Study on Influence of Unloading of Vacuum on Stability of Embankment Improved by Vacuum Combined with Preloading

2012 ◽  
Vol 178-181 ◽  
pp. 1688-1693
Author(s):  
Ji Fu Liu ◽  
Guan Feng An ◽  
Gang Zheng
Keyword(s):  
Shear Strength ◽  
Theoretical Analysis ◽  
Safety Factor ◽  
Laboratory Tests ◽  
Soft Clay ◽  
Undrained Shear Strength ◽  
Soft Ground ◽  
Analysis Laboratory ◽  
The Stability ◽  
Undrained Shear

In order to study influence of unloading of vacuum on stability of embankment whose soft ground is improved by vacuum combined with preloading, the change of effective stress of soft clay in the improved area is analyzed when vacuum is unloaded and the undrained shear strength of soft clay in the improved area after unloading of vacuum is deduced. Changes of undrained shear strength of soil and stability of embankment owing to unloading of surcharge are also analyzed for comparison. It is shown by theoretical analysis, laboratory tests and a project that the undrained shear strength of soft clay improved by vacuum combined preloading is decreased after unloading of vacuum and the stability of embankment after unloading of vacuum should be taken into account for design. Safety factor of stability of embankment increases after unloading of surcharge since decrease ratio of load of embankment is more than decrease ratio of undrained shear strength of clay.

On the evaluation of undrained shear strength and preconsolidation pressure from common field tests in clay

2005 ◽  
Vol 42 (4) ◽  
pp. 1221-1231 ◽  
Author(s):  
Rolf Larsson ◽  
Helen Åhnberg
Keyword(s):  
Shear Strength ◽  
Soft Clay ◽  
Field Tests ◽  
Undrained Shear Strength ◽  
Test Field ◽  
Cone Penetration ◽  
In Situ Tests ◽  
Cone Penetration Tests ◽  
The Stability ◽  
Undrained Shear

The undrained shear strength is a key parameter in the estimation of the stability of natural slopes and man-made constructions in soft clay. It is therefore important to develop relevant methods to evaluate the operative strength. Results from an investigation regarding the effect of excavations at slope crests to increase the stability of clay slopes are presented. This study has provided an opportunity to study the effect of overconsolidation on the evaluated parameters from common in situ tests in homogeneous and truly overconsolidated clays. Certain inconsistencies in the commonly used methods of interpretation of field vane tests, cone penetration tests, and dilatometer tests are highlighted, and modified interpretation methods taking the effects of overconsolidation into account are proposed.Key words: clay, overconsolidation, undrained shear strength, cone penetration test, field vane test, dilatometer test.

Uplift tests on full-scale pipe segment in lumpy soft clay backfill

2016 ◽  
Vol 53 (4) ◽  
pp. 578-588 ◽  
Author(s):  
R.P. Chen ◽  
B. Zhu ◽  
W.J. Ni
Keyword(s):  
Shear Strength ◽  
Soft Clay ◽  
Vertical Displacement ◽  
Undrained Shear Strength ◽  
Full Scale ◽  
Scale Model ◽  
Pressure Transducers ◽  
Pipe Segment ◽  
Clay Ground ◽  
Undrained Shear

Upheaval buckling of pipelines caused by thermal- and pressure-induced loading is an important issue in pipeline design. The uplift capacity of pipelines is determined by the pipe–soil interaction during pipeline upheaval in soil. Pipelines to be installed in soft clay are usually placed into trenches and then backfilled. In this paper, a set of test devices were developed and a series of full-scale model tests were carried out on a pipe segment buried in lumpy soft clay backfill, including backfilling tests, load-controlled uplift tests, and a displacement-controlled test. Eight total pressure transducers were embedded in the wall of the pipe segment to measure soil pressures on the pipe segment, and five linear variable differential displacement transducers (LVDTs) were arranged to record the vertical displacement of the pipe segment and the surface of the soft clay ground. The stabilizing force keeping the pipe segment in place during the backfilling process was found to fit a nearly linear relationship with the dimensionless undrained shear strength of soft clay. The variation of soil pressures on the pipe segment during uplift loading was significantly affected by the buried depth of the pipe segment and the undrained shear strength of the soil. For all present load-controlled tests in lumpy soft clay backfill, the test ultimate uplift resistances were only about 19%–81% of the results calculated by the Det Norske Veritas approach. Mainly due to the voids’ compression, shearing and strain softening of lumpy soft clay backfill, the difference between initial and stable displacements in a loading step for a load-controlled test or initial and stable loads in a displacement step for a displacement-controlled test is remarkable. The limits of uplift resistances are recommended for the instant and sustaining behaviors of the pipe segment, respectively.

Effect of sand percentage on the compaction properties and undrained shear strength of low plasticity soft clay

2021 ◽  
Author(s):  
Iyad Alkroosh ◽  
◽  
Ali Al-Robay ◽  
Prabir Sarker ◽  
Saif Alzabeebee ◽  
...  
Keyword(s):  
Shear Strength ◽  
Moisture Content ◽  
Soft Clay ◽  
Undrained Shear Strength ◽  
Optimum Moisture Content ◽  
Dry Density ◽  
Sand Content ◽  
Compression Tests ◽  
Maximum Dry Density ◽  
Undrained Shear

This study investigated the influence of sand content on the mechanical behaviour of a low plasticity clay found in Iraq. Samples were prepared with sand contents of 0%, 10%, 20%, 30%, and 40% of the weight of the clay. Standard Proctor and unconfined compression tests were carried out and the optimum moisture content, maximum dry density, and undrained shear strength were determined. The results showed a gradual increasing trend of the maximum dry density with the increase of the sand content up to 30%. The highest dry density reached was 1.90 gm/cm3 corresponding to an optimum moisture content of 12%. In addition, it was also found that the undrained shear strength was inversely proportional to the increase of the percentage of sand. Thus, the dry density of the clay could be increased well above 1.70 g/cm3, which is the minimum dry density accepted as a compacted subgrade according to the Iraqi General Specifications for Roads and Bridges (2003); hence, the rejected low plasticity clay could be utilised by mixing with sand. The reasons for the increase of the dry density and the decrease of the undrained shear strength has been extensively discussed in the paper.

Experimental and Statistical Study on Single and Groups of Stone Columns

2020 ◽  
Vol 857 ◽  
pp. 399-408
Author(s):  
Maki J. Mohammed Al-Waily ◽  
Mohammed Y. Fattah ◽  
Maysa Salem Al-Qaisi
Keyword(s):  
Shear Strength ◽  
Stress Concentration ◽  
Bearing Capacity ◽  
Soft Clay ◽  
Undrained Shear Strength ◽  
Stone Columns ◽  
Stone Column ◽  
Dependent Variables ◽  
Undrained Shear ◽  
Improvement Ratio

In the present study, 24 laboratory models on soft clay treated with stone columns were carried out. The results for each case are analysed for the purpose of constructing a statistical model linking the variables studied. The experiments showed that the stress concentration and bearing capacity of soil treated with stone column increase with increasing the undrained shear strength (cu), number of columns and L/d ratio. The models represent a single stone column and a group of stone columns. The studied variables are three dependent variables, the stress concentration ratio (n), bearing capacity of soil treated with stone column (q) and the settlement improvement ratio (Sr) due to the existence of stone columns. The independent variables are six: the undrained shear strength of clay soil, with three values (6, 9 and 12 kPa), the number of stone columns (1, 2, 3 and 4 columns) and the length (L) to the diameter (D) of the stone column or (L/D) ratio in two values (6 and 8). Besides, the bearing capacity of the soil treated (q) with stone columns and the settlement improvement ratio were used in some statistical models as independents. After regression analysis, a set of equations that correlate the previous variables have been suggested. The incepted values for dependent variables are close to the laboratory results.

Effects of Electro Osmotic Consolidation in South West of Johor: Small Laboratory Scale

2014 ◽  
Vol 803 ◽  
pp. 255-264
Author(s):  
Khairul Nizar Mohd Yusof ◽  
Fauziah Ahmad ◽  
Mohd Mustafa Al Bakri Abdullah ◽  
Muhammad Faheem Mohd Tahir
Keyword(s):  
Shear Strength ◽  
Water Content ◽  
Clay Soil ◽  
Soft Clay ◽  
Soil Improvement ◽  
Undrained Shear Strength ◽  
Engineering Structures ◽  
Vertical Loading ◽  
South West ◽  
Undrained Shear

Clay soil is one of the problematic soils due to its natural states which have low bearing capacity and high compressibility. The effect and problem of the clay soil characteristic creates a problem for construction especially excessive settlement and this can lead to unstable and potential cracks of engineering structures. At presents, there are few of soil improvement types can be carried out to overcome these problems, and electro osmotic consolidation is one of the options. This method has been applied many years ago especially in european countries. The study encompasses the determination of water content, atterberg’s limits and undrained shear strength after electro osmotic consolidation treatment of clay soils taken from 0.5 m and 1.5 m at southwest part of johor. All the samples were tested according to BS1377:1990. An experimental study was implemented in a pvc cylinder tube having dimensions of 300 mm height and 100 mm diameter. In the results of electro osmotic consolidation tests by installing copper spring electrodes, the measured undrained shear strength was increased considerably at the anodes especially compared to the initial undrained shear strength due to electro osmosis process and consolidation. As laboratory studies of its measurement have shown, the application of electro osmotic consolidation after the application of a direct current applied voltage of 10 volts, at the anodes especially: (i) a decrease by approximately 35% in water content; (ii) an increase around 29% in undrained shear strength; and (iii) a decrease about 21% in index plasticity. The results obtained in this study shows that the electro osmotic enhanced 15 kpa vertical loading consolidation is a feasible approach in strengthening of south west soft clay in johor. It can be clearly suggested that the higher the voltage applied in the system, the higher readings of undrained shear strength and the lower of water content especially at the anodes.

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