Subsidence and Pressure Grouting in Houston, TX
Subsidence from ground water depletion in the world is becoming a big problem for man. The reason is that ground water usage by man is causing depletion of our ground waters in our strata formation. The ground water depletion, which causes depletion in our sand/silt lense at lower depths, affects buildings and the soils at grade by subsidence. The reason why subsidence occurs is the water in the formation has a hydraulic head pressure and when the water is depleted the hydraulic head pressure is reduced and the overburden has no place to go but down. The subsidence then affects land values and structures over the subsided area. When subsidence occurs the soil mass at grade subsides and acts like a bowl and water can pond where it never has before. Pier-A-Mid has a Patent Pending for a method which is not like installing bell bottom piers, driven piers, columns or footers to lift structures. Bell Bottom piers and footers can usually only be installed above water tables in formations and driven piers can only support the weight load of the diameter of the driven column which if the strata has a low PSF and the driven column or cylinder is only 6” or 2’ in diameter and placed on soils that only have a 1500 psf this is usually not enough PSF to support the load. Pier-A-Mid method is to drive/ drill a 3” pipe into the formation to find the weak zone which is usually a sand/silt lens and then hydraulically pump a stiff low mobility cement grout into the weak zone and lift the overburden to level. These weak zones can be found at depths that are from -20’ and lower. These voids which are located in water zones in rock formations, sand/silt lens in clay formations and Aquifers.
This process does not deal with differential movement of a grad slab like a road, floor slab or structure at grade. When a zone is found in the formation at any depth (weak zone) in the formation is located the stiff low mobility cement grout which is about a 1.5” to a 2” slump grout is injected into this zone. The injected grout under injection pressure first squeeze’s out any ground water if present and then as lateral pressure increases in the targeted injection zone from the injected grout the overburden starts to heave. The formation above the lens starts lifting everything from the targeted injection zone to the structure at grade or below grade. This process can lift structures that are in flood plains or have flooding issues from rain water, or rivers that overflow their banks causing flood damage.