DONETSK PROVINCE, Ukraine, Feb 27 (Reuters) - Russian forces were trying to close their circle around the small mining city of Bakhmut on Monday, while rain and an early spring thaw turned eastern Ukraine's battlefields to mud which could hamper both sides as they try to take the initiative. The spring thaw, known as the rasputitsa, has a long history of ruining plans by armies to attack across the soil of Ukraine and western Russia, turning roads into rivers and fields into impenetrable bogs. See here for a complete list of exchanges and delays