Finite element modelling of the sismic behaviour of water front structures

Water front structures have suffered significant damage in many of the recent earthquakes. These include gravity type quay walls, vertically composite walls, cantilever retaining walls, anchored bulkheads and similar structures. One of the primary causes for the poor performance of these classes of structures is the liquefaction of the foundation soil and in some instances liquefaction of the backfill soil. The liquefaction of the soil in-front of the quay wall tends to cause large lateral displacements and rotation of the wall. Often such gravity walls are placed on rubble mound deposited onto the sea bed.This paper presents finite element analyses of such a problem in which strength degradation of the foundation soil and the backfill material will be modelled using PZ mark III constitutive model. The performance of the wall in terms of its lateral displacement, vertical settlement and/or the rotation suffered by the wall will be presented. In addition, the contours of the horizontal and vertical effective stresses and the excess pore pressure ratio will be presented at different time instants together with hyrdraulic gradients. Immediately after the earthquake, the hydraulic gradients indicate migration of pore water into the region below the wall, suggesting further softening of the foundation soil below the wall.

Stochastic analysis of seepage under water-retaining structures

This paper investigated the problem of confined flow under dams and water retaining structuresusing stochastic modelling. The approach advocated in the study combined a finite elementsmethod based on the equation governing the dynamics of incompressible fluid flow through aporous medium with a random field generator that generates random hydraulic conductivity basedon lognormal probability distribution. The resulting model was then used to analyse confined flowunder a hydraulic structure. Cases for a structure provided with cutoff wall and when the wall didnot exist were both tested. Various statistical parameters that reflected different degrees ofheterogeneity were examined and the changes in the mean seepage flow, the mean uplift forceand the mean exit gradient observed under the structure were analysed. Results reveal that underheterogeneous conditions, the reduction made by the sheetpile in the uplift force and exit hydraulicgradient may be underestimated when deterministic solutions are used.

An automated method for mapping physical soil and water conservation structures on cultivated land using GIS and remote sensing techniques

An efficient and reliable automated model that can map physical Soil and Water Conservation (SWC) structures on cultivated land was developed using very high spatial resolution imagery obtained from Google Earth and ArcGIS, ERDAS IMAGINE, and SDC Morphology Toolbox for MATLAB and statistical techniques. The model was developed using the following procedures: (1) a high-pass spatial filter algorithm was applied to detect linear features, (2) morphological processing was used to remove unwanted linear features, (3) the raster format was vectorized, (4) the vectorized linear features were split per hectare (ha) and each line was then classified according to its compass direction, and (5) the sum of all vector lengths per class of direction per ha was calculated. Finally, the direction class with the greatest length was selected from each ha to predict the physical SWC structures. The model was calibrated and validated on the Ethiopian Highlands. The model correctly mapped 80% of the existing structures. The developed model was then tested at different sites with different topography. The results show that the developed model is feasible for automated mapping of physical SWC structures. Therefore, the model is useful for predicting and mapping physical SWC structures areas across diverse areas.

251.8-251.9 D.E #5

Sample contains well dispersed clasts ranging from small to medium in size. They are sub-angular to sub-rounded in shape. Organic rich domains can be seen throughout the sample with clear boundaries. It also contains water escape structures, seen mainly through clay. Lineations are also present.

293.9-294.0 DE # 7

Brown sediment with well dispersed clasts. Clasts range from small to medium in size and angular to sub-rounded in shape. Some appear to have been weathered. Water escape structures can be seen, mainly in finer, clay rich sediment. Lineations can also be seen throughout the sample. Minor grain stacking and crushing are also present.

HG 316.65-316.80

Fine grained, dark brown sediment. Minor amounts of lineations can be seen. Faint water escape structures are also abundant.

HG 326.65-326.75

Dark brown sediment with clasts ranging from small to large. Grains are sub-angular in shape. Faint water escape structures are present.

HG 384.60-384.70

Dark brown sediment with scattered amounts of small clasts and medium clasts as well. Clast shape ranges from sub-angular to sub-rounded. Lineations and water escape structures are abundant in this sample.

HG 388.75-388.85

Dark brown sample with clasts that range from small to large. The clast shape ranges from angular to sub-rounded. Grain crushing is present in this sample along with some lineations. Faint water escape structures can also be seen.

HG 393.60-393.85

Brown sediment with clasts that range from small to large. The clast shape ranges from angular to sub-rounded. Lineations and water escape structures are present. Grain crushing and minor amounts of rotation are also present.

HG 404.20-404.30

Brown sediment with clasts ranging from small to medium in size. The clast shape ranges from angular to sub-rounded. Lineations are abundant in this sample. Faint water escape structures can also be seen as well as grain crushing/stacking.

HG 421.15-421.25

Brown sediment with a coarse grained domain and a fine grained domain. The coarse grained domain contains clasts that are small to medium in size. The clast shape ranges from sub-angular to sub-rounded. The coarse grained domain is abundant in lineations. The fine grained domain contains many faint water escape structures. A few rotation structures can also be seen throughout the sample.

HG 437.50-437.55

Light brown sample with clasts ranging from small to large. The clast shape ranges from sub-angular to sub-rounded. Grain crushing is common in this sample and mainly involves the larger clasts. Many grains are also crushed into one another. The larger grains are also fractured. Lineations and faint water escape structures can also be seen. This sample also contains a finer grained domain, darker in colour.

HG 458.25-458.35

Dark brown sediment, with clasts ranging from small to large. The sample mainly contained smaller clasts. The clast shape ranges from sub-angular to sub-rounded. Lineations were common throughout the sample. It also contained areas with dark organic material, and a few faint water escape structures.

HG 496.40-496.55

Brown sediment with grains ranging from small to medium in size. The sample mainly contains smaller clasts. Clast shape ranges from sub-angular to sub-rounded. Water escape structures and lineations can be seen in this sample. Grains stacking and comet structures are also present in minor amounts.