Rate of strength increase of unsaturated lateritic soil

2008 ◽  
Vol 45 (9) ◽  
pp. 1335-1343 ◽  
Author(s):  
Meen-Wah Gui ◽  
Chun-Ming Yu
Keyword(s):  
Shear Strength ◽  
Failure Criterion ◽  
Matric Suction ◽  
Slope Instability ◽  
Lateritic Soil ◽  
Strength Increase ◽  
Residual Soil ◽  
Strength Tests ◽  
Soil Shear Strength ◽  
Intact Soil

Lateritic soil is a kind of residual soil that is widely distributed in Asia. The water table of the soil is normally very deep so the upper part of the soil is often unsaturated. The largest lateritic soil area in Taiwan is the Linkou terrace. Because the soil here is loosely cohered and consolidated, the problem of slope instability and landslides has always been a major concern. To evaluate the triggering mechanism of landslides, it is necessary to obtain the failure criterion that represents both the saturated and unsaturated conditions of the soil before any analysis is carried out. The parameter required to define such a failure criterion is the rate of shear strength increase, tan φb, which can be obtained via a series of laboratory strength tests in a modified triaxial system under various matric suction levels. Both the intact and remolded lateritic soils taken from Linkou terrace have been tested for this purpose. The results confirm that matric suction in the lateritic soil contributes significantly to the soil shear strength and that intact soil has a higher strength than remolded soil.

The Experimental Study of the Influence of the Matric Suction on the Unsaturated Soil Strength

2014 ◽  
Vol 580-583 ◽  
pp. 514-517 ◽  
Author(s):  
Cui Ran Liu
Keyword(s):  
Experimental Study ◽  
Shear Strength ◽  
Moisture Content ◽  
Unsaturated Soil ◽  
Matric Suction ◽  
Saturated Soil ◽  
Triaxial Apparatus ◽  
Soil Shear Strength ◽  
Soil Triaxial Apparatus ◽  
Water Contents

With modified unsaturated soil triaxial apparatus, unsaturated soil shear strength of the tests under the condition of different water contents are done. Experimental results show that the matric suction exist in unsaturated soil and increases with the decrease of moisture content. And the shear strength of unsaturated soil is higher than that of saturated soil. Shear strength of unsaturated soil varies as the matric suction and water content. The shear strength increases when the matric suction increases. when soil tend to be saturated, the matric suction will tend to be zero. And the shear strength of unsaturated soil values gradually close to the strength of the saturated soil.

scholarly journals Contribution of root tensile of Pennisetum polystachion on shear strength of sandy soil in slope bio-engineering technique

2021 ◽  
Vol 42 (3(SI)) ◽  
pp. 857-864
Author(s):  
Z.A. Rahman ◽  
◽  
A.E. Ettbeb ◽  
W.M.R. Idris ◽  
S.N.A. Tarmidzi ◽  
...  
Keyword(s):  
Shear Strength ◽  
Sandy Soil ◽  
Slope Failure ◽  
Tensile Force ◽  
Root Diameter ◽  
Slope Instability ◽  
Strength Parameter ◽  
Experimental Program ◽  
Soil Shear Strength ◽  
Bio Engineering

Aim: In soil bio-engineering, plant has been widely adopted as important material in promoting sustainable ecological function in slope instability measures. Plant canopy provides shelter and at subsurface level, root networking attributes toward stability of soil against erosion and slope failure. To investigate the potential of selected P. polystachion as biological material in soil bio-engineering for improving the soil shear strength of sandy soil planted with P. polystachion. Methodology: The selected species was initially planted using hyroseeding technique on studied plots which facilated with and without fiber netting (made of paddy straw). A control plot was also prepared for reference of this study. The plots were routinely watered twice a day for six months before experimental program was scheduled for determining of root tensile and soil shear strength tests. Results: The root tensile strength of P. polystachion exhibited a positive significant relationship between root tensile force and root diameter. The shear strength of soil was affected by the presence of root if compared to that of soil without root (control). Biomass analysist also agree with the soil water content, ws. High biomass contributed to the increase in the values of soil shear strength parameter of cohesive, c and angle of friction, q for root-permeated soil with P. polystachion. Interpretation: This study has suggested that the potential application of this selected species for slope vegetation in improving the erosion control and slope stability in soil-bioengineering scheme.

Shear-strength characteristics of a residual soil

1995 ◽  
Vol 32 (1) ◽  
pp. 60-77 ◽  
Author(s):  
H. Rahardjo ◽  
T.T. Lim ◽  
M.F. Chang ◽  
D.G. Fredlund
Keyword(s):  
Shear Strength ◽  
Internal Friction ◽  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Matric Suction ◽  
Residual Soil ◽  
Test Results ◽  
Angle Of Internal Friction ◽  
Slip Surfaces

Shallow landslides in natural residual soils slopes are common all over the world. The slip surfaces associated with these landslides are often situated above the groundwater table. Therefore, it is important to quantify the contribution of negative pore-water pressure to the shear strength of soil. The shear-strength characteristics of residual soil from the Jurong Formation in Singapore were assessed using multistage, consolidated drained triaxial tests. These tests involved shearing under either a constant net confining pressure and varying matric suctions or under a constant matric suction and varying net confining pressures. An extended form of the Mohr–Coulomb equation was used to interpret the test results. The test results show that for matric suctions up to 400 kPa, the angle of internal friction associated with the matric suction, [Formula: see text], is similar to the effective angle of internal friction, [Formula: see text], which averages 26° for the residual soil of the Jurong Formation. The residual soil can maintain a high degree of saturation for matric suctions as high as 400 kPa. Examples involving stability analyses of a residual soil slope with varying pore-water pressure profiles indicate that soil suction contributes significantly to the factor of safety, particularly for shallow slip surfaces. Key words : residual soil, unsaturated soil, matric suction, shear strength, multistage triaxial test, slope stability.

scholarly journals A Determination Method of Rainfall Type Based on Rainfall-Induced Slope Instability

2021 ◽  
Author(s):  
Yafen ZHANG ◽  
Yulong ZHU ◽  
Xiaoyu YAN ◽  
Shu LI ◽  
Qijing YU ◽  
...  
Keyword(s):  
Shear Strength ◽  
Slope Failure ◽  
Slope Instability ◽  
Determination Method ◽  
Shear Strength Parameters ◽  
Strength Parameters ◽  
Failure Initiation ◽  
Soil Shear Strength ◽  
Rainfall Type

Abstract This work presents a determination method of rainfall types based on rainfall-induced slope instability to eliminate the current dilemma of the inconsistent classification of rainfall types. Firstly, 5,808 scenarios of slope instability are simulated with 11 kinds of soil properties under 528 designed intensity-duration (I−D) conditions. Then through analysis of the I−D conditions when slope failure occurred, rainfall is classified into two types: short-duration − high-intensity (SH) type, and long-duration − low-intensity (LL) type. According to the analysis results, it indicates that rainfall types affect the initiation of slope failure, i.e., different I−D conditions will affect the slope failure initiation under LL type rainfall, while the slope failure initiation will not be affected by the change of I−D conditions under SH type rainfall. In addition, the results show that the classification of rainfall types does not depend on the soil shear strength parameters (cohesion and internal friction angle), although the change of soil shear strength parameters will cause the shift of threshold curve of slope failure in the I−D conditions two-dimensional (2D) plane. The findings in this study benefit to understanding the effect of rainfall type on the mechanism of slope failure initiation, which will promote the development of an early warning system of slope failure in the future by considering the identification of rainfall types.

scholarly journals Prediction of soil shear strength in agricultural and natural environments of the Brazilian Cerrado

2015 ◽  
Vol 50 (1) ◽  
pp. 82-91 ◽  
Author(s):  
Reginaldo Barboza da Silva ◽  
Moacir de Souza Dias Junior ◽  
Piero Iori ◽  
Francisca Alcivânia de Melo Silva ◽  
Sergio Mauro Folle ◽  
...  
Keyword(s):  
Shear Strength ◽  
Conventional Tillage ◽  
Control Area ◽  
Natural Environments ◽  
Multivariate Models ◽  
Undisturbed Soil ◽  
Strength Tests ◽  
Soil Shear Strength ◽  
The Relationship ◽  
Water Contents

The objective of this work was to develop uni- and multivariate models to predict maximum soil shear strength (τmax) under different normal stresses (σn), water contents (U), and soil managements. The study was carried out in a Rhodic Haplustox under Cerrado (control area) and under no-tillage and conventional tillage systems. Undisturbed soil samples were taken in the 0.00-0.05 m layer and subjected to increasing U and σn, in shear strength tests. The uni- and multivariate models - respectively τmax=10(a+bU) and τmax=10(a+bU+cσn) - were significant in all three soil management systems evaluated and they satisfactorily explain the relationship between U, σn, and τmax. The soil under Cerrado has the highest shear strength (τ) estimated with the univariate model, regardless of the soil water content, whereas the soil under conventional tillage shows the highest values with the multivariate model, which were associated to the lowest water contents at the soil consistency limits in this management system.

UTILISATION OF PLASTIC SACKS FIBRE AND BRAN ASH FOR SOFT CLAY SHEAR STRENGTH

2016 ◽  
Vol 78 (8-5) ◽  
Author(s):  
Nyimas Septi Rika Putri ◽  
Ratna Dewi ◽  
Muhammad Ilham
Keyword(s):  
Shear Strength ◽  
Soft Soil ◽  
Soft Clay ◽  
Dry Weight ◽  
Strength Properties ◽  
Optimum Level ◽  
Soil Stabilisation ◽  
Strength Tests ◽  
Bearing Load ◽  
Soil Shear Strength

Soft soil possess poor mechanical properties, thus produce problems when bearing load. To overcome the problems, soft soil has to be stabilised. To do soil stabilisation, it Is imperative to add some mixture as additional substance in order to improve the characteristic of the soft soil. Plastic sacks fibre is one of the easily obtainable material which consists of high density profile, while bran ash contains good carbon and silica. This research aimed to determine the optimum level of plastic sacks waste fibre and bran ash to obtain the maximum soil shear strength and to compare the original soil shear strength with the modified mixture soil shear strength. The strength tests were conducted on the laboratory scale using the triaxial test device for the Unconsolidated Undrained (UU) test. Soft clay sample was mixed with the chop of plastic sacks fibre with the following level of composition : 0.4 % , 0.6 %, 0.8 %, 1 %, and also the bran ash composition content of  0 %, 2 % and 4 % to the dry weight of soil with the test unit of 36 pieces. Based on laboratory testing, the maximum cohesion value reside on variation of 0.8 % plastic sacks fibre and 2 % bran ash with the value of 0.65 kg/cm2, and the maximum shear angle lays on variation of 1 % of plastic sacks fibre and 0 % of bran ash with the value of 9.95 degree. For the mixture variation of 0.8 % plastic sacks fibre and 2 % of bran ash, it produced a shear strength of 0.67 kg/cm2 and abled to increase the soil shear strength by 87.08 %. As a conclusion, the use of plastic sacks fibre and bran ash was found to be able to improve the soft clay shear strength properties.

scholarly journals Slope instability in relation to timber harvesting in the Chilliwack Provincial Forest

1975 ◽  
Vol 51 (2) ◽  
pp. 59-63 ◽  
Author(s):  
T. M. Ballard ◽  
R. P. Willington
Keyword(s):  
Shear Strength ◽  
Sedimentary Rock ◽  
Road Construction ◽  
Timber Harvesting ◽  
Slope Instability ◽  
Site Conditions ◽  
Slope Failures ◽  
Stability Problems ◽  
Soil Shear Strength ◽  
Specific Factors

Slope instability problems in the Chilliwack Forest are particularly prominent in areas of sedimentary rock and where very steep glaciated slopes persist. Increased frequency of slope failures often appears related to recent logging and road construction. Specific factors contributing to instability can be analyzed by interpreting site conditions in relation to soil shear strength and stress equations. Such analysis can be applied in planning roads and harvesting to minimize stability problems.

Finite Element Modeling of a Mechanically Stabilized Earth Trial Wall

2021 ◽  
pp. 036119812110164
Author(s):  
Andrew Lees ◽  
Michael Dobie
Keyword(s):  
Finite Element ◽  
Shear Strength ◽  
Retaining Wall ◽  
Back Analysis ◽  
Soil Parameters ◽  
Failure Behavior ◽  
Valuable Insight ◽  
Deformation And Failure ◽  
First Case ◽  
Soil Shear Strength

Polymer geogrid reinforced soil retaining walls have become commonplace, with routine design generally carried out by limiting equilibrium methods. Finite element analysis (FEA) is becoming more widely used to assess the likely deformation behavior of these structures, although in many cases such analyses over-predict deformation compared with monitored structures. Back-analysis of unit tests and instrumented walls improves the techniques and models used in FEA to represent the soil fill, reinforcement and composite behavior caused by the stabilization effect of the geogrid apertures on the soil particles. This composite behavior is most representatively modeled as enhanced soil shear strength. The back-analysis of two test cases provides valuable insight into the benefits of this approach. In the first case, a unit cell was set up such that one side could yield thereby reaching the active earth pressure state. Using FEA a test without geogrid was modeled to help establish appropriate soil parameters. These parameters were then used to back-analyze a test with geogrid present. Simply using the tensile properties of the geogrid over-predicted the yield pressure but using an enhanced soil shear strength gave a satisfactory comparison with the measured result. In the second case a trial retaining wall was back-analyzed to investigate both deformation and failure, the failure induced by cutting the geogrid after construction using heated wires. The closest fit to the actual deformation and failure behavior was provided by using enhanced fill shear strength.

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