Influence of using Micropiles as Retrofitting Method for Bridge Shallow Footing: Numerical Study

Seismic retrofitting of the existing bridges, which was not properly constructed for seismic loading, is necessary. This paper examines and evaluates the effect of using micropiles as retrofitting method to improve seismic performance for bridge shallow footing. Numerical simulations using Plaxis-3D have been performed to study the effect of using micropiles to mitigate the seismic hazard and enhance the deformation characteristic of bridge shallow footing. Displacement and acceleration induced by seismic loading before and after retrofitting were assessed and compared. The results showed a significant influence of the micropiles on the control of the displacement and acceleration during the seismic period

APPLICATION THE POINT FOUNDATION (PF) METHOD FOR SOFT SOIL IMPROVEMENT: A CASE STUDY FROM VETNAM

The point foundation method is the head enlarged cement deep mixing columns with high-quality control which can be used for soft ground improvement. The article aims to present the application of this method to treat soft soil for the foundation of Samse Vina factory, Ninh Binh province. The thickness of soft soil varies from 5.4 m to 7.4 m with high compressibility and low shear strength. Thus, point foundation was used to improve this layer. The prediction methods of soil bearing capacity and the settlement on the point foundation were calculated. After the treatment of soil, the unconfined compression strength of the point foundation column was determined and the static compression test for the point foundation column was also performed. The research results show that this method can significantly reduce the settlement of shallow footing and improved the bearing capacity of the soil. The final settlement of shallow footing was smaller than 2.54 cm and the bearing capacity of soil treatment can be satisfied with the requirement of construction building. This is a successful case of the application of point foundation to improve soft soil in Vietnam.

Experimental and Theoretical Determination of Settlement of Shallow Footing on Liquefiable Soil

A high settlement may take place in shallow footing when resting on liquefiable soil if subjected to earthquake loading. In this study, a series of shaking table tests were carried out for shallow footing resting on sand soil. The input motion is three earthquake loadings (0.05g, 0.1g, and 0.2g). The study includes a reviewing of theoretical equations (available in literatures), which estimating settlement of footings due to earthquake loading, calibration, and verification of these equations with data from the shaking table test for improved soil by grouting and unimproved soil. It is worthy to note that the grouting materials considered in this study are the Bentonite and CKD slurries. A modification to the seismic settlement equations, by statistical analysis using SPSS software, had been done to account for the liquefaction state. The modified equation showed a good convergence with the measured settlement values.

Experimental and numerical investigation of the effect of pre-existing utility tunnel on the bearing capacity of shallow footing in sandy soils

Purpose The purpose of this study is to investigate the effect of presence of buried flexible pipe on the bearing capacity of shallow footing. First, a model study is performed where shallow footing model is tested for its load settlement behavior, with and without the existence of buried PVC pipe lying vertically below the base of the footing. Design/methodology/approach The experimental set-up consisted of a steel box filled with sand at two different relative density values [RD = 50 per cent (medium dense) and RD = 80 per cent (dense sand)] and vertical load was applied on the model footing through hydraulic jack and reaction frame arrangement connected with a proving ring. Test results are verified numerically using commercially available finite element code PLAXIS 2D. With due verification, a parametric study has been conducted, numerically, by varying the range of input parameters, such as unit weight, angle of internal friction, diameter of buried conduit and the Elastic modulus of the soil to assess the pre cent reduction in the capacity of the foundation soil because of the presence of underlying buried flexible pipe. Findings Results show that for each footing, there exists a critical depth below which the presence of the buried conduit has negligible influence on the footing performance. When the conduit is located above the critical depth, the bearing capacity of the footing varies with various factors, such as geotechnical parameters of soil and location and diameter of the buried conduit. Originality/value It is an original paper performed to assess the presence of buried flexible pipe on the bearing capacity of the shallow footing.