Outline. Definitins. Parameters 3. Cmressibility f Chesinless Sils (Sand and Gravel) 4. Cmressibility f Chesive Sil 5. The edmeter Test fr Cmressin Measurements 6. Swelling f Clay 7. Cllasibility f Sand 009 Dr. Omar Y. Ezzeldine /
. Definitins Cmressibility is the rerty thrugh which articles f sil are brught clser t each ther due t escae f air and/r water frm vids under the effect f an alied ressure. Nrmally Cnslidated Clay is a clay layer where the effective ressure is equal t the vercnslidatin ressure. This means the resently acting effective ressure is the highest ressure it has been subjected t during its gelgical histry. This clay will be highly cmressible. Precnslidated Clay r Overcnslidated Clay is a clay layer where the effective ressure is less than the vercnslidatin ressure. This means that this clay has been, in the ast, subjected t a higher ressure than the ne resently acting. This clay will be f lw cmressibility. Under cnslidated Clay is a clay layer where the effective ressure is higher than the vercnslidatin ressure. This means that this clay has nt "felt" yet f the ttal effective ressure it is currently subjected t. Precnslidatin Pressure r vercnslidatin ressure f a certain clay layer, is the largest ressure that has been acting n this layer during its gelgical histry. Swelling Pressure is the ressure caable t maintain cnstant vlume (r t bring back t riginal vlume) f clay when subjected t water innundatin and can be determined by the edmeter Cllasible Sil is a cemented sandy sil in dry cnditin. When this tye f sil is submerged, it underges severe decrease in vlume due t lss f cementatin. 009 Dr. Omar Y. Ezzeldine /
. Parameters Cefficient f Cmressibility Definitin Cefficient f Cmressibility is the rate f change f vid rati (e) with resect t the alied effective ressure () during cmressin. Symbl and Equatin e a v Δe Δ a v changes accrding t stress level ( ) Dimensin [L F - ] /MPa, cm /kg, m /t Δe Δ Cefficient f Vlume Cmressibility Definitin Cefficient f Vlume Cmressibility is the vlume decrease f a unit vlume f sil er unit increase f effective ressure during cmressin. V ΔVΔe Δ V s ev s Water ev s Water V Slids Slids V s V s Befre After Symbl and Equatins m v ΔV V Δ Δe V ( + e ) Δ s V s ( + e ) Δ ( + e ) Δe a v Dimensin [L F - ] /MPa, cm /kg, m /t 009 Dr. Omar Y. Ezzeldine 3/
Mdulus f Elasticity Definitin Mdulus f Elasticity is the relatinshi between ressure in a certain directin and the resultant strain in the same directin. Symbl and Equatin Δ E Δε Linear Elastic Dimensin [FL - ] MPa, kg/cm, t/m Δε Δ Nn linear Nn Elastic ε Cmressin Index Definitin Cmressin Index Fr a nrmally cnslidated clay, the cefficient f cmressibility is the sle f the linear relatinshi between vid rati(e) and lg () where () is the alied effective ressure. Symbl and Equatin e c c Δe Δ lg Dimensins [Dimensinless] Over Cnslidated Δe c Δ lg() Nrmally Cnslidated lg () 009 Dr. Omar Y. Ezzeldine 4/
3. Cmressibility f Chesinless Sils (Sand and Gravel) Chesinless sils (sand and gravel) have higher ermeability than chesive sils (clay and silt). Under nrmal lading cnditins, cmressibility is immediate. E Dense Sand Cmressibility f chesinless sils is lwer than that f chesive sils. Stress Strain curves f sands are as shwn in figure. E Medium The relatinshi between stress and strain f sands is nt linear and strains are nt recverable. Hwever, because sand cmressin is small and immediate as cmared t chesive sils, elastic mdel culd be used t reresent sand cmressibility. E 3 Lse ε Tyical values f Mdulus f Elasticity f Sand: E Sand (kg/cm ) Lse Medium Dense Very Dense 00 50 50 750 750 500 500 4000 Hw t determine Mdulus f Elasticity f natural sands It is difficult t btain sand samles that reresent natural sand cnditin fr labratry testing. Therefre, the mdulus f Elasticity f sand is determined based n field tests r based n exerience based estimatins 009 Dr. Omar Y. Ezzeldine 5/
4. Cmressibility f Chesive Sil Chesive sils (clay and silt) have very lw ermeability. Under nrmal lading cnditins, cmressibility is deendent n re water dissiatin rate. Cmressibility f chesive sils is time deendent and large in magnitude. Cmressibility f chesive sils is determined in the labratry using the edmeter Effect f Stress Histry n Clay Cmressibility When a clay layer is frmed fr the first time, its cmressibility is high. The relatinshi between the rate f reductin f vids rati (e) and the increase f verburden stress n the lg scale is linear: the virgin curve. If a clay layer is frmed fr the first time with a ttal height (H), it is under an effective stress ( c ). It fllws the ath ( ). 3 In the case verburden ressure is reduced t ressure ( ), due t ersin fr examle, the clay des nt fllw the same curve (it is nt elastic) but fllws a mre mild cmressibility sle ( 3). 4 At Pint (3) the clay is vercnslidated, the vercnslidatin rati is equal t ( c / ).If the clay is subjected t additinal stress its cmressibility very small as cmared t the virgin curve as lng as the additinal ressure is less than ( c ). 5 6 The clay cntinue t act as vercnslidated clay as lng as its effective stress is less than the vercnslidatin ressure ( c ) (3 4). If the effective stress is increased further, the clay acts as nrmally cnslidated clay (4 5). Cnsider a clay samle taken frm a certain deth (H), hw can we determine if this samle is vercnslidated r nrmally cnslidated? 3 Calculate the verburden ressure at this deth ( ). Determine the recnslidatin ressure c frm the edmeter test. If c, the clay is nrmally cnslidated. 4 If < c, the clay is vercnslidated. 5 If > c, the clay is under cnslidated. H γ H + abvegwt γ sub belwgwt H 009 Dr. Omar Y. Ezzeldine 6/
Effective ressure Overcnslidatin ressure e Nrmally Cnslidated Nrmally Cnslidated Clay frmed by sedimentatin - 3 4 Effective ressure 3 Overcnslidatin ressure 3 < Over Cnslidated 5 Ersin is resnsible fr vercnslidatin. Overcnslidatin rati / 3-3 c lg () Δ Δ Clay acts as Overcnslidated as lng as the effective stress under lad (Δ) is less than c. Clay acts as Nrmally Cnslidated when the effective stress under lad (Δ) is higher than c. 3-4 4-5 009 Dr. Omar Y. Ezzeldine 7/
5. The edmeter Test fr Cmressin Measurements Objectives: T study cmressibility f clay secimen: 3 Establish relatinshi between vlume changes with resect t changes in effective ressure. Define effect f stress histry n the tested secimen. Verify relatinshis related t thery f cnslidatin: Pre water dissiatin. Relatinshi between re water dissiatin and vlume change Equiment: The set u f the test L include a cmressin cell where the saturated Cmressin secimen is laced and a P Cell hanging weight (P Table Lad acting n the cmressin cell is magnified by the Lever Arm Rati (LAR). L P LAR L P P L P Prcedure Measure initial cnditin: e, w, G s. Preare the secimen by trimming int the metal ring. 3 4 5 6 Place the ring inside the cmressin cell between tw rus lates. A Metal cver is lace abve the uer rus late t receive the alied lad. Set u the dial gage t zer reading. Fill the cmressin cell with water u t the uer rus late level. Place the hanging lad such that the ressure n the clay secimen is equal t the first lading ste (0.5 kg/cm fr examle). Take readings f dial gage (cmressin f the secimen) with time until cmressin sts r fr 4 hurs. 009 Dr. Omar Y. Ezzeldine 8/
7 Increase the ressure n the secimen accrding t a certain scale. Unlading and relading cycles culd be carried ut. Fr examle: 0.5, 0.50,.00,.00,.00,.50,.00, 4.00, 8.00, 6.00 kg/cm. Results: - Results are resented in term f relatinshi between alied Δe ΔH cell ressure and cmressin (ΔH) e Water Water - Change f vids rati is calculated +e H H ΔH Δe Slids Slids ( e ) H + - Plt e- curve Vlume Samle - Plt e-lg() curve Outut Parameters: Cefficient f cmressibility (a v ). Cefficient f vlume cmressibility (m v ). 3 recnslidatin ressure ( c ). 4 Cmressin Index (c c ). 5 Recmressin Index (c r ). 6 Overcnslidatin Rati (OCR). Cefficient f cmressibility (a v ). Frm e- lt, calculate the sle f the curve at varius stress levels. Cefficient f vlume cmressibility (m v ). Fr all values f a v, calculate m v by dividing a v by (+e ) e e lg 009 Dr. Omar Y. Ezzeldine 9/
3 Precnslidatin Pressure A P α/ α/ Vid Rati e σ vm E c r c c c Vertical Stress σ (lg scale) 3 4 5 6 Cnsider e-lg lt. Determine the int f maximum curvature (A). Frm this Pint (A), draw a hrizntal line and a tangent line. Draw the line bisecting the angle ( α ) between the hrizntal and the tangent. Determine the int at the start f the linear rtin f the curve (E). Extend the linear rtin f the curve frm Pint (E) until it meets the bisectin line at Pint (P). 7 Precnslidatin ressure c is the x-crdinate f Pint (P) n the lg scale. 4 5 6 Cmressin Index (c c ). Cmressin Index is the sle f the linear rtin f the cmressin curve. c c Δe Δ lg e e ( ) lg( ) lg( ) e e lg Recmressin Index (c r ). Cmressin Index is the sle f the equivalent linear rtin f the lading-unl Overcnslidatin Rati Calculate the verburden ressure at the level where the secimen is taken frm ( ). c OCR 009 Dr. Omar Y. Ezzeldine 0/
6. Swelling f Clay General Remarks Swelling clay is nrmally hard dry clay. A swelling clay increases in vlume when it has an access t water and is naturally f lw water cntent. Such clays are f secial mineralgical and chemical cmsitin: - - - Mntmrillnite Illite Kalinite Clay has a very high swelling tential Clay has a Slight swelling tential Clay has n swelling tential Measurement f Swelling Pressure Use the Oedmeter t measure swelling ressure. Tw tests are alicable: N swell test and recmressin test. A) N Swell Test Preare a dry samle in the edmeter ring Add water t innundate the cmressin cell. 3 Watch the uward mvement f the samle. Increase vertical ressure after every small uward mvement t kee the dial gage reading t zer. 4 Kee increasing the ressure n the cell until n uward mvement culd be measured. 5 The final alied vertical ressure is the swelling ressure. B) Recmressin Test Preare a dry samle in the edmeter ring Aly vertical ressure n the samle n stages until reaching a ressure level cmared t the verburden ressure ( ). 3 Add water t innundate the cmressin cell. 4 Allw sme time t fr the secimen t underg swelling until the vertical uward mvement is sted. 5 Increase the vertical ressure t vercme the uward mvement f the secimen until the dial gage is back t zer. 6 The vertical ressure added after innundatin is the swelling ressure. Treatment f swelling clay Swelling clay layer is t be relaced by cmacted sand. Restrict water use and use effective water insulatin rhibit water frm reaching the swelling clay layer. 3 Use rigid fundatin system t resist the detrimental effect f differential heave. 4 Use chemical stabilizatin t reduce swelling (lime fr examle). 009 Dr. Omar Y. Ezzeldine /
7. Cllasibility f Sand General Remarks A cllasible sil suffers a reductin in vlume due t wetting and/r submergence and lading. Usually f fine sands and silts and smetimes lw cntent f clay in a lse structure state and mstly in a dry r near dry cnditin. As in Less (wind blwn fine sands and silts, slightly cemented by silt r chemicals as calcium carbnates). The danger is assciated nrmally with uneven wetting which causes differential settlement. Measurement f Cllasibility (Cllase Rati) Use the Oedmeter h Δh Cllase Rati h c Cllase Rati (% Danger f Prblem Frm T 0.0%.0% N Prblem.0% 5.0% 0%Mderate Prblem 5.0% 0.0% Prblem c 0.0% 0.0% Dangerus Prblem 0.0% >0.0% Very Dangerus Prblem h is the initial secimen height c is the exected stress frm structure r as er cde (00 kpa). h Δh c Treatment By submerging sil by water fr sufficient time (4, 48, 7, hurs) fllwed by heavy vibratry cmactin. Smetimes and fr high cllasibility, sil relacement may be used. 009 Dr. Omar Y. Ezzeldine /
5. The edmeter Test fr Cmressin Measurements Objectives: T study cmressibility f clay secimen: Establish relatinshi between vlume changes with resect t changes in effective ressure. Define effect f stress histry n the tested secimen. 3 Verify relatinshis related t thery f cnslidatin: - Pre water dissiatin. - Relatinshi between re water dissiatin and vlume change Equiment: The set-u f the test include a cmressin cell where the saturated secimen is laced and a hanging weight (P ) system Lad acting n the cmressin cell is magnified by the Lever Arm Rati (LAR). L Cmressin Cell P Table L P L P LAR L ( P ) P Prcedure Measure initial cnditin: e, w, G s. Preare the secimen by trimming int the metal ring. 3 Place the ring inside the cmressin cell between tw rus lates. A Metal cver is lace abve the uer rus late t receive the alied lad. 4 Set-u the dial gage t zer reading. Fill the cmressin cell with water u t the uer rus late level. 5 Place the hanging lad such that the ressure n the clay secimen is equal t the first lading ste (0.5 kg/cm fr examle). 6 Take readings f dial gage (cmressin f the secimen) with time until cmressin sts r fr 4 hurs. 009 Dr. Omar Y. Ezzeldine 8/