Subgrade Reinforcing Geotextile Engineering Cases

Expressway Widening Project (New & Old Subgrade Connection)

1. Project Overview

Shandong Provincial Expressway Reconstruction Project, total reconstruction length 32.6km. The original two-lane highway was expanded to four lanes. The core problem was differential settlement and longitudinal cracks at the joint of new and old subgrade; local foundation was silty clay with high water content, prone to mud pumping after rainfall.

2. Geotextile Application Details

• Material: 400g/m² polyester filament subgrade reinforcing geotextile

• Laying position: Full-width paving at the bottom of widened roadbed, crossing the junction of old and new subgrade

• Construction: Flat laying, horizontal overlap 15cm, fixed by U-shaped steel nails every 1.8m; extend geotextile 2m into original road shoulder anchor trench

• Structure: Geotextile + 20cm graded gravel base course

3. Core Functions Played

1. Reinforcement: Balance stress difference between new and old roadbed, limit lateral sliding of filling soil

2. Separation: Prevent soft foundation silt from mixing into gravel layer

3. Filtration drainage: Discharge underground water to avoid roadbed softening

4. Acceptance & Operation Effect

• Post-construction monitoring: Differential settlement controlled within 3cm, far below the design limit of 8cm

• After 4 years of operation: No longitudinal cracks at the splicing section, no rutting or mud pumping

• Cost advantage: Cancel 18,000 m³ fine sand cushion, save total engineering cost by 26%