Non-uniform Settlement Research Articles

Centrifuge model tests on liquefaction-induced settlement and pore water migration in non-homogeneous soil deposits

This paper presents the results of dynamic centrifuge model tests conducted to investigate the liquefaction mechanism in non-homogeneous soil deposits. Four types of model tests were conducted: one model test involved a uniform soil deposit; one involved continuous layered soil deposit; and two involved discontinuous layered soil deposits. Non-homogeneity in the tests was incorporated by including periodically distributed discontinuous silty sand patches. It was found that more excess pore water pressure (EPWP) remains for a longer period of time in the discontinuous region in non-homogeneous soil deposits compared with the continuous layered and uniform soil deposits. The generation of pore water pressure ceases the supply of a new mass of water after seismic excitation; therefore the dissipation of EPWP becomes the dominant factor for settlement after seismic excitation. The rapid dissipation of EPWP through the discontinuous part in the non-homogeneous soil deposits manifests as a larger settlement in the discontinuous part, causing non-uniform settlements.

Study on Engineering Materials with Results of the Analysis of the Influence of Foundation Pit Surrounding Buildings Settlement

In this project, some engineering materials will be used, such as reinforcing bar, commercial concrete. Because the site underground water level is higher, in order to prevent the surrounding buildings and roads happens the non-uniform settlement, the settlement must be observed, using single double station observation way, each settlement will draw up the curve, and according to the settlement curve for foundation pit precipitation to the influence of the architecture around the research.

Analysis of Foundation Non-Uniform Settlement for Building on Collapsible Loess

The primary causes of non-uniform settlement for buildings on collapsible loess are large settlement of subsoil, local subsidence foundation, frost heaving of ground, infusion foundation, underground water level decrease and the influence of adjacent buildings and so on. According to the characteristics of the project, analysis the reasons of building that non-uniform settlement and fissure on the wall. Combine the method of reinforce the rectification for original building, put forward the method of reinforce the rectification which is applicable to the project. And put forward some suggestions for collapsible loess area construction, for the colleague reference.

Assessment on the stress state and the maintenance schemes of the transmission tower above goaf of coal mine

FEA model of a transmission tower was established. According to the monitoring data of the non-uniform settlement for the temporarily strengthened tower, the bearing capacity analyses were carried out with the wind loads of different velocities and directions. When the wind velocity is up to the design value, the stress of the main member exceeds the design stress by 34%. For the frequent velocity, stresses of all the members are lower than the design stress. By considering the settlements at the four foots are stochastic, one single installing program of the staying wires cannot decrease the stress of the members for all cases. For the settlement case which the member stress is up to the maximum value, the member stress decreases a little but even higher than the design value. By applying the large panel foundation, the bearing capacity of the tower can be enhanced significantly, and the settlement limit was determined by the structural analysis.

The numerical analysis of cracks development under nonuniform settlements of a construction

We investigate the stress-strain state of a three-dimensional construction at the given settlements of columns. In the framework of the theory of bending plates and rectilinear rods, a dangerous area in the floor plate has been revealed. A three-dimensional model has been developed for this area of the plate, which allows us to determine the damage level of the floor plate material. The values of settlements at which the first cracks appear in the examined segment of the construction have been obtained

Study on the Frame Structure under Nonuniform Settlement

In this paper, the effect of the non-uniformity settlement of ground foundation on the upper frame structure is studied. It takes a four-story space frame structure with two spans as an example. The different pedestals are installed at the joint of column footing, which respectively form the fixed supported model and the elastic supported model. Basin shaped settlement is applied in each model. The result shows that the beams are principally suffered with the bending moment and the columns principally suffered with axial force, shear force and bending moment, and that the elastic support model has certain economy.

Construction Technology and Quality Control Measures of Bored Pile

Filling pile is a common form of pile foundation work, it passes the superstructure loads to the deep stabilitily soil or rock , reducing the non-uniform settlement of ground and foundation. Because of bored piles is done underground, underwater, quality control is difficult. The construction technology and quality control measures of bored pile is been introduced.

Modeling of the cyclic behavior of shallow foundations resting on geomesh and grid-anchor reinforced sand

Storage tank foundations with frequent discharges and filling or road embankments under repeated traffic loads are examples of foundations subjected to the cyclic loading with the amplitude well below their allowable bearing capacity. The concern exists for the amount of uniform and non-uniform settlement of such structures. The soil under such foundations may be reinforced with geosynthetics to improve their engineering properties. This paper deals with the effects of using the new generation of reinforcement, grid-anchor, for the purpose of reducing the permanent settlement of these foundations under the influence of proportion of the ultimate load. Unloading-reloading field tests were performed to investigate the behavior of a square footing on the sand reinforced with this system under such loads. The effects of footing size and reinforcement types on the cyclic behavior of the reinforced sand were studied experimentally and numerically by the aid of computer code. The large-scale results show that by using the grid-anchors, the amount of permanent settlement decreases to 30%, as compared with the unreinforced condition. Furthermore, the number of loading cycles reaching the constant dimensionless settlement value decreases to 31%, compared with the unreinforced condition. Another goal of this paper is to present the equations for reinforced soil under cyclic loading to prevent such complicated calculation involved in deformation analysis. According to these equations, calculation of the permanent settlement and the number of load cycles to reach this amount for each foundation with a given size on the geomesh and grid-anchor reinforced sand, without further need to carry out the large-scale test, is supposed to perform easily.

Study on the Limited Values of Foundation Deformation for a Typical UHV Transmission Tower

The tower foundation above the goal of the coal mine is easily deformed, which causes a serious threat to the safe operation of ultra-high voltage (UHV) transmission lines. In this paper, the finite-element model of a typical 1000-kV UHV ac transmission tower was established in general software ANSYS, and the axial forces of the members as well as their variation trends were analyzed under different load cases, which include foundation settlement, slip, and inclination combined with normal design cases. Limited values of the foundation deformation under different cases for the analyzed tower were determined. It shows that the limited values of longitudinal deformation, transverse deformation, nonuniform settlement, and horizontal slip are decreased, in turn, with the same external loads. The limited value of the foundation deformation under 60° wind is the minimum, which is the control load case of the foundation deformation. The limited value of nonuniform settlement through computation is lower than that of the current regulation, and it is dangerous to evaluate the stress state by the regulation method. In the righting process of the tower with foundation deformation, the axial forces of the members are not more than than the critical bearing capacities except the horizontal slip case, and the tower is in a safe state.

Subsidence Control of Construction on Soft Soils with “Akar Foundation”

Good quality soils are always preferred in development projects, where the bearing capacity of the grounds is sufficiently high and the resulting subsidence is non-excessive. However these sites may not be as readily available with increased population and land use, making it inevitable to construct on less favourable soils, like soft organic materials. To ensure long term stability of structures erected on such soft soils, elaborate and extensive foundation systems are generally required. Alternatively, pre-treatment with ground improvement techniques is necessary. Both these methods tend to incur high costs and labour as well as require prolonged construction period, while making a rather negative impact on the environment in terms of raw material sourcing, heavy machinery mobilization and exposure to the risk of groundwater contamination. This paper describes an exploratory study on a simple shallow foundation system for construction on soft soils, which can be a potentially cheaper and more sustainable approach. The foundation system, termed the “Akar Foundation”, literally translates as “Root Foundation”, is essentially a lightweight platform supported by a group of hollow stumps (i.e. PVC pipes). The ‘root’ base served dual functions: 1. to collectively assert a stronger grip of the soft soils, hence giving higher bearing capacity; 2. to spread the imposed structural load evenly into the subsoil, thus avoiding excessive and non-uniform settlements. The effects of the end condition of the pipes (i.e. open or close) as well as the spacing between the pipes on the foundation settlement mechanism were examined, with static load tests conducted using a lab-scale simulation chamber. The findings showed that the effectiveness of the “Akar Foundation” depends on the compatibility of the pipe spacing and individual pipe lengths, highlighting the inter-relationship between the mobilisation of end resistance, skin friction and formation of soil plug in the open-end system. In a promising light, the reduced subsidence suggest the potential of the “Akar Foundation” as an economical yet effective foundation system in economically challenged soft soil areas.

Level-adjustable foundations for monolithic reinforced-concrete buildings

Practical experience gained with use of adjustable foundations, which permit strengthening and cut-off of the foundation from the building in the basement section, and elimination of nonuniform settlements, is cited.

EXPERIENCE OF STRENGTHENING BASES OF EMERGENCY BRIDGE

The creation of the cascade of hydroelectric power stations in Dnepr-river channel was accompanied by creation of artificial water basins. Change of hydro-geological conditions has resulted in flooding of adjoining territories and necessity of maintenance of the operational suitability of buildings and constructions located on them. The results of works on restoration of automobile overbridge above railroad tracks with intensive movement of trains in the city of Nikopollocated on the coast ofKakhovskoewater basin are presented. During operation more than 40 years, the inadmissible deformations in the above-ground overbridge constructions, caused by non-uniform settlements of foundations of supports, have taken place. The non-uniformity of foundations settlements has achieved600 mm.The foundations settlements were due to the changes of physical-and-mechanical characteristics of loessial soil of foundation owing to heaving of the underground water level.

Good Practice in Mitigation of Construction Vibrations

Construction activities involve various sources of vibrations such as blasting, pile driving, dynamic compaction of weak soils, and operating heavy machines. Dynamic effects of these sources may create substantial vibration problems for adjacent and remote structures, sensitive devices, and people, Woods 1997 and Svinkin 2004. The level of ground and structure vibrations depends on the dynamic construction source, the soil medium where waves propagate from the source, the distance from the source, soilstructure interaction, and the condition of structures surrounding a construction site. Ground movements from construction sources may induce direct vibration effects on diverse buildings, trigger soil layer and structure resonant vibrations, and be the cause of nonuniform dynamic settlements, Svinkin 2006.

Comparison between responses of reinforced and unreinforced embankments due to road widening

The objective of this work is to compare the responses of geosynthetically-reinforced embankment and unreinforced embankment due to road widening by using the centrifuge model tests and a two-dimensional (2D) finite element (FE) model. The measured and calculated responses of the embankment and foundation exposed to road widening include the settlement, horizontal displacement, pore water pressure, and shear stresses. It is found that the road widening changed the transverse slope of the original pavement surface resulting from the nonuniform settlements. The maximum horizontal movement is found to be located at the shoulder of the original embankment. Although the difference is small, it is clearly seen that the geosynthetic reinforcement reduces the nonuniform settlements and horizontal movements due to road widening. Thus the reinforcement reduces the potential of pavement cracking and increases the stability of the embankment on soft ground in road widening.

Centrifuge Testing of Fiber-Reinforced Soil Liners for Waste Containment Systems

The objective of this paper is to study the deformation behavior of moist-compacted soil liners with and without inclusion of discrete and randomly distributed fibers for waste containment systems at the onset of nonuniform settlements in a geotechnical centrifuge. First, scaling considerations pertaining to simulation of discretely mixed fibers in a centrifuge are presented. A series of centrifuge tests were carried out by varying aspect ratio and dosage of fibers in a soil liner of 1.2 m thick and compacted at its standard Proctor compaction. Controlled in-flight simulation of nonuniform settlements in a centrifuge was carried out using a trap-door arrangement at 40 g . It was observed that the aspect ratio and fiber content has a significant affect in restraining cracks for a randomly reinforced soil liner at the onset of nonuniform settlements. In addition to centrifuge test results, flexural behavior of soil beams with and without discrete and randomly distributed fibers was evaluated in the laborato...

植生の吸水作用が地盤の安定性に及ぼす影響

Empirically, it is known that the vegetation influences on the earth structure. Kawai et al. focused on the effects of water uptake induced by the vegetation. They regarded it as an effect of decreasing soil moisture and applied the effect to unsaturated soil/water coupled F. E. analysis. In this study, the soil/water coupled F. E. analysis code is rearranged with the constitutive model for unsaturated soil proposed by Ohno et al.. In their model, the effective degree of saturation are applied as a parameter expressing stiffness of unsaturated soil to enable application of unsaturated soil mechanics to actual problem in geotechnical engineering site. To verify the applicability of soil/water coupled analysis, the accident that the vegetation uptake work brought about the non-uniform settlement of the ground and damaged the building in Poland are simulated. Consequently, it was found that the uptake increased suction and encouraged non-uniform settlement of ground surface. Its effects appeared prominently in a dry ground having low groundwater level and much uptake. This method is effective to understand the effects of vegetation.

Influence of Geogrid Layer on the Integrity of Compacted Clay Liners of Landfills

The objective of this paper is to examine the influence of geogrid layer on the integrity of clay liners of landfills. A series of centrifuge model tests were performed on model clay liners subjected to non-uniform settlements with and without a geogrid layer embedded within the top one-third portion of the clay liner moist-compacted on the wet side of its optimum moisture content at 40 g. The model clay liner material has been selected in such a way that it envelopes the material characteristics of the clay liners, which are used for constructing an impermeable barrier in a lining system. By maintaining type and location of the geogrid within the clay liner as constant, the thickness of clay liner is varied to check the possibility of reducing the thickness of a geogrid reinforced clay liner. Digital image analysis technique was employed to ascertain the initiation of cracking and to compute strains both on the surface and along the cross-section of the clay liner with and without any geogrid layer. It was observed that clay liners compacted at moulding water content towards wet side of their OMC found to experience multiple cracking at the onset of non-uniform settlements. Contrary to this, geogrid reinforced clay liner was observed to sustain large distortions and experience only tiny cracks limited up to a location of a geogrid. With an increase in thickness of the clay liner reinforced with a geogrid, geogrid reinforced compacted clay liner was observed to retain its integrity and restrains cracking completely.

Non-Uniform Settlement of Compacted Earth Structures Caused by the Deformation Characteristics of Unsaturated Soil on Wetting

The soil/water-coupled analysis for unsaturated soil mechanics with the finite element method is used to express the behavior of compacted earth structures exposed to rainfall. The constitutive model, which is proposed by Karube et al. (1996, 1997) and modified by Karube and Kawai (2001), is formulated for initial and boundary problems and coded as DACSAR-U (Iizuka et al., 2000). A deep fill, which consists of compacted, unsaturated soil, was analyzed with DACSAR-U. Different patterns of rainfall were applied to deep fills in finite element simulations. As a result, non-uniform settlement of deep fill can be calculated and the magnitude of settlement of deep fills is dependent on the amount of collapse, namely, the compression due to the decrease in suction. Moreover, delayed settlement due to rainfall and an accumulation of an irreversible settlement due to cyclic rainfall was observed.

Centrifuge Modeling of Geosynthetic Reinforced Clay Liners of Landfills

Imperviousness of clay liners is essential in landfills in order to safeguard the environment from contamination. To accomplish this task, the behavior of clay liner of landfills with and without reinforcement inclusion has been explored by carrying out controlled in-flight simulation of nonuniform settlements of landfill in a geotechnical centrifuge using a trap-door arrangement. The reinforcement ability of geosynthetic materials such as geogrid is used to control the crack propagation and permeability of clay liner even at large settlement differences. Centrifuge model test results demonstrate a potential of reinforced clay liners to retain its integrity without significant cracking and crack propagation. Test results have shown that a geogrid layer that is placed within the top portion of the clay liner restrains cracking and enhances the sealing efficiency due to soil–geogrid frictional resistance. The adoption of geosynthetic reinforced clay liner (GRCL) provides an ideal solution for enhancing the ...

Studies on scaling and instrumentation of a geogrid

The scaling down of geosynthetic materials is essential in small-scale physical modeling studies in order to obtain the correct response of prototype structure. In this paper, similitude conditions concerning modeling of geosynthetic materials in 1 g and Ng conditions are examined with an emphasis on geogrids. In order to model soil–geosynthetic behavior satisfactorily, it was observed that there is a substantial requirement of modeling geosynthetic materials for studies pertaining to the behavior of reinforced soil structures. Secondly, one of the selected model geogrids was instrumented with special type of tiny strain gauges adhered to base material formed with strengthened epoxy adhesive and calibrated. Guidelines are presented for selecting scaled-down geogrids along with demonstration of an application through a centrifuge model test on geogrid reinforced clay liner and calibration aspects of the model geogrid. The geogrid layer was used as a reinforcement inclusion within the model clay liner subjected to non-uniform settlements in a geotechnical centrifuge. The results indicated that the model geogrid is required to be calibrated several times by loading and unloading cycles till a reproducible response is accomplished. The measured tensile strength and observations made during the centrifuge test were reported. The results revealed that the strain gauges can be used to measure in-plane tensile strength characteristics of embedded geogrid within the soil, however the influence of base material on the tensile strength–strain behavior of the geogrid need to be considered.