Sometimes it's hard to even know what to search to find answers, so maybe someone here can help me. I'll have a written thing (may be pretty confusing) and a makeshift 'diagram' that might be a bit simpler to understand for trench networks of WWI.
TLDR: How were trench networks set up behind the front trenches? I know there were back trenches for various things (storing supplies/food/barracks/etc.). But were there completely separate (or somehow connected) trench networks behind the trench network of the front line constructed in case of needing to retreat and quickly be able to defend/counterattack effectively? **I could be completely misunderstanding how trench networks were set up and/or constructed.
Simpler 'Diagram':
Each letter = a trench network, complete with both front and back trenches/bunkers/barracks; A = a British trench network, B= another British trench network, C=German " ", D=" "; space between B and C = no man's land; I'm unsure about whether there would have been a gap between A/B or C/D, or maybe they were connected via another trench/pathway?
A B C D
The British assault from front trench of network B and take the front trench of the C network. Since C also includes back trenches, do the Germans set up shop again in the back trenches of C (if they know they cannot retake the front trench of C), or do they retreat to the farther back to the 'front' trench of D network to give themselves some breathing room?
The probably confusing written question:
Edit: For simplicity's sake, in this scenario the British are on offense, taking the front of the German trench network. The Germans are the defenders here.
So in general many times the initial objectives needing taken care of at the start of a British offensive was to take at least the Germans' front trench and then hold it. When this happened, was it common for the Germans to fall back to their back trenches (that are part of the same trench network as the front trench they just lost) and counterattack from those back trenches, or was it more common for the Germans/defenders to retreat even more and construct/utilize a new trench network farther back? Basically, did the Germans abandon the whole trench network to give themselves new space/breathing room from the British in the trench/trench network they just lost, instead of heavy fighting in their former front trench (if the front trench had been firmly taken by the Brits and the Germans were 100% unable to retake it)?
If there is anything I can clarify, please let me know. If I'm dumb please also let me know.
I've tried to respond in several parts, first exploring how trenches developed to give some context, then how trenches were used, then the mentality surrounding networks.
The history of trench development varies across the different theatres of war. Typically, they evolved over time. The first scratches at the surface of the earth quickly developed into what were colloquially known as 'coffin pits' [see Nathan Wise, Anzac Labour]. Then, these deepened to larger holes, which were linked together to form a trench. Over time, a combination of regular infantry, with more skilled sappers, engineers, and dedicated labourers would work on that basic system to make it safer and more complex. But, the nature of that development varied from place to place, and varied between the forces undertaking the labour. On Gallipoli, in 1915, for example, all men were required to undertake all manner of trenchwork [see Wise '"Dig, dig, dig, until you are safe": constructing the Australian trenches on Gallipoli' - https://www.tandfonline.com/doi/abs/10.1080/19475020.2012.652444]. In May, 1915, men with mining experience in the ranks were called on to volunteer for special mining work, but they were also joined in that work by others. The trenches were basically built all over the terrain, wherever there was room, including tunnels that connected various parts of the landscape, and at their closest points the two opposing lines of trenches were about 10m apart!
On the Western Front the situation was entirely different, and the Allied forces generally developed three types of trench lines [see Wise, Anzac Labour again]. The front lines, the support trenches, and reserves. Both sides learned that artillery tended to target the front lines, so they often held those with relatively minimal forces. Stronger forces were then held in the support trenches, which might be about 100m behind the front. A further 500-2000m behind those were reserve trenches, which were generally safer. There are various maps of the trenches showing these networks, and of course it varies immensely from location to location, and the spacing between trenches varies, and often there'll be additional lines here and there. So much of this merely developed over time, as situation and needs dictated.
Front line trenches were generally designed with a firing step facing the enemy, but the back side of the trench wall [the side facing friendly ground] was designed to make it difficult for an enemy to fire from, thus making re-capture easier.
So, there was an expectation that in an attack, the front line would be hit by artillery, and possibly captured by the enemy. Friendly forces in the support trenches could then easily counter-attack and the enemy in those 'friendly' front line trenches would have trouble defending [as there was no fire step on the reverse side].
Attacks were obviously designed to advance quickly and capture as much ground as possible. Throughout 1914-1916 on the Western Front, many Allied officers maintained hope that the initial infantry advance could be followed up by a cavalry breakthrough [see for example analyses of the Somme, and the waiting role cavalry played in mid 1916]. However, the reality was that many attacks struggled beyond that first line. Support trenches linking the front and support lines could easily be collapsed, creating a new 'no man's land' between the former front and support lines. Attacking formations were broken up, and it was hard enough capturing one secure line of trenches, and maintaining that hold, let alone having to then push again onto a second, maybe even third line, often without artillery support/preparation, and typically more strongly held than that first line.
Reserve trenches were a third line of defence, and were generally considered the safer of the three, and they provided a third line of defence just in case.
Patrols into no man's land and raids into enemy trenches [typically to capture prisoners for intel] were the most common form of activity, and they typically took place at night, and didn't press beyond the front lines.
Larger attacks typically occurred at first light, or very early morning, and thus men would typically take a position every morning on their firing step ready for an attack [see Wise, Anzac Labour, for some descriptions of this]. Once the morning passed without an attack, they would be a little more relaxed [relatively speaking].
To get to the latter part of your question, nobody gave up any ground without a very strong fight. The main occurrence of this was when the Germans withdrew to the Hindenburg Line in 1917. They recognised [moreso than the Allies], the power of defensive warfare, and established a very solid series of defensive lines in good defensive terrain, that also cut their salient in the area. Generally though, it was a lot of work to establish a trench line, and the preference was almost always to regather, and retake the trenches than fall back.
For this reason, the Germans established far more complex and comfortable trench networks with deep [and relatively comfortable] underground bunkers. The Allies tended to see their positions as temporary, and, whilst they laboured endlessly, they didn't put as much work into creating a permanent environment.