Figure 4. Diaphragm wall problems, causes and corrections Location of defect Nature of defect Body of concrete wall Concrete contaminated with soil or bentonite Cold joint Pockets of coarse aggregate Vertical crack for full depth of panel Bulges Probable cause Inadequate desanding or improper cage installation Loss of Tremie seal due to concreting problems Poorly graded concrete mix, excess slump or aggregate in excess of 1-1/4 inch Two or more separate cages placed in panel Improper mix of bentonite slurry or polymer suspension Inadequate concrete cover Panel joint Concrete contaminated with soil or bentonite Misformed joint, misplaced water stop Bottom of wall above final subgrade Leak below final subgrade Wall not properly constructed in cutoff strata Void or gap in diaphragm wall Inadequate or loss of breaking of wire ties Corrective work. See note 1 Remove and replace defective concrete, grout as necessary Remove and replace defective concrete, grout as necessary Remove and replace defective concrete Grout at leaks, laterally connect future cages in Pretench if unstable fill area and place flowable fill. Line drill or jackhammer face or use rotary mill facer. Install dowels, shotcrete face or pour new concrete cover. spacers, Remove and replace defective concrete, grout as necessary Inadequate cleaning of panel and/or desanding Difficulty extracting stop end device or delays in Tremie placement Inadequate cleaning of panel and/or desanding Inadequate cleaning of panel or concrete placement problem, irregular subgrade/drop at bottom of wall, fractured rock or seams Reinforcing steel cage Misaligned or deformed cage Inadequate spacers Low slump concrete Reinforcing steel congestion Tieback trumpets not properly attached Loose splice or bundled bars Cage flotation Inserts within steel cage Misaligned or mislocated insert Insert not encased in concrete Inadequate connection of to reinforcing steel cage Oversized or obstructive insert Inadequate cleaning of panel and/or desanding insert Remove and replace defective grout as necessary concrete, Clean joint and grout, dry pack voids as necessary Remove and replace defective concrete, grout as necessary Grout outside wall with conventional or grout. Check for additional leaks. Provide additional wall cores. Do not proceed with excavation until leak is sealed. No practical corrective action available Revise concrete design and cage details as necessary Provide adequate spacers Double tie or strap inserts and closure plates Provide couplers or adequate wire ties Too many blockouts in panel, change panel dimensions or properly balance weight of cage Seal leaks, re move defective concrete. Core concrete and realign insert, restore concrete, grout as necessary Remove defective concrete, realign insert, restore concrete Note 1 - In cases where conventional grouting practices can not seal a leak it may be necessary to install a permanent drainage system along the alignment of the leak system and minimized water entry into the parking levels. Seepage water that bypasses the “waterproofing” collects in curb trenches at each floor level then drains vertically to the lowest basement level where it is collected by a gravity system of gutter drains and sump pumps. Precast Panels, Boston. At a private site in Boston, precast panels were substituted for a conventional reinforced concrete diaphragm wall for the exterior basement walls for a 3-level, 35 ft deep (11 m) basement parking structure. The project site was adjacent to salt water and was 40 • DEEP FOUNDATIONS • JAN/FEB 2012 contaminated when passing through high pH soils. The precast panels proved a satisfactory structural alternative; however the cement bentonite grout seal and the intended steel waterstop at the joints could not be executed properly. The plastic filler installed at the joint as a repair deteriorated due to chemical attack by the contaminated groundwater. The construction team made many attempts to seal the joint leak with chemical grouts, however, the grout materials did not swell and harden sufficient to create a watertight joint. The problem was solved by saw cutting a wide slot at the vertical joint, forming a .75 to 1.25 in (19 to 32 mm) gap between the panels. A drainage sock fabric and alkaline resistant, elastomeric joint cover was then applied to the joint. The sock channeled the seepage water vertically down to the lowest basement level where it was collected by a gutter drainage system and drained to sump pumps for eventual disposal. Other Potential Defects. Panels longer than 21 ft (6.4 m) have been cast successfully, however, problems can occur when tremie concrete cannot flow due to a low slump concrete mix, and/or restrictions jet
