Fase en tres dimensiones, 3D

The main aim of this study was to investigate and assess the impact of climate change on residential footing design and construction. The primary focus was the climate indicator Thornthwaite moisture index (TMI), which has been used to quantify the past climatic variations and predict the future climate changes for Victoria. An Excel spreadsheet-based TMI calculation software has been developed, which allows the design engineers to calculate TMI using various equations and methods for any area and any period. The most up-to-date as well as the predicted future TMI isopleth maps of Victoria have been produced to assist practitioners and engineers for routine residential footing and pavement design.

The collection method of meteorological parameters which were used to compute TMI for 60-year period (in three by twenty 60-year intervals, i.e. 1954-1973, 1974-1993 and 1994-2013) was introduced. Step by step TMI derivation procedural using both the original (Eq. 2-17) and simplified Thornthwaite (Eq. 2-19) equations in conjunction with year-by-year method were described. Methodology for predicting future climate conditions of Victoria based on the projected climate trend was also presented. Worked examples were conducted in three densely populated regions of Victoria to investigate how meteorological parameters (e.g., precipitation) influence the computed TMI results. Three case studies were carried out to facilitate further understanding on the use of different equations and methods in estimating TMI as well as to evaluate the effect of climate change on the amount of future characteristic surface movement ys,which was predicted using the climate indicator TMI based on the projected climate trend.

The following conclusions can be drawn from this research study.

1. The computed TMI values for Victoria over the past 60 years using year-by-year method applied on the original (Eq. 2-17) and simplified (Eq. 2-19) equation have shown that, there is a significant difference for TMI value computed use Eq. 2-17 and Eq. 2-19, with latter equation has generally a more negative TMI tendency which indicate more arid climate condition. The computed mean TMI results showed Victoria has experienced an increasing severity of the desiccation of soils over the past several

decades where the most noticeable growth of drying had occurred in recent 20 years (1994-2013) since there was a rapid decrease of TMI value for almost all studied weather stations except Wonthaggi with a positive growth of 3 TMI units.

2. Melbourne City (086071), Laverton (087031) and Geelong (087025) were selected to investigate how meteorological parameters influence the computed TMI. The analyzed results indicate that the highest positive TMI value may not always occur in the same year that had the heaviest precipitation event and this can be attributed to the effect of potential evapotranspiration. Moreover, according to the linear correlation between TMI and precipitation, it is seen that variation about the trend line can be explained by the temporal rainfall distribution within any given year. It is noted that the highest coefficient of determination R² has always occurred in recent 20-year period, which indicated a very good linear correlation between TMI and precipitation. In addition, long drought of 4 consecutive years (from 2006 to 2009) was presented for all three study sites, which was considered as an important factor in contributing the most noticeable growth of drying in recent 20 years.

3. TMI contour maps delineated based on Eq. 2-17 and Eq. 2-19 have shown that Victoria has experienced a significant growth of drying over the past 60 years with a presence of wetting climate in north-east part of the state. Generally speaking, TMI variation tends are quite similar for maps developed by using these two TMI computation equations, with more severe soil desiccation shown in maps produced by Eq. 2-19. In terms of climate zone classification, it is seems that maps developed based on Eq. 2-17 may present a better climate zoning since the drought was not as severe as those presented in maps delineated based on Eq. 2-19. However, this is only an empirical inference, uncertainties involved are attributable to the non-rigorous climate classification system itself since it does not clearly define which TMI calculation method was employed to correlate TMI and climate zone. The overall drying of Victorian climate implies an increase in the severity of desiccation of the soil profile, which could potentially result in a higher incidence of soil moisture variation induced ground movement and the subsequent structural failure.

4. TMI contour maps developed for Victoria in 2030 (A1B scenario), 2050 (A1FI scenario) and 2070 (A1FI scenario), based on the predicted TMI values have

demonstrated an overall significant growth of drying for Victoria, where the most noticeably increase of aridity is expect to occur in 2070. It is predicted that, Victoria will suffer an overall increase of aridity if these climate trends are persisted, with the mean TMI tends to be more negative, soil shrinkage and the subsequent desiccation is very likely to be more pervasive.

5. The first case study was carried out to assess and compare TMI values derived by three equations (i.e. Eq. 2-17 to 2-19) and two methods (i.e. year-by-year and average year) in various locations across Victoria over 60-year period. The results show that for Eq.

2-17 and Eq. 2-18, the average year analysis method is very susceptible to the assumed initial storage values and thus this method should be avoided. The year-by-year analysis method does not significantly influenced by the initial storage value assumed and the TMI values computed by Eq. 2-18 are quite similar to those derived by Eq. 2-19 using both year-by-year method and average year method. It is suggested that if continuous weather record data of statistically significant number of years are available, Eq. 2-18 in conjunction with the year by year method or the simplified equation (Eq. 2-19) with either the average year analysis method or the year by year method, can be adopted. If there are discontinuous weather data, the average year analysis method should be used in in conjunction with Eq. 2-19 since it eliminates the need to carry out the water balance analysis. This study also evaluated the impact of the number of years employed on the final TMI result for the study sites. It is the author’s opinion that weather record for at least 20 continuous years can produce a reliable TMI. A longer study period (e.g., 30 years) will give more reliable TMI result but the climatological data for more than 20 years may not readily available from many weather stations.

6. The second case study was to compare TMI results of three selected sites from 1993 to 2013, using different PET equations and models (i.e. Eq. 2-9 and Eq. 2-16). The calculated PET results show that the differences between Thornthwaite equation and ASCE Standardized Penman-Monteith equation are quite significant. This can be attributed to the different assumptions and the input parameters adopted. As a result of large PET discrepancy, the difference of its corresponding TMI value is large as well.

According to the TMI results shown in Table 5-7, climate in Maryland is the wettest since it has the biggest TMI value. The climate condition in Melbourne and Walkley Heights is quite similar, which have experienced the intense soil desiccation in the past

20 years and thus the higher incidence of residential footing movement induced structural failure.

7. The third case study has been performed to compare and evaluate the effect of climate change on characteristic ground surface movement for various cities in Australia. The predicted results indicated that as the result of climatic change, top five largest cities in Australia except Sydney have experienced and will continue to experience an increased ground surface movement as the result of climatic change. Based on the estimated results, class H1 (Highly reactive site) is assigned for Sydney and Brisbane whilst class E (Extremely reactive site) or E-D (Extremely reactive site with deep-seated moisture changes) is given to Melbourne and Adelaide. It is interesting to note that ys value in Perth increased from 68mm (1990) to 75mm (2013) whilst it remains the same in other cities.