Geotechnics

The study investigates the suitability of using waste glass (WG) as admixture to cement stabilized black cotton soil (BCS) for roads, fills and embankment. The soil was classified as A-7-5 and CH according to the American Association of State Highway and Transport Officials (AASHTO) and the Unified Soil Classification System (USCS) Classifications. Chemical analysis revealed that WG is rich in main oxides such as Silicon Oxide (69.2), Aluminium Oxide (2.29), Iron Oxide (1.57), Calcium Oxide (15.1) and Sodium Oxide (8.75). The soil was stabilized with 0, 2, 4, 6 and 8% cement and 0, 5 10, 15 and 20% WG by weight of the dry soil. Laboratory tests were carried out using the Standard Proctor (SP) compactive efforts, California Bearing Ratio (CBR), Unconfined Compressive Strength (UCS), and compaction characteristics tests to evaluate the effectiveness of WG on Ordinary Portland cement (OPC) stabilized BCS. The results obtained showed a decrease in the plasticity index (PI), liquid limit (LL), plastic limit (PL) and increase Maximum Dry Density (MDD) with increase in WG content in all cement proportions used and as compared to the values obtained for the natural soil. The peak 7 days UCS values of 1152kN/m 2 was obtained at 8% OPC and 20% WG. Similarly, highest CBR value of 53.8% was obtained at an optimum blend of 8% OPC/20%WG. The results indicate that there is a potential in the use of WG as admixture to strengthen Black cotton soils.

This dissertation project attempts a comprehensive review of the deterioration factors that are deemed responsible for the highway embankment failures across the United Kingdom. The aim was set to chalk out a possible deterioration model for highway embankments which become deteriorated particularly due to flooding. The proposed model is based on several external and internal factors and variables, which are responsible for the possible deterioration of these crucial highway structures. Several deterioration models were being developed for pavements, bridges and roads. However currently there is no such model existing in the U.K to address the issue of deterioration of the highway embankments and slopes.
Some of the highway embankments of UK are built long ago and got deteriorated with passage of time. One of the important factors of this deterioration is flooding across the UK, which occurs especially due to the current weather changing patterns and torrential rains in summers. This causes rise in water levels, which may reach upto the height of embankment and subsequently causing deterioration to the highway embankment once dropped down. These embankments are mostly constructed on soft soils such as clay, which is susceptible to weathering, erosion, scour and wash-out during flooding.
The seasonal variation in flood water levels together with the constructed embankments on soft soils (clay) has resulted in mainly two types of failures in the U.K. These failures are categorized in bearing capacity failures and slope stability failures, resulting in foundation settlement and slope failures respectively. Several design methods are available to be adopted to prevent these failures, which often take into account the prevailing geological conditions of the site. A framework for deterioration process has been produced, which can be adopted according to the geology, environment and site locations.
A deterioration model based on rapid drawdown has been presented, which could be used by the highway agency in dealing with deteriorated highway embankments across the U.K. The factor of safety was discussed in detail used during the stability analyses phases of deterioration, additionally the softening of soils and rocks due to weathering was also taken into consideration. However following the model during the design stage of highways embankments, and addressing the stress deformations, weathering effects and factor of safety selection for the drawdown conditions, a more robust and stable design can be derived.
The maintenance and remediation of these embankments is of crucial importance, therefore a lost in time and cost may be saved for any defects found during the inspection of embankments at site, if dealt in time. The proposed model will give an insight into the issues of deteriorated embankments caused due to flooding and a possible remediation options. This may help in future planning for designing such structures on highways and can help reduce the cost incurred on maintenance and remediation.
A case study site for the deteriorated highway embankments across the U.K was reviewed, and the proposed model was validated based on the failure factors and environments of failures due to flooding. The constituents of proposed model have been correlated with the deterioration factors and events from the site reports, which are tabulated to judge the deterioration occurrences and hence consequently used in validating of the model.