Temporary Cofferdam Project in a River Regulation Works in Jiangsu Province, China: Application of Woven Geotextile

Project Background

In 2021, the Water Affairs Bureau of a city in Jiangsu Province decided to construct a temporary cofferdam in the middle reach of a main river channel to facilitate dry construction for dredging and embankment reinforcement. The cofferdam was designed to be approximately 380 meters long, with a maximum water depth of 4.2 meters and a design head pressure of about 3 meters. A water engineering company won the tender for this cofferdam project and selected a professional geosynthetic supplier to provide all required geosynthetic materials. The contractor installed approximately 28,000 square meters of high-strength woven geotextile on both the upstream and downstream faces of the cofferdam to enhance overall stability, prevent hydraulic erosion, and control fine particle loss. The cofferdam system included: woven geotextile (minimum tensile strength 50 kN/m, polypropylene material), sand-filled geotextile bags, and an anti-slip geogrid at the base.

Challenges

The river section where the project was located experienced relatively high flow velocities (maximum 1.8 m/s) and frequent water level fluctuations due to tidal influence. The technical specification clearly required that the woven geotextile be tested for tensile strength, tear resistance, puncture resistance, and interface friction, with particular attention to material durability and erosion resistance under temporary cofferdam conditions. The supervision unit requested interface shear testing between the woven geotextile and the sand fill to ensure compliance with design clause 4.2.3: "The friction angle at the interface between the woven geotextile and the fill material shall be no less than 25 degrees, or achieve an equivalent Mohr-Coulomb strength parameter combination, to prevent sliding of the cofferdam slope during construction and service."

Solution

The supplier performed all required tests, including wide-width tensile tests, trapezoidal tear tests, CBR puncture tests, and large-scale interface shear tests. The measured data showed that the woven geotextile achieved a tensile strength of 62 kN/m, a tear strength of 0.55 kN, and an interface friction angle of 28.6 degrees, all significantly exceeding the specification requirements. All test results were submitted on time, with no impact on the construction schedule.

The main challenges for the supplier included a tight project schedule (only 45 days), requiring the woven geotextile to be delivered in three batches, and the local rainy season (plum rain) which made the access roads muddy and difficult for trucks. To complete the cofferdam filling as planned, the contractor made use of every rain-free day, working double shifts and laying more than 1,500 square meters of geotextile per day. The supplier’s logistics team worked closely with the contractor, optimizing delivery routes and adding waterproof coverings to ensure all materials arrived on site on time and in good condition.

Results

The temporary cofferdam was successfully closed in July 2021. After withstanding a full flood season (about four months), the cofferdam remained stable, and the woven geotextile showed no significant tearing or erosion damage. After construction, the cofferdam was removed as planned, and part of the woven geotextile was recovered, achieving the goal of rapid and economical construction of a temporary structure.