SOIL MECHANICS & TESTINGSOIL COMPACTION By Kamal Tawfiq, Ph.D., P.E. Fall 2008 . . . Sheep foot Roller 1.Rubber-Tire .Rammers 2.Smooth Rollers 4.Dynamic Compaction 3.Soil Compaction in the Field: 5.Vibratory Plates 6. soil (2)> soil (1) Load Air Air Water Water Soil Matrix Compressed soil Solids Solids soil (1)= WT1 VT1 soil (2)= WT1 VT2 .Definition: Soil compaction is defined as the method of mechanically increasing the density of soil by reducing volume of air. Reduce Soil Settlement 3.Increase Soil Strength 2.Compaction Effort Required (Energy) Types of Compaction : (Static or Dynamic) 1.Kneading 4.Impact 3.Reduce Erosion Damage Factor Affecting Soil Compaction: 1.Water Content (wc) 3.Pressure Water is added to lubricate the contact surfaces of soil particles and improve the compressibility of the soil matrix .Soil Type 2.Vibration 2.Reduce Frost Damage 5.Why Soil Compaction: 1.Reduce Soil Permeability 4. Soil Compaction in the Lab: 1.Standard Proctor Test 2.Modified Proctor Test 3.Gyratory Compaction Standard Proctor Test Modified Proctor Test Gyratory Compaction . 5 pound hammer d max 3 H = 12 in 4 2 5 1 25 blows per layer wc1 wc2 wc3 wc4 wc5 d1 d2 d3 d4 d5 (OWC) Optimum Water Content Increasing Water Content 4 inch diameter compaction mold.Standard Proctor Test Gs w dry 1e G s w ZAV = Dry Density 1+ Wc Gs Sr Zero Air Void Curve Sr =100% 5. (V = 1/30 of a cubic foot) Wet to Dry to Optimum Optimum dry = wet 1+ Wc% 100 Compaction Curve Water Content .Soil Compaction in the Lab: 1. 375 foot-pounds per cubic foot 2.Soil Compaction in the Lab: 1.Modified Proctor Test ASTM D-1557 or AASHTO T-180 d max Zero Air Void Curve Sr < 100% d max Compaction Curve for Modified Proctor Energy = 56.520 foot-pounds per cubic foot Compaction Curve for Standard Proctor (OMC) (OMC) Energy = Number of blows per layer x Number of layers x Weight of hammer x Height of drop hammer Volume of mold Moisture Content .Standard Proctor Test Dry Density Zero Air Void Curve Sr = 60% Zero Air Void Curve Sr =100% ASTM D-698 or AASHTO T-99 Energy = 12. Effect of Energy on Soil Compaction Increasing compaction energy Dry Density Lower OWC and higher dry density Higher Energy V ZA In the field increasing compaction energy = increasing number of passes or reducing lift depth In the lab increasing compaction energy = increasing number of blows Water Content . the maximum dry density in the field may reach 90% to 95%.Field Soil Compaction Because of the differences between lab and field compaction methods. Dry Density ZAV d max d max (OMC) Moisture Content . 7 126.88 4.4 127.28 4.70.19 116.09 4.8 106.0 103. draw the ZAV curve. Solution: Volume of Proctor Mold (ft3) Weight of wet soil in the mold (lb) Water Content (%) Volume of Mold (ft3) 1/30 1/30 1/30 1/30 1/30 1/30 3.4 108.88 4.23 4.Example: The laboratory test for a standard proctor is shown below.9 128.23 4. Determine the optimum water content and maximum dry density.4 122. If the Gs of the soil is 2.2 125.7 Water Content (%) Dry Unit Weight (lb/ft3) 12 14 16 18 20 22 103.6 109.0 dry = wet 1+ Wc % 100 ZAV = G s w 1+ Wc Gs Sr .24 4.24 4.09 4.28 4.19 12 14 16 18 20 22 1/30 1/30 1/30 1/30 1/30 1/30 Weight of wet Wet Unit soil in the Weight mold (lb) (lb/ft3) 3.9 107. dry max Optimum Water Content . then dried and weighed again to determine its moisture content. This density is compared to the maximum Proctor density obtained earlier. . The soil is removed and weighed. A soil's moisture is figured as a percentage.Checking Soil Density in the Field: 1. The dry weight of the soil removed is divided by the volume of sand needed to fill the hole. which gives us the relative density of the soil that was just compacted. The isotope source gives off photons (usually Gamma rays) which radiate back to the mater's detectors on the bottom of the unit.Nuclear Density (ASTM D2292-91) Nuclear Density meters are a quick and fairly accurate way of determining density and moisture content.Sand Cone (ASTM D1556-90) A small hole (6" x 6" deep) is dug in the compacted material to be tested. This gives us the density of the compacted soil in lbs per cubic foot. 2.Balloon Dens meter The same as the sand cone. The specific volume of the hole is determined by filling it with calibrated dry sand from a jar and cone device. Dense soil absorbs more radiation than loose soil and the readings reflect overall density. Water content (ASTM D3017) can also be read. except a rubber balloon is used to determine the volume of the hole 3. The meter uses a radioactive isotope source (Cesium 137) at the soil surface (backscatter) or from a probe placed into the soil (direct transmission). all within a few minutes. Nuclear Density Sand Cone . number of passes. This method. most economical method of meeting the required specs. lift depths. A "recipe" is given as part of the job specifications to accomplish the compaction needed. gives the contractor much more flexibility in determining the best.End-result Specification Only final compaction requirements are specified (95% modified or standard Proctor). . 2. machine speed and moisture content.Compaction Specifications: Compaction performance parameters are given on a construction project in one of two ways: 1.Method Specification detailed instructions specify machine type.