1. on soft clay using finite element method Road & Highway Engineering
The 2nd International Conference on Buildings, Construction and Environmental Engineering- BCEE2
17-18 October 2015
Beirut, Lebanon
Variation of pore water pressure under embankment
on soft clay using finite element method
Materials and Methods
Finite element computer programs:
In order to model accurately embankment over soft
soils coupled finite element analysis SIGMA/W
and SEEP/w has been shown to be capable of predicting
the settlement and pore pressure response. A fully coupled
analysis requires both the stress – deformation and
seepage dissipation equations be solved simultaneously.
A trail embankment constructed on AL-Basrah city south
of Iraq is suggested for analysis. The geological section is
shown in Figure (1). Table (1) summarized some of the
physical properties of Basrah area. (after Ministry of
Transposition).
A. Nahla M. Salim, Falah H. Rahil and Zahraa Qasim Mohammed
Road & Highway Engineering
Background
Type of Soil
Parameter
Value
Model
Clay
Liquid limit(LL)
Compression index (CC)
Slope of normal consolidation line ()
Slope of swelling line ()
Coefficient of volume compressibility (mv)
Hydraulic conductivity (k)
Effective friction angle ()
Coefficient of earth pressure at rest (K0)
Poisson, s ratio ()
Over-consolidation ratio (OCR)
Unit weight ()
38%
0.22
0.13
0.013 1
3×10-9 m/s 25
0.5
0.4
17kN/m
M CC
Sand
Modulus of elasticity (E)
35 mPa
0.3
1×10 m/s
20kN/m
Linear
Elastic
In the field of geotechnical building emerges when embankments of moderate to extensive statures are to be built on exceptionally delicate soils with low shear strength and high compressibility in particular time. The full heights of the embankment can't be built at once and the staged construction must be carryout. To build the embankment in stages, the time of construction in every stage ought to be sufficient for the excess pore water pressure to dissipate and consolidation occurs. In the field, it is so difficult to control this process, so the finite element coupled Sigma-Seep program was used to give an indication of the time required for each stage for excess pore water pressure to dissipate and consolidation takes place. Vertical sand drains are generally used to enhance the characteristics of soft clays. The principle function of vertical drain application is to quicken soil consolidation by shortening the seepage way and enacting radial drainage. Using vertical sand drains increasing the shear strength of the soil while diminishing its post-construction settlement (Holtz et al. 1991).
Conclusions:
1-Finite element analysis is powerful method in predicating vertical, horizontal settlement and excess pore water pressure.2-In general, the maximum settlement occurs under the center of the embankment, this settlement is reduced as moving
towards the toe of the embankment.3-The modified-Cam clay model can mimic the soil conduct successfully. When the consequences of analysis are contrasted and the measured qualities, good agreement was obtained.
4-The vertical settlement increases by 38% via using sand drain while the horizontal displacement decreases by 52%. 5-The excess pore water pressure reduces by 83% via using sand drain.6-Toe berm causes increase in maximum vertical displacement to reach to 25%while the horizontal displacement decreases by 10%. 7-The maximum increase in pore water pressure reaches 17%.
Objectives
review and estimate the excess pore water pressure, the total and rate of consolidation settlement in embankments constructed on soft soils. Methods of improving stability in these cases include constructing the embankment in stages. Furthermore, establishment of vertical drains is a standout amongst the most generally utilized methods for enhancing the characteristics of soft clays.