What impact did big bertha have on ww1?

None really. It was an impressive gun system, the statistics of its capabilities are mind boggling. But it could not be aimed with sufficient accuracy to hit anything smaller than a massive city the size of Paris. Where the shells landed was completely random, and nothing of military value was damaged in the slightest way. It took a long time between shots to reload. The value of the "Paris Gun" was mostly for its terrifying effect on the civilian population of Paris, which was not too significant. It killed several hundred civilians, some of whom probably had jobs in war industries, but no one truly crucial.

There were actually half a dozen of these large cannon. They could fire only forty or fifty rounds before they had to be laboriously returned all the way to the Krupp works in Germany for the installation of a new liner in the barrel, which was worn out by the tremendous forces released in those few discharges. Each gun had a crew of over 3000 men, so the equivalent of one to two divisions of manpower was tied up in this largely pointless and ineffectual exercise in terrorism (the WWI Germans had a policy of "schrecklichheit" - "frightfulness", which they used to justify their cruelty and bullying, thinking to cow the opposition, but it was a double edged sWord as it also made people want to kill them all). So the diversion of the material and industrial resources to make these few guns, which accomplished nothing, and which could have been used to make several hundred at least of more useful caliber weapons, the railroad resources, the tremendous amount of manpower, all were expended for basically no return, except to satisfy the Germans in their fascination with great big guns.