Grammar JLPT Level N3 - Lesson 9

Structure of ばかりだ:

Verb［る］+ ばかりだ
Verb［る］+ ばかりで + Phrase

Details about ばかりだ:

Occasionally, the adverbial particle ばかり is combined with verbs in their attributive form, to show that (A) is the only thing that is occuring. It may also imply that (A) is happening 'more and more', or that 'it keeps on (A)'. This phrase utilizes ばかり's standard meaning of 'only', and combines it with the auxiliary verb だ (or です).

ガソリンの値段(ねだん)は上(あ)がっていくばかりだ。
The price of gas keeps rising.
最近(さいきん)は全然(ぜんぜん)体(からだ)を鍛(きた)えていないから、筋肉(きんにく)がなくなっていくばかりだ。
Recently I haven't been working out, so I keep on losing muscle.
日本(にほん)の人口(じんこう)は減(へ)るばかりです。
Japan's population continues to drop.
この辺(へん)は犯罪(はんざい)が多(おお)いので、治安(ちあん)が悪(わる)くなるばかりです。
Because there are so many crimes around here, the public safety of the area continues to get worse.

As can be seen with these sentences, this use of ばかり is paired almost exclusively with verbs that describe some form of change (higher/lower, stronger/weaker, better/worse, faster/slower, etc).
If the speaker would like to express further information in a (B) part of the sentence, だ will simply get changed to its conjunctive form で, before continuing.

この町(まち)の治安(ちあん)が悪(わる)くなるばかりで、しばらく良(よ)くなりそうもない。
The reputation of this town keeps on getting worse, and it doesn't look like it will get better anytime soon.
観光客(かんこうきゃく)が減(へ)るばかりで、周(まわ)りの店(みせ)が潰(つぶ)れていっている。
The amount of tourists keeps on dropping, and the stores around us are closing.

ばかりだ

Usage Notes for ばかりだ:

This use of ばかり is primarily seen with negative trends. However, this is not a grammatical rule, and positive trends may also sometimes appear with ばかりだ.

毎日(まいにち)夜(よる)遅(おそ)くまで働(はたら)いているから、疲(つか)れがたまっていくばかりだ。
Because I work until late at night everyday, I keep getting more exhausted.
病院(びょういん)を変(か)えてから、体調(たいちょう)が良(よ)くなっていくばかりだ。
Ever since I changed hospitals, my health keeps on getting better.