The building is a single story structure approximately 80 feet by 125 feet in size and consists of wood post and beam framing, such as a pole building. The walls are constructed of wood posts, embedded in concrete piers at approximately 8 feet on center. The posts provide the vertical and lateral support for the walls and roof. The roof is framed with pre-engineered wood roof trusses. The floor of the building consists of a 6 inch thick reinforced concrete slab on grade. A septic tank and a leach field are situated along the west side of the building.
Problems That Prompted Repair
The building and concrete slab on grade were experiencing settlement. The settlement had caused cracks in the concrete slab on grade and interior finishes of the office area of the building. The majority of settlement occurred along the west side of the building and the concrete slab on grade in the warehouse were cracked the entire length of the building. Cracking ranged 3 to 8 feet east of the west wall. A slab construction joint existing in the center of the building and spans north/south. The joint appeared to have separated as a result of the slab settlement along the building.
A structural Observation and Geotechnical Soil Study were performed. Field investigation also performed with the use of a Dynamic Cone Penetrometer (DCP). The primary purpose of this tool is to locate the weak zones in the soils and quantify the comparative degree of ground densification improvement achieved by the deep injection process, as exhibited by the increased number of percussive blows required to penetrate the treated soil mass, when compared to a pre-injection test performed within the confines of the treated mass.
The geotechnical study and structural observation indicated that the soils underlying the foundation and concrete slab on grade consisted of soft clays with considerably high moisture content. These soils are notorious for settlement and collapse upon wetting. It was determined that the settlement had high potential to continue if the problem was not addressed. Separation of the slab joint was determined to have been caused by the settlement of underlying soils. DCP Test results indicated weak soils at depths of 7 feet.
Causes of Deterioration
Deterioration was caused by a leak from a collapsed water tank in 2008 west of the building, effluent from the septic system, surface runoff, or a combination of these influences. Soft clay soils surrounding and beneath the structure and slab contributed to the settlement and associated damaged slab and interior finishes of the building.
Repair System Selection
Selection of the repair system was based on recommendations resulting from structural evaluation of the building. Due to the soil conditions and probability of future settlement, “Deep Injection”, using expanding structural Geo-Polymer, was chosen for correcting the settlement issues.
Penetrometer testing was performed and reviewed. Mapping of the warehouse floor was completed. Profiles for settlement and finish target elevations were performed.
No demolition of the existing concrete slab on grade was necessary due to the utilization of the “internationally patented Geo-polymer injection system”. All soil remediation work was completed “In Situ”.
Surface preparation of the slab, and soil surrounding the outer perimeter of the building, prior to injecting was unnecessary. This is due to the unique nature of the expanding Geo-Polymer technology utilized. Minimal cleanup of the joint area was performed before epoxy was injected and caulking repairs were performed in the west joints and wide joint in the center of the warehouse. The crack repair and joint sealing was performed in the floor slab. Cracks were mechanically routed and gravity fed structural epoxy was injected into the cracks. Caulking of the joints was completed using a urethane sealant as specified by the engineer. Approximately 136 linear feet of cracks and approximately 124 linear feet of control joints were primed and caulked.
Application Method Selection
Repairs required utilization of a specialty technique. The foundation type (posts embedded in shallow concrete piers) does not lend itself well to helical pier stabilization. Stabilization of the underlying soils, individual concrete piers, and the concrete slab on grade itself needed to be modified in order to arrest future settlement. Therefore, the best method of application and method of repair was determined to be the injection of expanding structural Geo-Polymer.
Repair Process Execution
Initial testing of the soils were performed and analyzed to determine injection depths necessary to stabilize the underlying soil structure. Areas to be addressed were mapped and injection ports were prepared beforehand to accommodate frozen soil conditions at the time of repair. The injection of the patented Geo-Polymer material was used to penetrate deeply into the sub grade at depths of an estimated seven feet. Voids beneath the slabs were filled, and slabs lifted back to original elevations. Sub grade soils were stabilized using this Internationally Patented Technology. Deep Injection permanently altered the soil structure, thus stabilizing and preventing future settlement. Once soils were treated, the slab joints were sealed and caulked with epoxy as specified by the project engineer.
Structural floor repair: Sub contractor, gravity fed low viscosity epoxy into the floor cracks to re- establish the original monolithic strength.
Control joint sealants: Sub contractor mechanically cleaned the sides of the existing control joint and caulked with urethane primer and sealant.
Unforeseen Conditions Found: The work was performed in January which added concern for frozen ground and cold temperatures. The settlement originated below frost line. The Project Superintendent made additional efforts to keep equipment warm. The exothermic reaction of the Geo-polymer materials provided further protection against frozen conditions.
It was decided to perform the work on the client’s preferred schedule if possible. One of the unique characteristics of the Geo-Polymer is that it will not freeze during injections (it is not a water based material). Since unit weight was minimized and polymer did not add burden to weakened sub- grade, frozen ground and cold temps did not interfere with the work schedule.
Special Features and benefits of Geo-Polymer Deep Injection Repair Process:
- Eliminated cause of settlement and future potential settlement resulting from the water spill.
- Raised building and slabs to original elevation.
- Saved concrete slab, and interior finish from further damage.
- No downtime to business, timely, safe, clean.
- All work done from above ground without excavation, In-Situ.
- The Business was able to remain fully open during repairs with very little disruption to activities.
- Floor sub-grade was restored to give full support for heavy forklift traffic.
- Structural repair of floors was completed with full co-ordination of warehouse use.
- Project was completed using permanent and economical, “Deep Injection” of Geo-Polymer.