3483
Application of The Tangent Modulus Method in Nonlinear Settlement Analysis of
Sand Foundation
Application de la méthode du module tangent dans le calcul du tassement non-linéaire de
fondations sur sol sableux
Yang G.-H.
1, 2, 4
, Luo Y.-D.,
2, 3
, Zhang Y.-C.
1,4
, Wang E.-Q.
1,4
1.Guangdong Research Institute of Water Resources and Hydropower, Guangzhou 510610, China; 2. School of Civil and
Architectural Engineering, Wuhan University, Wuhan 430072, China; 3. Shenzhen Geotechnical Investigation &
Surveying Institute Co. Ltd., Shenzhen
，
518028, China
；
4. The Geotechnical Engineering Technology Center of
Guangdong Province, Guangzhou 510610, China
ABSTRACT: Foundation settlement computation method is always a hot and difficult issue in geotechnical engineering for the
difficulty in which soil parameters obtained from laboratory test are quite different from undisturbed soil in the field. Especially for
sand foundation and stiff clay foundation with strong structure, settlement calculating with laboratory test parameters makes distinct
error from actual situation. The tangent modulus method, based on calculation parameters determined from in-situ plate loading test,
can overcome this shortcoming, and can be used in analyzing nonlinear foundation settlement. This method makes a new progress in
foundation settlement computation. In this paper, systematic geotechnical test data from Texas A&M University Riverside Campus
are utilized to test the hyperbola model of soil and the tangent modulus method. Then, methods for soil parameter determination in
different depth are studied through such simple in-situ tests such as pressuremeter test and cone penetration test, and these methods
are verified through plate loading test with different size. The analysis results prove that the tangent modulus method has better
accuracy of nonlinear settlement computation. Also, it is feasible to obtain the computation parameters for the tangent modulus
method from some simple in-situ tests, which provides an easier way in determining parameters of the tangent modulus method.
RÉSUMÉ : Le calcul de tassement des fondations est toujours un problème difficile dans les études géotechniques, et la difficulté
réside dans la différence très grande entre les paramètres géotechniques obtenus à partir d’essais de laboratoire et ceux obtenus à
partir d’essais in-situ, en particulier pour les fondations sur sol sableux et les fondations sur argile raide surconsolidée. L'erreur entre
les résultats du calcul de tassement basés sur les paramètres issus d’essais de laboratoire et la valeur réelle du tassement peut être très
grande. La méthode du module tangent, basée sur le calcul de paramètres déterminés à partir d’essais de plaque, permet de
s’affranchir de ce défaut, et peut être utilisée dans une analyse non-linéaire du tassement des fondations. Cette méthode représente un
nouveau progrès dans le calcul du tassement des fondations. Dans cet article, on a utilisé les données d’essais géotechniques
systématiques réalisés au Campus Riverside de l’Université A & M au Texas pour valider un modèle hyperbolique de comportement
du sol et la méthode du module tangent. Puis on a déterminé des méthodes de calcul des paramètres géotechniques à différentes
profondeurs à partir d’essais in-situ simples comme l’essai pressiométrique ou le CPT, et on a validé ces méthodes au moyen de
résultats d’essais de chargement de fondations superficielle (plaques de différentes tailles). Les résultats montrent que la méthode de
module tangent utilisé pour le calcul de tassement non linéaire de la fondation a une meilleure précision. Egalement, il est possible
d’obtenir les paramètres de calcul de la méthode au module tangent à partir d’essais in-situ comme l’essai pressiométrique ou le CPT.
KEYWORDS: foundation settlement; tangent modulus method; in-situ test; nonlinear; sandy soil subgrade
1 INTRODUCTION
Due to the complexity of the geomaterial, the calculation
of foundation deformation is not accurate, which can be
specifically attributed to the unreasonable calculation method
and less accurate value of geotechnical parameters. Due to the
disturbance of undisturbed soil in the sampling and sample
making preparation process, the foundation deformation
parameters accessed by the laboratory test will be seriously
distorted. Therefore, the development of settlement deformation
calculation method based on the in-situ tests has practical
significance on the improvement of accuracy of the ground
deformation calculation. As to sand foundation, due to the sand-
sampling difficulties, currently the international recognized way
- Schmertmann semi-empirical method is based on the
experience of cone penetration test to determine the deformation
modulus of the sand, using the layer-wise summation method to
calculate foundation settlement
[1]
. The existing methods are
difficult to fully calculate the nonlinear settlement of the
foundation. Based on plate loading test, Yang Guanghua
[2~6]
proposed that the tangent modulus method can better solve the
problem of the accuracy of the foundation settlement
calculation. However, as parameters are derived from the plate
loading test which has high cost and can not apply to deep soil.
Therefore, to explore other simple tests instead of in-situ plate
loading test to determine the required parameters is very
important. This paper
[7]
discusses how to use the pressuremeter
test to determine the required parameters.
American scholar Briaud JL, Gibbens R M., et, al
[8]
have
carried out the plate loading test with five different sizes’ plates,
static cone penetration test, pressuremeter test and other
systematic soil tests on the sand foundation in Riverside
Campus, Texas A & M University. The shape of plates are
square and the sizes are 1m, 1.5m, 2.5m, 3m, 3m. The purpose
is to test the effectiveness of a variety of foundation settlement
calculation methods. By making use of these valuable test data,
this paper further testifies the applicability of the tangent
modulus method
[4]
for nonlinear settlement computaion and
studies how to use the static cone penetration test and
pressuremeter test and other simple in-situ tests to determine the
parameters of the foundation parameters required in the tangent
modulus method, and it can further develop and improve the
tangent modulus method.
1.1
Calculation Principle of Tangent Modulus Method
[4]
The tangent modulus method is a new method based on the
in-situ plate loading test to create the P-S curve of soil, in order
