2873
Experimental Study on the Method of Rebound and Recompression Deformation
Calculation in Deep and Large Foundation Design
Etude expérimentale sur la méthode de calcul des déformations de résilience et de recompression
pour les fondations larges et profondes
Teng Y., Li J., Wang S.
Institute of Foundation Engineering China Academy of Building Research
ABSTRACT: By analyzing the data from the consolidation-rebound-recompression test of in-situ soil, bearing test, model experiment
and field measurement test, the calculating methods of rebound and recompression deformation are proposed, which based on stress
history of ground soil, the loading and unloading conditions.
Some conclusions can be drawn: i) the progress of rebound deformation
exhibits three-phases characteristics, and the critical unloading ratio could be used to determine the calculating depth of rebound
deformation; ii) the recompression deformation of foundation soil can be computed as two-phase mode, in fact, the controlled
deformation emerges when the reloading ratio exceed the critical reloading ratio; iii) the recompression deformation is larger than
rebound one, and the increase proportion varies with different kinds of soil; iv) in actual constructions, the parameters of rebound and
recompression deformation can be gotten by compression-rebound-recompression test on in-situ soil of corresponding depth in the
site, or bearing test in site that include the process of load-unload-reload.
Then the recompression deformation can be calculated by
using the parameters responding to the real stress history. According to model experiment and in-situ tests, the calculated rebound and
recompression deformation has a well agreement with measured datum, and the accuracy of predicted deformation is improved.
RÉSUMÉ : Par une analyse de données d’essai de compression sur sol intact, de test de portance, d’expérimentation à grande échelle,
et de mesure faites in situ, il est possible de proposer une méthode de calcul des déformations de résilience et de recompression pour
fondation profonde et large sur la base de l’histoire des contraintes (conditions de chargement et déchargement lors de l’exécution des
travaux). Les résultats importants de cette étude se synthétisent comme suit: 1. l’évolution de la résilience et de la recompression du
sol de fondation se caractérisent par trois phases et la profondeur de résilience calculée peut être utilisée pour déterminer celle de
profondeur critique; 2. La déformation de recompression du sol de fondation est calculée en deux phases; en fait au cours de la
réalisation des travaux les grandes déformations se produisent durant la phase où la charge excède la recharge critique; 3. La valeur de
la déformation globale de recompression est supérieure à celle de déformation de résilience; 4. Dans un cas réel de réalisation des
travaux, le calcu de déformation de recompression de sol de fondation se fait suivant les paramètres recueillis de l’épreuve dite
compression-rebond-recompression avec un échantillon du sol original prélevé in situ par sondage à une profondeur convenable, ou
de l’essai s’applique in situ soit chargement-déchargement-rechargement sur le bloc de charge du sol de fondation, avec ces
paramètres de résilience et de recompression, on peut procéder au calcul de déformation dans l’état réel des chargements de travaux.
L’affirmation des résultats de l’essai de modèle et de l’épreuve in situ, les paramètres obtenus par calcul de déformation de résilience
et de recompression correspondent bien à ceux recueillis par les essais in situ; dans ce cas-là, on peut dire que la précision de
prédiction de déformation est acceptable.
KEYWORDS: deformation control design, rebound-recompression deformation, critical depth, critical reloading ratio.
1 INTRODUCTION
In the past decades, with the developing of engineering
technique, building foundation engineering in china shows
some new features such as bulky, deeply buried, large load
differences, multiple-storey buildings or high-rise buildings
built on the basis of the same large area raft foundation. For this
kind of buildings, the deformation-controled foundation design
is very important, and some deformation index should be pay
more attention to prevent structure from cracking or damaging,
such as overall deflection of main buildings, differential
settlement between the main and podium buildings, etc. In the
process of construction and normal service of this kind of
buildings, the foundation soil deformation unually includes
rebound deformation of foundation soil caused by the
excavation of deep foundation pit, recompression deformation
and consolidation deformation caused by addtional stress. The
deeper the foundation buried, the proportion of recompression
deformation to total settlement is larger. So the calculation of
foundation deformation is more complicated. There are some
mature methods to calculate consolidation deformation caused
by addtional stress, but the reasearch and calculating mathod to
rebound-recompression deformation are seldom reported. In this
paper, the calculating methods of rebound and recompression
deformation are proposed by analyzing the data from the
consolidation-rebound-recompression test of in-situ soil,
bearing test, model experiment and field measurement test.
According to model experiment and in-situ tests, the calculated
rebound and recompression deformation has a well agreement
with measured datum, and the accuracy of predicted
deformation is improved.
2 THE LAW OF REBOUND AND RECOMPRESSION
DEFORMATION
2.1 The Law of Rebound Deformation
Figure 1. The typical
e-p
curves of soil.
The typical
e
-
p
curves of soil by the consolidation-rebound-
recompression test are shown as figure 1. The basic law of
rebound deformation under unloading condition and
recompression deformation under reloading condition, usually
can be described by some parameters such as unloading ratio
R
,
modulus of resilience
E
c
, rebound ratio, critical unloading ratio
R
cr
, limit unloading ratio
R
u
, and some new parameters
[1, 2]
such
as rebound proportion, reloading ratio
R
’, recompression ratio
r
’
are proposed, and some relation curves can be used to analyze
