Latest Advancements in Instrumentation, Monitoring and QA/QC Techniques for Deep Excavation Support Systems: Al Hilal Project, Abu Dhabi – A Case History : Khaldoun Fahoum (Langan International) Hussein Hatata (Al-Ghurair Construction – Foundations) Presentors: Khaldoun Fahoum (Langan International) Hussein Hatata (Al-Ghurair Construction – Foundations)

Table Of Contents  Project Description  Applied Instrumentation Techniques  Monitoring Process and Analysis Data  QA/QC Techniques Implemented in the Project  Efficiency of the QA/QC Techniques, Instrumentation and Monitoring  Importance of Instrumentation, Monitoring and QA/QC Techniques for Al Hilal Bank Project.

Project Description

Client: Al Hilal Bank Structural Engineer: DESIMONE Engr. & Architect of Record: SEREX Geotechnical Consultant: Langan International Contractor: Al-Ghurair Construction – Foundations Plot area: 4,650 m² Scope of Works: Shoring: mm thick diaphragm wall – 300 m Length – 19 to 24 m Pit depth - 34 Tubular Steel Struts in 2 rows and 10 Concrete Struts in 2 or 3 rows at corners. Piling: mm Dia. Bored cast in situ Tension Piles – 197 Nos. – 8.0m to 11.0m Long. Project Key Data

DW Layout Existing Bridges Site Location

Al Hilal Bank Tower Site Location Site Condition and Constraints

Boreholes Location

BH-2 BOREHOLES BH-7BH-4  The ground water table was at 2.0m below existing ground, making a water head of average 20.0 meter.  Soil stratification from top to bottom starting from existing ground was as follows: - 1.5m thick of made ground - 5.5m thick of medium dense SAND m thick of very weak, moderately weathered SANDSTONE/CALCARENITE - very weak, moderately weathered MUDSTONE inter-bedded with GYPSUM layers down to 50.0m from ground. Site Ground Condition

Importance of Instrumentation, Monitoring and QA/QC Techniques for Al Hilal Bank Project

Bridges Foundations in the Vicinity of the Shoring System 800mm THK D. Wall X X

Cross Section of Shoring near Existing Bridge Foundation

 Continuous dewatering is needed to ensure dry excavation and continuous monitoring of dewatering system is essential during excavation and construction of the basements to maintain the safety of neighboring structures and pit base. Specific Engineering Risks and Limitations Associated with Al Hilal Tower Site Specific Engineering Risks and Limitations Associated with Al Hilal Tower Site  DW was flush with existing bridge deck on 3 sides. Safety has to be ensured and excessive movement of the existing structures has to be prevented.  Space allowed for shoring system including its movement and waterproofing is 1.0 meter from bridge deck edges.

QA/QC Techniques Implemented in the Project

Measures Taken for Protection of Neighboring Structures  During the construction of the guide wall, trial pits were carried out in the proximity of potential locations of bridges foundations. Wherever a foundation location showed to be critical, the soil in the vicinity of the foundation was carefully excavated to expose it.  The top of diaphragm wall was adjusted on localized reaches along the bridge sides to suit the existing bridges foundations levels.  Alignment of guide wall was highly controlled by survey techniques to minimize deviation from theoretical position of the wall and maintain a minimum safe clearance from the bridge deck and foundation during excavation.  The side of the bridge deck was covered by rubberized sheet of approximately 20 to 50mm thick as a protection.

Measures Taken for Protection of Neighboring Structures

Supporting & Formation of Excavated Trench Sides  During trench excavation, fluctuation of supporting fluid level was carefully controlled. Its level was not allowed to fall below the level required for trench stability.  Bentonite slurry quality was controlled through a comprehensive testing routine to ensure consistent characteristics.

Supporting & Formation of Excavated Trench Sides  Adjacent panel joints were formed by means of special stop ends fitted with PVC water stops for a better water tightness of the wall, more control on cages vertical alignment and formation of an effective shear key.

Surveying, Monitoring & Testing Routine During Construction & Excavation Works  Survey monitoring of position of diaphragm wall and depth checking was routinely performed during trench excavation.  During site excavation, monitoring of diaphragm wall and existing bridges surrounding the site was carried out on a regular basis.  Coordination between Contractor & Engineer to ensure the full compliance with the project QA/QC plans and the implementation of strict reputable international standards in that field.  Observation wells were installed and used for both preliminary pumping test and monitoring ground water head during excavation works and onwards.  The trench cutting machine was equipped with a depth and inclination monitoring system offering an effective tool to control the plumbness of excavation and the depth of the trench.

Applied Instrumentation Techniques

Shoring Wall Movement Instrumentation Inclinometer  10 Inclinometers were installed along the shoring periphery at an average spacing of 30.0 meters down to the toe of diaphragm wall to measure the horizontal deflection of the wall. Inclinometer

Shoring Wall Movement Instrumentation Monitoring Point on DW.  80 survey points were marked along the internal face of the diaphragm wall at top level and bottom of pit excavation at intervals not exceeding 10.0 meters to monitor the movement of the wall. Ground surface survey points were further fixed.

Ground Water Level Measurement System Observation Well  3 observation wells were installed before starting of excavation works to monitor the ground water level.

Monitoring Process and Analysis of Data

Pit Excavation Stages  Diaphragm wall Construction.  Running the dewatering system.  Progress of excavation works with installation of struts as lateral restraint system.  Maintaining the finally excavated pit in dry condition.

Pit Excavation Stages

Shoring Wall Monitoring  Monitoring of constructed shoring wall and surrounding structures was carried out regularly to ensure the stability of the whole area.  Inclinometers readings were taken once a week.  Survey Points were monitored twice weekly.  Readings were promptly recorded, rigorously analyzed and compared to values anticipated in the design and specification warning threshold.

Wall Movement Monitoring by Inclinometers + Indicates deflection towards the Excavation side. + Indicates deflection towards the Excavation side. - Indicates deflection towards the Earth side. - Indicates deflection towards the Earth side.

Wall Movement Monitoring by Land Survey

Ground Water Level Monitoring  Ground water level was regularly observed through the observation wells to enable tracing anomalies related to ground water flow, hence allowing raising early warnings about the complexities associated with severe fluctuations on the overall stability of the system.

Efficiency of the QA/QC Techniques, Instrumentation and Monitoring

Efficiency of the Instrumentation, Monitoring & QA/QC Techniques  The specified deviation of the internal face of the diaphragm wall was less than 100mm along the whole depth, the strict application of QA/QC techniques resulted in successfully achieving this tolerance along the whole perimeter of the wall.  Proper implementation of QA/QC techniques throughout all phases of the project from design to final construction, helped controlling the wall deflection to a maximum of 18mm.  As part of the project quality requirements, a pumping test was conducted to produce an enhanced final design of the dewatering system. Consequently, a dry and safe excavation could always be maintained.

Efficiency of the Instrumentation, Monitoring & QA/QC Techniques  The inclusion of the instrumentation and monitoring techniques into the project allowed a better understanding of the system behavior and contributed to an reliable construction risk management through continuous monitoring along the intended life span of the system.  Thanks to the effective implementation of QA/QC procedures and the efficient use of instrumentation and monitoring techniques, site neighboring structures were unaffected and their functionality was maintained, despite being sensitive to ongoing construction activities.

Found it with Quality Build it with Confidence PERSPECTIVE VIEW OF THE SUPERSTRUCTURE TO BE CONSTRUCTED ON TOP OF THE SHORING SYSTEM