Simile in Crime and Punishment
The use of this simile (a figure of speech comparing two unlike things and often introduced by like or as) helps provide a better understanding of how small the young man's room actually is.
The purpose of this simile is to not only inform the readers that Raskolnikov has retreated away from everyone physically, but that he has also begun to do so mentally. This latter retreat in particular has helped to develop the crime he is contemplating as well as his antisocial behavior.
A "pikestaff" refers to the wooden shaft of a pike, a spear-like weapon. Razumihin uses this simile to mean that something was very obvious or "as plain as day."
This simile is a common phrase for describing people as being extremely close and friendly. It also suggests that they are so close that they would share secrets and possibly conspire together, which is exactly how Raskolnikov is viewing Zametov and Porfiry's relationship.
Dostoevsky uses this simile to reinforce the kind of image he wants readers to have in their minds of Sonia: very small, delicate, and innocent. Even when she is agitated or angry, she still does not possess the ability to be aggressive or hostile.
India-rubber is another term for natural rubber, or caoutchouc, made from the latex of certain trees and other plants in Indonesia and other places around the globe. It is highly elastic and flexible, which is probably why Porfiry uses it in his simile for emphasizing just how much he sometimes shakes with laughter.
Dostoevsky uses this simile to show how Porfiry Petrovitch awkwardly behaves in the room; he appears to be stalling or waiting for something, merely going back and forth around the room until something he wants to happen will happen. The simile also helps reinforce the image of Porfiry--a short, round man who can't quite sit still.
This simile does more than represent the physical characteristics of Svidrigaïlov's face. By referring to his face as a mask, Raskolnikov is suggesting that Svidrigaïlov is a very difficult person to read; it is hard to tell what he is thinking and feeling.