8 per cent) and five levels for the montmorillonite soils (0,2,4,8,12 per cent). Two periods of curing (seven and 28 days) were employed. Firstly the maximum dry density optimum moisture content relationships for the 27 different mixtures were determined using one compactive effort. Test specimens for these mixtures were then fabricated at their corresponding optimum compaction conditions. The effect of the type and content of the clay fraction on the specimens' compressive strength, Q, cohesion, C, angle of internal friction, phi, and elastic modulus, e, was determined. The results showed that regardless of the clay content in the soil, increases in the values of q, C, and e due to lime-treatment are significantly higher for the montmorillonite than for the kaolinite specimens. Generally the most significant increase in any of these parameters occurs at two per cent lime for the kaolinite specimens, while for the montmorillonite specimens these strength parameters tend to develop progressively with lime content up to about eight per cent or even beyond. The pattern of increase in the angle of internal friction due to lime treatment is comparable for the two types of soil. The most significant increase occurs mostly up to two per cent lime where it reaches about 10 degrees. Good correlations between unconfined compressive strength and both cohesion and elastic modulus were observed. Linear regression equations for the prediction of and e for lime-treated soils from known values of g were accordingly established. (Author/TRRL)

Abstract: The paper describes two computer programs which have been developed to optimise the total cost of constructing and using a road. The one depends upon the method of dynamic programming while the second is based upon the method of the variational calculus. An example of their use is reported. /TRRL/

Abstract: The use of geomorphological mapping techniques in highway engineering, and an example of its application in the investigation for the taff vale trunk road, south wales, is discussed. Geomorphological studies used in the initial design stage, can identify geotechnical and ground-water problem areas, so that alterations of the route alignment to avoid such areas can be considered and a more realistic budget estimate made for earthworks. If geomorphological mapping is carried out by experienced personnel, it is quick, inexpensive and enables the subsequent site investigation to be designed more efficiently with a resultant saving in cost. (A). /TRRL/

Abstract: This section describes the geotechnical data that can lead to a reasonable prediction of the amount of settlement resulting from highway engineering load-bearing components. The roadway itself is a component; however, even more concentrated loads can result from the supports for overpass bridges, and settlement for ancillary components such as culverts running underneath roadways cannot be ignored. In this section, geotechnical data gathering consists of several steps: (1) selection and collection of appropriate soil samples, (2) classification of samples based on particle size and moisture retention, (3) determination of key properties needed to determine the settlement, (4) compaction testing and results, and (5) calculation of the expected settlement and the rate of settlement. It is strongly argued that postconstruction settlement remediation is costlier than a carefully designed geotechnical sampling and analysis preconstruction investigation and site preparation.