Case study on terzaghi’s theory

Group members:1. Bhavik Kalariya (14soecv11023)

2. Arjun mandaliya (14soecv11030) 3. Kinjal marakana (14soecv11032)

Intoduction Terzaghi's Principle states that when a rock is subjected to a stress, it

is opposed by the fluid pressure of pores in the rock.More specifically, Karl von Terzaghi's Principle, also known as

Terzaghi's theory of one-dimensional consolidation, states that all quantifiable changes in stress to a soil [compression, deformation, shear resistance] are a direct result of a change in effective stress. The effective stress σ is related to total stress σ and the pore pressure u ′by the relationship.

Total stress is equal to the sum of effective stress and pore water pressure.

Introduction• Objective: The following objectives are set forth to achieve the aim of the research: i. To develop consolidation equipment that could be used to run rapid consolidation using constant rate of strain consolidation method. ii. To compare the result of the compression characteristic of the soil, coefficient of consolidation (cv) and compression index (cc) obtained from CRS test to the results of conventional oedometer test. iii. To establish the new criteria of acceptance for Constant Rate of Strain consolidation test. • Scope:i. Disturbed samples are collected from Kluang, Gemas and Air Papan, Johor . Kaolin soil was used as the control sample for the study. ii. The specimens used for the study is remoulded sample. In the case all the disturbed soil samples were dried and grinded into powder and remoulded from slurry under 100, 200 and 300 kPa pre-consolidation pressure using self made remoulded sampler equipment. iii. Conventional oedometer test and the Constant Rate of Strain consolidation test will be conducted to a maximum of 8.5 kN and 1100 kPa vertical pressure respectively.

Introduction

• Materials: A porous medium or a porous material is a solid (often called matrix) permeated by an interconnected network of pores (voids) filled with a fluid (liquid or gas). Usually both solid matrix and the pore network (also known as the pore space) are assumed to be continuous, so as to form two interpenetrating continua such as in a sponge. Many natural substances such as rocks, soils, biological tissues, and man made materials such as foams and ceramics can be considered as porous media.

Assumptions1. The soil is homogenous (uniform in composition throughout) and

isotropic(show same physical property in each direction).2. The soil is fully saturated (zero air voids due to water content being so

high).3. The solid particles and water are incompressible.4. Compression and flow are one-dimensional (vertical axis being the one

of interest).5. Strains in the soil are relatively small.6. The coefficient of permeability and the coefficient of volume

compressibility remain constant throughout the process.

Terzaghi’s formula

Terzaghi's Bearing capacity equations:• Strip footings: Qu = c Nc + γD Nq + 0.5 γB Nγ • Square footings:Qu = 1.3 c Nc + γD Nq + 0.4 γB Nγ • Circular footings:Qu = 1.3 c Nc + γD Nq + 0.3 γB Nγ

Literature viewSr. no. Author Year Title Publish1. Darshana Perera April 24, 2016 Analytical model for

vacuum consolidation incorporating soil disturbance caused by mandrel-driven drains

14 November 2016

2. Caihui Zhu March 22, 2016. Prediction and analysis of surface settlement due to shield tunneling for Xi’an Metro

14 November 2016.

3. Muniram Budhu October 22, 2011. Design of shallow footings on heavily overconsolidated clays

20 January 2012.

Summary(conclusion)

1. Analytical model for vacuum consolidation incorporating soil disturbance caused by mandrel-driven drains :

When vacuum preloading is applied with vertical drains, the rate of consolidation can be increased, and the stability of an embankment is enhanced due to the inward lateral movement. The aim of this study is to develop an analytical solution for vacuum preloading that accurately captures the more realistic variations in compressibility and permeability in actual ground conditions as a result of drain installation.

Summary(conclusion)

2. Prediction and analysis of surface settlement due to shield tunneling:This estimation method is able to take into account the support pressure of the shield head at the tunnel face, the lining support pressure around the tunnel opening, the filling effect of tail grouting, yawing, and pitching of the shielding machine, and the long-term deformation of the remoulded surrounding soil.It is suggested that the new estimation method can be used effectively in estimating the Surface Settlement induced by the shield tunneling method.

Summary(conclusion)3. Design of shallow footings on heavily overconsolidated clays:This method pro-vides a unified analysis rather than two separate analyses to determine the limit bearing capacity and settlement of shallow foundations. It represents the soil consistently. In comparison, the conventional method treats the soil mass below the bottom of the footing as a rigid –perfectly plastic body for the determination of the failure (collapse) load and then treats that same soil as an elastic material for the calculation of settlement. This method can be extended to dense coarse-grained soils, the difficulty is in defining an overconsolidation ratio for these soils .

Results and discussion1. Evaluation of Load Bearing Capacity of Foundations with

Different Vertical Crosssectional Shapes

Result and discussion

Result and discussion

Result and discussion• From the figures, it is observed that the load bearingcapacity of T shape foundation is generally

higher than those of rectangular and wedge shapes. The lowest load bearing capacity was observed with rectangular shape. The relatively higher load bearing capacity recorded with T and wedge shapes is attributed to additional resistance offered by the soil above their bases from the compression by their flanges.

• From fig. 5, it is observed that for rectangular shape foundation, the load-settlement curve is linear up to 0.5 kN load, after which the settlement begins rapid increase with subsequent load increments. But for wedge and T shape foundations,rapid increase in settlement with subsequent load applications begin after 0.62 kN load. This observation is attributed to additional resistance offered by the soil above the bases of T and wedge shapes from the compression by their flanges. Note that the difference in the patterns of the curves becomes more defined after these defined loads.

Result and discussion

2.   ULTIMATE BEARING CAPACITY AND SETTLEMENT FOR RECTANGULAR FOOTINGS• For depth of sand cushion of 900mm for rectangular footing of sizes

100mmx125mm,100mmx150mm 100x175mm 100x200mm, ultimate bearing capacity values are found to be95.49 kN/m², 104.71kN/m², 109.64kN/m²and 114.81kN/m² respectively. As compared to100mmx125mm rectangular footing, the percentage increase in the ultimate bearing capacity for 100x150mm, 100x175mm and 100x200mm rectangular footing are found to be9.65%,14.81% and 20.23 % respectively. Thus it indicates that as footing size increases, ultimate bearing capacity goes on increasing.

• For rectangular footing of size 100x125mm,100x150mm,100x175mm and100x200mm depth of sand cushion below the footing Dsc= 900mm, the values of settlements goes on increasing. The percentage increase as compare to 100x125mm rectangular footing are found to be 4.60%,31.79% and 37.93% respectively. Thus it indicates that as footing size increases, settlement also increases.

References

1) http://eprints.utm.my2) https://en.wikipedia.org/wiki/Poromechanics3) http://www.nrcresearchpress.com4) http://www.rroij.com5) http://www.academia.edu