Building foundation structure, and construction method therefor

A construction method for a building foundation structure that includes:

• a plurality of foundation concrete structures formed from foundation concrete;
• a ground improved body, comprising a compacted solidification material, obtained by improving a surface layer ground, the ground improved body having a shape to define a foundation concrete shape when the foundation concrete is placed into the ground improved body on site, wherein:
• the plurality of foundation concrete structures directly supporting building steel pillars,
• each of the foundation concrete structures having an upper element and a lower element having shapes different from each other,
• the lower element having a reverse acute trapezoidal sectional shape in a cross section taken along a vertical plane including a horizontal direction perpendicular to a horizontal line connecting the building steel pillars that are adjacent to each other,
• the upper element having a brim element protruding in the horizontal direction, from a side edge at an upper end in the sectional shape of the lower element,
• a thickness of the brim element being not less than 0.05 m and not greater than 0.3 m,
• a protruding length of the brim element being not less than 0.1 m and not greater than 0.6 m,
• the protruding length of the brim element being 1 to 4 times the thickness of the brim element;
• and
• a top surface of the brim element is below or flush with a top surface of the ground improvement body,
• the construction method comprising a ground improvement step, a foundation excavation step, and a foundation placing step, wherein
• the ground improvement step is a step of backfilling soil obtained by digging the surface layer ground down, mixing and stirring the soil while adding and mixing a solidification material, and then performing compaction to form the ground improved body,
• the foundation excavation step includes
• a step of excavating an upper part of the ground improved body located below a building pillar, into the shape of the upper element of the foundation concrete structure, to form an upper excavated portion, and
• a step of excavating a part below the upper excavated portion into the shape of the lower element of the foundation concrete structure, to form a lower excavated portion, and
• the foundation placing step is a step of placing leveling concrete into the lower excavated portion, performing foundation reinforcing bar arrangement in the upper excavated portion and the lower excavated portion, and placing the foundation concrete.

A building foundation structure comprising:

• a plurality of foundation concrete structures formed from foundation concrete;
• a ground improved body, comprising a compacted solidification material, obtained by improving a surface layer ground, the ground improved body having a shape to define a foundation concrete shape when the foundation concrete is placed into the ground improved body on site, wherein:
• the plurality of foundation concrete structures directly supports building steel pillars,
• each of the plurality of foundation concrete structures has an upper element and a lower element having shapes different from each other,
• the lower element has a reverse acute trapezoidal sectional shape in a cross section taken along a vertical plane including a first horizontal direction perpendicular to a horizontal line connecting the building steel pillars that are adjacent to each other,
• each side of the lower element extends from a bottom surface of the lower element to an upper periphery of the lower element, each side being acutely angled upward to meet a bottom surface of the upper element;
• the upper element has a brim element protruding along an entirety of a width of each of the sides along the upper periphery of the lower element;
• and
• a top surface of the brim element is below or flush with a top surface of the ground improvement body.