In this paper, horizontal seismic responses of a structure built on a sunken mat foundation were compared with those built on a solid embedded mat foundation to investigate the effect of a sunken mat foundation on the horizontal response of a structure. Seismic analyses of a structure laid on the embedded mat foundation were performed by utilizing a pseudo-3D finite element software of P3DASS. Three bedrock earthquake records downloaded from the Pacific Earthquake Engineering Research Center database were scaled to reproduce weak-moderate earthquakes. Weak, medium, and stiff soil layers were considered for the seismic analyses of the structure-foundation-soil system. Parametric studies were performed for foundation radius, foundation embedment depth, and shear wave velocity of a soil layer to investigate their effect on the seismic response spectrum. The study result showed that the design spectrum of a structure built on a sunken mat foundation was similar to that with a solid embedded mat foundation showing a slight difference due to almost the same seismic base motion beneath both embedded foundations.

Seismic analyses of a pile under a large rigid basement foundation embedded in the homogeneous soil layer were performed practically by a response displacement method assuming a sinusoidal wave form. However, it is hard to take into account the characteristics of a large mat foundation and a heterogeneous soil layer with the response displacement method. The response displacement method is relevant to the 2D problems for longitudinal structures such as tunnel, underground cave structure, etc., but might not be relevant with isolated foundations for building structures. In this study, seismic pile analysis by a pseudo 3D finite element method was carried out to compare numerical results with results of the response displacement method considering 3D characteristics of a foundation-soil system which is important for the building foundation analyses. Study results show that seismic analyses results of a response displacement method are similar to those of a pseudo 3D numerical method for stiff and dense soil layers, but they are too conservative for a soft soil layer inducing large soil pressures on the foundation wall and large pile displacements due to ignored foundation rigidity and resistance.

This study is to be suggest the optimal mat foundation mixing design of high strength concrete by using fly ash and retarding admixture. This study applied retarding admixture to high strength concrete over 40MPa, and tested the mechanical properties of concrete according to binder content(385∼415kg/㎥), fly ash substitution rate(0~25%), and adding rate of retarding admixture(0~1.2%) As a results, For the concrete to be applied to lower part of mat foundation, it is suitable to substitute FA 25% with binder contents 385kg/㎥ and to apply the mixing with adding retarding admixture 1% in order to repress hydration heat and to cast concrete at once through congelation delay. As a result of experiments of adiabatic temperature rising, coefficients of adiabatic temperature rising K and α were 40.68 and 1.08 for retarding-type concrete and 42.8 and 1.13 for standard concrete, respectively, under the condition of initial concrete temperature about 19℃. In the identical temperature condition, differences of adiabatic temperature rising speed according to use of retarding admixture were not different, and maximum value of adiabatic temperature rising of retarding-type concrete was lower than standard concrete. Keywords: Retarding Admixture, High Strength Concrete, Mat Foundation, Fly Ash, Adiabatic Temperature Rise