In large-scale geomechanical model

because of the fragility and low strength of similar model material

it is difficult to get its complete bending stress-strain curve or load-displacement curve. This paper performed mechanical analysis on the bending experiment process

and got the stiffness designing principle of elastic element through some derivation for the solution of increasing the auxiliary elastic element.Based on this principle

we assembled a test prototype and obtained complete bending load-displacement curves for the specimens with different joints(homogeneous

layered and massive) containing different angles bolt. In addition

the dead weight of specimen was considered in the experiment due to the similar material's characteristics of low strength and bulk density. Experimental studies have shown that

the increasement of elastic element has a noteworthy improvement for the decreasing segment of the complete bending load-displacement curve. When the composite stiffness of the elastic element and prototype system is greater than the maximum stiffness of the specimen

the curve can be measured . The dead weight of specimen can be equivalent to the concentrated force in the bending experiment

and the equivalent load for the 550 mm long Standard specimen is 50% of its own weight or 9% of the peak load in homogeneous specimen’s experiment.