Performance of soil instrumentation on settlement prediction (original) (raw)
Related papers
On the Evaluation of Settlement Measurements Using Borehole Extensometers
Geotechnical and Geological Engineering – an International Journal, 2011
Borehole extensometers are commonly utilized in field monitoring programs to measure settlement. In order to secure the targets of the extensometer, the borehole is typically backfilled with cement-bentonite grout. In the absence of standardsfor grout mix designs and due to non-universality of the properties of the backfilling grout, the accuracy of settlement furnished by borehole extensometers may be questionable. A preliminary parametric study was conducted to investigate the influence of grout stiffness on settlement measurements using borehole extensometers. The finite element program ABAQUS was used to model a borehole extensometer installed in an isotropic homogeneous elastic soil layer of a finite depth subjected to a uniform surface surcharge. Effect of the grout–soil elastic moduli ratio, soil/grout interface parameters (friction angle and shear strength), and extensometer embedment depth were investigated. Soil/grout interface behavior was assumed to comply with the elastic-perfectly plastic Coulomb friction model. The mechanism of measuring settlement using borehole extensometers was studied. The numerical study revealed that minimum errors in settlement can be obtained if the grout–soil elastic moduli ratio is made equal to about 1.0. Depending on the grout–soil moduli ratio, larger grout/soil interface friction angle and interface shear strength are generally associated with smaller settlement errors. Compared to fully embedded extensometers, partial embedment yields smaller settlement errors for grout–soil moduli ratio significantly above unity. In view of the findings of this preliminary parametric study, it is suggested to adopt the grout–soil moduli ratio in conjunction with grout compressive strength as the controlling criterion rather than the grout compressive strength only (current standard of practice). Additionally, it is evident that cement-bentonite grout mix should be carefully designed as part of the settlement monitoring programs to match the expected deformability (stiffness) of the soil mass under consideration. Future laboratory, field and numerical studies are needed to investigate more complex soil stratifications and to evaluate the behavior of various grout mixes.
Comparatve Study on Predicted and Measured Settlement of Foundation
2011
The stability of foundation depends on the bearing capacity of soil beneath the foundation. However for any structure, the allowable bearing pressure cannot be assessed without considering the effect of settlement. Although empirical equations are available for the calculation of settlement, they need to be used with caution taking in to account its limitations. Hence an attempt is made in the present investigation to compare the settlement of shallow foundation using empirical relations with the same measured in the field by conducting plate load test. The measured settlement is lesser than the predicted settlement. IS method gives conservative value of SBC for both shear and settlement criterion. However, the rate of increase in SBC is higher for increase in depth compared to increase in size. In this paper, the safe bearing capacity (SBC) based on shear is calculated based on five methods such as Vesic, Meyerhof, Hansen, Terzaghi and IS method. Then the settlement is calculated b...
Evaluation of Foundation Settlement Characteristics and Analytical Model Development
Leonardo Electronic Journal of Practices and Technologies, 2018
Foundation settlement characteristics were evaluated based on standard penetration test (SPT) results obtained from the six zones of Nigeria using some conventional analytical models and numerical modelling. The study aimed at developing an improved approximation of foundation settlement based on numerical modelling method that better represents soil constitutive behaviour and to determine the most appropriate settlement prediction analytical methods that are most suitable to Nigerian soil peculiarities based on SPT data, being the most commonly used geotechnical field test in Nigeria. Footing dimension of 2 x 2 x 0.4 m size and applied foundation pressure of 300 kN/m2 at foundation embedment depths of 0.6, 2.1, 3.6, 5.1, 6.6, 8.1, 9.6, 11.1 and 12.6 m were considered. Results show that the predicted compressibility is higher in the southern zones compared with their northern counterparts based on the recommendation of Eurocode 7 which allows a maximum total settlement of 25 mm for serviceability limit state. Based on the numerical analysis results using Plaxis 3D Foundation, a finite element code package, it was observed that settlement prediction methods proposed by Schmertmann et al., Burland and Burbidge, Canadian Foundation Engineering Manual and Mayne and Poulos gave good estimations of foundation settlement among others. The analytical models developed with soil parameters N60, angle of internal friction and Poisson ratio as predictor gave the best results and are recommended for foundation settlement prediction.
The influence of the choice of strain modulus value on foundation settlement
Studia Geotechnica et Mechanica, 2011
The paper is aimed at presentation of the influence of strain moduli chosen at the stage of designing on the obtained values of foundation settlements. The settlement forecasting prevailing now is still based on readings of primary and secondary values of soil deformation moduli from standard PN-81/B-0320 as values depending on their state and the type or origin. Such an approach is contradictory to the discovery of a strong nonlinearity of strain characteristics in the range of small strains (10-5 ÷ 10-3) and does not take into consideration the increase in the modulus with the depth (with increasing mean effective stress). Therefore for the needs of this paper Young's moduli E have been determined for silt based on precise triaxial tests using a local measurement of strains and also a numerical FEM analysis has been carried out using the Z_Soil software, v. 2007. The analysis carried out for small foundations (footing 2.0x2.0 m, load 400 kPa and footing 0.5x0.5 m, load 600 kPa) and for a large foundation (raft 40.0x40.0 m, load 200 kPa) has shown a clear reduction of settlement, even threefold, assuming a variable value of modulus E. This reduction is especially visible for large foundations. Streszczenie: Tematem artykułu jest przedstawienie wpływu modułów odkształcenia dobieranych na etapie projektowania, na otrzymywane wartości osiadań fundamentów. Dominujące obecnie prognozowa-nie osiadań, wciąż bazuje na odczytach z normy PN-81/B-03020 wartości pierwotnych i wtórnych modułów odkształcenia gruntów jako wielkości zależnych od ich stanu oraz rodzaju lub genezy. Takie podejście pozostaje w sprzeczności 8. Mair R. J.: Development in geotechnical engineering research: application to tunnels and deep excavations.
Direct method for determination of shallow foundation settlements
Journal of the Croatian Association of Civil Engineers, 2017
Direct method for determination of shallow foundation settlements A direct procedure for determining settlement of shallow foundations, combining the modified hyperbolic function for nonlinear stress and strain ratio with correlations from penetration test results, is presented in the paper. The 10% load, i.e. 1% of settlement to equivalent foundations diameter ratio, is used in correlations. Laboratory tests are not needed in this novel procedure, which is a considerable advantage for coarse-grained soils. A very good correspondence was established between the load-based settlement curve calculated in this way, and the settlements measured in sand during load testing of five square foundations of variable size.
Analysis of foundation settlement from progressive
Nisu retki primeri vidljivih oštećenja (pukotine i prsline po fasadnim zidovima) na starijim građevinama Beograda koje su fundirane plitko. Najčešće je to posledica neravnomernih sleganja koja često nastaju usled nepredviđenog provlažavanja tla ispod temelja. Ovo provlažavanje je uglavnom lokalnog karaktera i u takvim uslovima je neminovna pojava diferencijalnih sleganja. U ovom radu su izloženi rezultati istraživanja koji ukazuju da pored veličine zone uticaja promene vlažnosti u tlu u horizontalnom pravcu i proračunatih vrednosti sleganja, treba anlizirati i ukupnu promenu zapremine tla ispod temelja.
Japanese Geotechnical Society Special Publication
This paper presents long-term predictions of the ground behavior, including secondary consolidation via the particle filter, using model test results. There have been some difficulties in evaluating lateral displacements, because an unsuitable value for Poisson's ratio and the constitutive model are generally employed for consolidation simulations. In this paper, the Poisson's ratio is identified in addition to the compression index, the permeability, the initial volumetric strain, and the secondary compression index in the modified Cam-clay model considering anisotropy, to achieve more accurate predictions of lateral displacements. The prediction is performed using the identified parameters, and numerical examples of accurate predictions of the ground behavior are shown.
Case Histories of Settlement Performance Comparisons on Ground Improvement Using Soil Stiffness
2008
Ground improvements often aim to reduce settlement risks for foundations and this requires reliable methods of prediction. Current approaches are based on empirical procedures and methods developed over 30 years ago. This has resulted historically in designs and installations of unnecessarily sophisticated foundations. In addition many developments now encountered by ground improvement contractors involve previously developed or 'brownfield' sites made up of heterogeneous and variable made ground. Methods to predict settlements traditionally use destructive and invasive approaches such as SPT or CPT that can be insensitive to time dependent changes, which often occur when brownfield sites are improved. By comparison geophysical methods are both non-invasive and nondestructive. One such technique that has demonstrated considerable promise is that of continuous surface wave determinations, which allows stiffness depth profiles to be obtained in a cost effective way. A recently developed method to determine settlements from these data has shown through four case studies presented in this paper to accurately predict settlements measured from zone tests. Thus offers a potentially more reliable way to predict settlement profiles than traditionally used methods.
The Importance of Amount of Settlement in Determining the Bearing Capacity of Soils
2017
In this study, the aim was to determine safe bearing capacity of soils, which outcrop around Tamzi and Akcakale located in Gumushane, providing allowable settlement conditions for optimum foundation design. To define the geotechnical properties of soils, three trenches were dug and two seismic refractions with Multichannel Spectral Analysis of Surface Waves (MASW) were carried out in each research area. Sieve analyses, shear box tests, and triaxial compression tests were carried out on disturbed and undisturbed samples taken from the trenches. Seismic velocities of the soils were determined by seismic refraction and MASW methods. While determining the safe bearing capacity; the equations proposed by Terzaghi, Meyerhof, Kurtulus, Tezcan and Ozdemir, Turker, and Keceli were used and the obtained safe bearing capacity values were compared with each other. Then, the soils were modeled numerically by using finite element methods and safe bearing capacities providing allowable settlement ...
2018
The expansion of the settlement trough is an important factor in the risk assessment of the tunneling induced settlement. The increase of settlement trough requires buildings to be included in the impact zone, which causes damages. This paper conducts estimation of the settlement trough width (STW) using empirical approaches, field measurement data and numerical solutions. The credibility of the numerical results is affected by accuracy of the input data such as geotechnical parameters (E, c, and φ). Therefore, an approach in which 3D finite element modeling (FEM) and a Taguchi’s experimental design are combined to estimate the geotechnical parameters (E, c, and φ), is used. The field settlement measurements are used to validate the numerical modeling results. The results indicate that Taguchi’s (DOE) method is an effective approach to estimate the geotechnical parameters. In addition, numerical modeling provides a wider settlement trough than the empirical methods and instrumentati...