At-rest Conditions Research Articles

Ground Deformation Induced by Vacuum Consolidation

The deformation characteristics of soil subjected to vacuum pressure are discussed and an approximate method is proposed for calculating settlement and lateral displacement of the ground induced by vacuum consolidation. Laboratory oedometer test results indicate that if the vacuum pressure alone is larger than the lateral stress required to maintain an at-rest (no horizontal strain) condition, there will be inward lateral displacement and the vacuum pressure will induce generally less settlement than a surcharge load of the same magnitude. In the case of field vacuum consolidation, the confining stress acting on a soil element can be regarded as consisting of two parts: Due to vacuum pressure and earth pressure. Assuming a value of the lateral earth pressure coefficient acting in the ground under vacuum consolidation ( kao ) , somewhere between the active and at-rest values, an equation defining the depth—below which there will be no significant inward lateral displacement—is derived. Further, assuming th...

Computer-aided limit states analysis of bridge abutments

This paper presents a computer program developed for limit states analysis of abutments. The program can perform both structural and geotechnical analysis of bridge abutments and check their resistances in compliance with limit states design criteria. In the program, the earth pressure coefficient for the backfill soil is calculated as a function of abutment’s lateral non-linear displacement. Therefore, for abutments partially restrained against lateral movement, an earth pressure coefficient less than that of at-rest conditions may be obtained. This may result in a more economical design.

Full-Scale Field Trials of Tire Shreds as Lightweight Retaining Wall Backfill Under At-Rest Conditions

A 4.88-m (16-ft), full-scale retaining wall test facility was constructed to investigate the use of tire shreds as backfill for conventional retaining walls. The facility can test backfill at at-rest and active conditions and is instrumental for measuring horizontal stress and interface shear. Tire shreds from three suppliers were tested. The results for at-rest conditions are presented. The average at-rest horizontal stress for tire shreds was about 45 percent less than expected for conventional granular backfill. Moreover, the at-rest horizontal stress was about the same for tire shreds from the three suppliers. Design parameters were developed by using two procedures. The first used the coefficient of lateral earth pressure and the other was based on equivalent fluid pressure. The horizontal and shear forces acting on the concrete face of the wall were used to determine the angle of wall friction, which ranged from 30° to 32° for tire shreds from the three suppliers.

Vertical Shear Loads on Nonmoving Walls. I: Theory

Retaining walls that do not move are customarily designed based on the assumption of at-rest conditions, with no consideration of vertical shear loads applied by the backfill. However, field and laboratory measurements have shown that vertical shear loads do act on nonmoving walls. A simple theory for calculating the magnitude of vertical shear loads on nonmoving walls is presented in this paper, and typical results from the theory are discussed. A companion paper presents the results of finite-element calculations, case history data, and recommendations for retaining wall design.

Relationship between diabetic autonomic dysfunction and heart rate variability assessed by recurrence plot.

Beat-to-beat heart rate (HR) and blood pressure were measured by the Finapres system in 44 healthy and 64 diabetic subjects in the at-rest condition. Autonomic control in diabetic subjects was assessed by the Ewing test. HR variability was explored by both linear and nonlinear methods. Linear methods used HR standard deviation and power spectrum. The percentage of the spectrum in the low frequencies was used to assess the sympathetic tone of the autonomic control. The nonlinear method used the "recurrence plot." This method explored long parallel subsequences in the HR time series. These sequences characterize the dependence of the HR dynamics on initial values. The HR standard deviation was reduced in the diabetic subjects compared with the healthy subjects (2.80 +/- 1.17 vs. 3.64 +/- 1.45 beats/min; P < 0.001). In the diabetic subjects, the HR standard deviation and the percentage of the spectrum in the low frequencies showed no correlations with the Ewing score (P > 0.10). In contrast, the longest length index was very strongly correlated to the Ewing score (r = -0.60; P < 0.0001). The results suggest that nonlinear methods might be powerful to explore the autonomic dysfunction in diabetic subjects.

Transition of active lateral earth pressures behind retaining walls

An approximate analytical solution is described to estimate the developed lateral earth pressures behind rigid retaining walls experiencing various types of outward movements with horizontal cohesionless backfill soil. Included are various stages of wall movement, starting from an atrest condition to a full active condition. The at-rest condition is defined as a stage of no wall movement, whereas the full active condition occurs when the soil elements along the entire depth of the wall are in active state. The predictions from the developed method of analysis are compared with model test measurements. The comparisons show very good agreements at various stages of retaining wall movement. Finally, examples are given to illustrate the transitions of the lateral earth pressures behind a smooth and a rough retaining wall experiencing rotational and translational movements.

Performance and design of slurry walls in soft clay : Karlsrud, K Norw Geotech Inst PublN149, 1983, 9P

Extensive field tests on instrumentation, construction control, etc. were carried out on the performance and design of slurry trench walls in soft clay. These tests were designed to establish criteria and methods for evaluating the stability of slurry-filled trenches in soft day, to acquire data on the practical aspects of such construction, and to determine the performance of slurry-trench walls as earth-retaining structures. This article documents some of the extensive data that was gathered. The study found that there were on particular problems associated with construction of slurry-trench walls in soft clay. It is possible to construct such walls in soft clay with only clean water as supporting fluid. The special use of cross-lot walls to prevent bottom heave failure functioned well for two tunnel projects that were studied. For economical design, it is necessary to apply analytical methods that account for the interaction between soil-wall and support system and the actual sequence of excavation and installation of supports. It was found that earth pressures increased with time after completion of construction and approached the at-rest condition.

Strength and Stiffness of Silicate Grouted Sand with Different Stress Histories

Abstract The effects of stress history and relative density on the short-term strength and stiffness of a granular soil (Ottawa 20–30 sand) that was chemically stabilized with a sodium silicate grout, a solution of hydrated sodium silicate, water, ethyl acetate, and formamide, were investigated. A system was developed to inject grout into sand specimens that were prepared in a triaxial cell; the specimens were subjected to a confining stress of 360 kPa and grouted under a pressure of 144 kPa. The results are analyzed in terms of Mohr-Coulomb failure theory, and comparisons are made among the compressive strength, initial tangent modulus, angle of internal friction, and cohesion of the specimens for different test conditions. The strength of the specimens grouted under a confining stress is seen to be a function primarily of their relative density. Little difference in mechanical behavior was observed between specimens grouted under a confining stress and those grouted under at-rest conditions. The angle of internal friction of grouted specimens with a low or high relative density differed only slightly from that of ungrouted specimens with a low or high relative density. However, the compressive strength of loose and dense grouted specimens increases relative to that of ungrouted specimens because of an increase in the cohesion, although the initial tangent modulus of loose and dense grouted specimens is similar to that of dense ungrouted specimens.

Retrogressive slope failures at Beaver Creek, south of Saskatoon, Saskatchewan, Canada

Active landslides are occurring along the banks of the South Saskatchewan River at Saskatoon. A field investigation and stability analysis indicated that a multiple retrogressive mechanism is valid in explaining the failures at Beaver Creek, 28 km south of Saskatoon. Computations indicated that lateral pressures ranging from the active to something greater than the at-rest condition tend to support the successive blocks but are not high enough to stabilize the slides. It was assumed that the rate of movement of the blocks varies and probably increases downslope. Valuable information was obtained about the soil properties in the area and the mechanism of failure that seems to apply over a long section along the river bank south of Saskatoon.