Local deep excavation and backfilling structural subgrade and its rapid construction method

A subgrade with local deep excavation and backfilling structure, comprising:

• a line-shaped foundation pit, disposed in a subgrade structure and passing through an underground pipe gallery;
• supporting cast-in-place piles, arranged on inner walls of the line-shaped foundation pit;
• and
• anchor rods, fixed into soil of the subgrade structure and the supporting cast-in-place piles by drilling and grouting, and connected with geogrids;
• wherein a cement cushion layer, a macadam stabilized base layer and cement-soil mixing piles are sequentially arranged from top to bottom below a bottom of the underground pipe gallery;
• a coarse aggregate cement mixed backfilled soil, block geobag reinforced fillers and the geogrids are sequentially arranged from inside to outside on a top of the underground pipe gallery;
• and the underground pipe gallery are laid with block geobag reinforced fillers there around;
• wherein the subgrade with local deep excavation and backfilling structure is excavated and assembled by using the construction method, the construction method comprises:
• laying longitudinally supporting cast-in-place piles on both sides of an underground pipe gallery at positions where the underground pipe gallery is arranged in a subgrade structure, and excavating longitudinally soil between the supporting cast-in-place piles to form a line-shaped foundation pit;
• reinforcing a bottom of the line-shaped foundation pit to support the underground pipe gallery, and backfilling lateral peripheral regions and top peripheral regions of the underground pipe gallery with block geobag reinforced fillers;
• and
• placing geogrids on a top of the underground pipe gallery, then backfilling, compacting and reinforcing the top of the underground pipe gallery, and fixedly assembling anchor rods on the geogrids;
• wherein inserting the anchor rods into the geogrids, the supporting cast-in-place piles and the subgrade structure, and filling gaps among the block geobag reinforced fillers with cement solidified slurry;
• wherein the reinforcing a bottom of the line-shaped foundation pit to support the underground pipe gallery comprises:
• setting cement-soil mixing piles below a bottom of the underground pipe gallery, wherein the cement-soil mixing piles penetrate through a soft soil layer and then are inserted into a hard soil layer or a designed depth;
• and
• laying a macadam stabilized base layer and a cement cushion layer in sequence from bottom to top between the bottom of the underground pipe gallery and tops of the cement-soil mixing piles;
• wherein the backfilling lateral peripheral regions and top peripheral regions of the underground pipe gallery with block geobag reinforced fillers, comprises:
• laying the block geobag reinforced fillers in the lateral peripheral regions as well as the top peripheral regions of the underground pipe gallery respectively;
• and
• filling the cement solidified slurry among the block geobag reinforced fillers, and making the cement solidified slurry be higher than a top of the block geobag reinforced fillers and fill up the gaps;
• wherein grouting holes into the subgrade structure on the supporting cast-in-place piles, reinforcing the subgrade structure by split grouting, installing the anchor rods in the holes and grouting the holes for sealing;
• wherein the placing geogrids on a top of the underground pipe gallery, then backfilling, compacting and reinforcing the top of the underground pipe gallery, and fixedly assembling anchor rods on the geogrids comprises:
• backfilling a middle location on the top of the underground pipe gallery with coarse aggregate cement mixed backfilled soil, making the geogrids wrap the coarse aggregate cement mixed backfilled soil and form a loop with the block geobag reinforced fillers, fixing the anchor rods and the geogrids by strip gaskets and bolts, and connecting soil of the subgrade structure with an overall structure of the block geobag reinforced fillers under an action of mechanical compaction;
• and
• securing the anchor rods and the geogrids onto the supporting cast-in-place piles through the bolts and the strip gaskets, drilling the grouting holes in the soil of the subgrade structure, inserting and fixing the anchor rods in the grouting holes, and then grouting the grouting holes.