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Bearing Capacity of Coal Measure Rocks

 

1.1 Introduction

 

Design of surface footing on rock encompasses the following examination of different aspects of foundation.

  1.  
  2. The Bearing capacity of Rock to ensure that there will be no crushing or creep of material within the loaded zone.
  3.  
  4. Settlement of the foundation, which will result from elastic strain of the rock and possibly inelastic compression of weak seams within the volume of rocks, compressed by applied load.
  5.  
  6. Sliding and shear failure of blocks of rocks formed by intersecting fracture within the foundation.

The performance of a foundation must be checked with respect to all three of this condition, because they are independent of each other.

The Bearing capacity of an earth material is important in that it determines the maximum value of contact pressure that can be applied to the material without causing shear failure.

The Bearing capacity is defined as the maximum load exerted through a single punch per unit area that the rock is capable of withstanding before the failure.

The bearing capacity is of important in the design of strata control system in coal mines and rock drilling.

Plastic yield of rock material in the mass is important in relation to the hartd rock boring and tunneling m/c operating at high values of the thrust unaccompanied by impact in cutting.

It's important too, in connection with the operation of mine - strata control system in which the interposition of a rigid support component may be require d in order to form a strong "break off" line to induce caving of the roof beds.

The rigidity of such a support system is determined by the ability of the roof and floor strata to take the pressure generated by the imposed load. Without yielding in such a way that the support penetrates the rock, with they are in contact.

It's well known that with exception of some soft rock most rock masses are excellent and trouble free foundation material. In fact where the loads are large, when the rock is weak or highly fragmented or even the structural requirement are significant there is a need for a more rigorous method to establish the ultimate Bearing capacity of the rock involved, and consequently the allowable load.

Till date various researchers particularly in the fields of soil mechanics have made lots of theoretical studies. A very few investigations have been carried out in case of rock foundation particularly in cola measure rocks ie rock having low compressive strength.

The ultimate bearing capacity of foundation on rock masses have not been studied in details from a experimental point of view.

Keeping in view all these factors the following objectives have been laid in the present investigation.

 

1.2 Objective

    1.  
    2. Detail investigations of the failure criteria of floor bearing coal measure strata under the simulated form under various conditions in the lab.
    3.  
    4. To cater the knowledge of influence of plastification of floor rock masses under the heavy stress condition.
    5.  
    6. To formulate various equation which governs the stress field including the numerical solution to the problem of the mass forces.
    7.  
    8. Failure element analysis of fracture plane under the various simulated conditions.
    9.  
    10. Computerization of the total work and pin pointing the compatibility of the floor bearing strata under the actual work situation and specific condition.

 

1.3 Approach to fulfill the objective.

Bearing Capacity problems usually relates to the details of the structural geology.

Analysis of bearing capacity is being done under the following rock mass behavior model.

  1. Intact rock without any overlying strata.

    Fractured and weathered rock

  1. Single discontinuity

    Several sets of Discontinuity

    Jointed rock mass

  1. Shallow dipping bedding planes.

    Bearing capacity of layered formation.

 

1.4 Work done so far:

 

So as to fulfill these objective, artificial rock mass models representing the actual rock mass of varying uniaxial compressive strength (ranging from 50 kg/cm2 to 300 kg/cm2 i.e. low to medium strength rock) are being created using cement mortar.

In order to achieve the artificial samples of different strength, a large number of samples were casted using cylindrical molds of hard PVC pipe of 52-mm diameter with L/D ratio ranging from 2.5 - 3.0

Different sets of cast parameters were used to achieve the desired compressive strength.

Same curing condition was applied for all the samples. All the samples were kept in water tank for a minimum of 28 days, and another 28 days in open atmosphere for normal drying up of the samples.

All the samples were prepared as per ISRM specification for the testing of Uniaxial Compressive Strength. As far as possible the densities of particular sets of sample representing a particular Uniaxial Compressive strength were kept constant.

Work is still under process..................

Details will be published later on................

 

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