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.

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.

Behaviour of a sensitive clay during pile driving

1981 ◽  
Vol 18 (1) ◽  
pp. 67-85 ◽  
Author(s):  
M. Roy ◽  
R. Blanchet ◽  
F. Tavenas ◽  
P. La Rochelle
Keyword(s):  
Scale Effects ◽  
Test Site ◽  
Penetration Resistance ◽  
Pile Driving ◽  
A Value ◽  
Pore Pressures ◽  
Tip Resistance ◽  
Average Unit ◽  
Sensitive Clay ◽  
Static Zone

A full scale investigation with six instrumented test piles has been carried out on the Saint-Alban test site in order to study the behaviour of friction piles in soft sensitive soils. The first part of this investigation, reported in this paper, deals essentially with the effects of pile driving on the induced pore pressures and their dissipation and on the disturbance of the clay around the pile.It is shown that the induced pore pressures at the pile tip ΔuT, and at the pile surface Δus, correspond to 1.6σvo and 0.8σvo respectively. If the failure pattern developed during driving is interpreted by means of the theories of expansion of cavities, it is shown that the induced pore pressures calculated at the pile–soil contact agree well with the measured values; these pore pressures are fully dissipated after 600 h.Immediately after driving, a decrease in the undrained shear strength varying between 0 and 30% was observed in a zone of 3 diameters around the pile. The strength in that zone was nearly fully recovered after the pore pressures had dissipated.The tip resistance measured during driving was quite in excess of the static zone penetration resistance qc, indicating possible scale effects. The average unit skin friction was observed to decrease from a value in the order of cu to about 0.10σvo′ and to be directly related to the pore pressures, i.e., to the effective stresses in the clay around the pile.

Pulling capacity of concrete cast in situ bored piles

1970 ◽  
Vol 7 (4) ◽  
pp. 482-493 ◽  
Author(s):  
V. A. Sowa
Keyword(s):  
Shear Strength ◽  
Sandy Soil ◽  
Empirical Relationship ◽  
Sandy Soils ◽  
Undrained Shear Strength ◽  
Cohesive Soils ◽  
Concrete Piles ◽  
Bored Piles ◽  
Undrained Shear

The pulling capacity of cylindrical concrete piles cast in situ in bored holes is examined for piles constructed in sandy or cohesive soils. On the basis of the data presented, it is concluded that the pulling capacity of these piles in cohesive soils can be estimated approximately, while the pulling capacity of piles in sandy soil is considerably more difficult to estimate. Estimating the pulling capacity of piles in cohesive soils is based on an empirical relationship between soil adhesion and the undrained shear strength. A possible explanation for the difficulty in estimating the pulling capacity of piles in sandy soils is suggested.

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.

The adhesion factor: applications and limitations

1992 ◽  
Vol 29 (2) ◽  
pp. 322-326 ◽  
Author(s):  
J. A. Sladen
Keyword(s):  
Shear Strength ◽  
Effective Stress ◽  
Clay Soil ◽  
Horizontal Stress ◽  
Undrained Shear Strength ◽  
Shaft Resistance ◽  
Soil Shear Strength ◽  
Shaft Friction ◽  
Adhesion Factor ◽  
Undrained Shear

The conventional concept of an empirical adhesion factor that relates undrained shear strength of a clay soil to ultimate shaft friction can be shown to have a theoretical basis for vertical piles, even though conditions at the interface are fully drained. The adhesion factor approach and the effective stress approach for shaft resistance are in fact consistent. This is because horizontal stress at the interface and undrained shear strength are both influenced by the same factors. The general implication of the conventional approach that the mechanism is undrained and that the mobilized shear resistance between a structure and clay is a fraction of the undrained soil shear strength is, however, incorrect. This concept can lead to significant errors if it is extrapolated to situations, for which the empirical data were not derived, such as beneath gravity structures on clay foundations, where effective stress normal to the interface is independent of soil undrained shear strength. Key words : piles, clay, adhesion, shaft friction.

Effects of Pile Driving in Clays

1972 ◽  
Vol 9 (1) ◽  
pp. 81-88 ◽  
Author(s):  
Kaare Flaate
Keyword(s):  
Shear Strength ◽  
Undrained Shear Strength ◽  
Pile Driving ◽  
Surface Strength ◽  
Deformation Properties ◽  
Average Water ◽  
Strength And Deformation ◽  
Pile Type ◽  
Timber Piles ◽  
Undrained Shear

This study summarizes the information given in the literature as well as observations made by the author. The effects of driving piles on remolding, stresses, and properties of the clay are considered. It is concluded that timber piles cause strong remolding of a zone extending to 10–15 cm from the pile surface. Strength and deformation properties will undergo changes beyond this zone as well. Pile type, pile density, soil properties, and driving conditions influence the results. There seems to be very small changes in the average water content, since the reduction adjacent to the pile is counter-balanced by an increase between the piles. The undrained shear strength adjacent to the pile is in one case found to be much higher than the skin friction at failure.

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