Constitutive modeling of unsaturated soil behavior using a refined suction-controlled true triaxial cell

2010 ◽  
pp. 671-676 ◽  
Author(s):  
L Hoyos ◽  
D Pérez-Ruiz ◽  
A Puppala
Keyword(s):  
Unsaturated Soil ◽  
Constitutive Modeling ◽  
Soil Behavior ◽  
True Triaxial ◽  
Triaxial Cell

Modified state-surface approach to the study of unsaturated soil behavior. Part I: Basic concept

2009 ◽  
Vol 46 (5) ◽  
pp. 536-552 ◽  
Author(s):  
Xiong Zhang ◽  
Robert L. Lytton
Keyword(s):  
Unsaturated Soil ◽  
Unsaturated Soils ◽  
Stress Path ◽  
Complex Stress ◽  
Soil Behavior ◽  
Elastic Surface ◽  
Surface Approach ◽  
Basic Model ◽  
Plastic Hardening ◽  
Complex Stress Path

The traditional state-surface approach to the study of unsaturated soil behavior is becoming much less popular these days, as it uses unique constitutive surfaces to represent unsaturated soil behavior. This approach is essentially a nonlinear elastic formation and cannot be used to explain complex stress-path dependency for unsaturated soils. In this paper, a modified state-surface approach (MSSA) is proposed to represent unsaturated soil behavior under isotropic stress conditions in which a conventional void-ratio state surface is considered to be made up of an elastic surface and a plastic hardening surface. The plastic hardening surface remains stationary at all times, whereas the elastic surface remains unchanged when the soil experiences elastic deformation and moves downward when there is plastic hardening occurrence. Using the MSSA, the loading–collapse (LC) and the suction increase (SI) yield curves in the Barcelona basic model (BBM) are derived. The prediction of three typical cases of soils under isotropic conditions and experimental results using the proposed approach confirmed its feasibility, simplicity, and potential for the study of unsaturated soil behavior.

Active monitoring of hydraulic fracture propagation: an experimental and numerical study

2011 ◽  
Vol 51 (1) ◽  
pp. 479 ◽  
Author(s):  
Amin Nabipour ◽  
Brian Evans ◽  
Mohammad Sarmadivaleh
Keyword(s):  
Hydraulic Fracturing ◽  
Real Time ◽  
Hydraulic Fracture ◽  
Numerical Study ◽  
Fluid Pressure ◽  
Active Monitoring ◽  
Fracture Width ◽  
True Triaxial ◽  
Transmitted Waves ◽  
Triaxial Cell

Hydraulic fracturing is known as one of the most common stimulation techniques performed in oil and gas wells for maximising hydrocarbon production. It is a complex procedure due to numerous influencing factors associated with it. As a result, hydraulic fracturing monitoring techniques are used to determine the real-time extent of the induced fracture and to prevent unwanted events. Although the well-known method of monitoring is the microseismic method, active monitoring of a hydraulic fracture has shown capable of providing useful information about the fracture properties in both laboratory conditions and field operations. In this study, the focus is on laboratory experiment of hydraulic fracturing using a true-triaxial cell capable of simulating field conditions required for hydraulic fracturing. By injecting high-pressure fluid, a hydraulic fracture was induced inside a 20 cm cube of cement. Using a pair of ultrasonic transducers, transmission data were recorded before and during the test. Both cases of an open and closed hydraulic fracture were investigated. Then, using a discrete particle scheme, seismic monitoring of the hydraulic fracture was numerically modelled for a hexagonally packed sample and compared with the lab results. The results show good agreements with data in the literature. As the hydraulic fracture crosses the transducers line, signal dispersion was observed in the compressional wave data. A decrease was observed in both the amplitude and velocity of the waves. This can be used as an indicator of the hydraulic fracture width. As the fracture closes by reducing fluid pressure, a sensible increase occurred in the amplitude of the transmitted waves while the travel time showed no detectable variations. The numerical model produced similar results. As the modelled hydraulic fracture reached the source-receiver line, both amplitude and velocity of the transmitted waves decreased. This provides hope for the future real-time ability to monitor the growth of induced fractures during the fraccing operation. At present, however, it still needs improvements to be calibrated with experimental results.

A New Suction-Controlled True Triaxial Apparatus for Unsaturated Soil Testing

2020 ◽  
Vol 44 (4) ◽  
pp. 20190015
Author(s):  
Fang Zheng ◽  
Shengjun Shao ◽  
Yongxin Wang ◽  
Shuai Shao
Keyword(s):  
Unsaturated Soil ◽  
Soil Testing ◽  
True Triaxial ◽  
Triaxial Apparatus ◽  
True Triaxial Apparatus

scholarly journals Unsaturated soils in the context of tropical soils

2021 ◽  
Vol 44 (3) ◽  
pp. 1-25
Author(s):  
José Camapum de Carvalho ◽  
Gilson Gitirana
Keyword(s):  
Unsaturated Soil ◽  
Unsaturated Soils ◽  
Structural Characteristics ◽  
Soil Formation ◽  
Soil Classification ◽  
Tropical Soils ◽  
Engineering Practice ◽  
Soil Behavior ◽  
Specific Behavior ◽  
Engineering Problems

The practice of geotechnical engineering in tropical climate regions must consider the use of unsaturated soil concepts. However, these concepts must also take into account the specific behavior traits of tropical soils, particularly those related to soil aggregation, pore structure, and mineralogy. This paper will initially present considerations on the typical properties of unsaturated tropical soils as well as fundamental concepts. Throughout the article, several engineering problems will be presented alongside reflections on the complex interaction between the numerous variables involved in the modeling and engineering practice of tropical unsaturated soil behavior. The paper addresses issues related to soil formation, chemical and mineral composition, physical properties, tropical soil classification, and structural characteristics of soils. Issues related to compaction and the influence of weathering, geomorphology and bioengineering are also addressed.

Laboratory testing on an unsaturated soil: equipment, procedures, and first experimental results

1999 ◽  
Vol 36 (1) ◽  
pp. 1-12 ◽  
Author(s):  
C Rampino ◽  
C Mancuso ◽  
F Vinale
Keyword(s):  
Unsaturated Soil ◽  
Unsaturated Soils ◽  
Soil Mechanics ◽  
Stress Path ◽  
Matric Suction ◽  
Silty Sand ◽  
Compression Tests ◽  
Water Drainage ◽  
Triaxial Cell ◽  
Unsaturated Soil Mechanics

This paper describes two new apparatuses recently developed at the Università di Napoli Federico II (Italy) in order to test soils under unsaturated conditions. The related experimental procedures and the first results obtained on a dynamically compacted silty sand are also discussed. The devices mentioned are a Bishop and Wesley stress-path cell and a Wissa oedometer, modified to control matric suction and to measure all the stress-strain variables relevant to unsaturated soil mechanics. Specific experimental procedures were established to perform tests under general conditions and were carefully verified during several tests. Using the triaxial cell, isotropic and anisotropic compression stages were carried out under constant suction levels of 0, 100, 200, and 300 kPa. Furthermore, two deviator stages were performed following different stress paths and water drainage conditions. Using the oedometer, an additional suction level (400 kPa) was investigated during compression tests driven up to 5 MPa of vertical net stress (sigmav - ua). This research is a part of a major project in progress at the Dipartimento di Ingegneria Geotecnica of Naples; it is aimed at the experimental analysis of the behaviour of several dynamically compacted soils and at the numerical modelling of boundary problems related to earth structures.Key words: unsaturated soils, equipment layout, silty sand, matric suction.

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