Mechanical properties

As illustrated in figure 6.3, the undrained strength of the dredged material is quite low. It was found that cu ranges from 2 to 4 kPa. For the design phase, an initial value of cu 3 kPa has been assumed as the most representative. Furthermore, laboratory tests have been focused on the evaluation of a undrained strength ratio (S0 cu a'v). From a series of triaxial CU tests on isotropically consolidated specimens (Fig. 6.6), a value of S0 0.49 was found. This confirmed also the fact that this...

Infinitesimal strain versus finite strain theory

As demonstrated in the previous section the conventional one-dimensional consolidation theory is nothing but a special case of the more general theory formulated by Gibson et al. (1967). Figure 5.6 shows the results of a comparative study performed for a 10 m thick, normally consolidated St. Herblain clay layer subjected to a surcharge of 200 kPa (Schiffman, 1994). In finite strain consolidation analysis, unlike in infinitesimal theories, there are two measures of the progress of consolidation...

Taw

CPT test on sand overlying the SSI improved foundation soil, example 2 sand to be most stressed some distance above the interface with foundation layer while the sand below is barely receiving any surcharge. On the other hand, sand overlying the non-improved foundation soil where there are no SSI columns show a more regular pattern of qc with depth. In fact, an almost linear trend was observed. The sand shear angle correlated from CPT complies, in all cases, with the design...

Deep mixing applications

Worldwide DM methods have been implemented in special construction techniques for onshore and offshore civil works. They have also been used for improvement of foundations of a number of structures such as dams, embankments, tanks, bridges, retaining structures, high-rise buildings, etc. On land, the method has been employed on temporary stability works for deep excavations, protection of adjacent structures and stabilization of slopes. Deep mixing can be executed in mass or column...

Ocr

Behavior will yield a constant value of cu a'v, at least at the two higher stresses. If cu a'v varies consistently with stress, the NSP concept does not apply to the clay. 2. To obtain cu a'v vs. OCR, use the minimum value of a'v giving normalized behavior as the laboratory preconsolidation pressure and perform tests at OCR values of 2 0.5, 4 1 and 6 2. Compare the results to those plotted in figure 3.5 to check their reliability. The data point should form a smooth concave upward curve It...

Risk of liquefaction

Soil liquefaction is a major concern for structures with or on loose sandy soils. Liquefaction can be caused by earthquakes by inducing a progressive buildup of excess pore water pressure due to cyclic shear stresses. When the pore pressure builds up to a level equal to the initial confining stress, soil loses its strength and large deformation occurs. To evaluate the potential for soil liquefaction at a particular site, it is important to determine the soil stratigraphy and the state of the...

Undrained analysis

A factor of safety of 1.3 was adopted here as minimum requirement to guarantee the safety during construction. As illustrated in figure 7.2, the first phase goes up to level +4.0TAW, that means up to an embankment height of about 20 m. This phase was divided in 10 sublayers to be constructed in stages every 2 months approximately to allow for some consolidation and strength increase of the soft soil. The following relationship (see also section 6.3.1 for the choice of parameters) was adopted to...

Info

Effective stress increment at midpoint Figure 5.3. Consolidation analysis of staged loading (SSCON-FD) Figure 5.3. Consolidation analysis of staged loading (SSCON-FD) Figure 5.4. Contour lines of excess pore water pressure (SSCON-FD) as a function of space (vert. axis) and time(horiz. axis)

References

AAS, Stability of natural slopes in quick clays. Proc. 10th Int. Conf. Soil Mechanics and Foundation Engineering. Stockholm (1981). J.H. ATKINSON, P.L. BRANSBY, The mechanics of soil An introduction to critical state soil mechanics. McGraw-Hill, UK (1978). L. BARDEN (1963) Stresses and displacements in a cross - anisotropic soil. Geotechnique, vol. 13, 198-210. L. BARDEN (1965) Consolidation of clay with non-linear viscosity. Geotechnique, vol. 15, no. 4, 345-362. R.A. BARRON (1948)...

Geometry of the embankment

The general profile of the embankment and soil conditions are illustrated in figure 7.2. As already described, the soil profile consists of about 8 m of soft material, 2m of sand and a deep highly overconsolidated clay (Boom clay). The water depth to the sediments level is about 20 m. The soft material was once subjected to vacuum consolidation to accelerate the self-weight consolidation. That means that there exist drains installed in the soft material that could help at accelerating the pore...

Ta760v3576 2007

ISBN 0-203-94629-4 Master e-book ISBN ISBN 978-0-415-42603-9(Hbk) ISBN 978-0-203-94629-9(eBook) About the List of symbols 2 Construction on soft 2.1 Clay foundation 2.2 Staged 2.2.1 Methodology for 2.2.2 Consolidation analysis 3 Discussion on undrained shear strength of soft soils 11 3.2 Shear behavior of normally consolidated 3.3 Normalized 3.4 Shear behavior of overconsolidated clay 3.5 Laboratory testing 3.5.2 SHANSEP 3.6 Undrained strength 3.7 Final 4 Discussion on slope stability 4.2...

Deep mixing assessment on the underwater site

The soil investigated here, as described in chapter 6, is a soft deposit of fine grained material, result of a prolonged sedimentation and self-weight consolidation process of dregs removed from the waterways within the harbor of Antwerp. In many harbor areas all around the world, there is an increasing need of reclaimed land. This fact has encouraged the design and ongoing construction in the Antwerp harbor of a partially submerged 27-m high sand embankment on the soft material previously...

Solution

Again, SSCON-FD was used to solve the problem. Free draining conditions were adopted at the top boundary and impermeable at the bottom. The results are shown in figure 5.5. From the excess pore water pressure profiles, numerically predicted up to 3 years, one can clearly note that the one-dimensional consolidation of the upper layer goes faster than in case of the lower layer due to the considerable difference in consolidation parameters. Since SSCON-FD allows the modeling of multilayered...

Finite strain theory

General three-dimensional consolidation approaches have been discussed already in literature starting from the important work of Biot (1941) however, all of it related to small strain levels of deformations of the soil skeleton. The most general theory of a one-dimensional type of consolidation is that proposed by Gibson et al. (1967). This analysis overcomes the limitations that the classical, small strain, theory entails but at the same time the problem becomes so complex that only numerical...

Shansep

Stress History And Normalized Soil Engineering Properties (SHANSEP) is the basis of the technique. It consists of evaluating the stress history of the clay deposits by evaluating profiles of vertical effective stress (a'v) and preconsolidation pressure (a'p) to determine OCR profiles through the deposit and then applying the appropriate normalized values to give the representation of strength properties for design. The basic steps are as follows (Ladd and Foot, 1974 Jamiolkowski et al., 1985)...

WF Van Impe RD Verastegui Flores

University of Ghent, Laboratory of Geotechnics, Zwijnaarde, Belgium LONDON LEIDEN NEW YORK PHILADELPHIA SINGAPORE Taylor amp Francis is an imprint of the Taylor amp Francis Group, an informa business 2007 Taylor amp Francis Group, London, UK This edition published in the Taylor amp Francis e-Library, 2007. To purchase your own copy of this or any of Taylor amp Francis or Routledge's collection of thousands of eBooks please go to www.eBookstore.tandf.co.uk. All rights reserved. No part of this...

Effect of the temperature

In an attempt to more reliably recreate the conditions in the field, a large cylindrical specimen with a height H 0.8 m and diameter ft 0.6 m was prepared in the laboratory employing blast furnace cement, with the aim of evaluating and monitoring the temperature changes due to exothermic reactions within the stabilized mass. The virgin soil was kept at a temperature of 10 C prior to mixing. After mixing of the soil and blast furnace cement slurry in a concrete mixer, the stabilized mass was...

Overview

The present chapter illustrates the design of the underwater sand embankment on soft soil dredged material . The water depth to the sediments level is about 20 m. As detailed in the previous chapter, the soil profile at the site consists of an upper soft layer overlying sand and a deep tertiary clay layer. Several alternatives have been evaluated. More details one these alternatives can be found elsewhere Verastegui, 2001 . Figure 7.1 illustrates a scheme of each of the options already studied...

Boom clay

The bottom layer on the soil profile consists of Boom clay. This material has also been extensively studied in a number of papers i.e. De Beer, 1967 Bouazza et al., 1996 . De Beer 1967 studied the shear characteristics of the Boom clay for a project of a tunnel under the Scheldt river in Antwerp, nearby the current site of investigation. According to a geological study carried out at that site, the Boom clay was covered by about 40 m of Antwerpian sand at the beginning of the continental...

Creep In Soil Mechanics

0 10 20 30 40 50 60 70 80 90 Plasticity index, Figure 3.10. Undrained strength anisotropy from CK0U tests on NC clay Jami-olkowski et al., 1985 Figure 3.10. Undrained strength anisotropy from CK0U tests on NC clay Jami-olkowski et al., 1985 Figure 3.11. Anisotropy of cu ff'v for different soil at OCR 1 Jardine and Menkiti 1999 Another means to study anisotropy is through the Hollow Cylinder Apparatus HCA which has shown to be an excellent tool of anisotropy investigation as it allows the...

Infinitesimal strain theory

As initiated by the early work of Terzaghi on stress strain analysis of saturated soils, the one-dimensional small strain consolidation theory can be expressed in a rather easy way. Let's consider a saturated element of porous material with characteristics fulfilling the assumptions above. In order to obtain the equation governing the consolidation, we start from the continuity requirement for the solid and liquid interaction. The continuity equation for the solid phase requires In the same...

Conclusions

Analyzing the stability problem of quick clay masses taking into account excess pore water pressures, the slope angle 3 seems to be limited to 3 lt 12 when assuming that the phreatic level coincides with the ground surface and stress conditions are changed slowly. In the case of a relatively quick change of external loading, such slope angle is reduced to 3 lt 5 30'. For smaller slope angles a succession of retrogressive shell shaped slid-ings can occur. Even with a very simple assumption of...