TL;DR: In this paper, the use of cement as a stabilising agent was eliminated by mixing the naturally occurring gravels with varying quantities of crushed stone, crusher waste and dune sand, the latter to combat a high plasticity index.
Abstract: Triaxial testing of naturally occurring, slightly silty, medium-graded, coarse sand, derived from completely weathered granite (with some gypsum), compacted to 95 % of Mod AASHTO density generated unload / reload Young's modulus E-values of about 300 MPa at a representative confining stress of 90 kPa. This is some 80 % higher than what would usually be expected for this type of G5 material. Mohr-Coulomb shear strength parameters of c = 15,9 kPa and φ = 51,4o were obtained from the high-quality triaxial tests. Taking into account the variability of the materials, it is suggested that these be downgraded to c = 12,7 kPa and φ = 48,8o for use as design parameters. It is common practice to stabilise natural gravel materials to generate weakly cemented sub-base layers. However, the presence of naturally occurring gypsum within the in-situ granite generated concern as negative effects were observed on elements of past construction. The use of cement as a stabilising agent was eliminated by generating a nearly equally strong layer by mixing the naturally occurring gravels with varying quantities of crushed stone, crusher waste and dune sand, the latter to combat a high plasticity index. The best result was obtained by using a blend of 50 % natural gravel, 30 % crusher waste and 20 % dune sand. These blended materials, generated unload / reload Young's modulus E-values of some 560 MPa at 95 % Mod AASHTO compaction and a confining stress of 247 kPa. This E-value is very similar to what is thought would be attained for a cracked and hydrated cement-stabilised layer but without the disruptive effects of a lowered confining stress that would be the case when a stabilised layer shrunk and cracked on hydration of the cement stabilising agent.
TL;DR: In this article, a modified Mohr-Coulomb criterion for triaxial compression of soils is presented, which takes into account the axial strain of the sample material and the angle of internal friction of the material.
Abstract: A modified Mohr – Coulomb criterion is presented. This criterion, in addition to adhesion and the angle of internal friction, contains the third parameter of the material (d). Depending on the value of this parameter (d), the modified criterion can take the form of the original Mohr – Coulomb criterion (with d = 0.5) or the original Treska criterion (with d = 0). For all other values of the parameter (d), varying in the range of 0
01 Aug 2015
TL;DR: In this article, the authors evaluated the rut propensity of asphalt surfaces using Model Mobile Load Simulator (MMLS) tests and Constant Height Repeated Simple Shear Tests (CH-RSSTs).
Abstract: Asphalt production and paving in remote regions of Africa can be problematic in terms of logistics, material sourcing and production quality. Airport planning also tend to project high growth rates of aircraft movements which don’t always realize. A further complication is the tendency to use roads design and specifications on airports in such remote regions. A recent airport runway upgrade and asphalt overlay on the west coast of Africa taxed these realities. Dynamic creep modulus was specified as main criteria for rut resistance. The dynamic creep modulus gave variable results partly due to the proven inherent unreliability aspects of the test procedure. Therefore the asphalt had to be evaluated against fit-for-purpose criteria. Actual asphalt thicknesses were variable and in some instances significantly thicker than the specified 50mm. The thicker asphalt, in particular, raised questions about perceived rut propensity. The air traffic movements at this remote airport are low and in future will also be low, which potentially lowers the potential impact of excessive rut development. A number of additional tests including the Light Weight Falling Weight Deflectometer (LFWD) and Falling Weight Deflectometer (FWD) were done to determine and confirm the overall structural pavement strength. Asphalt rut propensity was evaluated with Model Mobile Load Simulator (MMLS) tests. MMLS tests were done on site and additional MMLS tests were done in South Africa on cores from site. Constant Height Repeated Simple Shear Tests (CH-RSSTs) were also done. The latter test allowed comparison of data obtained from Heavy Vehicle Simulator (HVS) tests and associated CH-RSST data base developed in California, USA. All these tests to determine rut potential have different quirks and positives. A comparative triangulation approach had to be followed to arrive at a weighted best evaluation of this asphalt surfacing. The net result was positive.