I’ve posted here some diagrams from the book Inzhenernoe delo [Engineering], full title of which is Vremennoe nastavlenie po inzhenerno-tekhnicheskomu delu dlia komandnogo sostava vsekh rodov voisk [Provisional Manual for Engineering and Technical Matters for Commanders of All Troop Types], put together by the Red Army Staff and published by the Red Army in 1926. As far as I can tell, it isn’t even listed in WorldCat.
The book covers roads, bridges, demolition, and a variety of other subjects, but what I’ve posted here is fortifications. The Red Army was not focusing on continuous trenches, though that had been the experience of the imperial army for long stretches of the First World War. Instead, the Red Army, judging by this manual, emphasizes separate positions within an overall defensive zone. This first illustration is of a variety of squad / section [otdelenie] firing positions, seen from above. Note the communication trench exiting out the back of the position, and the bends in the position to prevent fire due to enemy penetration of one part of the position from sweeping the entire thing.
This isn’t so interesting by itself, but it gives a little context to this, which is a company defensive position as part of a continuous front. The enemy is at the top, and the company defends a frontage of 1000 meters with a depth of 800 meters. You see two platoons up, one back (I haven’t figured out how to do cyrillic in this post–the word that starts with the letters B3B is vzvod, or platoon). Each platoon has rifle squads (co), a rifle / machine-gun squad (cno), and machine gun squad (no).
Compare that to this company defensive strongpoint without a continuous front–this comes from the section on maneuver warfare: The strongpoint takes the form of a salient rather than a belt, and is strikingly similar to an 18th-century bastioned fort, and for similar reasons. While you have the same “two up, one back” arrangement of platoons, the barbed wire is quite different. It forms straight lines and nice angles, all the better for defense by automatic fire. Note how the machine-gun platoons (nB), the platoon from a machine-gun company (Bnr), and the medium machine-gun squads (ocn) are placed to sweep the lines of barbed wire. To the right, the same is true of the rifle squads (co). The defense includes bunkers (y) for protection against artillery bombardment. Note that there’s no provision for anti-tank defense. This is 1926, after all, when the Red Army was preparing to fight Poland and Romania and tanks were thin on the ground. Indeed, the section on defenses against armor in the entire book of 367 pages is only eight sentences long.