scholarly journals Effects of sampling disturbance in geotechnical design

2019 ◽  
Vol 56 (2) ◽  
pp. 275-289 ◽  
Author(s):  
Guan Tor Lim ◽  
Jubert Pineda ◽  
Nathalie Boukpeti ◽  
J. Antonio H. Carraro ◽  
Andy Fourie
Keyword(s):  
Soil Mechanics ◽  
Soft Clay ◽  
Excess Pore Pressure ◽  
Soil Parameters ◽  
Test Results ◽  
Sample Quality ◽  
Laboratory Test Results ◽  
Geotechnical Design ◽  
Pore Pressure Response ◽  
Shallow Footing

This paper describes an experimental study of the effects of sampling disturbance in an Australian natural soft clay and the consequences of different sample quality on the representativeness of soil parameters used in geotechnical designs. The paper is divided into three sections. Laboratory test results obtained from specimens retrieved using three different tube samplers as well as the Sherbrooke (block) sampler are first described. Then, the sample quality assessment, using available indices proposed for soft soils, is presented. It is shown that sample quality varies with the stress paths and boundary conditions applied in laboratory tests. Finally, mechanical soil properties derived from specimens retrieved using the different samplers are used in the prediction of two classical problems in soil mechanics: the settlement and excess pore pressure response underneath an embankment as well as the settlement and bearing capacity of a shallow footing. These two examples are used here to highlight the consequences of poor sampling in practice.

Deformability and consolidation characteristics of soft Bangkok clay using screw plate tests

1990 ◽  
Vol 27 (5) ◽  
pp. 531-545 ◽  
Author(s):  
D. T. Bergado ◽  
K. C. Chong ◽  
P. A. M. Daria ◽  
M. C. Alfaro
Keyword(s):  
Graphical Method ◽  
Soft Clay ◽  
Stress Path ◽  
Soil Parameters ◽  
Test Results ◽  
Coefficient Of Consolidation ◽  
Plate Test ◽  
Settlement Time ◽  
Oedometer Tests ◽  
Test Embankment

This study centred on the performance of the screw plate test (SPLT) to determine the deformability and consolidation characteristics of soft Bangkok clay. For comparison, a series of stress-path-controlled triaxial consolidation tests (tri) were carried out on good quality samples of Bangkok clay taken from the same testing sites and imposed with the same loading conditions as the screw plate tests. Undrained and drained moduli and coefficients of consolidation were obtained from the stress-path-controlled triaxial consolidation tests and were compared with the corresponding values of the screw plate test. In addition, the ultimate bearing capacity was derived from the pressure–deformation relationships of the screw plate test results. A graphical method was used to compute the coefficient of consolidation from the screw plate tests and from stress-path-controlled triaxial consolidation test results. The compressibility data were also obtained from conventional oedometer tests (oed). Both cv (SPLT)/cv (tri) and cv (SPLT)/cv(oed) ratios compared favorably with the cv (field)/cv (laboratory) ratio obtained from past investigations. The data from pressure–settlement–time relationships of the screw plate tests were used to successfully predict values that compared favorably with the measured values at each stress level. The pressure–deformation–time relationship from stress-path-controlled triaxial consolidation tests were also evaluated, and they indicated behaviour similar to that of the screw plate test results. Soil parameters obtained from screw plate tests were subsequently used to predict the settlement of two test embankments, giving fairly close agreement with the observed values. Key words: soft clay, settlement, deformation, consolidation, screw plate test, triaxial test, embankment, prediction, stress path.

Effect of cementation on the small-strain parameters of sands

2001 ◽  
Vol 38 (1) ◽  
pp. 191-199 ◽  
Author(s):  
A L Fernandez ◽  
J C Santamarina
Keyword(s):  
Laboratory Test ◽  
Experimental Studies ◽  
Small Strain ◽  
Test Results ◽  
Loading History ◽  
Viscous Losses ◽  
Laboratory Test Results ◽  
Geotechnical Design ◽  
Selection Of

Natural cementation affects the properties of soils, the interpretation of in situ and laboratory test results, and the selection of criteria for geotechnical design. In this paper, published experimental studies are reviewed, a microscale analysis is presented of the effect of cementation on small-strain stiffness for distinct stress-cementation histories, and the effect of cementation on small-strain velocity and damping is experimentally studied. Observations include the prevailing effects of cementation over effective stress, the coexistence of frictional and viscous losses, and the effects of decementation when the medium is unloaded from the level of confinement prevailing during cementation.Key words: wave velocity, seismic response, stiffness, damping, sampling effects, loading history.

ESTIMATING LOAD-DISPLACEMENT BEHAVIOR OF SOFT CLAYS

2016 ◽  
Vol 3 (2) ◽  
Author(s):  
Murat Tonaroglu ◽  
Cem Akguner ◽  
Murat E. Selcuk
Keyword(s):  
Laboratory Test ◽  
Field Measurements ◽  
Soil Parameters ◽  
Model Parameters ◽  
Time Behavior ◽  
Test Results ◽  
Engineering Structures ◽  
Laboratory Test Results ◽  
Study Laboratory

Prediction of long term settlement of soft soils below civil engineering structures is an important issue in geotechnical engineering. The data from laboratory consolidation tests are used to estimate the ultimate settlement and problems arise in predicting settlement-time behavior in the field. In order to overcome this difficulty some empirical models or adjustments have been proposed based on field settlement measurements, even if they are available at least for the early stages of loading. In this study, laboratory test results and field settlement measurements obtained for the long term settlement of clayey layers underlying the Alibey Dam in Istanbul, Turkey are used in conjunction with a model proposed by Edil and Mochtar (1984) for peat-like soils. The soil parameters of the proposed model have independently been obtained using both laboratory test data and field measurements, and model predictions are compared with actual recorded settlements. It is observed that the field measurements could be predicted more closely if the model parameters are obtained from field measurements, but predictions based on laboratory consolidation and creep test results also provide satisfactory results following the initial stages of loading.

scholarly journals Evaluasi Daya Dukung Tanah Lunak Hasil Stabilisasi Kimia dengan Terra Firma di Daerah Gedebage, Kota Bandung, Provinsi Jawa Barat. (Hal. 93-109)

2019 ◽  
Vol 5 (4) ◽  
pp. 99
Author(s):  
Bayu Arifianto ◽  
Benny Moestofa
Keyword(s):  
Bearing Capacity ◽  
Clay Soil ◽  
Soft Clay ◽  
Physical And Mechanical Properties ◽  
High Sensitivity ◽  
Laboratory Scale ◽  
Test Results ◽  
Terra Firma ◽  
Laboratory Test Results ◽  
Scale Test

ABSTRAK Tanah lempung lunak adalah salah satu jenis tanah dasar yang sering menyebabkan masalah dalam berbagai jenis konstruksi karena daya dukungnya rendah dan kepekaan terhadap perubahan kadar air cukup tinggi. Oleh karena itu, perlu dilakukan perbaikan tanah dasar menggunakan bahan kimia Terra Firma untuk meningkatkan daya dukung tanah dasarnya. Penelitian ini dilaksanakan dengan pengambilan sampel dari Proyek Summarecon di Gedebage, Kota Bandung, termasuk pengujian skala laboratorium, untuk menentukan sifat fisik dan mekanik tanah lempung lunak. Uji skala laboratorium telah dilaksanakan pada berbagai variasi campuran tanah dengan komposisi Terra Firma 3%, 6%, dan 9%. Berdasarkan hasil uji laboratorium diperoleh nilai CBR tanah dasar sebesar 2,7% dan UCS 2,02 kg/cm², sedangkan hasil pengujian menunjukkan bahwa campuran Terra Firma yang paling efektif adalah 6% dengan waktu pemeraman selama 21 hari, dimana nilai CBR yang diperoleh sebesar 37,28% dan UCS 9,66 kg/cm². Oleh karena itu dapat disimpulkan bahwa penggunaan stabilisasi kimia Terra Firma dapat meningkatkan daya dukung tanah lempung lunak hingga 14 kali. Kata kunci: tanah lempung lunak, daya dukung, stabilisasi kimia, Terra Firma. ABSTRACT Soft clay soil is one of the basic types of soil that often causes problems in any kinds of construction due to its low bearing capacity and high sensitivity to changes in moisture content. Therefore, the soil needs to be repaired by applying Terra Firma chemicals to increase the bearing capacity of the soil. This research is conducted by taking soil samples from the Summarecon Gedebage Project area, Bandung City, and was conducted laboratory scale testing, to determine the physical and mechanical properties of soft clay soil. The laboratory scale test was conducted with various variations of ground mixture with Terra Firma 3%, 6%, and 9%. Based on laboratory test results it is found that the base soil CBR value is 2.7% and UCS 2.02 kg/cm², while the applied Terra Firma chemicals comparison result shows that the 6% mixture is the most effective with 21 days curing time, CBR value of 37.28% and UCS 9.66 kg/cm². Therefore it can be concluded that the use of Terra Firma chemicals can increase the bearing capacity of soft clay soil up to 14 times. Keywords: soft clay soil, bearing capacity, chemical stabilization, Terra Firma.

Influence of state and compressibility on liquefied strength of sands

2013 ◽  
Vol 50 (10) ◽  
pp. 1067-1076 ◽  
Author(s):  
Abouzar Sadrekarimi
Keyword(s):  
Shear Strength ◽  
Critical State ◽  
Soil Mechanics ◽  
State Parameter ◽  
Test Results ◽  
Confining Stress ◽  
Stress Variation ◽  
Laboratory Test Results ◽  
Flow Failure ◽  
Underlying Mechanisms

Critical-state soil mechanics is a useful framework to understand sand behavior. In this paper, a relationship is developed for estimating undrained critical shear strength of sands based on the critical-state framework. The application of this relationship is demonstrated by comparison with laboratory test results and sand liquefied strength from field liquefaction flow failure case histories. Using this relationship, the effects of effective stress variation and density on undrained critical shear strength are studied for different combinations of critical-state line parameters corresponding to several reference sands. The parametric study indicates that depending on sand void ratio, undrained critical shear strength may increase, remain the same or decrease as sand shearing–compressibility (represented by the slope of the critical-state line) increases. The underlying mechanisms of field failures in dense sands and reverse behavior of compressible sands are explained through this relationship. It is suggested that the critical-state parameter alone is insufficient for describing the behavior of liquefiable sands and sand shearing–compressibility should be also taken into account for estimating undrained shear strength corresponding to the changes in density and effective confining stress.

Experimental Research on Determining the Geotechnical Parameters with CPTU Methods

2011 ◽  
Vol 250-253 ◽  
pp. 1798-1803
Author(s):  
Yan Yong An ◽  
Bao Tian Wang
Keyword(s):  
Soft Clay ◽  
Cohesive Soil ◽  
Sensor Technology ◽  
Soil Parameters ◽  
Cone Penetration ◽  
Test Technique ◽  
Geotechnical Parameters ◽  
Cone Tip Resistance ◽  
Laboratory Test Results ◽  
Tip Resistance

Cone penetration test is a fast and efficient in-situ test technique. With the development of sensor technology and the use of new probes, such test is employed in more fields and reveals more soil parameters. Based on the advanced CPTU equipment, porewater pressure dissipation processes were measured at different depths, dissipation characteristics of the sandy soil and cohesive soil were analyzed respectively; Then, consolidation and permeability coefficients of the cohesive soil were calculated, the results are close to the laboratory test results. Undrained shear strength of soft clay were determined use theoretical and empirical methods, calculation accuracy of these methods were analyzed and the results show that the total cone tip resistance method is in good consistence with the measured values. CPTU is able to provide plenty of geotechnical parameters; therefore, more experience of regional tests should be drawn so as to produce more economic and technical benefit in the future.

Consequences of sample disturbance when predicting long-term settlements in soft clay

2016 ◽  
Vol 53 (12) ◽  
pp. 1965-1977 ◽  
Author(s):  
Mats Karlsson ◽  
Arnfinn Emdal ◽  
Jelke Dijkstra
Keyword(s):  
Constitutive Model ◽  
Soft Clay ◽  
Laboratory Data ◽  
Engineering Properties ◽  
Model Parameters ◽  
Sample Quality ◽  
Laboratory Test Results ◽  
Lateral Displacements ◽  
Sample Disturbance

An approach for assessing the effects of sample quality is presented. Soil samples were taken using a 50 mm Swedish STII piston sampler and the Norwegian University of Science and Technology (NTNU) mini-block sampler from a soft clay test site. Differences in laboratory test results are identified for several stress paths, assisted by simulations made using an advanced constitutive model. Hitherto such comparisons have focused on differences in basic engineering properties such as strength and stiffness. The effect of choosing alternative model parameters from piston and block samples is demonstrated through the analysis of the long-term settlement of an embankment. The simulations show that substantially larger settlements and lateral displacements are predicted using parameters obtained from the piston samples. Furthermore, the magnitude of the differences is larger than expected. This demonstrates that for this application, relatively small differences in the assessed sample quality, using traditional laboratory data interpretation methods, are amplified when applied to a prototype boundary value problem. It is suggested that a little more care in sampling and testing can result in large cost savings as a result of the more reliable model parameters that can be extracted, particularly when the improved sampling is combined with the use of an advanced constitutive model.

Stress Path Tests on 100 mm Diameter Samples

1986 ◽  
Vol 2 (1) ◽  
pp. 133-137
Author(s):  
J. H. Atkinson ◽  
D. B. Clinton
Keyword(s):  
Stress Path ◽  
Triaxial Tests ◽  
Test Results ◽  
Design Problems ◽  
Strain Behaviour ◽  
Engineering Design Problems ◽  
Geotechnical Design ◽  
Pore Pressure Response ◽  
The City ◽  
Test Stress

AbstractThe use of stress path tests is discussed in relation to geotechnical design, and a description is given of the triaxial test stress path apparatus developed at The City University.Test results are presented from a series of triaxial tests following stress paths commonly encountered in engineering design problems. These are compared with the results of conventional triaxial tests.The stress-strain behaviour and pore pressure response of soil are shown to be very much dependent on the stress path followed, and the advantages of using stress-controlled loading in triaxial tests is demonstrated.

scholarly journals A method of estimating excess pore pressures beneath embankments on sensitive clays

1979 ◽  
Vol 16 (4) ◽  
pp. 691-702 ◽  
Author(s):  
K. T. Law ◽  
M. Bozozuk
Keyword(s):  
Pore Pressure ◽  
Plane Strain ◽  
Strain Curve ◽  
Elastic Response ◽  
Test Results ◽  
Pore Pressures ◽  
Laboratory Test Results ◽  
Pore Pressure Response ◽  
Excess Pore Pressures ◽  
Excess Pore

A laboratory testing program for predicting undrained excess pore pressures beneath embankments constructed on sensitive clays is reported. A study of the pore pressure response, based on Henkel's equation applied to triaxial and plane strain tests performed on marine clay from South Gloucester, Ontario, provides a basis for comparing behaviour under conditions of axisymmetry and plane strain. Comparison shows that (1) pore pressure is smaller in plane strain than in axisymmetric conditions; (2) a below-elastic response prevails at the prepeak stage of the stress–strain curve; and (3) there is an elastic response at the peak.Finite element and modified elastic methods are developed for estimating undrained excess pore-water pressures from laboratory test results. The estimated values are used to evaluate the effect of consolidation under the center of an embankment during construction. The procedure is illustrated with case records.

scholarly journals Evaluation of sample quality from different sampling methods in Finnish soft sensitive clays

2019 ◽  
Vol 56 (8) ◽  
pp. 1154-1168 ◽  
Author(s):  
Bruno Di Buò ◽  
Juha Selänpää ◽  
Tim Tapani Länsivaara ◽  
Marco D’Ignazio
Keyword(s):  
Storage Time ◽  
Soft Clay ◽  
Test Results ◽  
Geotechnical Parameters ◽  
Sample Quality ◽  
Constant Rate ◽  
And Performance

The determination of reliable geotechnical parameters from laboratory testing is highly dependent on sample quality. Over the past decades, undisturbed sampling of soft sensitive clays has been performed using various apparatuses and procedures. This paper outlines details of the design and performance of a new Laval-type tube sampler employed for the investigation of five soft clay sites located in Finland. The investigation was conducted using the new tube sampler and two different piston samplers. The sample quality was evaluated based on the recompression volume during reconsolidation to the in situ effective stress in constant-rate-of-strain oedometer tests. Test results show that tube samples are generally characterized by higher quality, especially in low-plasticity clays. In particular, the quality of piston samples is highly affected by the apparatus condition and sampling operations. Furthermore, the influence of storage time on tube samples was investigated. To guarantee a proper confinement, and thus reduce swelling, a pressurized system was applied to the tube samples obtained in two soft clay sites. Results demonstrate that the sample quality is not significantly affected by storage time as long as the soil is properly stored in the tube.

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