Cross the river and then tear down the bridge
When someone abandons those who helped them upon realizing their goal
Negative
你成功後不应该过河拆桥 | Nǐ chénggōng hòu bù yìng gāi guòhéchāiqiáo
You shouldn't kick down the ladder after you have succeed
[Source]
受人之恩，须永志于心，千万不能过河拆桥 | Shòu rén zhī ēn, xū yǒng zhì yú xīn, qiān wàn bù kěyǐ guòhéchāiqiáo
People must always remember when others help them. They absolutely cannot abandon their benefactors.
[Source]
Kick down the ladder
None
Careful - this chengyu does not have the same meaning as the English idiom "burn your bridges."
The imperial examination 科举考试 (kējǔ kǎoshì) was a sort of civil service exam that determined whether one could enter the bureaucracy. By the time of this story, it had been in place for over 700 years, so attempting to get rid of it was a big deal. (Note that the test wasn't abolished permanently until 1905.)
《李逵负棘》(Lǐ Kuí Fù Jí), a work by Yuán Dynasty (元, 1279 - 1368) writer 廉进之 (Lián Jìn Zhī)
During the Yuán Dynasty (元, 1279 - 1368), there was a court minister named 彻里帖木儿 (Chè Lǐ Tiē Mù Ér). 彻里帖木儿 fervently loathed the imperial examination system for its corrupt nature and exorbitant cost to students, and he managed to convince the emperor to abolish it.
This decision sent shock waves throughout the court, and many ferociously protested. One of those protesting officials was named 许有壬 (Xǔ Yǒu Rén), and he got into many arguments those who agreed with the emperor's decision. 许有壬's opposition efforts were ultimately unsuccessful, and the imperial edict to abolish the system was drafted.
The next day, when the emperor gathered everyone together to read the edict aloud, an extremely unwilling 许有壬 was forced to sit in the very front row. When the order was read and the court was then dismissed, another official mockingly said to him, "With you sitting up there in the very front of the court listening to His Majesty's edict, it seemed as though you were leading the effort to abolish the examination system. Since you made it into the court through that system, it seems as though you were kicking down the ladder."