Soil Compaction PDF

Soil Compaction  Soil Compaction Objective Increase density, strength, bearing capacity and reduce permeability and compressibility Laboratory work (lab.) Field Compaction Obtain maximum dry density (contractors) by rollers and and op...

Soil Compaction  Soil Compaction Objective Increase density, strength, bearing capacity and reduce permeability and compressibility Laboratory work (lab.) Field Compaction Obtain maximum dry density (contractors) by rollers and and optimum water content compactors Check Compaction execution in the field by several methods Compaction: the process of increasing soil unit weight by soil solid particles into tighter state, i.e reducing the soil void ratio by means of mechanical devices. Compaction: ‫ بطرد فراغات الهواء من‬،‫زيادة كثافة التربة المحدولة بنسبة معينة من الرطوبة‬. ‫بين حبيباتها باستخدام وسائل ميكانيكية‬ γd max ‫الهدف من استخدام الرطوبة المثلى هو إلعطاء اكبر كثافة ممكنة‬  Compaction - Consolidation  Compaction means  Consolidation means the removal of air- the removal of water- filled porosity. filled porosity.  Principles of Compaction Compaction of soils is achieved by reducing the volume of voids. It is assumed that the compaction process does not decrease the volume of the solids or soil grains· uncompacted compacted uncompacted compacted What Does Compaction Do? 1) Increased Shear Strength, density, and bearing capacity This means that larger loads can be applied to compacted soils since they are typically stronger. ‫زيادة الكثافة والمقاومة وقابلية التحمل‬ 2) Reduced Permeability ‫تقليل النفاذية‬ This inhibits soils’ ability to absorb water, and therefore reduces the tendency to expand/shrink and potentially liquefy 3) Reduced Compressibility ‫تقليل قابلية االنضغاط‬ This also means that larger loads can be applied to compacted soils since they will produce smaller settlements. 4) Swelling & Shrinking ‫االنتفاخ واالنكماش يتغير حسب نوع التربة‬  Mechanism of compaction Cohesive Cohesionless principles: principles: 1- interaction between 1- rearrangement of soil grains Adsorbed layer interpretable force 2- breaking up of some 2- breaking up of some old bonds cementation and establishment of some new 3- bending and distortion of soil bonds between particles particles 3- bending and distortion of soil particles Lambe theory (physico-chemical concept) Proctor theory (1933) lubrication theory ‫إضافة الماء تسبب طبقة رقيقة تمتص من قبل حبيبات‬ ‫التربة>>زيادة الماء تزيد من الطبقة‬  Water Role in Compaction Process  Water lubricates the soil grains( cohesionless soil ) so that they slide more easily over each other and can thus achieve a more densely packed arrangement.  Expansion of double layer and a tendancy to more orderly arrangement of particles which gives higher density (clayey soil). – A little bit of water facilitates compaction – too much water inhibits compaction.  The Goal of Compaction  Reduce air-void volume Va in soils as much as is possible. Phase Diagram  For a given water content w, the va Air wA max. degree of compaction that can be achieved is when all of the air Water wW vt vw voids have been removed, that is (S=1). vs Solids wS  Since S = w Gs/e , the corresponding void ratio  (for S=1) will be: e = w Gs ‫اذن ما هو الهدف من عملية الحدل؟‬ ‫الهدف هو إجراء تجارب مختبريه على التربة المراد استعمالها في الحقل‬ ‫ وكذلك كمية الحدل (جهد‬o.m.c )‫وإيجاد الكمية المناسبة من الماء (الرطوبة‬.‫ حسب المواصفات‬،‫الحدل) أي تحديد الرطوبة المثلى والكثافة الجافة العظمى‬  : ‫اذن باستعمال‬ ‫أهم عالقة يتوجب دراستها هي بين الرطوبة‬ ‫جهد معين‬ ‫والكثافة الجافة وكما في الشكل‬ ‫وتربة معينة‬ weight of wet soil (compacted soil ) Find w/c  wet W  wet  d   1 w / c V (1  w / c) volume of mold γd max γd dry wet side O.M.C side M.C% Typical compaction curve  Zero-Air-Void Curve ‫وهو يمثل منحني أقصى حدل ممكن بنسبة ماء معينة أي أن التربة تبقى ماء وتربة فقط‬ ZAV:The curve represents the Degree of Saturation fully saturated condition 2.0 60% 80% 100% (S=100%). ZAV cannot be reached by "Zero compaction. Air ( Mg / 3m ) 1.9 Line of Line of Optimum: A line drawn Voids" optimums through the peak points of 1.8 Modified several compaction curves at Proctor different compactive efforts for Dry density the same soil will be almost 1.7 parallel to a 100 % S curve Standard Proctor Entrapped Air: is the distance 1.6 0 5 10 15 20 25 between the wet side of the Water content w (%) compaction curve and the line of 100% saturation. Points from the ZAV curve can be calculated from: dry = Gsw / 1+ e  ‫‪The Standard Proctor Test‬‬ ‫وضع العالم ‪ R. R. Proctor‬عام ‪ 1933‬أسس هذه الطريقة‪ ،‬ويتضمن‬ ‫الفحص رص التربة على شكل طبقات تحت تأثير عدد من الضربات لكل طبقة‬ ‫باستعمال دقاقة اسطوانية قطرها ‪ 2‬انج وتسقط بحرية من ارتفاع معين‪.‬‬  The Standard Proctor Test Equipments Hammer Weight 5.5 lb Drop Height h=12” soil Volume 1/30 ft3 or 944 cm3 Diameter 4 in or 10.16 cm Height 4.584 in or11.643cm  Standard Energy (Effort) Compactive effort (energy) applied to soil per unit volume: (# blows/layer) * (# of layers) * (hammer we ight) * (height of drop)  Volume of mold (25blows/layer) * (3 of layers) * (5.5 lbs) * (1.0 ft)   12,375 ft  lb / ft 3 (1/30)ft 3  No.of blows  Hightof fall  No.of layers  Wt.of hammer compactive effort  Vol. of mold 25  1   3  5.5lb compactive effort( standard )  1 / 30  12,375 lb. ft / ft 3 25 1.5  5  10 compactive effort( modified )  0.075  56250 lb. ft / ft 3 4.54 56250  ‫النسبة بين الطاقة المستخدمة في الطريقتين‬ 1 12375 Mold (fine soil) D × h = 4" × 4.6" = 1/30=0.033 ft3 Mold (granular soil) D × h = 6" × 4.6" =0.075 ft3 )h=2.5"( ‫) ارتفاعه‬Collar( ‫غطاء‬  Standard Proctor Test o The soil is mixed with varying amounts of water to achieve different water contents. o For each water content,the soil is compacted by dropping a hammer 25 times onto the confined soil o The soil is in mold will be divided into three lifts o Each Lift is compacted 25 times o This is done 4-6 times from dry-wet Layer or lift # 3 soil Layer or lift # 2 Layer or lift # 1 25 Blows/Layer  Modified Proctor Test  Was developed during World War II  By the U.S. Army Corps of Engineering  For a better representation of the compaction required for airfield to support heavy aircraft.  Modified Proctor Test  Same as the Standard Proctor Test with the following exceptions:  The soil is compacted in five layers  Hammer weight is 10 Lbs or 4.54 Kg  Drop height h is 18 inches or 45.72cm  Then the amount of Energy is calculated  Remember Standard Proctor Energy  12,375 ft  lb / ft 3 (25blows/layer) * (5 of layers) * (10 lbs) * (1.5 ft) modified energy  (1/30)ft 3 E MP  56,250 ft  lb / ft 3 #5 #4 soil E MP 56,250 ft  lb / ft 3 #3   4.55 #2 E SP 12,375 ft  lb / ft 3 #1  Comparison-Summary Standard Proctor Test Modified Proctor Test  Mold size: 1/30 ft3  Mold size: 1/30 ft3  12” height of drop  18” height of drop  5.5 lb hammer  10 lb hammer  3 layers  5 layers  25 blows/layer  25 blows/layer  Energy 12,375 ft·lb/ft3  Energy 56,250 ft·lb/ft3 Dry Density (gd) Modified E=E2 Standard E=E1 Water Content (w)  Compaction Procedure in Lab The Drop Compactio Method Mold size No. of No. of Soil type hammer distance n effort type (dia.*h.) drops layers (lb) (inch) (lb.ft/ft3) Standard 4 * 4.6 5.5 12 25 3 12400 Fine material Modified 4 * 4.6 10 18 25 5 56000 Standard 6 * 4.6 5.5 12 55 3 12400 Course material Modified 6 * 4.6 10 18 55 5 56000  Range of Optimum w/c Sand (sub- (Silty sand) base material (sandy silt) Silt Clay 6-10 8-12 12-16 15-22  Results from Standard Proctor Test Maximum dry  Optionally, the unconfined unit weight compressive strength of the  Dry Density (gd) soil is also measured    A sample from the mold  Optimum water content Water Content (w)  Results-Explanation Below womc At womc Dry of Optimum The density is at the Above womc As the water content maximum, and it does not increase any further. Wet of Optimum increases, the particles Water starts to replace develop larger and larger OMC soil particles in the water films around them, which tend to “lubricate” Dry Density (gd)   mold, and since w