Behavior of Low Height Embankment Under Earthquake Loading

Low height embankments are widely used for construction of highways and rural roads in India. Sometimes, it becomes necessary to construct such types of embankment on soft foundation soil under unavoidable circumstances. In addition to the stability under static loading, seismic excitation very often plays a major role in the stability of such an embankment. So, to study the behaviour of such embankment under seismic loading becomes very important as the failures may lead to huge loss of property and life. The present study analyses the response of a low height embankment overlying soft foundation soil under seismic loading with the help of finite difference analysis using FLAC. The Mohr-Coulomb failure criterion is used to define the soil constitutive model for both embankment and foundation soil. A stiffer half-space has been considered below the soft foundation soil and the analysis has been performed varying the shear wave velocity of the stiffer half-space. Low to moderate level of shaking has been applied at the base of the stiffer half-space by scaling the original input motion of 1987 Loma Prieta earthquake.

Simplified analytical solution for time dependent deformation of soft soil improved with pervious column considering load transfer between column and soil

Experimental study on soil-structure interaction of steel frame under seismic excitations

There are significant identification errors in the vibration displacement identification of deep-water pile foundation bridge piers on soft soil foundations. Therefore, this paper proposes a new method for identifying the vibration displacement of deep-water pile foundation bridge piers on soft soil foundations based on multi-source information fusion. The characteristics of soft soil structure are analyzed and the stress relationship between soft soil and solid soil skeleton is calculated. Deep water pile foundation bridge piers on soft soil foundation determine the structural characteristics of deep water pile foundation bridge piers on soft soil foundation, construct displacement curves based on the elastic deformation curvature of deep water pile foundation bridge piers on soft soil foundation, and determine the curvature of each point when the bridge pier displacement occurs. Analyze the factors that cause the vibration of deep-water pile foundation bridge piers on soft soil foundations, and determine the characteristics of the vibration of deep-water pile foundation bridge piers on soft soil foundations by calculating the amplitude under different factors. Analyze the different failure modes and shear strength, bending strength, displacement ductility coefficient under the vibration conditions of bridge piers, and analyze the load on the bridge piers to complete the extraction of multi-source information on the vibration displacement of deep-water pile foundation bridge piers on soft soil foundation. Analyze the multi-source information fusion structure, introduce the least squares support vector machine method to complete the fusion of information on the vibration displacement impact of deep-water pile foundation bridge piers on soft soil foundation. Based on this, select strain measurement points for deep-water pile foundation bridge piers on soft soil foundation, and arrange displacement identification along the entire bridge pier at equal intervals to achieve accurate displacement identification. The experimental results show that the proposed method reduces the error of displacement recognition.

Rubble-mound breakwaters are subject not only to wave action but, also, to other types of environmental loading, such as earthquakes. High seismic activity combined with soft foundation soil can lead to large settlements and even to failures of these structures. This paper reports on some aspects of the investigation undertaken to study the behaviour of rubble-mound breakwaters under seismic loading. The investigation comprised physical and mathematical modeling of two breakwaters: the first one sitting on a rigid bed, and the second on a yielding base of loose sand. Input earthquakes induced horizontal acceleration with increasing magnitude at consecutive tests. Measurements of hydrodynamic pressures and accelerations were taken. It was found that in general rubble-mound breakwaters resting on rigid bed are quite seismic resistant structures. However, a soft foundation soil plays a dominant role in the seismic behaviour of such breakwaters and may lead to quite high residual deformations. Extra care should be taken during the design phase whenever rubble-mound breakwaters are to be placed on soft soil in areas of high seismicity.

Crashworthiness of Civil Aircraft Subject to Soft Soil and Concrete Impact surface

In the last few decades, it has been observed that raft foundations are very commonly used as a foundation solution for moderate to high rise structures either by resting on stone columns or on piles in soft soils. It is believed that, combining stone columns and piles in one foundation system is the more suitable foundation for medium rise structures. The combined foundation system provides a superior and more economical alternative to pile, and a more attractive alternative to stone columns in respect to ground improvement. This paper presents the review of existing studies reported in the literature in the last two decades about the behaviour of stone columns under raft foundations and piled raft foundation in soft soil, notably the failure mechanism and the bearing capacity. Also, a limited work from the literature concerning the performance of combined (pile/stone columns) foundation system in soft soil is comprised. Furthermore, very extensive ongoing research work regarding the investigation and study on the performance of combined (pile/stone columns) foundation system in soft soils is discussed. The main goals and methodology to study the performance of the combined (pile/stone columns) foundation systems in soft soil are also addressed.

Assessment of soil–pile–structure interaction influencing seismic response of mid-rise buildings sitting on floating pile foundations

Abstract:: According to the universal one-dimensional consolidation equation introduced by Gibson, the governing equation with the excess pore water pressure as the control variable is derived, and the Fourier series solution under the boundary condition of single-sided drainage is deduced in detail by the standard mathematical physical method. It verifies the correspondence between the analytical solution and the numerical solution from a theoretical point of view. Using this analytical solution, the nonlinear distribution of the excess pore pressure along the depth direction is obtained, and the traditional small strain consolidation is compared in terms of the average consolidation degree and the final settlement. Soft soil foundation, large deformation foundation Derive a consolidation equation for soft soils with large deformations using the super-static pore pressure as the control variable Formula derivation, Example analysis Based on Gibson's general equation of consolidation and its theory, the detailed derivation process of differential equations with excess pore water pressure as the control variable is given. According to the example, the image shows the distribution of excess pore pressure with depth, and comparative analysis of large and small strains, If all other conditions are the same, When mv1=1 MPa-1, it can be calculated according to the large and small strains, but when mv1≥3MPa-1, the two errors are large, The calculation must be considered separately.

The widespread distribution of soft rock and soft soil in hydrological wetland environment is a common geotechnical engineering problem encountered in coastal engineering construction. To solve this problem, a study method for consolidation and deformation characteristics of soft rock and soft soil foundation in hydrological wetland environment is proposed. Taking K9+280-K11+120 section along Fu-Nehe section of National Highway 111 as the research object, the consolidation and deformation characteristics and loading conditions of soft soil foundation under embankment filling load, treatment methods of soft rock foundation, stratum conditions, temperature changes and time effects are analyzed. The results show that although the wetland soft rock and soil layer is not thick, the settlement of soft rock and soil accounts for more than 80% of the total settlement. Negative temperature has a certain influence on the consolidation settlement of soft rock foundation, which is mainly manifested in the difference between the settlement process of the central separation zone and the roadbed soft soil foundation; the pore water pressure of soft rock foundation dissipates to varying degrees. According to the monitoring results of settlement and pore water pressure, bagged sand wells are more suitable for soft rock foundation engineering treatment in hydrological wetland. The research results can provide a reference for the study, calculation and design of consolidation and deformation of soft rock foundation in hydrological wetland.

The stability of an embankment on soft foundation soil is most critical during the construction period, because of the relatively low permeability of the soft foundation. Since the stability increases as the foundation consolidates, related design is controlled by short-term constraints. Geosynthetics for basal reinforcement enhance the stability of an embankment over soft soil by preventing lateral sliding of the fill, extrusion of the foundation and rotational failure. The stabilizing force developed by the reinforcement is generated by shear stresses mobilized along both the interface surfaces of the reinforcement, with the foundation soil and the embankment fill respectively. In fact, the reinforcement has the double function of carrying the outward shear stresses transmitted by the embankment fill and of providing inward shear stresses to restrain the foundation soil from lateral squeezing-out. For each of the limit states mentioned above, the associated reinforcement strength and bond length should be checked to ensure that the limit state tensile load can be generated in the reinforcement. Starting from considerations proposed by the British Standard 8006:2010, this paper focuses on lateral sliding and foundation extrusion limit states by presenting a design method to evaluate the reinforcement strength and bond length required to provide the maximum improvement for an embankment on soft soil.

Because of its unstable structure, SSF (soft soil foundation) will appear obvious deformation after being subjected to external force, which will cause the foundation settlement of buildings and the overall life of buildings will be affected to some extent. With a large number of construction projects, land resources are increasingly scarce, and a large number of SSF will be used as construction land foundations. The base material in soft soil has many physical and chemical properties and active properties different from other soft soil materials. Under the action of strong external pressure, the SSF of high-speed tunnel is easy to bend. Because there are many defects in SSF, there are great security risks in industrial buildings, so it is necessary to use SSF treatment technology to change the problems in SSF during construction. By analyzing the characteristics of SSF, this paper focuses on the importance of SSF treatment and discusses the application of common foundation treatment technology in industrial building construction.

SUMMARYThe two large‐scale shaking table tests of tall buildings on soft soils in pile group foundations are performed to capture the effect of the seismic pile‐soil‐structure interaction (PSSI) on the dynamic responses of the pile, soil, and structure. The two different model conditions are observed, including a fixed‐base structure and a structure supported by 3‐by‐3 pile group foundation in soft soil, representing the situations excluding the soil‐structure interaction (SSI) and considering the SSI, respectively. In the tests, the superstructure is a tall building with 12‐story reinforced concrete frame. The pile‐soil‐structure system rests in a shear laminar soil container, which is designed to minimize the boundary effects during shaking table tests. The two models are subjected to various intensity seismic excitations of Shanghai bedrock waves, 1995 Kobe earthquake, and 1999 Chi‐Chi earthquake events. According to the experimental and analytical results, SSI systems have longer natural periods than the fixed‐base structure. In addition, soft soil has amplification effect under smaller seismic excitations and isolation effects under larger earthquake intensities. The strain amplitude at the top of pile is large, and the strain at the middle and tip is relatively small. Whereas the contact pressure is small at the top of pile and large at the middle and tip. From the dynamic responses of the superstructure, it is found that the PSSI amplifies the peak displacements and interstory drifts of the structures supported by pile group foundations by comparing with the fixed‐base structure. Whereas the peak acceleration and interstory shear force of the structure are reduced considering seismic PSSI. The results show that the seismic SSI is not always favorable, however, it may increase certain dynamic responses of the structure. Consequently, the seismic SSI should be considered reasonably, providing insight towards the rational seismic design of buildings rested on soft soils.

The prefabricated vertical drain (PVD) is an essential means to mitigate the settlement of soft soil foundations in coastal areas of South China. The commonly used elastoplastic analytical method cannot directly reflect the interaction of different PVDs and the resulting displacement of soft soil. At the same time, these elastoplastic analysis and numerical simulation methods are greatly influenced by the values adopted for rock and soil material parameters. In this paper, we present a stochastic medium model that can directly reflect the interaction of different PVDs and the resulting displacement of soft soil. It is not affected by the characteristics of rock and soil themselves and can also reflect the actual deformation process of soft soil. According to engineering practice, the settlement curves of soft soil foundations in coastal areas of South China with PVDs exhibited distinct normal distribution characteristics, which was consistent with the description of settlement by the stochastic medium model. Hence, based on the stochastic medium model, this paper analyzed the settlement mechanism of PVDs and established a stochastic medium model for the settlement calculation of PVDs. A function for the soft soil foundation in the coastal area of South China cross-section settlement curve was presented by back analysis of the PVD model. We chose the stochastic medium model based on this methodology to explore the interaction between different PVDs. The above models were then applied to an expressway in South China. Comparing actual settlement monitoring values to calculated values obtained with the PVD model, the error between the two models was less than 15%. This research provides a new settlement calculation method of PVDs in soft soil foundations in the coastal area of South China and a new basis for designing soft soil foundations.

Lattice-shaped diaphragm wall (hereafter referring to LSDW) is a new type of bridge foundation, and the relevant investigation on its horizontal behaviors is scant. This paper is devoted to the numerical study of the comparison on the static and seismic responses of LSDW and pile group under similar material quantity in soft soil. It can be found that the horizontal bearing capacity of LSDW is considerably larger than that of pile group, and the deformation pattern of LSDW basically appears to be an overall toppling while pile group clearly shows a local bending deformation pattern during the static loading process. The acceleration response and the acceleration amplification effects of LSDW are slightly greater than that of pile group due to the existing of soil core and the difference on the ability of energy dissipation. The horizontal displacement response of pile group is close to that of LSDW at first and becomes stronger than that of LSDW due to the generation of plastic soil deformation near the pile-soil interface at last. The pile body may be broken in larger potential than LSDW especially when its horizontal displacement is notable. Compared with pile group, LSDW can be a good option for being served as a lateral bearing or an earthquake-proof foundation in soft soil.