1. Để biết mức độ và độ dày của tầng đất yếu 2. Nén của tầng lớp đất yếu phải được xác định 3. Theo tải trọng nhất định, nó là cần thiết để ước tính thời gian cần thiết để hoàn thành việc hợp nhất 4. Các vị trí của bảng nước đôi khi cần thiết để kiểm soát tính khả thi của một dự án 5. | Pier Hole Cleaning To ensure that the bottom of the pier hole is clean and free of loose earth the pier hole must be properly cleaned. This can usually be accomplished by adding a small amount of water into the pier hole and spinning the auger lightly so that the loose earth will adhere to the auger and be removed. If loose rocks and soft mud are present in the bottom of the hole it may be necessary to send a helper down the hole to clean the hole by hand. Such an operation is possible only for large-diameter piers. Failure to clean the bottom of the pier hole can sometimes result in excessive settlement. Fortunately most of the small-diameter piers are overdesigned and the skin friction alone is sufficient to support the column load. The condition of the pier bottom is therefore not as critical. Dewatering Groundwater can seep into the pier hole through the upper overburden soils or through the lower bedrock. A pier-drilling operation usually seals the seams in the soil and stops seepage temporarily. Consequently if concrete is available at the site and poured immediately after the completion of the drilling dewatering can be avoided. On the other hand if the pier hole is allowed to stand for a long period of time water will seep into the hole and must be pumped out before pouring concrete. Pier holes left open for a long time can also result in costly hole remediation. An experienced driller under such conditions would rather fill up the hole and re-drill the hole when concrete is available for immediate pouring. If water enters into the pier hole rapidly through the upper granular soils it will be necessary to case the hole above bedrock to control seepage. In most instances the use of casing will seal all seepage through the overburden soils. However casing above bedrock cannot stop the infiltration of water through the seams and fissures of the bedrock. Such water must be pumped out. If water is mixed with auger cuttings in a form of slurry such
