Search

The growing pressures of climate change, increased usage and unprecedented geo-hazards impose a modification in the way civil engineering structures are designed and constructed. This isparticularly true for geotechnical works, which are very sensitive to changes of environmental conditions. For instance, the response of a pile under lateral loading is strongly influenced by the stiffness and strength of the first few metres of soil below the surface, which are often partly saturated. To consider this effect, the present paper describes an analytical method, which extends the well-known Broms approach to predict thelateral capacity of piles in unsaturated soils. More specifically, the proposed method considers the combined effects of the position of the ground water table and the extra strength of the partially saturated soil above it. Compared to Broms approach, the solution introduces four additional non-dimensional parameters that relate the soil-water retention behaviour to the geometry of the pile. The method provides a direct evaluation of the lateral pile capacity in partly saturated soils, which can be used as a basis for more accurate design.

Rewetting agricultural peatland abates carbon dioxide (CO2) emission, but the resulting waterlogged anaerobic soil condition may create hotspots of methane (CH4) emissions. In this study, we measured CH4 emissions from side-by-side replicated plots in an agricultural fen cultivated with reed canary grass under a control and two experimental rewetting (i.e., paludiculture) conditions as either continuously flooded to soil surface or semi-flooded where water from the flooded plots intruded from sub-surface. Fluxes were measured for two successive years at 1–2 week intervals (total 59 measurement dates) using static chambers. Annual emissions were estimated by trapezoidal linear interpolation of the measured fluxes between the measurement dates. Two-year time-weighted average ground water tables (GWT) in the flooded, semi-flooded and control plots were 1, 3 and 9 cm below soil surface, respectively. The annual average emissions from flooded plots were 82 and 116 g CH4 m−2 yr−1 in Year 1 and 2, respectively, which were significantly higher than the emissions from semi-flooded plots (35 and 69 g CH4 m−2 yr−1 in Year 1 and 2, respectively) and from control plots (3 and 9 g CH4 m−2 yr−1 in Year 1 and 2, respectively). Overall, the results showed that the GWT in paludiculture should be maintained few cm below soil surface during high temperature periods to prevent risks of high CH4 emissions.

The behavior of a slope reinforced by passive piles 15 years ago was studied during removal of some passive piles, additional steeper slope cutting, and reinforcement by soil nails and anchors. Through a comparison of the measured value and numerical analysis results, it was found that the maximum lateral displacement developed at bench No. 4, which was the nearest bench to the additional steep slope cutting, and it could be correlated with the groundwater table. In particular, the relaxation of the ground from past failure sliding could affect the slope stability.

Modeling of ground water table depth response to precipitation was based on data obtained from the drainage field Radmilovac near Belgrade. Drainage field was consisted of drainage treatment I and II representing drain spacing of L;=l0 m and L2= 30 m, respectively. For the modeling of stochastic process, moving average model (MA) was used. Assuming that rank of the model n was known, estimation of the MA parameters was carried out. Obtained data were used for calculation of the criterion J. Then, criterion J response to parameter n was plotted. Obtained values range from 1 to 35. Starting from the lower value of the parameter n and by increasing it gradually value of the criterion was significantly reducing until the moment when further increment had neglected influence. Plateau of the function was established on n=27 and this value can be assumed for the responding rank of the model. Such a great rank of the model could be explained by the lowest topography of the drainage field regarding the whole catchments area, to whom surface and groundwater runoff gravitate. The value of the mean square error was significantly lower on the drainage treatment I with narrower drain spacing (L/=10m). Logically, groundwater table depth cannot response to precipitation simultaneously. Therefore, certain delay caused by filtration characteristics of the soil was assumed to be in the range from 0 to 5 days in order to estimate its influence on value of the criterion 7. However, results show that assumption of significant delay on groundwater depth variation is not sustainable. Assuming the rank value of the model and rank of the delay (n=27, d=0) theirs responses to groundwater table depths above the drains (h) both by measurement and by model estimation are represented. Mainly, MA model can be used for multistage prediction of the process consequence y (groundwater table depth) based on the measurement of the process cause x (precipitation). U radu je izvršeno modeliranje zavisnosti dubine podzemne vode od padavina na dreniranom području na kome su rastojanja između drenova 10 i 30 m. U cilju modeliranja stohastičkih procesa koji su u ovom radu od interesa upotrebljen je MA (Moving Average) model. Pretpostavljeno je da je red modela n poznat procenjeni su parametri tako usvojenog MA modela i sračunata je vrednost kriterijuma. Zatim je skicirana zavisnost kriterijuma J od vrednosti parametra n koji se kretao u opsegu od 1 do 35. Polazeći od malih vrednosti parametra n i njegovim postepenim povećavanjem vrednost kriterijuma značajno smanjuje sve do trenutka kada se daljim povećavanjem efekat na kriterijumu ne vidi. Plato funkcije se uspostavlja na n=27, i ova vrednost se može usvojiti za odgovarajući red modela. Ovako veliki red modela može se objasniti topografskim položajem dreniranog područja, ka kome gravitiraju vode sa okolnih viših terena. Vrednost srednje kvadratne greške značajno manja za drenažni sistem za manjim međudrenskim rastojanjem (L;=10m) Logično je očekivati da padavine ne utiču na nivo podzemnih voda momentalno, već da postoji izvesno kašnjenje, uslovljeno filtracionim karakteristikama zemljišta, pa je u analizu uvedeno kašnjenje 0-5 dana da bi se procenilo koliko ono utiče na vrednost kriterijuma /. Međutim, rezultati pokazuju da pretpostavka o značajnom uticaju kašnjenja na promenu nivoa podzemnih voda nije održiva. Za vrednosti koje su usvojene kao red modela i red kašnjenja (n=27, d=0) prikazane su vrednosti visine vode iznad drena (h), i to vrednosti dobijene merenjem i vrednosti koje sračunava model. Ovako dobijen MA model se prvenstveno može iskoristiti za višekoračnu predikciju procesa posledice y (nivo podzemnih voda) na osnovu merenja procesa uzroka x (padavine).