DIAPHRAGM WALL

Construction Method and Application

INTRODUCTION Diaphragm Wall:

Diaphragm wall is an underground wall constructed from the ground level to support excavation sides from lateral earth pressure and water pressure and to provide water tightness to the underground structure.

Features:1. As a cut-off provision to support deep excavation.2. As a retaining wall.3. It is also used as a permanent basement walls for

facilitating Top-down construction method.4. Typical wall thickness varies between 0.6 to 1.5m5. Panel width varies from 2.5m to about 6.5m or

even more depending on various conditions.

CONSTRUCTION PROCEDURE1. Construct the

guide wall.2. Excavation to

form the diaphragm wall trench.

3. Support the trench cutting using bentonite slurry.

4. Installation of stop ends and cage.

5. Concreting.

EQUIPMENTTrench Cutter Mechanical Hydraulic Grab Reverse Mud Circulation Rig

GUIDE WALL INSTALLATION Guide wall is two parallel

concrete beams constructed along the side of the wall as a guide to the clamshell which is used for the excavation of the diaphragm wall trenches.

Typically 1-1.5 meter deep.

TRENCHING PROCEDURE Trench excavation In normal soil condition excavation is

done using a clamshell or grab suspended by cables to a crane

Excavation support The sides inside the trench cut can

collapse easily. Bentonite slurry is used to protect the

sides of soil. Bentonite is a specially selected fine clay,

when added to water, forms an impervious cakelike slurry with very large viscosity.

The slurry will produce a great lateral pressure sufficient enough to retain the vertical soil.

PLACEMENT OF REINFORCEMENT AND CONCRETE Reinforcement Cage Reinforcement is inserted in the form

of a steel cage, but may be required to lap a few sections in order to reach the required length.

Concreting Placing of concrete is done using

tremie pipes to avoid the segregation of concrete.

As Concrete being poured down, bentonite will be displaced due to its lower density than concrete.

Bentonite is then collected and reused.

CONCRETING PROCEDURE

Concreting

DIAPHRAGM WALL CONSTRUCTION IN BANGLADESH

ADVANTAGES The process of constructing the wall is relatively

quiet & has small vibration. Can be constructed to a great depth. The wall provides temporary supports during

excavation hence expensive steelwork is eliminated. Good water cutoff. No dewatering is necessary. Serves both as external work for the basement and

foundation for superstructure. Suitable for deep basement. It can be up to 50m

depth. Commonly used in congested areas. Installed in close proximity to existing structure. Suitable for unstable soil profiles below water table. Limited construction time. Designable to carry vertical loads. Minimize the settlement of adjacent building.

DISADVANTAGES The cost is higher than conventional

methods. Special Equipment is necessary. Larger space is required at site for the

special equipment.

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