http://devbukkit.fr/index.php?threads/tntlimit.1037/

plugin.yml

name: TNTLimit
version: 1.0
author: NeatMonster
main: fr.neatmonster.tntlimit.TNTLimit

TNTLimit.java

package fr.neatmonster.tntlimit;

import org.bukkit.ChatColor;
import org.bukkit.Material;
import org.bukkit.block.Block;
import org.bukkit.block.BlockFace;
import org.bukkit.event.EventHandler;
import org.bukkit.event.Listener;
import org.bukkit.event.block.BlockPlaceEvent;
import org.bukkit.plugin.java.JavaPlugin;

public class TNTLimit extends JavaPlugin implements Listener {

    public static Block getAbove(final Block block) {
        return block.getRelative(BlockFace.UP);
    }

    public static Block getBelow(final Block block) {
        return block.getRelative(BlockFace.DOWN);
    }

    public static boolean isTNT(final Block block) {
        return block.getType() == Material.TNT;
    }

    @Override
    public void onEnable() {
        getServer().getPluginManager().registerEvents(this, this);
    }

    @EventHandler
    public void onBlockPlace(final BlockPlaceEvent event) {
        if (event.getPlayer().isOp())
            return;
        final Block block = event.getBlockPlaced();
        if ((isTNT(block) && isTNT(getAbove(block)) && isTNT(getAbove(getAbove(block))))
                || (isTNT(block) && isTNT(getBelow(block)) && isTNT(getBelow(getBelow(block))))) {
            event.getPlayer().sendMessage(ChatColor.RED + "Les colonnes de TNT sont interdites !");
            event.setCancelled(true);
        }
    }
}