Settlement of Mat Foundation on Thick Stratum of Sensitive Clay

1965 ◽  
Vol 2 (4) ◽  
pp. 299-312 ◽  
Author(s):  
L Casagrande ◽  
P Firing ◽  
G Schoof ◽  
E John Tttrcke
Keyword(s):  
Groundwater Level ◽  
Industrial Plant ◽  
Effective Stresses ◽  
Preconsolidation Pressure ◽  
Load Increase ◽  
Order Of Magnitude ◽  
Mat Foundation ◽  
Building Load ◽  
Sensitive Clay ◽  
Thick Stratum

Foundation investigations for an industrial plant on a thick stratum of preconsolidated, sensitive clay are presented. In spite of the fact that the effective stresses in the clay caused by the building load remained below the average preconsolidation pressure of the clay, the settlement of the buildings locally appreciably exceeded the anticipated order of magnitude. It is shown that a drop in the groundwater level by a few feet would result in the effective stresses exceeding the preconsolidation pressure within the upper portion of the clay stratum. With such an assumption, the consolidation would not be governed by the very flat recompression branch of the consolidation curve, but in part also by the steep virgin compression branch of the consolidation curve. It is concluded that, when dealing with preconsolidated, sensitive clays, the total effective stresses caused by a proposed structure should be kept within a safe margin below the average preconsolidation pressure in order to make provision for any unforeseen load increase such as might arise from a drop in the groundwater elevation.

The effects of electroosmotic field treatment on the soil properties of a soft sensitive clay

1991 ◽  
Vol 28 (6) ◽  
pp. 763-770 ◽  
Author(s):  
K. Y. Lo ◽  
K. S. Ho
Keyword(s):  
Soil Properties ◽  
Ph Value ◽  
Soft Clay ◽  
Triaxial Tests ◽  
Carbonate Content ◽  
Failure Envelope ◽  
Effective Stresses ◽  
Copper Electrodes ◽  
Preconsolidation Pressure ◽  
Sensitive Clay

A field test was undertaken to assess the effectiveness of the electroosmotic strengthening of the soft sensitive (Champlain Sea) clay in the Gloucester Test Fill site by using specially designed copper electrodes to improve treatment efficiency. Tube samples, 127 mm in diameter, were recovered before and after field treatment for detailed laboratory tests. Isotropically consolidated undrained triaxial tests with pore-pressure measurements were performed. It was found that the failure envelope after treatment was significantly higher than the initial envelope, indicating that the strength in terms of effective stresses increased. Consolidation tests showed that, as a result of treatment, the preconsolidation pressure increased from 53 to 98 kPa. The soft clay is virtually "overconsolidated" by the process. Additional effects of electroosmosis on the properties of the soft clay are the increase in plasticity, carbonate content, and salinity and the decrease in sensitivity. There is, therefore, a general improvement in soil properties after treatment, both in terms of total and effective stresses. Key words: electroosmosis, soft sensitive clay, failure envelope, sensitivity, preconsolidation pressure, pH value.

Electroosmotic strengthening of soft sensitive clays

1991 ◽  
Vol 28 (1) ◽  
pp. 62-73 ◽  
Author(s):  
K. Y. Lo ◽  
I. I. Inculet ◽  
K. S. Ho
Keyword(s):  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Strength Increase ◽  
Sample Length ◽  
Voltage Distribution ◽  
Steady Current ◽  
Preconsolidation Pressure ◽  
Sensitive Clay ◽  
Pressure Stress

A comprehensive experimental investigation on the electroosmotic strengthening of soft sensitive clay was performed to assess the effectiveness of the treatment and to study the mechanism of the process. A specially designed electroosmotic cell was developed to prevent gas accumulation near the electrodes, to allow better electrode-soil contact, and to improve the treatment efficiency. This apparatus also enables the monitoring of the generated negative pore-water pressure along the sample length, settlement, voltage distribution, and current variation during treatment. The investigation covered two different types of soil trimmed at different orientations: the vertically and horizontally trimmed overconsolidated Wallaceburg clay and the vertically trimmed slightly overconsolidated soft sensitive Gloucester (Leda) clay. Results of this study showed that the voltage distribution and induced negative pore pressure at equilibrium along the sample are linear with steady current flow across the sample, indicating that the electrode design in the electroosmosis test apparatus is efficient. The electroosmotic consolidation curve is similar to that of the conventional consolidation curve, and the preconsolidation pressure was increased by 51–88% with an applied voltage up to 6 V. The undrained shear strength increased to a maximum of 172%, and the moisture content decreased by 30%. The technique of electrode reversal is employed, and a relatively uniform strength increase between the electrodes is observed. Key words: electroosmosis, electroosmotic cell, soft sensitive clay, negative pore-water pressure, preconsolidation pressure, stress–strain behaviour.

A novel technique of electrical strengthening of soft sensitive clays by dielectrophoresis

1992 ◽  
Vol 29 (4) ◽  
pp. 599-608 ◽  
Author(s):  
K. Y. Lo ◽  
K. S. Ho ◽  
I. I. Inculet
Keyword(s):  
Shear Strength ◽  
Electric Field ◽  
High Voltage ◽  
Alternating Current ◽  
Novel Technique ◽  
Strain Behaviour ◽  
Preconsolidation Pressure ◽  
Electro Osmosis ◽  
Sensitive Clay ◽  
Applied Electric Potential

A novel technique of electrical strengthening of soil by dielectrophoresis was developed. The process employs an alternating current at high voltage, generating a converging electric field towards the electrode by which a net resultant movement of water in the clay mass is produced towards the direction of stronger electric field intensity. Laboratory tests were developed to investigate the mechanism of this process and to explore the possibility of its application in electrical strengthening of soft sensitive clays. The preliminary results of this study showed that the process is effective, and the shear strength of the treated clay (Wallaceburg clay) increased drastically by several times with a reduction of moisture content of approximately 25% at an applied electric potential of 20 kV for 28 days. When compared with electro-osmosis, similar results are obtained in dielectrophoresis, such as the increase in preconsolidation pressure, decrease in sensitivity, and improvement of stress–strain behaviour. It is also shown that the improvement of soil properties can be greatly enhanced by increasing the applied voltage and electrode depth. Key words : dielectrophoresis, alternating current, converging electric field, high-voltage electrode, dielectric constant, electro-osmosis, soft sensitive clay, shear strength, consolidation.

Mechanical and hydraulic behaviour of a soft inorganic clay treated with lime

1996 ◽  
Vol 33 (4) ◽  
pp. 654-669 ◽  
Author(s):  
Jacques Locat ◽  
Hélène Trembaly ◽  
Serge Leroueil
Keyword(s):  
Hydraulic Conductivity ◽  
Curing Time ◽  
Dredged Sediments ◽  
Secondary Minerals ◽  
Clayey Sediment ◽  
Hydraulic Behaviour ◽  
Preconsolidation Pressure ◽  
Order Of Magnitude ◽  
Lime Concentration ◽  
Sorption Potential

A comprehensive series of laboratory tests was conducted on an inorganic clayey sediment in order to predict the mechanical behaviour of dredged sediments used in reclamation projects. The soil used was a Louiseville clay, which was mixed with various quantities of lime (0–10%) and had a varied water content (122–650%). Tests were carried out with special large cells and standard oedometers to look at both the compressibility and the hydraulic conductivity. Once pozzolanic reactions are begun, for a given curing time, a linear relationship between preconsolidation pressure and lime concentration is observed. Compressibility results indicate that it is possible to define a separate compression curve for each lime concentration and curing time. Adding lime will influence the hydraulic conductivity both by flocculation and by the formation of secondary minerals. If only flocculation occurs, an increase in hydraulic conductivity follows. If enough lime is added, the resulting secondary minerals will create major changes in the micropore network and this will decrease the hydraulic conductivity by up to one order of magnitude. The development of a secondary micropore network along with the cementation of large flocs induce significant increases in both the liquid and plastic limits. This results in a significant increase in the water sorption potential and higher Atterberg limits. Key words: dredged sediments, compressibility, hydraulic conductivity, lime, stabilization, microstructure.

Electrical strengthening of clays by dielectrophoresis

1994 ◽  
Vol 31 (2) ◽  
pp. 192-203 ◽  
Author(s):  
K.Y. Lo ◽  
J.Q. Shang ◽  
I.I. Inculet
Keyword(s):  
Shear Strength ◽  
Electric Field ◽  
Soil Improvement ◽  
Nonuniform Electric Field ◽  
Experimental Program ◽  
Effective Polarizability ◽  
Clay Particles ◽  
Shearing Resistance ◽  
Preconsolidation Pressure ◽  
Sensitive Clay

The theory of dielectrophoresis in clay–water–electrolyte systems is developed in this paper. Dielectrophoresis is the motion of particles generated by a nonuniform electric field. The dielectrophoretic forces on clay particles are determined by the effective polarizability and configuration of the nonuniform electric field. In most clay–water–electrolyte systems, including natural clays, the dielectrophoretic forces are directed towards the lower field intensity, determined by the negative polarizability. In the experimental program, an ac voltage of 60 Hz and 15 kV was applied through insulated electrodes on block samples of Leda clay for 28 days. The relationship between the soil undrained shear strength after treatment and the distribution of electric field provides direct experimental support for the theory developed. Under three electrical-field configurations, the overall shear strengths increased up to 44.0%, concurrent with significant reduction of sensitivity. The improvement of soil properties was also reflected as increases of preconsolidation pressure and shearing resistance in terms of effective stresses. The electrochemical reactions associated with electric current were minimized by insulation to the electrodes. Key words : dielectrophoresis, electrokinetics, soil improvement, sensitive clay, shear strength.

Evaluation of preconsolidation pressure and the overconsolidation ratio from piezocone tests of clay deposits in Quebec

2002 ◽  
Vol 39 (1) ◽  
pp. 174-192 ◽  
Author(s):  
Denis Demers ◽  
Serge Leroueil
Keyword(s):  
Mechanical Behaviour ◽  
Laboratory Tests ◽  
Local Data ◽  
Overconsolidation Ratio ◽  
Clay Deposits ◽  
Pressure Profiles ◽  
Preconsolidation Pressure ◽  
Tip Resistance ◽  
Sensitive Clay

The preconsolidation pressure and overconsolidation ratio profiles are the most important factors related to the mechanical behaviour of clay deposits. They are interpreted on the basis of a limited number of laboratory tests, but the near-continuous information provided by the piezocone can allow local data to be extrapolated to an entire site. Numerous methods have been proposed for relating piezocone data to preconsolidation pressure and the overconsolidation ratio, but their validity is still uncertain. In this paper, nine methods are compared on the basis of data collected on 31 sensitive clay sites in Quebec whose preconsolidation pressure profiles are well known. Each method is briefly presented and the most promising are identified. The simplest method, which directly relates preconsolidation pressure to net tip resistance, also appears to be the most effective.Key words: clay, preconsolidation pressure, overconsolidation ratio, piezocone, correlations.

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