الفهرس 
Application of lime-soil stabilizationOnly 14 pages are availabe for public view
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Abstract
The geological distribution of soft clay soils in the northern Nile Delta region as well as the various aspects of soil improvement by lime-mixing technique, have been studied throughout an experimental programs. In order to accomplish this, a total of 822 soil profiles were collected from 41 1 places in the northern Nile Delta region, from Tanta City in the center to the Mediterranean Sea in the North and from El-Manzaia City in the east to Idku City in the west. The soil profiles represent the upper 20 m of the Holocene Bilqas Formation. To evaluate the effect of lime on soft clays, the natural soil samples were collected fiom five places (Idku, Al-Burullus, Fuwa, El-Manzala and Tanta Cities) cover nearly all types of soft clay soils. The lime was added to each soil in room temperature in the amount of 1, 3, 5 and 7 % by weight of natural sample and thoroughly mixed by hand until homogeneity is nearly reached. The study includes geological (grain size analysis, mineralogical composition, microstructure observations) and engineering studies (index properties, soil strength and compressibility behaviors). Soft clays are normally soft in consistency due to their higher moisture content and thus they cause many settlement problems and extensive damages of buildings. In views of this, their aerial distribution is of almost importance for engineering purposes. The study of the distribution of soft clay soils in the northern Nile Delta region using facies maps (depth and thickness) and longitudinal cross-sections has revealed the following remarks: 1- soft clay soils are widely distributed in the central and northern parts of the Nile Delta. They range in thickness from less than one meter in the central part to more than 15 m in the northern sector. Their depth varies also from 13 m to less than 1 m in the same direction. 2- Soft clays are generally overlain by medium to stiff clayey soils (q,, more than 0.5 kg/cm2) and underlain by the medium to coarse sands with gravels. In some parts, particularly near to the Nile branches, these soft clays are associated with peat soil, which is also unstable for supporting structure of any kinds. 3- The thickness of soft clays increases with the rising of water table ofthe Quaternary aquifer as evidenced by the increase of thickness of soft clays towards the north. This is suggests that fine-grained soils may change gradually to soft consistency with increasing water content. 4- As, soft clays are usually overlain by stiff to medium clayey soils the fkture rise of water table may change the latter to soft clays, which may cause considerable settlement problems. The data of grain-size analysis suggest that the natural soft clay soils in the study area consist primarily of silt (47.6 %) and clay (38.9 %) with little amount of sands (1 1.5 %) and can be classified as mud or sand mud sediments. The study also suggests that these sediments were deposited from suspension in deltic and fluviomarine environments. 150 Granulometric analysis of the lime-treated soils in different areas has shown that the percentage of sand-size fractions increases while clay-size fractions decrease with increasing lime percent and curing time. Meanwhile, silt-size fractions may increase or decrease with increasing lime percent and curing time depending on the sand-and clay-size contents. This increase in the sand- and siltsize fractions is attributed to flocculation and agglomeration of fine-grain particles. In contrast, the decrease in silt-size fraction is probably due either to partial aggregation of silt to sand-size or deaggregation of silt to clay-size particles as a result of dispersing agent. X-ray diffraction analysis has indicated that smectite, illite and kaolinite are the principal clay minerals encountered in the clay fraction in the natural soils. Quartz and feldspars are the predominant non-clay minerals in all samples, whereas halite, gypsum and calcite are recorded as secondary minerals in some areas. In lime-treated soils, many of these minerals, especially, clay minerals and feldspar were affected by lime-soil reactions (pozzolanic reactions). Meanwhile, several new minerals and compounds were formed as reaction products such as calcite, afwillite, margarite, nekolite, CSH, CAH and CASH. These products increase with increasing lime percent, depending on the initial composition of the natural soil. Scanning electron microscope observations of the microstructures reflect the growth in fabric of lime-treated soft clay soils, and the reduction of porosity and permeability. This is attributed to lime-soil reaction leading to new cementing material and filling soil interparticles, but this depends on the lime percent, curing time and original composition of the natural soils. from the engineering point of view, the natural soft clay soils of the present study are classified, according to the USC system, into OH (organic clays of 151 medium to high plasticity) and OL (organic silts and organic silty clays of low plasticity) types. Accordingly, the soil samples of Idku, Fuwa and El-Manzala are classified as OH-type, whereas Al-Burullus and Tanta samples as OL-type soil. However, when the lime is added to the soil, both liquid and plastic limits (LL and PL) increase, as lime content increases in all types of soil. In contrast, these limits may increase or decrease with curing time, depending on the type of soft clay soils. On the other hand, The plasticity index (PI) shows reduction in its value with the addition of lime to fine-grained soils. This may reduce significantly the swelling potential of the soil. Regarding the unconfined compressive strength (q,), the untreated soil of the study areas lies in the category of very soft soil. But, there is a good support to establish the improvement in strength behavior of soil with the addition of lime to soil. The soil that treated with 7 % lime and tested after 60 days shows the highest improvement in strength and can be classified as medium to stiff or even very stiff soil depending on the initial soil composition and fabric. The maximum strength improvement reached about 1400 % was recorded in Al-Burullus soils, whereas the minimum strength improvement was obtained fiom Tanta samples (530 %). Both cohesion (c) and deformation modulus (Es) show improvement with the addition of lime to soil. This improvement is positively correlated with lime percent and curing time. However, the improvement is mainly attributed to increased formation of cementing material as detected by XRD and SEM. The data of consolidation test show that the untreated samples from Idku, Fuwa and El-Manzala Cities have (Cc) values greater than 0.3 cm2/rnin and lie in the category of very high compressibility soil, whereas samples from Al-Bumllus and Tanta showed low (Cc) values and lie in the category of high compressibility soil. In lime-treated soils, the compressibility behavior improves due to the 152 development of new cementing material, but this depends on the lime percent and curing time. This is indicated fiom; the decrease of strain, void ratio, permeability and compression index and the increase in coefficient of consolidation and preconsolidation pressure with increasing lime percent and curing time. from the results and analysis presented in this thesis, it is clear that soft clay soils are widely distributed in northern Nile Delta and cause many of foundation problems, which may be increased in feature with rise of the ground water level. So that there is a necessity to improve his engineering properties to suit the foundation requirements of several structures. Also it is clear that limemixing technique can significantly improve the engineering behavior of fine-grained soils due to short-term and long-term reactions which take place between lime and soil minerals. The reductions in plasticity index suggest an overall improvement in the soil behavior and this indicates improvement in the strength and reduction in compressibility. Possibly, the reduced values of plasticity index can significantly reduce the swelling potential. In view of this, the lime-mixing technique can be used to improve the engineering behavior of soil that may increase the performance of the foundations of buildings. Consequently, this technique can be considered as the most promising one to tackle several foundation problems encountered in fine-grained soils due to its low cost and proven success in several structures.