In february 1917 why did riots break out in st. petersburg

The peasants were frustrated with harsh conditions and the Tsar's apparent lack of interest in helping the poor 

On March 11, the troops of the Petrograd army garrison were called out to quell the uprising. In some encounters, regiments opened fire, killing demonstrators, but the protesters kept to the streets, and the troops began to waver. That day, Nicholas again dissolved the Dumas. When the frustrated Russian army at Petrograd unexpectedly switched their support to the demonstrators, the imperial government was forced to resign and a provisional government was established. Three days later, Nicholas formally abdicated his throne, effectively ending nearly four centuries of czarist rule in Russia.