What is the effect of expansionary fiscal policy in case liquidity trap situation?

I will try to explain this through ISLM model.

Consider you are an employee working for the government and earn $1000 per month. Government follows expansionary fiscal policy and increases your pay to $1500. Your purchasing power increases by $ 500 when prices are held constant. This increase in your income will translate into money demand because obviously you will demand money to purchase goods and services with your extra income. This is known as transmission mechanism where increase in demand in real market transmits to money market.

In ISLM framework this could be shown as follows:

If you look carefully one interesting thing is happening here. IS curve shifts rightward due to multiplier effect because your expenditure will be somebody else's income and so on. But due to increase in the demand of money the price of money or the rate of interest also increases. This increase in rate of interest incentivizes you to reduce your demand and save more de-incentivizes the borrowers. Thus, this has an offsetting effect on the level of income. This phenomenon is known as crowding out of private investment.

Now let us see what happens in a liquidity trap situation. Consider the same scenario where your income increases by $500 and your money demand also increases. But rate of interest is trapped (that is why it is known as trap) here and they will not increase. This will result in no offsetting effect or no crowding out or full multiplier effect.

If an economy is below full employment level, a corresponding increase in money supply will produce an offsetting effect on increase in money demand thereby keeping the rate of interest at their original level.

If I've understood correctly (it's not entirely clear from the question), you're asking about a policy of fiscal expansion in a depressionary environment, accompanied by a monetary expansion.

It is conceivable that an increase in money supply, coupled with an increase in money demand, would lead to unchanged interest rates, if those two opposing forces balanced out.