Civil Engineering May 2021 | Vol 29 No 4

Civil Engineering May 2021 31 and elasto-hardening-softening for un- saturated soil conditions. In the current form of the study, measurement of component behaviour is still laboratory based, and data processing and analytics, together with models for predictive behaviour, are manual. Moving forward, planned improvements include the installation of complimentary field sensors and automation of data processing and analytics using the Internet of Things (IoT) and machine learning to predict future behaviour. HIGH-TECH INSTRUMENTATION FOR CLIMATE CHANGE The scientific consensus is that climate change is a current problem requiring intervention. Changing climatic condi- tions will significantly influence the soil layers at the surface of the soil profile which remain in an unsaturated state most of the time. Much of our transporta- tion infrastructure is constructed on or within this unsaturated layer. The formation layers of conventional railway tracks are no exception. This means that railway formations will be significantly affected by the extreme weather condi- tions predicted by climatologists. These extremes include heavier rainfall and longer drought periods. We need to formulate our models using unsaturated soil mechanics in order to understand the behaviour of in-service railway formations and to determine the impact that these predicted climate changes will have on our railway infrastructure. Unsaturated soil mechanics relies heavily on the determination of a soil function called the soil water retention curve (SWRC). The SWRC is the relation- ship between the suction in the soil and the soil’s water content. The effective stress state which governs all soil behaviour can be directly linked to the SWRC. Measurement of the SWRC has typi- cally been a time consuming and costly exercise reserved solely for the most patient of researchers. However, recent developments in low-cost suction sensors, coupled with wireless apparatuses, have enabled the rapid, cost effective, and accurate determination of the SWRC. A new apparatus for the determination of the SWRC was developed at UP incorporating low cost tensiometers, wireless data loggers, and laser displace- ment transducers (Figure 2). This new apparatus allows for automated testing whereby the drying path can be stopped at a predetermined level of suction and a wetting path started without the pres- ence of an operator. This is important as tensiometers can cavitate if the suction becomes too high, which regularly occurs if not continuously monitored. The sample mass must be monitored to the nearest 0.01 g during SWRC testing to accurately trace the soil moisture be- haviour. This means that no cables should be allowed to run from sensors located on the mass balance to logging equipment located off the mass balance. This was completely mitigated in the current setup Pressure controllers Full scale: 2 000 kPa Volume: 200 cm 3 Pressure transducers Measure pore-pressures De-airing system Removes air in testing water Pneumatic controller Introduces air and matric suction up to 1 000 kPa (unsaturated conditions) Double-wall cell Separates ∆ V α and ∆ V w Three sample sizes Actuator unit Max load: 10 kN Max frequency: 2 Hz Figure 1 Cyclic triaxial apparatus for saturated and unsaturated soil testing