Zhongwei Baiyun Shanju- Raft Foundation

Introduction

Raft foundation construction requires a minimum curing period of 14 days after concrete pouring for impermeable concrete base slabs

As a type of spread foundation, raft foundations are typically used in high-rise frame structures, frame-shear wall structures, and shear wall structures. They are adopted when strip foundations cannot meet bearing capacity requirements or when the structure demands sufficient stiffness to mitigate differential settlement Raft foundations are categorized into beam-slab raft foundations and flat-plate raft foundations.

Classification
Also termed mat foundations or full-mat foundations, raft foundations integrate isolated column foundations or strip foundations through tie beams, with a monolithic base slab poured beneath

The two structural types are:

Flat-plate raft foundations: Allow localized slab thickening.

Beam-slab raft foundations: Support upper-flat or lower-flat rib beams

They are suitable for uneven or weak soil conditions, with shallow embedment depths (including non-embedded designs)

Note: Impermeable concrete base slabs require a curing period ≥14 days

Application Scope
Foundation selection depends on soil types and stratification. Raft foundations are ideal when:

1. Subsurface strata (e.g., weathered residual soil, fully/strongly weathered rock, or moderately weathered soft rock) permit natural foundations

2. High-rise basements serve as parking garages requiring minimal internal walls, eliminating box foundations

3. Balancing bearing capacity utilization, differential settlement adjustment, and spatial functionality is critical

Flat-plate types dominate high-rise projects due to simpler construction.

Purpose
Raft foundations efficiently:

• Distribute structural loads over a large area, reducing base pressure.

• Enhance rigidity to resist uneven settlement.

• Adapt to underground parking layouts by eliminating internal wall constraints

Raft Slab
A raft slab is a concrete base supporting columns/walls above ground. Resembling a "raft" floating on soil, it transfers loads uniformly

Applicability relies on geological conditions—where natural foundations (e.g., weathered rock layers) are feasible, raft slabs integrate directly with the substructure.