Characteristics Of Foundation Soil Research Articles

Experimental Analysis on Mechanical Characteristics of Foundation Soil in Rift Valley Area of Kenya Nairobi-Malaba Railway

The Rift Valley section of Kenya Nairobi-Malaba Railway locates in the Great Rift Valley of East Africa, with complex engineering geological conditions and well-developed geological structures. During the rainy season from March to May 2018, four large-scale ground fissures were formed in the first-stage project of the Nairobi-Malaba Railway of the valley floor section, accompanied by uneven surface settlement and trenches, seriously endangering the safety of the railway and its nearby projects. Through field investigation, it is preliminarily considered that the main reason induced ground fissures and surface settlement is the underlying soil layer being eroded by groundwater. The gully is further formed by surface water erosion on a base of uneven surface subsidence. The geological exploration trench at DK77 ground fissure revealed that the overlying soil layer is respectively grayish-yellow silty clay, cyan-gray volcanic ash, and brownish-yellow silty clay from top to bottom, and the underlying bedrock is volcanic tuff with wide cracks. The fluid flows out or into the bedrock through the cracks developing channels for groundwater up-down flowage. Under the erosion of groundwater to the underlying soil, this study proved the possibility of the occurrence of uneven settlement. When exposed to the groundwater, the underlying soil will exhibit special physical and mechanical properties which are conducive to the occurrence of ground cracks and subsidence. The conventional geotechnical tests are conducted for the three types of overlying soil, and the results reveal the causes of ground fissures and surface settlement from the physical and mechanical properties of the overlying soil and provide a basis for the further qualitative analysis of the mechanism of ground fissures and surface settlement.

Research on the Settlement Regulation and Stability of Large Building Foundation over Gobs: A Case Study in the Xiangcheng Coal Mine, China

Due to the acceleration of urbanization in China, the land use and new building construction in mining subsidence areas are increasing. However, a large high-rise building (100 m × 80 m × 100 m) was planned to be built above gob areas in the Xiangcheng Mine subsidence area. According to the analysis of the borehole exploration data, borehole TV observations, and theoretical calculations, there were broken bedrock and developmental fractures in the fracture and caved zones above the gob areas. In addition, the depth affected by the building load is less than 9 m from the top of the fracture zone; thus, the stabilities of the gobs are low. Then, through the theoretical analysis of the space stress, compression settlement of foundation soil, and residual settlement of the gob and coal pillar under loads, combining the similar simulation study on settlement characteristics of foundation soil and gobs, the total settlement of the foundation can be regarded as the vector superposition of the compression settlement and residual settlement; then, the maximum settlement is calculated as 555 mm and the maximum tilt is 14.9 mm/m under the building load, which are greater than the permissible values of 200 mm and 2 mm/m, indicating that the foundation’s stability is inadequate. Therefore, the treatment measures of the deep pile group foundations in the soil layer and grouting reinforcement in the gobs were simultaneously put forward to effectively improve the stability of the building foundations.

Effect of Tea Waste on Cracking of Foundation Soil

Desiccation cracks form on the surface of foundation soils due to matric suction and surface shrinkage with water loss. This paper investigates the effect of tea waste on the change of water content and cracking characteristics of foundation soil during drying. Digital image processing was carried out based on laboratory experiments. The characteristics are monitored with a variation in water content. The effects of different amounts of tea waste on soil drying and cracking were obtained, in order to provide an efficient and new green sustainable material for improving soil evaporation cracking under drought conditions. The results show that the development of cracks of soil samples with tea waste can be categorized into three stages in accordance with the fractal dimension of the desiccation cracks: Stages I, II, and III. The desiccation cracks in Stage III are wider and longer than those in Stages I and II, however, the maximum fractal dimension and stability are also obtained in Stage III. The residual water content of the sample without tea waste is 1.5%. The residual water content of the samples containing 4% and 8% tea waste is 4.6% and 5.4%, respectively, which shows that the tea waste can effectively improve the residual water content of the foundation soil and the water holding capacity of the soil. The fractal dimension of cracks on the soil samples increases gradually with drying. The total length of cracks increases and the development of cracks is more complex. The cracking time of soil samples with different tea waste contents is different. The soil samples with 8% tea waste content crack first. Combined with the variation characteristics of water content, tea waste has water absorption and improves the water holding capacity and stability of foundation soil.

Numerical Study of the Mechanical Behavior of a Foundation Raft under the Hydrodynamic Influence of the Mechanical Characteristics of Clay Soils

The clay soils of the city of Douala are constantly saturated with water, which permanently favors the hydrodynamic behavior of the soils (swelling or consolidation). This phenomenon can cause serious disturbances in the structure of buildings resulting in the appearance of cracks in structures (buildings, road bridge, viaduct, etc.). The foundation raft is a very important structure in the dimensioning of structures. Given the soil-structure interactions, its mechanical characteristics must be the subject of a special study linked to the building environment. In this article, we present a study of the mechanical behavior of a foundation raft anchored in a laminate floor. The aim is to highlight the influence of the mechanical properties of the foundation soil on the evolution of the mechanical behavior of the raft. The method used is a numerical simulation. A physical model taking into account a 5-storey building based in Douala in the Denver district is studied. The foundation on the raft foundation of this building follows an elastic constitutive law with Mazars damage, and rests on a laminated soil of plastic elastic model with Camclay plasticity criterion. The ground-raft and ground-ground interfaces are carried out with the finite elements joined to three nodes (JOI3), and obey the Coulomb model; it is an expansion joint model with Mohr-Coulomb type criterion and associated flow. The numerical resolution is carried out by the finite element method, and the numerical simulations via the Cast3M calculation code. The results from the simulations show that the mechanical characteristics of foundation soils, in this case the water content, the compactness, the state of consolidation, greatly influence the mechanical behavior of the foundation slab. There is indeed a significant settlement and a great deformation of the raft foundation when the water content of the soil layers increases, and when the states of consolidation and compactness are low. This article allows us to predict and control the evolution of the behavior of the ground-structure interface of a raft foundation and to adopt a new model appropriate for the sizing of civil engineering structures.

Influence of sand content on the flow characteristics of soft soil under cyclic and high-frequency vibration

The flow characteristics of foundation soils subjected to train loads can present engineering hazards in high-speed railways. In order to verify the feasibility of blending coarse sand in modifying soft subsoil, undrained pulling sphere tests were carried out and the train loads were simulated through localized and cyclic vibration at various frequencies. Laboratory testing results indicate that the flow characteristics of soft soil can be significantly enhanced by high-frequency vibration; meanwhile the continuous increase in flow characteristics caused by cyclic vibration may be an important reason for the long-term settlement of soft subsoil. The influence of sand content on flow characteristics is also studied in detail, and it is shown that the addition of coarse sand can weaken the flow characteristics of soft soil induced by sudden vibration at lower than 50 Hz. Under the condition of cyclic vibration, the growth of the flow characteristics of sand-clay mixtures is mainly caused by the first-time vibration in the cycle, and the increase in sand content can make the flow characteristics present a faster convergent tendency.

The Impact of Site Characteristics on the Development of Wind Turbines, as Sources of Recoverable Energy

For the design of wind turbines it is necessary to consider several conditions such as: wind, turbulence, temperature variations, geology and characteristics of foundation soils on site, earthquake and neighborhood restrictions. The selection of the types and dimensions of the wind turbines foundations are dependent on the geotechnical conditions, the maximum power of turbines and the type of tower. This paper presents various tower structures correlated with the corresponding types of foundations currently used for wind turbines. For this research, the authors performed a variety of analyses and studies involving different characteristics of the locations for the wind turbines. The research shows the solutions obtained for the pile foundations and their impact upon the environment. The paper points out the influence of the pile length on the slope stability as resulted for the soil stratification from the investigated locations.

Selection of Support Form and Water-Sealing Measure for Deep Excavation in Miscellaneous Interphase Distribution Strata

This paper summarizes the possible supporting forms of deep excavation which will provide some useful suggestions for retaining structure pattern selection based on the geological characteristics of foundation soil in Kaifeng. Then combing with the irregular-shaped deep excavation of certain civil air defense engineering, a comparatively effective waterproof measure is proposed. Moreover possible problems encountered in the process of construction are discussed, and their corresponding solving ways are illustrated systematically. The research results will contribute to choose the supporting pattern and water sealing measure for deep excavation in Kaifeng region.

Study on Re-Radiated Noise in Futian Underground Hub of Guangzhou-Shenzhen-Hongkong High-Speed Rail

A finite element model considering the high-speed train excitation loads, track structure, vibration reduction measures, station construction, characteristics of foundation soils was established to study the problems of vibration and re-radiated noise in the underground Futian hub of Guangzhou-Shenzhen-Hongkong high-speed rail under the excitation of trains. The first 200 natural frequencies of the station are all within 40Hz, the vibration energy concentrates mainly in the second and third floors, in form of bending vibration mode; the modes of orbital plate mainly accounts for vertical vibration, and the lowest frequency is near 26Hz.When the train passes by at a speed of 200km/h, without damping rubber pads, the maximum vibration level is 57.9 dB, while with damping pads the vibration level decreases by 5~6dB. The re-radiated noise level at the surface of the structure is between 38~55.1dB;with damping measures at the orbits, the corresponding acoustic gain in upper floors is 6dB or so; some low-frequency noise excess the standard, but considering the acoustic measures in upper floors, it should be manageable. It is suggested that the train pass by at lower speed, to further reduce the re-radiated noise, to a create amore comfortable environment.

Study on Vibration of Futian Underground Hub in Guangzhou-Shenzhen-Hong Kong High-Speed Rail

A finite element model considering the high-speed train excitation loads, track structure, vibration reduction measures, station structure, characteristics of foundation soils was established to study the problem of vibration in the underground Futian hub of Guangzhou-Shenzhen- Hong Kong high-speed rail. The first 200 natural frequencies of the station are all within 40Hz, the vibration energy concentrates mainly in the second and third floors, in the form of bending vibration mode; the modes of local orbital plate mainly accounts for vertical vibration, and the lowest frequency is near 26Hz.The additional displacement and stress induced by vibration is not great in general, vibration energy of the structure is mainly concentrated in the band of 15~20Hz. When the train passes by at a speed of 200km/h, without damping rubber pads, the maximum vibration level at upper floors is 57.9 dB, while with damping pads under the orbits the vibration level decreases by 5~6dB,which is a significant effect.

Effects of Driving Displacement Piles in Lean Clay

Investigations were conducted to determine the characteristics of foundation soils for two large pumping plants of the Bureau of Reclamation's Weber Basin Project near Ogden, Utah. Normal investigations showed that saturated lean clays of low strength and high compressibility would be encountered for appreciable depth below plant grades. Because a pile foundation, with embedment in lower firmer layers, was indicated, it was necessary to determine if the upper soils would be remolded during pile driving to the extent that they would consolidate under their weight and add load to the piles. Several special laboratory and field tests were conducted to investigate this possibility. These were one-dimensional consolidation tests on undisturbed and remolded specimens, three-dimensional consolidation tests in which model piles were driven into undisturbed specimens, model pile load tests in undisturbed samples, and vane shear tests adjacent to test piles driven at the site. The tests showed the clay soils to be borderline with respect to sensitivity, but the driving of piles did not cause significant loss of strength or increased compressibility. The behavior of the soils during and after construction confirmed this conclusion.