scholarly journals Undrained shear strength from piezocone tests

1987 ◽  
Vol 24 (3) ◽  
pp. 392-405 ◽  
Author(s):  
J.-M. Konrad ◽  
K. T. Law
Keyword(s):  
Shear Strength ◽  
Undrained Shear Strength ◽  
Cavity Expansion ◽  
Pore Pressures ◽  
Clayey Silt ◽  
Tip Resistance ◽  
Sensitive Clay ◽  
Rigidity Index ◽  
New Interpretation ◽  
Undrained Shear

With the advent of piezocones — penetrometers measuring both the mechanical resistance and induced pore pressures near the tip during penetration into the soil — a new interpretation of penetrometer test data is possible. This paper presents a review of available interpretation methods for obtaining the undrained shear strength of soft soils, and introduces a new interpretation taking into account measured pore pressures. The undrained shear strength is considered to be solely related to the ultimate cavity expansion pressure, which is one of the components of the tip resistance. The other component is calculated assuming that effective friction is developed at the cone–soil interface.Parametric studies on the parameters required for strength determination based on the proposed method are also presented. Special self-boring pressuremeter tests to obtain relevant values of soil rigidity index, which is a key parameter for cavity expansion modelling, are described. Tests were conducted at three sites having the characteristics of soft sensitive clay, stiff sensitive clay, and clayey silt. The operational undrained strength mobilized during the cone insertion derived from the proposed model is equal to or lower than the CK0U triaxial strength, which depends on soil brittleness. The proposed approach yields results consistent with known soil behaviour at all three sites. Key words: piezocone penetrometer, pressuremeter, excess pore-water pressure, undrained shear strength, rigidity index, in situ tests, laboratory test.

scholarly journals Geotechnical Centrifuge Modelling of Retrogressive Sensitive Clay Landslides

2020 ◽  
Author(s):  
Ray Kennedy ◽  
W. Andy Take ◽  
Gregory A. Siemens
Keyword(s):  
Shear Strength ◽  
Slope Angle ◽  
Physical Modelling ◽  
Failure Surface ◽  
Undrained Shear Strength ◽  
Stability Number ◽  
Surface Stability ◽  
Geotechnical Centrifuge ◽  
Sensitive Clay ◽  
Undrained Shear

Sensitive clay landslides represent a significant geohazard due to their well-known potential for extensive retrogressive failures, on the scale of multiple hectares, which could encompass surrounding communities and infrastructure. Interpretation of retrogression mechanisms is often limited since only forensic investigations are possible. This work presents the results of a physical modelling study to examine retrogressive failures, analysis of each failure episode, and interpretation of the results using published relationships. Five novel centrifuge model tests were conducted under a defined range of undrained shear strength and slope angle conditions. The models are constructed of a sensitive cement-soil mixture that allows for a consistent contractile material with bespoke shear strength. Results indicate the observed retrogression distance correlates with Taylor’s stability number. The addition of a 5-degree slope angle to invoke a static shear stress on the model provoked notably larger retrogression distances. Post-test undrained shear strength measurements quantified softening of the material along the failure surface. Stability analyses on each failure episode captured the observed failure geometry and factor of safety. Results indicate that the geometric parameters of a slope, specifically the slope angle, may be able to explain a component of the scatter for relating the Taylor’s stability number with retrogression distances.

The September 5, 1987, landslide on the La Grande River, James Bay, Quebec, Canada

1991 ◽  
Vol 28 (2) ◽  
pp. 263-275 ◽  
Author(s):  
Guy Lefebvre ◽  
Peter Rosenberg ◽  
Jean Paquette ◽  
J. G. Lavallée
Keyword(s):  
Shear Strength ◽  
Ground Surface ◽  
Bank Erosion ◽  
Undrained Shear Strength ◽  
Silty Clay ◽  
James Bay ◽  
River Bank ◽  
River Erosion ◽  
Sensitive Clay ◽  
Undrained Shear

The September 5, 1987, landslide at kilometre 82.5 on La Grande River affected a slope about 60 m high inclined at about 35°. The site had been identified as presenting high risks of a major landslide and had been under observation for several years. The conditions existing before the landslide are relatively well documented from a deep boring put down in 1975 at the slide location and from prior observations and photographs of the river bank erosion. The overburden deposit, sand at the ground surface changing to a silty clay at depth, was normally consolidated but affected by a strong underdrainage. Stability analyses confirm the strong underdrainage deduced from the 1975 piezometric reading. The slide retrogressed 290 m from the river on a surface inclined at 6°. The location of the retrogression surface appears related to the undrained shear strength profile. Key words: landslide, earthflow, sensitive clay, groundwater, river erosion, slope stability.

scholarly journals Modeling of large-deformation behaviour of marine sensitive clays and its application to submarine slope stability analysis

2016 ◽  
Vol 53 (7) ◽  
pp. 1138-1155 ◽  
Author(s):  
Rajib Dey ◽  
Bipul Hawlader ◽  
Ryan Phillips ◽  
Kenichi Soga
Keyword(s):  
Shear Strength ◽  
Shear Band ◽  
Large Scale ◽  
Critical Length ◽  
Undrained Shear Strength ◽  
Model Parameters ◽  
Submarine Landslides ◽  
Weakened Zone ◽  
Sensitive Clay ◽  
Undrained Shear

Post-slide investigations suggest that many large-scale submarine landslides occur through marine sensitive clay layers. A nonlinear mathematical model for post-peak degradation of undrained shear strength of sensitive clay is proposed based on experimental results. A method for estimation of model parameters is presented. Incorporating the model, an analytical solution is developed to examine possible mechanisms of large-scale submarine landslides. Analyses are performed for mild infinite slopes where the failure initiates from a “fully weakened zone” of soil having undrained shear strength lower than the shear stress acting parallel to the slope. The driving force, in excess of resistance, generated from the fully weakened zone is then transferred to the surrounding soil elements resulting in shear band formation due to strain-softening behaviour of sensitive clays. When the length of the fully weakened zone is greater than a critical length, catastrophic shear band propagation (self-driven without any additional external force) occurs, which could result in large-scale offshore landslides. A simple design chart is developed to calculate the critical length. Compared with a 2005 study by Puzrin and Germanovich based on a linear post-peak shear strength degradation model, the present study gives a conservative estimation of critical length for catastrophic shear band propagation.

Excavation d'argile sensible au site de l'aménagement hydroélectrique LG-2

1985 ◽  
Vol 22 (2) ◽  
pp. 186-194
Author(s):  
J. J. Paré ◽  
J. G. Lavallée
Keyword(s):  
Shear Strength ◽  
Undrained Shear Strength ◽  
Strength Analysis ◽  
Site Conditions ◽  
Embankment Dams ◽  
Clay Deposits ◽  
Undrained Strength ◽  
Sensitive Clay ◽  
Tailrace Tunnel ◽  
Undrained Shear

This paper is a review of the design adopted to establish the slopes for deep clay excavations (3 000 000 m3) made for founding rockfill embankment dams on bedrock and for clearing the tailrace tunnel portals at the LG-2 hydroelectric site. The design and excavation of soft sensitive clay deposits down to 22 m had been undertaken at a period of time when very few precedents were existing (1974). During the excavation works, only a few minor slides occurred, indicating that the design approach, using undrained shear strength analysis, was appropriate for the site conditions. Methods of excavation and hauling of material to disposal areas are also described. Key words: slope, sensitive clay, undrained strength analysis, safety factor, excavation method, behaviour.

scholarly journals Determination of the Undrained Shear Strength of Sensitive Clay Using Some Laboratory Soil Data

2021 ◽  
Vol 8 (1) ◽  
pp. 14
Author(s):  
Tahar Ayadat
Keyword(s):  
Shear Strength ◽  
Soil Properties ◽  
Bearing Capacity ◽  
Fine Particles ◽  
Undrained Shear Strength ◽  
Clay Layer ◽  
In Situ Tests ◽  
Sensitive Clay ◽  
Undrained Shear

The undrained shear strength is a paramount parameter in determining the consistency and the ultimate bearing capacity of a clay layer. This resistance can be determined by in-situ tests, such as the field vane test or by laboratory tests, including the portable vane test, the triaxial, the simple compression test, and the consistency penetrometer test (i.e. the Swedish cone). However, the field vane test and the Swedish cone are the most commonly test used by geotechnical experts. In this paper, relationships between the field undrained shear strength of sensitive clay and some laboratory soil properties were developed. The soil properties consisted of the percentage of fine particles (less than 2 µm), the moisture content and the Atterberg limits. Furthermore, a correlation was proposed associating between the undrained shear strength of sensitive clay as obtained by the field vane test and the laboratory cone penetration test (Swedish cone). In addition, some applications of the proposed correlation on some geotechnical problems were included, such as the determination of the consistency and the bearing capacity of a clay layer. Comparison of the results of the developed correlations with the experimental results of the present investigation and the results reported in the literature show acceptable agreement.

Interpretation of piezocone penetration and dissipation tests in sensitive Leda clay at Gloucester test site

2018 ◽  
Vol 55 (12) ◽  
pp. 1781-1794 ◽  
Author(s):  
Shehab S. Agaiby ◽  
Paul W. Mayne
Keyword(s):  
Shear Strength ◽  
Water Pressure ◽  
Triaxial Compression ◽  
Test Site ◽  
Undrained Shear Strength ◽  
Text Input ◽  
Piezocone Penetration Test ◽  
Leda Clay ◽  
Rigidity Index ◽  
Undrained Shear

A modified piezocone penetration test (CPTu) analytical solution based on spherical cavity expansion and critical state soil mechanics (SCE–CSSM) is employed for assessing yield stress, undrained shear strength, and flow parameters in sensitive Leda clay at the Gloucester test site. For sensitive and structured clays, the formulation relies on the mobilized effective stress friction angle ([Formula: see text]) defined at two parts of the stress–strain curve: (i) peak stress ([Formula: see text]) and (ii) maximum obliquity ([Formula: see text]). Input parameters for assessing the overconsolidation ratio ([Formula: see text], where [Formula: see text] is preconsolidation stress and [Formula: see text] is current effective vertical stress) from CPTu results include: undrained rigidity index (IR = G/su, where G is shear modulus and su is undrained shear strength), plastic volumetric strain potential (Λ = 1 – (Cs/Cc), where Cs is swelling index and Cc is virgin compression index), and effective friction angles ([Formula: see text] and [Formula: see text]). A direct CPTu means of assessing the undrained rigidity index in a reliable manner is also developed that gives the Nkt cone factor and matches profiles of undrained shear strength from triaxial compression tests (suTC). The modified solution is also implemented on two additional sites: a sensitive-quick clay in Norway and structured varved clay from New England. Interpretations of the coefficient of consolidation and permeability from pore-water pressure dissipation tests at Gloucester are evaluated using the SCE–CSSM formulation and shown to be comparable with independent laboratory and field tests.

Strain-rate effects in pressuremeter testing using a cuboidal shear device: experiments and modeling

1998 ◽  
Vol 35 (1) ◽  
pp. 27-42 ◽  
Author(s):  
Dayakar Penumadu ◽  
Arumugam Skandarajah ◽  
Jean-Lou Chameau
Keyword(s):  
Shear Strength ◽  
Strain Rate ◽  
Strain Path ◽  
Undrained Shear Strength ◽  
Cavity Expansion ◽  
Lateral Strain ◽  
High Water Content ◽  
Single Element ◽  
Stress Strain ◽  
Undrained Shear

The objective of the present research was to study the effect of rate of probe expansion in pressuremeter testing for cohesive soil. Emphasis in this paper was given to quantifying and modeling the effect of strain rate on the undrained shear strength. The strain path followed by an element of clay adjacent to the expanding probe was simulated using an automated flexible boundary cuboidal shear device (CSD) typically up to a magnitude of strain level of 10%. Two types of soil (kaolin, kaolin-silica mix) were used consistently for all the testing. Repeatable cubical cohesive specimens were obtained from a high water content slurry consolidation technique. K0 consolidation was performed by using a constant vertical stress - zero lateral strain boundary condition using a closed-loop pneumatic system. A series of strain-controlled tests with increasing strain rates from 0.01 to 5%/min was performed under undrained conditions. The effects of increase of strain rate on shear stress - strain behavior and undrained shear strength were quantified. A numerical model based on cylindrical cavity expansion theory which accounts for higher strain rate and its variation with radial distance from an expanding probe membrane was calibrated using the single-element CSD test data.Key words: strain rate, pressuremeter, stress-strain, shear strength, strain path, cavity expansion.

Testing of drivability of concrete piles and disturbance to sensitive clay

1976 ◽  
Vol 13 (2) ◽  
pp. 139-160 ◽  
Author(s):  
Bengt H. Fellenius ◽  
Laval Samson
Keyword(s):  
Shear Strength ◽  
Pile Group ◽  
Undrained Shear Strength ◽  
Strength Reduction ◽  
Glacial Till ◽  
Pile Driving ◽  
Shaft Resistance ◽  
Concrete Piles ◽  
Pore Pressures ◽  
Sensitive Clay

The results reported are of an investigation of a group of thirteen 12 in. (30 cm) diameter precast concrete piles driven through 60 ft (18 m) of sensitive marine clay followed by 10 ft (3 m) of silt and sand and 13 ft (4 m) of very dense silt to end bearing in glacial till. The purpose of the test is to study the drivability of the piles through very dense soil and to measure the disturbance caused to the sensitive clay by the driving of displacement piles. Following a literature review, the paper presents the soil conditions at the site and the testing program. The test results are discussed and experience gained from the follow-up of the driving of 520 piles at the site is presented.Visual observations during pile driving, and analysis of driving records, show that a high pile quality is necessary at the site. The large driving resistance encountered in the very dense silt (150 to 300 blows/ft) would prevent low quality piles from reaching the competent glacial till and developing the needed bearing capacity.Pile loading tests showed the piles to have an ultimate bearing capacity exceeding 450 tons (4.0 MN). It was established that the shaft resistance in the clay during test loading was between 100 and 125% of the undrained shear strength of the clay as measured by field vane testing. In comparison, an uplift test to failure showed that the uplift shaft resistance along the pile in the clay was only 60% of the undrained shear strength of the clay.The pile driving developed large pore pressures in the clay which exceeded the effective overburden stresses. The excess pore pressures dissipated over a period of slightly more than 3 months. Vane testing within the pile group immediately after driving showed that a shear strength reduction of about 15% was caused by the piles. At a distance of 2 ft (0.6 m) outside the pile group, no strength reduction was found. The reduction within the group was gradually regained during the dissipation of the induced pore pressures. Laboratory testing on clay samples obtained within the pile group 75 days after pile driving showed a smaller value of the preconsolidation pressure of the clay, but no change in the compression indices.

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