Print ISSN: 1681-6900

Online ISSN: 2412-0758

Keywords : clay


Consistency Characteristics of Dispersive Clays

Roaa H. Ismael; Mohammed Y. Fattah; Mohammad F. Aswad

Engineering and Technology Journal, 2021, Volume 39, Issue 12, Pages 1753-1759
DOI: 10.30684/etj.v39i12.1650

Dispersive soils are characterized by three features: (1) unstable structure, (2) they are readily flocculate in water, and (3) very erodible. The use of dispersed clay soils in hydraulic structures, dams and road dams can cause serious engineering problems when this soil is not identified and used befittingly. There is a simple way to determine soil dispersion and more difficult to measure dispersion.  (Atterberg’slimits) (grain size analysis), and (visible classification) are not enough to recognize between (normal clays) and (dispersive clays).ASTM tests can identify dispersive clay, these include: (double hydrometer test), (chemical tests), (Crumb test), and (Pinhole test). In this paper, the dispersed soil has been artificially prepared by adding Na2CO3  to  natural clay in different proportions. The proportions are 5%, 15%, 25%, 30%, 35%, and 40% by weight. The target of this investigation is to investigate the effect of degree of dispersion of the soil on Atterberg limits. The study showed that the percentage of dispersion increases  with Atterberg’slimits  and the dispersion ratio and the plasticity index relationship are related by a direct relationship.

Cyclic Settlement of Footings of Different Shapes Resting on Clayey Soil

Aseel N. Najim; Mohammed Y. Fattah; Makki K. Al-Recaby

Engineering and Technology Journal, 2020, Volume 38, Issue 3A, Pages 465-477
DOI: 10.30684/etj.v38i3A.483

An experimental investigation is carried out to investigate the impact of the footing shape, when rested on clayey soil under cyclic loading condition. The model footings used in this study are circular, square and the area of footings is fixed. Cyclic load test is carried out on the cohesive soil with three undrained shear strengths (20 kPa, 40 kPa and 70 kPa). Two depths of foundation embedment (at surface and 5 cm) to know the effect of the depths of the foundations on the change of settlement and total vertical stress and two rates of loading (3 mm/sec and 6 mm/sec) are used. It has been observed that the bearing capacity varies in increasing order as Solid, Circular and Square. It is found that the cyclic settlement in the square foundation is less than the circular foundation. The results reveal that the shape of the footing has a significant effect on its bearing capacity and the settlement characteristics. The vertical stress reaches a constant value which is greater below circular footing and it is about (70.9 - 92.7) % greater than below square footing.

Comparison of the Behavior for Free Standing Pile Group and Piles of Piled Raft

Awf Al-Kaisi; Falah H. Rahil; Mohanned Waheed

Engineering and Technology Journal, 2018, Volume 36, Issue 4A, Pages 373-380
DOI: 10.30684/etj.36.4A.3

The intended task of this paper is studying the behavior of free standing pile groups and piles of piled raft driven in clayey soil under axial loading. The raft-piles interaction is investigated as well through the two series of tests. Each one of these series includes twelve tests, the two series are conducted with the same configuration, spacing, size of piles and undrained shear strength of soil except that in the free standing group there is a gap of about (20-25 mm) between the raft and the soil surface to have the applied load transferred to the piles only in order to compare the behavior of piles in the two cases. Three grades of undrained shear strength (cu) of clayey soil are selected which are (20 or 40 or 60 kPa) and the configuration of the pile groups used in all tests is (2 x 2). Two different pile lengths (L) are selected (300 and 450 mm). These lengths represent the slenderness ratio (L/D) of (10) and (15) respectively, so that the center-to-center spacing between the piles (S) used are (3D) and (5D). It is observed that piles exhibited a very high stiffness at initial loading stages till the settlement is about 0.5mm, beyond this level, even for a small increment in the load, the pile settled rapidly, which means that once the friction is overcome the piles failed instantaneously. In addition, most of the load capacity of piles is mobilized at settlement of around (1 – 2 mm), corresponding to (5 %) of pile diameter.
Moreover, the increasing the undrained shear strength of clay from (20 to 60 kPa) has no significant effect on the load transfer mechanism of piles in the two cases .
It can be concluded that the load capacity of the free standing pile group is about equal to the piles in piled raft case, indicating that the interaction effect is not significant, therefore, it is suggested to apply an efficiency factor (αG) of (1) in designing the piled - raft foundation in clayey soil when calculating for pile load share.

Development Bearing Capacity of Piles Embedded in Clayey Soil

Awf Al-Kaisi; Falah H. Rahil; Mohanned Q. Waheed

Engineering and Technology Journal, 2018, Volume 36, Issue 3A, Pages 315-321
DOI: 10.30684/etj.36.3A.10

The load carrying capacity of piles resulting from base resistance and shaft resistance, the load transfer mechanism of piles is complicated since the mode of failure of these components is different in addition to the effect of pile installation on the soil surrounding of piles .The intended task of this paper is studying the behavior of pile group model driven in clayey soil subjected to vertical axial loading, and the assessment of the development of resistance of each of the two components, tip resistance and skin friction of the piles of during loading. Twelve piles group tests are conducted at three grades of undrained shear strength (cu) of clayey soil which are (20 or 40 or 60 kPa) where the configuration of the pile groups used in all tests is (2 x 2). Two different pile lengths (L) are selected (300 and 450 mm), these lengths represent the slenderness ratio (L/D) of (10) and (15) respectively, so that the center to center spacing between the piles (Sp) used are (3D) and (5D). It was observed that the most of the load capacity of piles is mobilized at settlement of around (1 – 2 mm), corresponding to (5 %) of pile diameter (D) , however, the development of full shaft resistance of piles appears at a low displacement range and is only of about (1 to 2 %) of the pile diameter while the pile end bearing will mobilize at a higher displacement range in the range of (5 to 10%).The changing of undrained shear strength of clay from (20 to 60 kPa) has no significant effect on the load transfer mechanism and the mobilization of shaft resistance and end bearing with increasing the settlement. It was concluded that a low ratio load sharing of piles tip, especially with increasing slenderness ratio (L/D) , which supports the fact that the piles in the weak clayey soils behave as a floating pile which leads to neglecting end bearing capacity in calculating the total pile load capacity as indicated by some references.

Bearing Capacity of Closed and Open Ended Pipe Piles in Clayey Soil

Ban S. Hussein; Falah H. Rahil; Mohammed A. Mahmoud

Engineering and Technology Journal, 2016, Volume 34, Issue 8, Pages 1615-1623
DOI: 10.30684/etj.34.8A.12

This paper investigates the impact of close and open ended condition on the capacity of pipe piles installed in medium clayey soil using pressed or jacked and hammered techniques and tested under the effect of vertical static compression load. 36 experimental model steel pipe piles (18 models for each open and closed ended) introduced and analyzed to clarify the influence of soil plug formation on the behavior of pipe piles.Different parameters are studied such as pile diameters (2.5, 3.5 and 4.1) cm, piles lengths (30, 40 and 50) cm and type of installation methods (pressed and hammered(. Results of the test program indicated that the ultimate load capacity of open-ended pipe piles tended to increase as the pile diameter and length increase for both pressed and hammered. The plugging of open piles does not contribute significantly on the capacity of pile in clay. For all model pile tests the load capacity of the closed ended piles is (5 – 30) % greater than that of the open ended for both type of installation (pressed and hammered) under the same geometric conditions.