Page 1 Objectives_template Module 4:Preloading and vertical drains Lecture 12:Preloading without vertical drains The Lecture Contains: Preloading and sand drains file:///D|/Dr.patra/ground_improvement_techniques/lecture12/12_1.htm [10/11/2011 4:25:52 PM] Page 2 Objectives_template Module 4:Preloading and vertical drains Lecture 12:Preloading without vertical drains The Lecture Contains: Preloading and sand drains file:///D|/Dr.patra/ground_improvement_techniques/lecture12/12_1.htm [10/11/2011 4:25:52 PM] Objectives_template Module 4:Preloading and vertical drains Lecture 12:Preloading without vertical drains Preloading and sand drains Preloading without vertical drains: Settlement calculations: Figure shows the case where a soft, normally consolidated foundation is preloaded. With earth fill exerting a pressure equivalent to a future building with a raft foundation. Initial void ratio where water content specific gravity of soil solids compression index = initial vertica pressure After 90% of this settlement has taken place, the surcharge is removed and construction of the building begins. Figure 12.1 file:///D|/Dr.patra/ground_improvement_techniques/lecture12/12_2.htm (1 of 2) [10/11/2011 4:25:52 PM] Page 3 Objectives_template Module 4:Preloading and vertical drains Lecture 12:Preloading without vertical drains The Lecture Contains: Preloading and sand drains file:///D|/Dr.patra/ground_improvement_techniques/lecture12/12_1.htm [10/11/2011 4:25:52 PM] Objectives_template Module 4:Preloading and vertical drains Lecture 12:Preloading without vertical drains Preloading and sand drains Preloading without vertical drains: Settlement calculations: Figure shows the case where a soft, normally consolidated foundation is preloaded. With earth fill exerting a pressure equivalent to a future building with a raft foundation. Initial void ratio where water content specific gravity of soil solids compression index = initial vertica pressure After 90% of this settlement has taken place, the surcharge is removed and construction of the building begins. Figure 12.1 file:///D|/Dr.patra/ground_improvement_techniques/lecture12/12_2.htm (1 of 2) [10/11/2011 4:25:52 PM] Objectives_template Figure 12.2 file:///D|/Dr.patra/ground_improvement_techniques/lecture12/12_2.htm (2 of 2) [10/11/2011 4:25:52 PM] Page 4 Objectives_template Module 4:Preloading and vertical drains Lecture 12:Preloading without vertical drains The Lecture Contains: Preloading and sand drains file:///D|/Dr.patra/ground_improvement_techniques/lecture12/12_1.htm [10/11/2011 4:25:52 PM] Objectives_template Module 4:Preloading and vertical drains Lecture 12:Preloading without vertical drains Preloading and sand drains Preloading without vertical drains: Settlement calculations: Figure shows the case where a soft, normally consolidated foundation is preloaded. With earth fill exerting a pressure equivalent to a future building with a raft foundation. Initial void ratio where water content specific gravity of soil solids compression index = initial vertica pressure After 90% of this settlement has taken place, the surcharge is removed and construction of the building begins. Figure 12.1 file:///D|/Dr.patra/ground_improvement_techniques/lecture12/12_2.htm (1 of 2) [10/11/2011 4:25:52 PM] Objectives_template Figure 12.2 file:///D|/Dr.patra/ground_improvement_techniques/lecture12/12_2.htm (2 of 2) [10/11/2011 4:25:52 PM] Objectives_template Module 4:Preloading and vertical drains Lecture 12:Preloading without vertical drains Preloading & Sand drains Upon reloading the foundation soil, the final settlement of the building (Exerting a pressure could be expressed in terms of reloading index The curve was assumed to show a distinct break at the original overburden pressure of the normally consolidated soil element, this means the overburden pressure was assumed to be equal to the pre consolidation pressure. For soil samples obtained in the pre consolidation pressure has to be deduced using Casagrandeâ€™s graphical procedure. Figure 12.3 AB - secondary consolidation under overburden pressure. BC- primary consolidation due to surcharge. CD-secondary consolidation due to surcharge. file:///D|/Dr.patra/ground_improvement_techniques/lecture12/12_3.htm [10/11/2011 4:25:53 PM] Page 5 Objectives_template Module 4:Preloading and vertical drains Lecture 12:Preloading without vertical drains The Lecture Contains: Preloading and sand drains file:///D|/Dr.patra/ground_improvement_techniques/lecture12/12_1.htm [10/11/2011 4:25:52 PM] Objectives_template Module 4:Preloading and vertical drains Lecture 12:Preloading without vertical drains Preloading and sand drains Preloading without vertical drains: Settlement calculations: Figure shows the case where a soft, normally consolidated foundation is preloaded. With earth fill exerting a pressure equivalent to a future building with a raft foundation. Initial void ratio where water content specific gravity of soil solids compression index = initial vertica pressure After 90% of this settlement has taken place, the surcharge is removed and construction of the building begins. Figure 12.1 file:///D|/Dr.patra/ground_improvement_techniques/lecture12/12_2.htm (1 of 2) [10/11/2011 4:25:52 PM] Objectives_template Figure 12.2 file:///D|/Dr.patra/ground_improvement_techniques/lecture12/12_2.htm (2 of 2) [10/11/2011 4:25:52 PM] Objectives_template Module 4:Preloading and vertical drains Lecture 12:Preloading without vertical drains Preloading & Sand drains Upon reloading the foundation soil, the final settlement of the building (Exerting a pressure could be expressed in terms of reloading index The curve was assumed to show a distinct break at the original overburden pressure of the normally consolidated soil element, this means the overburden pressure was assumed to be equal to the pre consolidation pressure. For soil samples obtained in the pre consolidation pressure has to be deduced using Casagrandeâ€™s graphical procedure. Figure 12.3 AB - secondary consolidation under overburden pressure. BC- primary consolidation due to surcharge. CD-secondary consolidation due to surcharge. file:///D|/Dr.patra/ground_improvement_techniques/lecture12/12_3.htm [10/11/2011 4:25:53 PM] Objectives_template Module 4:Preloading and vertical drains Lecture 12:Preloading without vertical drains Consolidations under Structural fill with Surcharge Assume a highway embankment is placed on highly compressible soil. The expected amount of final settlement can be at the top of the embankment. ? How much extra surcharge has to be applied for a given time t in order to produce of the final settlement under the embankment load P alone? Step1 calculate for an assumed q. These are the final settlement due to embankment loading alone and embankment plus surcharge. Step 2 (settlement under p+q at time +) Step 3 Step 4 find Step 5 Step 6 increase q; if decrease q repeat the calculation till Example 12.1 A land reclamation project requires 3m sand & gravel fill to be placed in a deposit with the following profile. Ground water level at the surface Soft silty clay file:///D|/Dr.patra/ground_improvement_techniques/lecture12/12_4.htm (1 of 2) [10/11/2011 4:25:53 PM]Read More

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