Case study

The effects of water runoff and rainfall patterns over primary layers of the soil in Denizli area , related to stability of  foundations and the resulting special design requirements

Adriana-Daniela Sandu , Bachelor Student ,Faculty of Building and Civil Engineering
Ovidius University , Constanta , Romania

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Within the past years , Turkey had showen a substantial economical development, therefore ,an increase in construction areas is demanded .

Denizli is located in southwestern part of Anatolia and in southeast of the Aegean Region.It lies between 28°30’ and 29°30’ east longitude and 37°12’ and 38°12’ of north latitude. The ground water table is to be found in general to a minimum depth of 10 m .

A terrestrial climate may be found in the center of the area , as a consequence of being a pathway from seaside to inland parts. The land is open to winds coming from Aegean Sea , because of the perpendicularity of the mountains to the sea. Winters are rainy in general and mild in the most of the cases.

The soils from this part of region are classified in class 7 of soils. That means they have limitations very severe, being unable to be used for arable culture or permanent pasture, very drastic climate, low water-holding capacity , not too deep water level. May have also high capablity for forests and special fruit trees , as pomegranates and olive trees.

In the concept of active performance of stability design of a construction , the problem of water runoff and rainfall patterns demands an urgent evaluation of structures response at the limit stages of every possible scenario . In this paper , foundations design , stablity and performance under certain carried loads from precipitations water influence over the soil is subjected to a closer , theoretical approach and examination as a throwback response and its consequences thru the future .

Effects of rainfall patterns over primary layers of the soil represent an unusual problem to be analyzed for Denizli area, regarding the fact that the main concern for this part of Turkey is considered to be the influence of the earthquakes and the active faults over stabilty of the structures and not only.

Predicition of an inelastic displacement response by leveling dissipated energy of the foundations according to the one inputed by a combination of earthquake energy and reccuring displacements , displacements on the horizontal and vertical direction of the soil, obtained from the water influence and precipitations is demanded for the stablity of the structure. Response of a structure and its foundation in a short period range is going from 0 to higher limit in a short time, comparing to the fact that , in a long range , subjected to the same intensity of loads, forces and moments, is going to be constant. The most important parameters for evaluation of a dynamic response are shear mdulus and the damping ratio , both factors of cyclic shear strain.

Soil-structure interaction doesn't have to be regarded as a compact and unique connection . By defining the limits of each member ,both structure and soil to a lower level , the strength of the of the dynamic system will go to an appropriate safety form . Taking this into account , computation of all parameters such as bearing capacity , settlement , appropiate reinforcement , overburden pressure , acceleration and velocity of the displacements will be regarded not reaching safety limits.

Each substructure has a specific dynamic response due to external actions . Choosing the most suitable type of foundation as a result of a cumulative factors is the first most important thing . As it is mentioned before , ground water table is an important element for this . It is very important that GWT should be maintained under the footing level , in order to prevent a future uplift or flotation , that it will be added to a doubtful safety of the footing.

The presence or the lack of water in the soil is vital for computation of soil strength and future settlement. Water exceeding in the soil is one of the most dangerous factors regrding the safety of a permanent settlement of a construction or a future collapse or ,in the best case only the occurence of a cracking.

Obermeyer claimed the fact that for a saturated soil mass , the stress release during excavation can result in significantly more negative pore pressure in the underlying soils . Thus , water can flow into the soil beneath the subjected area and cause swelling. If the water will subject the pores to a pressure enough to carry the load , it will result a hold apart of the particles , resulting an alomost quicksands behavior .The initial part of the soil which has accumulated pressure will succesively move the points of concentrations, once they will be liquefied. Chu had noticed an important factor of influnce : fatigue of swelling . Considering it , if the drying and wetting cycles are going to be repeated , the swelling during the first cycle would going to be appreciably higher than in subsequent cycles.

Rainfall Distribution (1971-2000) 

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