Static Triaxial Compression Tests Research Articles

Effect of pre-dynamic loading on static liquefaction of undisturbed loess

Static liquefaction can make the loess unstable when the shear stress subjected to a monotonic loading exceeds the undrained peak shear strength of undisturbed saturated loess. It is a phenomenon in the failure of soil deposits caused by a sudden increase of pore water pressure accompanied by large deformations and loss of effective stress that can make soils behave like flowing liquids. In general, the static liquefaction is influenced by confining pressure, microstructure and particle size of the undisturbed loess. The composition and particle size of loess are not easy to be changed, but it is not the case for microstructure during the earthquake. A few scholars focused on the characteristics of static liquefaction when the natural loess was disturbed by pre-dynamic loading. The deviator stress, pore pressure, effective confining pressure of undisturbed loess will respond differently to liquefaction if the loess experienced pre-dynamic loading. This study examined static liquefaction phenomenon in saturated undisturbed loess considering the effects of pre-dynamic loading and confining pressure. Pre-dynamic loading tests with different peak ground acceleration (PGA) showed that the cumulative strain is in the range of 0.019–0.189% under the conditions of PGA = 0.15g, PGA = 0.30 g, PGA = 0.40 g, respectively. Undrained static triaxial compression tests at three different confining pressures (100, 150, and 200 kPa) were implemented on undisturbed loess samples. Static liquefaction was observed at confining pressures of 100 kPa and 150 kPa with different pre-dynamic loadings, and the liquefaction potential of the undisturbed loess decreased with the increases of confining pressure. Loess specimens treated with pre-dynamic loading were easier to liquefy than the samples without pre-dynamic loading treatment. Samples treated with pre-dynamic loading exhibited higher excess pore water pressure than those without pre-dynamic loading treatments. Therefore, the internal friction angle and cohesive force were 5.13%∼15.04% and 26.44%∼82.04% lower than untreated loess. It reveals that the normalization between the maximum and the minimum principal stresses can be used to quantify the liquefaction potential of undisturbed loess.

Effect of Particle Shape on Monotonic Liquefaction: Natural and Crushed Sand

This study investigates the effect of particle shape on monotonic liquefaction of the soil by performing a series of static triaxial compression tests. The tests conducted on three types of natural sand (NS), crushed sand (CS), and mixed sand (MS) (i.e., 50% natural sand +50% crushed sand by dry weight of the soil) with different particle shape descriptors consist of roundness (R), sphericity (S), and regularity (ρ). The shearing responses showed that the CS and MS specimens showed a dilative response whereas the natural sand had a strain-softening contractive behaviour. Also, the interpreted results based on a framework of the critical state of the soil mechanic (CSSM) showed that in e-p′ plane, the specimen with a higher amount of crushed particles have a greater strength due to a higher packing characteristics. The investigations on critical state locus on q-p′ plane showed that by increasing the roundness, sphericity and regularity of the specimens the critical friction angle (ϕ cs ) decreased. Also, studies on flow liquefaction in undrained instability state (UIS) showed that by increasing the particle shape descriptor values, the specimens are more prone to be liquefied.

Static liquefaction of very loose sand–slag–bentonite mixtures

Static liquefaction is a highly destructive mechanism in the failure of soil deposits caused by a sudden loss of effective stress accompanied by vast deformations and a rapid build-up of pore water pressure that can cause soils to behave like liquids. This study examined liquefaction phenomena in saturated clean Perth sand, sand containing 3% bentonite, sand containing slag (2%, 4%, and 6%), and sand containing both 3% bentonite and slag (2%, 4%, and 6%). Undrained static triaxial compression tests were implemented on very loose mixtures at three initial confining pressures (100, 150, and 200kPa). Static liquefaction (zero deviatoric stress and zero effective confining pressure) was observed at the lowest relative density and the lowest confining pressure. The liquefaction potential of the clean sand and the sand mixtures decreased with increases in confining pressure and relative density. The slag reduced the liquefaction susceptibility by reducing the inter-particle voids and producing a stable fabric. The optimum slag content was found to be 4%. Mixing clean sand with 3% bentonite produced a vulnerable fabric which exhibited high compressibility and a high level of excess pore water pressure. All sand–slag–bentonite mixtures showed non-flow behaviour and low excess pore water pressure. The mixture of sand with 4% slag and 3% bentonite exhibited the highest effective stress and the lowest excess pore pressure. It was revealed that the normalisation between the maximum and the minimum deviatoric stresses, namely, the brittleness index, can be used to quantify the liquefaction potential of clean sand and sand-slag-bentonite mixtures.

Use of Recycled Tire Rubber to Modify Track–Substructure Interaction

Resiliently bound ballast (RBB) is a new engineered material being developed as an alternative or supplement to conventional ballast for use in transit, passenger, and freight railways to improve mechanical behavior and control the modulus and damping when recycled tire waste material is used. RBB is a stable mixture of standard ballast stone and tire-derived aggregate (TDA) bound together with a purpose-designed resilient epoxy binder. Initial laboratory tests were conducted on specimens 6 in. (151 mm) and 10 in. (254 mm) in diameter of two mixes of RBB. Tests were conducted on fully bound (cemented) samples of ballast, TDA, and epoxy as well as individual particles with TDA bound to the individual ballast particles with the resilient epoxy binder. The tests included static triaxial compression tests and dynamic cyclic triaxial tests. Static tests indicated that the addition of the TDA and epoxy resulted in an increase in cohesive strength. The dynamic tests indicated changes in modulus and damping depending on the mixture of rock, TDA, and epoxy. One proposed use of RBB is to affix the RBB to the bottom of concrete ties to modify the interaction between the tie and the ballast material and improve ballast durability and modify resilience and damping. Box tests were conducted on a section of concrete tie with and without RBB attached. The tie with a section of rail attached was vertically loaded with a sinusoidal load to model repetitive axle loading. Observations indicated that the box test that used a concrete tie without RBB produced more ballast breakage compared with the test that used a concrete tie with RBB; however, more abrasion between particles occurred with the RBB-bound tie.

The Effects of Grain Size Distribution and Structure on Mechanical Behavior of Silty Sand

In order to investigate the effects of the grain size distribution and the micro-structure of soils on the mechani- cal characteristics, some static triaxial compression tests were carried out, and then the relationship of stress-strain and the strength behavior of silty sand were compared among undisturbed samples with different grain size distribution, undis- turbed and remolded samples with the same grain size distribution, and reconstituted samples (or called mixed samples) with different grain size distribution. The effects of grain size distribution and structure on the mechanic behavior of silty sands were mainly analyzed. It is shown that the obvious differences of the mechanical characteristics between undis- turbed soils and remolded soils are caused by the differences of soil structures. Although the grain size distribution are different between two soil samples, their mechanical characteristics may be close to each other, or may have obvious differences because of the effects of micro-structure.

Deformation Properties of Untreated and Enzyme-Treated Bottom Ash Waste for Use in Foundations

The use of waste and recycled materials in different construction applications is a widespread approach. In this work, incinerator bottom ash (IBA) waste was mixed with limestone at different levels, namely, 0%, 30%, 50%, and 80%, to produce blends for use as pavement foundation layers. The study focused on evaluating the resistance to permanent deformation of IBA–limestone blends, which is vital to prevent or minimize pavement rutting. An experimental program was undertaken to investigate the influence of plant-based enzyme treatment on the behavior of these blends. Cyclic and static triaxial compression tests were adopted to determine the materials’ mechanical characteristics. Emphasis was on examining the effect of various parameters, such as IBA content, enzyme content, moisture content, curing time, stress level, and number of load applications, on the behavior of the investigated blends. The accumulated permanent strain and strain rate were used to describe the blends’ shakedown stress limits. Results showed that IBA blends gave a favorable performance as foundation layers in comparison with the control limestone blend. Enzyme addition improved the permanent deformation resistance for the control limestone blend; however, it did not have any noticeable effect on the IBA blends. According to the shakedown concept analysis, all blends, at a cyclic stress level of more than 21% of the static failure stress, underwent excessive plastic strain.

Characterization of a Shallow Horizontal Fracturing Treatment in Western Missouri

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 102342, "Characterization of a Shallow Horizontal Fracturing Treatment in Western Missouri," by L.K. Britt, SPE, NSI Technologies Inc.; S. Dunn- Norman, SPE, U. of Missouri-Rolla; M.B. Smith, SPE, NSI Technologies Inc.; E. Atekwana, U. of Missouri-Rolla; L. Slater, Rutgers U.; A. Gupta, SPE, and D. Numbere, SPE, U. of Missouri-Rolla; J.V. Fontana and J.H. Viellenave, Direct Geochemical; and J. Pelger, SPE, J-Environmental Inc., prepared for the 2006 SPE Annual Technical Conference and Exhibition, San Antonio, Texas, 24–27 September. A research project, sponsored by the U.S. Dept. of Energy, was undertaken to demonstrate a development method for the heavy-oil reserves that exist at ultrashallow depth in southwestern Missouri and southeastern Kansas. The principal objective was to demonstrate an economically viable method of producing the shallow heavy oil by use of a combination of microbial-enhanced oil-recovery treatments and horizontal fracturing in vertical wells. Introduction Heavy oil (8 to 25°API) exists in the shallow Pennsylvanian sands that occur over approximately 8,000 sq miles along the Kansas/Missouri border. The area covers portions of the northeast Oklahoma platform and the Cherokee and the Forest City basins. The Cherokee group is a sequence of alternating shales and sandstones with thin coal and limestone beds. The main productive units within the Cherokee group are the Bluejacket and Warner sandstones. The Warner sand has been drilled throughout Vernon County, Missouri, and several areas of known oil deposits have been defined. In the latter part of 2000, seven boreholes were continuously cored to a total depth (TD) of approximately 220 ft. All wells encountered heavy oil in both the Bluejacket and Warner sandstones. The Bluejacket sand occurred at approximately 130 to 135 ft with 8 to 12 ft of net pay, and the Warner sand occurred at approximately 160 to 170 ft with 15 to 30 ft of net pay. Warner-sand porosity ranged from 14 to 25%, and permeability in the Upper Warner ranged from 100 to 400 md. Five wells were drilled to produce the shallow heavy-oil deposits in the Warner sandstone, the Fauvergue Wells 1 through 5 (Fig. 1). The Cushard Wells 4 and 5 were cored wells in the project area. These wells were cored to TD and the cores analyzed as part of the project. Although it was believed that older wells drilled in the Warner sandstone had been fracture stimulated, no information regarding any historical fracture treatments, execution, or performance was available. Geomechanical Data Set The geomechanical data set includes profiles with depth of Young's modulus, in-situ stress, and fracture-fluid leakoff. Core from the Bluejacket and Warner sandstone formations and surrounding shales was available from the coreholes drilled, and static triaxial compression tests were conducted on samples to determine Young's modulus. Evaluation of the triaxial compression tests indicated that the Bluejacket and Warner sandstones have an average Young's modulus of 3.1×106 and 1.3×106 psi, respectively. The Rowe coal and the bounding shales have an average Young's modulus of 2.0×106 and 1.8×106 psi, respectively.

A study of increasing ground bearing capacity for road using geotextile-grid-cell oriented vertically

At the first stage, static triaxial compression tests were conducted on models installed singular geotextile-grid-cell and compared the difference in stress and modulus of deformation with geotextile plane installed horizontally and without geotextile. At the second stage, unconfined compression tests were conducted on the models installed plural geotextile-grid-cells in dry and wet conditions.Dynamic triaxial tests were conducted on models installed singular geotextile grid-cell.